A skin inspired bio-smart composite with water responsive shape memory ability

Learned from skin, advanced functions have been added to existing materials with applications in regenerative machine and electronic skin. In this study, a skin collagen fiber/polyurethane (SCF/PU) composite with a dual-network based on a skin structural model was successfully prepared by a facile "paper-making" procedure. The first collagen nonwoven network was built up by spontaneous entangling and sticking of collagen fibers recycled from animal skin. Such a fibrous structure was then interpenetrated by waterborne PU. By virtue of chemo-mechanical adaptability of both the collagen fiber and PU elastomeric matrix, a water responsive shape memory with high shape fixation (99%) and shape recovery (>90%) has been achieved. Destruction and reformation of hydrogen bonds within the collagen fiber works as a "switch" to achieve shape deformation and fixation. This "switch" opens under the stimulation of water, while elastic entropy of PU promotes shape recovery. The obtained SCF/PU composite can be degradable in simulated body fluid whilst biological evaluation in vitro (MTT assay) proved that the SCF/PU composite has better biocompatibility than pure PU. The reported work offers a novel, simple and eco-friendly route for fabrication of a bio-smart material, which has potential for biomimetic sensors, regenerative medicine and artificial skins.