Piezoelectric bioorganic thin films
Piezoelectric materials allow a reversible conversion between mechanical pressure and electrical charge and are useful for high precision sensors, actuators and motors. Yang et al. has developed a method for making high-quality crystalline thin films of piezoelectric γ-glycine crystals that are grown and refined between layers of polyvinyl alcohol (PVA) (see Perspective from Berger). PVA layers are essential to promote crystallization of the preferred crystal phase with the polar axis oriented perpendicular to the plane of the film due to hydrogen bonding at the PVA-glycine interface. Thin films show macroscopic piezoelectric response and high stability in aqueous environments. The films are water soluble and, when properly packaged, could be implanted in a biodegradable energy recovery device.
Science, abf2155, this issue p. 337; see also abj0424, p. 278
Piezoelectric biomaterials are inherently suited to couple mechanical and electrical energy in biological systems to achieve real-time sensing, actuation, and power generation in vivo. However, the inability to synthesize and align the piezoelectric phase on a large scale remains an obstacle to practical applications. We present a wafer-scale approach to create thin films of piezoelectric biomaterials based on -glycine crystals. The thin film has a sandwich structure, where a layer of crystalline glycine self-assembles and automatically aligns between two thin films of polyvinyl alcohol (PVA). Heterostructured glycine-PVA films exhibit piezoelectric coefficients of 5.3 picocoulombs per newton or 157.5 × 10-3 voltmeters per newton and an improvement of nearly an order of magnitude in mechanical flexibility over pure glycine crystals. With their natural compatibility and degradability in physiological environments, glycine-PVA films may enable the development of transient implantable electromechanical devices.