Abstract
Introduction
Diaphyseal bone defect represents a significant problem for orthopaedic surgeons and patients. Bone is a complex tissue whose structure and function depend strictly on ultrastructural organization of its components: cells, organic (extracellular matrix, ECM) and inorganic components. The purpose of this study was to evaluate bone regeneration in a critical diaphyseal defect treated by implantation of a magnetic scaffold fixed by hybrid system (magnetic and mechanical), supplied through nanoparticle-magnetic (MNP) functionalized with Vascular Endothelial-Growth-Factor-(VEGF) and magnetic-guiding.
Methods
A critical long bone defect was created in 8 sheep metatarsus diaphysis: it was 20.0 mm in length; the medullary canal was reamed till 8.00 mm of inner diameter. Then a 8.00 mm diameter magnetic rod was fitted into proximal medullary canal (10 mm in length).
After that a scaffold made of Hydroxyapatite (outer diameter 17.00 mm) that incorporates magnetite (HA/Mgn 90/10) was implanted to fill critical long bone defect. A magnetic rod (6.00 mm diameter) was firmly incorporated at proximal side into the scaffold. Both magnets had 10 mm length. To give stability to the complex bone-scaffold-bone a plate was used as a bridge; it was fixed proximally by 2 screws and distally by 3 screws.
Scaffolds biocompatibility was previously assessed in vitro using human osteoblast-like cells. Magnetic forces through scaffold were calculated by finite element software (COMSOL Multiphysics, AC/DC Model).
One week after surgery, magnetic nanoparticles functionalized with VEGF were injected at the mid portion of the scaffold using a cutaneous marker positioned during surgery as reference point in 4 sheep; other sheep were used as control group. After sixteen weeks, sheep were sacrificed to analyze metatarsi. Macroscopical, radiological and microCT examinations were performed.
Results
Samples obtained didn't show any inflammatory tissue around the scaffold and revealed bone tissue formation inside pores of the scaffolds and we could see also complete coverage of the scaffolds. Formation of new bone tissue was more evident at magnetized bone-scaffold interface.
X-rays showed a good integration of the scaffold with a good healing process of critical bone defect: new cortical bone formation seemed to be present, recreating continuity of metatarsus diaphysis. No signs of scaffold mobilization was showed (Fig. 1).
All these datas were confirmed by the microCT: new bone formation inside the scaffolds was evident, in particular at proximal bone-scaffold interface, where permanent magnet were present (Fig. 2).
These preliminary results lead our research to exploiting magnetic forces to stimulate bone formation, as attested in both in vitro and in vivo models and to improve fixation at bone scaffold interface, as calculated by finite element software, and moreover to guide targeted drug delivery without functionalized magnetic nanoparticles dissemination in all body.
