Effects of crystallization of polyhydroxyalkanoate blend on surface physicochemical properties and interactions with rabbit articular cartilage chondrocytes

As a new member of polyhydroxyalkanoate (PHA) family, poly(3-hydroxybutyrate-co-3-hydroxyhexanoate) (PHBHHx) has better mechanical properties compared with poly(3-hydroxybutyrate) (PHB). Still, many properties of PHBHHx and its blend with PHB may be exploited for a wide range of applications, such as tissue engineering and drug delivery. In this study, PHBHHx was found to be completely miscible with PHB in their blends. Crystallization behavior of these polyester blends played an important role in determination of the surface physicochemical properties including surface free energy, chemical states and polarity, and could subsequently govern the cellular responses. Interaction between PHB and PHBHHx influenced the non-dispersion surface free energy component, which governed the total surface free energy. It was shown that the blend with a 1:1 ratio of PHB/PHBHHx possessed the highest surface free energy, which was the most optimal material for chondrocytes adhesion. After 24 h, the amount of chondrocytes adhered on films of PHB/PHBHHx (1:1) was 2.1×104 cells/cm2, 5-times more compared with that on the PHB films (0.4×104 cells/cm2). The polarity of the blends increased with decreasing crystallinity. After 8 days of cultivation, the chondrocytes attached on PHB films were surrounded by both collagen II and collagen X, the amount of extracellular collagen X decreased with increasing polarity contributed by increasing PHBHHx content in the blend, while chondrocytes changed shapes from spherical to flat with increasing polarity. It indicated that endochondral ossification of chondrocytes was remarkably influenced by the crystallinity of the polyesters.