Histological effects on ex vivo rat tendon from focused ultrasound treatment

• Published in: The Journal of the Acoustical Society of America 2020-10, Vol.148 (4), p.2775-2776
• Main Authors: Smallcomb, Molly, Elliott, Jacob C., Khandare, Sujata, Butt, Ali A., Vidt, Meghan E., Simon, Julianna
• Format: Article
• Language: English
• ISSN: 0001-4966; 1520-8524
• DOI: 10.1121/1.5147727

Focused ultrasound (fUS) therapy can induce controllable mechanical damage through bubble creation, oscillation, and collapse. However, highly collagenous tissues like tendon are resistant to mechanical fractionation with fUS. Our objective is to histologically evaluate whether fUS-induced mechanical disruption is achievable in rat tendon. Ex vivo Achilles (AT) and supraspinatus (ST) tendons were exposed to 1.5 MHz pulses of 0.1–10 ms repeated at 1–100 Hz for 15–60 s with peak pressures p + = 69 MPa, p − = 24 MPa. B-mode ultrasound was used to monitor hyperechogencity during treatment. Samples were stained with Hematoxylin and Eosin (H&E) or alpha-nicotinamide dinucleotide diaphorase (αNADH-d). Results showed successful bubble creation for all samples; however, all samples did not show histological injury. Samples treated with 10-ms pulses at 1 Hz for 15 s displayed only slight disruption (2/5 AT, 2/5 ST). When treatment time increased to 30 s, thermal injury dominated over mechanical effects. Shorter pulse lengths (1 ms at 10 Hz; 0.1 ms at 100 Hz) resulted in localized fiber separation (5/10 AT, 2/10 ST). Future work will investigate how fUS influences mechanical properties of tendon and whether it can induce a healing response in vivo. [Work supported by NIH NIBIB EB027886; NSF GRFP DGE1255832 (Smallcomb).]