Formation of mesoporous calcium sulfate microspheres through phase conversion in controlled calcination

Abstract

Calcium sulfate has been used as a biomedical material for over a century thanks to its biocompatible, biodegradable and cementitious properties. However the dense structure and low surface area of existing materials exclude its adsorption properties and restrict the applications. In this work, mesoporous calcium sulfate microspheres are prepared through topological conversion of monodisperse α-calcium sulfate hemihydrate (α-HH) microspheres under controlled calcination. The calcination process contributes to the phase conversion from α-HH to calcium sulfate anhydrite (AH) along with the elimination of structural water and the reduction of crystallite size, resulting in the formation of mesopores. The microspheres composed of 29.56 wt% α-HH and 70.44 wt% AH demonstrate a maximum surface area of 30.62 m² g⁻¹ and an ibuprofen (IBU) loading capacity of 22.44 mg g⁻¹, which shows a one hundred times improvement in surface area compared with traditional calcium sulfate materials. This is the first time drugs have been loaded directly to calcium sulfate particles, showing that the mesoporous calcium sulfate microspheres with uniform particle size and ordered pore structure could be a promising carrier as a biomaterial.