From Halopedia, the Halo wiki
Biofoam (short for biomedical foam) is a self-sealing, space-filling coagulant and an antimicrobial, tissue-regenerative foam polymer used by the United Nations Space Command as a form of medical first aid. This foam keeps damaged organs in place and helps stop bleeding and hemorrhaging. The medicinal compound is morphophetamine in a polyethyltriphosphate foaming medium dispensed with nitrous oxide. The standard dosage is 10 centiliters (10cL) or 3.38 fl. oz. Within the Unified Earth Government, biofoam is an OTC-legal product; biofoam can be purchased legally "over-the-counter".
Biofoam canisters are prefilled with an expansion agent and liquid polyethyltriphosphate. The two mix and are exposed to air when biofoam is applied to a wound, immediately producing a foaming reaction. The foam strongly adheres to tissues and simultaneously releases encapsulated medical compounds that advances clotting, disinfects the wound, and eventually numbs pain. After a short duration of time, the foam applied will set and become a semi-rigid, porous mass internally, which forms a hardened skin on regions of the body exposed to air.
Biofoam is rubbed into the skin or injected deeper into the body. It is very painful to use, at least initially, described as feeling like "burning ants crawling around the wound" and "thousands of tiny knives" stabbing the recipient. However, biofoam has been described as being able to numb pain.[note 1] It is likely that only the application is painful, and that the biofoam quickly numbs the wound after settling. Biofoam does not seem to have this kind of painful reaction when applied to an unwounded area, as the Rookie is seen spraying a small amount on his uninjured fingers and does not react in pain. It is often used as a medical option when there are no medical personnel available. Bottles of biofoam are found in health packs. Often UNSC medics will use it as a sealing agent during treatment in field hospital. While exploring the abandoned New Mombasa by himself, the Rookie used civilian biofoam canisters, with the brand name Optican, to heal his wounds, as no military medical supplies were available.
The effects of biofoam are temporary, and after a time, usually a few hours, it simply breaks down. Therefore, it is normally a form of first aid, used only as a temporary sealant until proper medical attention can be sought. In extremely rare cases, allergic reactions to biofoam have been documented. Edema is another rare side effect of biofoam, caused by excess fluid trapped in the body's tissues.
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