Ultrasound-Guided Photoacoustic Monitoring of Vascular Ischemia in Implant-Induced Skin Necrosis

Implant-induced skin necrosis remains a significant clinical challenge in subcutaneous implant applications, believed to result from vascular ischemia caused by mechanical stress. However, this hypothesis remains largely qualitative and lacks direct quantitative validation. This study investigates the potential of ultrasound-guided photoacoustic (US/PA) imaging as a non-invasive diagnostic tool for detecting vascular changes and predicting sites of breakdown in response to subcutaneous implants.

Three designs of 3-D-printed porous poly-ɛ-caprolactone implants - a unimodal cube, a bimodal cube and a unimodal dome - were implanted subcutaneously in 16 SKHl-Elite hairless mice. Longitudinal US/PA imaging was performed bi-weekly for 12 weeks to monitor PA vasculature (532 nm), vascular density (532 nm) and total hemoglobin levels (700-950 nm). Skin health was scored using a modified National Pressure Injury Advisory Panel-based system. Temporal and spatial analyses were conducted to evaluate the relationship between PA-derived biomarkers and skin health deterioration.

Mice with implant exposure (N = 5) exhibited a progressive decrease in PA biomarkers, with reductions of up to 48% by week 12. These changes preceded visible skin necrosis by approximately 2-4 weeks. In contrast, the healthy group (N = 11) maintained stable signals. PA vasculature at 532 nm showed the most significant temporal differentiation (p = 0.0013) and strong correlation with skin health (R >0.85). Spatial hemoglobin maps revealed that local reductions in vascularity preceded localized skin dehiscence.

Ultrasound-guided PA imaging enables early, non-invasive detection of vascular compromise associated with implant-induced skin necrosis. Among the tested biomarkers, PA vasculature at 532 nm emerged as the most sensitive and practical for early detection, offering a promising tool for guiding implant design and improving post-implantation monitoring.