Numerical simulation of 3D acoustophoretic motion of microparticles in an acoustofluidic device

Acoustic streaming is typically found in addition to acoustic radiation forces in acoustofluidic devices. Simulation of acoustic streaming is a crucial step for the understanding of its origins, which can provide efficient guidance on creating designs to limit or control this phenomenon. However, most existing methods can only simulate the streaming field in a local area, typically a cross-section of fluid channel. In this work, the three-dimensional (3D) Rayleigh streaming pattern in an acoustofluidic device is simulated and its effects on the movement of microparticles with various sizes are demonstrated. The viability of the simulation of 3D Rayleigh streaming presented here not only can provide better understanding and more comprehensive prediction of experiments in full acoustofluidic devices, but also can offer instructions on the simulation of unusual acoustic streaming patterns, e.g. transducer-plane streamin

Effects of surface profile on a boundary-driven acoustic streaming field

Acoustic streaming fields in two-dimensional rectangular enclosures that have structured boundaries are simulated and the effects of surface profile amplitude on a boundary-driven acoustic streaming field are numerically investigated. The standing wave fields in the enclosures are generated by excitation of a boundary and a sine-wave shaped profile on a boundary parallel to the particle oscillations is considered. This surface profile is found to have a large influence on the magnitude of both outer and inner streaming velocities. In terms of streaming pattern, it is found that the number of inner streaming vortices is dependent on the wavelength of profile while this profile has a less significant effect on the outer vortex pattern

Effects of surface profile on a boundary-driven acoustic streaming field

Control of boundary-driven streaming in acoustofluidic systems is vital for various microfluidic applications either to generate it as a positive mechanism (e.g. microfluidic mixing, heat/mass transfer and fluid pumping) or suppressing it as an undesired disturbance (e.g. particle/cell focusing). It has been shown that two-dimensional (2D) and three-dimensional (3D) boundary-driven streaming can be solved from the limiting velocity method as long as the curvature of the surface is small compared to the viscous penetration depth. In this work, acoustic streaming fields in 2D rectangular enclosures that have structured textures, which do not satisfy this condition are numerically studied by full modelling of Reynolds stresses and the effects of surface profile amplitude on a boundary-driven acoustic streaming field are investigated. Specifically, a sine-wave shaped profile on a boundary parallel to the particle oscillations is considered, which is found to have large influences on both the magnitude of acoustic streaming velocities and streaming patterns

Modelling and control of acoustic streaming in standing wave fields

In acoustofluidic particle manipulation and sorting devices streaming flows are typically found in addition to the acoustic radiation forces. Understanding their origins is essential for creating designs to limit or control this phenomenon.In addition to the classical Rayleigh streaming, experimental work from various groups has described ‘unusual’ acoustic streaming, transducer-plane streaming, typically a four-quadrant streaming pattern with the circulation parallel to the transducer face. The cause of this kind of streaming pattern has not been previously explained as it is different from the well-known classical streaming patterns such as Rayleigh streaming[1] and Eckart streaming[2].In this work, both 3D Rayleigh streaming and transducer-plane streaming are investigated using both experimental and numerical methods. Furthermore, acoustic streaming field due to two orthogonal standing wave fields in a microfluidic device is simulated and analysed

Modal Rayleigh-like streaming in layered acoustofluidic devices

Classical Rayleigh streaming is well known and can be modelled using Nyborg’s limiting velocity method as driven by fluid velocities adjacent to the walls parallel to the axis of the main acoustic resonance. We have demonstrated previously the existence and the mechanism of four-quadrant transducer plane streaming patterns in thin-layered acoustofluidic devices which are driven by the limiting velocities on the walls perpendicular to the axis of the main acoustic propagation. We have recently found experimentally that there is a third case which resembles Rayleigh streaming but is a more complex pattern related to three-dimensional cavity modes of an enclosure. This streaming has vortex sizes related to the effective wavelength in each cavity axis of the modes which can be much larger than those found in the one-dimensional case with Rayleigh streaming. We will call this here modal Rayleigh-like streaming and show that it can be important in layered acoustofluidic manipulation devices. This paper seeks to establish the conditions under which each of these is dominant and shows how the limiting velocity field for each relates to different parts of the complex acoustic intensity patterns at the driving boundaries

The effect of ultrasound-related stimuli on cell viability in microfluidic channels

Background: In ultrasonic micro-devices, contrast agent micro-bubbles are known to initiate cavitation and streaming local to cells, potentially compromising cell viability. Here we investigate the effects of US alone by omitting contrast agent and monitoring cell viability under moderate-to-extreme ultrasound-related stimuli.Results: Suspended H9c2 cardiac myoblasts were exposed to ultrasonic fields within a glass micro-capillary and their viability monitored under different US-related stimuli. An optimal injection flow rate of 2.6 mL/h was identified in which, high viability was maintained (~95%) and no mechanical stress towards cells was evident. This flow rate also allowed sufficient exposure of cells to US in order to induce bioeffects (~5 sec), whilst providing economical sample collection and processing times. Although the transducer temperature increased from ambient 23 [degree sign]C to 54[degree sign]C at the maximum experimental voltage (29 Vpp), computational fluid dynamic simulations and controls (absence of US) revealed that the cell medium temperature did not exceed 34[degree sign]C in the pressure nodal plane. Cells exposed to US amplitudes ranging from 0--29 Vpp, at a fixed frequency sweep period (tsw = 0.05 sec), revealed that viability was minimally affected up to ~15 Vpp. There was a ~17% reduction in viability at 21 Vpp, corresponding to the onset of Rayleigh-like streaming and a ~60% reduction at 29 Vpp, corresponding to increased streaming velocity or the potential onset of cavitation. At a fixed amplitude (29 Vpp) but with varying frequency sweep period (tsw = 0.02-0.50 sec), cell viability remained relatively constant at tsw &gt;= 0.08 sec, whilst viability reduced at tsw &lt; 0.08 sec and minimum viability recorded at tsw = 0.05 sec.Conclusion: The absence of CA has enabled us to investigate the effect of US alone on cell viability. Moderate-to-extreme US-related stimuli of cells have allowed us to discriminate between stimuli that maintain high viability and stimuli that significantly reduce cell viability. Results from this study may be of potential interest to researchers in the field of US-induced intracellular drug delivery and ultrasonic manipulation of biological cells.<br/

The clinical predictive value of geriatric nutritional risk index in elderly rectal cancer patients received surgical treatment after neoadjuvant therapy

ObjectiveThe assessment of nutritional status has been recognized as crucial in the treatment of geriatric cancer patients. The objective of this study is to determine the clinical predictive value of the geriatric nutritional risk index (GNRI) in predicting the short-term and long-term prognosis of elderly rectal cancer (RC) patients who undergo surgical treatment after neoadjuvant therapy.MethodsBetween January 2014 and December 2020, the clinical materials of 639 RC patients aged ≥70 years who underwent surgical treatment after neoadjuvant therapy were retrospectively analysed. Propensity score matching was performed to adjust for baseline potential confounders. Logistic regression analysis and competing risk analysis were conducted to evaluate the correlation between the GNRI and the risk of postoperative major complications and cumulative incidence of cancer-specific survival (CSS). Nomograms were then constructed for postoperative major complications and CSS. Additionally, 203 elderly RC patients were enrolled between January 2021 and December 2022 as an external validation cohort.ResultsMultivariate logistic regression analysis showed that GNRI [odds ratio = 1.903, 95% confidence intervals (CI): 1.120–3.233, p = 0.017] was an independent risk factor for postoperative major complications. In competing risk analysis, the GNRI was also identified as an independent prognostic factor for CSS (subdistribution hazard ratio = 3.90, 95% CI: 2.46–6.19, p &lt; 0.001). The postoperative major complication nomogram showed excellent performance internally and externally in the area under the receiver operating characteristic curve (AUC), calibration plots and decision curve analysis (DCA). When compared with other models, the competing risk prognosis nomogram incorporating the GNRI achieved the highest outcomes in terms of the C-index, AUC, calibration plots, and DCA.ConclusionThe GNRI is a simple and effective tool for predicting the risk of postoperative major complications and the long-term prognosis of elderly RC patients who undergo surgical treatment after neoadjuvant therapy