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A novel noncontact method to assess the biomechanical properties of wound tissue

A novel noncontact optical coherence tomography based air‐jet indentation system was developed for characterizing the biomechanical properties of soft tissue in a noncontact way. This study aimed to measure the stiffness of diabetic foot ulcer tissues by using this air‐jet indentation system, and examining the test/retest reliability. Eight subjects with diabetes (seven males, one female), with a total of 10 foot ulcers between them, participated in the study. A total of 20 measuring sites located at the central wound bed (n=10) or peri‐ulcer areas (n=10), respectively, were evaluated with the air‐jet indentation system. Four cycles of loading and unloading, each with a duration of approximately 36 seconds at an indentation rate of 0.08 mm/s, were carried out for each indentation trial. The test/retest reliability was examined at all measuring points. The average stiffness coefficient of the peri‐ulcer area (mean±SD: 0.47±0.15 N/mm) was significantly larger than that of the central wound bed area (mean±SD: 0.35±0.23 N/mm; p=0.042). A high value for test/retest reliability was shown (intraclass correlation coefficient: 0.986; Pearson's correlation: r=0.972, p<0.001). Our preliminary findings showed that the peri‐ulcer area had greater stiffness than the central wound bed. This greater magnitude of hardness and inelasticity at the peri‐ulcer region may scatter part of the contractile forces for wound contraction during the healing process. We found the novel air‐jet system to be a reliable tool for characterizing the stiffness of soft tissues around the wound in a noncontact way.