In vitro degradation and swelling behaviour of rubbery thermoplastic starch in simulated body and simulated saliva fluid and effects of the degradation products on cells

Degradation in vitro is of importance in implanted biological industry. This research investigated the swelling and degradation behaviours of glycerol plasticized thermoplastic starch (GTPS) in simulated body fluid (SBF) and simulated saliva fluid (SSF), respectively. The weight loss, swelling degree and linear extensibility as a function of time were measured. Changes in the morphology (SEM), chemical structure (FT-IR), crystal property (XRD) and thermogravimetic property (TG) during degradation were also investigated. Results show that the degradation in SSF was much quicker than that in SBF. About 1 h was needed for the swelling equilibrium in SBF, which was a little quicker than that in SSF. In alkaline solution the swelling speed and the swelling degree were larger than those in neutral and acidic solutions. The degradation in SBF was typical bulk degradation. In SSF the surface and bulk degradation took place synchronously, but the surface degradation played an important role in the first 2 h. Results from FT-IR and XRD suggest that the glycosidic linkages in starch chains were broken and the crystal structure in GTPS was destructed during degradation. Cytotoxicity test was used to investigate the effects of the short-term extracted dilutions and long-term degradation products on the cells, which illustrates that the degradation products not only had non-toxicity but also accelerated the cells' growth.