Fusion TEM holder tip
Image courtesy of J. Am. Ceram. Soc.

Abstract

This work reports the processing–microstructure–property correlation of novel HA–BaTiO3-based piezobiocomposites, which demonstrated the bone-mimicking functional properties. A series of composites of hydroxyapatite (HA) with varying amounts of piezoelectric BaTiO3 (BT) were optimally processed using uniquely designed multistage spark plasma sintering (SPS) route. Transmission electron microscopy imaging during in situ heating provides complementary information on the real-time observation of sintering behavior. Ultrafine grains (≤0.50 μm) of HA and BT phases were predominantly retained in the SPSed samples. The experimental results revealed that dielectric constant, AC conductivity, piezoelectric strain coefficient, compressive strength, and modulus values of HA-40 wt% BT closely resembles with that of the natural bone. The addition of 40 wt% BT enhances the long-crack fracture toughness, compressive strength, and modulus by 132%, 200%, and 165%, respectively, with respect to HA. The above-mentioned exceptional combination of functional properties potentially establishes HA-40 wt% BT piezocomposite as a new-generation composite for orthopedic implant applications.

Impact Statement

In this paper the authors report the synthesis and characterization of a HA – BaTiO3 alloy. Adding BaTiO3 (BT) to HA creates a better analog to bone, closely mimicking the electrical and mechanical properties. After HA and BT powders were made, densification was done via spark plasma sintering, where an electrical current is passed through the powder. The electrical current heats the sample and the powder sinters. This method results in better mechanical properties compared to more traditional sintering techniques. The authors used a Fusion 100 system to visualize the densification process in situ inside an FEI Tecnai T20 TEM. They heated the samples up to 950°C and imaged densification as a function of temperature and ramp rate. They found that samples sintered differently when temperature ramp rates were controlled fast ramp rates (100° C/min) resulted in denser agglomerates, while slower rates (10°C/min) the particles were less dense.