The Analysis of Wall Shear Stress Modulated by Acute Exercise in the Human Common Carotid Artery with an Elastic Tube Model

Assessment of the magnitude and pattern of wall shear stress(WSS)in vivo is the prerequisite for studying the quantitative relationship between exercise-induced WSS and arterial endothelial function.In the previous studies,the calculation of the WSS modulated by exercise training was primarily based upon the rigid tube model,which did not take non-linear effects of vessel elastic deformation into consideration.In this study,with an elastic tube model,we estimated the effect of a bout of 30-minute acute cycling exercise on the WSS and the flow rate in the common carotid artery according to the measured inner diameter,center-line blood flow velocity,heart rates and the brachial blood pressures before and after exercise training.Furthermore,the roles of exerciseinduced arterial diameter and blood flow rate in the change of WSS were also determined.The numerical results demonstrate that acute exercise significantly increases the magnitudes of blood flow rate and WSS.Moreover,the vessel elastic deformation is a non-negligible factor in the calculation of the WSS induced by exercise,which generates greater effects on the minimum WSS than the maximum WSS.Additionally,the contributions of exercise-induced variations in blood flow rate and diameter are almost identical in the change of the mean WSS.

A multiscale model for analyzing the synergy of CS and WSS on the endothelium in straight arteries

A multiscale model was proposed to calculate the circumferential stress （CS） and wall shear stress （WSS） and analyze the effects of global and local factors on the CS, WSS and their synergy on the arterial endothelium in large straight arteries. A parameter pair [Zs, SPA] （defined as the ratio of CS amplitude to WSS amplitude and the phase angle between CS and WSS for different harmonic components, respectively） was proposed to characterize the synergy of CS and WSS. The results demonstrated that the CS or WSS in the large straight arteries is determined by the global factors, i.e. the preloads and the afterloads, and the local factors, i.e. the local mechanical properties and the zero-stress states of arterial walls, whereas the Zs and SPA are primarily determined by the local factors and the afterloads. Because the arterial input impedance has been shown to reflect the physiological and pathological states of whole downstream arterial beds, the stress amplitude ratio Zs and the stress phase difference SPA might be appropriate indices to reflect the influences of the states of whole downstream arterial beds on the local blood flow-dependent phenomena such as angiogenesis, vascular remodeling and atherosgenesis.

Microfluidic-based single cell trapping using a combination of stagnation point flow and physical barrier

Single cell trapping in vitro by microfluidic device is an emerging approach for the study of the relationship between single cells and their dynamic biochemical microenvironments. In this paper, a hydrodynamic-based microfluidic device for single cell trapping is designed using a combination of stagnation point flow and physical barrier.The microfluidic device overcomes the weakness of the traditional ones, which have been only based upon either stagnation point flows or physical barriers, and can conveniently load dynamic biochemical signals to the trapped cell. In addition, it can connect with a programmable syringe pump and a microscope to constitute an integrated experimental system.It is experimentally verified that the microfluidic system can trap single cells in vitro even under flow disturbance and conveniently load biochemical signals to the trapped cell. The designed micro-device would provide a simple yet effective experimental platform for further study of the interactions between single cells and their microenvironments.

Transfer characteristics of dynamic biochemical signals in non-reversing pulsatile flows in a shallow Y-shaped microfluidic channel: signal filtering and nonlinear amplitude-frequency modulation

The transports of the dynamic biochemical signals in the non-reversing pulsatile flows in the mixing microchannel of a Y-shaped microfluidic device are ana- lyzed. The results show that the mixing micro-channel acts as a low-pass filter, and the biochemical signals are nonlinearly modulated by the pulsatile flows, which depend on the biochemical signal frequency, the flow signal frequency, and the biochemical signal transporting distance. It is concluded that, the transfer characteristics of the dynamic biochemical signals, which are transported in the time-varying flows, should be carefully considered for better loading biochemical signals on the cells cultured on the bottom of the microfluidic channel.

Active tuning of electromagnetically induced transparency from chalcogenide-only metasurface

Electromagnetically induced transparency(EIT)is a coherent optical process that provides a narrow transparent peak within a broad absorption line in an atomic medium.All-dielectric metasurface analogues of EIT have enabled new developments in the nanophotonics field for obtaining smaller,more effective slow-light devices and highly sensitive detectors without a quantum approach.However,the dynamic control of the EIT response of all-dielectric metasurfaces has been rarely reported hitherto for the near-infrared(N-IR)region,although a broader range of applications will be enabled by a reconfigurable EIT system.In this study,we realise a chalcogenide(germanium antimony telluride,GST)metasurface,which possesses a dynamically tunable EIT response by optically driving the amorphous-crystalline phase change in the GST medium.Only a few tens of nanometres thick,the nanostructured GST film exhibits Mie resonances that are spectrally modified via laser-induced phase transitions,offering a high relative modulation contrast of 80%in the N-IR region.Moreover,an extreme dispersion that results in the‘slow light’behaviour is observed within this transparency‘window’.Furthermore,the group delay of the N-IR beam switches reversibly under the phase transition.The measurement is consistent with both numerical simulation results and phenomenological modelling.Our work facilitates the development of new types of compact ultrafast N-IR holograms,filtering,and ultrasensitive detectors.

Evaluation of the performance of Ca-deficient hydroxyapatite(CDHA)/MgF_(2)bilayer coating on biodegradable high-purity magnesium in a femoral condyle defect model in rabbits

The two most critical factors in promoting the clinical translation of magnesium(Mg)are reducing its degradation rate and improving its osteogenesis.In this study,a Ca-deficient hydroxyapatite(CDHA)/MgF_(2)bilayer coating was prepared on high-purity magnesium(HP Mg)rods by fluorination and hydrothermal treatment.Scanning electron microscope showed that the thickness of the bilayer coating was 3.78 lm and that the surface morphology was nanoscale.In an in vivo experiment on femoral condyle defects in rabbits,the serum magnesium ion levels of rabbits were always in the normal range after surgery,and the liver and kidney functions were not abnormal,which indicated that the CDHA/MgF_(2)bilayer coating has good biosafety.Micro-CT showed that the CDHA/MgF_(2)bilayer coating significantly reduced the degradation rate of the HP Mg rods and enhanced the promotion of bone formation.Hard tissue sections showed that the CDHA/MgF_(2)bilayer coating gave the bone tissue a tight contact interface with the HP Mg rod and improved the bone mass.Immunohistochemistry showed that the expression of vascular endothelial growth factor and BMP-2 was more obvious.These results confirm that the CDHA/MgF_(2)bilayer coating can improve the properties of HP Mg and provide a basis for the further transformation of HP Mg in the future.It also provides a new reference for the surface modification of magnesiummetal.