الفهرس 
GENERAL INTODUCTIONOnly 14 pages are availabe for public view
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Abstract
1.1. Biodegradable Polymers
Non-degradable polymers, e.g., ethylcellulose, were initially used as an alternative to the natural polymers e.g., albumin and gelatine for microparticle production. However, due to the need for surgical removal after use and their tendency to produce microparticles with high burst releases and poor morphologies, their use in drug delivery is now limited (Chasin 1990; Jalil 1990; Flandory 1993; Whateley 1993). Nowadays, the synthetic biodegradable polymers e.g. polyesters and polyanhydrides (Chasin 1990; Giunchedi 1995; Fiegel 2004) have great applications in biomedical field.
Characteristics of synthetic biodegradable polymers
Synthetic biodegradable polymers have many advantages e.g. they are most commonly used for medical applications as they are more versatile (in terms of their physical and chemical properties which can be altered). Also, they are generally cheaper with higher purity than natural polymers. Furthermore, they have a good biocompatibility profile and upon their degradation they produce degradation products which are easily eliminated without the need for surgical removal (Flandory 1993; Flandroy 1997; Jain 2000).
Poly (Lactic acid) (PLA) is hyDROPhobic, aliphatic polyester with limited wettability and water uptake that can affect its degradation (Engelberg 1991; Clarke 1998). In addition, poly(glycolide), PGA, is a hyDROPhobic aliphatic polyester, however, it is less hyDROPhobic than PLA (Engelberg 1991; Jain 2000). Furthermore, this polyester is not very useful in microparticle production due to its higher crystallinity and insolubility in most organic solvents (Tice 1984; Engelberg 1991; Whateley ).