Characterisation of mechanical and surface properties of novel biomimetic interpenetrating alumina-polycarbonate composite materials

Objective . To determine the mechanical and surface characteristics of two novel biomimetic interpenetrating phase alumina-polycarbonate (Al₂O₃-PC) composite materials, comprising aligned honeycomb-like porous ceramic preforms infiltrated with polycarbonate polymer. Method . Two composite materials were produced and characterised. Each comprised a porous structure with a ceramic-rich (polymer-poor) top layer, graduated through to a more porous ceramic-poor (polymer-rich) bottom layer. In addition, pure polycarbonate and dense alumina specimens were subjected to the same characterisation namely: density, compression, three-point bend, hardness, surface loss and surface roughness testing. Scanning electron microscopy and micro computerised tomography were employed for structural examination. Results . Three-dimensional aligned honeycomb-like ceramic structures were produced and full interpenetration of the polymer phase was observed using MicroCT. Depending on the ceramic volume in the initial aqueous ceramic suspension, the density of the final interpenetrating composites ranged from 2.64 to 3.01 g/cm 3 , compressive strength ranged from 192.43 to 274.91 MPa, flexural strength from 105.54 to 148.47 MPa, fracture toughness from 2.17 to 3.11 MPa.m ½ , hardness from 0.82 to 1.52 GPa, surface loss from 0.71 to 1.40 µm and surface roughness, following tooth brushing, from 0.70 to 0.99µm. Composite specimens showed characteristic properties part way between enamel and polycarbonate. Significance . There was a correlation between the initial solid ceramic loading in the aqueous suspension, used to produce the porous ceramic scaffolds, and the subsequent characteristic properties of the composite materials. These novel composites show potential as aesthetic orthodontic bracket materials, as their properties fit part way between those of ceramic, enamel and polycarbonate.