Wound Healing Revealed by a Novel Automated Indentation Technique

Methods: Wounded pig skin samples (4x8cm centered 3 cm incision length) were placed skin surface up on a flat platform of a multiaxial mechanical tester equipped with a 6.35mm diameter spherical indenter under its load cell (Mach-1v500css, Biomomentum Inc., Canada). Following top-view photodocumentation, a position grid (>130 positions) was superimposed over the image. At each position, the tester was programmed to precisely measure overall skin thickness through detection of contact with the surface and to perform an indentation ramp of 1.5mm at 200um/s. Subsequently, the sample was reshaped in two adjacent dumbbell-shaped strips (perpendicularly to the wound), mounted in tension grips and tensile rupture tests were performed at 2mm/s.

Results: High-resolution mapping of maximum load and thickness were generated (about 30s per position). These mappings revealed significant spatial variation of the mechanical properties and thickness over the wound region compared to the uniform properties of the intact skin observed at least 1cm away from the incision site. Also, quantitative information about the hypertrophy/atrophy of the wound could be calculated where a sample revealed a 12.25 mm2/mm of wound hypertrophy. Considering the load at rupture in the tension tests, a correlation could be observed with the maximum load in indentation (or thickness) measured at the rupture site.