The use of translational models to assess potential novel strategies in bone tissue engineering

Black, Cameron Russell Macgregor (2017) The use of translational models to assess potential novel strategies in bone tissue engineering. Doctoral Thesis, 325pp.

Record type: Thesis (Doctoral)

Abstract

The success of novel developments in the disciplines of stem biology and tissue engineering can be measured by the real-world impact each strategy achieves, this impact hinges on the transformation of core science into clinical application. In the field of Bone Tissue Engineering, progression from in vitro and small animal in vivo research towards a clinical application is constrained by a common translational barrier; designing and implementing a suitable pre-clinical experimental model in which to demonstrate any relevant clinical efficacy. In this thesis, a translational pathway is set out, mapping the progression from early in vitro development through successive upscaling into a true translational large animal segmental defect model, potentially bridging the gap from benchtop to bedside.

Multi-modal novel therapeutics in bone tissue engineering are formed of basic units. The cellular building block, scaffold material which acts as a vector for cell delivery whilst providing a framework to deliver and facilitate the growth of cells and host tissue and, biologically active stimulating factors which regulate the differentiation of both host and delivered cell components. The intelligent development of relevant large animal translational models needs to be able to address each of these core elements of a bone tissue engineering strategy, and prior to any large animal experimentation it was first necessary to characterise the host stem cell population so that accurate comparisons could be made from any data generated.

Chapter III characterises the ovine skeletal stem cell population selected for by Stro-4 antibody, its growth, capacity for self-renewal and differentiation both in vitro and through a functional assay in vivo.

Simultaneously we examined the potential of a novel extracellular matrix hydrogel to enhance bone formation in the absence and presence of a skeletal stem cell precursor. These promising results using basic in vivo models identified a candidate therapy for translational investigation.

As part of the developmental pathway towards establishing a large animal model, it was necessary to work first with a more conservative orthopaedic model, and the ovine condyle drill defect model was chosen accordingly. Chapter IV documents the condyle model development over successive experimental procedures, a standard surgical protocol was established and the model validated with positive and negative controls, resulting in a characterised model in which to assess novel tissue engineering strategies.

A nanosilicate hydrogel, which had been developed by the Bone and Joint Research Group and had demonstrated clinical promise in small animal work, was then examined in the newly developed ovine condyle model. Chapter V documents the application of the ovine condyle model investigating the ability of nanosilicates to control the delivery of a biologically active peptide, Bone Morphogenic Protein-2 in low doses within a large bone defect.

In Chapter VI, building on the experience developed through the ovine condyle model and, in collaboration with Queensland University of Technology, we utilised the Stro-4 and ECM hydrogel constructs characterised in Chapter III in an ovine tibial critical sized defect model. This model, considered as a true clinically-relevant model demonstrated the importance of large animal experimentation in translational medicine as results generated in vitro and using small animal models in vivo were not emulated in the large animal model.

A Pathway from early basic science through subsequent in vivo models into a clinically relevant translational model was established. An enriched stem population was characterised and the potential of the stem cell population in engineering new bone growth evaluated in combination with a novel ECM hydrogel. Concurrently, a proprietary nanosilicate hydrogel was successfully progressed though the translational pathway revealing exciting directions for future work.