Ferroelectric polarization in nanocrystalline hydroxyapatite thin films on silicon.

Hydroxyapatite nanocrystals in natural form are a major component of bone--a known piezoelectric material. Synthetic hydroxyapatite is widely used in bone grafts and prosthetic pyroelectric coatings as it binds strongly with natural bone. Nanocrystalline synthetic hydroxyapatite films have recently been found to exhibit strong piezoelectricity and pyroelectricity. While a spontaneous polarization in hydroxyapatite has been predicted since 2005, the reversibility of this polarization (i.e. ferroelectricity) requires experimental evidence. Here we use piezoresponse force microscopy to demonstrate that nanocrystalline hydroxyapatite indeed exhibits ferroelectricity: a reversal of polarization under an electrical field. This finding will strengthen investigations on the role of electrical polarization in biomineralization and bone-density related diseases. As hydroxyapatite is one of the most common biocompatible materials, our findings will also stimulate systematic exploration of lead and rare-metal free ferroelectric devices for potential applications in areas as diverse as in vivo and ex vivo energy harvesting, biosensing and electronics.

Microprocessor-assisted screening techniques.

The important features of microprocessor design of medical instrumentation are discussed, and the Mammoscan dielectric breast scanner being developed in our laboratories is given as a specific example. The principles of dielectric breast scanning are explained, and the implementation of the technique in a working Mammoscan is is described. Typical results of Mammoscan examinations are given, including both normal and suspicious findings. Preliminary attempts at image classification are discussed, as well as the necessity of large-scale clinical data gathering for improving classification methods. The use of microprocessors makes devices such as the Mammoscan possible, both because of the power of microprocessor control and number handling, and because of its ability to store examination data locally and analyze it off-line at a central location.

Pyroelectricity and Induced Pyroelectric Polarization in Leaves of the Palmlike Plant Encephalartos villosus.

Quantitative pyroelectric measurements were made on the leaves of the palmlike plant Encephalartos. A pyroelectric response almost 50 times higher than the normal one could be induced by a small bias electric field, offering a means for highly increasing the efficiency of conversion of thermal to electrical energy. No evidence of ferroelectricity was found.

Elastic coefficients of animal bone.

The elastic stiffness coefficients of dried bovine phalanx and femur and of fresh bovine phalanx were measured by an ultrasonic technique. An analysis of the crystallographic structure of the principal components of bone and its piezoelectric and pyroelectric behavior showed that bone is a texture that has the same elastic coeffcient matrix as a hexagonal single crystal. The five elastic stiffness coefficients of fresh phalanx are: C(1l), 1.97; C(12), 1.21; C(13), 1.26; C(33), 3.20; and C(44), 0.54 (all in units of 10(11) dynes per square centimeter). Value of axial and transverse Young's and shear moduli, compressibility, and the three Poisson's ratios were calculated.