Biological matrix composites from cultured plant cells.

We present an approach to fabricate biological matrix composites made entirely from cultured plant cells. We utilize the cell's innate ability to synthesize nanofibrillar cell walls, which serve as the composite's fundamental building blocks. Following a controlled compression/dehydration process, the cells arrange into lamellar structures with hierarchical features. We demonstrate that the native cell wall nanofibrils tether adjacent cells together through fibrillar interlocking and intermolecular hydrogen bonding. These interactions facilitate intercellular adhesion and eliminate the need for other binders. Our fabrication process utilizes the entire plant cell, grown in an in vitro culture; requires no harsh chemical treatments or waste-generating extraction or selection processes; and leads to bulk biocomposites that can be produced in situ and biodegrade in soil. The final mechanical properties are comparable to commodity plastics and can be further modulated by introducing filler particles.

Biomimetic temperature-sensing layer for artificial skins.

Artificial membranes that are sensitive to temperature are needed in robotics to augment interactions with humans and the environment and in bioengineering to improve prosthetic limbs. Existing flexible sensors achieved sensitivities of <100 millikelvin and large responsivity, albeit within narrow (<5 kelvin) temperature ranges. Other flexible devices, working in wider temperature ranges, exhibit orders of magnitude poorer responses. However, much more versatile and temperature-sensitive membranes are present in animals such as pit vipers, whose pit membranes have the highest sensitivity and responsivity in nature and are used to locate warm-blooded prey at distance. We show that pectin films mimic the sensing mechanism of pit membranes and parallel their record performances. These films map temperature on surfaces with a sensitivity of at least 10 millikelvin in a wide temperature range (45 kelvin), have very high responsivity, and detect warm bodies at distance. The produced material can be integrated as a layer in artificial skin platforms and boost their temperature sensitivity to reach the best biological performance.

Wave propagation in granular chains with local resonances.

We study wave propagation in a chain of spherical particles containing a local resonator. The resonant particles are made of an aluminum outer spherical shell and a steel inner mass connected by a polymeric plastic structure acting as a spring. We characterize the dynamic response of individual particles and the transmitted linear spectra of a chain of particles in contact. A wide band gap is observed both in theoretical and experimental results. We show the ability to tune the acoustic transmission by varying the contact interaction between particles. Higher driving amplitude leads to the generation of nonlinearities both in the response of a single particle and that of the whole chain. For a single resonant particle, we observe experimentally a resonant frequency downshift, which follows a complex nonlinear behavior. In the chain of particles, nonlinearity leads to the generation of nonlinear harmonics and the presence of localized modes inside the band gap.