Pour chitosan on my wound

Russian scientists have developed aerogels that stop bleeding in a few minutes, and tested them on pigs

Scientists from the D.I. Mendeleev Russian State Technical University have developed aerogels based on the chitosan biopolymer to quickly stop massive bleeding. These are highly porous particles that can be injected locally into wounds: they swell, absorbing red blood cells and other blood components, and as a result, a dense blood clot is formed. Together with colleagues from SPCFU The Russian Ministry of Health scientists conducted tests on laboratory animals (pigs), which showed that aerogel particles stop bleeding in 2-3 minutes, and do not have characteristic disadvantages or side effects of direct analogues on the market. An article about the study was published in September in the journal Polymers.

According to statistics, heavy blood loss is the first cause of death in injuries, while blood can be stopped in various ways. Often, bandages like gauze or bandages are enough to stop bleeding. But there may be cases of massive pulsating bleeding, during which a person can lose a critical amount of blood in a matter of minutes, and they cannot be dealt with in the usual ways. Now they are stopped mainly with the help of porous materials based on zeolites, but they have a serious side effect – when zeolites get into wounds, reactions with heat release begin, and as a result burns remain on the body. Therefore, scientists are looking for new hemostatic materials that will be both effective and safe. 

The development of Russian scientists is based on chitosan, a popular biopolymer that is obtained from the shells of crustaceans. It has a high biocompatibility and therefore chitosan is used in prosthetic coatings (including artificial heart valves), targeted drug delivery systems, skeletons for bone restoration and other biomedical purposes. And in the new work, scientists have made an aerogel based on chitosan – the so-called solid, highly porous materials that consist of 99% air. They have such a large total pore area that if they could all be rolled out on the same plane, then 10 grams of aerogel would be enough for one football field. 

"We combined the properties of chitosan with the unique properties of aerogels and thus obtained a new highly effective hemostatic material that works not only better than chitosan itself, but also better than many modern analogues – it is safer and more convenient at comparable cost and hemostatic properties," says the first author of the work, a researcher at the International Educational andScientific Center for the Transfer of Pharmaceutical and Biotechnologies of the Russian State Technical University, Daria Lovskaya. – Together with colleagues from the St. Petersburg State Chemical and Pharmaceutical University, we conducted tests on pigs: they were damaged by the main vessel, after which there was active bleeding for 45 seconds, and then aerogel particles were injected into the wound using an applicator. After 2-3 minutes, a stable blood clot formed, tightly fitting to the edges of the wound and the bleeding stopped completely."

After the particles of chitosan aerogel enter the wound, they begin to swell rapidly: they absorb various biological fluids and gases released from the wound, and due to the positive charge of chitosan molecules, erythrocytes are attracted, the surface of which is negatively charged. As a result, the aerogel swells and completely closes the wound, stopping the bleeding.

The secret of production – supercritical fluid technology

Aerogel was obtained in several stages: first, chitosan hydrogel was synthesized, that is, a mesh structure with an abundance of pores filled with water. After that, the hydrogel was treated with alcohol in such a way as to replace all the water. And finally, after that, the resulting gel was dried in a supercritical fluid – carbon dioxide, which is located in a special apparatus at a pressure of 73 atmospheres and a temperature of 31 degrees. Under such conditions, the fluid gradually displaced all the alcohol, freeing the pores, but without destroying the structure of the material, and as a result, the hydrogel finally turned into an aerogel.

Scientists used chitosan with different molecular weights and analyzed the structure of the resulting materials. Aerogels based on the shortest chitosan molecules showed the best characteristics: their porosity was 97%, and their density was only 28.6 kg /^m3, that is, almost the entire volume of the material fell on the pores filled with air (for comparison: a standard–sized brick made of such an aerogel would weigh no more than 60 grams). At the same time, most of the pores were more than 0.5 microns in diameter, which is ideal for the adsorption of red blood cells.

After that, the scientists tested the best samples on laboratory animals – six adult pigs. Pigs were injured in the femoral artery, simulating a bullet wound, and after 45 seconds of free blood flow, drugs were injected and then their effect was determined according to the standard procedure for testing hemostatic agents. To evaluate the effectiveness of the new materials, scientists compared the effect of particles of chitosan-based aerogels with pure chitosan in powder form.

Chitosan aerogels and pure chitosan showed similar results: bleeding stopped 2-3 minutes after administration of the drug and did not resume within three hours of observation, the average volume of blood lost was 425 ml, and at the end of the tests all animals successfully passed the march test: they bent and unbent the injured leg, imitating walking, but the bleeding did not resume.

At the same time, aerogels had a number of advantages over pure chitosan particles. Firstly, pure chitosan in powder form can be unevenly distributed over the surface of the wound, that is, it will be partially open to infection, while aerogel particles can be locally and accurately injected with an applicator, and after their rapid swelling they will close the entire wound without gaps. Secondly, chitosan powder often sticks to the edges of the wound and then it is very difficult to separate them from the tissues, which complicates surgical work after stopping bleeding, while with aerogels such problems do not arise, and they are easy to remove from the wound. 

Golden Hour

Hemostatic preparations based on pure chitosan powders have already been presented in scientific papers and even put on the market, but apart from other disadvantages, they have another serious side effect – pure chitosan can disperse through the body along with the blood flow and cause thrombosis. Chitosan aerogels have no such side effects because they have the shape of spherical particles ranging in size from 1 to 3 cm: such particles cannot escape into the bloodstream due to their size, and individual chitosan molecules do not separate from the cross-linked structure of the aerogel.

However, chitosan aerogels have not been considered as hemostatic materials before – there are only some scientific papers where the structure of such materials is optimized for the sorption of oil spills. Nevertheless, all experiments have shown the promise of chitosan aerogels as hemostatic agents, and therefore the researchers plan to further develop the technology of production of the created material.

"In military medicine, there is such a term as the golden hour – if you do not provide proper assistance during the first hour, it can cause death. And with massive venous or arterial bleeding, the bill generally goes for minutes, and if some remedy wins even one minute compared to analogues, this is already a huge achievement," says Daria Lovskaya. – We have shown that our remedy stops bleeding for 2-3 minutes without the characteristic side effects of analogues – it does not cause burns like zeolites and is not capable of causing thrombosis like pure chitosan. In addition, according to our calculations, the cost of chitosan-based aerogels is even lower than that of similar hemostatic agents, because all the starting substances and reagents, the same CO ₂, are quite inexpensive. So our results on a relatively small sample of six animals are a very good starting point for further research."

Scientists have already received a patent for their material, in the future they will modernize its structure in such a way as to further reduce the bleeding time, while preserving all the other advantages and features of the material.

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