Defense Date

7-28-2011

Graduation Date

Fall 2011

Availability

Immediate Access

Submission Type

dissertation

Degree Name

PhD

Department

Pharmacology

Committee Chair

Paula Witt-Enderby

Committee Member

Ellen Gawalt

Committee Member

David Johnson

Committee Member

Jane Cavanaugh

Committee Member

James Rutkowski

Keywords

Bone regeneration, Calcium aluminate, Human adult mesenchymal stem cells, Melatonin, Platelet-rich plasma

Abstract

Over 500,000 bone graft procedures are conducted annually within the United States. Autografts contribute to donor site complications and disease transmission with allografts has been described. Many ceramics are only osteoconductive and are brittle, limiting their clinical use. Thus, the objective of this study was to create a bone substitute with osteoinductive properties similar to natural bone using the ceramic biomaterial calcium aluminate (CA). Calcium aluminate materials are durable and remain moldable for an extended period of time at room temperature. Further, the surfaces of CA scaffolds can be modified with biological agents through simple chemical means to locally deliver agents directly to sites of injury. In order to enhance local bone regenerating characteristics of CA scaffolds, melatonin and platelet-rich plasma (PRP) were utilized for their known osteoinductive properties. Platelet-rich plasma enhances soft and hard tissue formation primarily through growth factor-mediated signaling pathways. Melatonin augments osteoblast differentiation and inhibits osteoclast-mediated bone resorption through receptor-dependent signaling and free radical scavenging activity, respectively. Thus, it was hypothesized that melatonin and/or PRP would provide osteoinductive properties to CA scaffolds to promote bone regeneration in a rodent model of critical-size calvaria defects. Modified CA scaffolds (CA-Mel) were produced by immobilizing melatonin to the CA surface through a covalent linkage. The biocompatibility of unmodified and modified CA scaffolds was initially tested in vitro and indicated that modified surfaces had a preference for the adhesion and proliferation of normal human osteoblasts versus NIH 3T3 fibroblasts. Moreover, the immobilization of melatonin to the CA surface may delay the differentiation of human adult mesenchymal stem cells (hAMSCs) and may have facilitated their migration across the CA surface. Two-month-old ovariectomized rats were randomized into implant groups receiving unmodified or modified scaffolds in the absence (CA and CA-Mel) or presence of PRP (CA+PRP and CA-Mel+PRP). Histological sections confirmed that both CA scaffold types were well-tolerated and provided evidence of tissue infiltration and scaffold biodegradation over time. Bone regeneration in animals was assessed by fluorochrome labeling at three and six months. While there was a lack of synergism between melatonin and PRP in the CA-Mel+PRP group, animals implanted with CA-Mel showed the greatest intensity and abundance of bone remodeling at both time points compared to all other groups. Radiographic data indicated a significant increase in the density of newly formed bone over time in all groups. The absence of a detectable decrease in density suggests that the modest biodegradation of CA scaffolds is balanced with processes of bone formation. Finally, both unmodified and modified CA scaffolds continued to provide a supportive surface for bone formation out to six months. Overall, results from this study suggest that CA scaffolds modified with melatonin may enhance bone remodeling activity in calvarial defects through hAMSC differentiation and recruitment and by preferentially supporting the viability and function of mature osteoblasts. This novel bioactive ceramic scaffold has the potential to change the dogma of bone grafting in fields like dentistry and reconstructive surgery. Continued optimization of this therapy is warranted and the attachment of other osteoinductive biomolecules is being considered.

Format

PDF

Language

English

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