Experimental configuration. The sensors are placed four sites from the actuator and at the end of the crystal. The sensor located four sites away from the actuator is used to measure the localized vibrations within the vicinity of the defect (without being in direct contact with it, so as to avoid affecting its dynamics). The sensor at the end of the crystal is used to measure the transmission through the crystal. For our rectifier geometry, the bifurcation-based rectification mechanism is only clearly evident with a defect placed two particles away from the actuator. For defect particles placed three or more particles away from the actuator, the high attenuation of the signal (with frequency within the band gap 1 ) does not allow sufficient energy from the actuator to arrive to the defect particle.For defect particles placed next to the actuator, we observe that the effect of the boundary is dominant, and the dynamics of the system becomes more chaotic. The chain length of 19 particles was selected as a balance between having high enough attenuation (arising from the band gap) to demonstrate the rectification effect, and having a small enough dissipation of the signal to maximize the experimental tractability. In our numerical simulations, we observe that decreasing the dissipation in the system can increase the transmission efficiency in the forward configuration.

Vertically aligned yet laterally spaced nanoscale TiO2 nanotubes have been grown on Ti by anodization, and the growth of MC3T3-E1 osteoblast cells on such nanotubes has been investigated. The adhesion/propagation of the osteoblast is substantially improved by the topography of the TiO2 nanotubes with the filopodia of growing cells actually going into the nanotube pores, producing an interlocked cell structure. The presence of the nanotube structure induced a significant acceleration in the growth rate of osteoblast cells by as much as approximately 300-400%.

There is growing interest in creating untethered soft robotic matter that can repeatedly shape-morph and self-propel in response to external stimuli. Toward this goal, we printed soft robotic matter composed of liquid crystal elastomer (LCE) bilayers with orthogonal director alignment and different nematic-to-isotropic transition temperatures (TNI) to form active hinges that interconnect polymeric tiles. When heated above their respective actuation temperatures, the printed LCE hinges exhibit a large, reversible bending response. Their actuation response is programmed by varying their chemistry and printed architecture. Through an integrated design and additive manufacturing approach, we created passively controlled, untethered soft robotic matter that adopts task-specific configurations on demand, including a self-twisting origami polyhedron that exhibits three stable configurations and a “rollbot” that assembles into a pentagonal prism and self-rolls in programmed responses to thermal stimuli.

We report the experimental observation of discrete breathers in a one-dimensional diatomic granular crystal composed of compressed elastic beads that interact via Hertzian contact. We first characterize their effective linear spectrum both theoretically and experimentally. We then illustrate theoretically and numerically the modulational instability of the lower edge of the optical band. This leads to the dynamical formation of long-lived breather structures, whose families of solutions we compute throughout the linear spectral gap. Finally, we observe experimentally such localized breathing modes with quantitative characteristics that agree with our numerical results.