Autologous serum improves bone formation in a primary stable silica-embedded nanohydroxyapatite bone substitute in combination with mesenchymal stem cells and rhBMP-2 in the sheep model

Abstract

New therapeutic strategies are required for critical size bone defects, because the gold standard of transplanting autologous bone from an unharmed area of the body often leads to several severe side effects and disadvantages for the patient. For years, tissue engineering approaches have been seeking a stable, axially vascularized transplantable bone replacement suitable for transplantation into the recipient bed with pre-existing insufficient conditions. For this reason, the arteriovenous loop model was developed and various bone substitutes have been vascularized. However, it has not been possible thus far to engineer a primary stable and axially vascularized transplantable bone substitute. For that purpose, a primary stable silica-embedded nanohydroxyapatite (HA) bone substitute in combination with blood, bone marrow, expanded, or directly retransplanted mesenchymal stem cells, recombinant human bone morphogenetic protein 2 (rhBMP-2), and different carrier materials (fibrin, cell culture medium, autologous serum) was tested subcutaneously for 4 or 12 weeks in the sheep model. Autologous serum lead to an early matrix change during degradation of the bone substitute and formation of new bone tissue. The best results were achieved in the group combining mesenchymal stem cells expanded with 60 μg/mL rhBMP-2 in autologous serum. Better ingrowth of fibrovascular tissue could be detected in the autologous serum group compared with the control (fibrin). Osteoclastic activity indicating an active bone remodeling process was observed after 4 weeks, particularly in the group with autologous serum and after 12 weeks in every experimental group. This study clearly demonstrates the positive effects of autologous serum in combination with mesenchymal stem cells and rhBMP-2 on bone formation in a primary stable silica-embedded nano-HA bone grafting material in the sheep model. In further experiments, the results will be transferred to the sheep arteriovenous loop model in order to engineer an axially vascularized primary stable bone replacement in clinically relevant size for free transplantation.

Comment on ‘Basic concepts regarding fractures healing and the current options and future directions in managing bone fractures’

“…Bigham-Sadegh and Oryan claim that critical issues associated with BMPs have to be considered, including heterotopic bone formation, excessive osteoclast activation, short half-lives and ineffectiveness. We share the concerns with the authors and are aware of possible side-effects of BMPs; however, we can report a positive impact of using BMP-2 for bone tissue engineering so far (5,8) (Figure 2). Further studies have to be performed to investigate the BMP effects more closely.…”

“…In the sheep model, we demonstrate a positive effect while implanting autologous mesenchymal stem cells (MSCs) with and without an ex vivo culture period (3,5) ( Figure 2). Moreover, MSC implanted in combination with autologous serum induced better remodelling and vascularisation of bone scaffolds compared to the control fibrin (8). In a further study, MSC were cultivated in cell culture medium supplemented with autologous serum instead of the standard procedure using xenogenic foetal bovine serum.…”

3D perfusion bioreactor‐activated porous granules on implant fixation and early bone formation in sheep

“…Even though dexamethasone and FGF‐2 were added to the media during the incubation period, this might not be sufficient for establishing an osteoinductive environment, mimicking the complex natural bone forming process. Others have suggested using surface microtextures with biochemical supplements to achieve osteogenic differentiation of human mesenchymal stem cells (hMSCs) and revascularization of the implants in vivo ; or using autologous serum to improve bone formation in a primary stable silica‐embedded nanohydroxyapatite bone substitute in combination with mesenchymal stem cells and rhBMP‐2 in the sheep model …”

“…Others have suggested using surface microtextures with biochemical supplements to achieve osteogenic differentiation of human mesenchymal stem cells (hMSCs) and revascularization of the implants in vivo 48 ; or using autologous serum to improve bone formation in a primary stable silica-embedded nanohydroxyapatite bone substitute in combination with mesenchymal stem cells and rhBMP-2 in the sheep model. 49 Some concerns regarding a perfusion bioreactor system have been formulated. Cells at the periphery of the scaffold are in danger of being washed away by the fluid flow.…”

Intra- and Postoperative Blood Flow Monitoring in a Sheep Model of Uterus Transplantation

“…Smooth muscle cells were visualized with an antibody to α-smooth muscle actin (clone 1A4) and ZytoChemPlus (AP) Polymer Bulk Kit (both from Zytomed Systems GmbH, Berlin, Germany). With a CD31 antibody (Anti-CD31/PECAM-1; MorphoSys AG, Martinsried/Planegg, Germany), vessels were immunohistochemically stained as described previously (21). Proliferating cells were visualized using a Ki67 antibody (mouse anti-human Ki67 clone MIB-1; Dako, Glostrup, Denmark) as described previously (21).…”