A human blood-clotting factor used to treat some people with haemophilia and accident victims suffering serious bleeding has been produced using genetically modified fish.
There is still a long way to go before any product reaches the market, but if the fish project is a commercial success many other proteins might be made in this way.
"We have a list of 20 other human therapeutic proteins that could be produced via fish to treat lung disease, liver problems, even tumours," says Norman Maclean of the University of Southampton in the UK.
Maclean has been working on producing human coagulation factor VII in fish together with AquaGene of Alachua, Florida. Factor VII can be purified directly from human blood, but there is a risk of diseases being transmitted this way.
The only alternative, called NovoSeven, is produced using genetically modified hamster cells. But growing mammalian cells is very expensive, and the cost of a single injection can be as high as $10,000.
Gunshot wounds
Factor VII is used to treat people with a rare form of haemophilia that means they cannot make the protein themselves, and it is often needed to treat other forms of the disease as well.
Many doctors, including US army medical staff in Iraq, are now also using it to stem internal bleeding caused by accidents or gunshot wounds, even though NovoSeven is not approved for this purpose.
AquaGene is hoping to produce a much cheaper rival product using tilapia, a fast-growing freshwater fish widely farmed for food. Maclean has now managed to produce several lines of transgenic tilapia that produce human factor VII.
His team added a genetic switch from the tilapia to the human gene. This ensures that the gene is switched on in the liver of modified fish, and the protein secreted into the blood.
"Each millilitre of human blood has about 500 nanograms of the protein. We were able to match that yield in the blood of our fish," says Maclean. He hopes to produce tilapia that will make 10 times that level within a year.
Silkworm larvae
The next step will be to convince regulators that the fish-derived protein is the same as the human form, and that it is safe. The researchers have already tested it on samples of blood taken from patients with haemophilia, but many more studies will have to be done.
Other groups are exploring rival ways of producing proteins, from plants and chicken eggs to silkworm larvae and cattle, but Maclean thinks fish are a serious contender.
There is no evidence that any disease can be transmitted from fish to humans, for starters. Transgenic fish are also relatively cheap and easy to make, whereas it can cost millions to produce transgenic cattle.
Because tilapia breed so quickly, production could easily be adjusted to meet demand. "But escape is a concern," says John Matheson of the US Food and Drug Administration. For commercial production, transgenic tilapia could be grown in contained facilities.
Friday, February 29, 2008
Blood-staunching bandages
Conventional gauze bandages do not work well enough because, although they absorb blood, they do not prevent its flow. Thomas Fischer and colleagues at the Francis Owen Blood Research Laboratory at the University of North Carolina at Chapel Hill think they may have the solution.
His team has discovered that bandages made from about 65% glass fibre and 35% bamboo fibre not only absorb blood but also stimulate the body's ability to staunch the flow by triggering the release of blood-clotting factors such as thrombin or fibrinogen. They say the bandages work even better if they are themselves impregnated with blood-clotting factors.
Given the number of military casualties in Afghanistan and Iraq this is an idea that could well be fast-tracked. The idea is part-owned by a company called Entegrion, which was co-founded by Fischer. So all the pieces are in place for the bandages to be commercialised soon.
Read the full patent application for blood-staunching bandages.
His team has discovered that bandages made from about 65% glass fibre and 35% bamboo fibre not only absorb blood but also stimulate the body's ability to staunch the flow by triggering the release of blood-clotting factors such as thrombin or fibrinogen. They say the bandages work even better if they are themselves impregnated with blood-clotting factors.
Given the number of military casualties in Afghanistan and Iraq this is an idea that could well be fast-tracked. The idea is part-owned by a company called Entegrion, which was co-founded by Fischer. So all the pieces are in place for the bandages to be commercialised soon.
Read the full patent application for blood-staunching bandages.
Shrimp-shell wound healant to get space test
A biopolymer produced from shrimp shells that has proved invaluable in treating wounded soldiers will be put to a new test in August – aboard the space shuttle Endeavour.
A commercial experiment will assess how the material, called chitosan, affects human immune cells in space, where they are less responsive than on the ground.
The US Army equips its troops in Iraq with chitosan-laden bandages both to speed blood clotting in fresh wounds, and to stop bacterial infections. NASA does not expect astronauts to fight battles in space, but has to plan for accidents, and worries that slow healing or infection of wounds could imperil long-duration missions to Mars or other distant targets.
The test also could pay dividends on the ground. They are being paid for by Hawaii Chitopure, which makes the highly purified chitosan used in military bandages and hopes to show that chitosan can reduce inflammation, as well as kill bacteria. That could reduce scarring and other harmful byproducts of immune response, says Shenda Baker, a chemist at Harvey Mudd College in California, US, and president of BioSTAR west, the company which will carry out the experiments.
"While mammalian cells don't like microgravity, bacteria grow very well," Baker told New Scientist. The best-known example was the thriving colony of terrestrial bacteria that contaminated the Russian Mir space station so badly that cosmonauts became sick.
Biofilms have also been found on the space shuttle. Without help from materials like chitosan, bacteria could overwhelm mammalian immune systems during long space missions.
Charged exoskeleton
Chitosan is a water-soluble form of chitin, an abundant long-chain natural biopolymer that is a key component of the semi-transparent exoskeletons of arthropods from insects to lobsters, and in the cell walls of fungi.
Some researchers believe natural chitin helps protect arthropods from bacterial infection, important because they lack a conventional immune system. The soluble chitosan carries a positive charge that attracts the negatively charged membranes of bacteria, stopping them from multiplying and in some cases killing them. The charge also initiates clotting of red blood cells.
Baker's experiment will monitor the behavior of human monocytes, a type of white blood cell that rapidly responds to wounds and infections.
Three sets of monocyte samples will fly on the shuttle – one mixed with fragments of bacterial cell walls known to trigger immune reactions, one mixed with chitosan alone, and a third mixed with both chitosan and bacterial fragments. Microarrays will monitor activity of the monocytes, including the genes activated, proteins produced, and short chains of RNA that mediate gene activity.
By comparing the space cultures with identical samples from the ground, Baker and her colleagues at California-based BioSTAR West hope to learn how the immune system turns on and off in both environments.
Their key goal is to see if chitosan can stop the bacterial threat well enough to block the immune system's normal inflammatory response, which causes scarring and other harmful effects.
Life after death for empty shells: Crustacean fisheries create a mountain of waste shells, made of a strong natural polymer, chitin. Now chemists are helping to put this waste to some surprising uses
Chitin is the main structural component of the shells of crustaceans, molluscs and insects. It also makes up parts of the jaws and body spines of certain worms, and is found in the cell walls of fungi and in some algae. Henri Bracannot was the first to describe chitin - he called it fungine - as long ago as 1821. We now know that it is a natural polymer that strongly resembles cellulose, the main component of plant cell walls. Chitin is almost as common as cellulose - an estimated billion tonnes are synthesised every year - and this ubiquity holds a clue to some of its potential uses.
At first sight, however, chitin does not look at all promising. Chemically, it is a fairly dull molecule. Like cellulose, it can be broken down by enzymes, but only slowly, and it will not dissolve in most ordinary solvents like water or alcohol. It is usually bound to porteins to form large, complex molecules and its purity varies enormously. Even chitin from the same animal varies in the length of its molecular chain, its cyrstalinity, and in the number of acetyl (CH3C)O groups hanging off the chain.
But in 1959, a chemist called Rouget found that heating chitin with a very concentrated sodium hydroxide converts it to a related and much more useful chemical, called chitosan. This reaction removes some of the acetyl groups from the molecular chain, leaving behind complete amino (NH2) groups (see Figure). Increasing the temperature or the strength of the sodium hydroxide solution removes more acetyl groups. In this way chemists can produce a range of chitosan molecules with different properties and applications. Unlike chitin, chitosan dissolves easily in acidic solvents like acetic acid.
Chitosan's versatility depends almost entirely on its amino (NH2) groups. When dissolved in acids, these groups add proton, becoming (NH3)+ and giving chitosan a positive electrical charge overall. This makes the molecule extremely effective for removing negatively charged particles that are dissolved or suspended in water, such as lignosulphates and natural tannins. Chitsan form ionic, or sometimes hydrogen bonds with these molecules, desotabilising the suspension so that they precipitate out as insoluable solids.
One of the earliest uses of chitin was to purify waste water from the processing of shellfish. Processing plants produce contaminated water as well as solid waste, such as shells and viscera. Crustacean fisheries are very wasteful - up to 85 per cent by weight of each animal is thrown away, which amounts to over 3 million tonnes of solid waste every year. Some fisheries already use chitin derived from the solid waste to purify their own waste water. A study of one crawfish processing plant in Louisiana in 1989 showed that chitosan derived from the waste could be used to remove 97 per cent of the solids suspended in waste water this way.
Now some companies are promoting chitin for the clarification and purification of other types of contaimined water. Chitin and chitosan are also good chelators. This means they can bind at several points, rather like the grip of a claw, to metal atoms in solution, especially heavy metals such as mercury, lead and uranium, although no one knows quite how. This useful property could be exploited as the basis of a method for treating waste water that is toxic or radioactive. Japanese firms such a Kurita Industries sell chitosan as a flocculant. So does the Norwegian company Protan, which recommends it for the clarification of swimming pools and spas as its flocculates microbes and removes metals.
Waste-water treatment is only one of many suggested and proven uses for chitin and chitosan. Of these, cosmestics is one of the longest established. Chitin was first used in cosmetics in 1969; more recently, Japanese and German companies have been developing chitosan salts - soluble in water, and formed simply by treating chitosan with acid - for use is cosmetics for skin and hair. The German cosmetics giant Wella has been researching chitosan as hair treatment for 10 years. It has experimented with the film-forming properties of chitosan in hair sprays and nail varnishes and uses its thickening effects in creams and conditioners. In Japan, at least five companies manufacture chitin and chitosan, mainly from crab shells.
Chito-Bios of Ancona in Italy sell N-carboxybutyl chitosan, under the trade name EvalsanR, for shampoos, bath foams, liquid soaps, toothpaste, personal-hygiene detergent and face creams. The company uses this derivative of chitin as a replacement for hyaluronic acid, a common component of creams and lotions. It emphasises that chitosan is 'more than a comestic ingredient' and could be useful for dressing wounds, for surgery and dentistry.
But perhaps the greatest potential application is paper manufacture. Adding only 1 per cent by weight of chitin to pulp increases the strength of the paper, speeds up the rate at which water drains from the pulp and increases the quantity of fibres retained when making sheets of paper. So manufacturers can use cheaper, weaker fibres, without reducing quality, while saving up to 90 per cent of the energy they use to beat the pulp. Chitin also makes the paper easier to print on.
Paper that incorporates chitin has greatly improved wet strength - an advantage for diposable nappies, shopping bags and paper towels. But these benefits must be offset against the problems of supply. The current world production of chitin from all sources would be overwhelmed by an industry which in 1986 produced 172 million tonnes of newsprint. Any move towards the general use of chitin in paper manufacture would require a huge increase in chitin production. Where would it come from?
Maintaining fisheries of shellfish or molluscs just to harvest their chitin is unlikely to be economic, as they only contain around 1 per cent chitin by weight. This leaves two possible sources of chitin: shellfish waste and fungal fermentation. The pharmaceutical industries of most countries already exploit molecules, including vitamin C and penicillin. The process also produces large quantities of chitinous waste - estimates are difficult to find, but in 1977, one researcher gave a figure of 790,000 tonnes. Unlike shellfish waste, this source of chitin is predictable - a set input will produce a set output - and its quality can be controlled.
Several countries, including the US, Japan, Norway, Italy and India, already have chitin/chitosan plants based on shellfish waste as their source. The little they produce is used by the pharmaceutical industry and in the treatment of waste waters. There are no reliable data for how much chitin should in theory be available from crustacean fisheries, but according to the FAO's latest figures, in 1987 the world crustacean harvest was 3.69 million tonnes. Assuming chitin forms 1 per cent of the wet weight of a crustacean, on average, we are squandering about 36,700 tonnes of chitin each year as waste from the processing of shrimps, prawns, lobsters and crabs. The main problem is that it would be unecomomic to collect the waste from many small processing plants, so this source can only be tapped where large quantities of crustaceans are being handled.
The largest potential source of animal chitin is the zooplankton that inhabit the upper layers of the sea. But only one crustacean which could be loosely considered a member of the zooplankton is currently being harvested to any significant degree. This is the Antarctic krill. In 1989/90, fishing fleets caught 375,000 tonnes, making it the largest crustacean fishery in the world ('Who's counting on krill?', New Scientist, 11 November 1989). The krill fishery is only marginally economic. Most of the catch is either processed for its tail meat, which is destined for human consumption, or is used whole for aquaculture.
Peeling krill is no easy task and leaves 85 per cent by weight as waste. Of this waste, 85 per cent is recoverable protein. Almost a quarter of the deproteinised waste is chitin, compared wiht 3.2 per cent in the whole animal. About 90 per cent of this chitin can be recovered by conventional extraction techniques. This is half as efficient again as from crab chitin, although the figure would not be so high on board a trawler.
The fishery will probably expand from its current levels and the total krill stock in the southern ocean is now thought to be between about 100 and 400 million tonnes. Several millions tonnes of this could be harvested annually. Such a catch would dominate the total world curstacean catch of about 4 million tonnes and would be a major potential source of chitin. Other sources include squid, whose pens are 40 per cent chitin and largely free of minerals and bivalve molluscs, whose shells oftain contain a high proportion of minerals. (Minerals add to the weight of material and therefore the cost of processing.) Insects have chitin but it is quinone tanned, which makes it difficult to extract, and there is no consistent source.
So it seems that the major source of chitin in the future will probably be biotechnology rather than seafood waste. The infant chitin/chitosan industry will probably develop by using cheap supplies of waste materials, but if demand increased sufficiently, manufacturers could develop genetically engineered microorganisms to produce these useful molecules. Cultured strains of microorganisms will be able to produce chitin with desired properties under controlled conditions and in fixed quantities. This would sever the link between chitin production and the widely fluctuating market for protein. Chitin is easily extracted from fungal hyphae and some species even produce up to 14 per cent by weight of chitosan. Culturing chitosan-producing strains would eliminate the deacetylation step that converts chitin to chitosan. Although this step is fairly simple, it makes chitosan nearly twice as expensive to product as chitin.
Certain algae produce pure chitin in the form of extracellular fibres which can be between 10 and 15 per cent of the dry weight of the cells and can be readily separated from the non-chitinous structures with a yield of 80 per cent. But these algae grow only slowly under normal conditions. Researchers hope that advances in biotechnology will give them fast-growing strains that retain large amounts of chitin.
Chitin and its derivatives are shaping up to be as versatile as plastics. Unfortunately, although chitin and its derivatives can do many things well, there are few functions that they alone can carry out. Chitin-based products usually have to compete with those produced by established biochemical technologies. On the other hand, a 'natural' material that uses up waste, is biodegradable and does not damage the environment may have a bright future.
* * *
Industry shells out for chitin
Many chemical, medical and pharmaceutical companies are now researching and in some cases developing and patenting chitin-based products. Protan, a Norwegian company, has been producing and selling chitin and chitosan from shellfish waste since 1984. It lists 13 broad areas for its products, from 'personal care' to detoxification of industrial waste.
Other applications include treatment of sewage, dairy waste, paper mill effluent, food-factory waste, liquid radioactive waste and purfication of drinking water. In Japan about 500 tonnes of chitin are used every year as a water purifier, and the US Environmental Protection Agency rates chitosan as acceptable for the purfication of drinking water.
Using chitosan to remove suspended solids from food-processing wastes, such as cheese whey, has an additional benefit. As well as purified effluent, the method yields coagulated by-products rich in proteins which can be added to feed for domestic animals. This seems to make the feed more digestible.
Chitin and its derivatives also have some very useful properties in the medical field. Between 1968 and 1975 researchers working for the American pharmaceuticals company Lescarden of Goshen, New York, filed five patents for the use of chitin and chitosan to accelerate wound healing. They found the chitin mats, fibres, sponges, sutures and films were much better than standard cartilage-based ones. The pharmaceuticals company Katakurachikkarin based in Hokkaido makes an artifical skin - a chitosan-collagen composite - that appears to enhance recovery from surgical wounds or burns. In 1983, doctors working for the Veterans Administration Medical Center in Omaha discovered that chitosan could also speed up blood clotting and used it to reduce the loss of blood following blood vessel grafts.
Chitosan can be produced in numerous forms - powder, paste, solution, film, fibre or spray - giving manufacturers huge scope for incorporating it into bandages, dressings, salves, sutures or disposable contact lenses. The body does not seem to reject these and they break down slowly to harmless carbohydrates, carbon dioxide and water. Because chitosan is absorbed completely in the body, it is an ideal carrier for drugs that must be released slowly. After tests on rats in 1978, some Japanese researchers claimed that chitosan reduces serum cholestrol. In Japan you can now buy biscuits and noodles sold for the alleged benefits of the chitin they contain.
The food industry is developing ways of exploiting the emulsifying properties of chitosan to make mayonnaise and peanut butter. Chitosan could eventually find its way into an area where non-toxic, high strength films are required, form sausage casings to oven wraps and food packaging.
Some researchers even think these chemicals will be the basis of a biodegradable plastic. Technics, the hi-fi manufacturer, of Schizuoka in Japan has even made the vibrators of flat-panel speakers from chitosan, an idea which is supposedly based on the acoustic properties of crickets' wings.
A commercial experiment will assess how the material, called chitosan, affects human immune cells in space, where they are less responsive than on the ground.
The US Army equips its troops in Iraq with chitosan-laden bandages both to speed blood clotting in fresh wounds, and to stop bacterial infections. NASA does not expect astronauts to fight battles in space, but has to plan for accidents, and worries that slow healing or infection of wounds could imperil long-duration missions to Mars or other distant targets.
The test also could pay dividends on the ground. They are being paid for by Hawaii Chitopure, which makes the highly purified chitosan used in military bandages and hopes to show that chitosan can reduce inflammation, as well as kill bacteria. That could reduce scarring and other harmful byproducts of immune response, says Shenda Baker, a chemist at Harvey Mudd College in California, US, and president of BioSTAR west, the company which will carry out the experiments.
"While mammalian cells don't like microgravity, bacteria grow very well," Baker told New Scientist. The best-known example was the thriving colony of terrestrial bacteria that contaminated the Russian Mir space station so badly that cosmonauts became sick.
Biofilms have also been found on the space shuttle. Without help from materials like chitosan, bacteria could overwhelm mammalian immune systems during long space missions.
Charged exoskeleton
Chitosan is a water-soluble form of chitin, an abundant long-chain natural biopolymer that is a key component of the semi-transparent exoskeletons of arthropods from insects to lobsters, and in the cell walls of fungi.
Some researchers believe natural chitin helps protect arthropods from bacterial infection, important because they lack a conventional immune system. The soluble chitosan carries a positive charge that attracts the negatively charged membranes of bacteria, stopping them from multiplying and in some cases killing them. The charge also initiates clotting of red blood cells.
Baker's experiment will monitor the behavior of human monocytes, a type of white blood cell that rapidly responds to wounds and infections.
Three sets of monocyte samples will fly on the shuttle – one mixed with fragments of bacterial cell walls known to trigger immune reactions, one mixed with chitosan alone, and a third mixed with both chitosan and bacterial fragments. Microarrays will monitor activity of the monocytes, including the genes activated, proteins produced, and short chains of RNA that mediate gene activity.
By comparing the space cultures with identical samples from the ground, Baker and her colleagues at California-based BioSTAR West hope to learn how the immune system turns on and off in both environments.
Their key goal is to see if chitosan can stop the bacterial threat well enough to block the immune system's normal inflammatory response, which causes scarring and other harmful effects.
Life after death for empty shells: Crustacean fisheries create a mountain of waste shells, made of a strong natural polymer, chitin. Now chemists are helping to put this waste to some surprising uses
Chitin is the main structural component of the shells of crustaceans, molluscs and insects. It also makes up parts of the jaws and body spines of certain worms, and is found in the cell walls of fungi and in some algae. Henri Bracannot was the first to describe chitin - he called it fungine - as long ago as 1821. We now know that it is a natural polymer that strongly resembles cellulose, the main component of plant cell walls. Chitin is almost as common as cellulose - an estimated billion tonnes are synthesised every year - and this ubiquity holds a clue to some of its potential uses.
At first sight, however, chitin does not look at all promising. Chemically, it is a fairly dull molecule. Like cellulose, it can be broken down by enzymes, but only slowly, and it will not dissolve in most ordinary solvents like water or alcohol. It is usually bound to porteins to form large, complex molecules and its purity varies enormously. Even chitin from the same animal varies in the length of its molecular chain, its cyrstalinity, and in the number of acetyl (CH3C)O groups hanging off the chain.
But in 1959, a chemist called Rouget found that heating chitin with a very concentrated sodium hydroxide converts it to a related and much more useful chemical, called chitosan. This reaction removes some of the acetyl groups from the molecular chain, leaving behind complete amino (NH2) groups (see Figure). Increasing the temperature or the strength of the sodium hydroxide solution removes more acetyl groups. In this way chemists can produce a range of chitosan molecules with different properties and applications. Unlike chitin, chitosan dissolves easily in acidic solvents like acetic acid.
Chitosan's versatility depends almost entirely on its amino (NH2) groups. When dissolved in acids, these groups add proton, becoming (NH3)+ and giving chitosan a positive electrical charge overall. This makes the molecule extremely effective for removing negatively charged particles that are dissolved or suspended in water, such as lignosulphates and natural tannins. Chitsan form ionic, or sometimes hydrogen bonds with these molecules, desotabilising the suspension so that they precipitate out as insoluable solids.
One of the earliest uses of chitin was to purify waste water from the processing of shellfish. Processing plants produce contaminated water as well as solid waste, such as shells and viscera. Crustacean fisheries are very wasteful - up to 85 per cent by weight of each animal is thrown away, which amounts to over 3 million tonnes of solid waste every year. Some fisheries already use chitin derived from the solid waste to purify their own waste water. A study of one crawfish processing plant in Louisiana in 1989 showed that chitosan derived from the waste could be used to remove 97 per cent of the solids suspended in waste water this way.
Now some companies are promoting chitin for the clarification and purification of other types of contaimined water. Chitin and chitosan are also good chelators. This means they can bind at several points, rather like the grip of a claw, to metal atoms in solution, especially heavy metals such as mercury, lead and uranium, although no one knows quite how. This useful property could be exploited as the basis of a method for treating waste water that is toxic or radioactive. Japanese firms such a Kurita Industries sell chitosan as a flocculant. So does the Norwegian company Protan, which recommends it for the clarification of swimming pools and spas as its flocculates microbes and removes metals.
Waste-water treatment is only one of many suggested and proven uses for chitin and chitosan. Of these, cosmestics is one of the longest established. Chitin was first used in cosmetics in 1969; more recently, Japanese and German companies have been developing chitosan salts - soluble in water, and formed simply by treating chitosan with acid - for use is cosmetics for skin and hair. The German cosmetics giant Wella has been researching chitosan as hair treatment for 10 years. It has experimented with the film-forming properties of chitosan in hair sprays and nail varnishes and uses its thickening effects in creams and conditioners. In Japan, at least five companies manufacture chitin and chitosan, mainly from crab shells.
Chito-Bios of Ancona in Italy sell N-carboxybutyl chitosan, under the trade name EvalsanR, for shampoos, bath foams, liquid soaps, toothpaste, personal-hygiene detergent and face creams. The company uses this derivative of chitin as a replacement for hyaluronic acid, a common component of creams and lotions. It emphasises that chitosan is 'more than a comestic ingredient' and could be useful for dressing wounds, for surgery and dentistry.
But perhaps the greatest potential application is paper manufacture. Adding only 1 per cent by weight of chitin to pulp increases the strength of the paper, speeds up the rate at which water drains from the pulp and increases the quantity of fibres retained when making sheets of paper. So manufacturers can use cheaper, weaker fibres, without reducing quality, while saving up to 90 per cent of the energy they use to beat the pulp. Chitin also makes the paper easier to print on.
Paper that incorporates chitin has greatly improved wet strength - an advantage for diposable nappies, shopping bags and paper towels. But these benefits must be offset against the problems of supply. The current world production of chitin from all sources would be overwhelmed by an industry which in 1986 produced 172 million tonnes of newsprint. Any move towards the general use of chitin in paper manufacture would require a huge increase in chitin production. Where would it come from?
Maintaining fisheries of shellfish or molluscs just to harvest their chitin is unlikely to be economic, as they only contain around 1 per cent chitin by weight. This leaves two possible sources of chitin: shellfish waste and fungal fermentation. The pharmaceutical industries of most countries already exploit molecules, including vitamin C and penicillin. The process also produces large quantities of chitinous waste - estimates are difficult to find, but in 1977, one researcher gave a figure of 790,000 tonnes. Unlike shellfish waste, this source of chitin is predictable - a set input will produce a set output - and its quality can be controlled.
Several countries, including the US, Japan, Norway, Italy and India, already have chitin/chitosan plants based on shellfish waste as their source. The little they produce is used by the pharmaceutical industry and in the treatment of waste waters. There are no reliable data for how much chitin should in theory be available from crustacean fisheries, but according to the FAO's latest figures, in 1987 the world crustacean harvest was 3.69 million tonnes. Assuming chitin forms 1 per cent of the wet weight of a crustacean, on average, we are squandering about 36,700 tonnes of chitin each year as waste from the processing of shrimps, prawns, lobsters and crabs. The main problem is that it would be unecomomic to collect the waste from many small processing plants, so this source can only be tapped where large quantities of crustaceans are being handled.
The largest potential source of animal chitin is the zooplankton that inhabit the upper layers of the sea. But only one crustacean which could be loosely considered a member of the zooplankton is currently being harvested to any significant degree. This is the Antarctic krill. In 1989/90, fishing fleets caught 375,000 tonnes, making it the largest crustacean fishery in the world ('Who's counting on krill?', New Scientist, 11 November 1989). The krill fishery is only marginally economic. Most of the catch is either processed for its tail meat, which is destined for human consumption, or is used whole for aquaculture.
Peeling krill is no easy task and leaves 85 per cent by weight as waste. Of this waste, 85 per cent is recoverable protein. Almost a quarter of the deproteinised waste is chitin, compared wiht 3.2 per cent in the whole animal. About 90 per cent of this chitin can be recovered by conventional extraction techniques. This is half as efficient again as from crab chitin, although the figure would not be so high on board a trawler.
The fishery will probably expand from its current levels and the total krill stock in the southern ocean is now thought to be between about 100 and 400 million tonnes. Several millions tonnes of this could be harvested annually. Such a catch would dominate the total world curstacean catch of about 4 million tonnes and would be a major potential source of chitin. Other sources include squid, whose pens are 40 per cent chitin and largely free of minerals and bivalve molluscs, whose shells oftain contain a high proportion of minerals. (Minerals add to the weight of material and therefore the cost of processing.) Insects have chitin but it is quinone tanned, which makes it difficult to extract, and there is no consistent source.
So it seems that the major source of chitin in the future will probably be biotechnology rather than seafood waste. The infant chitin/chitosan industry will probably develop by using cheap supplies of waste materials, but if demand increased sufficiently, manufacturers could develop genetically engineered microorganisms to produce these useful molecules. Cultured strains of microorganisms will be able to produce chitin with desired properties under controlled conditions and in fixed quantities. This would sever the link between chitin production and the widely fluctuating market for protein. Chitin is easily extracted from fungal hyphae and some species even produce up to 14 per cent by weight of chitosan. Culturing chitosan-producing strains would eliminate the deacetylation step that converts chitin to chitosan. Although this step is fairly simple, it makes chitosan nearly twice as expensive to product as chitin.
Certain algae produce pure chitin in the form of extracellular fibres which can be between 10 and 15 per cent of the dry weight of the cells and can be readily separated from the non-chitinous structures with a yield of 80 per cent. But these algae grow only slowly under normal conditions. Researchers hope that advances in biotechnology will give them fast-growing strains that retain large amounts of chitin.
Chitin and its derivatives are shaping up to be as versatile as plastics. Unfortunately, although chitin and its derivatives can do many things well, there are few functions that they alone can carry out. Chitin-based products usually have to compete with those produced by established biochemical technologies. On the other hand, a 'natural' material that uses up waste, is biodegradable and does not damage the environment may have a bright future.
* * *
Industry shells out for chitin
Many chemical, medical and pharmaceutical companies are now researching and in some cases developing and patenting chitin-based products. Protan, a Norwegian company, has been producing and selling chitin and chitosan from shellfish waste since 1984. It lists 13 broad areas for its products, from 'personal care' to detoxification of industrial waste.
Other applications include treatment of sewage, dairy waste, paper mill effluent, food-factory waste, liquid radioactive waste and purfication of drinking water. In Japan about 500 tonnes of chitin are used every year as a water purifier, and the US Environmental Protection Agency rates chitosan as acceptable for the purfication of drinking water.
Using chitosan to remove suspended solids from food-processing wastes, such as cheese whey, has an additional benefit. As well as purified effluent, the method yields coagulated by-products rich in proteins which can be added to feed for domestic animals. This seems to make the feed more digestible.
Chitin and its derivatives also have some very useful properties in the medical field. Between 1968 and 1975 researchers working for the American pharmaceuticals company Lescarden of Goshen, New York, filed five patents for the use of chitin and chitosan to accelerate wound healing. They found the chitin mats, fibres, sponges, sutures and films were much better than standard cartilage-based ones. The pharmaceuticals company Katakurachikkarin based in Hokkaido makes an artifical skin - a chitosan-collagen composite - that appears to enhance recovery from surgical wounds or burns. In 1983, doctors working for the Veterans Administration Medical Center in Omaha discovered that chitosan could also speed up blood clotting and used it to reduce the loss of blood following blood vessel grafts.
Chitosan can be produced in numerous forms - powder, paste, solution, film, fibre or spray - giving manufacturers huge scope for incorporating it into bandages, dressings, salves, sutures or disposable contact lenses. The body does not seem to reject these and they break down slowly to harmless carbohydrates, carbon dioxide and water. Because chitosan is absorbed completely in the body, it is an ideal carrier for drugs that must be released slowly. After tests on rats in 1978, some Japanese researchers claimed that chitosan reduces serum cholestrol. In Japan you can now buy biscuits and noodles sold for the alleged benefits of the chitin they contain.
The food industry is developing ways of exploiting the emulsifying properties of chitosan to make mayonnaise and peanut butter. Chitosan could eventually find its way into an area where non-toxic, high strength films are required, form sausage casings to oven wraps and food packaging.
Some researchers even think these chemicals will be the basis of a biodegradable plastic. Technics, the hi-fi manufacturer, of Schizuoka in Japan has even made the vibrators of flat-panel speakers from chitosan, an idea which is supposedly based on the acoustic properties of crickets' wings.
Wednesday, February 27, 2008
Collagen Based Hemostats
Davol Inc., a subsidiary of C. R. Bard Inc., develops, manufactures, and markets Avitene Microfibrillar Collagen Hemostat and Ultrafoam™ Collagen Sponge, topical hemostatic agents, and other specialty medical products for use in surgical procedures worldwide.
J&J (Ethicon) Collagen Hemostat for precise application. Controlled application minimizes product waste. Handles easily without sticking to wet gloves or instruments.
Gelita Medical The FDA has classified Pharmaceutical Gelatin as GRAS (Generally Recognized As Safe) and it has been used in over 200 million procedures.
Vascular Solutions D-Stat Flowable is a thick, yet flowable hemostat designed for topical application to stop bleeding at vascular access sites following percutaneous procedures.
Orthovita Vitagel is composed of microfibrillar collagen and thrombin in combination with the patient’s own plasma which contains fibrinogen and platelets.
B Braun Lyostypt® is a wet-stable collagen hemostat. Collagen leads to thrombocyte adhesion and to activation of coagulation factor XII. Therefore, collagen is very effective in hemostasis
J&J (Ethicon) Collagen Hemostat for precise application. Controlled application minimizes product waste. Handles easily without sticking to wet gloves or instruments.
Gelita Medical The FDA has classified Pharmaceutical Gelatin as GRAS (Generally Recognized As Safe) and it has been used in over 200 million procedures.
Vascular Solutions D-Stat Flowable is a thick, yet flowable hemostat designed for topical application to stop bleeding at vascular access sites following percutaneous procedures.
Orthovita Vitagel is composed of microfibrillar collagen and thrombin in combination with the patient’s own plasma which contains fibrinogen and platelets.
B Braun Lyostypt® is a wet-stable collagen hemostat. Collagen leads to thrombocyte adhesion and to activation of coagulation factor XII. Therefore, collagen is very effective in hemostasis
Tuesday, February 26, 2008
Arista - Plant based Hemostat
Medafor
Arista™AH is an absorbable hemostat, based on Medafor's patented MPH® (Microporous Polysaccharide Hemospheres) Technology that is used in the control of profuse bleeding in general surgery when conventional procedures are ineffective or impractical.
•Direct-from-the-shelf, rapid-delivery hemostat.
•A totally Biocompatible, non-biological, resorbable hemostatic agent (2 Days).
•A fast acting, versatile clotting agent that produces an “instant gelling” followed by the formation of a fibrin mesh.
Arista™AH is an absorbable hemostat, based on Medafor's patented MPH® (Microporous Polysaccharide Hemospheres) Technology that is used in the control of profuse bleeding in general surgery when conventional procedures are ineffective or impractical.
•Direct-from-the-shelf, rapid-delivery hemostat.
•A totally Biocompatible, non-biological, resorbable hemostatic agent (2 Days).
•A fast acting, versatile clotting agent that produces an “instant gelling” followed by the formation of a fibrin mesh.
Chitosan and Emergency Hemostats
Chitosan is a derivative of solid waste from shell fish processing and can be extracted from fungus culture. Chitosan is a water insoluble cationic polymeric material.
Chitosan is converted to glucosamine by the enzyme lysosyme and is therefore excreted from the body naturally. It is not necessary to remove chitosan from the body. The chemical properties of chitosan related to hemostatis possibly include: molecular weight, extent of ionization, counter ion, degree of deacetylation, and degree of crystallinity. Also, its ability to bind with tissues are a function of these parameters. Chitosan can be used in medical and surgical procedures by its direct application to a bleeding surface using the various physical forms such as powder, solution, coating, film, hydrogel, and filament composite.
A recent review detailing the role of new hemostatic agents for battlefield hemorrhage control describes the interest in and necessary specifications for such materials. As a consequence, the Defense Department authorized the development and use of three deployable and FDA approved hemostatic agents: Zeolite "Quikclot" and chitosanic "Hemcon" and the American Red Cross Fibrin Dressing.
Celox
CELOX is a proprietary blend of materials that contains Chitosan. It is both safe for the caregiver and the victim. It can control the most severe arterial bleeding, even when applied within moments of the onset of high pressure, high volume bleeds.
Quikclot
QuikClot® hemostatic agent is a molecular sieve, sifting molecules by size. When QuikClot® comes into contact with blood in and around a wound, it rapidly takes in the smaller water molecules from the blood. The larger platelet and clotting factor molecules remain in the wound in a highly concentrated form. This promotes extremely rapid natural clotting and prevents severe blood loss.
Hemcon
HemCon Bandages work by becoming extremely sticky when in contact with blood. This adhesive-like action seals the wound and controls bleeding. HemCon products are fabricated from chitosan, a naturally occurring, bio-compatible polysaccharide. Because chitosan has a positive charge, it attracts red blood cells, which have a negative charge. The red blood cells create a seal over the wound as they are drawn into the bandage, forming a very tight, coherent seal.
Abbott
A potent hemostatic agent intended for use in the management of bleeding wounds, including vascular access sites to peripheral puncture sites
Chitosan is converted to glucosamine by the enzyme lysosyme and is therefore excreted from the body naturally. It is not necessary to remove chitosan from the body. The chemical properties of chitosan related to hemostatis possibly include: molecular weight, extent of ionization, counter ion, degree of deacetylation, and degree of crystallinity. Also, its ability to bind with tissues are a function of these parameters. Chitosan can be used in medical and surgical procedures by its direct application to a bleeding surface using the various physical forms such as powder, solution, coating, film, hydrogel, and filament composite.
A recent review detailing the role of new hemostatic agents for battlefield hemorrhage control describes the interest in and necessary specifications for such materials. As a consequence, the Defense Department authorized the development and use of three deployable and FDA approved hemostatic agents: Zeolite "Quikclot" and chitosanic "Hemcon" and the American Red Cross Fibrin Dressing.
Celox
CELOX is a proprietary blend of materials that contains Chitosan. It is both safe for the caregiver and the victim. It can control the most severe arterial bleeding, even when applied within moments of the onset of high pressure, high volume bleeds.
Quikclot
QuikClot® hemostatic agent is a molecular sieve, sifting molecules by size. When QuikClot® comes into contact with blood in and around a wound, it rapidly takes in the smaller water molecules from the blood. The larger platelet and clotting factor molecules remain in the wound in a highly concentrated form. This promotes extremely rapid natural clotting and prevents severe blood loss.
Hemcon
HemCon Bandages work by becoming extremely sticky when in contact with blood. This adhesive-like action seals the wound and controls bleeding. HemCon products are fabricated from chitosan, a naturally occurring, bio-compatible polysaccharide. Because chitosan has a positive charge, it attracts red blood cells, which have a negative charge. The red blood cells create a seal over the wound as they are drawn into the bandage, forming a very tight, coherent seal.
Abbott
A potent hemostatic agent intended for use in the management of bleeding wounds, including vascular access sites to peripheral puncture sites
Oxidized Cellulose Manufacturers
Gelita Medical
J&J Surgicel
Alltracel
Lifescienceplus
Synthesia
Lifescience Plus
Feel free to leave more in the comments section
J&J Surgicel
Alltracel
Lifescienceplus
Synthesia
Lifescience Plus
Feel free to leave more in the comments section
Oxidized Cellulose
Oxidized cellulose (Surgicel) is widely used for intraoperative hemostasis. When saturated with blood, Surgicel rapidly swells into a gelatinous mass. This property is particularly significant in a confined space containing neural tissue. Six cases of paraplegia following the use of oxidised cellulose in thoracic surgery have been reported.
Above - Hyperdense mass displacing and compressing the spinal cord
There have been several reports of neurological complications associated with the use of oxidized cellulose. There are six case reports of cord compression by a mass of this substance, causing paraplegia following thoracotomy. In all these cases, oxidized cellulose was used to control bleeding at the posterior end of a right T5-T6 interspace incision, in the region of the costo-transverse junction. Migration of an expanded mass of Surgicel through the adjacent intervertebral foramen into the epidural space caused significant cord compression.
Monday, February 25, 2008
Hemostat Manufacturers Links
Links:Advanced Medical Solutions (Winsford, U.K.; http://www.admedsol.com/)Aesculap (Center Valley, PA; http://www.aesculap.com/)Angiotech (Vancouver, Canada; http://www.angiotech.com/)B. Braun (Melsungen, Germany; http://www.bbraun.com/)Baxter Healthcare (Deerfield, IL; http://www.baxter.com/)Chemence (Corby, U.K.; http://www.chemence.com/)Closure Medical (Raleigh, NC; http://www.closuremed.com/)Covidien (Norwalk CT; http://www.covidien.com/)CSL Behring (King of Prussia, PA; http://www.cslbehring.com/)Daiichi Sankyo (Montvale, NJ; http://www.daiichius.com/)Ethicon (Somerville, NJ; http://www.ethicon.com/)GEM (See Synovis Life Technologies)Genzyme Biosurgery (Cambridge, MA; http://www.genzyme.com/)GluStitch (Delta, Canada; http://glustitch.com/)Harvest Technologies (Plymouth, MA; http://www.harvestech.com/)Interpore Cross Medical (Irvine, CA; http://www.interpore.com/)Johnson and Johnson (Somerville, NJ; http://www.ethus.jnj.com/)Kaketsuken (Kumamoto, Japan; http://www.kaketsuken.or.jp/)MedLogic Global (See Advanced Medical Solutions)Nissui Pharmaceutical (Tokyo, Japan; http://www.nissui-pharm.co.jp/)Omrix Biopharmaceuticals (Kiryat Ono, Israel; http://www.omrix.com/)Pharming Group (Leiden, The Netherlands; http://www.pharming.com/)Plasmaseal (San Francisco, CA; http://www.plasmaseal.com/)Protein Polymer Technologies (San Diego, CA; http://www.ppti.com/)Synovis Life Technologies (St. Paul, MN; http://synovislife.com/)SyntheMed (Iselin, NJ; http://www.synthemed.com/)SysCore (E-mail: Helmut.Kranzmaier@cnc-communications.com)ThermoGenesis (Rancho Cordova, CA; http://www.thermogenesis.com/)U.S. Surgical (Norwalk, CT; http://ussurg.com/)
Hemostatic Agents
Disclaimer: The information contained within the Grand Rounds Archive is intended for use by doctors and other health care professionals. These documents were prepared by resident physicians for presentation and discussion at a conference held at Baylor College of Medicine in Houston, Texas. No guarantees are made with respect to accuracy or timeliness of this material. This material should not be used as a basis for treatment decisions, and is not a substitute for professional consultation and/or peer-reviewed medical literature.
Julina Ongkasuwan, M.D.
Hemostasis: As you probably remember from your basic science courses, hemostasis begins with damage to tissues. The first phase is the vascular phase in which you have vasoconstriction, which decreases the amount of blood flow to the area. The damage to the vascular endothelium exposes collagen, which then causes platelet aggregation and adhesion. These platelets release various clotting factors, which I will talk about in more detail shortly and initiates the clotting cascade and clot formation. This is followed by a clot retraction phase and finally a clot destruction phase in which plasminogen is converted to plasmin which then causes clot lysis. Of note this patient was taking Amicar, an agent that inhibits the conversion of plasminogen to plasmin and thus helps stabilize clots.
The clotting cascade traditionally is broken up into two basic pathways, the intrinsic pathway and the extrinsic pathway. The intrinsic pathway is primarily activated as we said before by collagen, which is exposed and then it binds factor XII and initiates this entire cascade. In addition, collagen attacks platelets, which then subsequently become activated with the use of several other different cofactors. They release various factors as well. The extrinsic pathway is stimulated by tissue factor, which is exposed by the tissue injury and through factor VII activation, stimulates this pathway. These two pathways then converge in a common pathway where thrombin converts fibrinogen to fibrin monomers, which are then cross linked with the aid of factor XIII and calcium to form fiber polymer and thus clot. The hemostatic agents have been around for a very long time. There is a report that the Egyptians used various high temperature cautery and waxes and poultices on wounds in order to stop bleeding. There are reports that Native Americans also use scrapping on the inside of animal hides and applied those to wounds. The Greek scholar, Hippocrates, described the use of high temperature cautery as well as various topical hemostatic agents and Celsus, the Roman philosopher and physician who gave us the concept of dolor, color, rubor also described the use of various stypticand high temperature cautery and ligation in order to stop bleeding. In the more modern era, the idea of fibrin used as a topical hemostatic agent was introduced in the early 1900s and Gelfoam was introduced in the 1940s and used in neurosurgical procedures.
So what do we want in a good hemostatic agent? First, the ideal hemostatic agent would of course be such that the agent itself is as well as any of its metabolic breakdown products would be safe to use within the body. Secind, you want it to work and you want it to be efficacious.
The definition of efficacy can vary between the different uses, for example a vascular surgeon may want something that polymerizes very quickly in order to stop bleeding, but does not cause clot of the vessel that they spent all this time anastomosing, where as a reconstructive surgeon for example may want something that polymerizes very slowly to give them time to reposition their flaps or grafts.
Third is usability; you want something that is easy to use and that you can use in a variety of different circumstances. Fourth is affordability. This may be more relevant to a hospital administrator or pharmacist who actually does the purchasing, but it impacts the surgeon because that determines what you have available to you in the operating room. And finally, fifth, approvability. Any of these agents need to be approved by the FDA in order to be used in the US. So the different types of hemostatic agents, which I will be addressing in this talk are listed below and I am going to go through each one of these specifically.
Gelatin sponge or Gelfoam®, which is also known as commercially as Surgifoam again was first introduced in the 1940s by Dr. Gray in the neurosurgical procedures. What it is is purified pork skin gelatin which you can kind think of like Jello®, as it is the same thing that Jello® is made out of.
As you can see on this microscopic view, it has a very amorphous form and has a lot of air spaces and it stains very eosinophilic on H&E stain. Basically the way it works is that its surface essentially acts in the intrinsic pathway causing contact activation and thus platelets. Since it works very proximally within this cascade, you have to have functioning cofactors or clotting factors in order for this to work in helping create clot. Of note, it does absorb approximately 45 times its weight in blood and can expand to approximately 200% of its initial volume. It is absorbed in approximately four to six weeks and on the nasal mucosa it liquifies within two to five days. In the case presentation, this child was initially packed with Gelfoam® approximately a week prior to the time she was seen in the ER and at that point there was no evidence of any Gelfoam left within her nasal cavity. Now the way Gelfoam® can be used, you can either apply dry, directly to the bleeding surface and hold pressure over it or you can wet it in saline and then squeeze out all the air bubbles and use it that way.
Oxidized regenerated cellulose is also known as Surgicel or Oxycel in its commercial forms. It is derived from alpha-cellulose that is actually plant-based. As you can see on microscopic view, Surgicel comes in knit formwhere as Oxycel comes in a microfibrillar form and on microscopic view Surgicel has these fibers which are knit together and they are solid fibers whereas Oxycel has the hollow fibers but they essentially work the same way. Surgicel is relatively acidic and is thought to cause some small vessel contraction. Like Gelfoam, it works at the same point in the intrinsic pathway of clotting causing contact activation. So again the same thing holds that functional clotting factors are needed in order for this to work. It is thought to berelatively bacteriostatic when compared to other hemostatic agents. The theory behind this is that because of its relatively low pH, it deactivates and denatures some of the bacterial proteins especially those related to antibiotic resistance, thus making them more susceptible to antibiotics. It needs to be applied dry and absorbs within four to eight weeks. Of note, on postop imaging Surgicel sometimes causes a ring-enhancing lesion as you can see here on postop imaging, which can be mistaken for an abscess cavity or tumor recurrence. That is something to keep in mind if you are imaging a patient within two months of having operated on them and Surgicel was used during the procedure. On microscopic view, you can see a giant cell reaction.
Our next agent is microfibrillar collagen commercially known as Avitene ®. It is most commonly used in a light flour form, but it does also come in a non-woven web form. This is collagen, which is derived from bovine skin. Under the microscope it is very eosinophilic and of note, under polarizing light it does have periodicity. It binds tightly to blood surfaces, so you do not actually need to achieve a relatively dry field in order to apply it. It causes minimal swelling especially when compared to Gelfoam ®. T he way it works is slightly different because in addition to being collagen and causing contact activation, it does somehow directly activate platelets. But again, it works very proximally within the intrinsic pathway. It is absorbed in three months and it needs to be applied dry.
Collagen sponges, these come in a wide variety of different commercial forms. Again it is similar to Avitene ® and it is derived from bovine Achilles tendon or bovine skin and it works in basically the exact same way as Avitene works and it absorbs in 8-10 weeks.
The next class of hemostatic agents is slightly different: topical thrombin. The idea of topical thrombin has been around since the early 1900s in order to try to achieve clot and in addition the idea of using topical thrombin plus other hemostatic agents such as Gelfoam ® has been around for quite a longtime. In 1999 a new agent was introduced called Floseal™ which basically consists of bovine thrombin plus cross-linked gelatin granules mixed together. So the way it works is your bovine thrombin directly activates fibrinogen and converts it into fibrin monomers. So you can see that this works in a completely different place within the clotting cascade. It works down here in the common pathway bypassing all of the other necessary clotting factors. You do however have to have functional fibrinogen in order for this to work. The product Floseal™ itself is a little bit different from just using topical thrombin plus Gelfoam ® because the gelatin granules have been cross linked in such a way that they do not swell to nearly the same extent. It is absorbed in approximately 6-8 weeks.
Fibrin sealants are the last class of the hemostatic agents that I am going to address. Commercially it comes in many forms including tisseal and crosseal and there are many variations on the idea of fibrin sealants. One of those basic ideas is that you take pure human fibrinogen and combine it with bovine thrombin and they usually throw in an antifibrinolytic agent into the mix as well. So the way this works is that we take the bovine thrombin, it then converts this exogenous human fibrinogen to fibrin monomers, but you do need intrinsic, you need the patient’s own factor XIII and calcium, which then converts it into fibrin polymer. In addition, they usually add an antifibrinolytic agent to the mix as well in order to stabilize the clot. So this does require functional factor XIII and calcium in order for these fibrin sealants to work. They are absorbed within 10-14 days and need a relatively dry field in order to work.
I am going to briefly mention some of the other classes of agents which are out there, but I am not going to address these in detail. There are some completely autologous fibrin sealants. The patient’s own serum is taken and the fibrinogen and thrombin are purified. This achieves essentially the same effect as the fibrin sealants previously mentioned. There are a target platelet gels where again you purify the platelet with plasma and the patient’s own serum combined with thrombin and you get similar agent to the fibrin sealants only there are some additional benefits: you do have some platelet direct growth factors involved which help with wound healing. There are some completely synthetic agents, which are made from polyethylene glycol gels that when you combine them make a completely synthetic hydrogel. Another product is bovine serum plus albumin plus glutaraldehyde, and poly N-acetyl glucosamine is something that the military is investigating as a hemostatic agent and it is a seaweed-based agent. This is just an idea of what is out there in addition to the agents I addressed previously.
Gelfoam ® and Surgicel, work here very proximally in the intrinsic coagulation pathway via contact activation. Collagen also works via contact activation, but also activates platelets. In a completely separate class we have agents that work in the common pathway, which includes Flowseal™, which is essentially topical thrombin and as well as fibrin glue and its variants.
Safety, three things to remember that Gelfoam® swells and it swells a lot. This has proven to be a problem when used within confined spaces such as the spinal foramina where in it can cause spinal cord nerve compression and brain compression.
Surgicel, of note, even though it does have an antimicrobial effect relative to the other hemostatic agents, it is still a nidus for infection. Avitene®, and in fact all of these agents, do cause a certain amount of foreign body reaction and granulation formation. But Avitene® has been found to be the worst offender in this way. You can see in this particular slide, they have the Avitene® cavity here, and then a large amount of surrounding edema and a foreign body reaction with giant cells here surrounding the Avitene®. In this picture you can see the periodic nature of Avitene® under polarized light. In fact, the manufacturers recommend that you apply these agents, then hold pressure and wait a while for a clot to form and then you remove the agent afterwards so that you do not leave it within the cavity in order to try to prevent foreign body reaction as much as possible. In addition, Avitene® because it comes in a light fluffy form, has been known to occasionally cause arterial embolization and it had been reported that it is causing laryngospasm when used in tonsillectomy. Collagen sponge has many of the same side effects as any of the bovine derived agents because there are known allergic reactions to some of these bovine antigens, which are containing these agents.
Floseal™ again as I mentioned before has much less swelling than the Gelfoam so it can be used within some of the more enclosed spaces. Because it is Gelfoam beads it can cause arterial embolization if it is used near a larger vessel. In fact Gelfoam beads themselves have been used in order to embolize arterial malformation. Because it contains bovine antigens, it can have antibody formation, which I am going to talk about a little bit more in detail later. Some of the fibrin sealants use pooled human fibrinogen, in which there is always the potential for transmission of infectious agents. Also again, risks of arterial embolization and antibody formation.
Antithrombin antibodies: These are foreign antigens. A study of 200 patients showed 90% of those exposed to topical thrombin do have a transient elevation in IgG titers. Tadokoro et al in Japan also noted that you can have development of IgE antibodies. This can result in a prolonged thrombin time. Of note, thrombin time is actually a measure of fibrinogen count.
Thrombin time: the way this test was done, you add bovine thrombin to the patient’s fibrinogen and see how long it takes for it to form a monomer. Because you have development of antibodies to bovine thrombin, you can have elevation in your thrombin time. This antibovine thrombin antibody can cross-react with human thrombin, but interestingly enough, this rarely ever causes any sort of clinical bleeding.
The real problem is with antifactor V antibody, as most commercial form of thrombin is contaminated with a certain amount of other bovine antigens and most importantly bovine factor V. So if you can get these antibovine factor V antibodies, which then cross-react with human factor V this can lead to a very severe coagulopathy and because this antibody can act as an inhibitor of factor V. On laboratory tests you can find a very decreased factor V level, increased PT and PTT, which does not correct when you add FFP and vitamin K. When you mix the patient’s sera with a normal human sera, you do not get correction of the PT and PTT which suggest that it is not a cofactor deficiency, but it is actually an inhibitor causing the problem. So as you can see here the factor V is an activator of the conversion of prothrombin to thrombin and this is where you end up with problems. The same study noted that 50% of the 200 patients that they found that were exposed to topical thrombin did develop human factor V antibodies. The problem usually does not happen on the initial exposure, but it is when they are exposed again in the later point to the topical thrombin is when the potential for coagulopathy is exposed. Fortunately these IgG titers do fall off rapidly three to four weeks after the exposure and the treatment if you do encounter this is steroids, cyclophosphamides, IVIG plasmapheresis and platelet transfusion. Of note, I did not see actually any reports of this in the head and neck literature per se; most of the case reports of these events are in the cardiovascular and vascular literature.
Another requirement of a good hemostatic agent is efficacy. Basically there have been lots of studies both in vitro and in vivo using various animal models as well as human studies comparing these various hemostatic agents. The general gist of them is that fibrin sealant work better than Floseal™ which is better than Avitene® and then the collagen sponge, Surgicel and Gelfoam® are essentially equivocal. They do work better than placebo but can barely differentiate efficacy between any of them. Of note, Floseal™ and Avitene® do cause more inflammatory reactions than the others.
Usability: Gelfoam®, Surgicel, Avitene® and these collagen sponge can be stored at the room temperature and are basically ready to use out of the box. Floseal™ does require two to five minute prep time, you combine the thrombin with calcium and combine that to the gelatin granules. Fibrin sealants on the other hand need to be kept in cold storage and thawed prior to usage; it depends on what company you are using and what type and the prep time can be anywhere up to 20-30 minutes. So it is something to keep in mind if you think you want to use fibrin sealant during your case you should be prepared ahead of time in order to do so.
Affordability: This is an average or sort of an idea of what the cost is for some of these agents. Gelfoam®, Surgicel, collagen sponges are relatively inexpensive in a $10-20 per individual piece, whereas Avitene®, Floseal™ and fibrin sealants are much more expensive.
Approvability: All of these agents are regulated through the FDA as a class III medical device, which means they are subjective to this medical device reporting systems so that the manufacturers are obligated to report to the FDA when an adverse event happens. In fact, in 2004 the FDA released notification to users about Gelfoam® and its swelling and use in neurosurgical procedures because of the potential for paralysis.
Summary: These agents are of course not a substitute for meticulous surgical technique. However, they can help decrease OR time and postop bleeding. In my review of the literature I did not see any difference in use or in complications between children and adults. In the case that I presented initially, if you do have a patient who has a known bleeding disorder, a hematology consult obviously can be useful. Hemostatic agents are of limited use because you do have problems in the clotting cascade so they can help you with other more systemic hemostatic agents. Again, this is a summary of the specific agents that I addressed in this talk. The big thing is to remember about the individual ones. Gelfoam® swells, so lot of it is a mechanical effect and you really should not be using it within an enclosed bony cavity. Surgicel has a relative antimicrobial effect when compared to other hemostatic agents. Avitene® has the worst foreign body reaction of all of these particular agents. The collagen sponge has sort of the same problems because is contains bovine parts that do have some antigenetic potential. Floseal™ and fibrin sealants are the most effective. These are the ones that involve thrombin, but something to keep in mind is the potential for antibody formation. Fibrin sealants have a longer prep time and higher cost than some of the other agents.
Julina Ongkasuwan, M.D.
Hemostasis: As you probably remember from your basic science courses, hemostasis begins with damage to tissues. The first phase is the vascular phase in which you have vasoconstriction, which decreases the amount of blood flow to the area. The damage to the vascular endothelium exposes collagen, which then causes platelet aggregation and adhesion. These platelets release various clotting factors, which I will talk about in more detail shortly and initiates the clotting cascade and clot formation. This is followed by a clot retraction phase and finally a clot destruction phase in which plasminogen is converted to plasmin which then causes clot lysis. Of note this patient was taking Amicar, an agent that inhibits the conversion of plasminogen to plasmin and thus helps stabilize clots.
The clotting cascade traditionally is broken up into two basic pathways, the intrinsic pathway and the extrinsic pathway. The intrinsic pathway is primarily activated as we said before by collagen, which is exposed and then it binds factor XII and initiates this entire cascade. In addition, collagen attacks platelets, which then subsequently become activated with the use of several other different cofactors. They release various factors as well. The extrinsic pathway is stimulated by tissue factor, which is exposed by the tissue injury and through factor VII activation, stimulates this pathway. These two pathways then converge in a common pathway where thrombin converts fibrinogen to fibrin monomers, which are then cross linked with the aid of factor XIII and calcium to form fiber polymer and thus clot. The hemostatic agents have been around for a very long time. There is a report that the Egyptians used various high temperature cautery and waxes and poultices on wounds in order to stop bleeding. There are reports that Native Americans also use scrapping on the inside of animal hides and applied those to wounds. The Greek scholar, Hippocrates, described the use of high temperature cautery as well as various topical hemostatic agents and Celsus, the Roman philosopher and physician who gave us the concept of dolor, color, rubor also described the use of various stypticand high temperature cautery and ligation in order to stop bleeding. In the more modern era, the idea of fibrin used as a topical hemostatic agent was introduced in the early 1900s and Gelfoam was introduced in the 1940s and used in neurosurgical procedures.
So what do we want in a good hemostatic agent? First, the ideal hemostatic agent would of course be such that the agent itself is as well as any of its metabolic breakdown products would be safe to use within the body. Secind, you want it to work and you want it to be efficacious.
The definition of efficacy can vary between the different uses, for example a vascular surgeon may want something that polymerizes very quickly in order to stop bleeding, but does not cause clot of the vessel that they spent all this time anastomosing, where as a reconstructive surgeon for example may want something that polymerizes very slowly to give them time to reposition their flaps or grafts.
Third is usability; you want something that is easy to use and that you can use in a variety of different circumstances. Fourth is affordability. This may be more relevant to a hospital administrator or pharmacist who actually does the purchasing, but it impacts the surgeon because that determines what you have available to you in the operating room. And finally, fifth, approvability. Any of these agents need to be approved by the FDA in order to be used in the US. So the different types of hemostatic agents, which I will be addressing in this talk are listed below and I am going to go through each one of these specifically.
Gelatin sponge or Gelfoam®, which is also known as commercially as Surgifoam again was first introduced in the 1940s by Dr. Gray in the neurosurgical procedures. What it is is purified pork skin gelatin which you can kind think of like Jello®, as it is the same thing that Jello® is made out of.
As you can see on this microscopic view, it has a very amorphous form and has a lot of air spaces and it stains very eosinophilic on H&E stain. Basically the way it works is that its surface essentially acts in the intrinsic pathway causing contact activation and thus platelets. Since it works very proximally within this cascade, you have to have functioning cofactors or clotting factors in order for this to work in helping create clot. Of note, it does absorb approximately 45 times its weight in blood and can expand to approximately 200% of its initial volume. It is absorbed in approximately four to six weeks and on the nasal mucosa it liquifies within two to five days. In the case presentation, this child was initially packed with Gelfoam® approximately a week prior to the time she was seen in the ER and at that point there was no evidence of any Gelfoam left within her nasal cavity. Now the way Gelfoam® can be used, you can either apply dry, directly to the bleeding surface and hold pressure over it or you can wet it in saline and then squeeze out all the air bubbles and use it that way.
Oxidized regenerated cellulose is also known as Surgicel or Oxycel in its commercial forms. It is derived from alpha-cellulose that is actually plant-based. As you can see on microscopic view, Surgicel comes in knit formwhere as Oxycel comes in a microfibrillar form and on microscopic view Surgicel has these fibers which are knit together and they are solid fibers whereas Oxycel has the hollow fibers but they essentially work the same way. Surgicel is relatively acidic and is thought to cause some small vessel contraction. Like Gelfoam, it works at the same point in the intrinsic pathway of clotting causing contact activation. So again the same thing holds that functional clotting factors are needed in order for this to work. It is thought to berelatively bacteriostatic when compared to other hemostatic agents. The theory behind this is that because of its relatively low pH, it deactivates and denatures some of the bacterial proteins especially those related to antibiotic resistance, thus making them more susceptible to antibiotics. It needs to be applied dry and absorbs within four to eight weeks. Of note, on postop imaging Surgicel sometimes causes a ring-enhancing lesion as you can see here on postop imaging, which can be mistaken for an abscess cavity or tumor recurrence. That is something to keep in mind if you are imaging a patient within two months of having operated on them and Surgicel was used during the procedure. On microscopic view, you can see a giant cell reaction.
Our next agent is microfibrillar collagen commercially known as Avitene ®. It is most commonly used in a light flour form, but it does also come in a non-woven web form. This is collagen, which is derived from bovine skin. Under the microscope it is very eosinophilic and of note, under polarizing light it does have periodicity. It binds tightly to blood surfaces, so you do not actually need to achieve a relatively dry field in order to apply it. It causes minimal swelling especially when compared to Gelfoam ®. T he way it works is slightly different because in addition to being collagen and causing contact activation, it does somehow directly activate platelets. But again, it works very proximally within the intrinsic pathway. It is absorbed in three months and it needs to be applied dry.
Collagen sponges, these come in a wide variety of different commercial forms. Again it is similar to Avitene ® and it is derived from bovine Achilles tendon or bovine skin and it works in basically the exact same way as Avitene works and it absorbs in 8-10 weeks.
The next class of hemostatic agents is slightly different: topical thrombin. The idea of topical thrombin has been around since the early 1900s in order to try to achieve clot and in addition the idea of using topical thrombin plus other hemostatic agents such as Gelfoam ® has been around for quite a longtime. In 1999 a new agent was introduced called Floseal™ which basically consists of bovine thrombin plus cross-linked gelatin granules mixed together. So the way it works is your bovine thrombin directly activates fibrinogen and converts it into fibrin monomers. So you can see that this works in a completely different place within the clotting cascade. It works down here in the common pathway bypassing all of the other necessary clotting factors. You do however have to have functional fibrinogen in order for this to work. The product Floseal™ itself is a little bit different from just using topical thrombin plus Gelfoam ® because the gelatin granules have been cross linked in such a way that they do not swell to nearly the same extent. It is absorbed in approximately 6-8 weeks.
Fibrin sealants are the last class of the hemostatic agents that I am going to address. Commercially it comes in many forms including tisseal and crosseal and there are many variations on the idea of fibrin sealants. One of those basic ideas is that you take pure human fibrinogen and combine it with bovine thrombin and they usually throw in an antifibrinolytic agent into the mix as well. So the way this works is that we take the bovine thrombin, it then converts this exogenous human fibrinogen to fibrin monomers, but you do need intrinsic, you need the patient’s own factor XIII and calcium, which then converts it into fibrin polymer. In addition, they usually add an antifibrinolytic agent to the mix as well in order to stabilize the clot. So this does require functional factor XIII and calcium in order for these fibrin sealants to work. They are absorbed within 10-14 days and need a relatively dry field in order to work.
I am going to briefly mention some of the other classes of agents which are out there, but I am not going to address these in detail. There are some completely autologous fibrin sealants. The patient’s own serum is taken and the fibrinogen and thrombin are purified. This achieves essentially the same effect as the fibrin sealants previously mentioned. There are a target platelet gels where again you purify the platelet with plasma and the patient’s own serum combined with thrombin and you get similar agent to the fibrin sealants only there are some additional benefits: you do have some platelet direct growth factors involved which help with wound healing. There are some completely synthetic agents, which are made from polyethylene glycol gels that when you combine them make a completely synthetic hydrogel. Another product is bovine serum plus albumin plus glutaraldehyde, and poly N-acetyl glucosamine is something that the military is investigating as a hemostatic agent and it is a seaweed-based agent. This is just an idea of what is out there in addition to the agents I addressed previously.
Gelfoam ® and Surgicel, work here very proximally in the intrinsic coagulation pathway via contact activation. Collagen also works via contact activation, but also activates platelets. In a completely separate class we have agents that work in the common pathway, which includes Flowseal™, which is essentially topical thrombin and as well as fibrin glue and its variants.
Safety, three things to remember that Gelfoam® swells and it swells a lot. This has proven to be a problem when used within confined spaces such as the spinal foramina where in it can cause spinal cord nerve compression and brain compression.
Surgicel, of note, even though it does have an antimicrobial effect relative to the other hemostatic agents, it is still a nidus for infection. Avitene®, and in fact all of these agents, do cause a certain amount of foreign body reaction and granulation formation. But Avitene® has been found to be the worst offender in this way. You can see in this particular slide, they have the Avitene® cavity here, and then a large amount of surrounding edema and a foreign body reaction with giant cells here surrounding the Avitene®. In this picture you can see the periodic nature of Avitene® under polarized light. In fact, the manufacturers recommend that you apply these agents, then hold pressure and wait a while for a clot to form and then you remove the agent afterwards so that you do not leave it within the cavity in order to try to prevent foreign body reaction as much as possible. In addition, Avitene® because it comes in a light fluffy form, has been known to occasionally cause arterial embolization and it had been reported that it is causing laryngospasm when used in tonsillectomy. Collagen sponge has many of the same side effects as any of the bovine derived agents because there are known allergic reactions to some of these bovine antigens, which are containing these agents.
Floseal™ again as I mentioned before has much less swelling than the Gelfoam so it can be used within some of the more enclosed spaces. Because it is Gelfoam beads it can cause arterial embolization if it is used near a larger vessel. In fact Gelfoam beads themselves have been used in order to embolize arterial malformation. Because it contains bovine antigens, it can have antibody formation, which I am going to talk about a little bit more in detail later. Some of the fibrin sealants use pooled human fibrinogen, in which there is always the potential for transmission of infectious agents. Also again, risks of arterial embolization and antibody formation.
Antithrombin antibodies: These are foreign antigens. A study of 200 patients showed 90% of those exposed to topical thrombin do have a transient elevation in IgG titers. Tadokoro et al in Japan also noted that you can have development of IgE antibodies. This can result in a prolonged thrombin time. Of note, thrombin time is actually a measure of fibrinogen count.
Thrombin time: the way this test was done, you add bovine thrombin to the patient’s fibrinogen and see how long it takes for it to form a monomer. Because you have development of antibodies to bovine thrombin, you can have elevation in your thrombin time. This antibovine thrombin antibody can cross-react with human thrombin, but interestingly enough, this rarely ever causes any sort of clinical bleeding.
The real problem is with antifactor V antibody, as most commercial form of thrombin is contaminated with a certain amount of other bovine antigens and most importantly bovine factor V. So if you can get these antibovine factor V antibodies, which then cross-react with human factor V this can lead to a very severe coagulopathy and because this antibody can act as an inhibitor of factor V. On laboratory tests you can find a very decreased factor V level, increased PT and PTT, which does not correct when you add FFP and vitamin K. When you mix the patient’s sera with a normal human sera, you do not get correction of the PT and PTT which suggest that it is not a cofactor deficiency, but it is actually an inhibitor causing the problem. So as you can see here the factor V is an activator of the conversion of prothrombin to thrombin and this is where you end up with problems. The same study noted that 50% of the 200 patients that they found that were exposed to topical thrombin did develop human factor V antibodies. The problem usually does not happen on the initial exposure, but it is when they are exposed again in the later point to the topical thrombin is when the potential for coagulopathy is exposed. Fortunately these IgG titers do fall off rapidly three to four weeks after the exposure and the treatment if you do encounter this is steroids, cyclophosphamides, IVIG plasmapheresis and platelet transfusion. Of note, I did not see actually any reports of this in the head and neck literature per se; most of the case reports of these events are in the cardiovascular and vascular literature.
Another requirement of a good hemostatic agent is efficacy. Basically there have been lots of studies both in vitro and in vivo using various animal models as well as human studies comparing these various hemostatic agents. The general gist of them is that fibrin sealant work better than Floseal™ which is better than Avitene® and then the collagen sponge, Surgicel and Gelfoam® are essentially equivocal. They do work better than placebo but can barely differentiate efficacy between any of them. Of note, Floseal™ and Avitene® do cause more inflammatory reactions than the others.
Usability: Gelfoam®, Surgicel, Avitene® and these collagen sponge can be stored at the room temperature and are basically ready to use out of the box. Floseal™ does require two to five minute prep time, you combine the thrombin with calcium and combine that to the gelatin granules. Fibrin sealants on the other hand need to be kept in cold storage and thawed prior to usage; it depends on what company you are using and what type and the prep time can be anywhere up to 20-30 minutes. So it is something to keep in mind if you think you want to use fibrin sealant during your case you should be prepared ahead of time in order to do so.
Affordability: This is an average or sort of an idea of what the cost is for some of these agents. Gelfoam®, Surgicel, collagen sponges are relatively inexpensive in a $10-20 per individual piece, whereas Avitene®, Floseal™ and fibrin sealants are much more expensive.
Approvability: All of these agents are regulated through the FDA as a class III medical device, which means they are subjective to this medical device reporting systems so that the manufacturers are obligated to report to the FDA when an adverse event happens. In fact, in 2004 the FDA released notification to users about Gelfoam® and its swelling and use in neurosurgical procedures because of the potential for paralysis.
Summary: These agents are of course not a substitute for meticulous surgical technique. However, they can help decrease OR time and postop bleeding. In my review of the literature I did not see any difference in use or in complications between children and adults. In the case that I presented initially, if you do have a patient who has a known bleeding disorder, a hematology consult obviously can be useful. Hemostatic agents are of limited use because you do have problems in the clotting cascade so they can help you with other more systemic hemostatic agents. Again, this is a summary of the specific agents that I addressed in this talk. The big thing is to remember about the individual ones. Gelfoam® swells, so lot of it is a mechanical effect and you really should not be using it within an enclosed bony cavity. Surgicel has a relative antimicrobial effect when compared to other hemostatic agents. Avitene® has the worst foreign body reaction of all of these particular agents. The collagen sponge has sort of the same problems because is contains bovine parts that do have some antigenetic potential. Floseal™ and fibrin sealants are the most effective. These are the ones that involve thrombin, but something to keep in mind is the potential for antibody formation. Fibrin sealants have a longer prep time and higher cost than some of the other agents.
Fibrin Sealants
Most FS products used clinically outside of the U. S. pose certain risks and, as a result, have not been approved by the Food and Drug Administration for use in the U. S. A. For example the FS products available in Europe contain proteins of non-human origin, e. g., aprotinin and bovine thrombin. Consequently, certain individuals are at risk of developing allergic reactions to such non-human protein additives. U. S. Patent No. 6,183, 498 reports that the use of biomedical adhesives have been observed to induce inflammatory tissue reactions.
Both liquefaction processes, however, are associated with significant effort and a considerable time lag before the product can be used in FS products, which can place an already injured patient into a life-threatening situation. Therefore, significant effort has been undertaken to improve the solubility of lyophilized fibrinogen preparations. For example, one manufacturer requires the use of a magnetic stirrer added to the vials of protein to provide significant agitation while heating. This results in dissolution times which are faster than those obtained for the same product without significant mixing, but it still requires 30-60 minutes of preparation time simply to get the fibrinogen ready to use.
Moreover, when heat inactivation is used to inactivate any viruses that may be present in the FS, the process may result in the formation of denatured proteins, which may also be allergenic. For example, the European heat inactivation methods do not inactivate prions which cause bovine spongiform encephalopathy ("mad cow disease"), which has been epidemic recently in bovine herds in European, and hence disease could be carried in the bovine proteins used in the foreign FS products, risking human infection when those products are used for their intended purpose.
Nevertheless, at a sufficiently high fibrinogen concentration, FS preparations provide safe hemostasis, good adherence of the seal to the wound and/or tissue areas, high strength of the adhesions and/or wound sealing, and complete resorbability of the adhesive in the course of the wound healing process (Byrne et al., Br. J. Surg. 78: 841-843 (1991) ). For optimal adhesion, a concentration of fibrinogen of about 15 to 60 mg/ml is required in a ready-to-use tissue adhesive solution (MacPhee, personal communication). The clinical uses of FS products have been reviewed (e. g., by Brennan, Blood Reviews 5: 240-244 (1991) ; Gibble et al., Transfusion 30: 741-747 (1990); Matras, J. Oral Maxillofac. Surg. 43: 605-611 (1985); Lemer et al., J Surg. Res. 48: 165-181 (1990)).
Baxter/Hyland (Los Angeles, Calif.) in conjunction with The American National Red Cross have co-developed Tisseel, the first commercial fibrin sealant to be approved in the United States (see, e. g., U. S. Patent Nos. 6,054, 122; 6,117, 425; and 6,197, 325 (MacPhee et al.). This FS product has advantages over those available in Europe because it is free of bovine proteins. For example, it contains human thrombin, and it contains no aprotinin, thereby reducing the potential for allergenicity. In addition, it is virally inactivated by a solvent detergent method, which produces fewer allergenic denatured proteins.
However, not only does the need to slowly liquefy the protein components cause a significant delay in the formation of the FS preparation, a significant problem arises once fibrinogen is solubilized because its instability results in a tendency to prematurely self- coagulate. In fact, once prepared, the Baxter instructions indicate that the reconstituted solutions can be kept in their respective vials or syringes for a maximum of only 4 hours, after which any unused sealant must be discarded. As a result, the Baxter FS cannot be stored in a ready-to-use condition for any useful length of time.
Both liquefaction processes, however, are associated with significant effort and a considerable time lag before the product can be used in FS products, which can place an already injured patient into a life-threatening situation. Therefore, significant effort has been undertaken to improve the solubility of lyophilized fibrinogen preparations. For example, one manufacturer requires the use of a magnetic stirrer added to the vials of protein to provide significant agitation while heating. This results in dissolution times which are faster than those obtained for the same product without significant mixing, but it still requires 30-60 minutes of preparation time simply to get the fibrinogen ready to use.
Moreover, when heat inactivation is used to inactivate any viruses that may be present in the FS, the process may result in the formation of denatured proteins, which may also be allergenic. For example, the European heat inactivation methods do not inactivate prions which cause bovine spongiform encephalopathy ("mad cow disease"), which has been epidemic recently in bovine herds in European, and hence disease could be carried in the bovine proteins used in the foreign FS products, risking human infection when those products are used for their intended purpose.
Nevertheless, at a sufficiently high fibrinogen concentration, FS preparations provide safe hemostasis, good adherence of the seal to the wound and/or tissue areas, high strength of the adhesions and/or wound sealing, and complete resorbability of the adhesive in the course of the wound healing process (Byrne et al., Br. J. Surg. 78: 841-843 (1991) ). For optimal adhesion, a concentration of fibrinogen of about 15 to 60 mg/ml is required in a ready-to-use tissue adhesive solution (MacPhee, personal communication). The clinical uses of FS products have been reviewed (e. g., by Brennan, Blood Reviews 5: 240-244 (1991) ; Gibble et al., Transfusion 30: 741-747 (1990); Matras, J. Oral Maxillofac. Surg. 43: 605-611 (1985); Lemer et al., J Surg. Res. 48: 165-181 (1990)).
Baxter/Hyland (Los Angeles, Calif.) in conjunction with The American National Red Cross have co-developed Tisseel, the first commercial fibrin sealant to be approved in the United States (see, e. g., U. S. Patent Nos. 6,054, 122; 6,117, 425; and 6,197, 325 (MacPhee et al.). This FS product has advantages over those available in Europe because it is free of bovine proteins. For example, it contains human thrombin, and it contains no aprotinin, thereby reducing the potential for allergenicity. In addition, it is virally inactivated by a solvent detergent method, which produces fewer allergenic denatured proteins.
However, not only does the need to slowly liquefy the protein components cause a significant delay in the formation of the FS preparation, a significant problem arises once fibrinogen is solubilized because its instability results in a tendency to prematurely self- coagulate. In fact, once prepared, the Baxter instructions indicate that the reconstituted solutions can be kept in their respective vials or syringes for a maximum of only 4 hours, after which any unused sealant must be discarded. As a result, the Baxter FS cannot be stored in a ready-to-use condition for any useful length of time.
Baxters Floseal - bovine and human components
Click here for the Instructions Warnings for Baxters Floseal It's a Pdf so you'll need Adobe reader. The video below shows preparation of floseal.
Sunday, February 24, 2008
Hemostasis Market and Technologies
Topical hemostats and tissue sealants are assured of continued end-user interest due to their ability to improve the effectiveness of surgery and feasibility of minimally invasive surgery, as well as reduce complications and operating time. They also help prevent excess blood loss and aid reconstruction during surgical repair. However, these products are perennially locked in a battle for market dominance. While surgeons have shown a preference for topical hemostats for their lower costs, greater reliability, and established clinical record, there exist significant concerns regarding their use of animal source products.
The current total hemostat market size worldwide is 2B US$, 9% growth rate
–70 million surgical and procedure-based wounds annually worldwide
–20 million surgical procedures in the US
–“10-15% procedures would benefit from increased use of newly-developed adjunctive surgical closure and securement products”
The rising complexities of surgeries have triggered a simultaneous urgency for topical hemostats to control bleeding. These products are particularly useful in burn and wound care and a wide range of surgeries including cardiothoracic, neurosurgery, spine, orthopedic, vascular, dermatology/plastic, and many others. The increasing popularity of minimally invasive procedures is also boosting demand for topical hemostats, encouraging the development of niche products and application devices.
The current total hemostat market size worldwide is 2B US$, 9% growth rate
–70 million surgical and procedure-based wounds annually worldwide
–20 million surgical procedures in the US
–“10-15% procedures would benefit from increased use of newly-developed adjunctive surgical closure and securement products”
The rising complexities of surgeries have triggered a simultaneous urgency for topical hemostats to control bleeding. These products are particularly useful in burn and wound care and a wide range of surgeries including cardiothoracic, neurosurgery, spine, orthopedic, vascular, dermatology/plastic, and many others. The increasing popularity of minimally invasive procedures is also boosting demand for topical hemostats, encouraging the development of niche products and application devices.
- Topical Hemostats:
Collagen-based
Oxygen regenerated cellulose-based
Gelatin-based
Thrombin-based
Combination products - Tissue Sealants:
Fibrin
Synthetic polymer-based
Protein-based
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