Silk fibroin is a hierarchically structured fibrous protein that exhibits self-assembly and remarkable mechanical properties. In vivo, the silkworm (Bombyx mori) spins insoluble fibers from a soluble protein store in the gland via complex biological machinery, and in a laboratory setting cocoons can be reprocessed into a silk solution under simple conditions. The resulting silk fibroin solution can then be converted into biocompatible biomaterials such as ultra-thin films and 3D porous or solid matrices, which have demonstrated wide applicability in the fields of materials science and tissue engineering.¹  Silk fibroin can also be combined with other proteins, such as elastomeric tropoelastin, to provide materials with tunable mechanical properties.

The current work presents new materials generated from silk fibroin for soft robotics. One goal of soft robotics is to mimic biological motion – and use of biological actuators (bioactuators) and soft biological materials is one approach towards this goal. Our soft robotic system aims to exploit both of these features by combining tissue engineered muscle bioactuators with silk fibroin material substrates. 

Tissue engineered muscle bioactuators were formed from embryonic myoblasts isolated from the tobacco hornworm, Manduca sexta.²   The cells were differentiated and cultured in vitro to generate bioactuators that produced forces in the microNewton range. These bioactuators can be produced as scaffold-free 3D constructs as well as 2D and 3D formats supported by silk biomaterial substrates. Alignment of muscle cells via surface guidance enabled cell fusion and unidirectional force generation. Cell alignment cues were provided by both 2D (via patterned films) and 3D (via scaffolds with aligned pores) silk substrates. These bioactuators show long-term operability and wide environmental tolerance.  Combining the bioactuators  with flexible silk substrates can provide options for biocompatible and biodegradable robotic systems.