Twin screw extrusion of conductive citrate-based biomaterials

Abstract

The range of processing methods for thermoset bioelastomers is limited due to the insolubility of their highly crosslinked nature. In-line extrusion of biodegradable polyester elastomers and their composites would open new possibilities for high-precision manufacturing (i.e. 3D printing), solvent-free additive dispersion, and adhesion development for future clinical needs. An effective method to extrude elastomeric, conductive composites is demonstrated for the first time with polyoctanediol citrate/sebacate (POCS) as the bioelastomer. The POCS pre-polymer in its liquid form was blended with untreated multiwall carbon nanotubes (MWCNTs) and partially cured to produce the feedstock for twin-screw hot-melt extrusion. MWCNTs were mechanically sheered within the POCS matrix at a processing temperature of 120 °C, which thermocured from a viscoelastic liquid into an extrudable crosslinked composite rubber. Furthermore, the composite was thermally and electrically conductive with swelling and hydrolytic degradation kinetic properties dependent on MWCNT concentration. Extruded composite strings are classified as conductive polymers, with lowest resistivity of 3.5 kΩ cm measured for POCS-MWCNT-5% in comparison to POCS-MWCNT-1% at 22.7 kΩ cm. Extruded strings (∼2 mm in diameter) exhibit a tensile modulus of 5–7.5 MPa with an extensibility of 40–80%. The processing method lays the framework for rapid formulation development of citrate based biomaterial composites and scale-up production.