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Maxwell AD, Vlaisavljevich E. Cavitation-induced pressure saturation: a mechanism governing bubble nucleation density in histotripsy. Phys Med Biol 2024; 69:10.1088/1361-6560/ad3721. [PMID: 38518377 PMCID: PMC11212395 DOI: 10.1088/1361-6560/ad3721] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/18/2023] [Accepted: 03/22/2024] [Indexed: 03/24/2024]
Abstract
Objective.Histotripsy is a noninvasive focused ultrasound therapy that mechanically disintegrates tissue by acoustic cavitation clouds. In this study, we investigate a mechanism limiting the density of bubbles that can nucleate during a histotripsy pulse. In this mechanism, the pressure generated by the initial bubble expansion effectively negates the incident pressure in the vicinity of the bubble. From this effect, the immediately adjacent tissue is prevented from experiencing the transient tension to nucleate bubbles. Approach.A Keller-Miksis-type single-bubble model was employed to evaluate the dependency of this effect on ultrasound pressure amplitude and frequency, viscoelastic medium properties, bubble nucleus size, and transducer geometric focusing. This model was further combined with a spatial propagation model to predict the peak negative pressure field as a function of position from a cavitating bubble.Main results. The single-bubble model showed the peak negative pressure near the bubble surface is limited to the inertial cavitation threshold. The predicted bubble density increased with increasing frequency, tissue viscosity, and transducer focusing angle. The simulated results were consistent with the trends observed experimentally in prior studies, including changes in density with ultrasound frequency and transducerF-number.Significance.The efficacy of the therapy is dependent on several factors, including the density of bubbles nucleated within the cavitation cloud formed at the focus. These results provide insight into controlling the density of nucleated bubbles during histotripsy and the therapeutic efficacy.
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Affiliation(s)
- Adam D Maxwell
- Department of Urology, University of Washington School of Medicine, Seattle, WA, 98195, United States of America
- Department of Biomedical Engineering and Mechanics, Virginia Polytechnic Institute and State University, Blacksburg, VA, 24060, United States of America
| | - Eli Vlaisavljevich
- Department of Biomedical Engineering and Mechanics, Virginia Polytechnic Institute and State University, Blacksburg, VA, 24060, United States of America
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Singh R, Samaddar A, Duchene D, Waller S, Yang X. Recanalize ureteral stents with focused ultrasound. Med Phys 2023; 50:7349-7358. [PMID: 37153961 DOI: 10.1002/mp.16447] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/26/2022] [Revised: 03/23/2023] [Accepted: 04/18/2023] [Indexed: 05/10/2023] Open
Abstract
BACKGROUND Maintaining ureteral patency is imperative to preventing renal injury and systemic infection. Ureteral stents are small conduits connecting the kidney and the bladder. They have been widely used to treat ureteral obstructions and ureteral leaks. The most problematic and frequent stent-associated complication is stent encrustation. This occurs when mineral crystals (e.g. calcium, oxalate, phosphorus, struvite) are deposited onto the surface and internal lumen of the stent. Encrustation can lead to the obstruction of a stent and increases risk of systemic infection. As a result, ureteral stents need to be replaced typically every 2-3 months. PURPOSE In this study, we present a non-invasive, high-intensity focused ultrasound (HIFU)-based technique to recanalize obstructed stents. By taking advantage of the mechanical force produced by a HIFU beam, including acoustic radiation force, acoustic streaming, and cavitation, HIFU can break up encrustations, clearing the stent of obstruction. METHODS The ureteral stents for this study were obtained from patients undergoing ureteral stent removal. Under the guidance of ultrasound imaging, the encrustation in the stents were located, and then targeted by HIFU at frequencies of 0.25 and 1 MHz. The duty cycle of HIFU was 10%, and the HIFU burst repetition rate was 1 Hz, while the HIFU amplitude was varied to find the threshold pressure that would displace encrustations. The treatment duration was limited at 2 min (or 120 shots from HIFU). The treatments were carried out in two different orientations (parallel and perpendicular) of the ureteral stent with respect to the HIFU beam. For each setting, five treatments were conducted for a maximum duration of 2 min. During the entire treatment, an ultrasound imaging system was used to monitor the movement of encrustations inside the stent. The peak negative HIFU pressures needed to move the encrustations inside the stent was recorded for quantitative analysis. RESULTS Our results demonstrated that at both 0.25 and 1 MHz ultrasound frequencies, obstructed stents could be recanalized. At 0.25 MHz, the needed average peak negative pressure was 0.52 MPa in parallel orientation and 0.42 MPa in perpendicular orientation. At 1 MHz, the needed average peak negative pressure was 1.10 MPa in parallel orientation and 1.15 MPa in perpendicular orientation CONCLUSIONS: This first in-vitro study has demonstrated the feasibility of non-invasive HIFU to recanalize ureteral stents. This technology has a potential to reduce the need for ureteral stent exchange.
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Affiliation(s)
- Rohit Singh
- Institute for Bioengineering Research and Department of Mechanical Engineering, University of Kansas, Lawrence, Kansas, USA
| | - Abhirup Samaddar
- Institute for Bioengineering Research and Department of Mechanical Engineering, University of Kansas, Lawrence, Kansas, USA
| | - David Duchene
- Department of Urology, University of Kansas Medical Center, Kansas, Kansas, USA
| | - Stephen Waller
- Division of Infectious Diseases, University of Kansas Medical Center, Kansas, Kansas, USA
| | - Xinmai Yang
- Institute for Bioengineering Research and Department of Mechanical Engineering, University of Kansas, Lawrence, Kansas, USA
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Morse R, Childers C, Nowak E, Rao J, Vlaisavljevich E. Catheter-Based Medical Device Biofilm Ablation Using Histotripsy: A Parameter Study. ULTRASOUND IN MEDICINE & BIOLOGY 2023:S0301-5629(23)00203-X. [PMID: 37394375 DOI: 10.1016/j.ultrasmedbio.2023.06.010] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/19/2023] [Revised: 06/07/2023] [Accepted: 06/13/2023] [Indexed: 07/04/2023]
Abstract
OBJECTIVE Biofilm formation in medical catheters is a major source of hospital-acquired infections which can produce increased morbidity and mortality for patients. Histotripsy is a non-invasive, non-thermal focused ultrasound therapy and recently has been found to be effective at removal of biofilm from medical catheters. Previously established histotripsy methods for biofilm removal, however, would require several hours of use to effectively treat a full-length medical catheter. Here, we investigate the potential to increase the speed and efficiency with which biofilms can be ablated from catheters using histotripsy. METHODS Pseudomonas aeruginosa (PA14) biofilms were cultured in in vitro Tygon catheter mimics and treated with histotripsy using a 1 MHz histotripsy transducer and a variety of histotripsy pulsing rates and scanning methods. The improved parameters identified in these studies were then used to explore the bactericidal effect of histotripsy on planktonic PA14 suspended in a catheter mimic. RESULTS Histotripsy can be used to remove biofilm and kill bacteria at substantially increased speeds compared with previously established methods. Near-complete biofilm removal was achieved at treatment speeds up to 1 cm/s, while a 4.241 log reduction in planktonic bacteria was achieved with 2.4 cm/min treatment. CONCLUSION These results represent a 500-fold increase in biofilm removal speeds and a 6.2-fold increase in bacterial killing speeds compared with previously published methods. These findings indicate that histotripsy shows promise for the treatment of catheter-associated biofilms and planktonic bacteria in a clinically relevant time frame.
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Affiliation(s)
- Ryan Morse
- Virginia Tech Carilion School of Medicine, Virginia Tech, Roanoke, VA, USA.
| | | | - Elizabeth Nowak
- Internal Medicine, Division of Infectious Disease, Carilion Medical Center, Roanoke, VA, USA
| | - Jayasimha Rao
- Virginia Tech Carilion School of Medicine, Virginia Tech, Roanoke, VA, USA; Internal Medicine, Division of Infectious Disease, Carilion Medical Center, Roanoke, VA, USA
| | - Eli Vlaisavljevich
- Department of Biomedical Engineering and Mechanics, Virginia Tech, Roanoke, VA, USA
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Chu W, Ma Y, Zhang Y, Cao X, Shi Z, Liu Y, Ding X. Significantly improved antifouling capability of silicone rubber surfaces by covalently bonded acrylated agarose towards biomedical applications. Colloids Surf B Biointerfaces 2023; 222:112979. [PMID: 36435025 DOI: 10.1016/j.colsurfb.2022.112979] [Citation(s) in RCA: 4] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/16/2022] [Revised: 10/21/2022] [Accepted: 10/26/2022] [Indexed: 11/05/2022]
Abstract
Bacteria have the extraordinary ability to adhere to biomaterial surfaces and form multicellular structures known as biofilms, which have a detrimental impact on the performance of medical devices. Herein, an investigation highlighted the effective inhibition of bacteria adhesion and overgrowth on silicone rubber surface by grafting polysaccharide, agarose (AG), to construct hydrophilic and negatively charged surfaces. Because of the strong hydration capacity of agarose, the water contact angle of the modified silicone rubber surfaces was significantly reduced from 107.6 ± 2.7° to 19.3 ± 2.6°, which successfully limited bacterial adherence. Most importantly, the durability and stability of coating were observed after 10 days of simulated dynamic microenvironment in vivo, exhibiting a long service life. This modification method did not compromise biocompatibility of silicone rubber, opening a door to new applications for silicone rubber in the field of biomedical materials.
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Affiliation(s)
- Wenting Chu
- Key Laboratory of Biomedical Materials of Natural Macromolecules, Beijing University of Chemical Technology, Ministry of Education, Beijing, China; Beijing Laboratory of Biomedical Materials, Beijing University of Chemical Technology, Beijing, China
| | - Yuhong Ma
- Key Laboratory of Biomedical Materials of Natural Macromolecules, Beijing University of Chemical Technology, Ministry of Education, Beijing, China; Beijing Laboratory of Biomedical Materials, Beijing University of Chemical Technology, Beijing, China
| | - Yuning Zhang
- Key Laboratory of Biomedical Materials of Natural Macromolecules, Beijing University of Chemical Technology, Ministry of Education, Beijing, China; Beijing Laboratory of Biomedical Materials, Beijing University of Chemical Technology, Beijing, China
| | - Xinjie Cao
- Key Laboratory of Biomedical Materials of Natural Macromolecules, Beijing University of Chemical Technology, Ministry of Education, Beijing, China; Beijing Laboratory of Biomedical Materials, Beijing University of Chemical Technology, Beijing, China
| | - Zhongyu Shi
- Key Laboratory of Biomedical Materials of Natural Macromolecules, Beijing University of Chemical Technology, Ministry of Education, Beijing, China; Beijing Laboratory of Biomedical Materials, Beijing University of Chemical Technology, Beijing, China
| | - Ying Liu
- Key Laboratory of Biomedical Materials of Natural Macromolecules, Beijing University of Chemical Technology, Ministry of Education, Beijing, China; Beijing Laboratory of Biomedical Materials, Beijing University of Chemical Technology, Beijing, China
| | - Xuejia Ding
- Key Laboratory of Biomedical Materials of Natural Macromolecules, Beijing University of Chemical Technology, Ministry of Education, Beijing, China; Beijing Laboratory of Biomedical Materials, Beijing University of Chemical Technology, Beijing, China.
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Williams RP, Simon JC, Khokhlova VA, Sapozhnikov OA, Khokhlova TD. The histotripsy spectrum: differences and similarities in techniques and instrumentation. Int J Hyperthermia 2023; 40:2233720. [PMID: 37460101 PMCID: PMC10479943 DOI: 10.1080/02656736.2023.2233720] [Citation(s) in RCA: 8] [Impact Index Per Article: 8.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/20/2023] [Revised: 06/15/2023] [Accepted: 07/02/2023] [Indexed: 07/20/2023] Open
Abstract
Since its inception about two decades ago, histotripsy - a non-thermal mechanical tissue ablation technique - has evolved into a spectrum of methods, each with distinct potentiating physical mechanisms: intrinsic threshold histotripsy, shock-scattering histotripsy, hybrid histotripsy, and boiling histotripsy. All methods utilize short, high-amplitude pulses of focused ultrasound delivered at a low duty cycle, and all involve excitation of violent bubble activity and acoustic streaming at the focus to fractionate tissue down to the subcellular level. The main differences are in pulse duration, which spans microseconds to milliseconds, and ultrasound waveform shape and corresponding peak acoustic pressures required to achieve the desired type of bubble activity. In addition, most types of histotripsy rely on the presence of high-amplitude shocks that develop in the pressure profile at the focus due to nonlinear propagation effects. Those requirements, in turn, dictate aspects of the instrument design, both in terms of driving electronics, transducer dimensions and intensity limitations at surface, shape (primarily, the F-number) and frequency. The combination of the optimized instrumentation and the bio-effects from bubble activity and streaming on different tissues, lead to target clinical applications for each histotripsy method. Here, the differences and similarities in the physical mechanisms and resulting bioeffects of each method are reviewed and tied to optimal instrumentation and clinical applications.
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Affiliation(s)
- Randall P Williams
- Division of Gastroenterology, Department of Medicine, University of Washington, Seattle, WA, USA
- Center for Industrial and Medical Ultrasound, Applied Physics Laboratory, University of Washington, Seattle, WA, USA
| | - Julianna C Simon
- Graduate Program in Acoustics, The Pennsylvania State University, University Park, PA, USA
| | - Vera A Khokhlova
- Center for Industrial and Medical Ultrasound, Applied Physics Laboratory, University of Washington, Seattle, WA, USA
- Department of Acoustics, Physics Faculty, Moscow State University, Moscow, Russia
| | - Oleg A Sapozhnikov
- Center for Industrial and Medical Ultrasound, Applied Physics Laboratory, University of Washington, Seattle, WA, USA
- Department of Acoustics, Physics Faculty, Moscow State University, Moscow, Russia
| | - Tatiana D Khokhlova
- Division of Gastroenterology, Department of Medicine, University of Washington, Seattle, WA, USA
- Center for Industrial and Medical Ultrasound, Applied Physics Laboratory, University of Washington, Seattle, WA, USA
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Childers C, Edsall C, Mehochko I, Mustafa W, Durmaz YY, Klibanov AL, Rao J, Vlaisavljevich E. Particle-Mediated Histotripsy for the Targeted Treatment of Intraluminal Biofilms in Catheter-Based Medical Devices. BME FRONTIERS 2022; 2022:9826279. [PMID: 37850182 PMCID: PMC10521694 DOI: 10.34133/2022/9826279] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/09/2021] [Accepted: 05/25/2022] [Indexed: 10/19/2023] Open
Abstract
Objective. This paper is an initial work towards developing particle-mediated histotripsy (PMH) as a novel method of treating catheter-based medical device (CBMD) intraluminal biofilms. Impact Statement. CBMDs commonly become infected with bacterial biofilms leading to medical device failure, infection, and adverse patient outcomes. Introduction. Histotripsy is a noninvasive focused ultrasound ablation method that was recently proposed as a novel method to remove intraluminal biofilms. Here, we explore the potential of combining histotripsy with acoustically active particles to develop a PMH approach that can noninvasively remove biofilms without the need for high acoustic pressures or real-time image guidance for targeting. Methods. Histotripsy cavitation thresholds in catheters containing either gas-filled microbubbles (MBs) or fluid-filled nanocones (NCs) were determined. The ability of these particles to sustain cavitation over multiple ultrasound pulses was tested after a series of histotripsy exposures. Next, the ability of PMH to generate selective intraluminal cavitation without generating extraluminal cavitation was tested. Finally, the biofilm ablation and bactericidal capabilities of PMH were tested using both MBs and NCs. Results. PMH significantly reduced the histotripsy cavitation threshold, allowing for selective luminal cavitation for both MBs and NCs. Results further showed PMH successfully removed intraluminal biofilms in Tygon catheters. Finally, results from bactericidal experiments showed minimal reduction in bacteria viability. Conclusion. The results of this study demonstrate the potential for PMH to provide a new modality for removing bacterial biofilms from CBMDs and suggest that additional work is warranted to develop histotripsy and PMH for treatment of CBMD intraluminal biofilms.
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Affiliation(s)
| | - Connor Edsall
- Department of Biomedical Engineering and Mechanics, Virginia Tech, USA
| | - Isabelle Mehochko
- Department of Biomedical Engineering and Mechanics, Virginia Tech, USA
| | - Waleed Mustafa
- Department of Biomedical Engineering, Istanbul Medipol University, Turkey
| | | | - Alexander L. Klibanov
- Division of Cardiovascular Medicine (Department of Medicine) and Robert M. Berne Cardiovascular Research Center at University of Virginia School of Medicine, University of Virginia, USA
| | - Jayasimha Rao
- Department of Medicine, Division of Infectious Diseases, Virginia Tech Carilion School of Medicine, USA
| | - Eli Vlaisavljevich
- Department of Biomedical Engineering and Mechanics, Virginia Tech, USA
- ICTAS Center for Engineered Health, Virginia Polytechnic Institute and State University, USA
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Edsall C, Ham E, Holmes H, Hall TL, Vlaisavljevich E. Effects of frequency on bubble-cloud behavior and ablation efficiency in intrinsic threshold histotripsy. Phys Med Biol 2021; 66:225009. [PMID: 34706348 DOI: 10.1088/1361-6560/ac33ed] [Citation(s) in RCA: 12] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/10/2021] [Accepted: 10/27/2021] [Indexed: 11/11/2022]
Abstract
Objective.Histotripsy is a non-thermal focused ultrasound ablation method that destroys tissue through the generation of a cavitation bubble cloud. Previous work studying intrinsic threshold histotripsy has shown that dense bubble clouds can be formed by a single-cycle pulse when the negative pressure exceeds an intrinsic threshold of ∼25-30 MPa, with the ablation efficiency dependent upon the size and density of bubbles within the cloud. This work investigates the effects of frequency on bubble-cloud behavior and ablation efficiency in intrinsic threshold histotripsy.Approach.A modular transducer was used to expose agarose tissue phantoms to 500 kHz, 1 MHz, or 3 MHz, histotripsy pulses. Optical imaging was used to measure the bubble-cloud dimensions, bubble density, and bubble size. The effects of frequency on ablation efficiency were also investigated by applying histotripsy to red blood cell (RBC) phantoms.Main results.Results revealed that the bubble-cloud size closely matched theoretical predictions for all frequencies. The bubble density, which is a measure of the number of bubbles per unit area, was shown to increase with increasing frequency while the size of individual bubbles within the cloud decreased at higher frequencies. Finally, RBC phantom experiments showed decreasing ablation efficiency with increasing frequency.Significance.Overall, results demonstrate the effects of frequency on histotripsy bubble-cloud behavior and show that lower frequency generates more efficient tissue ablation, primarily due to enhanced bubble expansion.
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Affiliation(s)
- Connor Edsall
- Department of Biomedical Engineering and Mechanics, Virginia Polytechnic Institute and State University, 325 Stanger St., Blacksburg, VA 24061, United States of America
| | - Emerson Ham
- Department of Biomedical Engineering and Mechanics, Virginia Polytechnic Institute and State University, 325 Stanger St., Blacksburg, VA 24061, United States of America
| | - Hal Holmes
- Department of Biomedical Engineering and Mechanics, Virginia Polytechnic Institute and State University, 325 Stanger St., Blacksburg, VA 24061, United States of America
- Conservation X Labs, Seattle, WA 98103, United States of America
| | - Timothy L Hall
- Department of Biomedical Engineering, University of Michigan, Carl A. Gerstacker Building, 2200 Bonisteel Blvd, Ann Arbor, MI 48109-2133, United States of America
| | - Eli Vlaisavljevich
- Department of Biomedical Engineering and Mechanics, Virginia Polytechnic Institute and State University, 325 Stanger St., Blacksburg, VA 24061, United States of America
- ICTAS Center for Engineered Health, Virginia Polytechnic Institute and State University, 325 Stanger St., Blacksburg, VA 24061, United States of America
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