Researchers: Anthony Yu, Samuel Morais, Xinyue Huang
Colaborators: Jeong Hun Park, Scott Hollister
Background
Craniofacial implants are widely used in reconstructive surgery but are often associated with skin necrosis and implant exposure. Prior studies suggest implant-induced mechanical stress compromises skin vasculature and elasticity, leading to skin breakdown. However, quantitative assessment of both vascular and mechanical changes in the skin post-implantation remains limited. In this study, we combined ultrasound/photoacoustic (US/PA) imaging, photoacoustic tomography (PAT), and shear wave elasticity imaging (SWEI) to monitor temporal changes in skin vascularity and shear modulus non-invasively. From these metrics we identified biomarkers of implant-induced skin damage which can be used for early prediction of implant exposure.
Methods
Two types of 3D-printed polycaprolactone implants, block and dome (Fig. a), were subcutaneously implanted in mice (n=8), with an additional non-implanted control group (n=4). Imaging of the skin over the implant was performed biweekly for 12 weeks using (1) 3D US/PA imaging (Vevo LAZR, 700–950 nm) to calculate total hemoglobin, (2) 3D PAT (TriTom, 532 nm) to examine the vessel skeleton/density, and (3) SWEI (Vantage 128, 16 MHz) to calculate skin shear modulus. In addition, skin health was visually scored (1-5) based on the extent of skin damage.
Discussion
All mice in both the control and dome groups maintained healthy skin, while three mice in the block group exhibited implant exposure by week 12 (Fig. c). The skin breakdown over blocks was preceded by vessel loss in PAT (Fig. b, circled), while the skin over domes better preserved vascular structure. The initial post-implantation skin stress was high for both implanted groups, but the rate of subsequent stress relief was slower for the block group (Fig. d). This heightened sustained skin stress over the blocks may have led to the observed increase in vascular ischemia. Total hemoglobin levels in the block group decreased over time, whereas no significant changes were observed in the other groups (Fig. e). The vascular density in the block group temporarily increased before sharply declining prior to exposure (Fig. f).
Together, these findings highlight the diagnostic potential of US/PA/SWEI biomarkers to serve as early indicators of skin damage and offer critical insights for improving intervention and reconstructive outcomes.