Following dehydration through a graded series of ethanols (70100%), the samples were infiltrated and embedded in paraffin

Following dehydration through a graded series of ethanols (70100%), the samples were infiltrated and embedded in paraffin. nanofiber mesh tubes were fitted into the adjacent native bone such that the lumen of the tubes contained the defect (Kolambkar et al., 2011b). Silk hydrogels with or without BMP-2 were injected into the defect. Bone regeneration was longitudinally assessed using 2D X-ray radiography and 3D microcomputed topography (CT). Following sacrifice at 12 weeks after surgery, the extracted femurs were either subjected to biomechanical testing Leflunomide or assigned for histology. The results demonstrated that silk was an effective carrier for BMP-2. Compared to the delivery system without BMP-2, the delivery system that contained BMP-2 resulted in more bone formation (p < 0.05) at 4, 8, 12 weeks after surgery. Biomechanical properties were also significantly improved in the presence of BMP-2 (p < 0.05) and were comparable to age-matched intact femurs. Histological evaluation of the defect region indicated that the silk hydrogel have completely been degraded by the Splenopentin Acetate end of the study. Based on these results, we conclude that a BMP-2 delivery system consisting of an electrospun PCL nanofiber mesh tube with a silk hydrogel presents an effective strategy for functional repair of large bone defects. Keywords:bone regeneration, silk, biomaterials, growth factor carrier == Introduction == The timely repair of critically sized bone defects/damage remains a major unmet clinical challenge. Bone grafts have been the principal treatment modalities for augmenting or accelerating bone regeneration, but suffer from significant drawbacks. Autologous grafts suffer from the disadvantages of limited material available for grafting, the need for a second graft-harvesting surgery, and donor site morbidity (Kirker-Head et al., 2007;Kolambkar et al., 2011b;Wang et al., 2006). Allografts and xenografts exhibit high failure rates and carry the risks of immune-mediated rejections and transmission of infection from donor to host (Kirker-Head et al., 2007;Kolambkar et al., 2011b). These limitations have prompted research efforts to investigate the effects of combining scaffolds with biochemical cues to augment bone repair. A variety of scaffold technologies have been explored for bone tissue engineering. One of the more recent and promising scaffold technologies for the repair of critically sized long bone defects is based on placing an electrospun polycaprolactone (PCL) nanofiber mesh membrane (or tube) along the periosteal surface of the defect region (Boerckel et al., 2011;Kolambkar et al., 2011a;Kolambkar et al., 2011b). The main advantage of using a membrane compared to a 3D scaffold is that it will not impede cellular infiltration and bone formation in the defect region (Kolambkar et al., 2011b). Another important feature of using a membrane is that it will act as a barrier to separate the osseous and non-osseous regions (Kolambkar et al., 2011b). Bone repair can also be enhanced through biochemical cues via the delivery of growth factors (Luginbuehl et al., 2004;Wang et al., 2006). Bone morphogenetic protein 2 (BMP-2) has sparked interest due to its ability to promote new bone formation (Bessa et al., 2010a;Bessa et al., 2010b;Chen et al., 2007). However, the practical administration of growth factors is associated with numerous challenges. Large doses of BMP-2 are required, making potential therapies expensive (Chen et al., 2007;Kolambkar et al., 2011b). Delivery of growth factors via systemic or direct injection is limited by slow tissue penetration, short half-lives, and rapid diffusion from the Leflunomide injection site (Chen et al., 2007). Frequent, clinically-impractical injections would be required to maintain high growth factor concentrations for long time frames (Chen et al., 2007). If delivery is not localized, BMP-2 can induce systemic side-effects, including the formation of ectopic bone and excessive inflammation in adjacent soft tissues (Carragee et al., 2011;Luginbuehl et al., 2004;Wang et al., 2009). One option to improve the safety, efficacy, and feasibility of growth factor delivery is by incorporation into biomaterials. Local sustained delivery limits systemic exposure and increases the efficacy of a lower protein dose (Kolambkar et al., 2011b). Biomaterial carriers can also potentially increase growth factor lifetime and stability and exert control over release kinetics (Bessa Leflunomide et al., 2010a;Bessa et al., 2010b;Wang et al., 2009). The commercially-available delivery system based on rhBMP-2 solution applied to an absorbable collagen sponge (ACS) has significant limitations, including susceptibility of the collagen sponge carrier to premature resorption and compression (Suh et al., 2002), the use of high doses of rhBMP-2, and the need for bulking agent (grafting with the sponge alone results in a thin, structurally weak fusion and the need for high doses of rhBMP-2) (Glassman et al., 2007). Silk fibroin (a protein polymer isolated from the cocoons of the domestic silkworm,Bombyx mori) possesses unique properties for bone tissue engineering..