LACTIDE COPOLYMER

Similar to pure polyglycoHc acid and pure polylactic acid, the 90 10 glycolide lactide copolymer is also weakened by gamma irradiation. The normal in vivo absorption time of about 70 days for fibrous material can be decreased to less than about 28 days by simple exposure to gamma radiation in excess of 50 kGy (5 Mrads) (35). 

Lactic acid and levulinic acid are two key intermediates prepared from carbohydrates [7]. Lipinsky [7] compared the properties of the lactide copolymers [130] obtained from lactic acid with those of polystyrene and polyvinyl chloride (see Scheme 4 and Table 5) and showed that the lactide polymer can effectively replace the synthetics if the cost of production of lactic acid is made viable. Poly(lactic acid) and poly(l-lactide) have been shown to be good candidates for biodegradeable biomaterials. Tsuji [131] and Kaspercejk [132] have recently reported studies concerning their microstructure and morphology. 

SCHEME 8.8 Synthesis of statistical poly(trimethylene carbonate-co-D,L-lactide) copolymers. 

Occasionally in the synthesis of the copolymers, insoluble material is produced. This results from polymer containing blocks of polyglycolide rather than the desired random structure. Obviously, such compositions would have considerable effect on the performance of controlled release formulations utilizing those polymers. This problem is particularly evident when one is seeking to utilize the 50 50 glycolide/lactide copolymer as a biodegradable excipient. However, with carefully controlled polymerization conditions, useful 50 50 polymer is readily produced. 

A testosterone microsphere system for treatment of hypogonadol males has been developed and clinically evaluated (61,78). This formulation is based on a glycolide/DL-lactide copolymer and natural testosterone (Fig. 6). Because testosterone is not a very potent compound, about 600 mg of the drug is needed in adult males over a 90-day period. The performance of the testosterone system in baboons is shown in Fig. 7. Similar formulations have also been used in the control of the wild horse population of the western United States. Stallions were injected with a testosterone microsphere formulation designed to inhibit sperm production over a 6-month period (79). 

Tabata, Y. and Ikada, Y., Activation of macrophage in vitro to acquire antitumor activity by a muramyl dipeptide derivative encapsulated in microspheres composed of lactide copolymer, J Control. Rel.. 6, 189, 1987. 

Gardner, D. L., Battelle Development Corp., Process of preparing microcapsules of lactides or lactide copolymers with glycolides and/or c-caprolactones, U.S. Patent 4,637,905, A,... 

Poly-(vinyl alcohol)-lactide copolymer Vinyl alcohol Lactic acid [147]... 

TABLE 2. Physical Properties of Selected Poly(7V-vinyl-2-pyrrolidone)-A-poly-(D,L-lactide) Copolymers Prepared According to the Current Invention... 

Resulting poly(a-hydroxyacids) are important biomaterials used as resorbable sutures and prostheses [196]. The mechanism of polymerization is not well established. Polymerization may be initiated with Lewis acids (SbF3, ZnCl2, SnCl4) however, other typical cationic initiators (e.g, triethyloxonium or triphenylcarbenium salts) fail to initiate polymerization [197]. Thus, it is not clear whether polymerization proceeds by typical cationic mechanism or rather involves the coordination mechanism. The chain transfer to polymer resulting in transesterification was postulated [198,199] and confirmed later by detailed, 3C NMR studies of lactide copolymers [200]. 

Absorbable sutures are collagen sutures, polyglycolic acid and its lactide copolymers, and polydioxanone. Nonabsorbable sutures include silk, cotton, polyethylene, polypropylene, nylon, PET, and stainless steel. These fibers can be used as monofilaments or multifilaments (twisted or braided). Figure 2.16 shows examples of filters for medical purposes made of polyester, nylon, and metallic fibers. In summary, fibers are used in almost everything that we can see in our... 

Poly-p-dioxanone and copolymers Poly-p-dioxanone (PDS) Copolymers of PDS and 1-lactide Copolymers of PDS and glycolide Poly-p-dioxanone-co-morpholine-2,5 dione Copolymers of p-dioxanone and polyethlyene-p-phenylene diglycolate Copolymers of polytrimethylene malonate and p-dioxanone A, B, F, G A, B, G A, B, G A, B, G A, B, G, J A, B, G, H... 

Chu CC. The effect of pH on the in vitro degradation of poly (glycolide lactide) copolymer absorbable sutures. / Biomed Mater Res 1982 16 117-124. 

Lactic acid and levulinic acid are two key intermediates prepared firom carbohydrates. Lipinsky compared the properties of the lactide copolymers obtained from... 

Segmented high-lactide copolymers for use in implants with prolonged in vivo strength retention... 

Shalaby, S. W., High Strength Fibers of Z-Lactide Copolymers, e-Caprolactone, and Trimethylene Carbonate and Absorbable Medical Constructs Thereof, U.S. Patent (to Poly-Med, Inc.) 6,342,065, 2002. 

Results in this study demonstrated the feasibility of designing segmented, high-lactide copolymer chains as crystalline fiber-forming polymers for the... 

The results of the study demonstrated that different segmented, high-lactide copolymers can be used to prepare braided sutures with clinically... 

Fu, B., Hsiao, B., Chen, G., Zhou J., Koyfman, I., Jamiolkowski D. D. and Dormier E., Structure and property studies of bioabsorbable poly(glycolide-co-lactide) fiber during processing and in vitro degradation. Polymer, 43,5527,2002. Fischer, E. W., Sterzel, H. J. and Wegner, G., Investigation of the structure of solution grown crystals of lactide copolymers by means of chemical reactions, Kolloid-Z. Z. Polym., 251,980. 1973. 

The multifilament, coreless suture is preferably made of an absorbable material, such as a segmented lactide copolymer (such as those described in Chapter 2 of this book). The first sealing member 1, second sealing member 3, and the elongated member 2 are made of the flexible absorbable polyaxial copolymer, such as those described in Chapter 3. 

FIGURE 9.3 Functional glycolide, lactide, and morpholine-2,5-dione systems for the synthesis of functional lactide copolymers. 

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