Showing papers by "Scott Bair published in 1995"

Method of using fluid jet surgical cutting tool

Abstract: A pulsed fluid jet surgical instrument includes a cannula extending from a handpiece, the cannula emitting a pulsed fluid jet for cutting and emulsification purposes, and also providing suction for aspiration and evacuation of the fluid and tissue. A pressure intensifier piston arrangement receives fluid at relatively low pressure, and operates reciprocally and reiteratively to pump the fluid through the jet needle in a series of high pressure pulses, each having a nearly rectangular pressure waveform. The pressure intensifier piston is T-shaped, including a broad end which divides a drive bore into a driving chamber and a retracting chamber. A bistable valve is connected to admit high pressure gas into the actuating chamber, driving the piston to translate. The narrow end of the piston is disposed in a fluid pumping chamber connected to a supply of fluid. The translating piston drives the fluid from the pumping chamber through a first check valve into a fluid jet needle, which directs the high pressure fluid pulse to a tissue target. The bistable valve switches to admit pressurized gas to the retracting chamber, driving the piston retrograde and allowing the pumping chamber to refill with fluid through a second check valve. There is no high pressure fluid supplied to the handpiece, and only the pressure intensifying pumping action of the piston creates a high pressure fluid pulse. The gas supply to drive the piston is at a relatively low pressure, so that gas pressure cannot comprise a safety risk to the patient. Thus failure of the piston mechanism cannot result in the emission of a stream of high pressure fluid, and the instrument is inherently safer than prior art instruments that are connected to a high pressure fluid source.

“Recent Developments in High-Pressure Rheology of Lubricants”

Abstract: The rheological response of lubricants to a combination of shear and hydrostatic pressure has held the interest of tribologists working in elastohydrodynamics since it became accepted that thin lubricant films transfer the shear between solids in concentrated contact. Recently developed techniques allow us to probe the shear and bulk behavior of liquids at pressures and rates which overlap the conditions of lubricated concentrated contact. Results of high-pressure rheometry can be used to successfully predict EHD traction. It is now possible to actually view liquids in shear and in compression at high-pressure. Although with the proper assumptions valid traction predictions can be obtained using the concept of homogeneous shear in the load bearing region, flow visualization results require that we rethink previously held concepts of non-Newtonian flow at high-pressure.

Fluid jet surgical cutting tool and aspiration device

Abstract: An instrument for providing high pressure fluid pulses for cutting tissue including an internal pressure intensifying mechanism, and the provision of a suction force at the distal end of the instrument including an internal vacuum generating device to increase the suction force provided by a conventional suction source. A piston mechanism is provided for converting a low pressure fluid input to a high pressure fluid output, and a second piston mechanism is provided to intensify the suction force created by a conventional suction source at the surgical site.

Low shear viscosity and crystallization in dilute solutions of polymers at high pressures: Falling body viscometry of high molecular weight polyethylene solutions

Abstract: A specially designed falling body viscometer has been used to obtain low shear viscosities of dilute solutions of high molecular weight polyethylene in decalin and for detecting phase transitions at high pressures. The method provides valuable rheological data at pressures that correspond to those in lubrication and some extrusion processes. In addition, the method enables detection of phase transitions, such as crystallization, that result in detectable changes in rheology. The influence of pressures as high as 0.6 GPa (∼ 80,000 psi) is illustrated here through a study of crystallization, with verification from light scattering and calorimetry.