Engineered Bone Graft with Autogenous Stem Cell Improved Bone Reconstruction through Enhancing Graft Integration and Preventing Entropic Graft Resorption

Thursday, October 10, 2013: 9:50 AM
Sarindr Bhumiratana Ph.D., Biomedical Engineering, Columbia University, New York, NY
Jonathan Bernhard M.S., Biomedical Engineering, Columbia University, New York, NY
David M. Alfi DDS, MD, Oral and Maxillofacial Surgeon, Methodist Hospital, Houston, TX
Keith Yeager M.Eng., Biomedical Engineering, Columbia University, New York, NY
Ryan Eton , Biomedical Engineering, Columbia University, New York, NY
Jonathan Bova D.V.M., School of Veterinary Medicine, Louisiana State University, Baton Rouge, LA
Forum Shah B.S., Pennington Biomedical Research Center, Louisiana State University, Baton Rouge, LA
Jeffrey Gimble M.D., Ph.D., Pennington Biomedical Research Center, Louisiana State University, Baton Rouge, LA
Mandi Lopez D.V.M., Ph.D., School of Veterinary Medicine, Louisiana State University, Baton Rouge, LA
Sidney B. Eisig DDS, Division of Oral and Maxillofacial Surgery, Columbia University, New York, NY
Gordana Vunjak-Novakovic Ph.D., Biomedical Engineering, Columbia University, New York, NY

Statement of the problem

Maxillofacial surgeons are faced with the challenges of reconstructing complex deformities that require functional and cosmetic aesthetic precision. Current standards of practice depend on lengthy procedures, secondary surgical sites, and immense resources, yet, still yield compromised results in many instances. With advancements in tissue engineering, we are able to produce autogenous bone grafts engineered in vitro through regulation of osteogenic differentiation and functional assembly of stem cells. The effectiveness of reconstructing bone defects with tissue engineered grafts has been presented from various groups including ours; however, little is known in terms of the physiological phenomena that lead to its success. Here we report the long-term effectiveness of a tissue engineered bone graft through the enhancement of mandibular condyle/ramus bone reconstruction in a porcine model after 6 months and investigate the benefits of incorporating osteogenic differentiated autogenous stem cells into the commonly employed decellularized bone block.

Materials and methods

Yucatan minipigs received either scaffold implantation (n=6), or engineered autogenous bone graft implantation (n=6). The process for engineering anatomical-shape mandibular condyle/ramus bone graft for implantation was adapted from our previous work.1 Anatomically-shaped scaffolds for each pig were fabricated from trabecular bone of adult bovine knees based on previously reported methods.1 To engineer the autogenous bone graft, the scaffolds were seeded with autogenous adipose-derived stem cells (ASCs) isolated from subcutaneous fat of each pig.2 The grafts were cultured in osteogenic medium in specially designed perfusion bioreactors for 3 weeks prior to implantation to allow for stem cell growth, osteogenic differentiation, and bone matrix deposition. Condylectomies, including a portion of the ramus, were planned virtually and carried out under General Anesthesia. The pigs were reconstructed using either decellularized bone block or engineered autogenous bone graft. All grafts were rigidly fixated using 2.0mm titanium miniplates. We report here the effect of ASCs in engineered bone grafts in reconstructing bone after 3 and 6 months from CT and histological analysis.

Results

Cell seeding of scaffolds and cultivation resulted in grafts with fully cellularized osteogenic differentiated stem cells. All pigs survived the surgery without complications. Engineered bone grafts significantly restored the condyle height over the scaffold implantation group at 3 and 6 months (Figure 1). High resolution μCT illustrated the integration between implanted engineered bone graft and the native bone (Figure 1).  Histological analysis of the graft-host interface confirmed the results (Figure 1). The native bone infiltrated the proximity of the engineered bone graft resulting in intact graft-host integration (Figure 1). In contrast, a large separation consisting of fibrous tissues were present between native bone and the implanted bone block control (Figure 1). Furthermore, histology revealed that a majority of the implanted engineered bone graft was intact (Figure 1) while significant portion of the bone block was resorbed resulting in fibrous ingrowth (Figure 1) within the first 3 months.

Conclusions

The incorporated osteogenic differentiated adipose stem cells in the engineered bone graft communicate and regulate graft resorption and integration with the surrounding native tissue. As a result, the engineered bone graft improved TMJ condyle reconstruction and significantly restored the condyle height as compared to the controls.

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Figure 1. Engineered bone graft significantly restored condyle height over bone block scaffold implantation. The presence of stem cells enhanced graft-host integration and prevented entropic graft resorption as indicated by µCT and histology. (N: native bone, G: implanted graft, F: fibrous tissue, Bar: 500µm)

References

1.   Grayson WL et.al., Engineering anatomically shaped human bone grafts, Proc. Natl. Acad. Sci.; 2010, 107(8):3299-304

2.   Williams KJ et.al., Isolation and characterization of porcine adipose tissue-derived adult stem cells, Cells Tissues Organs, 2008; 188:251-258

Acknowledgements

The work was supported by BioAcellerate funding of the New York City Partnership Foundation (grant CU11-1915 to GVN). 

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