Keele Research Repository

Improving the differentiation capacity of stem cells by defining the ideal physico-chemical and spatial parameters will enhance the efficiency of stem cell-based clinical therapies. In this thesis the hypothesis that heat shock (elevated temperatures) could positively influence osteogenic differentiation was investigated. A methodology was developed to employ magnetic nanoparticle-based local heating (magnetic hyperthermia) to spatially control temperature distribution at the cellular level. For this purpose, bacterially synthesized zinc and cobalt doped iron oxide nanoparticles with tuned physical and magnetic properties were assessed for their interaction with cells, and their magnetic response and heating properties when in a cellular milieu. Nanoparticles with moderate levels of zinc doping showed strong heating effects and minimal cytotoxicity, proving to be promising candidates for cellular applications.

The effects of mild and severe heat stress were assessed by heating cells using conventional techniques such as water baths (bulk heat shock); using localised heating with extracellular nanoparticle suspensions; or by targeting different cellular regions with nanoparticles. The effect of the heat shock treatment on the osteogenic differentiation was assessed in primary bone marrow-derived human mesenchymal stem cells and a cancerous osteoblastic cell line, MG-63. With both bulk and nanoparticle-mediated extracellular mild heat shock (~420C), very little evidence for a positive effect on osteogenic differentiation was found in both cell types. On the other hand, severe heat shock treatments (>500C) showed differentiation enhancement though this also negatively impacted cell viability.

Further experimentation can shed light on the optimum temperature range within which the differentiation behaviour of cells can be influenced without compromising viability. The nanoparticle-based methodology developed here to apply heat shock to different cellular components, could lead to further work investigating how intracellular pathways translate the heat stimulus into a cellular response for stem-cell based applications.