Selective enzymatic digestion as a key to understand soft tissue microstructure

Dermis is a heterogeneous tissue in which extracellular matrix components change in relative amount and spatial assembly across the tissue thickness. In this work we aimed at gaining a better insight into the e®ect of extracellular matrix microstructure and composition on the mechanical behaviour of di®erent dermal strata by combining experimental mechanical analysis and selective enzymatic digestion of extracellular matrix components. In particular, the mechanical tests were DMA (dynamic-mechanical analysis) and three di®erent enzymes were also used. The results showed that the upper dermal stratum, richer in papillary dermis, was characterized by higher mechanical properties than the lower one, which was almost only composed of reticular dermis. Moreover the depletion of inter¯brillar proteins, proteoglycans and glycosamminoglycans decreased the dynamic moduli of dermis, especially at small frequencies. Interestingly, the disruption of the elastic network, greatly in°uenced the viscoelastic properties of upper dermis, inducing a dramatic decrease of both storage (G') and loss (G") moduli, suggesting that the spatial assembly of the elastin and collagen networks as well as their mutual interactions dominate the dynamical mechanical response of the tissue.