Human thumb and fingers are usually subjected to an external loading during daily activity. The information of how muscles in the forearm cooperate with each other in order to response to the external loading is still unknown. Such information may be helpful in understanding muscle function pathology and motor disorder. A novel method called electromyography computed tomography (EMG-CT) was developed to visualize muscle activity within a whole cross-section of the forearm by measuring surface EMG signals around the forearm. The current study aimed to extend the previous work by using the EMG-CT to investigate muscle cooperative activity under loading application to thumb or each finger. Loads of 0.98-9.8 N were applied to the thumb or each finger of four subjects in eight loading directions. The loading directions on thumb and index, middle, and little fingers were inner, outer, and upper directions. EMG signals around the subject’s forearm were recorded during the loading by using EMG band consisting of 40 pairs of bipolar electrodes. The results show different muscle cooperative activity pattern between loading conditions. During load was applied to thumb, muscle in lower region in pronation cross-section were highly active. When load was applied to a finger, muscles in lateral-lower region were highly active. In all subjects, total muscle activity in the whole cross-section and the maximum value of muscle activity increased in proportion to loading. This study demonstrates effectiveness of EMG-CT method by showing that the muscle cooperative activity of an individual is specific to force application conditions.

Bone tissue is subjected to multiple forms of mechanical stress. Even in the absence of external loads, however, residual stress is measured, although the underlying mechanisms remain unknown. This study measured the changes in residual stresses, diaphyseal size, and the micro- and nanostructures of bone during growth and maturation, periods associated with different in vivo mechanical loads due to increasing body weight. Mid-diaphyses from bovine femurs in the following three age groups were examined: 1) less than one month old, 2) two years old, and 3) 8−9 years old. Residual stresses along the bone axis at anterior, posterior, lateral, and medial positions on the diaphyseal surface were measured by X-ray diffraction and averaged. Diaphyseal size, porosity, mineral contents, and degree of hydroxyapatite crystal orientation of transverse cross-sections were investigated for relations with residual stress. Residual stress increased significantly from less than one month old (83.7 ± 53.3 MPa) to two years old (125.5 ± 61.9 MPa) in parallel with expanding diaphyseal width and cortical thickness. Residual stress plateaued until 8−9 years old (114.6 ± 42.2 MPa) and was correlated with local cortical thickness (p < 0.05). At the stage, diaphyseal width was only slightly greater than at 2 years and cortical thickness was not significantly different. For all measurements across groups, residual stress statistically correlated with porosity (p < 0.05), mineral contents (p < 0.01), and degree of crystal orientation (p < 0.01). These observations suggest that residual stresses are generated due to bone formation and reconstruction under changing in vivo mechanical loads with age. In conclusion, residual stresses in bone are generated during development and maintained in maturation, and are indirectly related to diaphyseal size and both bone micro- and nanostructure.

In order to improve bioactivity of hydroxyapatite (HA), the surface of HA was modified with calcium or magnesium ion irradiation. Calcium ion irradiation improved bioactivity of HA up to ion dose 10¹⁴ ions/cm², whereas magnesium ion irradiation did not affect bone-like apatite formation. It is found that this different phenomena were attributed to surface electrical potential. Ion irradiation generally induces surface nano-scopic damage, however the strength of HA was not significantly affected by ion irradiation. From cell proliferation, no toxicity of HA irradiated with calcium ions was confirmed. From these results, the effectiveness of calcium ion irradiation on the treatment of bone defect using HA is confirmed.

Poly(lactic acid) (PLA) has attracted much attention as a material for bioabsorbable bone fixation devices, however degradation rate of PLA is very low. Surface treatment of PLA has been investigated to increase degradation rate due to improvement in hydrophilicity. In this study, effects of ion-implantation on degradation rate and mechanical properties were investigated. Argon gas which is chemically stable was used as ion source, and argon ion was implanted in the surface of PLA. The contact angle and the surface roughness of the ion-implanted PLA were measured to evaluate hydrophilicity, and tensile tests and micro-indentation tests were conducted to evaluate mechanical properties. The difference in surface morphology after in vitro degradation test between ion-implanted and un-implanted region was observed to investigate degradation properties of ion-implanted PLA. As a result, tensile strength increased by 8.2 % compared to un-implanted specimen and Vickers hardness increased by 9.5%. The ion-implantation might affect mechanical properties in the overall specimen rather than those in the surface. The result of in vitro degradation test showed that an initial degradation rate was accelerated by ion-implantation. This result is consistent with the increasing hydrophilicity of ion-implanted PLA. Those results suggested that ion-implantation accelerates degradation of PLA without decreasing mechanical properties.

Skeletal fragility is an important orthopedic concern. In this study, the effect of the recovery period after damage under different mode of damage loading on the human cortical bone was investigated. Human cortical bone samples were damaged with one of three different loading modes (tension, compression and torsion) and the change of mechanical properties (stiffness, viscous relaxation and energy dissipation) before and after the damage with respect to different recovery time (1, 10, 30, 60 and 100 minutes) were measured. Results showed that measures of mechanical properties after damage varied significantly with recovery time and load modes. Typically, significant changes in property ratios occurred in the first 10 minutes for loading modulus measures in all loading modes. In addition, results showed that, with respect to loading mode effects, all torsional modulus changes were largest followed by tensile and then compressive modulus changes. We concluded that a minimum 10 minutes recovery period is required for all three loading modes while tension and torsion would require 30 minutes recovery time to obtain an accurate measure of the damage state and recovery effect because more than 90% of strain recovery and modulus recovery were observed during this period.

Development of the robust yet practical tissue culture systems for vascular grafting is one of the major challenges for biomedical engineering. The following questions should be solved in priority: (1) flexibility of the tissue reservoir allowing dynamic stretching, (2) seeding of cells and extraction of tissues should be easy and safe, (3) system must allow morphological observation in real time, (4) maintenance of metabolic activity of tissues should be performed automatically. In our study, we attempted to solve these problems designing in vivo-like culture chamber made of PDMS, and developed an integrated system with a perfusion bioreactor and a small digital microscope. We developed disposable cell chamber with following qualities: transparent, autoclave-sterilizable, non cell-adhesive, and having low autofluorescence. The polyacetal mold made it possible to prepare a chamber hosting the tissue of the desired shape and size. In our case, a porous tube made from PTFE was fixed inside the chamber and tubular cell culture space was prepared for loading of preformed cell spheroids. Perfusion of the media within the porous tube continuously supplied the nutrients and oxygen to the spheroids. Growth and fusion of the cell spheroids inside the chamber can be observed real time by the small digital microscope and analyzed retrospectively by time-laps movies. We loaded batches up to 900 goat fibroblast spheroids into the system; growth, development and morphological fusion of the spheroids were followed out for 10 days. Removal of the tissue without disturbing its structural integrity was possible, and histological analysis revealed reasonable fusion degree between spheroids, and 72.5 % cell survival rate as estimated by TUNEL staining. In conclusion, our system has the basic performance necessary for culturing cell spheroids for tissue-engineered vascular graft.