Poly glycolic acid

The main members of this class of polyesters are poly(glycolic acid) and poly (lactic acid) as well as their copolymers. The synthesis of these two polyesters is in many respects similar however, their physical properties are very different, as will be presented in the following text. 

---

In order to become useful dmg delivery devices, biodegradable polymers must be formable into desired shapes of appropriate size, have adequate dimensional stability and appropriate strength-loss characteristics, be completely biodegradable, and be sterilizahle (70). The polymers most often studied for biodegradable dmg delivery applications are carboxylic acid derivatives such as polyamides poly(a-hydroxy acids) such as poly(lactic acid) [26100-51-6] and poly(glycolic acid) [26124-68-5], cross-linked polyesters poly(orthoesters) poly anhydrides and poly(alkyl 2-cyanoacrylates). The relative stabiUty of hydrolytically labile linkages ia these polymers (70) is as follows ... 

Polymeric, prepared as thin smooth films (with the exception of poly(glycolic acid))... 

Poly(glycolic acid) Dexon Davis Geek Biomedical b... 

Poly (glycolic acid) (PGA), 41, 42, 85 preparation of, 99 Polyheterocyclization concept, 265 Poly(hexafluorobisphenol-A), 361 Poly(hexamethylene adipamide), 5 Poly(hexamethylene adipate), 5 Poly(hexamethylene fumarate) synthesis, 100-101... 

W. J., Degradation rates of polymei and copolymers of poly-lactic and poly glycolic acids. Oral Surg. Oral Med. Oral Pathol.,... 

FIGURE 22 Semilog plot of the in vitro rate of hydrolytic chain scission of PCL, poly glycolic acid-co-lactic acid, and a 1 1 blend of the two polymers, demonstrating the use of blends to modify degradation rates. (From Refs. 64 and 65.)... 

The rate of hydrolysis of the partially ethoxylated polymer was retarded, although not to the extent calculated from theory (Fig. 25), suggesting some contribution to the rate of chain scission by an uncatalyzed process. End-capping poly (glycolic acid-co-lactic acid) has a similar effect on the rate of hydrolysis of this polyester (100). 

Blending of PCL and poly(glycolic acid-co-lactic acid) has been also used to control the rate of chain scission of the composite. 

Thus, while these two polymers differ greatly in their rate of hydrolytic chain cleavage, gel permeation chromatography (GPC) analysis of a 1 1 blend of PCL and poly(glycolic acid-co-lactic acid) in pH 7.4 buffer showed that both components of the blend were subject to the same rate of chain cleavage (65). 

Based on these studies, it is obvious that poly(N-acylhydroxy-proline esters) are very slowly degrading polymers. These materials may therefore be useful for long-term applications, such as implantable, multiyear contraceptive formulations. For such applications the degradation rates of poly (lactic acid)/poly (glycolic acid) devices would probably be too rapid. 

In summary, preliminary results from two animal models (rabbit and mouse) indicate that poly(N-palmitoylhydroxyproline ester) elicits a very mild, local tissue response that compares favorably with the responses observed for established biomaterials such as medical grade stainless steel or poly(lactic acid)/poly(glycolic acid) implants. At this point, additional assays need to be performed to evaluate possible allergic responses, as well as systemic toxic effects, carcinogenic, teratogenic, or mutagenic activity, and adaptive responses. 

Common biodegradable polymers for medical devices are constructed from synthetic linear aliphatic polyesters. One material commonly used for internal sutures is poly(glycolic acid) (PGA). PGA is synthesized from the dimer of glycolic acid (Fig. 13.1.l). 1... 

Figure 13.1.1 The synthesis of poly(glycolic acid) (PGA) from the dimer of glycolic acid.

This field has been well reviewed by B. J. Tighe.(82) The polymers, for the most part, are polyesters. Poly(glycolic acid) (83) is widely used in sutures under the trade name of DEXON. Poly(lactic acid) is also used.(84) A copolymer of 92/8 mole percent poly(glycolic acid)/poly(lactic acid) (85,86) is another alternative. 

Recent advances have seen both Tighe(87) and Lenz(90)developing procedures for carboxylated polyesters. Tighe has evaluated biologically produced polymers.(88) American Cyanamid Company continues to modify poly(glycolic acid) by copolymerizing ethylene oxide.(89)... 

The most common synthetic biodegradable polymers for suture material and their corresponding weight loss in aqueous solution are listed in Table 3.10. Of these, poly(glycolic acid), PGA, poly(lactic acid), PLA, and copolymers of these two polyesters are the most widely used for resorbable sutme material. PGA is a tough. 

Poly(L-lactic acid) (PLLA 8%)-co-Poly(glycolic acid) (PGA 92%) 450... 

---