Implantable, wireless, self-fixing thermal sensors for continuous measurements of microvascular blood flow in flaps and organ grafts

Vascular pedicle thrombosis after free flap transfer or solid organ transplantation surgeries can lead to flap necrosis, organ loss requiring re-transplantation, or even death. Although implantable flow sensors can provide early warning of malperfusion and facilitate operative salvage, measurements performed with existing technologies often depend on extrinsic conditions such as mounting methods and environmental fluctuations. Furthermore, the mechanisms for fixing such probes to vascular or skeletal structures may disrupt the normal blood flow or cause unnecessary tissue damage. Requirements for wired connections to benchtop readout systems also increase costs, complicate clinical care and constrain movements of the patient. Here, we report a wireless, miniaturized flow sensing system that exploits sub-millimeter scale, multi-nodal thermal probes, with biodegradable barbs that secure the probes to the surrounding tissues in a manner that facilitates removal after a period of use. These smartphone-readable devices, together with experimentally validated analytical models of the thermal transport physics, enable reliable, accurate flow sensing in ways that are largely immune to variations in temperature and mechanical perturbations. In vivo demonstrations of this technology in porcine myocutaneous flap and kidney malperfusion models highlight the essential capabilities in microsurgical and transplantation-related biomedical application scenarios.