Piezoelectric biomaterials are intrinsically suitable for coupling mechanical and electrical energy in biological systems to achieve in vivo real-time sensing, actuation, and electricity generation. However, the inability to synthesize and align the piezoelectric phase at a large scale remains a roadblock toward practical applications. We present a wafer-scale approach to creating piezoelectric biomaterial thin films based on γ-glycine crystals. The thin film has a sandwich structure, where a crystalline glycine layer self-assembles and automatically aligns between two polyvinyl alcohol (PVA) thin films. The heterostructured glycine-PVA films exhibit piezoelectric coefficients of 5.3 picocoulombs per newton or 157.5 × 10−3 volt meters per newton and nearly an order of magnitude enhancement of the mechanical flexibility compared with pure glycine crystals. With its natural compatibility and degradability in physiological environments, glycine-PVA films may enable the development of transient implantable electromechanical devices.

The structures and physicochemical properties of acid‐thinned corn, potato, and rice starches were investigated. Corn, potato, and rice starches were hydrolyzed with 0.14 N hydrochloric acid at 50 °C until reaching a target pasting peak of 200—300 Brabender Units (BU) at 10% solids in the Brabender Visco Amylograph. After acid modification the amylose content decreased slightly and all starches retained their native crystallinity pattern. Acid primarily attacked the amorphous regions within the starch granule and both amylose and amylopectin were hydrolyzed simultaneously by acid. Acid modification decreased the longer chain fraction and increased the shorter chain fraction of corn and rice starches but increased the longer chain fraction and decreased the shorter chain fraction of potato starch, as measured by high‐performance size‐exclusion chromatography. Acid‐thinned potato starches produced much firmer gels than did acid‐thinned corn and rice starches, possibly due to potato starch's relatively higher percentage of long branch chains (degree of polymerization 13—24) in amylopectin. The short‐term development of gel structure by acid‐thinned starches was dependent on amylose content, whereas the long‐term gel strength appeared dependend on the long branch chains in amylopectin.

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Graphene and other two-dimensional materials have been proved to be able to offer low friction. Here we assembled van der Waals heterostructures with graphene and molybdenum disulphide monolayers. The Raman spectrum together with a modified linear chain model indicate a two-orders-of-magnitude decrease in the interlayer lateral force constant, as compared with their homogeneous bilayers, indicating a possible routine to achieve superlubricity. The decrease in the interlayer lateral force constant is consistent with the ultrasmall potential energy corrugation during sliding, which is derived from density functional theory calculations. The potential energy corrugation is found to be determined by the sliding-induced interfacial charge density fluctuation, suggesting a new perspective to understand the physical origin of the atomic scale friction of two-dimensional materials.