Abstract
Abstract
Three different types of pliable and bioabsorbable plates, 0.4 mm thick, were developed for guided bone regeneration to cover cranial defects. The processing (extrusion, melt-spinning, knitting and heat pressing) and in vitro degradation of the materials were studied. Materials used were poly-L, DL-lactide with an L/DL ratio of 70/30 (PLA70) and poly-L, D-lactide with an L/D ratio of 96/4 (PLA96). The initial tensile strengths of γ-sterilized PLA96, PLA70 and the PLA70-PLA96 composite plates were 45.7 ± 3.8, 51.2 ± 3.6 and 24.7 ± 5.1 MPa respectively. The composite plates were the stiffest and lasted for more than 24 weeks. The glass transition temperature (T g) of both polymers decreased in vitro. The crystallinity of PLA96 increased tenfold within 18 weeks. For initially amorphous PLA70 the highest melting enthalpy was 89 J/g at 60 weeks. PLA70 became partially crystalline and the plates changed from transparent to white and swollen. Extrusion and sterilization decreased the initially different molecular weight (M w) values to the same level. After 18 weeks of hydrolysis, M w was 15 000 Da for PLA96 and 12 000 Da for PLA70. For the components of the composite plate M w was 15 000 Da for the PLA70 plate and 27 000 Da for the PLA96 mesh. Morphologically, all the hydrolysed plates retained, for a long period, a solid surface layer under which a porous structure formed. Crystalline branches and some single crystals were seen. The composite plates had the slowest degradation rate and they remained intact the longest.
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