Strategic development of bone regeneration at scale using innovative materials.

Abstract

Bone tissue engineering is a rapidly advancing field combining biology and engineering to develop alternative methods of dealing with non-healing fractures and critical-sized bone defects. Healing complications arise due to trauma, disease, infection, aseptic loosening of orthopaedic implants or iatrogenic causes. Stimulation of bone healing by delivery of growth factors, drugs, cells, and materials must examine the ‘bigger picture’ of logistics and the practicalities of cell survival, communication, differentiation, and the creation of a vascularised extracellular matrix microenvironment, optimal tissue pH, and stimulatory mechanical forces for bone healing. These various factors change, as the environment progresses, from in vitro to in vivo animal models of increasing animal size and complexity of the defect site. Critically, this thesis explored the development of bone augmentation at scale through a range of preclinical models, using select biomimetic coated scaffolds, with the hypothesised potential to induce skeletal cell differentiation for healing critical-sized bone defects.
In vitro experiments were implemented for confirmation of hypothesised scaffold and coating material cytocompatibility, and the ability to effectively differentiate skeletal cell populations along the osteogenic lineage. Promising materials were subsequently examined using the chorioallantoic membrane (CAM) assay to verify the support of angiogenesis and biocompatibility. Further, the murine subcutaneous implantation model assessed heterotopic bone formed in response to the surface coatings. Development of a rabbit radius defect model was achieved, for use with suitable material constructs in the scale up from rodent to larger animal models. The murine femur defect model was refined to assess the coated scaffolds in an osseous defect.
Overall, Polycaprolactone (PCL) 900 was found to be an optimal robust scaffold material in cytocompatibility and biocompatibility. The nanoclay material Laponite™ with growth factor Bone Morphogenetic Protein-2 (BMP-2) applied as a coating showed consistent, significant bone formation compared to the plain uncoated polycaprolactone/methacrylate (PCL 900) scaffold in the murine subcutaneous implantation and femur defect models. Bone formed peripherally and within the pores of the scaffold, with no aberrant bone formed in the subcutaneous implantation model, and the scaffolds showed integration with the bone ends in the femur defect model. The other novel protein based and low-dose BMP-2 coatings investigated did not show significant or consistent in vitro results or bone formation in either in vivo model. Building upon the results of this thesis, the final step under development is examination of a larger-scale PCL 900 octetruss design scaffold and Laponite/BMP-2 coating, in the ovine femoral condyle defect model.
In conclusion, the current thesis has demonstrated the efficacy of Laponite and BMP-2 coated PCL 900 scaffolds, in inducing an in vitro cytocompatible osteogenic response, biocompatibility, and bone formation in vivo. The coated scaffolds performed in both heterotopic and orthotopic sites, bridging the critical-sized femur defect, leading to union of the bone ends with translation from in vitro, ex vivo to in vivo preclinical demonstration achieved.

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Identifiers

ORCID for Karen Marshall: orcid.org/0000-0002-6809-9807

ORCID for Richard Oreffo: orcid.org/0000-0001-5995-6726

ORCID for Janos Kanczler: orcid.org/0000-0001-7249-0414

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