Development of Tough Hydrogel Phantoms to Mimic Fibrous Tissue for Focused Ultrasound Therapies.

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From: Ultrasound in Medicine & Biology(Vol. 48, Issue 9)
Publisher: Elsevier B.V.
Document Type: Report
Length: 423 words

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Abstract :

Key Words Cavitation; Histotripsy; High-intensity focused ultrasound; Benign prostatic hyperplasia; Hybrid hydrogels; Fibrosis; Tissue-mimicking phantoms Abstract Tissue-mimicking gels provide a cost-effective medium to optimize histotripsy treatment parameters with immediate feedback. Agarose and polyacrylamide gels are often used to evaluate treatment outcomes as they mimic the acoustic properties and stiffness of a variety of soft tissues, but they do not exhibit high toughness, a characteristic of fibrous connective tissue. To mimic pathologic fibrous tissue found in benign prostate hyperplasia (BPH) and other diseases that are potentially treatable with histotripsy, an optically transparent hydrogel with high toughness was developed that is a hybrid of polyacrylamide and alginate. The stiffness was established using shear wave elastography (SWE) and indentometry techniques and was found to be representative of human BPH ex vivo prostate tissue. Different phantom compositions and excised ex vivo BPH tissue samples were treated with a 700-kHz histotripsy transducer at different pulse repetition frequencies. Post-treatment, the hybrid gels and the tissue samples exhibited differential reduction in stiffness as measured by SWE. On B-mode ultrasound, partially treated areas were present as hyperechoic zones and fully liquified areas as hypoechoic zones. Phase contrast microscopy of the gel samples revealed liquefaction in regions consistent with the target lesion dimensions and correlated to findings identified in tissue samples via histology. The dose required to achieve liquefaction in the hybrid gel was similar to what has been observed in ex vivo tissue and greater than that of agarose of comparable or higher Young's modulus by a factor 10. These results indicate that the developed hydrogels closely mimic elasticities found in BPH prostate ex vivo tissue and have a similar response to histotripsy treatment, thus making them a useful cost-effective alternative for developing and evaluating different treatment protocols. Author Affiliation: (*) Center for Industrial and Medical Ultrasound, Applied Physics Laboratory, University of Washington, Seattle, Washington, USA ([Dagger]) Department of Urology, University of Washington School of Medicine, Seattle, Washington, USA ([double dagger]) Department of Biomedical Engineering and Mechanics, Virginia Polytechnic Institute and State University, Blacksburg, Virginia, USA (§) Department of Gastroenterology, University of Washington School of Medicine, Seattle, Washington, USA 1 Address correspondence to: Yashwanth Nanda Kumar, Center for Industrial and Medical Ultrasound, Applied Physics Laboratory, University of Washington, 1013 NE 40th Street, Seattle WA 98105, USA. Article History: Received 19 January 2022; Revised 28 April 2022; Accepted 2 May 2022 Byline: Yashwanth Nanda Kumar [ynandaku@uw.edu] (*,1), Zorawar Singh ([Dagger]), Yak-Nam Wang, George R. Schade ([Dagger]), Wayne Kreider, Matthew Bruce, Eli Vlaisavljevich ([double dagger]), Tatiana D. Khokhlova (*,§), Adam D. Maxwell ([Dagger])

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Gale Document Number: GALE|A712235388