BMP-2-coated mineral coated microparticles improve bone repair in atrophic non-unions

Abstract

Atrophic non-unions are a major clinical problem. Mineral coated microparticles (MCM) are electrolyte-coated hydroxyapatite particles that have been shown in vitro to bind growth factors electrostatically and enable a tuneable sustained release. Herein, we studied whether MCM can be used in vivo to apply Bone Morphogenetic Protein-2 (BMP-2) to improve bone repair of atrophic non-unions. For this purpose, atrophic non-unions were induced in femurs of CD-1 mice (n = 48). Animals either received BMP-2-coated MCM (MCM + BMP; n = 16), uncoated MCM (MCM; n = 16) or no MCM (NONE; n = 16). Bone healing was evaluated 2 and 10 weeks postoperatively by micro-computed tomographic (µCT), biomechanical, histomorphometric and immunohistochemical analyses. µCT revealed more bone volume with more highly mineralised bone in MCM + BMP femurs. Femurs of MCM + BMP animals showed a significantly higher bending stiffness compared to other groups. Histomorphometry further demonstrated that the callus of MCM + BMP femurs was larger and contained more bone and less fibrous tissue. After 10 weeks, 7 of 8 MCM + BMP femurs presented with complete osseous bridging, whereas NONE femurs exhibited a non-union rate of 100 %. Of interest, immunohistochemistry could not detect macrophages within the callus, indicating a good biocompatibility of MCM. In conclusion, the local application of BMP-2-coated MCM improved bone healing in a challenging murine non-union model and, thus, should be of clinical interest in the treatment of non-unions.

VEGF‐loaded mineral‐coated microparticles improve bone repair and are associated with increased expression of epo and RUNX‐2 in murine non‐unions

“…The mSBF was prepared by adding the following reagents into deionized water in the following order: 141 mM NaCl, 4 mM KCl, 0.5 mM MgSO 4 , 1 mM MgCl 2 , 4.2 mM NaHCO 3 , 20 mM hydroxyethyl‐piperazineethanesulfonic acid, 5 mM CaCl 2 , and 2 mM KH 2 PO 4 . This composition was chosen upon previous studies . Because of the long observation period of 70 days in the present study, we used MCM with a low carbonate concentration (4.2 mM) in the present setting.…”

“…Because of the long observation period of 70 days in the present study, we used MCM with a low carbonate concentration (4.2 mM) in the present setting. Based upon previous results, these MCM are more suitable due to their higher stability and their release kinetics . The mSBF was changed daily during the preparation process in order to maintain consistent ion concentrations for mineral coating growth on the hydroxyapatite particles.…”

“…The femurs ( n = 8 each group) were scanned (Skyscan 1172, Bruker, Billerica, MA) at a spatial resolution of 8.9 µm with a standardized setup, as described previously . Images were stored in three‐dimensional (3D) arrays.…”

“…These include mineral‐coated microparticles (MCM), which enable a tunable growth factor delivery . They exhibit a good biocompatibility and do not adversely interfere with cell–cell interactions in vivo as it has been reported for other bone graft materials . Moreover, MCM can easily be injected into defect sites with complex and irregular geometries .…”

“…They exhibit a good biocompatibility and do not adversely interfere with cell–cell interactions in vivo as it has been reported for other bone graft materials . Moreover, MCM can easily be injected into defect sites with complex and irregular geometries . As a sophisticated carrier system, MCM allow the controllable binding and sustained release of growth factors, such as vascular endothelial growth factor (VEGF), providing a spatiotemporal control of bioactive signaling to regulate cell functions …”