Biohybrid Variable Stiffness Soft Actuators that Self-Create Bone.

Inspired by the dynamic process of initial bone development, in which a soft tissue turns into a solid load-bearing structure, we hereby present the fabrication, optimization, and characterization of bio-induced variable stiffness actuators that can morph in various shapes and change their properties from soft to rigid. We prepared bilayer devices by combining the electromechanically active properties of polypyrrole with the compliant behaviour of alginate gels that were uniquely functionalized with cell-derived plasma membrane nanofragments (PMNFs), previously shown mineralize within 2 days, which promoted the mineralization in the gel layer to achieve the soft to stiff change by growing their own bone. The mineralized actuator showed an evident frozen state compared to the movement before mineralization. Next, patterned devices showed programmed directional and fixated morphing. These variable stiffness devices could wrap around and, after the PMNF-induced mineralization in and on the gel layer, adhere and integrate onto bone tissue. The developed biohybrid variable stiffness actuators could be used in soft (micro-)robotics and as potential tools for bone repair or bone tissue engineering. This article is protected by copyright. All rights reserved.