Mechanically active materials in three-dimensional mesostructures.

Complex, three-dimensional (3D) mesostructures that incorporate advanced, mechanically active materials are of broad, growing interest for their potential use in many emerging systems. The technology implications range from precision-sensing microelectromechanical systems, to tissue scaffolds that exploit the principles of mechanobiology, to mechanical energy harvesters that support broad bandwidth operation. The work presented here introduces strategies in guided assembly and heterogeneous materials integration as routes to complex, 3D microscale mechanical frameworks that incorporate multiple, independently addressable piezoelectric thin-film actuators for vibratory excitation and precise control. The approach combines transfer printing as a scheme for materials integration with structural buckling as a means for 2D-to-3D geometric transformation, for designs that range from simple, symmetric layouts to complex, hierarchical configurations, on planar or curvilinear surfaces. Systematic experimental and computational studies reveal the underlying characteristics and capabilities, including selective excitation of targeted vibrational modes for simultaneous measurements of viscosity and density of surrounding fluids. The results serve as the foundations for unusual classes of mechanically active 3D mesostructures with unique functions relevant to biosensing, mechanobiology, energy harvesting, and others.

Self-adaptive hydrogels to mineralization.

Mineralized biological tissues, whose behavior can range from rigid to compliant, are an essential component of vertebrates and invertebrates. Little is known about how the behavior of mineralized yet compliant tissues can be tuned by the degree of mineralization. In this work, a synthesis route to tune the structure and mechanical response of agarose gels via ionic crosslinking and mineralization has been developed. A combination of experimental techniques demonstrates that crosslinking via cooperative hydrogen bonding in agarose gels is disturbed by calcium ions, but they promote ionic crosslinking that modifies the agarose network. Further, it is shown that the rearrangement of the hydrogel network helps to accommodate precipitated minerals into the network -in other words, the hydrogel self-adapts to the precipitated mineral- while maintaining the viscoelastic behavior of the hydrogel, despite the reinforcement caused by mineralization. This work not only provides a synthesis route to design biologically inspired soft composites, but also helps to understand the change of properties that biomineralization can cause to biological tissues, organisms and biofilms.