Fig. 16
Application of BEFAF model to explore the effects of pre-conditioning surgical flap delay technique. A representative workflow of flap delay technique using pedicled flaps in 10-month-old male SD rat is shown. A Left flap was raised, placed back onto the resultant wound, and left to fully heal for 7 days. B Delayed flap healing status on 7th POD. C BEFAF surgery was performed on the left and right sides of the animal creating regular non-advanced flaps. During this type of surgery, the microvascular supply at the base of the flap (pedicle) is left intact. D Flaps were allowed to heal under normal conditions for 2 days. E–F On 2nd POD for the right flap and on the 9th POD for the delayed left flap, biopsies were taken from the distal portion of each flap for molecular analysis. G The flaps were advanced and allowed to heal for 7 more days. H Flap healing efficacy was evaluated on 9th POD for the control (C) flap and POD 16th POD for the delayed (D) flap. I Flaps were harvested for additional comparative and correlative analysis with flap reoxygenation that was evaluated by the combined photoacoustic (PA) and Doppler ultrasound (US) imaging (J). Ultrasound coupling gel was applied to the animal skin before the images were captured on selected regions (left panel) at the 12 mm focal depth using the Vevo2100 LAZR imaging system (VisualSonics Inc, Toronto, Canada), which operates LZ-250 transducer (21 MHz) frequency transducer and has 20 Hz tunable near-infrared light laser (680–970 nm). Besides B-Mode, which displays a greyscale two dimensional cross-section of tissue, 2-D images were acquired using ‘Oxy-Hemo’ mode, which collects data at 750 and 850 nm wavelengths, and then creates and displays a parametric distribution map of oxygenated Hemoglobin (oxyHb) and total hemoglobin (tHb) at a rate of 1 Hz (right panel).The imaging probe was positioned between the medial and distal segments on 1) the day of flap delay surgery on the R flap to take baseline flap oxygen saturation level measurement designated as R0; 2) on 2nd POD after left-side flap delay on the D flap to take acute reoxygenation response measurement designated as D2; 3) on 2.nd POD after right-side flap raising surgery on the R flap to take acute reoxygenation response measurement (R2) and on the same day on the D flap to assess a secondary reoxygenation response designated as D9