Scan Parameter Optimization for Histotripsy Treatment of S. Aureus Biofilms on Surgical Mesh

Catheter-Based Medical Device Biofilm Ablation Using Histotripsy: A Parameter Study

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.

Particle-Mediated Histotripsy for the Targeted Treatment of Intraluminal Biofilms in Catheter-Based Medical Devices

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.

Focused Ultrasound Biofilm Ablation: Investigation of Histotripsy for the Treatment of Catheter-Associated Urinary Tract Infections (CAUTIs)

Urinary catheters often become contaminated with biofilms, resulting in catheter-associated urinary tract infections (CAUTIs) that adversely affect patient outcomes. Histotripsy is a noninvasive focused ultrasound therapy previously developed for the noninvasive ablation of cancerous tumors and soft tissues. Histotripsy has also previously shown the ability to treat biofilms on glass slides and surgical meshes. Here, we investigate the potential of histotripsy for the treatment of CAUTIs for the first time in vitro. Clinically relevant catheter materials (Tygon, Silicone, and latex catheter mimics) and commonly used clinical catheters were tested to determine the feasibility of producing luminal histotripsy bubble clouds. A Pseudomonas aeruginosa (strain PA14) biofilm model was developed and tested to produce luminal biofilms in an in vitro Tygon catheter mimic. This model was treated with histotripsy to determine the ability to remove a luminal biofilm. Finally, the bactericidal effects of histotripsy were tested by treating PA14 suspended inside the Tygon catheter mimic. Results showed that histotripsy produced precise luminal cavitation within all tested catheter mimics and clinical catheters. Histotripsy treatment of a PA14 biofilm with histotripsy reduced luminal biofilm OD590 signal down to background levels. Further, the treatment of suspended PA14 in Luria-Bertani (LB) showed a 3.45 ± 0.11 log₁₀ reduction in CFU/mL after six histotripsy scans across the catheter mimics. Overall, the results of this study demonstrate the potential of histotripsy to provide a new modality for removing bacterial biofilms from catheter-based medical devices and suggest that additional work is warranted to investigate histotripsy for the treatment of CAUTIs and other biomaterial-associated infections.

Histotripsy: the first noninvasive, non-ionizing, non-thermal ablation technique based on ultrasound

Histotripsy is the first noninvasive, non-ionizing, and non-thermal ablation technology guided by real-time imaging. Using focused ultrasound delivered from outside the body, histotripsy mechanically destroys tissue through cavitation, rendering the target into acellular debris. The material in the histotripsy ablation zone is absorbed by the body within 1-2 months, leaving a minimal remnant scar. Histotripsy has also been shown to stimulate an immune response and induce abscopal effects in animal models, which may have positive implications for future cancer treatment. Histotripsy has been investigated for a wide range of applications in preclinical studies, including the treatment of cancer, neurological diseases, and cardiovascular diseases. Three human clinical trials have been undertaken using histotripsy for the treatment of benign prostatic hyperplasia, liver cancer, and calcified valve stenosis. This review provides a comprehensive overview of histotripsy covering the origin, mechanism, bioeffects, parameters, instruments, and the latest results on preclinical and human studies.