In vitro degradation behaviour of biodegradable soy plastics: effects of crosslinking with glyoxal and thermal treatment

In-vitro degradation of soy-derived protein materials, non-crosslinked (SItp), crosslinked with glyoxal (X-SItp) or submitted to heat treatment (24TT-SItp), was studied with either an isotonic saline solution without enzymatic activity or containing bacterial collagenase. The changes in weight of the samples during the in-vitro degradation were studied and compared with the variations of the mechanical properties. The weight loss of SItp, X-SItp and 24TT-SItp were more pronounced when using collagenase. After 24 h of immersion, SItp lost 10.6% of its initial weight whereas 0.6X-SItp and 24TT-SItp lost 1.7 and 5.7%, respectively. In every case, the weight loss was found to be directly proportional to the respective crosslinking degree: 2.4% for SItp, 44% for 0.6X-SItp and 27.8% for 24TT-SItp. Consequently, the susceptibility of the soy materials towards enzymatic degradation could be controlled by varying the degree of crosslinking of the samples. The mechanical properties proved to be more sensitive to the loss of plasticiser (glycerol) during immersion than to the degradation of the polymeric matrices. After 24 h of immersion all the materials presented an increase in stiffness and brittleness due to the complete leaching of glycerol from the matrices. SItp, X-SItp and 24TT-SItp proved to be suitable materials for either load-bearing applications or temporary applications such as tissue engineering scaffolds or drug delivery systems. (C) 2003 Elsevier Science Ltd. All rights reserved.