Porous hydroxyapatite and gelatin/hydroxyapatite microspheres obtained by calcium phosphate cement emulsion

Abstract

Hydroxyapatite and hybrid gelatine/hydroxyapatite microspheres were obtained through a water in oil emulsion of a calcium phosphate cement (CPC). The setting reaction of the CPC, in this case the hydrolysis of α-tricalcium phosphate, was responsible for the consolidation of the microspheres. After the setting reaction, the microspheres consisted of an entangled network of hydroxyapatite crystals, with a high porosity and pore sizes ranging between 0.5 and 5 μm. The size of the microspheres was tailored by controlling the viscosity of the hydrophobic phase, the rotation speed, and the initial powder size of the CPC. The incorporation of gelatin increased the sphericity of the microspheres, as well as their size and size dispersion. To assess the feasibility of using the microspheres as cell microcarriers, Saos-2 cells were cultured on the microspheres. Fluorescent staining, SEM studies, and LDH quantification showed that the microspheres were able to sustain cell growth. Cell adhesion and proliferation was significantly improved in the hybrid gelatin/hydroxyapatite microspheres as compared to the hydroxyapatite ones.

Optimizing the Water-Oil Emulsification Process for Developing CPC Microspheres

“…Materials based on calcium phosphates (CaP) have been used in the repair of bone tissue as dense blocks, scaffolds and granules 1 . In the last few years, CaP granules and particulates had an increase in their applicability due to their higher specific surface area allowing greater contact area with body fluids and, consequently, a higher rate of in vivo resorption and cell adhesion [1][2][3][4] .…”

“…In the last few years, CaP granules and particulates had an increase in their applicability due to their higher specific surface area allowing greater contact area with body fluids and, consequently, a higher rate of in vivo resorption and cell adhesion [1][2][3][4] . CaP granules may be applied for filling bone defects in regions that do not require high mechanical strength 2 and for carrying drugs and biomolecules [5][6][7] that would assist and/ or accelerate the treatment of diseases, induce the growth of new bone tissues which may lead to a delay in the need for bone replacement surgeries 8 .…”

“…CaP granules may be applied for filling bone defects in regions that do not require high mechanical strength 2 and for carrying drugs and biomolecules [5][6][7] that would assist and/ or accelerate the treatment of diseases, induce the growth of new bone tissues which may lead to a delay in the need for bone replacement surgeries 8 . In these cases, controlling the size and the shape of the granules is crucial since irregular shapes may cause inflammatory reactions, and would make bone formation slower when compared to uniform and more spherical particles 1,9,5,10 . Commonly, the production of ceramic microspheres requires two steps: (i) microspheres consolidation and; (ii) microspheres stabilization which can be achieved by sintering or processes that involves gellification or crosslinking of organic phases 1 .…”

“…In these cases, controlling the size and the shape of the granules is crucial since irregular shapes may cause inflammatory reactions, and would make bone formation slower when compared to uniform and more spherical particles 1,9,5,10 . Commonly, the production of ceramic microspheres requires two steps: (i) microspheres consolidation and; (ii) microspheres stabilization which can be achieved by sintering or processes that involves gellification or crosslinking of organic phases 1 . Nevertheless, these processes are low yield, difficult in controlling the granules shape and, in addition, some processes use toxic substances such as, paraffin 9,6,11 .…”

“…The intrinsic porosity of CPCs is also crucial as it enhances the resorption rate of the material in addition to promoting increased surface area available for interaction with biological media and incorporation of drugs 10,14 . Some researchers employed emulsions of calcium phosphate pastes to fabricate microspheres and scaffolds 1,15 .…”