Robot-assisted retinal cannulation is an eye surgical procedure which can dissolve the obstruction by using robot to inject anticoagulant into occluded vessel. The current research on the critical parameters of cannulation for human is scarce because of the immature technology. Considering the influence of microneedle, this work investigated the effects of drug concentration, injection velocity, injection position, and size of clot on cannulation by theoretical analysis and finite element analysis. For finite element analysis, the multiphysics continuum model was established to demonstrate species transport and reaction which simulates the entire lytic process of the occlusive clot, and four cell zones were established to describe the generation of plasmin (PLS) with the addition of tissue-type plasminogen activator (tPA) and fibrinolysis of clot by importing subroutines into each cell zone under the conditions of constant clot size and variable size, respectively. The results imply that the most efficient value of tPA concentration is 50 nM, injection velocity is 60 mm/s for clot length of 0.1 mm, and the best position to insert the cannula is 0.5 mm in front of the thrombus. For different clot lengths of 0.1 mm to 0.6 mm, the optimal range of tPA concentration and injection velocity is from 20 nM to 70 nM and from 40 mm/s to 60 mm/s, respectively, and explores the reasonable injection position of 0.3 mm to 0.5 mm in front of clot in a vein of 100 μm. This conclusion can be used to perform robot-assisted cannulation surgery to improve fibrinolytic efficiency.
Focused jets have been widely studied owing to the abundance of attractive flow phenomena and industrial applications, whereas annular focused jets are less studied. This study combines experiments, numerical simulations, and analytical modeling to investigate the effect of the contact angle on the generation position and focusing efficiency of annular focused jets between parallel plates. In the experiment, a pulsed laser generates a cavitation bubble inside the droplet, and the rapidly expanding cavitation bubble drives an annular-focused jet on the droplet surface. Changing the plate wettability creates different contact angles and droplet surface shapes between the droplet and plates, which modulates the position and focusing efficiency of the annular jet. Based on the jet singularity theory and by neglecting gravity, the derived formula for the jet position offset is found to depend only on the contact angle, which is in good agreement with the experimental and numerical simulation results. Combined with numerical simulations to analyze the flow characteristics of the droplets between the parallel plates, a new calculation method for the jet focusing efficiency is proposed. Interestingly, when the liquid surface radius is small, the focusing efficiency can be improved by adjusting the contact angle to make the jet position closer to the flat plate, whereas the same operation reduces the focusing efficiency when the radius is large. The study of annular jets can expand the scope of traditional jet research and has the potential to provide new approaches for applications, such as high-throughput inkjet printing and liquid transfer.
A high-speed jet is formed when a pulse force acts on a concave interface of the liquid, which is due to the focus of the momentum on the center of curvature of the interface. We also found that there are fascinating jets in the experiments with a pulse acceleration imposed on the convex liquid interface while the arrangement is limited between two parallel panels. The mechanism of the convex interface jets is analyzed experimentally and numerically in this paper. A droplet with a diameter of approximately 12 mm is generated between two 0.8-mm spacing parallel plates coated with hydrophobic materials. A pulsed laser is focused at the center of the droplet through a convex lens to generate pulsed bubbles so that the movement of the interface is accelerated. The evolution of the liquid jets is observed by high-speed photography. A high-precision numerical method of the interface is established based on the volume of fluid method (VOF) and large eddy simulation (LES), which is enabled to capture the gas-liquid interface and small-scale flow structures exactly. An intriguing jet close to the plate is observed while the concave interface only forms that near the centerline. A charming entrainment phenomenon captured in the development of the jets, is mainly related to the big difference (Δθ) in contact angles between two plates, with a phase diagram given in the present work. Finally, a discussion responding to the influence of different contact angles on the tip velocity of a jet is done, concluding that the jet velocity increases gradually with the enlargement of Δθ to some extent. In addition, the hydrophobic plate, which is regarded as a mirrored plane and reflects the momentum of the fluid, plays a significant role in the formation of hydrophobic jets as well. Our findings offer a new understanding both of the formation of jets and surface cleaning.
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