Preparation of drug‐loaded microspheres of linear and star‐shaped poly(D,L‐lactide)s and their drug release behaviors

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 (T_g) of the PDLLs decreased steadily as the branch arm number increased for similar molecular weights. However, the intrinsic viscosity and T_g 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     

Surface modification of cellulose nanocrystals by grafting with poly(lactic acid)

The use of biopolymers obtained from renewable resources is currently growing and they have found unique applications as matrices and/or nanofillers in ‘green’ nanocomposites. Grafting of polymer chains to the surface of cellulose nanofillers was also studied to promote the dispersion of cellulose nanocrystals in hydrophobic polymer matrices. The aim of this study was to modify the surface of cellulose nanocrystals by grafting from L‐lactide by ring‐opening polymerization in order to improve the compatibility of nanocrystals and hydrophobic polymer matrices. The effectiveness of the grafting was evidenced by the long‐term stability of a suspension of poly(lactic acid)‐grafted cellulose nanocrystals in chloroform, by the presence of the carbonyl peak in modified samples determined by Fourier transform infrared spectroscopy and by the modification in C1s contributions observed by X‐ray photoelectron spectroscopy. No modification in nanocrystal shape was observed in birefringence studies and transmission electron microscopy. © 2013 Society of Chemical Industry     

合成丙交酯工艺的改进

采用氧化锌(ZnO)、氯化亚锡(SnCl2)、硫酸亚锡(SnSO4)、辛酸亚锡〔Sn(Oct)2〕以及它们的混合物催化合成丙交酯。实验结果表明,催化剂的种类和用量对丙交酯的收率有显著的影响。以ZnO/Sn(Oct)2为催化剂,用量为反应物总质量的2 0%时催化效果较好,能使丙交酯的收率高达45 2%。同时在N2流速为2L/min、压力为400Pa下采用减压气流法用于丙交酯的蒸出,收率比传统的减压法增加了8 1%。此外,还设计了一个在合成中能够有效分离丙交酯和乳酸的接收器用于接收丙交酯。     

Fully biobased biodegradable poly(l‐lactide)‐b‐poly(ethylene brassylate)‐b‐poly(l‐lactide) triblock copolymers: synthesis and investigation of relationship between crystallization morphology and thermal properties

Well‐defined poly(l ‐lactide‐b‐ethylene brassylate‐b‐l ‐lactide) (PLLA‐b‐PEB‐b‐PLLA) triblock copolymer was synthesized by using double hydroxyl‐terminated PEBs with different molecular weights. Gel permeation chromatography and NMR characterization were employed to confirm the structure and composition of the triblock copolymers. DSC, wide‐angle X‐ray diffraction, TGA and polarized optical microscopy were also employed to demonstrate the relationship between the composition and properties. According to the DSC curves, the cold crystallization peak vanished gradually with decrease of the PLLA block, illustrating that the relatively smaller content of PLLA may lead to the formation of a deficient PLLA type crystal, leading to a decrease of melting enthalpy and melting temperature. Multi‐step thermal decompositions were determined by TGA, and the PEB unit exhibited much better thermal stability than the PLLA unit. Polarized optical microscopy images of all the triblock samples showed that spherulites which develop radially and with an extinction pattern in the form of a Maltese cross exhibit no ring bond. The growth rate of the spherulites of all triblock samples was investigated. The crystallization capacity of PLLA improved with incorporation of PLLA, which accords with the DSC and wide‐angle X‐ray diffraction results. © 2019 Society of Chemical Industry     

聚乳酸微球的制备

以L-乳酸为原料,锡粒为催化剂,实现了丙交酯的开环聚合反应,红外光谱结果表明,合成了分子量可控的聚乳酸。以二氯甲烷为溶剂,聚乙烯醇为表面活性剂,制备了聚乳酸微球,研究了聚乙烯醇浓度对聚乳酸微球的影响。结果表明,当聚乙烯醇浓度增加时,微球半径变小,但粒径分布均匀度下降,聚乙烯醇浓度为1%时,聚乳酸成球效果较好。     

Blends of crystalline and amorphous poly(lactide). III. Hydrolysis of solution-cast blend films

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     

聚乳酸在生物医学领域中的应用

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。     

Poly(L‐lactide): v. effects of storage in swelling solvents on physical properties and structure of poly(L‐lactide)

The effects of storage at 25°C in swelling solvents having different solubility parameter (δ_s) values of 16.8–26.0 J^0.5 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 δ_s values much lower or higher than the value range of 19–20.5 J^0.5 cm^−1.5 and that the polymer solubility parameter (δ_p) for PLLA is in the value range of 19–20.5 J^0.5 cm^−1.5. The decrease in the glass transition temperature (T_g) and tensile properties and the increase in melting temperature (T_m) and crystallinity (x_c) were larger for PLLA films swollen in solvents having a high DS at 7 days (DS_7days). The slight increase in T_m and x_c for PLLA films after swelling in solvents with high DS_7days values was due to the crystallization of PLLA that occurred during swelling, while the small increase in T_g and elongation at break (ε_B) for PLLA films after immersion in the solvents having low DS_7days values was ascribed to stabilized chain packing in the amorphous region. The T_g, ε_B, 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 DS_7days or δ_s values. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 79: 1582–1589, 2001     

In vitro Degradation of Poly[(L‐lactide)‐co‐(trimethylene carbonate)] Copolymers and a Composite with Poly[(L‐lactide)‐co‐glycolide] Fibers as Cardiovascular Stent Material

TMC/LLA copolymers with several TMC/LLA ratios are synthesized and a composite is obtained by reinforcing with short PLGA fibers. In vitro degradation is studied at 37 °C in pH = 7.4 buffer and compared with a PLLA homopolymer. The degradation of the copolymers appears slower than that of PLLA, showing that TMC units are more resistant to hydrolysis than LLA. Compositional changes indicate a preferential degradation of LLA units as compared to TMC ones. Morphological changes with crystallization of degradation by‐products are observed. The composite degrades much faster than the neat copolymer and PLLA because the faster degradation of PLGA fibers speeds up the degradation of the matrix. The composite appears promising for the fabrication of totally bioresorbable stents.

     

Solid‐state linear viscoelastic properties of intercalated poly(L‐lactide)/organo‐modified montmorillonite hybrids

Hybrids of poly(L ‐lactide)/organophilic clay (PLACHs) have been prepared by a melt‐compounding process using poly(L ‐lactide) (PLLA) and different contents of surface‐treated montmorillonite modified with a dimethyl dioctadecyl ammonium salt. The dispersion structures of clay particles in PLACHs were investigated using wide‐angle X‐ray diffraction and transmission electron microscopy. The solid‐state linear viscoelastic properties for these PLACHs were examined as functions of temperature and frequency. The incorporation of organo‐modified silicate into PLLA matrix enhanced significantly both storage moduli (E′) and loss moduli (E″). The strong enhancement observed in dynamic moduli of PLACHs could be attributed to uniformly dispersed state of the clay particles with high aspect ratio (= length/thickness of clay) and the intercalation of the PLLA chains between silicate layers. Copyright © 2006 Society of Chemical Industry