Design of a novel pH sensor for flap monitoring and evaluation of its efficacy in an in vivo flap model

Introduction: In reconstructive surgery, free tissue transfer involves moving tissue with its blood supply to the recipient site via microvascular techniques to repair tissue defects. Currently, clinical observation remains the gold standard for flap monitoring. However, objective, laboratory-based technological monitoring modalities are needed. This study aims to design and produce a pH sensor that can be embedded in flap tissue and to test its effectiveness in predicting tissue loss from both arterial and venous sources. Materials and Methods: In the first stage, pH sensors were produced following in vitro studies conducted with the Physics Department at Yildiz Technical University. After in vitro testing, preliminary studies on three animals were carried out to assess the sensor's effectiveness in tissue and to define the experimental model. The Au/GS/nSi Schottky diode sensor prototype was then selected for further study. In the second stage, 15 epigastric flaps were elevated across three groups (n=5) depending on the occluded vessel. Each group underwent measurements as follows: 20 minutes of baseline, 20 minutes under arterial, venous or pedicle occlusion, 20 minutes after occlusion release, and an additional 20 minutes under occlusion. Results: Signal peaks were observed during arterial and venous occlusions, while noisy current values were noted in the pedicle group post-occlusion. Average response times were 104.8, 130, and 170 seconds for the arterial, venous, and pedicle groups, respectively. Conclusion: This novel pH sensor is a cost-effective, reliable tool for flap monitoring. Further studies are needed to develop bioabsorbable, remotely controlled versions for clinical use.