Histotripsy Treatment of S. Aureus Biofilms on Surgical Mesh Samples Under Varying Pulse Durations

Abstract

Prior studies demonstrated that histotripsy generated by high-intensity tone bursts to excite a bubble cloud adjacent to a medical implant can destroy the bacteria biofilm responsible for the infection. The goal of this study was to treat S. aureus biofilms on surgical mesh samples while varying the number of cycles in the tone burst to minimize collateral tissue damage while maximizing therapy effectiveness. S. aureus biofilms were grown on 1 cm square surgical mesh samples. The biofilms were then treated in vitro using a spherically focused transducer (1.1 MHz, 12.9 cm focal length, 12.7 cm diameter) using either a sham exposure or histotripsy pulses with tone burst durations of 3, 5, or 10 cycles (pulse repetition frequency of 333 Hz, peak compressional pressure of 150 MPa, peak rarefactional pressure of 17 MPa). After treatment, the number of colony forming units (CFUs) on the mesh and the surrounding gel was independently determined. The number of CFUs remaining on the mesh for the sham exposure (4.8±0.9-log10) (sample mean ± sample standard deviation-log10 from 15 observations) was statistically significantly different from the 3-cycle (1.9±1.5-log10), 5-cycle (2.2±1.1-log10), and 10-cycle exposures (1.0±1.5-log10) with an average reduction in the number of CFUs of 3.1-log10. The numbers of CFUs released into the gel for both the sham and exposure groups were the same within a bound of 0.86-log10, but this interval was too large to deduce the fate of the bacteria in the biofilm following the treatment.

Impact of High-Intensity Ultrasound on Strength of Surgical Mesh When Treating Biofilm Infections

“…For the ultrasound exposures, 10 mm × 10 mm Polypropylene mesh samples (PPKM301, Surgical Mesh Division, Textile Development Associates Inc., Brookfield, CT) were inserted into Aquaflex Ultrasound Gel Pad Standoffs (Parker Laboratories Inc., Fairfield, NJ) as was done in our prior studies [9, 10]. The gel pads serve as easily reproducible sterile tissue mimics as they have approximately the same elastic modulus, ∼53 kPa, as abdominal muscle [28–30].…”

“…After insertion, the gel pad with the mesh was placed inside an aluminum holder inside a water tank. The focus of the ultrasound transducer was then aligned on the mesh sample using a low-power signal from a pulser-receiver (Panametrics 5900, Olympus Corporation, Tokyo, Japan) as was done previously [9, 10]. The mesh samples were then exposed to either a sham exposure or a series of high-intensity ultrasound pulses.…”

“…More recently, the studies have focused on treating S. aureus biofilms on surgical mesh samples [9, 10] due to the prevalence of S. aureus infections following hernia repair [15–17]. Infections on surgical mesh are one of the most significant complications and require mesh removal ∼70% of the time with a significant risk of hernia reoccurrence following mesh removal [15–19].…”

Sonobactericide: An Emerging Treatment Strategy for Bacterial Infections

“…Recalcitrant biofilms may be treated with shock waves (Gnanadhas et al 2015;Qi et al 2016) or histotripsy (Xu et al 2012;Bigelow et al 2017). Jetting from shock waves has been used in the clinic to destroy kidney stones and gallstones with lithotripsy (Vakil and Everbach 1993).…”

Treating Porcine Abscesses With Histotripsy: A Pilot Study

“…Much of the focused ultrasound research has been directed to treat biofilms (Bigelow, et al 2009, Bigelow, et al 2017 and solid tumors (Orsi, et al 2010, Al-Bataineh, et al 2012. To ablate tumors, not only does the temperature need to be elevated (and controlled), but the focal spot must be steered to cover the entire tumor, extending into the tumor margins.…”