A vision-guided robotic platform for mechanical loading, ultrasound-visible tissue deformation assessment, local and systemic tolerability evaluation in rat and mouse skeletal muscle

Controlled and reproducible mechanical stimulation is essential for preclinical mechanotherapy research, yet existing small-animal loading systems often lack integrated anatomical targeting, force control, tissue-level mechanical assessment, and tolerability evaluation. We developed a vision-guided desktop robotic platform integrating RGB-D-based anatomical localization, real-time force sensing, closed-loop force control, and ultrasound-based tissue deformation assessment. The platform was evaluated in 24 male Sprague-Dawley rats and 24 male C57BL/6 mice across two anatomical regions and graded loading conditions. Body-surface-area scaling was used only as a geometric reference for loading-head dimensions, whereas loading-force ranges were selected from previous robotic mechanotherapy studies and preliminary observations. Rats received 0.6, 0.8, or 1.0 N loading to the tibialis anterior region, and mice received 0.1, 0.2, or 0.4 N loading to the bilateral cervical muscle region. Ultrasound imaging demonstrated force-related increases in tissue deformation area in both species, confirming that prescribed external force produced measurable tissue-level mechanical responses. Repeated loading for 14 days elicited behavioural responses, particularly in mechanical withdrawal thresholds and rotarod performance, although responses varied across endpoints and loading conditions. Local assessment showed no overt tissue injury, while muscle-fibre cross-sectional area, collagen-positive area, and CD31-positive signals changed with loading. Body weight, haematological indices, serum biochemical markers, and major-organ histology showed no consistent loading-related adverse changes, whereas serum cytokines exhibited limited, species-dependent variation. Overall, the platform enables reproducible force-controlled mechanical loading together with quantitative assessment of ultrasound-visible tissue deformation and provides a standardized experimental framework for investigating mechanical loading-tissue response relationships in small-animal mechanotherapy research.