Biostable polymers

Biostable Polymers with Hydrophilic or Bioactive Surfaces... 

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. 

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). 

Based on their behavior in living tissue, polymeric biomaterials can be divided into two groups biostable and biodegradable. Biostable polymers are used when permanent aids are needed, e.g., as prostheses [13]. Biostable polymers, typically polyethylene and poly(methyl methacrylate), should be physiologically inert in tissue conditions and maintain their mechanical properties for decades [11]. 

Poly(propylene) is one of the biocompatible, biostable polymer used widely in clinical applications ranging from sutures to load-bearing implants (Figure 18.1b). Poly(propylene) has fiber-forming characteristics and has been used in the treatment of ventral incisional hernia [22,23]. Poly(propylene) has excellent stiffness and strength when compared to polyethylene [24]. Superior mechanical performance in fatigue and temperature resistance offers sufficient mechanical property even at body temperature and able to bear millions... 

Presently enzymes can hardly be used to degrade artificial synthetic polymers unless it is under special conditions. It is worth noting that compounds like poly(vinyl alcohol), PVA, bacterial polymers and poly(e-caprolatone), PCL, that are biodegradable under outdoor conditions are degraded abiotically and thus very slowly in an animal body where they are not biodegradable. Despite this difficulty the number of artificial polymers proposed as biodegradable biomaterial candidates to replace biopolymers or biostable polymers is increasing. 

Polymers for medical applications are engineered to be either biostable or biodegradable. The insulation on a pacemaker lead should be stable in the body for at least 10 years. A catheter that is used for 1 h need not be constmcted of highly biostable polymers. A tissue engineering scaffold should degrade in the body over the time period that the new tissue reconstmcts -when the new tissue is complete, the scaffold should be gone. 

The body is a highly reactive environment that challenges our abilities to design perfectly biostable polymers - in time (20+ years), aU polymers will degrade to some degree in vivo. 

Due to the fact that the application of an implant material can be permanently or temporary required biostable or biodegradable biomaterials are used. In case of polymers the term biostable is to view with the limitation that also biostable polymers, such as PE intended mainly for non-vascular applications such as... 

From an environmental point of view, solving solid waste problems associated with the use of biostable polymers by their replacement with biodegradable polyesters is obviously a good choice. Recycling of polymers is also of... 

GiU and Andrulis described the use of platinum amines complexed with water-soluble biodegradable or biostable polymers. The platinum is bonded covalently through the oxygen of the salt of the acid functionality as shown in 54, producing the square-planar platimun... 

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