Fragmentation of brittle material by shock wave lithotripsy. Momentum transfer and inertia: a novel view on fragmentation mechanisms

The interaction of shock waves with biological tissue - momentum transfer, the key for tissue stimulation and fragmentation

BACKGROUND

Shock waves in medicine have gained enormous importance and have spread since 1980, and the first kidney stone was successfully fragmented in a patient in Munich. Meanwhile, the spectrum of medical applications of shock waves ranges from powerful fragmentation of kidney stones to diverse indications such as wound healing, chronic pelvic pain, spasticity, erectile dysfunction, and others, to neuro-stimulation in the context of Alzheimer's disease. A comprehensive working mechanism for this diverse field of medical indications is still missing.

OBJECTIVE

Investigation of the physical basis of the working mechanism of shock waves in medical applications.

METHODS

We developed a model based on the mechanical forces generated by the momentum transfer at the acoustic interfaces of different layers of biological tissue. The generated forces are strong enough to crash brittle material and provide an adequate mechanical stimulus to activate mechano-transduction and mechano-sensory-transduction with nerve stimulation, thereby affecting the neural memory function of the central nervous system.

RESULTS

The key to generating appropriate forces in the millisecond range is the mechanism of momentum transfer at the interfaces between tissue layers with different acoustic impedances. According to Newton's laws of motion, a change in momentum (momentum transfer) generates force F = d P /d t . The inherent shear forces can stretch biological membranes to release biomolecules such as vascular endothelial growth factor and nitric oxide. A most favorable feature of this mechanism is the selective effect on soft tissue interfaces and small tissue inhomogeneities to generate small forces in the range of few (≤10) Newton to stimulate tissue and nerve cells, while the same shock wave can generate forces ≥200 Newton and more on hard tissue interfaces such as bones or stones.

CONCLUSION

The mechanism of momentum transfer is the basis for mechano-transduction and mechano-sensory transduction. It offers the opportunity to stimulate peripheral nerves and modify the motor reflex patterns of "pathologic" reflexes by hyper stimulation. The new technique of transcranial pulse stimulation may be based on direct stimulation and reactivation of neurons in the brain. Momentum transfer is the basic physical mechanism and the initiator for successive biological processes in medical shock wave therapy.

Ultrasonic-assisted preparation of SBS modified asphalt: Cavitation bubble numerical simulation and rheological properties

SBS (styrene-butadiene-styrene block copolymer) is currently the most widely used asphalt modifier, and SBS modified asphalt is usually prepared by high-speed shearing. This paper combines the cavitation effect of ultrasonic to assist in the preparation of SBS modified asphalt, and conducts numerical simulation and rheological properties research on the cavitation bubbles in the molten SBS modified asphalt fluid. The cavitation bubbles in the modified asphalt fluid will expand and contract as the pressure changes inside and outside the bubbles. When the cavitation bubble is compressed to the minimum and the pressure inside the bubble reaches 1.94 × 105Pa, the direction of the velocity vector near the cavitation bubble will change with the expansion and compression of the bubble. The expansion-contraction process of a single cavitation bubble can release 6.41 × 10-7J of energy, thus breaking the long bonds in asphalt and generating a large number of free radicals react with the unsaturated C = C bonds in the SBS molecules. According to the preparation process of modified asphalt, the influence of ultrasonic wave on rheological property of modified asphalt was studied through experiments. The results show that ultrasonic treatment can enhance the elasticity of asphalt and improve the temperature sensitivity of asphalt. With the increase of ultrasonic treatment time, the anti-rutting deformation ability of SBS modified asphalt is greatly improved. At the same temperature, the recovery rate of asphalt also increases with the increase of ultrasonic treatment time, and the non-recoverable compliance (Jnr) decreases Combined with the numerical simulation of cavitation bubbles, the ultrasonic process is added to asphalt production, which is of great significance for the green production of modified asphalt and the improvement of the rheological properties of modified asphalt.

Use of artificial stones in training and laboratory studies, have we found the right material? Outcomes of a systematic review from the European School of Urology

Objective

In this review, we investigated the current literature to find out which artificial stones (AS) are available in endourology, and in which experimental and training schemes they are used.

Materials and Methods

A systematic review was performed according to the Preferred Reporting Items for Systematic Reviews and Meta-Analyses statement. Twenty-one out of 346 studies met our inclusion criteria and are presented in the current review. The inclusion criteria were the existence of AS and their use for laboratory and training studies.

Results

There is a wide variety of materials used for the creation of AS. BegoStone powder (BEGO USA, Lincoln, Rhode Island) and plaster of Paris™ were used in most of the studies. In addition, Ultracal-30 (U. S. Gypsum, Chicago, IL) was also used. Other materials that were used as phantoms were AS created from plaster (Limbs and Things, UK), standardized artificial polygonal stone material (Chaton 1028, PP13, Jet 280; Swarovski), model stones consisting of spheres of activated aluminum (BASF SE, Ludwigshafen am Rhein, Deutschland), Orthoprint (Zhermack, Badia Polesine, Italy), and a combination of plaster of Paris, Portland cement, and Velmix (calcium sulfate powder). Many experimental settings have been conducted with the use of AS. Our research demonstrated nine studies regarding testing and comparison of holmium: yttrium-aluminum-garnet laser devices, techniques, and settings. Six studies were about extracorporeal shock wave lithotripsy testing and settings. Three experiments looked into treatment with percutaneous nephrolithotomy. Additionally, one study each investigated imaging perioperatively for endourological interventions, stone bacterial burden, and obstructive uropathy.

Conclusion

AS have been used in a plethora of laboratory experimental studies. Independent of their similarity to real urinary tract stones, they present a tremendous potential for testing and training for endourological interventions.

High-frequency shock wave lithotripsy: stone comminution and evaluation of renal parenchyma injury in a porcine ex-vivo model

BACKGROUND

The electrohydraulic high-frequency shock wave (Storz Medical, Taegerwilen, Switzerland) is a new way to create small fragments with frequencies up to 100 Hertz (Hz). This study evaluated the efficacy and safety of this method in a stone and porcine model.

MATERIALS AND METHODS

BEGO stones were put in a condom in a specifically designed fixture treated with different modulations to see stone comminution. Standardized ex vivo porcine model with perfused kidneys with 26 upper and lower poles of 15 kidneys was treated with the following modulations: voltage 16-24 kV, capacitor 12 nF and frequency up to 100 Hz. 2000-20,000 shock waves were applied to each pole. The kidneys were perfused with barium sulfate solution (BaSO4) and x-ray was performed to quantify the lesions using pixel volumetry.

RESULTS

There was no correlation between the number of shock waves and the powdering degree or the applied Energy and the grade of pulverization in the stone model. Regarding the perfused kidney model, the number of shock waves, applied voltage and frequency had no direct correlation with the occurrence of parenchymal lesions The detected lesions of the renal parenchyma were minimal, technical parameters had no significant impact and the lesions did not differ from the results of former experiments using 1-1.5 Hz in the same model.

CONCLUSIONS

High-frequency shock wave lithotripsy can produce small stone fragments to pass in a very short time. The injury to the renal parenchyma is comparable to the results of the conventional SWL using 1-1.5 Hz.

GeoBioMed perspectives on kidney stone recurrence from the reactive surface area of SWL-derived particles

Shock wave lithotripsy (SWL) is an effective and commonly applied clinical treatment for human kidney stones. Yet the success of SWL is counterbalanced by the risk of retained fragments causing recurrent stone formation, which may require retreatment. This study has applied GeoBioMed experimental and analytical approaches to determine the size frequency distribution, fracture patterns, and reactive surface area of SWL-derived particles within the context of their original crystal growth structure (crystalline architecture) as revealed by confocal autofluorescence (CAF) and super-resolution autofluorescence (SRAF) microscopy. Multiple calcium oxalate (CaOx) stones were removed from a Mayo Clinic patient using standard percutaneous nephrolithotomy (PCNL) and shock pulse lithotripsy (SPL). This produced approximately 4-12 mm-diameter PCNL-derived fragments that were experimentally treated ex vivo with SWL to form hundreds of smaller particles. Fractures propagated through the crystalline architecture of PCNL-derived fragments in a variety of geometric orientations to form rectangular, pointed, concentrically spalled, and irregular SWL-derived particles. Size frequency distributions ranged from fine silt (4-8 μm) to very fine pebbles (2-4 mm), according to the Wentworth grain size scale, with a mean size of fine sand (125-250 μm). Importantly, these SWL-derived particles are smaller than the 3-4 mm-diameter detection limit of clinical computed tomography (CT) techniques and can be retained on internal kidney membrane surfaces. This creates clinically undetectable crystallization seed points with extremely high reactive surface areas, which dramatically enhance the multiple events of crystallization and dissolution (diagenetic phase transitions) that may lead to the high rates of CaOx kidney stone recurrence after SWL treatment.

Factors affecting the irrigation fluid temperature during laser lithotripsy: in vitro experimental study

OBJECTIVE

To investigate the effect of the diameter of laser fiber, pelvis volume, presence and type of the stone on irrigation fluid temperature rise.

MATERIAL AND METHODS

A 20ml syringe, 12/14 ureteral access sheath(UAS), a dual-lumen catheter and a thermocouple were used.  The 12/14Fr UAS(Cook Ireland Ltd., Limerick, Ireland) and the Thermocouple(SE001, Pico Technologies, Cambridgeshire, UK) were inserted in the syringe. The syringe was closed allowing outflow from the UAS with rate at 10ml/min. The Quanta Ho 150W(Quanta System, Samarate, Italy) laser was used and fired with 10W(2Jx5Hz), 20W(2 × 10 Hz), 40W(2 × 20 Hz), 60W(2 × 30 Hz). These power settings were tested in different conditions: fibers(200µm, 365µm and 550µm), volumes(5ml, 10ml and 20ml) and artificial stones(soft, hard). The laser was activated for 30 seconds and reactivation was performed when the temperature reached below 26 ⁰C.

RESULTS

For all trials 60W of energy resulted in higher temperature rise. No differences were observed when different fibers were used. The highest temperatures (up to 80 ⁰C) for 60W were reported in 5ml syringe and the lowest (<45 ⁰C) with 20ml.  The maximal temperature of >59°C was recorded for the power of 60W(1Jx60Hz). The temperature exceeded 43 ⁰C when power settings >40W were applied.

CONCLUSION

Increasing the overall power, increases the irrigation fluid temperature significantly. The smaller the volume of the pelvis, the greater the temperature elevation. The fiber size did not affect the temperature increase pattern. The presence of artificial stones was associated with the absorption of energy emitted by the laser.

What is the impact of pulse modulation technology, laser settings and intraoperative irrigation conditions on the irrigation fluid temperature during flexible ureteroscopy? An in vivo experiment using artificial stones

PURPOSE

To investigate the effect of different combinations of laser power settings and irrigation conditions using the pulse modulation technology of Quanta™ on irrigation fluid temperature (IFT) during FURS (flexible ureteroscopy) on an in-vivo porcine model with artificial stones.

MATERIALS AND METHODS

A female pig was used. Following the insertion of artificial stones (Begostone™, BEGO USA, Lincoln, RI), a K-type thermocouple was fixed to the created percutaneous access tract. Real-time recordings of IFT during FURS were performed without UAS (ureteral access sheath), with 10/12 UAS, 12/14 UAS and 14/16 UAS. Stone fragmentation was achieved using Quanta Litho Cyber Ho 150 W™ (Samarate, Italy). The IFT was recorded for 30 s, during laser activation, with power settings of 20, 40, 60, 75 and 100 W under both manual pump and gravity irrigation.

RESULTS

The IFT rise above 54 °C was recorded above a power of 40 W when gravity irrigation was used. The use of UAS prolonged the time for IFT to reach high values, although high power settings increase IFT within seconds from the laser activation. Under pump irrigation, only the 100 W power setting without the use of UAS resulted in dangerous IFT after approximately 10 s.

CONCLUSION

The high-power Ho:YAG laser can cause a damaging thermal effect to the kidney exceeding the threshold of 54 °C, under gravity irrigation. Lower power settings (up to 40 W) can be used with safety. According to our experiment, when using high power settings, the use of UAS and manual pump irrigation, is the safest combination regarding renal thermal damage.

Multiphysics Analysis of Ultrasonic Shock Wave Lithotripsy and Side Effects on Surrounding Tissues

Background:

Today, the most common method for kidney stone therapy is extracorporeal shock wave lithotripsy. Current research is a numerical simulation of kidney stone fragmentation via ultrasonic shock waves. Most numerical studies in lithotripsy have been carried out using the elasticity or energy method and neglected the dissipation phenomenon. In the current study, it is solved by not only the linear acoustics equation, but also the Westervelt acoustics equation which nonlinearity and dissipation are involved.

Objective:

This study is to compare two methods for simulation of shock wave lithotripsy, clarifying the effect of shock wave profiles and stones’ material, and investigating side effects on surrounding tissues

Material and Methods:

Computational study is done using COMSOL Multiphysics, commercial software based on the finite element method. Nonlinear governing equations of acoustics, elasticity and bioheat-transfer are coupled and solved.

Results:

A decrease in the rise time of shock wave leads to increase the produced acoustic pressure and enlarge focus region. The shock wave damages kidney tissues in both linear and nonlinear simulation but the damage due to high temperature is very negligible compared to the High Intensity Focused Ultrasound (HIFU).

Conclusion:

Disaffiliation of wave nonlinearity causes a high incompatibility with reality. Stone’s material is an important factor, affecting the fragmentation

In-vitro comparison of two electromagnetic shock-wave generators: low-pressure-wide focus versus high-pressure small focus - the impact on initial stone fragmentation and final stone comminution

CONTEXT

Recently developed concepts for higher efficacy ESWL with low-pressure wide focus systems resulting in finer fragmentation of the calculi.

OBJECTIVE

To compare two different electromagnetic shock wave sources (low-pressure wide focus (XL) versus high-pressure small focus (SL)) by sound-field measurements and in-vitro fragmentation.

EVIDENCE ACQUISITION

The CS-2012A XX-ES lithotripter (self-focusing electromagnetic shock-wave generator with concave spherical curved electrical coil; Xinin Lithotripter = XL) was compared to the Siemens Lithoskop (= SL) (electromagnetic generator with a flat electric coil with an acoustical lens). Different sound-field measurements were performed using a fiber-optic hydrophone. Measurements at three different power settings (XL: 8.0kV, 9.3kV and 10.3kV; SL: Level 1, 5 and 8). 10 ATS-stones and 15 BegoStones (9.3 kV, Level 3) with a frequency of 90/minute (SL) and 20/minute (XL). Number of impulses to the first crack and for complete stone comminution (residual fragments <2mm) were documented.

RESULTS

The median number of shock waves for the first crack in ATS-stones with the XL was 12 (10-14), with the SL 7 (6-9). Complete disintegration was accomplished after 815 (782-824) shock waves with XL, 702 (688-712) with SL. The difference was not statistically significant. The median number of shock waves to produce the first crack in BegoStones was 524 (504-542) with XL and only 151 (137-161) with SL. Numbers of shock waves for complete disintegration did not differ significantly (XL:2518 vs SL:2287). Using a wide focus with low pressure shows more homogeneous disintegration.

CONCLUSION

Two stone models showed significant differences regarding form and time of the initial fragmentation. Impulses for stone comminution did not differ significantly. The advantages of a low-pressure wide focus-system include minimal trauma and a homogeneous fragment size but is more time consuming. High-pressure small focus systems are clinically effective.

Extracorporeal shock wave therapy: an update

Extracorporeal shock wave therapy (ESWT) is a safe therapy and there are only a few side effects known (such as pain during ESWT and minor haematomata), but no severe complications are to be expected if it is performed as recommended.

Contraindications are severe coagulopathy for high-energy ESWT, and ESWT with focus on the foetus or embryo and focus on severe infection.

The effect mechanism of ESWT is still a component of diverse studies, but as far as we can summarize today, it is a similar process to a cascade triggered by mechano-transduction: mechanical energy causes changes in the cellular skeleton, which provokes a reaction of the cell core (for example release of mRNA) to influence diverse cell structures such as mitochondria, endoplasmic reticulum, intracellular vesicles, etc., so the enzymatic response leads to the improvement of the healing process.

The usage of ESWT should be taught, to improve the outcome. Courses should be organized by national societies, since the legal framework conditions are different from one country to another.

In this update the musculoskeletal indications are addressed (mainly bone and tendons): pseudoarthrosis, delayed fracture healing, bone marrow oedema and osteonecrosis in its early stages, insertional tendinopathies such as plantar fasciitis and Achilles tendon fasciitis, calcifying tendonitis of the rotator cuff, tennis elbow, and wound healing problems.

Cite this article: EFORT Open Rev 2020;5:584-592. DOI: 10.1302/2058-5241.5.190067