It is considered that the endothelial dysfunction occurs in the initial step of atherosclerosis. Although assessments of the endothelial function and viscoelastic properties of the intima-media region are important for the diagnosis of early-stage atherosclerosis, regional viscoelasticity has not yet been measured in vivo. Our group has developed an ultrasonic method for measuring the transient change in viscoelasticity during flow-mediated dilation (FMD). However, in this method, the stress (blood pressure) and strain of the intima-media region of the radial artery are measured in different arms, and the change in pulse wave velocity (PWV) due to FMD has not yet been considered. In the present study, we measured blood pressure waveforms using two pressure sensors, which were placed along the same radial artery for the ultrasonic measurement, to obtain blood pressure waveforms and estimate the PWV between the two sensors. Using the measured PWV, the pulse wave propagation time from the pressure sensor to the position of the ultrasound probe was corrected, and viscoelasticity was estimated from the corrected stress-strain relationship. In the basic experiment, we applied the proposed method to a silicone tube phantom and evaluated the accuracy of the estimation of viscoelasticity by comparing the ultrasonic measurement to the results of the tensile test. In the in vivo measurements, the change in the propagation time delay of the pulse wave was also corrected using the two pressure sensors and the stress-strain relationship of the radial arterial wall was then obtained to estimate viscoelasticity. Furthermore, a decrease in elasticity owing to FMD after recirculation was clearly observed, and the unstable temporal variation in viscosity was significantly reduced. These results demonstrated the improvement in the accuracy of the measurement of viscoelasticity by the proposed method.
Stereolithography is the most precise three-dimensional (3D) printing technology and has been applied to various applications with various photocurable materials. However, most 3D-printed objects produced using conventional methods are made of uniform materials, limiting their functions. In this study, to produce heterogeneous 3D-printed objects, microphase-separated structures were controlled by the copolymerization of a photoinduced macro-reversible addition−fragmentation chain-transfer (macro-RAFT) agent and a monomer at different scanning speeds of an ultraviolet laser beam using a laboratory-constructed laserscanning micro-stereolithography system based on a bottom-up configuration in a fully open-to-air system. First, we demonstrated 3D printing using a RAFT agent by fabricating a pyramidal structure using a 375 nm laser. Copolymerization with styrene was performed to confirm that the synthesized poly(butyl acrylate) with dormant species at the end (DTC-PBA) formed block polymers upon photoirradiation. Nuclear magnetic resonance (NMR) and gel permeation chromatography (GPC) results indicated the formation of a block polymer. A homogeneous photocurable resin was prepared by mixing the synthesized DTC-PBA with multifunctional monomers, and 3D printing was performed using the prepared photocurable resin at different scanning speeds. As the scanning speed increased, the transparency of the 3D-printed model increased, whereas the mechanical strength decreased. It was suggested from scanning probe microscopy (SPM) observations that these differences were due to differences in the microphase-separation structure. As a result, it was demonstrated that heterogeneous 3D structures with sites have different mechanical and optical properties from those of a single material. Controlling the physical properties of 3D-printed parts by controlling the laser irradiation conditions is useful for functionalizing 3D-printed microdevices.
Quasiperiodic oscillations can occur in nonequilibrium systems where two or more frequency components are generated simultaneously. Many studies have explored the synchronization of periodic and chaotic oscillations; however, the synchronization of quasiperiodic oscillations has not received much attention. This study experimentally documents forced synchronization of the quasiperiodic state and the internally locked state of a thermoacoustic oscillator system. This system consists of a gas-filled resonance tube with a nonuniform cross-sectional area. The thermoacoustic oscillator was designed and built in such a way that nonlinear interactions between the fundamental acoustic oscillation mode and the third mode of the gas column are controlled by a temperature difference that is locally created in the resonance tube. Bifurcation diagrams were mapped out by changing the forcing strength and frequency. Separated Arnold tongues were found and both modes were entrained to the external force through complete synchronization. A saddle-node bifurcation was observed in the route from partial to complete synchronization when the forcing strength was relatively weak. However, a Hopf (torus-death) bifurcation was observed when the forcing was relatively strong. In the internally locked state, the bifurcation occurred after the internal locking was broken down by the external force.
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