Papers by Keyword: Poly(L-Lactide)

Abstract: Poly (3-hydroxybutyrate) (PHB)/poly (L-lactide) (PLLA)/nanohydroxyapatite (n-HA) composite Ultrafine Fibers with diameter of 610 ~ 830 nm were prepared by electro-spinning. The surface morphology was studied by scanning electron microscopy (SEM). The effect of the process of prepareing spinning solutions, the constituent of spinning solutions, the concentration of PHB/PLLA/ n-HA blends spinning solutions and the collection distance on the surface morphology of fibers were discussed. The results indicated that n-HA mixing with solvent prior to other materimals for electrospingning could prepare the homogeneity of the spinning mixture. In all of the spinning conditions investigated ,When using chloroform (CF) /N, N-dimethyl formamide (DMF ) mixture as spinning solvent , PHB/PLLA/HA composite ultrafine fibers were not fabricated by electro-spinning, but chloroform can do. The average diameter of as-spun fibers increased with increasing concentration of PHB/PLLA/HA blends spinning solutions and collection distance.

Abstract: Both poly(L-lactide) (PLLA) and poly(ethylene succinate) (PES) are biodegradable synthetic aliphatic polyesters with excellent biocompatibility. They are semicrystalline thermoplastic polymers processed by most conventional processing methods. In view of their complementary properties, blending PLLA with PES becomes a promising approach to improve the properties of PLLA without compromising its biodegradability. In the present work, fully biodegradable PLLA/PES blend(the weight ratio 90/10) was melt-blended in stainless steel chamber. The crystallization morphology was investigated using a polarized optical microscope (POM), showing more clear spherulites with typical crosslink extinction patterns and faster crystallization rate of PLLA in blend at the lower heating rate. It clearly showed that the addition of PES largely increased the crystallization rate of PLLA and improved the crystallinity of PLLA in blends.

Abstract: nanocomposites of poly (L-lactide) (PLLA) and hydroxyapatite (HAP) or surface grafted hydroxyapatite (g-HAP) were prepared by ultrafines hot-pressing method, and the properties were investigated by polarized optical microscopy (POM), scanning electron microscopy (SEM), mechanical test and cell culture. Results showed that the PLLA segment grafted onto the HAP surface played a positive role on improving the interfacial compatibility between the g-HAP and the PLLA matrix. Compared with the HAP/PLLA composites, the bending strength and bending modulus of the g-HAP/PLLA composites were obviously enhanced, which was proportional to the n_HAP:n_L-LA ratio. The result of POM showed that the g-HAP particles acted as an effective heterogeneous nucleating agent in the g-HAP/PLLA composite. Fibroblasts culture indicated that the g-HAP/PLLA composites had better cytocompatibility than PLLA and HAP/PLLA composites. Hence, g-HAP/PLLA composites will be a promising material for bone tissue engineering.

Abstract: SiO2-hemoglobin-poly(L-lactide) (SiO2-Hb-PLLA) microspheres were prepared in a process of solution-enhanced dispersion by supercritical CO2 (SEDS). SiO2 nanoparticles were loaded with Hb by adsorption firstly and then the Hb-SiO2 nanoparticles were further coated with PLLA by the SEDS process. The resulted microcapsules were characterized by scanning electron microscope (SEM), laser diffraction particle size analyser and Fourier transform infrared spectrometer (FTIR). The drug release profiles were also determined. The Hb-SiO2-PLLA microspheres have a narrow particle size distribution (PDI 0.189) with a mean particle size of 897nm and a drug loading of 7.1%. After coating with PLLA, the drug release from SiO2-Hb-PLLA showed a sustained process mainly in zero-order kinetics; only 3.7% drug was released in the first 24 hours, versus 51.9% for those without coating, which revealed that the coating of PLLA significantly retarded the drug release. The results also indicate that the SEDS process is a typical physical process to produce protein-loaded polymer microspheres without changing the molecular structure of proteins, which is potential in the application of designing proteins drug delivery system.

Abstract: Poly (3-hydroxybutyrate) (PHB)/poly (L-lactide) (PLLA)/poly (ethylene-oxide) (PEO) composite Ultrafine Fibers were prepared by solution dry spinning technique. Scanning electron microscope (SEM) and X-ray diffraction (XRD) were used to characterize the PHB/PLLA/PEO composite Ultra-fine fibers. In all of the spinning conditions investigated, the average diameter of the as-spun PHB/PLLA/PEO fibers was 2.1 μm and increased with increasing the mass ratio of PHB/PLLA. The degree of crystallinity of as-spun PHB/PLLA/PEO fibers increased with increasing PHB content in their blends, and the α-form crystals of PHB and PLLA in as-spun fibers were obtained. When the mass ration of PHB/PLLA in as-spun PHB/PLLA/PEO fibers was 3:1,the structure of as-spun fibers was the skin-core, which PHB formed core of fibers and PLLA form skin of fibers; when the mass ration of PHB/PLLA in as-spun PHB/PLLA/PEO fibers was 1:1, PLLA and PEO were embedded into PHB phase by droplet and febrile morphology to form matrix-fibril structure of as-spun PHB/PLLA/PEO fibers.

Abstract: Poly(L-lactide) and poly(ε-caprolactone) (PLLA/PCL) blends with various weight ratios were compounded by melt mixing and their shape memory properties were investigated. The thermal properties, surface morphology and dynamic mechanical properties of the blends were characterized. The results demonstrate that the introduction of PCL improves the process of crystallization of PLLA whereas the reverse situation is for PCL. PLLA/PCL blends were found to exhibit an immiscible behavior from the characterizations of surface morphology. DMA tests show the blends with different weight ratios have different transition temperatures. The properties of blends provide the basis of owning shape memory behavior. The strain recovery ratio (Rr) of PLLA/PCL blend with the weight ratio of 1:3 was about 95% within 22s, whereas the Rr of other blends were less than 75% within 23~30s. It was found that lower transition temperature combined with increased crystallization of PLLA with the increasing PCL content contribute to such a good shape memory effect.

Abstract: Blends of poly (3-hydroxybutyrate-co-4-hydroxybutyrate) [P (3HB-co-4HB)] with poly(L-lactide) (PLA) were prepared by melt-mixing and subsequent injection molding, and their mechanical properties and morphology were investigated. The results show that the tensile properties, impact strength and spherulitic morphology depend strongly on the composition of the blend. The point of transition shows that phase inversion takes place at composition with 40 weight fraction of PLA in the blend.

Abstract: A new surface modification method by modifying low molecular weight ploy (L-lactide) (LMW PLLA) onto the β-tricalcium phosphate (β-TCP) superfine particles has been developed. The surface-modified β-TCP is characterized by FT-IR, XRD, digital microscope and contact angle measurement, et al. FT-IR spectra confirmed that LMW PLLA was connected onto the β-TCP surface through ionic interaction. XRD results indicated that the LMW PLLA did not affect the crystalline form of β-TCP, but the XRD patterns of the p-β-TCP showed a little difference with β-TCP. The p-β-TCP particles could be dispersed uniformly in dichloromethane. In contrast, unmodified β-TCP particles are apt to agglomerate after dispersed into dichloromethane. Wet angle measurement showed that hydrolyzed LMW PLLA significantly improves hydrophobicity of modified β-TCP particles. For the preparation of composites, PLLA was mixed with β-TCP and p-β-TCP, respectively, in a ratio of 85/15 (w/w) and moulded into tensile test specimens. Tensile tests showed that mechanical properties were improved, scanning electron microscopy (SEM) exhibited that modified β-TCP is an effective approach to prepare a homogeneous composites, moreover, it indicated a better interfacial phase interaction in the composite with the p-β-TCP. Chemical bonds between filler and PLLA matrix are assumed to be formed by ionic interaction.

Abstract: Nano-hydroxyapatite (n-HAP) surface-grafting poly(L-lactide) (g-HAP) was synthesized by ring-opening polymerization of L-lactide (L-LA) using stannous octoate as initiator and n-HAP as co-initiator under microwave irradiation. An optimal reaction condition was obtained as follows: temperature of 140 °C, irradiation time of 45 min and microwave power of 50 W. The products were characterized by FTIR, TGA, x-ray scattering and particle size analysis. Results showed that the feeding ratio of n_n-HAP：n_L-LA had a significant influence on the grafting percentage of g-HAP. With increasing the n_n-HAP:n_L-LA feeding ratio from 1:50 to 1:400, the grafting percentage of g-HAP increased correspondingly from 14.91% to 35.88%. The g-HAP particles showed a smaller size than that of pristine n-HAP, suggesting that the grafted poly(L-lactide) segment facilitated to prevent the g-HAP particles from aggregating.

Abstract: Functional poly(L-lactide) (PLLA-OH) containing vinyl groups as well as hydroxyl end groups was synthesized by ring-opening polymerization (ROP), using stannous octanoate as the catalyst and 2-hydroxyethyl methacrylate (HEMA) as the initiator. The structure of the obtained PLLA-OH was characterized using both Fourier Transform Infrared (FT-IR) spectroscopy and 1H nuclear magnetic resonance (1H-NMR) spectroscopy, while their crystallinities and thermo behavior were studied by differential scanning calorimetry (DSC), separately. The best condition for the ROP of the studied PLLA-OH was found with the polymerization temperature of T= 145 °C, the weight percent of the catalyst of 0.03 wt%, the ROP duration of 48 h and the L-lactide/initiator molar ratio of 100/1.