Substrate Stiffness-Dependent Regulatory Volume Decrease and Calcium Signaling in Chondrocytes

The pericellular matrix stiffness is strongly associated with its biochemical and structural changes During the aging and osteoarthritis progresses of articular cartilage. However, how substrate stiffness modulates the chondrocyte regulatory volume decrease (RVD) and calcium signaling remains unknown. This study aims to investigate the effects of substrate stiffness on the chondrocyte RVD and calcium signaling by recapitulating the physiologically relevant substrate stiffness. Our results showed that substrate stiffness induced completely different dynamical deformation between the cell swelling and recovering progresses. Chondrocytes swelled faster on the soft substrate but recovered slower than the stiff substrate during the RVD response induced by the hypo-osmotic challenge. We found that stiff substrate enhanced the cytosolic Ca2+ oscillation of chondrocytes in the iso-osmotic medium. More importantly, chondrocytes exhibited a distinctive cytosolic Ca2+ oscillation during the RVD response. Soft substrate significantly improved the Ca2+ oscillation during the cell swelling whereas stiff substrate enhanced the cytosolic Ca2+ oscillation during the cell recovering. Our work also suggests that TRPV4 channel are involved in the chondrocyte sensing substrate stiffness and RVD response by mediating Ca2+ signaling in a stiffness-dependent manner. It helps to understand a previously unidentified relationship between substrate stiffness and RVD response under the hypo-osmotic challenge.

Electron Microscopy Study of Grain Boundary Behavior in Pb-Free Solder Materials for Mitigation of Whiskers

The changes of microstructure in pure-Sn after deformation were investigated by electron microscopy. Two types of specimens were prepared: Sample-1; pure-Sn/Fe-42Ni, Sample-2; single crystalline pure-Sn. The growth of curling whiskers on Sample-1 was observed in-situ in a scanning electron microscope (SEM). A thin foil specimen of the curling whisker was made with a focused ion beam (FIB) mill. Transmission electron microscope (TEM) analysis confirmed that the curling whisker was of a single crystal regardless of its external shape. New models for growth process of a bent single-crystalline whisker were proposed. The models are composed of epitaxial growth and recrystallization. Electron back scatter diffraction (EBSD) analysis was performed for Sample-2. The results of EBSD strongly suggested that recrystallization proceeds even at room temperature. These experimental results are very important to understand the behavior of dynamical deformation and recrystallization of Sn metal, and useful in consideration the mitigation of whiskers.