Chapter 10 Biodegradation

Abstract

Chronically implanted devices depending on polymers have contributed significantly to improving the quality of life for many people. Examples of such devices include joint prostheses, cardiac pacemakers, arteriovenous shunts for dialysis, vascular grafts, cerebrospinal fluid (CSF) shunts, urethral catheters, sutures, mammary prostheses, dental prostheses, heart valves, neural stimulators, and implantable defibrillators. Some of the more common examples of polymers generally considered to be implantable and biostable include polyethylene, polypropylene, polyether polyurethanes, (aromatic) polyesters, silicone rubbers, hydrogels (poly HEMA), (solid) acrylics, and fluoro polymers (such as teflon). Many other polymers have physical properties that are very desirable for use in implanted devices, but their biostability is controversial or limits them to use in relatively short-term implants. The polyamides (nylons) and (aliphatic) polyester polyurethanes are examples. Certainly there are implantable devices that are intentionally designed to biodegrade, such as tissue scaffolds. The purpose of this chapter, however, is to review the failure mechanisms that can affect biostable polymers: those polymers that are intended to maintain properties adequate to facilitate the long-term performance of implanted devices. In addition, this chapter will review some of the test methodology needed to qualify a biostable polymer for human use.