Fig. 4: Process for fabricating bioresorbable microvascular flow sensing probes.

Procedures. a Schematic illustration of the process, consisting of (1) vacuum deposition of a uniform Mg layer (thickness: 180 nm) on a PLA substrate (thickness: 50 µm), (2) ablation of the Mg layer to define four resistive-type devices, (3) and ablation of the PLA substrate to define a narrow, needle-shaped geometry. b Optical micrograph of such a device, with a magnified image in the inset to highlight the structures. c Temperature distribution around the probe. An input power of 33 mW generates a maximum temperature increase of ~16 °C in air. d Temperature distribution along with the flow probe at different heater powers. e Relationship between the resistance of the thermistor and temperature is linear over this range, with a sensitivity of ~3.3 Ω °C⁻¹. In vivo acute evaluations in a porcine model using a rectus abdominus myocutaneous flap. f Optical image of the left rectus abdominus flap of a porcine model. Occlusion of the artery and veins leads to ischemia and congestion, respectively. The gray pattern indicates the location of the bioresorbable microvascular flow sensing probe. g StO₂ status of the flap measured by a commercial reference device for different situations (R: release, no occlusion; I: ischemia, artery occlusion; C: congestion, vein occlusion). h Temperature difference between two thermistors measured by the bioresorbable device in these situations during operation of the heater. The temperature differences are ~0.35 °C in the R state, ~0.45 °C in the I and C states, respectively. i Corresponding microcapillary flow rate of the flap determined from these data for each situation. The microcapillary flow rates are 0.8 ± 0.2 mm s⁻¹ in the R state, 0.2 ± 0.1 mm s⁻¹ in the I state, and 0.05 ± 0.02 mm s⁻¹ in the C state, respectively.