Synthesis, Solid-State Structure, and Surface Properties of End-Capped Poly(l-lactide)

Thermo-Rheological and Shape Memory Properties of Block and Random Copolymers of Lactide and ε-Caprolactone

Biodegradable block and random copolymers have attracted numerous research interests in different areas, due to their capability to provide a broad range of properties. In this paper, an efficient strategy has been reported for preparing biodegradable PCL-PLA copolymers with improved thermal, mechanical and rheological properties. Two block-copolymers are synthesized by sequential addition of the cyclic esters lactide (L-LA or D,L-LA) and ε-caprolactone (CL) in presence of a dimethyl(salicylaldiminato)aluminium compound. The random copolymer of L-LA and CL was synthetized by using the same catalyst. Chain structure, molar mass, thermal, rheological and mechanical properties are characterized by NMR, SEC, TGA, DSC, Rheometry and DMTA. Experimental results show that by changing the stereochemistry and monomer distribution of the copolymers it is possible to obtain a variety of properties. Promising shape-memory properties are also observed in the di-block copolymers characterized by the co-crystallization of CL and L-LA segments. These materials show great potential to substitute oil-based polymers for packaging, electronics, and medicine applications.

Controlled fabrication, characterization and comparison of porous poly(l-lactide) and poly(d-lactide) films by electric breath figure

Porous poly(l-lactide), PLLA, and poly(d-lactide), PDLA, films were fabricated by the electric breath figure (EBF) method.

Nano-colloid printing of functionalized PLA-b-PEO copolymers: tailoring the surface pattern of adhesive motif and its effect on cell attachment

In this study, we investigate the preparation of surface pattern of functional groups on poly(lactide) (PLA) surfaces through the controlled deposition of core-shell self-assemblies based on functionalized PLA-b-PEO amphiphilic block copolymers from selective solvents. Through grafting RGDS peptide onto the functionalized copolymer surface, the presented approach enables to prepare PLA surfaces with random and clustered spatial distribution of adhesive motifs. The proposed topography of the adhesion motif was proved by atomic force microscopy techniques using biotin-tagged RGDS peptide grafted on the surface and streptavidin-modified gold nanospheres which bind the tagged RGDS peptides as a contrast agent. The cell culture study under static and dynamic conditions with MG63 osteosarcoma cell line showed that the clustered distribution of RGDS peptides provided more efficient initial cell attachment and spreading, and resistance to cell detachment under dynamic culture compared to randomly distributed RGDS motif when with the same average RGDS peptide concentration.

Interaction between poly[(R)-3-hydroxybutyrate] depolymerase and biodegradable polyesters evaluated by atomic force microscopy

Adsorption of PHB depolymerase from Ralstonia pickettii T1 to biodegradable polyesters such as poly[(R)-3-hydroxybutyrate] (PHB) and poly(l-lactic acid) (PLLA) was investigated by atomic force microscopy (AFM). The substrate-binding domain (SBD) with histidines within the N-terminus was prepared and immobilized on the AFM tip surface via a self-assembled monolayer with a nitrilotriacetic acid group. Using the functionalized AFM tips, the force-distance measurements for polyesters were carried out at room temperature in a buffer solution. In the case of AFM tips with immobilized SBD and their interaction with polyesters, multiple pull-off events were frequently recognized in the retraction curves. The single rupture force was estimated at approximately 100 pN for both PLLA and PHB. The multiple pull-off events were recognized even in the presence of a surfactant, which will prevent nonspecific interactions, but reduced when using polyethylene instead of polyesters as a substrate. The present results provide that the PHB depolymerase adsorbs specifically to the surfaces of polyesters and that the single unbinding event evaluated here is mainly associated with the interaction between one molecule of SBD and the polymer surface.

Thermal Degradation Processes of End-Capped Poly(l-lactide)s in the Presence and Absence of Residual Zinc Catalyst

Thermal degradation processes of end-capped poly(L-lactide)s (PLLAs) were investigated by means of several thermoanalytical techniques under both isothermal and nonisothermal conditions. Based on the thermogravimetric analysis, it was found that two distinct processes at temperatures below and above 330 degrees C were existed in the nonisothermal degradation for PLLA samples depending on the amounts of residual zinc compounds from synthesis process. Isothermal degradation experiments at different temperature regions showed that the sample weight of PLLA decreased linearly with time in both cases, whereas the changes in molecular weight revealed different tendency for the temperature. On the basis of characterization of the residual PLLA molecules after isothermal degradation at 330 degrees C, it was confirmed that the omega chain end of the residual molecules was an acrylic ester unit. Majority of volatile products during thermal degradation of PLLA was the lactide regardless of the degradation temperature. From these results, it is concluded that, during the thermal degradation of PLLA samples in the presence of large amounts of residual zinc compounds, the zinc compounds catalyze both the intermolecular transesterification generating PLLA with low molecular weights and the selective unzipping depolymerization of PLLA with low molecular weights at temperatures below 330 degrees C. In contrast, the primary reaction of thermal degradation for PLLA in the absence of residual zinc compounds above 330 degrees C is a competition between the random chain scission via a cis-elimination reaction and the cyclic rupture via intramolecular transesterification of PLLA molecules. In addition, it was evidenced that the racemization of lactic acid units in the main chain of PLLA molecules occurred at temperatures above 330 degrees C.