Advances in Bone Tissue Engineering

Sammanfattning: Bone deficiencies, caused by malformations, trauma or adverse effects from medical treatments, are a clinical challenge and often associated with reduced physical function and quality of life. Autologeous bone grafts can be used to reconstruct skeletal defects, but the right size and quality of bone might not always be available and even so, donor-site morbidity might follow. A pre-fabricated or tissue engineered material has been proposed as an alternative means of addressing these limitations. By combining bone forming cells, growth factors and scaffolding materials, this technique has the potential to generate custom made bone grafts.
The main objectives for this thesis were to optimize the conditions for bone tissue engineering, to introduce new perspectives and to gain further understanding of the involved components. In study I, the scaffolding material hydroxyapatite was coated with fibronectine and serum to augment the materials bioactivity and cell carrying capacity. Cell attachment and growth were significantly enhanced by the surface manipulation in vitro. Similar trends were found for in vivo cell delivery, but the difference was not statistically significant compared to the controls. In study II, mesenchymal stem cell (MSC) growth was accelerated in 2-D and 3-D cultures by transient downregulation of cell cycle regulator p21, using short interfering RNA. In study III, MSCs were transduced with adenoviruses to express BMP2 and VEGF. An interesting interaction was discovered, where VEGF was shown to inhibit simultaneous BMP2 expression. In study IV, a periosteum-like graft was engineered, using the dermal matrix AlloDerm and seeded MSCs. When the seeded cells were transduced to express BMP2, the created periosteum proved capable of inducing ectopic bone formation in muscle and healed a critical-sized bone defect in rat mandible.
Collectively, the presented studies highlight important aspects and current limitations of bone tissue engineering. A new approach was introduced in facilitating the process of bone formation and regeneration, and valuable insights were gained regarding stem cell manipulation and behavior. Furthermore, a novel strategy to induce bone formation and healing through the use of a manufactured periosteum was presented.