We investigated how the chemotactic behaviors of peritrichous bacteria that repeat straight swimming (runs) and directional changes (tumbles) differ depending on the chemical species and concentrations of the attractant. Quantification of the intensity of bacterial chemotaxis will be helpful for the prediction of the bacterial accumulation. We conducted microscopic observation of Salmonella typhimurium cells around a capillary filled with the attractant, L-aspartic acid or L-serine. At the same concentration, cells accumulate more rapidly around L-aspartic acid than L-serine, and the accumulation region around L-aspartic acid is larger than L-serine. Then we estimated the intensity of chemotaxis by comparison with the mathematical model, where characteristic behavior in the run-and-tumble motion of chemotactic bacteria is modeled; the cell decreases the tumble frequency when the cell swims toward the direction where the attractant concentration increases. Observed number density of cells is well approximated with exponentially decaying function of the distance from the capillary tip, which is similar trend to the simulation based on the mathematical model. The intensity of chemotaxis, determined from the slope of the exponential distribution, is almost the same regardless of the chemical species of the attractant or the concentration of L-serine or L-aspartic acid. It can be said that the behavior of a single bacterial cell (probability of suppressing tumble) is almost the same in the region where the cell senses the concentration gradient of the attractant, and that higher concentration of the attractant affects mainly the larger detectable region of the attractant.
The comfort fit of a limb prosthetic socket is one of the most important considerations for developing the socket for an amputee. The pressure at the touchpoint, which is the interface between the residual limb with natural skin and the prosthetic limb socket with a polymeric material, should be monitored precisely when fabricating the comfort fit. Even a small volume or shape discrepancy between the residual limb and prosthetic limb sock causes several problems in the residual limb, such as skin breakage, tissue irritation, and associated pain. Volume variations of the residual limb due to squeezing by a prosthetic limb sock result in pressure changes that can be detected using a pressure sensor. In this study, the interface pressures between the residual limb and prosthetic upper-limb socket were obtained using a 3D printed capacitive pressure sensor. An upper-limb prosthetic socket and capacitive pressure sensor were fabricated using a dual nozzle 3D Fused Deposition Modelling technique. Polylactic acid, polylactic acid-carbon black compound, and polyurethane were used as the personalized upper-limb socket and sensing electrode, and substrate material, respectively. The as-fabricated sensors were embedded into the sock wall, and their sensing properties were characterized. For a case study, the sensor-embedded sockets were worn on an amputee's residual upper-limb to characterize empirically the contact pressure occurring at the interfaces. A weight was attached to the end of the limb socket to examine the effects of weight on the local pressures acting on the residual upper limb. The observed interface pressures and pressure distribution at the interface can provide valuable information to clinicians and developers that can guide fit improvements.
This study presents a human elbow motor learning strategy responding to varying loads. Inspired by Kawato’s internal model theory, we suggest hypothesis that human minimize the internal model error by updating the joint stiffness to generate stable and robust motion during repetitive voluntary action with varying weight of load condition. We designed experimental robotics device to verify our hypothesis and the device is capable of precisely measuring human elbow joint stiffness very accurately. The subject was instructed to perform the prescribed elbow motion without notifying the weight of the load for neutral experimental condition and we recorded joint position, perturbation torque of actuator, reaction torque from torque sensor, and mean absolute value (MAV) of the surface EMG (sEMG) in forearm muscles and upper arm muscles as a reference criterion for elbow joint impedance modulation during motor learning. Modified ensemble-based system identification was applied to characterize the dynamic elbow mechanical impedance in transient state of moving loads. Experimental results show that subjects utilized high joint stiffness initially, but it decreases gradually and saturated to the level of 20%~60% of initial value after repetitive motion tests. The degree of saturation of motor learning varied with the weight of loads, this result supports the hypothesis that motor learning reduces joint stiffness by providing accurate internal model.
Model-based three-dimensional(3D)/two-dimensional(2D) image registration methods have been widely applied in measuring 3D kinematics of the knee during dynamic activities. However, the combined effects of bone model compositions (radiodensity vs. homogeneous-density) and the number of fluoroscopic views on the measurement accuracy remained unclear. The current study evaluated experimentally the accuracy of the four model-based 3D/2D image registration configurations on the accuracy of measured knee kinematics, namely homogeneous-density model/single-plane image (HS), radiodensity model/single-plane image (RS), homogeneous-density model/biplane images (HB), and radiodensity model/biplane images (RB). Computed tomography (CT) of the knee and asynchronous biplane fluoroscopic images of the simulated knee motions were collected from a cadaveric knee joint for the evaluation of the registration configurations. The results showed that the use of biplane fluoroscopic images ensured mean absolute errors (MAE) below 0.3 mm and 0.9° in each motion component regardless of the types of bone models. Application of radiodensity model could generate digitally reconstructed radiographs more similar to the fluoroscopic images, diminishing MAE in all motion components and measurement bias. As a result, the RS configuration was capable of reconstructing the 3D knee joint angles with MAE comparable to those obtained using the HB configuration. Among the four tested configurations, the RB configuration was most accurate and least affected by the fast skeleton motions.
The high sensitivity of mammalian hearing is achieved by cochlear amplification. The basis of this amplification is the motility of outer hair cells (OHCs), which are sensory cells in the inner ear. This motility may be due to voltage-dependent conformational changes of the motor protein prestin, which is densely embedded in the lateral membrane of OHCs. However, the membrane structure of prestin has not yet been elucidated. Therefore, the membrane structure of prestin was herein investigated by force spectroscopy using an atomic force microscope (AFM). The gene of prestin fused with an Avi-tag at its C terminus was transfected into Chinese hamster ovary (CHO) cells and the inside-out plasma membrane was isolated. The Avi-tag was enzymatically biotinylated and attached to a streptavidin-coated AFM cantilever via biotin-streptavidin binding. Prestin was then pulled out from the plasma membrane and the relationship between the force applied to the protein and the extension distance, i.e., the force-extension (FE) curve, was assessed. The curves obtained showed saw-toothed patterns. An attempt was then made to analyze these curves using the worm-like chain model. The force caused by stretching of the intracellular C terminus and that due to the extraction of one or several transmembrane domains were identified. The present results imply that the C terminus and the subsequent transmembrane domains of prestin correspond to those of the previously reported model with 12 transmembrane domains.