Leach K J, Mathiowitz E
Department of Molecular Pharmacology, Physiology, and Biotechnology, Brown University, Providence, Rhode Island 02912, USA.
Biomaterials. 1998 Nov;19(21):1973-80. doi: 10.1016/s0142-9612(98)00108-2.
Double-walled (DW) polymer microspheres with a core of poly(1,3-bis-(p-carboxyphenoxy propane)-co-(sebacic anhydride)20:80 (P(CPP:SA)20:80) and an external coat of poly(L-lactic acid) (PLLA) were degraded for up to 6 months in vitro. The effects of hydrolytic degradation on the polymers were studied by Fourier-transform infrared (FTIR) spectroscopy, differential scanning calorimetry (DSC), gel permeation chromatography (GPC) and scanning electron microscopy (SEM). The inner core of the polyanhydride copolymer (P(CPP:SA)20:80) degraded first, breaking down into oligomers during the first week and then into monomers which were trapped by the outer shell of PLLA, crystallized, and remained in the core for the duration of the study. As expected, the PLLA coat degraded at a slower rate due to the ester bonds between lactic acid monomers being more hydrolytically resistant than the anhydride bonds. The PLLA in the DW microspheres decreased from its original molecular weight (Mw) of 24,000 g mol(-1) to approximately 5,000 g mol(-1) over the 6 month study. The melting temperature of the PLLA decreased more than 30 degrees C during the study, but no changes were observed in the FTIR spectra. The 6 month samples were very brittle, showing the concomitant drop in mechanical strength with the decrease in Mw.
具有聚（1,3 - 双 -（对 - 羧基苯氧基丙烷）- 共 -（癸二酸酐）20:80（P（CPP:SA）20:80）核心和聚（L - 乳酸）（PLLA）外层的双壁（DW）聚合物微球在体外降解长达6个月。通过傅里叶变换红外（FTIR）光谱、差示扫描量热法（DSC）、凝胶渗透色谱法（GPC）和扫描电子显微镜（SEM）研究了水解降解对聚合物的影响。聚酸酐共聚物（P（CPP:SA）20:80）的内核首先降解，在第一周分解成低聚物，然后分解成单体，这些单体被PLLA外壳捕获、结晶，并在研究期间留在核心中。正如预期的那样，由于乳酸单体之间的酯键比酸酐键更耐水解，PLLA涂层降解速度较慢。在为期6个月的研究中，DW微球中的PLLA分子量从其原始的24,000 g mol⁻¹降至约5,000 g mol⁻¹。在研究期间，PLLA的熔点下降超过30℃，但FTIR光谱未观察到变化。6个月的样品非常脆，显示出随着分子量降低机械强度随之下降。
