Biostability

Polyurethanes as Biomaterials. Much of the progress in cardiovascular devices can be attributed to advances in preparing biostable polyurethanes. Biostable polycarbonate-based polyurethane materials such as Corethane (9) and ChronoFlex (10) offer far-reaching capabiUties to cardiovascular products. These and other polyurethane materials offer significant advantages for important long-term products, such as implantable ports, hemodialysis, and peripheral catheters pacemaker interfaces and leads and vascular grafts. 

Capone CD. Biostability of a non-ether polyurethane. J Biomater Appl, 1992, 7, 108-129. 

Reed AM, Potter J, and Szycher M. A solution grade biostable pol3mrethane elastomer ChronoFlex AR. J Biomater Appl, 1994, 8, 210-236. 

The ability of these peptidomimetic collagen-structures to adopt triple helices portends the development of highly stable biocompatible materials with collagenlike properties. For instance, it has been found that surface-immobilized (Gly-Pro-Meu)io-Gly-Pro-NH2 in its triple-helix conformation stimulated attachment and growth of epithelial cells and fibroblasts in vitro [77]. As a result, one can easily foresee future implementations of biostable collagen mimics such as these, in tissue engineering and for the fabrication of biomedical devices. 

However, most natural peptides are composed of L-form a-amino acids and because of the ubiquitous prevalence of peptidases they have limited biostability, and consequently low bioavailability. Thus, a novel field of peptidomimetics has emerged in drug discovery, in attempts to design non-peptide compounds mimicking the pharmacophore and thus the activity of the original peptide. 

Successful applications of materials in medicine have been experienced in the area of joint replacements, particularly artificial hips. As a joint replacement, an artificial hip must provide structural support as well as smooth functioning. Furthermore, the biomaterial used for such an orthopedic application must be inert, have long-term mechanical and biostability, exhibit biocompatibility with nearby tissue, and have comparable mechanical strength to the attached bone to minimize stress. Modem artificial hips are complex devices to ensure these features. 

Pinchuk L. A review of the biostabihty and carcinogenicity of pol3mrethanes in medicine and the new generation of biostable pol3mrethanes. J Biomater Sci Polym Ed 1994 6 225-267. 

The analysis of microporous Teflon-based arterial prostheses, which were retrieved along autopsies or along revision surgeries, confirmed the excellent biostability of these devices insofar as they had been carefully implanted. Few ruptures or tears were observed but had been likely caused either by a bad handling or by fibrosis expansion, the latter being more frequent for non-sheathed devices (Formichi et al. [22,23]). Taking into account the lack of stability of the prosthesis wall, the two major makers made tremendous efforts to improve this situation. W.L. Gore chose to fit their prostheses with a very thin external sheath, made also of microporous PTFE but almost impervious (Fig. 6). 

Szycher, M., Biostability of polyurethanes, 77 Annual Seminar on Advances in Medical-Grade Polyurethanes, Technomics Publishing, Somervillem Ma, 2000. 

PIB based block copolymers are of interest for biomedical applications due to their superior biostability and biocompatibility (30). 

PIB is well-known for its superior biostability and biocompatibility. Many copolymers based on PIB have been synthesized and studied in this aspect (38,39). 

U. Ojha, P. Kulkami, and R. Faust, Syntheses and characterization of novel biostable polyisobutylene based thermoplastic polyurethanes. Polymer, 50(15) 3448-3457, July 2009. 

Peptidomimetics have found wide application as biostable, bioavailable, and often potent surrogates of naturally occurring peptides. They form the basis of important families of enzyme inhibitors and they act as receptor agonists and antagonists. Peptide chemists are also gaining a deeper understanding of the structural features of this class of compounds that influence their ability to permeate biological membranes and their pharmacokinetic properties. 

Biostable Polymers with Hydrophilic or Bioactive Surfaces... 

Heudorf, U., Angerer, J., Drexler, H., 2003. curent internal exposure to pesticides in children and adolescents in Germany Blood plasma levels of pentachlorphenol (PCP), lindane (y-HCH), and dichloro (diphenyl) ethylene (DDE), a biostable metabolite of dichloro(di-phenyl) trichloroethane (DDT). Int. J. Hyg. Environ. Health 206, 485 191. 

Mathur AB, Collier TO, Kao WJ, Wiggins M, Schubert MA, Hiltner A, Anderson JM. In vivo biocompatibility and biostability of modified polyurethanes. Journal of Biomedical Materials Research 1997, 36, 246-257. 

Kim K, Kim C, Byun Y. Biostability and biocompatibility of a surface-grafted phospholipid monolayer on a solid substrate. Biomaterials 2004, 25, 33-41. 

Takahashi A, Palmer-Opolski M, Smith RC, Walsh K. Transgene delivery of plasmid DNA to smooth muscle cells and macrophages from a biostable polymer-coated stent. Gene Ther 2003 10(17) 1471-1478. 

Various synthetic and natural polymers in biostable and biodegradable classes were investigated over the last decade... 

Biostable polymers have been chosen for use in the majority of DES that are marketed or in clinical development. The main attractiveness of biostable polymers is their physical stability, inertness toward the drug, and predictable drug kinetics. In Cypher, a blend of poly(ethylene-co-butyl methacrylate) (PEVAc/PBMA) is used as the drug carrier. This hydrophobic polymer, along with additional polymer process steps, effectively controls the release of sirolimus, eluting 80% of the drug over 30 days after implantation. In the case of Taxus, atri-block copolymer of styrene-isobutylene-styrene (SIBS) is used as the hydrophobic polymer matrix that releases 10% of incorporated paclitaxel in the first 30 days (20). 

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