In the treatment of bone non-unions an alternative to bone autografts is the use of bone morphogenetic proteins (BMP-2, BMP-7) with powerful osteoinductive and osteogenic properties. In clinical settings, BMPs are applied using absorbable collagen sponges. Supraphysiological doses are needed and major side effects may occur as induce ectopic bone formation, chronic inflammation and excessive bone resorption. In order to increase the efficiency of the delivered for BMPs we designed cryostructured collagen scaffolds functionalized with hydroxyapatite, mimicking the structure of cortical bone (aligned porosity, anisotropic, ANI) or trabecular bone (random distributed porosity, isotropic, ISO). We hypothesize that anisotropic structure would enhance osteoconductive properties of the scaffolds increasing rhBMP-2 regenerative properties. In vitro, both scaffolds presented similar mechanical properties, rhBMP-2 retention and delivery capacity. For in vivo testing, a rat femoral critical size defect model was created. Four groups were assessed depending on the implant applied to the bone defect: ISO, unloaded isotropic sponge; ISO-BMP, isotropic sponge loaded with 5 μg of hrBMP-2; ANI, unloaded anisotropic sponge; and ANI-BMP, anisotropic sponge loaded with 5 μg of hrBMP-2. Regeneration was allowed for 10 weeks. X-ray, μCT, biomechanical testing and histology were used to evaluate repair. Independently of their structure, sponges loaded with rhBMP-2 demonstrate increased bone volume, and biomechanical properties than their controls (p<0.01 and p<0.05 respectively). Globally, ANI-BMP group demonstrated better bone regeneration outputs with increased defect bridging (p<0.05 when compared ANI-BMP vs ISO-BMP groups). In conclusion, anisotropic cryostructured collagen scaffolds improve the efficiency of rhBMP-2 in bone regeneration.

INTRODUCTION

In the treatment of nonunions, and other complications of bone repair, an attractive alternative to bone autografts would be the use of a combination of autologous mesenchymal progenitors cells (MSCs), biomaterials and growth factors. Our goal was to determine the therapeutic potential and contribution to the repair process of different sources of mesenchymal stem cells for the treatment of nonunions.