Actuators are materials that can move, similar to artificial muscles. In traditional robotics, movement is generated by motors. In order to develop soft robotics, a new method is required that can allow for quick, strong, repeatable motions, but does not require high modulus materials, such as metals. We have developed a method whereby a stiff fabric interphase provides mechanical support for silicone elastomer and polyampholyte hydrogel surface layers. By preferentially swelling or deswelling one of these layers, we can enable controlled, cyclable movement.

Publications:

• Hubbard, A. M.; Cui, W.; Huang, Y.; Takahashi, R.; Dickey, M. D.; Genzer, J.; King, D. R.*; Gong, J. P. “Hydrogel/Elastomer Laminates Bonded via Fabric Interphases for Stimuli-Responsive Actuators.” Matter (Cell Press) 2019, 1 (3): 674–689.

Biomaterials have some specific mechanical properties that are extremely difficult to achieve in synthetic materials, such as high strength and toughness and high fatigue resistance, all while maintaining a highly hydrated state. It is not possible to achieve all of these properties simultaneously in a homogenous material, and we therefore aim to utilize composite materials to achieve these properties. Beyond just mechanical response, synthetic biomaterials must be able to integrate well within the human body. They must be biocompatible, without causing immune system responses or rejection. Furthermore, they need to be able to integrate with already present biological tissues, either to improve healing, or to act as a permanent prosthetic.

The human body is incredibly complex, with important organ systems depending on liquid, solid, and gas inclusions. The circulatory system, controlled by the heart, pumps fluids to the entire body, enabling the active supply of nutrients based on feedback sensors, facilitating proper growth and healing. The skeletal system provides support and mechanical reinforcement for the entire body, allowing for smooth movement and protection from unintended impact. The respiratory system enables oxygen absorption and carbon dioxide release, controlling conditions for metabolic processes. From these examples, we see that these three states of matter work together to generate active materials to support human life: a single phase of matter is not able to perform all of these functions independently. To achieve an evolutionary step towards synthetic biomaterials, we must develop an architecture that can be expanded to support tri-phase (liquid, solid and gas) active materials while maintaining biocompatibility and robust mechanical performance.