11.1 INTRODUCTION

Polymers are large molecules synthesized from smaller molecules called monomers. Most polymers are organic compounds with carbon as the base element. Plastics are polymers that are rigid solids at room temperature and generally contain additional additives. Some common plastics used in biomedical applications are polymethyl methacrylate for intraocular lenses, braided polyethylene terephthalate for vascular grafts, and ultrahigh-molecular-weight polyethylene for the articulating surfaces of orthopedic implants. Polymers and biopolymers in particular encompass a much broader spectrum than plastics alone. Biopolymers include synthetic polymers and natural polymers such as proteins, polysaccharides, and polynucleotides. This chapter will only cover the most commonly used examples in each class but will provide references to more specific sources.

Many useful polymers are water-soluble and are used as solutions. Hyaluronic acid is a naturally occurring high-molecular-weight polymer found in connective tissues and is used to protect the iris and cornea during ophthalmic surgery. Polyvinyl pyrrolidinone is a synthetic polymer used as a binder or additive in 25 percent of all Pharmaceuticals.1 Hydrogels are another class of polymers that has many biomedical applications. Hydrogels are polymers that swell in water but retain their overall shape. They are therefore soft and moist and mimic many natural tissues. The most wellknown hydrogel series is poly(hydroxyethyl methacrylate) (PHEMA) and PHEMA copolymers, which are...