Many studies have reported that osteoblastic cells can sense the mechanical stimuli that result in rise in the intracellular calcium ion concentration as one of the cellular responses. However, the mechanical conditions, such as stress or strain, that induce the calcium signaling response are not clearly understood yet. In this study, we prepared osteoblastic cells with labelled cellular membrane and intracellular calcium ion using two fluorescence indicator, dyes. Localized deformation was applied to a single cell by direct indentation of a glass microneedle. Subsequently, initiation of calcium signaling response and deformation of cellular membrane were simultaneously observed. Obtained results suggested that the initiating point of localized calcium signaling response was located at the front area of the microneedle tip sliding. In the surrounding area of the needle tip, it could be imagined that there was localized and complicated strain distribution. Therefore, as a future study, the experiment with improved time- and spatial-resolutions is necessary.
Delamination fatigue crack propagation behavior was investigated for four kinds of CF/epoxy laminates (Toray T300/#3601, T800/#3601, T300/#3631, and T800/#3631). Tests were carried out under mode I opening loading by using double cantilever beam specimens. The effect of reinforcing fiber on the delamination fatigue crack growth behavior was very small. The fatigue crack growth behavior was mainly controlled by matrix resin. The analysis of the equivalent stress intensity range proposed by the present authors indicated that the contribution of maximum load was large in delamination fatigue crack propagation of the laminates tested here. The degree of the contribution of maximum load was higher for more brittle resin. The improvement of the interlaminar fracture toughness was not fully transferred to the improvement of threshold value of the fatigue crack growth. The mechanism of delamination fatigue crack propagation agreed well with the fractographic observation.
From an analysis of the change in the superconducting critical current at 4.2 K caused by pre-stressing treatment at room temperature, the distribution of tensile strength of Nb3Sn in multifilamentary bronze-processed composite wires heat-treated at 973 K for 8.6 (sample A), 43 (B) and 260 ks (C) is estimated using the two-parameter Weibull distribution function. The shape parameters of the Weibull distribution are 7.2, 12 and 14, and the average strengths of the Nb3Sn are 1.3, 1.0 and 0.79 GPa for samples A, B and C respectively for the present specimen length of 25 mm. This means that the scatter of strengths and also the average strength for specimens of length 25 mm decrease with increasing heat-treatment time. An attempt to predict the length dependence of the critical current of pre-stressed specimens from the data for short specimens is presented. It seems that the permissible pre-stress below which there is no breakage of Nb3Sn (for all Nb3Sn transport currents) is reduced by 20-30% when the specimen is lengthened from 25 mm to 300 m, while the average strength of Nb3Sn is reduced by 50-70%.
In the aim of tissue regeneration of an alveolar bone, we developed three-dimensional fabric structural composite scaffolds using a bioabsorbable polymer. This scaffold consists of a polylactic acid (PLLA) resin fiber and a 75/25 poly L-lactide-co-glycolide (PLGA) copolymer resin coat. Scaffold is woven on a new-type of three-dimensional loom, has high porosity (89%) and continuous hole. The compressive rigidity and collapse strength of scaffold are increased due to the resin bonding between fiber intersections. The strength of scaffold that did a dip to phosphoric acid buffer solution (PBS) decreased in half due to the hydrolysis in six weeks. Mouse osteoblast-like cells (MC3T3-E1) were seeded onto the scaffolds and cultured in vitro for six weeks. The cells proliferated during in culture and formed a space-filling tissue between polymer fibers. Bone regenerative messenger ALP/DNA levels remained high compared with those one of culture dish. Mineralization of the deposited collagen on scaffold was initially observed at four weeks. Culture of cell on scaffold constructs for six weeks led to formation of a bone tissue.
