Hydrolytic and enzymatic degradation of poly(trimethylene carbonate-co-d,l-lactide) random copolymers with shape memory behavior

A series of homo- and copolymers were synthesized by ring-opening polymerization of 1,3-trimethylene carbonate and d,l-lactide, using low toxic Zn(Lac)₂ as catalyst. The hydrolytic and enzymatic degradation of PTMC homopolymer and PTDLA copolymers was performed at 37 °C in pH 7.4 phosphate buffered saline or in pH 8.5 Tris buffer using proteinase K. Degradation was followed by using various analytical techniques such as NMR, GPC, DSC and ESEM. PTMC degrades extremely slowly by pure hydrolysis or in the presence of proteinase K. In contrast, PTDLA copolymers with different compositions degrade at various rates both in PBS and in enzyme solutions. The higher the LA content, the faster the degradation. LA units are preferentially degraded during hydrolytic degradation, indicating that ester bonds are more susceptible to hydrolytic cleavage than carbonate ones. Changes in surface morphology are observed during enzymatic degradation, in agreement with surface erosion process. The PTDLA11 copolymer with equivalent TMC/LA contents is highly elastic. Its residual strain is approximately 4% after the first cycle at a strain of 50%. The shape recovery ratio is up to 83%. Therefore, it is concluded that high molecular weight PTDLA copolymers are promising candidates for clinical applications in minimally invasive surgery.     

Biodegradable nanoparticles made from polylactide-grafted dextran copolymers

Polysaccharide-covered polyester nanoparticles were prepared using the emulsion/solvent evaporation process. The core of the nanoparticles was made either of PLA or of a blend of polylactide and polylactide-grafted dextran copolymer in various proportions. The surface of the nanoparticles was covered by dextran chains via the use of water-soluble polylactide-grafted dextrans as polymeric stabilizers during the emulsification step. The characteristics of the nanoparticles (size, surface coverage, thickness of superficial layer, colloidal stability) were correlated to the structural parameters (length and number of polylactide grafts) of the copolymers as well as to their surface active properties. The complete biodegradability of the nanoparticles was evaluated by considering the rate of hydrolysis of polylactide grafts in phosphate buffer and the rate of enzymatic degradation of dextran backbone by dextranase.     

Quantification of residual monomer in polylactide by gas chromatographic internal standard method

An analytical method has been developed to quantitatively determine the residual lactide monomer in polylactide (PLA) using an internal standard method of gas chromatography (GC). The experimental results showed that diphenyl ether (DPE) was an appropriate internal standard for quantitative analysis of residual lactide in PLA. PLA and DPE were dissolved in dichloromethane and precipitated in hexane. At the same time, the residual lactide in PLA and DPE as an internal standard were extracted to hexane from the polymer solution. The resulting solution could be directly injected into a GC system. Therefore, the residual lactide was determined quantitatively using an internal standard method of GC. This method is practical for measuring the residual lactide content in PLA. When the lactide content is 5.0%, the relative standard deviation (RSD) of the measurements is 1.7%, while RSD is 6.9% at the low level of 0.4%, which indicates that the method is sufficiently precise.     

Ageing of different biodegradable polyesters blends mechanical and hygrothermal behavior

The aim of this study is to better understand the performance of binary blends of biodegradable polyesters when exposed to hygrothermal ageing, in order to overcome some of their limitations such as water resistance. For this, blends have been prepared by extrusion using two P(L)LA (l-poly-(lactic acid)) of different molecular weights and P?CL (poly-?-caprolactone). Mechanical properties over ageing are reported and compared to pure P(L)LA. Blending P?CL to P(L)LA allowed to improve P(L)LA initial resilience. During ageing, crystallinity increase seemed to lower water uptake at short ageing times, while osmotic cracking was found to possibly occur in pure P(L)LA for long ageing times, thus increasing water uptake. Besides, P(L)LA/P?CL blends water uptake remained constant over ageing. Finally, while P(L)LA resilience decrease could be related to chain scission, blend aptitude to elongation decrease was related to interphase decohesion, at long ageing times. Results showed P(L)LA molecular weight influence on both initial mechanical properties and water uptake.     

Preparation of a biodegradable matrix through polyion complex formation by mixing polylactide-based microspheres having oppositely charged surfaces

The aggregation of polyions into microsphere (MS) complexes was studied as a preparative method for the construction of a biodegradable matrix. Aqueous suspensions of polylactide (PLA)-based MSs with positively and negatively charged surfaces, MS(K(3)(4+)-PLA) and MS(E(3)(4-)-PLA), respectively, immediately formed aggregates when mixed. The effects of the stoichiometry of the charged groups on the surfaces of the MSs and the ionic strength of the medium on aggregate formation, as well as the degradation behavior of the polyion complex (PIC) matrix over time, were investigated.     

Synthesis of Sulfated Polysaccharides and Oligosaccharide Derivatives with Potent Anti-Aids Virus Activity

Abstract

Sulfated synthetic polysaccharides (with both high anti-AIDS virus activity and high anticoagulant activity) were prepared by sulfating such synthetic polysaccharides as ribopyranan, ribofuranans, and dextrans. Sulfated natural polysaccharides with high anti-AIDS virus activity but low anticoagulant activity were synthesized from lentinan and curdlan. It is assumed that curdlan sulfate will be helpful as an AIDS drug. In addition, sulfated alkyl oligosaccharides with high anti-AIDS virus activity were prepared.     

Biodegradability of polylactide bottles in real and simulated composting conditions

As new biodegradable polymers and their packaging applications are emerging, there is a need to address their environmental performance. In particular, there is a need to understand the time required for their complete disintegration, before these materials are deployed in commercial composting processes. Standards developed by ASTM and ISO evaluate the biodegradation of biodegradable plastic materials in simulated controlled composting conditions. However, a more detailed understanding of the biodegradation of complete packages is needed in order to have a successful composting operation. This paper investigates the biodegradation performance of polylactide (PLA) bottles under simulated composting conditions according to ASTM and ISO standards, and these results are compared with a novel method of evaluating package biodegradation in real composting conditions. Two simulated composting methods were used in this study to assess biodegradability of PLA bottles: (a) a cumulative measurement respirometric (CMR) system and (b) a gravimetric measurement respirometric (GMR) system. Both CMR and GMR systems showed similar trends of biodegradation for PLA bottles and at the end of the 58th day the mineralization was 84.2±0.9% and 77.8±10.4%, respectively. PLA bottle biodegradation in real composting conditions was correlated to their breakdown and variation in molecular weight. Molecular weight of 4100 Da was obtained for PLA bottles in real composting conditions on the 30th day. The biodegradation observed for PLA bottles in both conditions explored in this study matches well with theoretical degradation and biodegradation mechanisms; however, biodegradation variability exists in both conditions and is discussed in this paper.