Bioerodible materials

Skeletal Biocompatibility. Two Substituent Groups Attached to the Same Phosphazene Skeleton. Hydrolytical Instability 0 II — NH- CH2— C- OC2H5 Glycine or Lower Alkyl Aminoacid Esters Hydrolytically Unstable Polymers. Bioerodible Materials. Drug Delivery Systems. Tissue Engineering... 

Skeletal Biocompatibility. Hydrolytical Instability Glycolic Esters or Lactic Esters Hydrolytically Unstable Polymers. Bioerodible Materials... 

Some of the most useful polyphosphazenes are fluoroalkoxy derivatives and amorphous copolymers (11.27) that are practicable as flame-retardant, hydrocarbon solvent- and oil-resistant elastomers, which have found aerospace and automotive applications. Polymers such as the amorphous comb polymer poly[bis(methoxyethoxyethoxy)phosphazene] (11.28) weakly coordinate Li " ions and are of substantial interest as components of polymeric electrolytes in battery technology. Polyphosphazenes are also of interest as biomedical materials and bioinert, bioactive, membrane-forming and bioerodable materials and hydrogels have been prepared. 

MAJOR APPLICATIONS Polymers have shown promise as bioerodible materials capable of (controlled degradation and sustained drug delivery for therapeutic cmd other related uses/ Polyphosphazenes have been evaluated for approximately two decades, but resecirch has become more focused in recent years. 

J. Kohn, R. Langer, Bioresorbable and bioerodible materials. Biomaterials Science An Introduction to Materials in Medicine, Academic Press, San Diego, 1996, pp. 64—72. 

Most bioinert rigid polymers are commodity plastics developed for nonmedical applications. Due to their chemical stability and nontoxic nature, many commodity plastics have bwn used for implantable materials. This subsection on rigid polymers is separated into bioinert and bioerodable materials. Table 11.6 contains mechanical property data for bioineit polymers and is roughly ordered by elastic modulus. Polymers such as the nylons and poly(ethylene terephthalate) slowly degrade by hydrolysis of the polymer backbone. However, they are considered bioinert since a significant decrease in properties takes years. 

Also, it may be desirable for a stent to be biodegradable. In many treatment applications, the presence of a stent in a body may be necessary only for a limited period. Therefore, stents fabricated from biodegradable, bioabsorbable, or bioerodable materials should be configured to completely disappear after the clinical need for them has ended (66). 

Polyphosphazenes are also of interest as biomedical materials and bioinert, bioactive, membrane-forming, and bioerodable materials (1). 

Bioerodable materials in current use are limited to applications that do not require long-term strength retention. It is acknowledged by the medical profession that problems exist with the current practices of bone fracture fixation. Two serious problems are osteoporosis due to stress shielding [1-3] and necessary second operations for device removal after bone healing. To alleviate these problems, polymers of a-hydroxy acids such as lactic and glycolic acid are being explored. They have shown potential utility as biocompatible, fully resorbable implant devices. The biocompatibility of poly(a-hydroxy acids) has been known for some time from in vivo acute and subacute tissue reaction [4], as well as in vitro cytotoxicity response [5]. Sutures of these materials have been in use now for many years. 

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