Quantification of thermal material degradation during the processing of biomedical thermoplastics

Three-dimensional plotting, a melt-based technique that involves the guided deposition of extruded filaments, is a promising method for the manufacture of thermoplastic scaffolds for tissue engineering. However, the polymer degrades during processing because of a prolonged residence time at an elevated temperature in the dispensing head before actual extrusion. This thermal degradation has been attributed to random chain scission; in this research, it has been quantified as a function of the residence time for a selection of polylactide-based polymers. The utilized techniques include thermogravimetric analysis (overall mass loss), differential scanning calorimetry (glass-transition, melting, and recrystallization temperatures), gel permeation chromatography (molecular mass), and inherent viscosity measurements. Experiments have shown that a static heating interval greater than 6 h is sufficient to destroy the molecular chain integrity of poly-(1-lactide) and poly(d,l-lactide). Copolymers with poly(e-caprolactone) and poly(glycolic acid) are more resilient to thermal loading but are still severely affected. Overall, the differential scanning calorimetry results have been judged to be a good source of complementary data for the quantification of the degradation phenomenon, whereas inherent viscosity measurements have been confirmed to be related to the gel permeation chromatography results, which indicate shortening of the polymer chain.