Evaluation of acoustic cavitation from focused ultrasound in commercial and native extracellular matrices

OBJECTIVE: Although commercial and native extracellular matrices (ECM) are studied as ultrasound-responsive materials, the influence of their viscoelastic properties on ultrasound responses remains unclear. This study examines how focused ultrasound (FUS) peak negative pressure (p-) and pulse length affect acoustic cavitation probability and dynamics in commercial and native ECM (nECM). Approach: A 3.68 MHz single element FUS transducer (f#=1) delivered 100-600 μs pulses at 1 Hz with p-≤6.2 MPa in commercial ECM scaffolds (PureCol EZ-Gel and Cultrex Ultimatrix) as well as nECM derived from decellularized porcine kidney and liver. A 3.68 MHz FUS transducer (f#=1) delivered 100-600 μs pulses at 1 Hz PRF with p-≤6.2 MPa. Cavitation events were captured using brightfield microscopy and high-speed imaging at 20,000 fps. A viscoelasticity corrected Rayleigh-Plesset based bubble model was compared with the experimental results. Main results: The nECM derived from decellularized porcine kidney and liver, having higher elastic moduli compared to PureCol and Cultrex, consistently exhibited higher cavitation thresholds. Increasing the pulse length from 200-600 μs reduced cavitation thresholds in liver (5.6-4.2 MPa, p=0.003) and kidney (5.5-4.1 MPa, p=0.005) nECM, whereas in commercial scaffolds EZ-Gel and Cultrex, thresholds showed minimal change beyond 300 μs. Experimentally, the largest bubble radii were observed in PureCol EZ-Gel (14.8±3.6 µm) and the smallest were observed in Cultrex (6.8±1.3 µm). The computational model qualitatively matched the experimental results for the smallest observed radius and indicated that viscosity was the primary factor in damping bubble expansion compared to elastic modulus. As Cultrex had the highest viscosity of all tested materials, it also showed the minimum radial expansion of r=5.4 µm. Significance: Results suggest that medium elasticity influences acoustic cavitation threshold and maximum bubble expansion is predominantly affected by the viscosity of the medium, which may help interpret cavitation behavior across different ECM conditions.