Histotripsy Bubble Dynamics in Elastic, Anisotropic Tissue-Mimicking Phantoms

Area of Science:

• Biomaterials Science
• Acoustic Engineering
• Tissue Engineering

Background:

• Histotripsy, a focused ultrasound technique, faces challenges in fractionating anisotropic tissues like tendons due to their mechanical properties.
• Understanding bubble dynamics during histotripsy is crucial for optimizing its application in tissue ablation and fractionation.
• Existing tissue models often lack the optical transparency and specific mechanical characteristics required for detailed bubble dynamics studies.

Purpose of the Study:

• To develop an optically transparent hydrogel mimicking the anisotropic properties of tendon.
• To evaluate the suitability of this hydrogel for studying histotripsy-induced cavitation bubble dynamics.
• To assess the relationship between tissue anisotropy and cavitation behavior during focused ultrasound treatment.

Main Methods:

• Fabrication of polyacrylamide, collagen, and fibrin hydrogels with varying formulations.
• Measurement of axial sound speeds at 1 MHz to quantify anisotropy.
• Histotripsy treatment using a 1.5-MHz focused ultrasound transducer, monitored by passive cavitation imaging and high-speed photography.

Main Results:

• Dehydrated fibrin hydrogels demonstrated similarity to tendon in cavitation emission energy and anisotropy.
• Bubble cloud area in dehydrated fibrin was significantly smaller compared to other tested hydrogels.
• A strong negative linear correlation was observed between anisotropy and both cavitation energy and bubble cloud size.

Conclusions:

• Dehydrated fibrin hydrogels show promise as a repeatable, transparent, tissue-mimicking material for histotripsy research.
• This model facilitates the evaluation of histotripsy bubble dynamics in elastic, anisotropic tissues.
• Findings contribute to advancing the understanding and application of focused ultrasound for tissue fractionation.