To better understand physical mechanisms of stone comminution in Holmium:YAG laser lithotripsy, high-speed microphotography was used to study the breakage of dry stones in air and hydrated stones in water. Surgically retrieved urinary calculi and hydroxyapatite pellets were pulsed with a Holmium:YAG laser at 0.2–1 J and recorded at ∼250 000 fps using a high-speed camera (Shimadzu HPV-X2) mounted to a Nikon microscope. In air, direct light–stone interactions were seen to produce photothermal melting, vaporization, and micro-explosions. The most apparent damage to stones was due to the micro-explosions, which erupt the stone surface producing craters and pits. The micro-explosions, however, were observed to progressively diminish with number of laser shots, typically stalling after several shots. Increasing the laser energy or moving the fiber tip to a new position was seen to restore the occurrence of micro-explosions before stalling a second time. In water, the laser produced cavitation bubbles, the collapse of which continued to fragment, pit, and erode the stone after each laser pulse. This study suggests that cavitation bubbles contribute strongly to stone comminution. Cavitation bubbles may have a particularly important role in sustaining micro-explosions after initial laser shots.

You have accessJournal of UrologyEndourology & Nephrolithiasis (V01)1 Apr 2019V01-04 HIGH-SPEED VIDEO MICROSCOPY INVESTIGATIONS OF THE MECHANISMS OF STONE BREAKAGE WITH HOLMIUM:YAG LASER LITHOTRIPSY Yuri Pishchalnikov*, William Behnke-Parks, Daniel Laser, and Marshall Stoller Yuri Pishchalnikov*Yuri Pishchalnikov* More articles by this author , William Behnke-ParksWilliam Behnke-Parks More articles by this author , Daniel LaserDaniel Laser More articles by this author , and Marshall StollerMarshall Stoller More articles by this author View All Author Informationhttps://doi.org/10.1097/01.JU.0000555076.94037.6cAboutPDF ToolsAdd to favoritesDownload CitationsTrack CitationsPermissionsReprints ShareFacebookLinked InTwitterEmail Abstract INTRODUCTION AND OBJECTIVES: Ureteroscopic laser lithotripsy most commonly uses a Holmium:YAG (Ho:YAG) laser to achieve urinary stone comminution. Stone erosion and fragmentation occurs through photothermal and cavitation-mediated mechanisms. To better understand the process of stone comminution in Ho:YAG laser lithotripsy, stone breakage was investigated in an in vitro model using high-speed video microscopy. METHODS: Surgically retrieved whole urinary calculi (calcium oxalate monohydrate) and model (synthetic hydroxyapatite pellets) stones were pulsed with a Ho:YAG laser delivering single shots at energies ranging from 0.2 to 1 Joules. Video images were captured at ∼250,000 fps using a high-speed camera (Shimadzu HPV-X2, Kyoto, Japan) mounted to a Nikon microscope. To better distinguish different mechanisms of stone fragmentation, laser pulses were delivered to dry stones in air and those hydrated in water . RESULTS: In air, high-speed videography revealed direct light–stone interactions on the stone surface producing photothermal melting, vaporization, and micro-explosions. After several initial (1-20) shots micro-explosions were no longer observed. Termination of the micro-explosions was weakly dependent on the distance between the stone surface and the laser tip. Increasing the laser energy however, restored the occurrence of micro-explosions for additional laser energy delivery before stalling a second time. Additionally, moving the fiber to a new position also restored micro-explosions, producing substantial breakage for the initial (1-20) shots. In water, laser pulses produced a vapor bubble that collapses on the surface of the stone concomitantly with light-stone interactions. Hydrophone measurements suggest this vapor bubble can collapse with sufficient pressure to contribute to stone fragmentation and erosion. Consistent with this finding, direct action of laser light in water upon the stone surface sustained erosion with stone breakage after the initial several shots. CONCLUSIONS: These in vitro findings provide important insights on different mechanisms of stone fragmentation and their interplay during Ho:YAG laser lithotripsy. The direct action of laser light on the stone surface produces substantial breakage that was observed to dramatically diminish in subsequent laser pulses at the same energy and fiber position. This study also suggests that cavitation bubbles contribute to fragmentation and erosion of urinary stones and may also sustain the direct action of laser light on the stone surface in subsequent laser pulses. Source of Funding: Applaud Medical, Inc. San Francisco, CA© 2019 by American Urological Association Education and Research, Inc.FiguresReferencesRelatedDetails Volume 201Issue Supplement 4April 2019Page: e86-e86 Advertisement Copyright & Permissions© 2019 by American Urological Association Education and Research, Inc.MetricsAuthor Information Yuri Pishchalnikov* More articles by this author William Behnke-Parks More articles by this author Daniel Laser More articles by this author Marshall Stoller More articles by this author Expand All Advertisement PDF downloadLoading ...

You have accessJournal of UrologySurgical Technology & Simulation: Instrumentation & Technology I (PD04)1 Apr 2019PD04-01 STONE TARGETING MICROBUBBLES ENHANCE LASER LITHOTRIPSY BY INCREASING FRAGMENTATION AND DECREASING STONE MASS Scott Wiener*, Matt Mellema, Yuri Pishchalnikov, William Behnke-Parks, Daniel Laser, and Marshall Stoller Scott Wiener*Scott Wiener* More articles by this author , Matt MellemaMatt Mellema More articles by this author , Yuri PishchalnikovYuri Pishchalnikov More articles by this author , William Behnke-ParksWilliam Behnke-Parks More articles by this author , Daniel LaserDaniel Laser More articles by this author , and Marshall StollerMarshall Stoller More articles by this author View All Author Informationhttps://doi.org/10.1097/01.JU.0000555049.05233.bcAboutPDF ToolsAdd to favoritesDownload CitationsTrack CitationsPermissionsReprints ShareFacebookLinked InTwitterEmail Abstract INTRODUCTION AND OBJECTIVES: Holmium:YAG lasers fragment urinary stones through both photothermal effects and generation of cavitation bubbles. Improved synthetic stone mass loss has been demonstrated for laser lithotripsy in the presence of stone targeting microbubbles. The present study hypothesizes that lipid-shell microbubbles with stone-binding properties also create smaller and more numerous stone fragments through enhancement of cavitation effects. METHODS: Synthetic hydroxyapatite (HA) discs [13 mm x 1.8 mm] were fragmented with a pulsed 100W Holmium:YAG laser (1000μm fiber) along a circular path 9 mm in diameter over 60 seconds (Figure). This was performed with (n=10) and without (n=10) targeting microbubbles composed of a lipid-shell with calcium-binding moieties and perfluoroalkane gas. HA discs were weighed dry before and after a single lithotripsy session in which all fragments > 0.5mm were recovered using a sieve mesh. Fragments were digitally photographed on a standardized stage such that number, size, and volume of fragments could be calculated using ImageJ software. Comparisons were made with a 2-tailed Mann-Whitney U-test. RESULTS: The mean number of stone fragments was 4.6±1.6 for control vs 6.9±1.9 (p=0.02) for targeting microbubbles. The median fragment volume was 31 mm3 (IQR 21-67) for control and 26 mm3 (IQR 10-45) for targeting microbubbles (p=0.041). Mean stone mass loss was 3.9±3 mg for control vs. 11.3±5 mg for targeting microbubbles (p=0.045). CONCLUSIONS: Targeting microbubbles fragment HA stones into smaller and more numerous fragments during in vitro Holmium:YAG laser lithotripsy in addition to causing increased mass loss. Stone targeting microbubbles, when used as an adjunct with Holmium laser lithotripsy, have the potential to reduce operative time, increase the number and decrease the size of stone fragments, and thereby result in higher stone-free rates and improved patient outcomes. Source of Funding: Study funded by Applaud Medical San Francisco, CA© 2019 by American Urological Association Education and Research, Inc.FiguresReferencesRelatedDetails Volume 201Issue Supplement 4April 2019Page: e73-e73 Advertisement Copyright & Permissions© 2019 by American Urological Association Education and Research, Inc.MetricsAuthor Information Scott Wiener* More articles by this author Matt Mellema More articles by this author Yuri Pishchalnikov More articles by this author William Behnke-Parks More articles by this author Daniel Laser More articles by this author Marshall Stoller More articles by this author Expand All Advertisement PDF downloadLoading ...

A novel treatment modality incorporating calcium-adhering microbubbles has recently entered human clinical trials as a new minimally-invasive approach to treat urinary stones. In this treatment method, lipid-shell gas-core microbubbles can be introduced into the urinary tract through a catheter. Lipid moities with calcium-adherance properties incorporated into the lipid shell facilitate binding to stones. The microbubbles can be excited by an extracorporeal source of quasi-collimated ultrasound. Alternatively, the microbubbles can be excited by an intraluminal source, such as a fiber-optic laser. With either excitation technique, calcium-adhering microbubbles can significantly increase rates of erosion, pitting, and fragmentation of stones. We report here on new experiments using high-speed photography to characterize microbubble expansion and collapse. The bubble geometry observed in the experiments was used as one of the initial shapes for the numerical modeling. The modeling showed that the bubble dynamics strongly depends on bubble shape and stand-off distance. For the experimentally observed shape of microbubbles, the numerical modeling showed that the collapse of the microbubbles was associated with pressure increases of some two-to-three orders of magnitude compared to the excitation source pressures. This in-vitro study provides key insights into the use of microbubbles with calcium-adhering moieties in treatment of urinary stones.

We report on engineered microbubbles designed to accumulate on surfaces of urinary stone and facilitate stone comminution through mechanical effects including inertial collapse and pressure focusing against the urinary stone surface. In one current application of these engineered microbubbles, small quantities of engineered microbubbles, suspended in an aqueous solution, are placed in the patient's upper urinary tract via a cystoscopically positioned catheter and energized by quasi-collimated beams of acoustic energy emanating from a treatment head positioned on the patient's lower back, with the peak pressures of the beam in the range of diagnostic ultrasound. Noninvasive acoustic monitoring of microbubble dynamics and correlating signatures of inertial collapse with treatment parameters presents a promising strategy for gaining further insights on the mechanism of action as well as intra-treatment monitoring for improving clinical outcomes. To explore this detection strategy, we seek to compare the change in mass loss of model stones and the inertial collapse of the microbubbles measured via acoustic spectroscopy as a function of time and pressure.

Ultra-high-speed video microscopy and numerical modeling were used to assess the dynamics of microbubbles at the surface of urinary stones. Lipid-shell microbubbles designed to accumulate on stone surfaces were driven by bursts of ultrasound in the sub-MHz range with pressure amplitudes on the order of 1 MPa. Microbubbles were observed to undergo repeated cycles of expansion and violent collapse. At maximum expansion, the microbubbles' cross-section resembled an ellipse truncated by the stone. Approximating the bubble shape as an oblate spheroid, this study modeled the collapse by solving the multicomponent Euler equations with a two-dimensional-axisymmetric code with adaptive mesh refinement for fine resolution of the gas-liquid interface. Modeled bubble collapse and high-speed video microscopy showed a distinctive circumferential pinching during the collapse. In the numerical model, this pinching was associated with bidirectional microjetting normal to the rigid surface and toroidal collapse of the bubble. Modeled pressure spikes had amplitudes two-to-three orders of magnitude greater than that of the driving wave. Micro-computed tomography was used to study surface erosion and formation of microcracks from the action of microbubbles. This study suggests that engineered microbubbles enable stone-treatment modalities with driving pressures significantly lower than those required without the microbubbles.

Urinary stone lithotripsy critically depends on the presence of cavitation nuclei at the stone surface. We hypothesized that introduction of stone-targeting microbubbles could increase cavitation activity at a stone surface sufficiently to allow stone erosion and fragmentation at peak negative pressures much lower than in acoustic energy-based urinary stone interventions with induced cavitation nuclei alone. Gas-filled microbubbles were produced with calcium-binding moieties incorporated into an encapsulating lipid shell. Stone surface coverage with these targeting microbubbles was found to approach an optimal (considering microbubble expansion during insonation) range of 5–15% with incubation times of three minutes or less. Using high-speed photomicroscopy, we observe bound microbubbles expanding 10- to 30-fold under insonation with quasi-collimated sources at mechanical indexes below 1.9. For observed stand-off parameters in the range of 0.2–0.6, the modeled collapse-generated shockwaves exceed 100 MPa. In swine model studies with these targeting microbubbles, stone fragmentation into passable fragments occurs with treatment times around 30 minutes, while post-treatment examination of ureters and kidneys shows no evidence of urothelium damage or renal parenchymal hemorrhage. The stone-targeting microbubbles reported on here have formed the basis for a new non-invasive urinary stone treatment which recently entered human clinical trials.

You have accessJournal of UrologyUrolithiasis & Endourology1 Apr 2018V03-03 TARGETING MICROBUBBLE ENHANCEMENT OF HOLMIUM LASER STONE ABLATION Scott Wiener, Matt Mellema, Yuri Pishchalnikov, William Behnke-Parks, Daniel Laser, and Marshall Stoller Scott WienerScott Wiener More articles by this author , Matt MellemaMatt Mellema More articles by this author , Yuri PishchalnikovYuri Pishchalnikov More articles by this author , William Behnke-ParksWilliam Behnke-Parks More articles by this author , Daniel LaserDaniel Laser More articles by this author , and Marshall StollerMarshall Stoller More articles by this author View All Author Informationhttps://doi.org/10.1016/j.juro.2018.02.828AboutPDF ToolsAdd to favoritesDownload CitationsTrack CitationsPermissionsReprints ShareFacebookTwitterLinked InEmail INTRODUCTION AND OBJECTIVES Holmium laser lithotripsy is the most common method of stone fragmentation during the ureteroscopic management of calculi in the United States. The laser achieves the therapeutic effect of stone fragmentation through multiple mechanisms, including a photothermic effect and the generation of cavitation bubbles and shockwaves at the interface of urine/fluid and the stone. We hypothesized that lipid-shell microbubbles with stone-binding properties could enhance stone fragmentation in holmium laser lithotripsy through enhancement of cavitation effects. METHODS Synthetic hydroxyapatite pellets and a pulsed holmium:YAG laser were used for the studies. Targeting microbubbles were acquired from a clinical trial-stage insonation-based stone treatment product. The microbubbles are a lipid-shell perfluoroalkane gas configuration with calcium-binding moieties incorporated into the shell to facilitate stone targeting. The laser settings were 0.2 Joules at 10 Hertz for 30 pulses per cycle. A high-speed Shimadzu Hyper Vision HPV-X2 camera (Shimadzu, Kyoto, Japan) was used to capture still and video images of the action of the targeting microbubbles and other pressure effects around the stone during laser pulsing. Pellets were weighed before and after each of 6 cycles, and ablation in the microbubble-inclusive runs was compared to a no-targeting-microbubble control with a two-tailed t-test. RESULTS Holmium laser ablation resulted in a mean loss of 6.0 ± .81 mg of hydroxyapatite per 30 pulse cycle at 0.2 Joules without targeting microbubles and 10.2 ± .98 mg per cycle with targeting microbubbles with a p value of <0.01. Under high speed videography, the lipid-shell targeting microbubbles are seen to expand and collapse violently in response to pressure waves emanating from the fiber tip. Furthermore, the targeting microbubbles appear to form clusters on the stone surface, and to expand and collapse in response to the laser generated shockwaves. CONCLUSIONS Targeting microbubbles appear to increase the per-cycle volume of ablated stone by holmium:YAG laser energy by 70%. Targeting microbubbles could improve the lithotripsy phase of endoscopic stone procedures resulting in decreased operative time, higher stone-free rates, and thereby improved patient outcomes during holmium laser lithotripsy. © 2018FiguresReferencesRelatedDetails Volume 199Issue 4SApril 2018Page: e322 Advertisement Copyright & Permissions© 2018MetricsAuthor Information Scott Wiener More articles by this author Matt Mellema More articles by this author Yuri Pishchalnikov More articles by this author William Behnke-Parks More articles by this author Daniel Laser More articles by this author Marshall Stoller More articles by this author Expand All Advertisement Advertisement PDF downloadLoading ...

You have accessJournal of UrologySurgical Technology & Simulation: Instrumentation & Technology II1 Apr 2018PD22-11 ABSENCE OF URETERAL/RENAL INJURY FOLLOWING LOW INTENSITY EXTRACORPOREAL ACOUSTIC ENERGY LITHOTRIPSY WITH STONE-TARGETING MICROBUBBLES IN AN IN VIVO SWINE MODEL Matthew Mellema, William Behnke-Parks, Alice Luong, Matthew Hopcroft, Claire Mills, Sunita Ho, Ryan Hsi, Daniel Laser, Thomas Kenny, Robert Grubbs, and Marshall Stoller Matthew MellemaMatthew Mellema More articles by this author , William Behnke-ParksWilliam Behnke-Parks More articles by this author , Alice LuongAlice Luong More articles by this author , Matthew HopcroftMatthew Hopcroft More articles by this author , Claire MillsClaire Mills More articles by this author , Sunita HoSunita Ho More articles by this author , Ryan HsiRyan Hsi More articles by this author , Daniel LaserDaniel Laser More articles by this author , Thomas KennyThomas Kenny More articles by this author , Robert GrubbsRobert Grubbs More articles by this author , and Marshall StollerMarshall Stoller More articles by this author View All Author Informationhttps://doi.org/10.1016/j.juro.2018.02.1179AboutPDF ToolsAdd to favoritesDownload CitationsTrack CitationsPermissionsReprints ShareFacebookTwitterLinked InEmail INTRODUCTION AND OBJECTIVES Reducing the stone-fragmenting extracorporeal acoustic energy threshold to levels ten- to fifty-fold lower than conventional shockwave lithotripsy makes stone-targeting microbubbles promising for urinary stones. Intermittent placement of microbubbles in the ureter obviates conventional shockwave lithotripsy's need for energy-intensive bubble nucleation as a precondition of inertial cavitation and localized bubble-associated shockwave generation. We sought to understand local safety outcomes through studies in a swine model. METHODS A treatment head with four centimeter-scale piezeoelectric elements within a rigid biocompatible housing functioned as a source of quasi-collimated extracorporeal acoustic energy. Targeting microbubble material was produced by aseptically manufacturing a lipid-perfluoroalkane gas blend and batch-filling into vials. The targeting moiety in the microbubble formulation is based on a phosphonate structure, conferring binding affinity for calcium constituents of urinary stones. Anesthetized juvenile swine (25-35 kg) were used as models of the human urinary tract. Calcium-based stones (both synthetic hydroxyapatite and de-identified human stones) were implanted. Milliliter-scale quantities of targeting microbubbles were cystoscopically placed via a 5 Fr ureteral catheter. RESULTS With quad-amplifier operation in a low-mid ultrasound frequency range (300kHz-1 MHz), the measured peak negative pressures (derated) were 1.2 MPa +/- 0.2 MPa within a treatment area extending to a depth of 14 cm from the treatment head face. With head aiming based on bony landmarks and microbubble placement every 90 seconds, fragmentation of 4-5 mm stones into fragments less than 2mm was achievable with a treatment time less than 30 minutes. Evidence of urothelium damage and renal parenchymal hemorrhage is consistently and entirely absent on histological and gross anatomical examination of post-procedure ureters and kidneys [Figure 1]. CONCLUSIONS Studies in the swine model indicate that combining stone-targeting microbubbles with low-intensity quasi-collimated extracorporeal acoustic energy can achieve urinary stone fragmentation without any visible injury to the urothelium or kidney parenchyma. © 2018FiguresReferencesRelatedDetails Volume 199Issue 4SApril 2018Page: e479 Advertisement Copyright & Permissions© 2018MetricsAuthor Information Matthew Mellema More articles by this author William Behnke-Parks More articles by this author Alice Luong More articles by this author Matthew Hopcroft More articles by this author Claire Mills More articles by this author Sunita Ho More articles by this author Ryan Hsi More articles by this author Daniel Laser More articles by this author Thomas Kenny More articles by this author Robert Grubbs More articles by this author Marshall Stoller More articles by this author Expand All Advertisement Advertisement PDF downloadLoading ...

Kidney stone disease is endemic. Extracorporeal shockwave lithotripsy was the first major technological breakthrough where focused shockwaves were used to fragment stones in the kidney or ureter. The shockwaves induced the formation of cavitation bubbles, whose collapse released energy at the stone, and the energy fragmented the kidney stones into pieces small enough to be passed spontaneously. Can the concept of microbubbles be used without the bulky machine? The logical progression was to manufacture these powerful microbubbles ex vivo and inject these bubbles directly into the collecting system. An external source can be used to induce cavitation once the microbubbles are at their target; the key is targeting these microbubbles to specifically bind to kidney stones. Two important observations have been established: (i) bisphosphonates attach to hydroxyapatite crystals with high affinity; and (ii) there is substantial hydroxyapatite in most kidney stones. The microbubbles can be equipped with bisphosphonate tags to specifically target kidney stones. These bubbles will preferentially bind to the stone and not surrounding tissue, reducing collateral damage. Ultrasound or another suitable form of energy is then applied causing the microbubbles to induce cavitation and fragment the stones. This can be used as an adjunct to ureteroscopy or percutaneous lithotripsy to aid in fragmentation. Randall's plaques, which also contain hydroxyapatite crystals, can also be targeted to pre‐emptively destroy these stone precursors. Additionally, targeted microbubbles can aid in kidney stone diagnostics by virtue of being used as an adjunct to traditional imaging methods, especially useful in high‐risk patient populations. This novel application of targeted microbubble technology not only represents the next frontier in minimally invasive stone surgery, but a platform technology for other areas of medicine.

We survey progress over the past 25 years in the development of microscale devices for pumping fluids. We attempt to provide both a reference for micropump researchers and a resource for those outside the field who wish to identify the best micropump for a particular application. Reciprocating displacement micropumps have been the subject of extensive research in both academia and the private sector and have been produced with a wide range of actuators, valve configurations and materials. Aperiodic displacement micropumps based on mechanisms such as localized phase change have been shown to be suitable for specialized applications. Electroosmotic micropumps exhibit favorable scaling and are promising for a variety of applications requiring high flow rates and pressures. Dynamic micropumps based on electrohydrodynamic and magnetohydrodynamic effects have also been developed. Much progress has been made, but with micropumps suitable for important applications still not available, this remains a fertile area for future research.

We are developing a class of electroosmotic micropumps fabricated from silicon substrates that can be used for integrated circuit thermal management applications. Prototype micropumps with 0.15 cm/sup 3/ packages produce a maximum flow rate of 170 /spl mu/L min/sup -1/ and a maximum pressure of 10 kPa operating at 400 V. These specifications approach the requirements for single-phase forced-convective cooling of small IC hot spots. The micropumps operate on less than 200 mW and, having no moving structural elements, offer inherent reliability advantages. The impact on pump performance of geometry, surface treatment, and choice of working fluid has been characterized.

Electroosmotic micropumps manufactured on silicon substrates using standard micromachining processes can generate pressures of 6 kPa and flow rates of 13 µL/min at 400 V.We present a novel micromachined silicon electroosmotic micropump structure that dramatically reduces die size requirements.We have investigated the prospects for using electroosmotic micropumps in microscale fluidic actuation by integrating a silicon membrane structure into the pump system.By monitoring the velocity of the membrane using a laser vibrometer, we have characterized the micropump's pressure response on timescales below 100 milliseconds.The silicon electrosmotic micropumps studied are found to have a finite pressure response within 10 ms of power activation.Maximum pressure generation, however, appears to take place on a much longer timescale.

We have developed a micromachined silicon parallel-plate electroosmotic pump. A silicon nitride dielectric thin film insulates the etched silicon substrate of the micropump, allowing it to operate at electrical potentials up to 500 volts. Standard silicon micromachining processes are used to fabricated the pump. Like all electroosmotic pumps, this micropump has the advantages of simple architecture, no moving parts, low power consumption, and robust operation. A recently-fabricated prototype micropump of this design generates flow rates in excess of 5 μL/min using deionized water as the working fluid. The finite thickness of the electric double layer must be taken into account when modeling the performance of this electroosmotic pump.