Papers by Keyword: Poly(D,L-Lactide) (PDLLA)

Abstract: Nanocomposite poly(D,L-lactide) (PDLL)-based microparticles containing silk fibroin (SF) nanoparticles were prepared by oil-in-water emulsification solvent evaporation technique of PDLL/SF nanocomposite. The PDLL/SF nanocomposite was obtained from nanoprecipitating SF into PDLL solution in acetone before dried in vacuum oven. The nanocomposite microparticles with PDLL/SF ratios of 20/1, 10/1 and 5/1 (w/w) were prepared and investigated. Interactions between PDLL and SF of microparticles can be observed from FT-IR and thermogravimetric results. Sizes of the SF nanoparticles and the nanocomposite microparticles from SEM micrographs were in the ranges of 50-500 nm and 50-200 µm, respectively. The sizes of SF nanoparticles and nanocomposite microparticles increased as increasing the SF ratio. Surface roughness of the resulted microparticles also increased with the SF ratio.

Abstract: Palmitic acid was added into drug-loaded poly(L-lactide) (PLLA) to modify the drug release profiles of the polymer. The acid was added in different concentrations and gradients across the thickness of the polymer. Drug release was monitored using a UV spectrometer over a period of 90 days. Degradation was studied using gel permeation chromatography and differential scanning calorimetry (DSC) to follow the change in the molecular weight and glass transition temperature respectively. Addition of palmitic acid was found to accelerate the degradation of PLLA and resulted in an accelerated release of the drug as expected. Modification of release profiles by designing the acid gradient was also attempted. It was found that the total acid concentration is still the dominant factor over the gradient design in affecting the degradation and subsequently the release profiles. Different drug concentrations also played a role in the different release profiles exhibited. Surprisingly the sample with lower drug concentration (2wt%) showed a much higher initial burst than the 5wt% loaded samples. This was due to the induced nucleation of the polymer by the drug at low concentration resulting in higher crystallinity of the polymer and consequently overall lower solubility of the drug.

Abstract: Nerve bridging is to suture a biomaterial-made conduit and to overpass the damaged nerve end to end with microsurgery. Poly L-lactide (PLLA) is an excellent biomaterial that has biocompatible, biodegradable and good mechanical properties; it is thus potential to be engineered as nerve conduits and manufactured as scaffolds for nerve tissue replacement. On the other hand, chitosan provides cell affinity and considerably promotes nerves regeneration. This study is to apply plasma processing for PLLA film modification, graft the plasma-modified film with vaporized acrylic acid (AAc) monomers and then immobilize chitosan by amide bonding on the pAAc-grafted surface. This work using plasma-activation and subsequent evaporation of AAc greatly avoids PLLA thermal cracking and remaining the PLLA film in good mechanical properties. Surface morphologies are evaluated by Nano Focus. Electron Spectroscopy for Chemical Analysis (ESCA) and Attenuated Total Reflectance Fourier-Transform Infrared Spectroscopy (ATR-FTIR) are respectively employed for determining elements’ functionalities and chemical structures. Moreover, biological functionalities of the chitosan-immobilized PLLA films are thereafter assessed by antibacterial test and in vitro fibroblastic cell growth assay. The result exhibits that chitosan is immobilized on the modified PLLA films, which is plasma-activated subsequent to the evaporation of AAc. The process does not induce thermal cracking. In vitro fibroblastic cell growth assay on the chitosan-immobilized PLLA films has demonstrated that fibroblast cells on the surface become circular in shape. It decreases cell growth rate and the development of scar tissues, which may thereafter promote the effect of nerve repairing.

Abstract: We had investigated the biocompatibility, osteoconductivity, and biodegradability of a porous composite of hydroxyapatite (HA) and poly-DL-lactide (PDLLA) implanted into rabbit femoral condyles. It showed excellent osteoconductivity and biodegradability as a bone substitute. Newly formed bones were remodeled, and materials were resorbed almost completely at 78weeks after implantation. In consideration of its biocompatibility and degradability, we investigated its potential for use as a cellular scaffold and evaluated its osteoinductive property. On implantation to the rat dorsal subcutaneous tissue loaded with syngeneic bone marrow cells, osteogenesis with enchondral ossification was seen both on and in the material at 3 weeks after implantation. This osteogenesis in the HA/PDLLA tended to get mature and newly formed bone tissues were found in the material by 6weeks. To investigate the osteoinductive property material itself has, we attempted to implant this porous composite material to extra-osseous canine dorsal muscle. At 2months, osteogenesis was seen in the pores of the material. It indicated the material induced osteogenesis with intramembranous ossification process. Therefore, HA/PDLLA might be a desirable material for bone substitutes and cellar scaffolds with osteoconductive and osteoinductive property.

Abstract: There are still some existing problems that are common to all absorbable materials; 1) It cannot be subjected to radiosterilization, 2) Sufficient strength cannot be maintained until the complete bone union is obtained. To solve these problems, PLLA and PLLA/HA were mixed with cross-bridge supplementary agent, Triallyl Isocyanurate (TAIC). Using these materials in vivo, we created and tested γ-ray radiosterilized absorbable bone fixation materials.

Abstract: In this paper, three different scale HA/PDLLA porous scaffolds, nano-HA/PDLLA, micro-HA/PDLLA and pure PDLLA were successfully fabricated using solvent casting/particulate leaching method. Chondrocytes adhesion and proliferation on these scaffolds were investigated. In detail, the cells attachment rate and proliferation on nano-HA/PDLLA, micro-HA/PDLLA and pure PDLLA were quantitatively evaluated by cytometry. The interaction between the scaffolds and chondrocytes were observed by optical microscope with HE staining and FE-SEM. The results exhibited that nano-HA/PDLLA scaffold has a modified cell adhesion property, and cells on the nano-scaffold grow much better both in biological and morphological characteristics than on the micro-HA/PDLLA and pure PDLLA scaffolds. This work suggested that nano-HA/PDLLA composite scaffold can significantly improved cell adhesion and proliferation tendency with the existing of nano-effects，and could be used as a potential scaffold material for bone defect repair.

Abstract: The triblock ABA copolymers of poly (D,L-lactide)-b-poly (ethylene glycol)-b-poly (D,L-lactide) (PDLLA-PEG-PDLLA) were synthesized by bulk ring-opening polymerization in the presence of N2 under normal pressure, using the D,L-lactide (DLLA) as monomer, hydroxyl endgroups of poly(ethylene glycol) (PEG) as initiator and the stannous octoate as the catalyst. The resulting copolymers were characterized by various analytical techniques. Effects of molar ratios of lactide to PEG and the chain length of PEG on the viscosity-average molecular weight of the copolymers, the biodegradation behaviors and hydrophilicity of the copolymers were investigated in detail. The results showed that the viscosity-average molecular weight and the contact angle of the copolymers increased with the molar ratio of lactide to PEG, but water uptake and degradability decreased.

Abstract: In order to improve the hydrophilicity of poly (D,L-latide) (PDLLA), a novel amphiphilic ABA-type triblock copolymers of poly-N-vinylpyrrolidone (A) and poly (D, L-lactide) (B), were successfully synthesized by atom transfer radical polymerization (ATRP) using N-vinylpyrrolidone (VP) as monomer, bromide-terminated poly (D,L-latide) oligomer (Br-PDLLA-Br) as functional macromolecular initiator which was prepared when hydroxy-terminated poly(D,L-latide) oligomer (HO-PDLLA-OH) reacted with 2-bromopropanoyl bromide, CuBr/2,2’-bipyridine complex as the catalyst system. The resulting copolymers were characterized by various analytical techniques. The results showed that the introduction of poly (N-vinylpyrrolidone) (PVP) segments into polylactide enhanced the surface hydrophilicity of the copolymers remarkably and amphiphilic polymer can self-assemble into core-shell structure (polymer micelle) in water by the balance of the hydrophilic and hydrophobic interaction.

Abstract: With the outstanding biocompatibility of hydroxyapatite (HA) and biodegradation of poly(D,L)lactide(PDLLA), and the expected good bio-mechanical compatibility, nano-HA / PDLLA (n-HA/PDLLA)composite has been paid great interests in hard tissue repair. One of the key factors affecting the potential of the composite is the degradation of the composite. That is what the mechanism of degradation in the composite is and if the degradation of the materials would induce the crack of the composite or a porous structure facile for tissue ingrowth would be formed. In this study, an n-HA/ PDLLA composite containing about 40% n-HA (wt%) was prepared and the degradation of the composite in bony tissue of rabbits and tissue response were studied by implanting composite rods and control HA rods into the femora of 16 New Zealand rabbits. After definite intervals, the histological analysis was completed by light microscopy and the degradation behavior was observed by scanning electron microscopy. The results suggested that a nano-HA/PDLLA composite was obtained and the materials showed good biocompatibility and osteoconductivity. The substantial degradation of the composite occurred at 8 weeks in vivo. After a longer period of implantation, the further degradation of the composite led to the formation of interconnected microporous and macroporous structure in the materials that might facilitate the tissue ingrowth in the composite.