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Micro-medical devices have found new life in medical applications, offering advanced control, precision, and safety in surgery to augment or sometimes replace surgeons. However, current medical devices’ utility is limited just as a surgeon is, with all the functionality, all but the end tool outside the patient. Many interventional procedures would benefit from having the active medical device scaled down to fit within a few hundred micrometers, to work in the confined space of the eye, vasculature, lymphatic vessels, and so on, enabling complex motion and sensing at such a scale via remote or external control by the surgeon. Due to their inherent rigidity and size, traditional robotic tools cannot be utilized to achieve the desired clinical needs, and are limited to a few hundred niche applications.The projects presented here have been constructed to deliver micro-scale tools for some of the most challenging clinical needs in endovascular surgery and ophthalmology. Endovascular surgical intervention for aneurysm and stroke treatment requires a means to controllably orient a catheter deep within a patient’s cerebral arteries in tortuous, complex, and challenging anatomical locations. The measurement of intraocular pressure is another, for patients with artificial corneas to enable prompt, preventative treatment to avoid glaucomatous damage. The absence of controlled actuation and sensing at the sub-millimeter length scale is the leading cause of procedural failures in these medical applications.Through a novel combination of large aspect ratio, soft-robotic structures and saline-driven micro-hydraulics, dexterous tools to translate commands of surgeons into complex motions within brain arteries are presented. High-resolution pressure sensors are combined with micro-scale needles to enable effective measurement of intraocular pressure for patients with artificial lenses. Unlike passive fundamental studies or bench-top innovations, these projects deliver clinically functional medical devices. These approaches were validated in vivo to assess their performance and the results obtained lay the foundation for an entirely new discipline of dexterous sub-milimeter scale soft robotic tools for surgical intervention and sensing.

Asymmetric surface acoustic waves have been shown useful in separating particles and cells in many microfluidics designs, mostly notably sessile microdroplets. However, no one has successfully extracted target particles or cells for later use from such samples. We present a novel omnidirectional spiral surface acoustic wave (OSSAW) design that exploits a new cut of lithium niobate, 152 Y-rotated, to rapidly rotate a microliter sessile drop to ∼10 g, producing efficient multi-size particle separation. We further extract the separated particles for the first time, demonstrating the ability to target specific particles, for example, platelets from mouse blood for further integrated point-of-care diagnostics. Within ∼5 s of surface acoustic wave actuation, particles with diameter of 5 μm and 1 μm can be separated into two portions with a purity of 83% and 97%, respectively. Red blood cells and platelets within mouse blood are further demonstrated to be separated with a purity of 93% and 84%, respectively. These advancements potentially provide an effective platform for whole blood separation and point-of-care diagnostics without need for micro or nanoscale fluidic enclosures.

Having accurate data to represent hyperelastic materials that underpin soft robotics would facilitate their analysis, design, and validation. We seek to provide the reader with a useful tool to overcome a mundane but crucially important problem in determining the hyperelastic material properties. We show how to employ first dimensionless and then dimensional comparisons between experimental data and the classic theoretical model representing this system to produce C(1) and C(2) for the Mooney–Rivlin model, closely representing a variety of soft polymers.

Catheters used for endovascular navigation in interventional procedures lack dexterity at the distal tip. Neurointerventionists, in particular, encounter challenges in up to 25% of aneurysm cases largely due to the inability to steer and navigate the tip of the micro-catheters through tortuous vasculature to access aneurysms. We overcome this problem with sub-millimeter diameter, hydraulically-actuated hyperelastic polymer devices at the distal tip of micro-catheters to enable active steerability. Controlled by hand, the devices offer complete 3D orientation of the tip. Using saline as a working fluid, we demonstrate guidewire-free navigation, access, and coil deployment in vivo, offering safety, ease of use, and design flexibility absent in other approaches to endovascular intervention. We demonstrate the ability of our device to navigate through vessels and to deliver embolization coils to the cerebral vessels in a live porcine model. This indicates the potential for microhydraulic soft robotics to solve difficult access and treatment problems in endovascular intervention.

The vacuum-exhausted isolation locker (VEIL) provides a safety barrier during the care of COVID-19 patients. The VEIL is a 175-L enclosure with exhaust ports to continuously extract air through viral particle filters connected to hospital suction. Our experiments show that the VEIL contains and exhausts exhaled aerosols and droplets.

Endovascular procedures are limited by an absence of effective actuation methods for navigation and precise device positioning. The existing panoply of passive guidewires and catheters for the treatment of cerebral aneurysms, in particular, leaves neurointerventionists without a treatment option in at least 25% of patients. A key reason is the inability to steer the tip of the microcatheters in vivo. We overcome this problem with sub-millimeter diameter hydraulically-actuated hyperelastic polymer devices connected over a 160 cm length. These provide controlled 3D orientation of acute tip curvatures beyond 180 degrees at pressures of 400kPa that achieves stable coil deployment in vivo. This method uses saline as the working fluid, and forms a closed system from the steerable tip to the hydraulic actuator offering safety, ease of use, and design flexibility absent in approaches that require external actuation. Disclosures T. Gopesh: None. J. Wen: None. D. Santiago-Dieppa: None. B. Yan: None. J. Scott-Pannell: None. A. Khalessi: None. A. Norbash: None. J. Friend: None.

Author(s): Girgis, Alexander M; Aziz, Merna N; Gopesh, Tilvawala C; Friend, James; Grant, Alex M; Sandubrae, Jeffrey A; Banks, Dalia A

Here, we propose an optimized ${Y}$ -rotated cut of lithium niobate (LN) for multidirectional surface acoustic wave (SAW) propagation, simultaneously minimizing the anisotropic effects while maximizing the electromechanical properties of this cut of LN. The goal is to offer a piezoelectric material suitable for acoustofluidics applications that require greater flexibility in wave generation and propagation than the currently ubiquitous $128^{\circ }~{Y}$ -rotated ${X}$ -propagating cut. The 128YX LN cut is known to most effectively generate Rayleigh SAW along the ${x}$ -direction alone. Any SAW veering from this propagation direction is affected by beam steering and changes in resonance frequency and electromechanical coupling coefficients, consequently limiting the use of LN in various acoustofluidics applications, where more diverse configurations would be beneficial. The ${\mathcal {L}_{{2}}}$ -norm of these properties was evaluated under rotational transformation to produce a physical model with closed governing equations for 40-MHz surface wave propagation on the surface of a piezoelectric material. This was then utilized to obtain the surface wave velocity and coupling coefficient of the specific ${Y}$ -cut LN with respect to the propagating direction. Next, the averaged coupling coefficients of various ${Y}$ -cuts of LN in all propagating directions were calculated and integrated to simultaneously minimize anisotropy and maximize the electromechanical properties of the LN substrate. A $152^{\circ }~{Y}$ -rotated cut was found to be the optimal choice under these constraints, enabling multidirectional SAW propagation with greater coupling and lower variation in wave performance for SAW generated across the surface in any direction. Compared with the 128YX LN cut, this cut provides a 66.5% improvement in the in-plane isotropy and a 37.0% improvement in the average electromechanical coupling for in-plane SAW propagation. Experimental devices operating at the frequency of 40 MHz were designed, fabricated, and tested on the surface of this 500- $\mu \text{m}$ -thick specific cut of LN and served to verify the supporting analysis and the superior isotropic properties of the $152^{\circ }~{Y}$ -rotated cut in generating SAW.

Author(s): Gopesh, Tilvawala; Camp, Andrew; Unanian, Michael; Friend, James; Weinreb, Robert N | Abstract: PurposeIntraocular pressure (IOP) is the primary modifiable risk factor for glaucoma. Current devices measure IOP via the dynamic response of the healthy cornea and do not provide the accurate IOP measurements for patients with altered corneal biomechanics. We seek to develop and test an accurate needle-based IOP measurement device that is not cornea dependent.MethodsOur device combines a high-resolution pressure microsensor with 30- and 33-gauge Luer lock needles to provide IOP measurements via a microcontroller and USB interface to a computer. The device was calibrated in a membrane chamber and then tested and validated in the anterior chamber and post-vitrectomy vitreous chamber of rabbit eyes. The results were compared to Tonopen readings across a pressure range of 0 to 100 mm Hg, imposed in increments of 10 mm Hg.ResultsBoth the needle based sensor device and the Tonopen demonstrated a linear relationship with changes in imposed pressure. The Tonopen was found to consistently underestimate the IOP both in the anterior and vitreous chambers. The Tonopen exhibited a significantly greater error than our needle-based sensor device. With increased pressure (g30 mm Hg), the error of the Tonopen increased, whereas the error of our device did not. The 30-gauge needle produces an insignificant improvement in accuracy over the 33-gauge needle.ConclusionsA needle-based sensor device enables accurate IOP measurements over a broad range of induced IOP.Translational relevanceDirect measurement of IOP in the anterior chamber circumvents the influence of corneal parameters on IOP measurement.

Entov and Hinch [J. Non-Newtonian Fluid Mech. 72,31-53 (1997)] predicted a Weissenberg number of 2/3 during capillary thinning of slender filaments of polymer solutions. Data from the experiments of Clasen et al. [J. Rheol. 50, 849-881 (2006)] however show that that is not the case. The Weissenberg number is observed to systematically decrease with concentration in nominally dilute solutions to values well below the critical value of 1/2 for the coil-to-stretch transition to reach a minimum around the critical-overlap concentration c*, and thereafter increase in semidilute solutions. Conformation dependence of the polymeric friction coefficient and the phenomenon of coil-stretch hysteresis are shown to play vital roles in determining capillary thinning dynamics. A key result is that when steady-state coil-stretch hysteresis exists, transient polymer conformations during capillary thinning evolve quasistatically along the unstable manifold of the hysteresis window. It is further found necessary to account for changes in polymeric friction due to intermolecular interactions as chains stretch in the flow. A new constitutive model for unentangled polymer solutions is proposed combining blob concepts to account for the effect of hydrodynamic screening on the average friction coefficient of partially stretched chains. It is shown that stretching causes intermolecular interactions to become stronger in the dilute regime and weaker in semidilute solutions. Predictions with this constitutive model agree well with the experimental data in capillary thinning. (C) 2016 The Society of Rheology.

Acoustic actuation of fluids at small scales may finally enable a comprehensive lab-on-a-chip revolution in microfluidics, overcoming long-standing difficulties in fluid and particle manipulation on-chip. In this comprehensive review, we examine the fundamentals of piezoelectricity, piezoelectric materials, and transducers; revisit the basics of acoustofluidics; and give the reader a detailed look at recent technological advances and current scientific discussions in the discipline. Recent achievements are placed in the context of classic reports for the actuation of fluid and particles via acoustic waves, both within sessile drops and closed channels. Other aspects of micro/nano acoustofluidics are examined: atomization, translation, mixing, jetting, and particle manipulation in the context of sessile drops and fluid mixing and pumping, particle manipulation, and formation of droplets in the context of closed channels, plus the most recent results at the nanoscale. These achievements will enable applications across the disciplines of chemistry, biology, medicine, energy, manufacturing, and we suspect a number of others yet unimagined. Basic design concepts and illustrative applications are highlighted in each section, with an emphasis on lab-on-a-chip applications.

The behaviour of complex fluids can be investigated by subjecting them to controlled rheometric flows such as extensional flow. A uniaxial extensional flow is generated at the necking plane of liquid filaments due to surface tension. Simple stress balances are often used to model capillary thinning dynamics at the necking plane, and extract the extensional viscosity of the sample fluid. Previous modelling studies have focussed on liquids where either viscous or inertial effects are dominant. Experimental observations on the other hand are obtained where effects of viscosity and inertia are both important. The failure to account for both effects simultaneously can cause discrepancies in interpreting experimental data. Here a stress-balance that simultaneously incorporates both viscous and inertial effects is used to predict the evolution of the mid-plane radius as a function of time in capillary thinning experiments. The stress-balance is extended to include non-Newtonian stresses, and is used to study the dynamics of slender filaments of polymer solutions and suspensions of motile microbes. The results of modelling the non-Newtonian fluids are used with new micro-structure based constitutive models for non-Newtonian stresses in extensional flow.