Jaclyn Lautz

Displacement of particles in microfluidics by laser-generated tandem bubbles

The dynamic interaction between laser-generated tandem bubble and individual polystyrene particles of 2 and 10 μm in diameter is studied in a microfluidic channel (25 μm height) by high-speed imaging and particle image velocimetry. The asymmetric collapse of the tandem bubble produces a pair of microjets and associated long-lasting vortices that can propel a single particle to a maximum velocity of 1.4 m∕s in 30 μs after the bubble collapse with a resultant directional displacement up to 60 μm in 150 μs. This method may be useful for high-throughput cell sorting in microfluidic devices.

Evaluation of Novel Ball-Tip Holmium Laser Fiber: Impact on Ureteroscope Performance and Fragmentation Efficiency.

PURPOSE A novel ball tip (BT) holmium laser fiber has recently been developed, which features a modified rounded tip. The modification is purported to aid in insertion and minimize damage to the ureteroscope working channel. We evaluated this laser fiber with regard to stone comminution, tip degradation, insertional force into the ureteroscope, and impact on ureteroscope deflection. MATERIALS AND METHODS A 242 μm BT fiber and a standard flat tip (SF) fiber were compared. Four kilojoules was delivered to a BegoStone over a constant surface area using settings of 0.2/50, 0.6/6, 0.8/8, and 1 J/10 Hz. Fiber tip degradation was measured at 1 and 4 kJ. Ureteroscope deflection was measured with the Olympus URF-P5, URF-P6, and URF-V. Insertion force into a 270° angled ureteroscope sheath model was measured. RESULTS A sample size of five fibers was used for each comminution energy setting. Comminution increased with pulse energy without significant difference between fibers. No significant differences in tip degradation were observed. Both fibers reduced deflection (10°-30°) in all ureteroscopes without significant differences between fibers. Four new fibers paired with new sheath models were used to test insertion force. The BT insertion forces were approximately one-third of the SF. One SF fiber caused significant damage to the sheath and could not be advanced completely. CONCLUSIONS The BT fiber has comparable comminution, tip degradation, and ureteroscope deflection performance compared with the SF fiber while exhibiting reduced insertion force within an aggressively deflected working sheath. The new tip design is likely protective of the working channel without loss of performance.

A non-axisymmetric, elongated pressure distribution in the lithotripter focal plane enhances stone comminution in vitro during simulated respiratory motion

A challenge in clinical shock wave lithotripsy (SWL) is stone translation due to a patient’s respiratory motion, in a direction perpendicular to shockwave propagation, which may negatively affect stone comminution while increasing the risk of tissue injury. We have developed a method using external masks and a modified lens geometry to transform the axisymmetric pressure distribution in the focal plane of an electromagnetic lithotripter into a non-axisymmetric elliptical distribution. At equivalent acoustic pulse energy (46 mJ), the peak pressure was reduced from 44 MPa to 38 MPa while the −6 dB focal width was increased from 7.4 mm for the original to 11.7 mm (major axis) and 7.9 mm (minor axis) of the modified field. In vitro stone comminution was performed in a tube holder (d = 14 mm) using a translation pattern with 12 breaths per minute and 15 mm in excursion distance. Stone comminution after 1000 shocks are 71.2 ± 4.4% and 65.2 ±8.3% (p < 0.05) along the major- and minor-axis of the modified field, ...

Synergistic interaction between stress waves and cavitation is important for successful comminution of residual stone fragments in shock wave lithotripsy

To assess the role of stress waves and cavitation in comminuting residual fragments during shock wave lithotripsy (SWL), cylindrical 4 × 4 mm BegoStone phantoms were treated in an electromagnetic lithotripter either at the focus (z = 0, p+  = ∼45 MPa) or pre-focally (z = −30 mm, p+  = ∼24 MPa). The treatment was performed with the stone immersed either in degassed water or in Butanediol, which has similar acoustic impedance to water but much higher viscosity to suppress cavitation. At the focus, the first fracture was observed after 26 ± 9 shocks, both in water and Butanediol (p = 0.7). However, when stones were moved pre-focally where comparable cavitation is produced (based on high speed imaging), the average shock number required for the initial fracture was increased to 66 ± 10 in water and 122 ± 20 in Butanediol (p = 0.002). Below −40 mm prefocally (p+  < 20 MPa), stones did not fracture in water even after 2,000 shocks, although cavitation was observed. Furthermore, stone comminution at the focus af...

Respiration gating beam steering to precisely target a movable stone in shock wave lithotripsy

In this study, a foam mask is introduced to elongate the beam width in the focal plane of a shock wave lithotripter, and a respiration gating beam steering strategy is proposed to accurately target stones, which are movable because of patient respiratory motion, radiation force, hydraulics, gravity, etc. The mask is steered to revolve the elongated elliptical focal zone of the acoustic field, so as to cover as much as possible the stone moving area. The beam steering strategy provides the most opportunity to deliver the shock wave energy straightly on the moving stones but not to the peripheral tissues, enhancing the stone fracture efficacy whilst reducing tissue injury. Simulation results with specific stone motion models are given to proof the advantages of the elongated focal zone in tracking stone target, and show that the stone overlap in the focal zone is improved significantly and competitively with the beam steering strategy, compared with no beam steering.

Elimination of cavitation-related attenuation in shock wave lithotripsy

In shock wave lithotripsy (SWL), acoustic pulses with a leading compression wave followed by a tensile wave are delivered into the patient’s body using a water-filled coupling cushion. Cavitation-related acoustic energy loss in the coupling unit depends critically on water conditions, e.g. dissolved gas concentration and exchange flow rate. We have systematically investigated the attenuation mechanism in the coupling water via pressure measurements and cavitation characterization. In non-degassed water the bubble cluster became progressively dense (i.e., proliferated because of gas diffusion into bubbles and splitting of bubbles into many daughter bubbles) in shock waves delivered at 1 Hz leading to reduction in the tensile wave duration from a nominal value of 4.6 to 1.8 µs. To reduce cavitation in the coupling water along the beam path, we have used a continuous jet flow to remove residual daughter bubbles between consecutive shocks. As a result, stone fragmentation efficiency was increased from 16±4% t...

Shockwave tensile phase transmission depends on the gas concentration of the coupling medium

Previous research shows that a shockwave’s tensile phase can be strongly attenuated as a function of gas concentration in the coupling medium. Here, we seek to elucidate the relationship between tensile attenuation and gas concentration via pressure measurements at the focus and highspeed imaging. By performing in vitro experiments with water of varying gas concentrations (2.05 mg/L, 4.30 mg/L, and 6.50 mg/L), the negative impulsive pressure is correlated to the density of the bubble cloud that occurs in the beampath. It is found that for gas contents below 4 mg/L the bubble cloud remains sparse and the shockwave’s tensile phase is successfully transmitted with no loss in impulsive pressure. For gas contents 4 mg/L and above the bubble cloud becomes highly dense and prevents transmission with up to a 75% loss in impulsive pressure. Corresponding stone comminution experiments show that the treatment efficiency sharply decreases with increasing gas concentration. These results underlie the importance of degassing the water used in the coupling medium before treatment.

Dynamics and flow field produced by coupled oscillation of tandem microbubble.

Coupled oscillations of two adjacent laser‐induced microbubbles have been shown to produce unique asymmetric bubble deformation and microjet formation. The resultant microstreaming and shear stress can cause localized cell membrane poration with potential application in targeted drug and gene delivery. In this study, we investigate the bubble dynamics and flow field produced by laser‐generated tandem microbubble in a microfluidic device. Flow field around the tandem microbubble is analyzed with respect to phase delay, inter‐bubble distance, and size ratio between the two microbubbles. In addition, micropatterning technique is used to control the adhesion site and growth pattern of HeLa cells in relation to the tandem microbubble. Flow vorticity is observed to be a key parameter that correlates with the strength of tandem microbubble oscillation and resultant macromolecule uptake efficiency. [Work supported by NIH Grant Nos. R01DK052985, R21CA135221, and S10RR016802].