Fabrication, characterization and in-vitro evaluation of apatite-based microbeads for bone implant science

Abstract

The fabrication and characterization of apatite microbeads, which are intended to be used for bone tissue engineering, will be featured in this work. Hydroxyapatite-Alginate (HA-Alg) suspension was extruded dropwise into a calcium chloride (CaCL) crosslinking solution. The HA-Alg beads were then sintered using a 4-stage sintering profile to form porous microbeads of uniform size. Different concentrations of Alg solution, CaCl2 crosslinking solution, and HA-to-Alg ratios, were used. Results showed that Alg concentration affected the ability for particles to form spherical microbeads during the drying process. HA-to-Alg ratio affected the packing density of the microbeads, and sufficient HA-to-Alg content would yield more spherical microbeads. CaCl2 concentration affected the extent of crosslinking within the HA-Alg microbeads. Insufficient Ca2+ ions available would cause microbeads having deep furrows, indicating incomplete crosslinking in the HA-Alg beads. Thermal analyses were conducted to characterize the HA-Alg microbeads and subsequently, a multi-stage sintering profile was designed to yield porous microbeads with less cracks and better necking. The sintered microbeads measured in the range of 850-1120 μm. X-ray diffraction (XRD) results showed that HA microbeads remained phase-pure even after sintering process since no other secondary phases of calcium phosphate were detected. It also revealed that HA crystallinity increased with sintering temperature. Fourier transform infrared (FTIR) analysis indicated several sharp phosphate bands coupled with a hydroxyl band (all belonging to HA), and several carbonate bands. A preliminary in-vitro test revealed that human fetal mesenchymal stem cells (hfMSCs) grew well and remained viable with culture time.