Rapid and Accurate Pressure Sensing Device for Direct Measurement of Intraocular Pressure.

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 (>30 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

Motility induced changes in viscosity of suspensions of swimming microbes in extensional flows

Suspensions of motile cells are model systems for understanding the unique mechanical properties of living materials which often consist of ensembles of self-propelled particles. We present here a quantitative comparison of theory against experiment for the rheology of such suspensions. The influence of motility on viscosities of cell suspensions is studied using a novel acoustically-driven microfluidic capillary-breakup extensional rheometer. Motility increases the extensional viscosity of suspensions of algal pullers, but decreases it in the case of bacterial or sperm pushers. A recent model [Saintillan, Phys. Rev. E, 2010, 81:56307] for dilute active suspensions is extended to obtain predictions for higher concentrations, after independently obtaining parameters such as swimming speeds and diffusivities. We show that details of body and flagellar shape can significantly determine macroscale rheological behaviour.Comment: 12 pages, 1 appendix, 7 figures, submitted to Soft Matter - under revie

Micro-to-meso scale approaches for deformable soft robots and sensing capabilities in biomedical microdevices

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

Micro-to-meso scale approaches for deformable soft robots and sensing capabilities in biomedical microdevices

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

Using inertia-viscous stress-balances to model the mid-filament dynamics of capillary-thinning of Newtonian and non-Newtonian liquid bridges

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