133. A Calvarial Defect Murine Model for the Investigation of the Osteogenic Potential of Umbilical Cord Stem Cells in Alveolar Cleft Repair

Abstract

Purpose: Cleft lip and/or palate (CLP) is one of the most common congenital anomalies and is frequently associated with an alveolar cleft. At many institutions, the standard graft material of alveolar cleft repair (ACR) is autogenous iliac crest bone; however, bone-morphogenetic-protein 2 has shown to be a viable alternative with similar success rates. An alternative potential graft adjunct, umbilical cord stem cells (UCSC), has yet to be explored in vivo. There is ample pre-clinical literature supporting the utility and advantages of UCSC in ACR. Their capacity for self-renewal, pluripotent differentiation, and proliferation allows UCSC to be harnessed for regenerative medicine. Our study seeks to evaluate the feasibility of using UCSC and their osteogenic and regenerative capabilities in a mouse model to improve ACR. Methods: Eighteen FoxN1 mice were included in the study, which were separated into three groups: (1) calvarial defect surgery and no treatment (n=6), (2) calvarial defect surgery with poly(D,L-lactide-co-glycolide) (PLGA) treatment (n=6), (3) calvarial defect surgery with UCSC mixed with PLGA. Calvarial defect surgeries consisted of a sagittal skin incision followed by creation of bilateral, 2mm diameter, full-thickness, parietal bone defects using a 1.8mm dental drill; of note, 2mm is the established critical size defect of murine calvarial bone. The mice underwent microCT imaging at 1-, 2-, 3-, and 4-weeks postoperatively. At 2-weeks postoperatively, one mouse from each group was sacrificed for histologic analysis. At 4-weeks postoperatively, the remaining mice were then sacrificed for histologic examination. Results: All 18 mice underwent calvarial defect surgeries without postoperative complications or infections. All mice were fully ambulatory with no signs of neurologic deficits throughout the 4-week follow-up period. As evidenced by microCT imaging, at 1-, 2-, 3, and, 4-weeks postoperatively, all calvarial defects in groups (1) and (2) remained patent without significant differences in defect sizes between the two groups. Histologically, group (1) and (2) defects demonstrated patency without significant size differences at both 2- or- 4 weeks postoperatively. In contrast, the UCSC group (3) had significantly greater bone fill in the defects at each of the postoperative time points on microCT imaging and demonstrated a lack of patency histologically at final follow-up. Conclusion: These results demonstrate a successful calvarial defect murine model for the investigation of UCSC-mediated osteogenesis and bone repair. Further, our findings provide evidence that PLGA alone has no short-term effect on bone formation nor any unwanted side effects, making it an attractive vehicle for graft substitutes. Further investigation using this UCSC and PLGA scaffold combination in a larger animal porcine model is warranted in hopes of future translation to ACR in patients with CLP.