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81.
Linear (1‐arm) and star‐shaped (4‐, 6‐, and 16‐arm) poly(D,L ‐lactide)s (PDLLs) were synthesized by ring‐opening polymerization in bulk of D,L ‐lactide monomer. Hydroxyl end‐group compounds and stannous octoate were used as the initiator and catalyst, respectively. The intrinsic viscosity and glass transition temperature (Tg) of the PDLLs decreased steadily as the branch arm number increased for similar molecular weights. However, the intrinsic viscosity and Tg values of the linear PDLL were less than the star‐shaped PDLL for similar each PDLL arm lengths. Ibuprofen, a poorly water soluble model drug was entrapped in the PDLL microspheres. All drug‐loaded PDLL microspheres were prepared by the oil‐in‐water emulsion solvent evaporation method, were spherical in shape, and had a smooth surface with fine dispersibility. In vitro drug release behaviors indicated that the drug release from the microspheres with higher branch arm number was faster than from those with lower branch arm number. Moreover, the drug release from the star‐shaped PDLL microspheres was slower than that of the linear PDLL microspheres for similar PDLL arm lengths. The drug release behavior could be adjusted through both the branch arm number and arm length of PDLL. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012 相似文献
82.
Danial Barati Kira Watkins Zhibin Wang Fan Yang 《Small (Weinheim an der Bergstrasse, Germany)》2020,16(22)
Poly(lactide‐co‐glycolide) (PLGA) has been widely used as a tissue engineering scaffold. However, conventional PLGA scaffolds are not injectable, and do not support direct cell encapsulation, leading to poor cell distribution in 3D. Here, a method for fabricating injectable and intercrosslinkable PLGA microribbon‐based macroporous scaffolds as 3D stem cell niche is reported. PLGA is first fabricated into microribbon‐shape building blocks with tunable width using microcontact printing, then coated with fibrinogen to enhance solubility and injectability using aqueous solution. Upon mixing with thrombin, firbornogen‐coated PLGA microribbons can intercrosslink into 3D scaffolds. When subject to cyclic compression, PLGA microribbon scaffolds exhibit great shock‐absorbing capacity and return to their original shape, while conventional PLGA scaffolds exhibit permanent deformation after one cycle. Using human mesenchymal stem cells (hMSCs) as a model cell type, it is demonstrated that PLGA μRB scaffolds support homogeneous cell encapsulation, and robust cell spreading and proliferation in 3D. After 28 days of culture in osteogenic medium, hMSC‐seeded PLGA μRB scaffolds exhibit an increase in compressive modulus and robust bone formation as shown by staining of alkaline phosphatase, mineralization, and collagen. Together, the results validate PLGA μRBs as a promising injectable, macroporous, non‐hydrogel‐based scaffold for cell delivery and tissue regeneration applications. 相似文献
83.
84.
丙交酯的合成与纯化研究 总被引:16,自引:0,他引:16
讨论了丙交酯制备过程中的影响因素,用重结晶法得到了高纯度的丙交酯,并通过熔点、红外光谱和氢核磁共振谱对丙交酯进行了表征。 相似文献
85.
Poly(ethylene glycol)‐poly(L ‐lactide) diblock and triblock copolymers were prepared by ring‐opening polymerization of L ‐lactide with poly(ethylene glycol) methyl ether or with poly(ethylene glycol) in the presence of stannous octoate. Molecular weight, thermal properties, and crystalline structure of block copolymers were analyzed by 1H‐NMR, FTIR, GPC, DSC, and wide‐angle X‐ray diffraction (WAXD). The composition of the block copolymer was found to be comparable to those of the reactants. Each block of the PEG–PLLA copolymer was phase separated at room temperature, as determined by DSC and WAXD. For the asymmetric block copolymers, the crystallization of one block influenced much the crystalline structure of the other block that was chemically connected to it. Time‐resolved WAXD analyses also showed the crystallization of the PLLA block became retarded due to the presence of the PEG block. According to the biodegradability test using the activated sludge, PEG–PLLA block copolymer degraded much faster than PLLA homopolymers of the same molecular weight. © 1999 John Wiley amp; Sons, Inc. J Appl Polym Sci 72: 341–348, 1999 相似文献
86.
Hydrolysis of blend films prepared from amorphous poly(DL-lactide) (a-PLA) and isotactic crystalline poly(D- or L-lactide) (c-PLA) having different c-PLA contents [X = c-PLA/(a-PLA + c-PLA)] was performed in phosphate buffered solution of pH 7.4 at 37°C. The blend films before and after hydrolysis were studied using gel permeation chromatography, tensile testing, differential scanning calorimetry (DSC), and optical rotation. The mass of the blend films remaining after hydrolysis of longer than 20 months was larger with the increasing initial X. The tensile strength of the blend films remained unchanged in the early stage of hydrolysis, followed by a rapid decrease with time, the duration of period for the tensile strength remaining unchanged was longer for the blend films of smaller X. The change in crystallinity, molecular weight, and specific optical rotation during hydrolysis of the blend films revealed that degradation took place preferentially in the amorphous region than in the crystalline region of the blend films. A double melting peak was observed in the DSC spectra of blend films with X = 0.75 and 0.5 after hydrolysis for 20 months. The time difference in the induction of reduction between the tensile strength and the mass due to hydrolysis of the blend films increased with an increase in X. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 63: 855–863, 1997 相似文献
87.
Polylactides with high and low L ‐isomeric ratios of the lactate units (PLA99.0 and 77.0, where the numbers correspond to the L ‐ratios) were melt‐blended to analyze the changes in properties and biodegradability with the polymer blend. The crystallinity of the blends was almost similar to that of the blends of PLLA and PDLLA. The glass transition behavior supported the compatibility of both polymers. The glass transition behavior was indicative of a compatible nature of both polymers. The tensile modulus of the blends was almost identical irrespectively of the blend ratio, while their tensile strength decreased with decreasing composition of PLA99.0. Above Tg, the storage modulus of the blends dropped from 2–3×109 Pa to 1–3×106 Pa and then increased to a different level depending on the crystalline nature of the blends. The biodegradability of the blends increased with decreasing composition of PLA99.0. This difference in degradability can be well explained by our random packing model of local helices of the L ‐sequenced chains for the L ‐rich PLA samples. 相似文献
88.
聚乳酸在生物医学领域中的应用 总被引:5,自引:0,他引:5
简要介绍高分子量聚乳酸的合成方法、良好的生物相容性、可吸收性及生物降解性。通过概述聚乳酸在药物释放材料、眼科材料、外科手术缝合线、骨折内固定材料以及组织工程修复等方面的应用,对其在生物医学领域的研究前景作了进一步展望。 相似文献
89.
90.
The effects of storage at 25°C in swelling solvents having different solubility parameter (δs) values of 16.8–26.0 J0.5 cm−1.5 on the physical properties and structure of as‐cast poly(L ‐lactide) (PLLA) films was investigated by the degree of swelling (DS), differential scanning calorimetry (DSC), and tensile tests. It was found that PLLA film shows durabity to swelling solvents having δs values much lower or higher than the value range of 19–20.5 J0.5 cm−1.5 and that the polymer solubility parameter (δp) for PLLA is in the value range of 19–20.5 J0.5 cm−1.5. The decrease in the glass transition temperature (Tg) and tensile properties and the increase in melting temperature (Tm) and crystallinity (xc) were larger for PLLA films swollen in solvents having a high DS at 7 days (DS7days). The slight increase in Tm and xc for PLLA films after swelling in solvents with high DS7days values was due to the crystallization of PLLA that occurred during swelling, while the small increase in Tg and elongation at break (εB) for PLLA films after immersion in the solvents having low DS7days values was ascribed to stabilized chain packing in the amorphous region. The Tg, εB, and Young's modulus of the PLLA films after swelling in the solvents varied in the ranges of 47–57°C, 4–8%, and 55–77 kg/mm2, depending on their DS7days or δs values. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 79: 1582–1589, 2001 相似文献