Poly-L-lactide

The actual time required for poly-L-lactide implants to be completely absorbed is relatively long, and depends on polymer purity, processing conditions, implant site, and physical dimensions of the implant. For instance, 50—90 mg samples of radiolabeled poly-DL-lactide implanted in the abdominal walls of rats had an absorption time of 1.5 years with metaboHsm resulting primarily from respiratory excretion (24). In contrast, pure poly-L-lactide bone plates attached to sheep femora showed mechanical deterioration, but Httie evidence of significant mass loss even after four years (25). 

The crystallinity of poly(lactide- (9-glycoHde) samples has been studied (36). These copolymers are amorphous between the compositional range of 25—70 mol % glycoHde. Pure polyglycoHde was found to be about 50% crystalline whereas pure poly-L-lactide was about 37% crystalline. An amorphous poly(L-lactide-i (9-glycoHde) copolymer is used in surgical cHps and staples (37). The preferred composition chosen for manufacture of cHps and staples is the 70/30 L-lactide/glycoHde copolymer. 

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. 

Bandyopadhyay, S., Chen, R. and Giannelis, E.P. 1999. Biodegradable organic-inorganic hybrids based on poly(L-lactide). polymer material science engineering 81 159-160. 

Kulinski, Z. and Piorkowska, E. 2005. Crystallization, structure and properties of plasticized poly(L-lactide). Polymer 46 10290-10300. 

Lannace, S., Ambrosio, L., Huang, S.J. and Nicolais, L. 1994. Poly(3- hydroxybutyrate)-co-(3-hydroxyvalerate)/poly-l-lactide blends thermal and mechanical properties. Journal of Applied Polymer Science 54 1525-35. 

Paul, M., Alexandre, M., Degee, P., Henrist, C., Rulmont, A., and Dubois, P. 2002. New nanocomposite materials based on plasticized poly(L -lactide) and organo-modified montmorillonites thermal and morphological study. Polymer 44 443-450. 

Zhenyang, Y., Jingbo, Y., Shifeng, Y., Yongtao, X., Jia, M. and Xuesi, G. 2007. Biodegradable poly(L-lactide)/poly(3-caprolactone)-modified montmorillonite nanocomposites Preparation and characterization. Polymer 48 6439-6447. 

Table 1 provides a summary of the glass transition temperatures of several lactide/glycolide polymers. Tg values range from about 40 to 65°C. Poly(L-lactide) has the highest Tg at about 65°C. 

Controlled release fiber systems based on aliphatic polyesters were investigated by Dunn and Lewis (51-54). The feasibility of hollow fibers spun from poly (L-lactide) and containing the contraceptive steroid levonorgestrel has been demonstrated (55). 

None of the early systems have enjoyed significant clinical success (67). This is most probably due to two factors. Most of the formulations were based on crystalline poly(L-lactide) rather than the... 

Several narcotic antagonists, including naloxone, naltrexone, L-methadone, and cyclazocine, have been incorporated in lactide homopolymers and lactide/glycolide copolymers. Cyclozocine was incorporated in poly(L-lactide) in the form of films (81,82). Lamination of drug-polymer films with a drug-free film created a reservoir device and eliminated the burst observed with the monolithic films originally tested. 

The use of polylactides for delivery of insect hormone analogs and other veterinary compounds (115,116) has been studied. Microspheres, pellets, and reservoir devices based on polyglycolide, poly-(DL-Iactide), poly(L-lactide), and various copolymers have been used to deliver methoprene and a number of juvenile hormone analogs. ... 

Rudolf, R. M., Boering, G., Roseman, F., and Leenslay, J., Resorbable poly(L-lactide) plates and screws for the fixation... 

Poly(L-lactide), R=alkoxide group as initiator fragment... 

By using a combination of RAFT and ring opening polymerization (ROP), (polyethylene oxide) methyl ether)(polystyrene)(poly(L-lactide) 3-miktoarm star terpolymers have been successfully synthesized [182]. The synthetic approach involved the reaction of the cw-functionalized - OH group of the poly(ethylene oxide) methyl ether with maleic anhydride under conditions where only one hydroxyl group can be esterified (MPEO). The double bond... 

Even more complex structures have been described. For example, chirality of blocks may lead to other morphologies. A polystyrene-fc-poly-(L-lactide) diblock copolymer, PS-fr-PLLA, constituting both achiral and chiral blocks was reported to form an array of hexagonally packed PLLA nanohelices with a left-handed helical sense in the bulk state (Fig. 3). The structure was found... 

Fig. 3 a TEM micrograph of polystyrene-fc-poly-(L-lactide), PS-fc-PLLA, neat (d>plla = 0.35). b Schematic representation of nanohelical morphology. From [16]. Copyright 2004 American Chemical Society... 

Nevertheless, we have often faced the problem that the nanocomposite shows fine and homogeneous distribution of the nanoparticles in the polymer matrix (e.g., poly (L-lactide)) without a clear peak shift of the mean interlayer spacing of the (001) plane, as revealed by wide-angle X-ray diffraction (WAXD) analysis [14], Furthermore we... 

Poly(L-lactide-co-epsilon-caprolactone) (PLC) nerve guides were found to yield faster and higher levels of nerve innervation compared to conduits... 

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