Fig. 6. Behavioral experiments in the rats with fully implanted Sm-PUEH device.

(A) The timeline for the whole experimental procedure. (B) The device implantation. (C) The first day after implantation. (D) The 10th day after implantation. (E) Schematic diagram of behavioral experiments of Sm-PUEH device for analgesia application. Three-percent formalin (50 μl) is injected at the beginning, and US (US-400 c/p, PRF = 50 Hz, 0.65 MPa) is applied during the 30th to 35th min. (F) Three main behavioral responses of rats to formalin: (I) paw down, (II) paw up, and (III) paw licking, showing differential pain levels from no pain to the heaviest pain. (G) The weighted score comparison of formalin-induced pain between the stimulation group (n = 6) and the control group (n = 6). (H) Total time (seconds) of paw up (left) and paw licking (right) during the 30th to 35th min in formalin test. All data are presented as means ± SEM. *P < 0.05, **P < 0.01, and ***P < 0.001 versus control group.