Documents / Report
This Defense Intelligence Agency reference document, dated 7 January 2010 and prepared under the Acquisition Threat Support series, surveys biomaterials used in medicine. It covers biocompatibility, biosensor membranes, silicones, Teflon, biodegradable polymers, hydrogels, titanium, bioceramics, tissue constructs, cardiovascular stents, contact lenses, drug delivery and dialysis. It concludes that biomaterial performance underlies many medical devices, that the industry is slow to adopt new materials because of testing costs, and that innovation mainly involves new applications of established materials.
UNCLASSIFIED/fFOll OPPllllliL 1111 a,•1r.t one free from concerns of immunogenicity. These polymers can be optically clear, exhibit good flexibility, and have strength comparable to that of many plastics. BIODEGRADATION ADVANTAGES In the human body, biodegradable polymers have good compatibility but also decompose to harmless materials and over time dissolve altogether. Biodegradable polymers undergo a chemical hydrolysis in the salty and wet environment of tissues by way of a labile chemical backbone of the polymer. The degradation starts immediately upon water exposure and occurs in two steps. In the first step, the material thoroughly hydrates, and the water attacks the polymer chains!' converting long chains into shorter, water-soluble fragments. The desirable aspect of this process is a reduction in molecular weight without a loss in physical properties, since the device matrix is still held together, even with the shorter chains. In the second step, the shorter polymer chains are attacked by enzymes that are naturally present in tissues. Basically, a metabolization of the fragments by the body tissues results in a rapid loss of polymer mass, what is referred to as bulk erosion. All the commercially available synthetic devices and sutures degrade by bulk erosion. DEGRADABLE BIOMATERIALS Different biodegradable polymers have different lifetimes in tissues, ranging from a few days to years. Combining two different biopolymers-for example, short-lived (days) PLA (polylac::tide) and longer lived (months) PGA (polyglycolide)-reveals that polymers can be produced with intermediate decomposition times. Thus, their decay times can be custom determined through their formulation. Biodegradable polymers fulfill a physician 1s desire to have an implanted device that will not require a second surgical intervention for removal, which is desirable in many applications. In orthopedic applications, for example, a fractured bone that has been fixated with a rigid, nonbiodegradable stainless implant has a tendency for refracture upon removal of the implant, making removal undesirable. This refracturing results from the offloading of the stress on the bone by the stainless steel support because the bone has not carried a sufficient load during the healing process. However, a fixation system prepared from a biodegradable polymer can be engineered to degrade at a rate that will slowly transfer the load to the healing bone, thereby avoiding the risk of refracture and eliminating the need to remove the implant. POLYLACTIC ACID AND POLYGLYCOLIC ACID Polylactic acid (PLA), polyglycolic acid (PGA), and their copolymers are the most widely used of the biodegradable polymers. These materials, when exposed to the sun and weather, will degrade into water and carbon dioxide and essentially vanish, given sufficient time. In the human body, combinations of PLA and PGA are used to control the longevity of a material by controlling its degradation rate when exposed to tissues. The degradation products in the human body are also water and carbon dioxide. 8 UNCLASSIFIEU/s'FOR: QFFIGl,l.al I P&i OIIL¥
Not linked to a story yet.
Report, from the dia collection. The PDF is mirrored here; the original link is above. 32 pages are in the text index: search them above, or from the library's search.