Two-photon 3D-printed BSA hydrogel fibers resemble native muscle contraction dynamics

Force generation dynamics in native muscle tissues have been stringently optimized by evolution. Realizing similar contractile dynamics in a widely available biomaterial and subsequently fabricating macroscopic functional modules from them remains challenging. Herein, we tailor two-photon stereolithography to 3D print synthetic muscles made from bovine serum albumin to realize 1 mm long contractile fibers. We show that pH-dependent contractions in these synthetic muscles follow parabolic force-length relationships similar to biological muscles. Achieved stress outputs of 0.78 ± 0.13 N cm^-2were within an order of magnitude of smooth and cardiac muscle. Stretch-shortening work loops performed under different strain rates in turn revealed a viscoelastic behavior and significant velocity dependence of work and net power, more similar to skeletal muscle. That an isotropic protein hydrogel can achieve such dynamics, reinforces the notion that these are not limited to sarcomere-level ordering and suggests a more general design space for non-canonical conformational dynamics to engineer performance improvements in artificial muscle materials.