Papers by Keyword: PLLA

Abstract: Controllable mechanical properties of highly performed Poly (L-lactide acid) (PLLA) monofilaments with oriented molecular structure could widen their applications, especially in biomedical field. Herein, different heat treatments were applied to regulate the degree of molecular relaxation of oriented PLLA monofilaments to tune their mechanical properties. These filaments were manufactured by melting spun and solid-state drawing processes. Then, they were processed by different heat treatments, including annealing, normalizing, and quenching. As the cooling time extension, an obvious molecular orientation loss in filaments happened and increased regularly, and it could reach up to about 35.1% maximumly. However, molecules only in crystal phase were limitedly affected. As a result, mechanical performances of these filaments exhibited a corresponding change after heat treatments. Young’s modulus and elongation at break were promoted after all kinds of post-processes and increased with longer cooling time gradually. But breaking strength showed a contrast change. It means that different heat treatments could be effective avenues to control mechanical properties of oriented PLLA materials by altering the orientation structure.

Abstract: Paper is focused on analysis of a local shrinkage and injection pressure of the biodegradable materials PLLA and PLA. Analysed products were prepared with thickness of 4 mm in the patent injection mould. The technological parameters of the injection moulding were established by the Taguchi method. In this article, the influence of these main technological parameters on the local shrinkage and injection pressure is evaluated.

Abstract: The Paper deals with problematics of analysis of shrinkage biodegradable polymer materials PLA and PLLA in consequence with setup of parameters. Samples for analysis were prepared by technology of injection molding with parameters set according to Taguchi method. The parameters setting consist of injection speed, holding pressure, temperature and wall thickness. Dependency of parameters measured inside of the mold was compared to parameters set on molding machine. By this comparison we have received data for material processing in praxis.

Abstract: In order to prepare the bone repair scaffold materials that could employ the sources of the injured bone, the bioactive HA and BMP-2 were added into the biomaterial PLLA. The four scaffold materials, PLLA, PLLA/HA, PLLA/BMP-2 and PLLA/HA/BMP-2 were prepared by electrospinning. The SEM results revealed that the morphology of the 7wt% PLLA fibers was better than the 5wt% PLLA fibers, and the HA nanoparticles were distributed uniformly in fibers. The calculated surface energy of the PLLA/HA/BMP-2 scaffold was higher compared with other three scaffolds, this result fit well with the result of MTT assay of the four scaffold materials, and the MTT assay showed that the MG63 cells on the PLLA/HA/BMP-2 scaffold material proliferated faster compared with the PLLA/HA or PLLA/BMP-2. It is logical to assume that PLLA/HA/BMP-2 scaffold material is a promising material for bony tissue repair.

Abstract: Non-isothermal crystallization method was performed for pure PLLA and a blend of 50/50 wt% PEO/PLLA samples. The spherulite radial growth rate was calculated and compared to what was acquired using the isothermal crystallization method. It is found that both the fitting order and the decimal number of the fitting polynomial functions heavily affect the resultant spherulite growth rate at different temperatures. It is also important to note that some subtle yet important features might be missed using the quick alternative, such as in the pure PLLA system.

Abstract: In this study, a nanofibrous poly (L-lactic acid) (PLLA) scaffold reinforced by Hydroxyapatite (HAP) and β-tricalcium phosphate (β-TCP) was fabricated using the thermally induced phase separation method. The composite scaffold morphology showed a nanofibrous PLLA matrix and evenly distributed β-TCP/HAP particles. The composite scaffold had interconnective micropores and the pore size ranged 2-10 μm. Introducing β-TCP/HAP particles into PLLA matrix significantly improved the mechanical properties of the composite scaffold. In summary, the new composite scaffolds show a great deal promise for use in bone tissue engineering.

Abstract: Anterior Cruciatum Ligament (ACL) injury may cause other tissue injuries and degenerative joint diseases, rendering major surgery compulsory. The ACL substitutions from patients other tissue (autograft), from cadaver (allograft), or from other species (xenograft) still cause problems like donor morbidity, reduction of mechanical strength in cryopreservation period, and the risk of transgenic infection. Tissue engineering approach is the proposed solution. For this, synthetic ligament scaffold is needed. Electrospinning is a method to produce porous scaffolds made of polymers. In this study, filaments were produced from electrospinning poly l-lactic acid. The filaments were then twisted with 60o angle to the horizontal to make a yarn. Subsequently, the yarns were braided with the variation of braiding angle 40o, 60o and 80o. The characterization on the scaffold includes degradation rate, porosity, tensile strength, and cytotoxicity. It was found that larger braiding angle gave higher degradation rate, bigger pore size, and lower mechanical strength. For cytotoxicity, in terms of pore size and percentage of living cell, scaffold with braiding angle of 80o also showed the optimum result.

Abstract: Synthesis of Poly(L-lactide) (PLLA) by the ring-opening polymerization (ROP) of L-lactides in supercritical carbon dioxide (SC-CO₂) with co-solvent were studied. Effects of kinds of co-solvent on the molecular weight (MW) and the molecular weight distribution (MWD) of the resultant polymers were investigated by the gel permeation chromatography (GPC). The resultant polymers were also characterized with ¹H NMR, ¹³C NMR and FT-IR. It was found that PLLA with high purity and almost without racemization could be obtained by this technology and the acetone is the best co-solvent for this kind of polymerization. By using stannous octoate as initiator and acetone as co-solvent, PLLA having a weight-average molecular weight (M_w) near to 9×10⁴ and polydispersity index (PDI) of 1.7 was successfully synthesized.

Abstract: A twin-screw extruder was used to carry out the ring opening graft polymerization of L-lactide onto cellulose through reactive extrusion process. Ionic liquid (1-butyl-3-methylimidazolium chloride) [Bmim]Cl and Sn(oct)2 were used as solvent and catalyst, respectively. FTIR, TGA and XRD were used to investigate the structure, thermal stability and crystalline behavior of the reaction products. The result showed a successful ring opening polymerization of L-lactide on cellulose. Furthermore, it showed a increased crystalline degree and thermal stability after being introduced the PLLA.

Abstract: Nano-PLLA/chitosan scaffolds were prepared through thermally induced phase separation(TIPS). With incorporation of chitosan fibers, composites not only improved the mechanical properties of nano scaffolds, but also reduced the degradation rate of mechanical properties which deepen the applications of scaffolds better.