Quantitative photoacoustic tomography of skin vasculature predicts subcutaneous implant exposure

Craniofacial implants are prone to skin necrosis and exposure, likely due to implant-induced stress and ischemia. However, this relationship has not been quantitatively validated. Identifying an imaging biomarker of skin vascular health could confirm this mechanism and help predict skin failure to mitigate implant complications.

Photoacoustic tomography (PAT) was used to monitor changes in the skin vasculature surrounding subcutaneous implants with the goal of obtaining a quantitative metric predictive of implant exposure.

Three designs of 3D-printed porous polycaprolactone (PCL) constructs-unimodal block, bimodal block, and unimodal dome-were implanted in 16 hairless mice. PAT was performed biweekly for 16 weeks, and a skeletonization algorithm was applied to quantify vascular density in skin overlying the implants.

Mice that developed implant exposure ( $N=6$ ) exhibited a progressive decline in vascular density beginning 6 weeks before visible exposure, whereas nonexposed mice ( $N=10$ ) remained stable. Group differences were significant 4 weeks ( $p=0.031$ ) and 2 weeks ( $p=0.001$ ) before exposure onset.

These findings establish a quantitative temporal relationship between vascular ischemia and implant exposure. PAT-derived vascular density serves as a predictive biomarker of skin failure, which can be used to enable interventional treatment and improve implant designs.