Zhijie Yang

Hydroxyapatite (HAp) has been widely researched on due to its chemical similarity to native bone. HAp microspheres can encourage good cellular attachment due to their high surface area to volume ratio, facilitating further proliferation and differentiation of cells at later stages. To ensure the reliability and effectiveness of HAp microspheres in physiological conditions, we investigated their behaviour and key characteristic changes in both static and dynamic conditions. We found both environments exhibiting similar results but noticeably the microspheres in the dynamic environment resulted in faster rate of degradation. The degradation mechanism follows that of a surface degradation process. Microspheres underwent reduction in size and weight loss upon release of Ca²⁺ ions into Dulbecco’s Phosphate Buffered Saline medium (DPBS). Apatite reprecipitation was visible in the form of granular deposits in both environments from day 1 and continued throughout 21 days which altered the size of the microspheres but not its shape.

Bone regeneration is a dynamic and complex process that encompasses active recruitment of osteogenic cells, proliferation and differentiation of such cells, formation of bone matrix and bone remodelling. In recent years, microspheres have garnered much attention due to their capability to serve as tissue engineering scaffolds and vehicles for drug delivery for trauma therapy. This review will present the use and evolution of microspheres over years of research in the field of bone regenerative medicine. Different types of microspheres such as polymeric, bioceramics and composite-based will be evaluated on how they play a role in aiding bone regeneration. Furthermore, the advantages and disadvantages of the applications of the types microspheres in bone engineering will be highlighted. This review will also include common fabrication methodologies utilised to produce such microspheres. Lastly, a brief perspective on the future direction of microspheres research for bone engineering will be discussed.

Bioresorbable composites consist of micro- and nano-sized α-tricalcium phosphate (α-TCP) particles in a poly(D,L-lactic-co-glycolic acid) (PLGA) matrix were compared for their ability to form bone-like apatite in simulated body fluid (SBF). Due to the uniform distribution of α-TCP nanoparticles over the nanocomposite surface, enhanced apatite formation was observed. This enhanced apatite formation was achieved through faster and more uniform apatite nucleation. The presence of abundant high energy boundaries between α-TCP nanoparticles and PLGA matrix in nanocomposite provided a large number of suitable sites for calcium phosphate (CaP) nucleation. A homogeneous distribution of CaP nuclei formed after 5 days. The resulting apatite crystals grew to form a flake-like apatite layer. In contrast, CaP nucleation was only observed on the micrometre-size α-TCP particles in the microcomposite. After 14 days, a dense flake-like apatite was visible covering the surface of nanocomposite, whilst this surface layer was formed only on α-TCP particles in microcomposite.