Viscoelastic properties of decellularized and freeze-dried human dermis between −90°C and 40°C

Abstract

BACKGROUND: Human donor skin is processed to make the acellular dermis matrix (ADM) for tissue repair and regeneration. There is no data on the viscoelastic properties of ADM at room and subzero temperatures. OBJECTIVE: The work evaluated the temperature dependence of viscoelastic properties of freeze-dried ADM. MATERIALS AND METHODS: Donor skin was de-epidermized, de-cellularized and freeze-dried with trehalose as the lyo-protectant. Glass transition of freeze-dried ADM was measured by differential scanning calorimeter (DSC), and viscoelastic properties were examined by dynamic mechanical analyzer (DMA). RESULTS: At the low moisture range (1.4 ± 0.5%), the glass transition temperature (Tg) of freeze-dried ADM was 90°C to 100°C. As the moisture content increased, the Tg decreased steadily. At the high moisture range (10.8 ± 2.9%), the Tg was 40°C to 60°C. There were large donor-to-donor variations in viscoelastic properties of freeze-dried ADM as demonstrated by the changes in storage modulus (G’), loss modulus (G”) and damping factor tan δ(G”/G’). However, the trends of the temperature dependence for G’, G” and tan δ were similar among all 8 donors. For each donor, changes in G’ and G” were relatively small between −90°C and 40°C, and G’ was at least one order of magnitude greater than G”. Two viscoelastic relaxations were observed in freeze-dried ADM, one at −20°C and the other at −60°C respectively. CONCLUSION: Freeze-dried ADM was protected in the glassy carbohydrate matrix. DMA observed two viscoelastic relaxations (i.e., α process at −20°C and β process at −60°C). Overall changes in G’ and G” of freeze-dried ADM were relatively small within one order of magnitude between −90°C and 40°C.