Critical-sized diaphysis defects are complicated by inherent sub-optimal healing conditions. The two-staged induced membrane technique has been used to treat these challenging defects since the 1980's. It involves temporary implantation of a membrane-inducing spacer and subsequent bone graft defect filling. A single-staged, graft-independent technique would reduce both socio-economic costs and patient morbidity. Our aim was to enable such single-staged approach through development of a strong bioactive glass scaffold that could replace both the spacer and the graft filling. We constructed amorphous porous scaffolds of the clinically used bioactive glass S53P4 and evaluated them in vivo using a critical-sized defect model in the weight-bearing femur diaphysis of New Zealand White rabbits. S53P4 scaffolds and standard polymethylmethacrylate spacers were implanted for 2, 4, and 8 weeks. Induced membranes were confirmed histologically, and their osteostimulative activity was evaluated through RT-qPCR of bone morphogenic protein 2, 4, and 7 (BMPs). Bone formation and osseointegration were examined using histology, scanning electron microscopy, energy-dispersive X-ray analysis, and micro-computed tomography imaging. Scaffold integration, defect union and osteosynthesis were assessed manually and with X-ray projections. We demonstrated that S53P4 scaffolds induce osteostimulative membranes and produce osseointegrative new bone formation throughout the scaffolds. We also demonstrated successful stable scaffold integration with early defect union at 8 weeks postoperative in critical-sized segmental diaphyseal defects with implanted sintered amorphous S53P4 scaffolds. This study presents important considerations for future research and the potential of the S53P4 bioactive glass as a bone substitute in large diaphyseal defects. STATEMENT OF SIGNIFICANCE: Surgical management of critical-sized diaphyseal defects involves multiple challenges, and up to 10% result in delayed or non-union. The two-staged induced membrane technique is successfully used to treat these defects, but it is limited by the need of several procedures and bone graft. Repeated procedures increase costs and morbidity, while grafts are subject to donor-site complications and scarce availability. To transform this two-staged technique into one graft-independent procedure, we developed amorphous porous scaffolds sintered from the clinically used bioactive glass S53P4. This work constitutes the first evaluation of such scaffolds in vivo in a critical-sized diaphyseal defect in the weight-bearing rabbit femur. We provide important knowledge and prospects for future development of sintered S53P4 scaffolds as a bone substitute.

Bone is a dynamic specialized connective tissue that undergoes continuous remodeling to preserve its health. Bone health is influenced throughout life by a combination of genetic, hormonal, and environmental factors, as well as physical activity and diet. This study aims to evaluate the effects of diets with different fat content on the femurs of mice fed for 16 or 20 weeks on a normal diet (ND16w and ND20w) or a Western diet (WD16w and WD20w) and for 20 weeks with their combinations on a ketogenic diet (KD) (WD + ND20w, ND + KD20w, and WD + KD20w). Micro-CT analysis on femoral cancellous bone revealed a non-significant trend toward decreased bone volume fraction (BV/TV) and trabecular thickness in mice fed a combined WD + KD20w compared to WD20w. Cortical bone thickness was significantly lower in mice fed WD16w and WD20w compared to those fed ND16w and ND20w (p = 0.049 and p = 0.039, respectively), in mice fed WD20w Ct.Th increased compared to WD + ND20w (p = 0.024) and a strong decrease is evident when comparing WD + ND20w to WD + KD20w (p < 0.0004). Consistently, histological analysis revealed that the number of osteoclasts per bone perimeter on cancellous bone increases compared with ND20w with ND + KD20w (p = 0.007) and WD + ND20w with ND + KD20w (p = 0.0006). In addition, a decrease in osteoblasts was observed (p < 0.041) in cortical bone, comparing ND20w with ND + KD20w; this suggests that the KD may have differential effects depending on the baseline condition. Osteocyte numbers did not significantly change when comparing the different treatments. Masson staining supports micro-CT results on both cortical and cancellous bone. In conclusion, transition from a high-fat diet to a normal diet may partially restore cortical bone health, whereas transition to a ketogenic diet exerts a trend toward additional detrimental effects on trabecular bone.