Geometric Bone Modeling:From Macro to Micro Structures

There is major interest within the bio-engineering community in developing accurate and non-invasive means for visualizing, modeling and analyzing bone micro-structures. Bones are composed of hierarchical bio-composite materials characterized by complex multi-scale structural geometry. The process of reconstructing a volumetric bone model is usually based upon CT/MRI scanned images. Meshes generated by current commercial CAD systems cannot be used for further modeling or analysis. Moreover, recently developed methods are only capable of capturing the micro-structure for small volumes （biopsy samples）. This paper examines the problem of re-meshing a 3D computerized model of bone micro- structure. The proposed method is based on the following phases： defining sub-meshes of the original model in a grid-based structure, remeshing each sub-mesh using the neural network （NN） method, and merging the sub-meshes into a global mesh. Applying the NN method to micro-structures proved to be quite time consuming. Therefore, a parallel, grid-based approach was applied, yielding a simpler structure in each grid cell. The performance of this method is analyzed, and the method is demonstrated on real bone micro-structures. Furthermore, the method may be used as the basis for generating a multi-resolution bone geometric model.

Transcriptomic alterations underline aging of osteogenic bone marrow stromal cells

BACKGROUND Multipotent bone marrow stromal cells(BMSCs)are adult stem cells that form functional osteoblasts and play a critical role in bone remodeling.During aging,an increase in bone loss and reduction in structural integrity lead to osteoporosis and result in an increased risk of fracture.We examined age-dependent histological changes in murine vertebrae and uncovered that bone loss begins as early as the age of 1 mo.AIM To identify the functional alterations and transcriptomic dynamics of BMSCs during early bone loss.METHODS We collected BMSCs from mice at early to middle ages and compared their selfrenewal and differentiation potential.Subsequently,we obtained the transcriptomic profiles of BMSCs at 1 mo,3 mo,and 7 mo.RESULTS The colony-forming and osteogenic commitment capacity showed a comparable finding that decreased at the age of 1 mo.The transcriptomic analysis showed the enrichment of osteoblastic regulation genes at 1 mo and loss of osteogenic features at 3 mo.The BMSCs at 7 mo showed enrichment of adipogenic and DNA repair features.Moreover,we demonstrated that the WNT and MAPK signaling pathways were upregulated at 1 mo,followed by increased pro-inflammatory and apoptotic features.CONCLUSION Our study uncovered the cellular and molecular dynamics of bone aging in mice and demonstrated the contribution of BMSCs to the early stage of age-related bone loss.

Selective serotonin re-uptake inhibitor sertraline inhibits bone healing in a calvarial defect model

Bone wound healing is a highly dynamic and precisely controlled process through which damaged bone undergoes repair and complete regeneration. External factors can alter this process, leading to delayed or failed bone wound healing. The findings of recent studies suggest that the use of selective serotonin reuptake inhibitors(SSRIs) can reduce bone mass, precipitate osteoporotic fractures and increase the rate of dental implant failure. With 10% of Americans prescribed antidepressants, the potential of SSRIs to impair bone healing may adversely affect millions of patients’ ability to heal after sustaining trauma. Here, we investigate the effect of the SSRI sertraline on bone healing through pre-treatment with(10 mg·kg-1sertraline in drinking water, n = 26) or without(control, n = 30) SSRI followed by the creation of a 5-mm calvarial defect. Animals were randomized into three surgical groups:(a) empty/sham,(b) implanted with a DermaMatrix scaffold soak-loaded with sterile PBS or(c) DermaMatrix soak-loaded with542.5 ng BMP2. SSRI exposure continued until sacrifice in the exposed groups at 4 weeks after surgery. Sertraline exposure resulted in decreased bone healing with significant decreases in trabecular thickness, trabecular number and osteoclast dysfunction while significantly increasing mature collagen fiber formation. These findings indicate that sertraline exposure can impair bone wound healing through disruption of bone repair and regeneration while promoting or defaulting to scar formation within the defect site.

Design of Implant Prosthesis for Bone Injury Repair Considering Stress Shielding Effect

The failure of bone injury repair surgery is mostly due to the stress shielding effect caused by the difference of elastic modulus between the implant prosthesis and human bone,result-ing in a great damage to patients.To solve this problem,in this study,the influencing factors of the elastic modulus of implant prosthesis were investigated,the relationship between the elastic modulus of the implanted prosthesis and the influencing factors was analyzed,and then a design method of the implant prosthesis to reduce the stress shielding effect by adjusting the unit module to control the elastic modulus was established.This method was used for the biomechanical simula-tion to simulate the displacement and stress distribution between the implant prosthesis and the surrounding bone tissue,and then the reliability of the method was verified.The implant prosthe-sis with an elastic modulus consistent with that of the experimental dog bone was made by this method,and used for the animal experiments.The effects of implant prosthesis with different mod-ulus on the growth of surrounding bone tissue were observed,and at the same time,the reliability of the implant design method and the results of biomechanical simulation were verified.It is con-firmed that this method can effectively reduce the stress concentration of implant prosthesis by more than 15.4%and increase the growth of bone tissue by more than 21%.

Administration of soluble activin receptor 2B increases bone and muscle mass in a mouse model of osteogenesis imperfecta

Osteogenesis imperfecta（OI） comprises a group of heritable connective tissue disorders generally defined by recurrent fractures, low bone mass, short stature and skeletal fragility. Beyond the skeletal complications of OI,many patients also report intolerance to physical activity, fatigue and muscle weakness. Indeed, recent studies have demonstrated that skeletal muscle is also negatively affected by OI, both directly and indirectly. Given the well-established interdependence of bone and skeletal muscle in both physiology and pathophysiology and the observations of skeletal muscle pathology in patients with OI, we investigated the therapeutic potential of simultaneous anabolic targeting of both bone and skeletal muscle using a soluble activin receptor 2B（ACVR2B） in a mouse model of type Ⅲ OI（oim）. Treatment of 12-week-old oim mice with ACVR2 B for 4 weeks resulted in significant increases in both bone and muscle that were similar to those observed in healthy,wild-type littermates. This proof of concept study provides encouraging evidence for a holistic approach to treating the deleterious consequences of OI in the musculoskeletal system.

Effects of time delays in a mathematical bone model

In this paper we propose a mathematical model of bone remodeling with time delays of both osteoclast-derived paracrine signaling of tumor and tumor-derived paracrine signaling of osteoclast. The effects of time delays on the growth of tumor cells and bone system are studied in multiple myeloma-induced bone disease. In the case of small osteoclast-derived paracrine signaling, it is found that the growth of tumor cells slows down, the oscillation period of the ratio of osteoclasts to osteoblasts is extended with increasing time delay, and there is a competition between the delay and osteoclast-derived paracrine signaling. In the ease of large tumor-derived paraerine signaling, the tumor-derived paracrine signaling can induce a more significant decline in tumor growth for long time delay, and thus slowing down the progression of bone disease. There is an optimal coupling between the tumor-derived paracrine signaling of osteoclasts and time delay during the progressions of bone diseases, which suppresses the tumor growth and the regression of bone disease.

New simulation model for bone formation markers in osteoporosis patients treated with once-weekly teriparatide

Daily 20-mg and once-weekly 56.5-mg teriparatide（parathyroid hormone 1–34） treatment regimens increase bone mineral density（BMD） and prevent fractures, but changes in bone turnover markers differ between the two regimens. The aim of the present study was to explain changes in bone turnover markers using once-weekly teriparatide with a simulation model. Temporary increases in bone formation markers and subsequent decreases were observed during once-weekly teriparatide treatment for 72 weeks. These observations support the hypothesis that repeated weekly teriparatide administration stimulates bone remodeling, replacing old bone with new bone and leading to a reduction in the active remodeling surface. A simulation model was developed based on the iterative remodeling cycle that occurs on residual old bone. An increase in bone formation and a subsequent decrease were observed in the preliminary simulation. For each fitted time point, the predicted value was compared to the absolute values of the bone formation and resorption markers and lumbar BMD. The simulation model strongly matched actual changes in bone turnover markers and BMD. This simulation model indicates increased bone formation marker levels in the early stage and a subsequent decrease. It is therefore concluded that remodeling-based bone formation persisted during the entire treatment period with once-weekly teriparatide.