Calcium phosphate cements are produced by the mixing of calcium phosphate powders in an aqueous solution resulting in a low-temperature synthesized hydroxyapatite. They have been used as bone substitutes and drug delivery systems. The present work examined the possibility of a machine-based modification to this process to derive a standardized preparation method of calcium phosphate cements that could be loaded with Pantoprazole. To examine the characteristics of these novel materials, the following analyses of hand- and machine-made cements, with and without Pantoprazole were undertaken: in vitro surface characterization, dissolution, hydroxyapatite conversion, Pantoprazole delivery, as well as in vivo reparative bone formation and particulate degradation. The in vitro surface characterization, dissolution at different pHs, and drug release analyses showed insignificant differences between hand- and machine-prepared cements. However, machine-made cements showed increased hydroxyapatite conversion, decreased dissolution at pH 7.4, and better in vivo outcomes than commercially available bone-substitute particulate biomaterials.

Calcium phosphate cements are produced by the mixing of calcium phosphate powders in an aqueous solution resulting in a low-temperature synthesized hydroxyapatite. They have been used as bone substitutes and drug delivery systems. The present work examined the possibility of a machine-based modification to this process to derive a standardized preparation method of calcium phosphate cements that could be loaded with Pantoprazole. To examine the characteristics of these novel materials, the following analyses of hand- and machine-made cements, with and without Pantoprazole were undertaken: in vitro surface characterization, dissolution, hydroxyapatite conversion, Pantoprazole delivery, as well as in vivo reparative bone formation and particulate degradation. The in vitro surface characterization, dissolution at different pHs, and drug release analyses showed insignificant differences between hand- and machine-prepared cements. However, machine-made cements showed increased hydroxyapatite conversion, decreased dissolution at pH 7.4, and better in vivo outcomes than commercially available bone-substitute particulate biomaterials.

Large bone defects pose a significant clinical challenge currently lacking an adequate therapeutic solution. Bone tissue engineering (BTE) therapies aim to provide that solution by combining structural scaffolds, bioactive factors, and/or osteogenic cells. Cellular therapies are likely vital to repair severe defects in patients lacking sufficient endogenous cells. Stem cells are attractive cell choices due to their osteogenic differentiation and extensive proliferation abilities, but their therapeutic potential is still uncertain, as studies comparing stem cell sources and delivery methods have produced inconsistent results. In this thesis, we developed a challenging in vivo large bone defect model for quantitative comparison of human stem cell-based therapies and then evaluated the abilities of adult or fetal stem cell-seeded constructs to enhance defect repair, with or without added osteogenic cues. First, we showed that cellular construct treatment enhanced defect healing over acellular construct treatment, although there were no differences between adult or fetal cell sources. We next labeled stem cells with a fluorescent tracking agent, the quantum dot, to determine biodistribution of implanted cells during the repair process. While quantum dots effectively labeled cells in vitro, they were ineffective in vivo tracking agents due to false positive signals and detrimental effects on stem cell-mediated repair. Finally, we developed a novel gene therapy technique using virus-coated scaffolds to deliver the osteogenic factor bone morphogenetic protein 2 (BMP2) to defect sites, either by in vitro (BMP2 transduction of seeded stem cells pre-implantation) or in vivo (BMP2 transduction of defect-site host cells) means. While defect-site BMP2 delivery through gene therapy methods improved repair, in vivo therapy enhanced healing more than stem cell-based in vitro therapy. This finding does not rule out the potential of stem cell-based in vitro gene therapy treatment for functional bone repair, as increases in viral dose may improve stem cell-mediated healing, but it does present evidence of a novel acellular BTE therapy with potential off-the-shelf clinical application in large bone defect repair, as scaffolds could be virally coated with the gene for BMP2 expression and frozen until implantation.

An understanding of the interactions between orthopaedic and dental implant surfaces with the surrounding host tissue is critical in the design of next generation implants to improve osseointegration and clinical success rates. Critical to the process of osseointegration is the rapid establishment of a patent neovasculature in the peri-implant space to allow for the delivery of oxygen, nutrients, and progenitor cells. The central aim of this thesis is to understand how biomaterials regulate cellular and host tissue response to elicit a pro-angiogenic microenvironment at the implant/tissue interface. To address this question, the studies performed in this thesis aim to 1) determine whether biomaterial surface properties can modulate the production and secretion of pro-angiogenic growth factors by cells, 2) determine the role of integrin and VEGF-A signaling in the angiogenic response of cells to implant surface features, and 3) to determine whether neovascularization in response to an implanted biomaterial can be modulated in vivo. The results demonstrate that biomaterial surface microtopography and surface energy can increase the production of pro-angiogenic growth factors by osteoblasts and that these growth factors stimulate the differentiation of endothelial cells in a paracrine manner and the results suggest that signaling through specific integrin receptors affects the production of angiogenic growth factors by osteoblast-like cells. Further, using a novel in vivo model, the results demonstrate that a combination of a rough surface microtopography and high surface energy can improve bone-to-implant contact and neovascularization. The results of these studies also suggest that VEGF-A produced by osteoblast-like cells has both an autocrine and paracrine effect. VEGF-A silenced cells exhibited reduced production of both pro-angiogenic and osteogenic growth factors in response to surface microtopgraphy and surface energy, and conditioned media from VEGF-A silenced osteoblast-like cell cultures failed to stimulate endothelial cell differentiation in an in vitro model. Finally, the results show that by combining angiogenic and osteogenic biomaterials, new bone formation and neovascularization can be enhanced. Taken together, this research helps to provide a better understanding of the role of material properties in cell and host tissue response and will aid in the improvement of the design of new implants.

Thesis (Ph. D.)--University of Hong Kong, 2010. / Includes bibliographical references (p. 253-274). Also available in print.

published_or_final_version / Mechanical Engineering / Doctoral / Doctor of Philosophy

M. Tech. Biomedical Technology. / Aims to gain more insights into the effect of a specific human derived BMP-complex, standardised according to the human BMP-2 content, by loading it at concentrations higher than the concentration of the morphogen found in human (hDBM), in order to determine changes in the osteogenic response.

Bone consists of collagen/hydroxyapatite (HA) composites in which poorly crystalline carbonated calcium phosphate is intercalated within the fibrillar structure. Normal bone mineral is a carbonated-apatite, but there are limited data on the effect of mineral containing carbonate on cell response. Although the exact biological role of silicate in bone formation is unclear, silicate has been identified at trace levels in immature bone and is believed to play a metabolic role in new bone formation. To mimic the inorganic and organic composition of bone we have developed a variety of bone graft substitutes. In the present body of research, we characterized the surface composition of human cortical and trabecular bone. When then characterized the surface compositions of the following potential bone substitutes: carbonated hydroxyapatite (CO₃²-HA), silicated hydroxyapatite (Si-HA), and collagen sponges mineralized with calcium phosphate using the polymer-induced liquid-precursor (PILP) process. In the latter substitutes, the PILP process leads to type I collagen fibrils infiltrated with an amorphous mineral precursor upon which crystallization leads to intrafibrillar HA closely mimicking physiological bone mineral. We then determined the osteoblast-like cell response to each bone substitute to characterize the substrate’s effect on osteoblast differentiation. The observations collectively indicate that cells are sensitive to the formatting of the mineral phase of a bone substitute and that this format can be altered to modulate cell behavior.

Thesis (M. Sc.)--University of Canterbury, 2009. / Typescript (photocopy). "June 2009." Includes bibliographical references (p. [113]-119).

Thesis--University of Turku, Finland, 2001. / Added t.p. with thesis statement inserted. Includes bibliographical references.