Hydrolysis Of PLLA Research Articles

One step bulk modification of poly(L-lactic acid) composites with functional additives to improve mechanical and biological properties for cardiovascular implant applications

Poly(L-lactic acid) (PLLA) has been widely used as a promising biomaterial in biomedical applications due to its biodegradability and high mechanical strength. However, because of the inherent brittleness, low impact resistance, and weak thermal stability of PLLA, the modification process is usually required to utilize it for biomedical devices. Furthermore, acidic byproducts resulting from the hydrolysis of PLLA after implantation reduce the pH of the surrounding environment and cause inflammatory responses in the implanted area, leading to the failure of their clinical applications. To this end, here, we demonstrate a novel modification process for the PLLA composite with various functional additives, such as cis-aconitic anhydride (AA), triacetin (TA), isosorbide derivative (ISB), and/or Pluronic® F127 (F). The modified PLLA composite with TA and F (PLLA/TF) showed significantly improved elongation at break and Young’s modulus and retained tensile strength. Moreover, incorporating magnesium hydroxide (MH) nanoparticles (PLLA/TFMH) significantly reduced acid-induced inflammation responses caused by the acidic degradation products of PLLA. Reduced plasma protein adsorption was observed in the PLLA/TFMH. These results suggest that the one step bulk modification of biodegradable PLLA using TA, F, and MH will have great potential in cardiovascular implant applications.

Nanoporous materials modified with biodegradable polymers as models for drug delivery applications

Polymers play a central role in the development of carriers for diagnostic and therapeutic agents. Especially the use of either degradable polymers or porous materials to encapsulate drug compounds in order to obtain steady drug release profiles has received much attention. We present here a proof of principle for a system combining these two encapsulation methods and consisting of a nanoporous polymer (NP) with the pores filled with a degradable polymer mixed with a drug model. Rhodamine 6G (R6G) mixed with Poly(l-Lactic Acid) (PLLA) were confined within the 14nm pores of a NP with gyroid morphology derived from a diblock copolymer precursor. Glass transition, crystallization and melting of free and confined PLLA were monitored by differential scanning calorimetry. Release profiles for R6G were measured in methanol–water solvents at pH 13, which works as an accelerated release test by speeding up the hydrolysis of PLLA. The obtained release profiles demonstrate that the degradation of PLLA in nanoporous confinement is significantly slower than the degradation of unconfined PLLA. The release of R6G encapsulated in PLLA becomes correspondingly slower, while the initial burst release virtually disappears. These findings suggest that the presented proof of principle constitutes a promising basis for the development of novel implantable drug delivery systems.

Synthesis and Recycle of Poly(L-lactic acid) using Microwave Irradiation

The theory and application of production and recycling of poly(lactic acid) are reviewed. Poly(L-lactic acid) (PLLA) production under microwave irradiation can make the molecular weight higher than that under conventional heating. However, it is limited by discharge in the sample tube. In contrast, depolymerization of oligo(L-lactic acid) (OLLA) is successfully achieved under microwave irradiation. Hydrolysis and alcoholysis of PLLA under microwave irradiation is also faster than those under conventional heating. Moreover, racemization of lactic acid during hydrolysis of PLLA can be reduced under microwave irradiation. The racemization of lactate during alcoholysis is small both with and without microwave irradiation.

Solvent-induced microdomain orientation in polystyrene- b-poly( l-lactide) diblock copolymer thin films for nanopatterning

A series of degradable block copolymers, polystyrene- b-poly( l-lactide) (PS–PLLA), with PLLA hexagonal cylinder (HC) morphology has been synthesized in this study. Well-oriented, perpendicular PLLA cylinders of PS–PLLA thin films were efficiently achieved by spin coating using appropriate solvents regardless of the use of substrates. After hydrolysis of PLLA, well-oriented HC nanochannel arrays over large area in addition to uniform surface with controlled thickness and domain size were obtained; providing a simple and efficient path to prepare nanopatterned templates for applications. The induced orientation of PS–PLLA microdomains was strongly dependent upon the evaporation rate of solvent and its solubility between constituted blocks. The origins for the formed perpendicular HC morphology were systematically studied. The primary concern of controlled morphology for nanopatterning is to develop ordered microphase-separated morphology by considering the time scale for segregation, namely segregation strength during solvent evaporation. The induced orientation is attributed to the permeation discrepancy between phase-separated microdomains. The perpendicular morphology is initiated from the air surface, and formed in order to create an optimized condition (i.e. the fastest path) for solvent evaporation whereas parallel morphology may impede the evaporation of solvent molecules. Following the nucleation of microphase separation, the perpendicular morphology can be kinetically induced by solvent evaporation.

Blends of aliphatic polyesters. VI. Lipase-catalyzed hydrolysis and visualized phase structure of biodegradable blends from poly(ε-caprolactone) and poly( l-lactide)

Phase-separated biodegradable polymer blends were prepared from poly(ε-caprolactone) (PCL) and poly( l-lactide) (PLLA), and Rhizopus arrhizus lipase-catalyzed hydrolysis and phase structure of the blend films were investigated. Gravimetry revealed that the lipase-catalyzed hydrolysis of PCL in PCL- and PLLA-rich phases is disturbed by the presence of PLLA. Polarimetry confirmed the occurrence of a predominant hydrolysis of PCL and subsequent removal of the hydrolyzed water-soluble PCL oligomers in the blend films. Gravimetry and gel permeation chromatography of the non-blended PLLA film indicated that R. arrhizus lipase has no catalytic effect on the hydrolysis of PLLA. The phase structure of the blend films could be visualized by selective enzymatic removal of one component and subsequent scanning electron microscopic observation.