Mesenchymal stem cell response to sputter deposited thin film surfaces

Abstract

The research presented in this thesis investigates the potential for sputter deposited titanium and calcium phosphate thin films, singularly and in combination, to directly induce osteogenic differentiation in human bone marrow derived mesenchymal stem cells (MSCs). The nature and scale of these substrate driven effects have been compared with osteogenesis induced in MSCs by exposure to biochemical stimulants in the culture media. MSCs hold great promise for use in bone tissue engineering applications, therefore the provision of biomaterials that can direct the osteogenic differentiation of MSCs has significant implications for improving the repair or replacement of damaged or lost bone tissue.

RF magnetron sputter deposition was used to create titanium and calcium phosphate thin films from titanium metal and hydroxyapatite powder targets respectively. The distinct chemical and topographical surface properties of each substrate were confirmed using XPS, FTIR, XRD, AFM and water contact angle analysis. The commercially obtained MSCs used for this work were characterised in detail to provide a benchmark data set for correlation with subsequent thin film substrate studies. To determine the previously unreported effects that these types of sputter deposited surfaces have on MSC behaviour, a range of relevant biological assays and detailed quantitative real time PCR gene expression studies were used. In this way, a comprehensive profile of MSC response to each type of surface condition was obtained over an in vitro culture period of up to 28 days. Early stage adhesion and morphology was also examined in order to attain a better understanding of the underlying mechanisms of the attendant MSC behaviour.

All of the sputter deposited thin film surfaces directly promoted significant levels of osteogenic differentiation, to varying degrees, without the use of biochemical stimulants. This work shows for the first time, that the topography of the sputtered titanium coatings and the bioactive chemistry of the calcium phosphate coatings can individually direct the differentiation of MSCs towards an osteogenic lineage.

Moreover, the addition of a topographical profile to the calcium phosphate coating, via the introduction of a sputtered polycrystalline titanium interlayer, was found to induce an enhanced prolife of differentiation compared to that observed for either of the individual titanium or calcium phosphate coatings. Hence, these results highlight the benefit of a novel strategy that combines defined surface topography and bioactive chemistry, for effectively directing MSC osteogenic differentiation in vitro.

Date of Award	Jan 2012
Original language	English
Supervisor	Brian Meenan (Supervisor)