|2009 Annual Meeting Abstracts
Porcine Allograft Mandible Revitalization Using Osteogenically-Induced Autologous Adipocyte-Derived Stem Cells and Periosteum
Jesse A. Taylor, MD, Donna C. Jones, PhD, Rian A. Maercks, MD, Christopher B. Gordon, MD, David A. Billmire, MD, Christopher M. Runyan, PhD.
Cincinnati Children's Hospital Medical Center, Cincinnati, OH, USA.
PURPOSE: Critical defects of the craniomaxillofacial region, as well as long bones, often are treated with vascularized osteocutaneous free flaps. These are lengthy operations, may be associated with considerable donor site morbidity, and often have suboptimal results, both functionally and aesthetically. The prospect of tissue engineering vascularized bone offers an attractive alternative.
The purpose of this study was to engineer a vascularized bone flap that approximates the pig hemi-mandible using acellular bone allograft, adipose-derived mesenchymal stem cells, and recombinant human BMP-2. Our experiment investigated the contribution of a vascular pedicle within the center of the construct and a complete vascularized periosteal envelope.
METHODS: Edentulous allograft porcine mandibles were separated at the symphysis and commercially Biocleansed (RTI) to remove all antigenic material. Adipocyte-derived mesenchymal stem cells (ASCs) were harvested from 10 pigs using liposuction, expanded in culture, and autogenously implanted into the allografts. The allografts were then surgically placed into one of two locations within the pig: 1) a complete periosteal envelope supplied by two adjacent intercostal vessels after extraction of two ribs (‘thoracic’), 2) wrapped within the rectus abdominis muscle after insertion of the superficial inferior epigastric vascular pedicle into the medullary cavity (‘abdominal’). In each model, BMP-2-soaked collagen-I sponge and ASCs were placed into the medullary space of the allograft. The constructs were allowed to incubate in vivo for 7-8 weeks, and then harvested to assess de novo bone formation using imaging studies and histology.
RESULTS: Micro-CT scans (100 μm slices) of each harvested implant were examined and calcitic tissue was quantified utilizing the gray scale X-ray attenuation coefficient and thee dimensional reconstructions of the bony versus soft tissue. Abdominal implants contained 143.20 (± 46.39) mL of calcitic tissue, while thoracic implants had 474.16 (± 75.93) mL. ANOVA demonstrated that thoracic implants had significantly more calcitic tissue than did abdominal ones (p < 0.006). Histologic analysis of abdominal allografts showed minimal new (woven) cancellous bone, indicating the calcitic tissue present was that of the implant. In contrast, thoracic allografts were almost entirely composed of extensive new (woven) cancellous bone and most of the implant had been absorbed. The thoracic allografts demonstrated Haversian systems, marrow elements and blood vessels resembling normal bone whereas abdominal allografts did not.
CONCLUSION: These data are the first to demonstrate revitalization of large volume allograft bone, and have positive implications for the tissue-engineering of the craniomaxillofacial and axial skeleton. The massive growth of bone in the thoracic but not abdominal allograft suggests that periosteum is critical in the formation of new bone. Further studies are ongoing to determine the exact role of periosteum and the interplay of ASCs and BMP-2 in the process.