Polylactide as a valuable biodegradable polymer is being widely investigated with respect to its synthesis, physical properties, biodegradation and application. The aim of this study is to evaluate hydrolytic degradation of poly (l-lactide) (PLLA) in the presence of added l-lactide dimer. High molecular weight PLLA was synthesized in presence of stannous octoate through the ring opening polymerization of l-lactide. PLLA films, containing 0, 1, 3 and 5% (w/w) l-lactide (as additive), were prepared by solution casting. In vitro degradation of the PLLA matrices were carried out in distilled water at 37°C for the definite periods. The degraded polymer matrices have been characterized by SEC, SEM and DSC techniques after periods of 3 and 6 months degradation time. It was found that during the first 3 months of degradation period, the number average molecular weight (¯Mn) of each PLLA film containing l-lactide reduced slower than the control sample. Also, it is shown that the films containing l-lactide have higher crystallinity and melting point in comparison with non-containing l-lactide samples. However, after 6 months, degradation rate of PLLA matrices containing l-lactide increased due to penetration of water by eluting and removal of l-lactide from PLLA matrices.

This study investigates the thermal, morphological, mechanical, and biodegradation properties of blends comprising poly(L-lactide)-b-poly (ethylene glycol)-b-poly(L-lactide) triblock copolymer (PLLA-PEG-PLLA) and polypropylene (PP) compared to the PLLA/PP blends. All the blends were prepared using a melt-blending technique. The ability to crystallize and the thermal stability of the PLLA-PEG-PLLA were enhanced by blending PP, whereas these properties were not enhanced for the PLLA. The crystallinity of PLLA-PEG-PLLA increased from 20.4% to 23.5-38.8%. The temperature at maximum decomposition rate (Td,max) of PLLA end-blocks increased from 310 °C to 327-332 °C. The phase compatibility between the PLLA-PEG-PLLA and PP was better than between the PLLA and PP, as indicated by the smaller size of dispersed PP particles in the PLLA-PEG-PLLA matrix. The PLLA-PEG-PLLA/PP blends showed greater flexibility, higher wettability, and faster biodegradation rates than the PLLA/PP blends. This suggests that these PLLA-PEG-PLLA/PP blends may be used as flexible and partially biodegradable plastics.

Controlling the rate and behaviour of the biodegradable polymer matrix is important in the development of drug delivery systems. In this project, we succeeded to control the speed of degradation and changing the degradation site from the bulk to the surface by addition of excipients. Antiacid excipients, such as Mg (OH)2 have significant effects on rate and behaviour of biodegradation, by neutralization of the acidic microclimate pH in polymer. We synthesized high molecular weight poly (L-lactide) by using tin- 2-ethyl hexanoate as catalyst. The polymer has been characterized by GPC, DSC and SEM. Mixtures of the polymer with Mg (OH) 2 at 1, 3 and 5% w/w were prepared and the degradation of the samples, kept at in vitro condition after 3 and 6 months, were studied. The results of average molecular weight changes, thermal characteristics and morphology of samples after 3 and 6 months revealed that it is possible to redirect the bulk degradation towards surface degradation. It is found that the ratio of bulk degradation to surface degradation and speed of degradation has reverse relationship with the additives concentration and when Mg (OH)2 increases, the speed of degradation decreases as well. In samples with Mg(OH)2, the polymer degradation rates were reduced by 2-3 folds and the percentage of crystallinity increased by maximum 90% (3% Mg(OH)2) after 6  months.

Biodegradable polymers have been extensively investigated as nano-carrier delivery systems in anti-cancer therapy. The anti-cancer drugs generally suffer from low aqueous solubility, short in vivo half-life and haphazard side effects. In this work, biodegradable poly(d,l-lactide-co-glycolide) nanoparticles (PLGA) containing tamoxifen citrate as a model anti-cancer drug were prepared using an o/w emulsification- solvent evaporation method. Dynamic light scattering (DLS), scanning electron microscopy (SEM) and analytical HPLC procedures were used to characterize the nanoparticles in terms of particle size, morphology and drug content. The characteristics of the nanoparticles including size, drug loading, and the efficiency of encapsulation were optimized by means of a full factorial experimental design over the influence of four different independent variables. Analyses of variance (ANOVA) were used to evaluate the optimized conditions for the preparation of nanoparticles. Based on the results, the most significant variables were homogenization speed and concentration of PLGA in organic phase with known total volume. Also, the interactions between the percentage of PVA and the amount of PLGA and organic phase volume were the most important cross-factor parameters. The optimum formulation condition with 192 nm mean size and 33 w/w% loading capacity was established by using 3 mg.mL-1 PLGA/dichloromethane in 7 w/v% PVA solution and 40% oil/water solvent ratio for emulsification at 24000 rpm homogenization rate. The results of this work facilitate the development of nano-carriers for tamoxifen delivery through optimization studies to control nanoparticles with specific properties and establish correlations between optimum production conditions and the required nano-carrier desired characteristics.