ELASTOMERIC MATERIAL CHEMISTRIES FOR ADDITIVE MANUFACTURING OF SOFT MACHINES

Abstract

Stereolithography is a rapid, high resolution, and scalable additive manufacturing technique that uses patterned light to build a solid object, layer-by- layer, from a liquid resin of photopolymerizable material. However, the material processing requirements, namely low viscosity and rapid photopolymerization, previously restricted printable materials to highly crosslinked and glassy polymers that exhibit low ultimate strains and prevent technical applications in biomedicine and soft robotics. This dissertation begins by reviewing the existing literature’s attempt to additively manufacture soft machines, particularly soft robots. With the problem defined, I then attempt to address the gaps in materials compatibility with stereolithography printing by designing two chemical platforms. First, by incorporating dynamic ionic linkages between anionic nanoparticles and cationic acrylates, we demonstrate tough, elastomeric polyacrylamide-based hydrogels. Such ionic composite hydrogels exhibit fast gelation, remarkable ionic conductivity (1MHz =1.8x10-3 S m-1 ), and large ultimate elongations (ult > 400%) and can be printed into osmotic actuators and soft conductive traces. Second, employing thiol-ene click chemistry of mercaptosiloxanes and vinylsiloxanes enables precise control of the polymer network density and thereby the mechanical properties over orders of magnitude (stiffness, 6 kPa < E < 330 kPa; ultimate elongation, 50% < ult < 400%). A simple, low cost modification to common commercial desktop printers enables printing of this silicone chemistry into highly resilient soft machines. Fluidic elastomer actuators, when fabricated through this method, can be pressurized with the base liquid resin to impart autonomic self-healing upon puncture in ambient sunlight.