Biodegradable and nonbiodegradable materials

There are many polymers which have been used as physical matrices for controlled delivery of drugs. In this paper, these polymers are separated into water-soluble, biodegradable, and nonbiodegradable materials. A description of each class of polymers is presented. Examples of polymers from each class that have been used as drug delivery matrices and the criteria for their selection are included in this general review. 

All of these opportunities, such as combination of synthetic and natural polymers, combination of biodegradable and nonbiodegradable materials, with or without incorporation of stem cells, potential functionalization of scaffolding, and tuning of mechanical properties open a complex but awesome medical field in tissue engineering. 

Figure 11.8 Mechanical properties of selected protein-based films compared with some biodegradable and nonbiodegradable materials. Adapted from S. Guilbert, N. Gontard, M.H. Morel, P. Chalier, V. Micard and A. Redl in Protein-based Films and Coatings, Ed., A. Gennadios, CRG Press, Boca Raton, FL, USA, 2002 [63]. All nonreferenced data are from Saechtling [6] and from commercial data sheets.

Biocompatibility is the ability of a biomaterial to perform with desired response(s) in a target application. In other words, it cannot be defined in terms of the material properties alone, but it is a combination of the material properties and the function for which it is intended. A variety of materials have been tested as medical devices, which include polymers, metals, ceramics, and their composites. These medical devices can be divided into two groups biodegradable and nonbiodegradable. 

PHAs have been blended with many biodegradable and nonbiodegradable polymers to improve their properties and lower material costs. Miscibility, crysMlization behavior, and biodegradability of the blends are the main topics of the published articles on PHA blending. PHB was found to be miscible with poly(ethylene oxide) (PEO), poly(vinyl acetate) (PVAc), poly(p-vinylphenol), poly(vinylidene... 

Holes can be cut to allow planting through the membrane as appropriate. Membranes may be covered with a loose mulch, to hold them in place, extend their life span, and improve their appearance. A mulch membrane must be permeable, to allow air and water into the soil, unless it is only to be kept in place for a few months. However, to suppress the more vigorous perennial weeds (see also pp.80-81), the membrane may need to be in place for several years while there are several biodegradable choices of membrane material, a nonbiodegradable material is the more practical option in such situations. 

The distinction between bio-based and conventional plastics is based on the source of feedstock and should not be confused with biodegradable polymers (discussed in Chapter 6). Biodegradability is merely a property or functionahty of a plastic material. Both bio-based and conventional polymers can be biodegradable or nonbiodegradable in the environment as illustrated in Table 4.9. As nonbiodegrada-ble is strictly a misnomer (see Chapter 6), the term durable is used in its place. 

Polymer Blends Incorporating PHA. The mechanical properties, morphology, biodegradability, and thermal and crystallization behavior of PHAs melt-blended or solvent-cast with nonbiodegradable pol5uners [such as poly(vinyl acetate)] and with biodegradable materials [such as wood cellulose fibers (21) and starch] have been reviewed (22). PHB blends with poly(ethylene oxide), poly(vinyl alcohol), poly (L-lactide), poly(D,L-lactide), poly( -caprolactone), poly(3-butyrolactone), P(HB-co-HV), and cellulose and starch derivatives have been... 

In the last few years, biodegradable polymers like PLA have been established in different nonbiodegradable applications. PLA is processed into fibers (e.g., for textiles) or is used for durable parts in electronics. The driver for these applications is the content of renewable materials and not the polymer s biodegradability. 

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