Synthetic bioresorbable polymers

Abstract The main families of synthetic bioresorbable polymers, which find wide medical application as temporary mechanical supports such as sutures, as tissue engineering scaffolds, and as mediators of release rate for the controlled release of drugs are outlined. The physical and chemical mechanisms by which they degrade are discussed and the factors that can affect their rates of degradation are examined. 

Key words poly(alpha-hydroxy acids), degradation rate, polyglycolide, polylactide, degradation. 

Note This chapter was previously published as Chapter 3 Synthetic bioresorbable polymers by R. E. Cameron and A. Kamvari-Moghaddam, originally published in Degradation rate of bioresorbable materials predication and evaluation, ed. F. J. Buchanan, Woodhead Publishing Limited, 2008 ISBN 978-1-84569-329-9. 

Polymer chemical stracture can be tailored to control degradation behaviour, making them, under physiological conditions, bioinert or bioresorbable over a defined period. Polymer degradation is generally denoted by a deterioration in the functionality of the polymeric material caused by a change in its physical and/or chemical properties. In this chapter, the different degradation 

What follows is a short overview of the properties and degradation mechanisms for the most widely used of the polymers listed in Table 5.1, with particular attention paid to the poly(a-hydroxy acids). 

---

Table 5.1 List of common synthetic bioresorbable polymers...

Using synthetic bioresorbable polymers for orthopedic tissue regeneration... 

Cameron, R.E., Kamvari-Moghaddam, A., 2008. Synthetic bioresorbable polymers. Degradation Rate of Bioresorbable Materials. Woodhead Pubishing Limited, Cambridge England, pp. 43 6. 

Synthetic bioresorbable polymers offer several advantages over namral polymers in the development of TE scaffolds (1) they can be produced on a large scale, at low cost, and in a reproducible manner (2) they have no risk of immunogenicity (3) they are easier to process and (4) their properties and degradation kinetics can be easily tailored for the required application. Main drawbacks are that they are less biocompatible than natural polymers and they typically do not present cell recognition sites. In addition, the degradation products of many of them are not natural metabolites and might cause problems if accumulated. 

One of the major classes of synthetic bioresorbable polymers is that of aliphatic polyesters or poly(a-hydroxy acids). Poly(a-hydroxy acids) such as PGA, poly(lactic acid) (PLA) stereoisomers poly(L-lactic acid) (PLLA) and poly(D-lactic acid), and pol-y(lactic-co-glycolic acid) (PLGA) copolymers are the most widely used and most popular bioresorbable polymers since they received Food and Drug Administration (FDA) approval for clinical use in humans in different forms (eg, fibers for sutures, injectable forms) (Nair and Laurencin, 2007). These polymers are commonly used in regenerative medicine applications. An example is the InQu Bone Graft Extender Substitute (ISTO Technologies), an osteoconductive biosynthetic product used as bone graft substitute in the skeletal system to support new bone formation. The resorption rate of... 

Table 19.1 Natural and synthetic bioresorbable polymers used in the field of cardiovascular regenerative medicine...

Because of such complex requirements, the number of synthetic bioresorbable polymers for practical use is limited. This must have been the limitation faced by nature too since all life on earth is based on only three polymeric backbones, namely, polynucleotide, poly(a-amino acid), and polysaccharide chains [11]. For the same reasons, synthetic bioresorbable polymers have been restricted only to certain classes of polymers and till now only a few of them have been approved by the FDA for certain specific applications. 

The earliest synthetic bioresorbable polymers were based on linear aliphatic polyesters. More recently, many other classes of polymers have been explored to develop new resorbable systems for various biomedical applications. Today, a variety of polymer systems having tailored bioresorption profiles are being used or researched for specific biomedical applications. All these bioresorbable polymeric... 

This review focuses on those synthetic bioresorbable polymers that can be spun into fibers or filaments, and subsequently used as biotextiles. We have listed and reported on the properties and applications of both conventional and commercially available fiber-forming bioresorbable polymers as well as those that are still being developed experimentally. Factors affecting the performance of these biomaterials are presented and the precautionary measures that may be taken to reduce the hydrolytic degradation during manufacturing and processing are discussed. 

---