Production of machined gypsum/polymer blocks for use in three-dimensional milling systems and later conversion to hydroxyapatite

Abstract

The chemical conversion of gypsum into synthetic hydroxyapatite is an attractive approach to enhance the value of gypsum, a low-cost material, which can be discreetly implanted. The addition of biopolymers improves the resistance of the materials both before and after conversion. In this study, hydroxyapatite was produced from gypsum using a fixed water-to-gypsum ratio (w/g) of 0.7, along with gypsum/polymer composites. The polymers employed were polyhydroxybutyrate (PHB) and polyvinyl acetate (PVAc) at various mass ratios. Two methods were used to create the bodies: molding the paste and subtractive manufacturing. Mechanical compression tests were conducted both pre- and post-conversion to evaluate the impact of the conversion on material resistance and to compare it with the strength of subtractive manufacturing composites. For the gypsum/PHB composite, the best result was achieved at a 1% polymer concentration, yielding a resistance of 9.1±0.4 MPa, while for gypsum/PVAc, a compressive strength of 9.3±0.3 MPa was obtained at a 2% polymer concentration.

Keywords:
gypsum; hydroxyapatite; machinability; subtractive manufacturing