The influence of hydroxyapatite nanoparticles on human mesenchymal stromal cells : application in tissue engineered constructs

Abstract

Osteoarthritis (OA) is a debilitating disease characterised by degradation of the articular cartilage and changes in the subchondral bone. Presently the gold standard treatment for OA is total joint replacement using metal, ceramic and non-degradable polymer materials. Tissue engineering using novel bioresorbable biomaterials has the potential to stimulate regeneration of bone and cartilage for early stage intervention in OA suffers. This thesis investigates the synthesis of hydroxyapatite nanoparticles (HAp) and techniques to generate poly (lactic acid) (PLA) HAp nanocomposites. The effect of the synthesised HAp on isolated OA donor derived human mesenchymal stem cells (hMSC) was investigated in both 2D and 3D culture conditions. A highly controllable sol-gel synthesis method demonstrated control over HAp morphology and composition, with modification of titration rate, addition methodology and reaction pH. Two novel nanocomposite fabrication techniques were developed and characterised with transmission electron microscopy (TEM) demonstrating HAp dispersion at the nanoscale throughout PLA. Dip-coated HAp PLA and fibrin substrates were fabricated and demonstrated maintenance of hMSC adherence, proliferation and osteogenesis on 2D substrates. Investigations into fibrin encapsulated hMSC illustrated HAp uptake within the cell following 24 hours incubation. Further studies examining fibrin/HAp encapsulated hMSC showed increased osteogenic gene expression, peripheral matrix deposition and mineralisation following 21 days in culture. 3D printed PLA constructs infused with fibrin and fibrin/HAp encapsulated hMSC demonstrated significant osteogenic gene expression differences at day 21. However, these data were variable between cell isolations from different patients further illustrating hMSC heterogeneity and hMSC donor–donor variability in-vitro.