Published papers

Purpose: The aim of this study was to investigate the biomechanical role of trabecular bone around dental implants in the mandible. Materials and Methods: The model in this study was made using micro-computed tomography data taken from a cadaver in whom endosseous implants had been in place for 15 years prior to death. Morphologic analysis and three-dimensional (3D) finite element analysis were performed to calculate the peri-implant loading path of the model in which the trabecular structure was accurately simulated. Results: As seen through multiscale analysis using the homogenization method, the trabecular bone architecture around implants was isotropic for the most part. Also, 3D finite element analysis showed that compressive stresses oblique to the implant axis were transmitted to the lower constrained surface; tensile stresses oblique to the implant axis were transmitted to the upper constrained surface, and they intersected each other with vertical loading. The highest stress in cancellous bone was observed on perpendicular loading, and stress produced in trabeculae decreased approaching horizontal loading. Conclusion: Cancellous bone architecture around the implant was generally isotropic. 3D finite element analysis showed that cancellous bone trabeculae around implants dispersed stress by forming load transfer paths. The results suggest that trabecular bone plays a major role in supporting functional pressure exerted via the implant. © 2010 by Quintessence Publishing Co Inc.

We demonstrate the fabrication of polymer microneedle arrays using soft lithography. A photomask was designed to use Fresnel diffraction of UV light to create sharp, tapered hollows in SU-8, a negative photoresist, after development. Polymer microneedles were formed using these SU-8 structures as a mold. These polymer needles may be applicable as flexible electrodes in brain-machine interfaces because they are more likely to survive movement of the skin than conventional brittle silicon needles. Similar needles, made from medicinal substances, could be used for transdermal drug administration. For these applications, the needles must be long, sharp, and stiff enough to penetrate the stratum corneum (∼20 m in thickness) and reach the viable epidermis (200-300 m in thickness), but must not reach the dermis, which contains sensitive nerve endings. We successfully manufactured 2020 microneedle arrays of polydimethylsiloxane with a needle length of 200 m. We experimentally verified that these manufactured electrodes successfully penetrated the stratum corneum of a cultured skin. © 2011 Society of Photo-Optical Instrumentation Engineers (SPIE).

This study presents a numerical methodology to clarify the morphology of complex trabecular network architecture in human lumbar vertebra by means of the new post-processing technique for calculated microscopic stress by the homogenization method. Micro-CT image-based modeling technique is used and careful but intuitive and easy-to-use method for microstructure model, in other words region of interest (ROI), is also presented. The macroscopic homogenized properties that include not only the Young's moduli but also shear moduli could explain the difference of morphology between healthy and osteoporotic bones. This paper focuses on the change of degree of anisotropy. Then, the microscopic stress under three basis load cases was analyzed. In this analysis, the homogenization method has a merit in the computational cost. The trabeculae are classified into eight groups from the viewpoint of load bearing function against three loading conditions in the proposed post-processing of numerical results. It contributes to the understanding of the mechanical role of trabecular bone in vertebra. The primary trabecular bone that has been supposed to support the self-weight and secondary bone that connects the primary bone are successfully visualized. The discussion on the mechanical role of plate-like trabecular bone in the load path network system is also highlighted. © 2011 by JSME.

Trabecular bone has a complicated porous microstructure and consists of interconnected plates and rods known as trabeculae. The microarchitecture of the trabeculae contributes to load distribution capacity and, particularly, the optimal bone strength. Many previous studies have shown that morphological parameters are used to characterize the microarchitecture of trabecular bone, but little is known about the mechanical role of trabecular morphology in the context of load-bearing behavior. Therefore, this study proposes a new segmentation method for examining the morphology of trabecular structure foci of load-bearing capability. A micro-finite element model of trabecular bone was obtained from the fourth lumbar vertebra on the basis of a three-dimensionally reconstructed micro-computed tomography (CT) image. We used an asymptotic homogenization method to determine microscopic stress by applying three unidirectional compressive loads in the vertical, anteroposterior, and right-left axes of two trabecular bone volumes. We then classified the complicated trabecular microstructure into three segments: primary and secondary trabeculae and trabeculae of no contribution. Next, a dynamic analysis was conducted by applying a force impulse load. The result indicated that 1/3 of the trabecular volume functions as primary trabecula. The morphology of the trabecular network could be visualized successfully highlighting the percolation of the stress wave in the primary trabecular segment. Further, we found that the role of the plate-like structures was that of a hub in the trabecular network system. © International Federation for Medical and Biological Engineering 2012.

© 2013 Taylor & Francis. An assessment of the mechanical properties of trabecular bone is important in determining the fracture risk of human bones. Many uncertainty factors contribute to the dispersion of the estimated mechanical properties of trabecular bone. This study was undertaken in order to propose a computational scheme that will be able to predict the effective apparent elastic moduli of trabecular bone considering the uncertainties that are primarily caused by image-based modelling and trabecular stiffness orientation. The effect of image-based modelling which focused on the connectivity was also investigated. A stochastic multi-scale method using a first-order perturbation-based and asymptotic homogenisation theory was applied to formulate the stochastically apparent elastic properties of trabecular bone. The effective apparent elastic modulus was predicted with the introduction of a coefficient factor to represent the variation of bone characteristics due to inter-individual differences. The mean value of the predicted effective apparent Young's modulus in principal axis was found at approximately 460 MPa for respective 15.24% of bone volume fraction, and this is in good agreement with other experimental results. The proposed method may provide a reference for the reliable evaluation of the prediction of the apparent elastic properties of trabecular bone.

A systematic modeling of uncertainty due to image processing, material characteristics and experimental works was developed in order to propose a novel stochastic image-based multi-scale method for heterogeneous media. The effective mechanical properties with application to three porous trabecular bone models were predicted by introducing the correction factor (β) to represent the miscellaneous errors or unknown factors. Finally, the probability density was obtained for the effective mechanical properties, which could evaluate the reliability of scattered experimental results. It has been concluded that variation in effective properties of heterogeneous media can be predicted even when only limited measured values are available by using the present extrapolation technique based on verified simulation results. © 2013 The Japan Institute of Metals and Materials.

Objective The present study elucidates the relationship between the locations of rib defects and loss of respiratory function. Methods Ten sets of three-dimensional finite element models were produced from computed tomography data of 10 persons and categorized as normal type models. These models were modified by removing part of the ribs, and the resultant models were categorized as defect type models. Varying the location of the defects, six types of defect model were produced from each of the 10 normal models; the defects were made on the anterior-superior, anterior-inferior, lateral-superior, lateral-inferior, posterior-superior, and posterior-inferior regions of the thorax. To simulate respiration, contracture forces were applied to nonlinear springs modeling respiratory muscles for each of the normal and defect models. Difference in volume of the thoracic cavity between inspiration and expiration phases was viewed as the indicator of respiratory function and was defined as ΔV. The values of ΔV were compared between normal type models and their corresponding defect type models. Results Among the six types of defect, the degree of functional loss was greatest with those defects on the lateral-inferior part of the thorax, where ΔV of the affected side hemithorax drops to 38 to 45% of normal values, whereas ΔV was 62 to 88% with other defect models. Conclusion Thoraces that have defects on their lateral-inferior regions present lower respiratory functioning than thoraces with other defect locations. Hence, in treating clinical cases where defects are expected to occur in this region, effort should be made to minimize the area of the defect. © 2014 Georg Thieme Verlag KG Stuttgart New York.

The aim of this study was to elucidate the association between the bone structure at implant insertion sites and stress distribution around the mandibular canal by means of three-dimensional finite element (3D FE) analysis. Four FE models were created with slice data using micro-computed tomography (micro-CT), and 3D FE analysis was performed. Mechanical analysis showed that the load reached the mandibular canal via the trabecular structure in all FE models. High levels of stress were generated around the mandibular canal when the distance between the mandibular canal and the implant decreased. High stress levels were also observed when cortical bone thickness and bone volume/total volume (BV/TV) were low. Our findings suggest that load is transmitted to the mandibular canal regardless of differences in the thickness of cortical bone or cancellous bone structure, but excessive load may be generated in bone with thin cortical and coarse cancellous structures.

The Monte Carlo method is a well-known method for calculating uncertainty, but it has the disadvantage of high computational cost because it usually requires 10,000 sampling points. In this paper, a practical sampling algorithm named Stepwise Limited Sampling (SLS) is proposed to obtain both accurate expected values and very accurate tail probability values in the Monte Carlo simulation. This method was then applied to a biomechanics problem concerning the risk prediction of pressure ulcers. It is known that the initial damage that leads to a fatal stage of pressure ulcer occurs in deep muscle, but its location has not been clarified. By modeling assumed damage at the bone-muscle interface in the human buttock as a cutout, and by judging whether the damage propagates or not, sets of material properties of muscle and fat in the tail probability that result in high interface shear strain were obtained as a function of body positioning during nursing. © 2014 by the Japan Society for Computational Engineering and Science.

This study presents a prediction of apparent elastic moduli of vertebral trabecular bone using the homogenization method. A micro-finite element (FE) model of trabecular bone was reconstructed from a sequential of cross-section micro-CT image by converting bone voxels to brick elements. Eight regions of interest (ROIs) were extracted from two lumbar vertebra bone specimens of healthy and osteoporotic. The homogenization method and finite element method was employed to analyze the microscopic trabecular bone. Bone tissue property was modeled as orthotropy material considering the biological apatite (BAp) crystallite orientation. This research focuses on the effect of morphological difference between healthy and osteoporotic bones to the apparent elastic moduli. The change of degree of anisotropy was also discussed. Comparison of the calculated Young's moduli in vertical axis with Keyak et al.'s experimental result showed good agreement and proved the reliability of the numerical model. © (2014) Trans Tech Publications, Switzerland.

© 2016 Georg Thieme Verlag KG Stuttgart · New York. Objective The present study aims to elucidate whether or not scoring deformed cartilages reduces postoperative pain after the Nuss procedure for pectus excavatum patients. Methods A total of 46 pectus excavatum patients for whom the Nuss procedure was conducted were included in the study. The patients were categorized into two groups, depending on whether or not the supplementary maneuver of scoring deformed cartilages was performed in addition to the Nuss procedure. Patients for whom deformed costal cartilages were scored were categorized as the Scoring Group (n = 24); those who received no such scoring were categorized as the Non-Scoring Group (n = 22). After evaluating the maximum stresses occurring on the thoraces by means of dynamic simulation using finite element analyses, intergroup comparison of the maximum von-Mises stress values was performed. Furthermore, after quantifying postoperative pain as the frequency with which patients injected anesthetics through an epidural pain-control system within 2 postoperative days, the degree of pain was compared between the two groups. Results The maximum stresses occurring on the thorax were significantly greater for the Non-Scoring Group than for the Scoring Group; injection frequency was also greater for the Non-Scoring Group (average 4.9 times for 2 days) than for the Scoring Group (average 2.5 times for 2 days). Conclusion High stresses occur due to the performance of the Nuss procedure, causing postoperative pain. The stresses can be reduced by performing supplementary scoring on deformed cartilages. Accordingly, postoperative pain is reduced.

© 2015, Springer-Verlag Wien. Surgical success of drilling in oral implantology depends on the sense of force on the fingers or feeling of a dental clinician, which is related to the quality of trabecular bone in the jawbone expressed by apparent mechanical characteristics. As the mechanical properties of trabecular bone depend on the bone volume fraction, microstructure, and many other factors closely related to individual differences, a probabilistic numerical procedure to assess drilling force is proposed. Using a micro-CT-based jawbone model, a first-order perturbation-based stochastic homogenization method was employed to estimate the possible scattering of apparent mechanical properties of the trabecular bone region. The complicated drilling problem was simplified to sequential linear static FEAs, to which the predicted apparent Young’s modulus and shearing moduli in the drilling direction were applied. The FEAs demonstrated that the homogenized mechanical properties showed anisotropy, which might lead to differences in the drilling forces at different drilling angles. The numerically estimated drilling forces were shown by the expected value, 50 %-probability result, and 90%-probability result and revealed that one patient among two or ten patients would probably have poor bone quality. There was a remarkable difference in the drilling forces between the expected value and the 90%-probability result.