An In Vitro Phantom Study for the Development of Novel Reconstructive Flap Monitoring Systems

Background: Free flap monitoring remains reliant on clinical observation, which is subjective and may delay detection of vascular compromise. Photoplethysmography (PPG) offers promise as a non-invasive tool, but suitable in vitro models to evaluate its utility are lacking. Methods: Custom silicone artery and vein phantoms were fabricated using adjustable ratios of deadener and hardener to replicate the mechanical properties of human forearm vessels. These were embedded in a tissue phantom at a depth of 3 mm to simulate pedicle positioning and integrated into a perfusion system. Internal pressure was modulated to reproduce normal, ischemic, and congested states. Red (660 nm) and infrared (940 nm) PPG signals were recorded, and amplitude differences between conditions were analyzed using Kruskal–Wallis and Dunn’s post hoc tests. Results: Mechanical testing confirmed that a hardener ratio of 0.6 reproduced arterial properties, while a deadener ratio of 0.4 matched venous characteristics. PPG amplitude increased under ischemia and decreased under congestion compared with normal flow. These changes were statistically significant for both red and infrared signals (p < 0.001). Conclusion: This study demonstrates the feasibility of a customizable vascular-tissue phantom for simulating perfusion states and detecting flow abnormalities via PPG, providing a platform for future flap monitoring technologies.