Distinct degradation behaviors of semi-crystalline poly (4-hydroxybutyrate) containing a nucleating agent under enzymatic or alkaline conditions

Abstract

Poly(4-hydroxybutyrate) (P4HB) is an absorbable thermoplastic polyester with excellent mechanical properties, good biodegradability and biocompatibility, and has great application prospects in the biomedical field. Therefore, it is of great significance to adjust the degradation rate of P4HB to meet the needs of different application scenarios. In this work, the effects of multimethyl-benzilidene sorbitol (TM6) on the crystallization and degradation behaviors of P4HB were studied. The differential scanning calorimetry, polarized optical microscopy and atomic force microscopy results indicated that TM6 increased the crystallization rate of P4HB as heterogeneous nuclei. The results of weight loss and gel permeation chromatography measurements indicated that both enzymatic and alkaline degradation proceeded via a surface erosion, while the effects of TM6 on the respective degradation rates were quite different. When TM6 content reached 0.5 wt%, the enzymatic degradation rate of P4HB was significantly reduced, and the degraded surface showed a network structure, indicating that TM6-induced crystals were difficult to be degraded, which may be attributed to the high local crystallinity around linear TM6 and/or the different spatial arrangements of TM6-induced crystals. However, the alkaline degradation rate of P4HB was slightly increased because the introduction of TM6 decreased the overall crystallinity. The scanning electron microscope results of P4HB composites after degradation suggested that the enzymatic degradation had higher selectivity to the local physical structure. Based on the degradation results, microspheres with holes or loose nanofibrous structures on the surface were prepared. The cell culture results on the microspheres indicated that nanofibrous structure were more conducive to the adhesion and growth of MG-63 cells. This method for regulating the surface structure of scaffolds is simple and easy to implement, so it has great application potential in the field of tissue engineering.