The biomechanical and histological sequelae of common skin banking methods

Human skin allografts are used worldwide as an adjunct for the healing of burns when autograft skin is not available or not indicated. Allograft skin comes from human cadaveric donors, and so must be preserved until use. This study forms the first investigation to compare the mechanical and histological integrity of human split-thickness skin grafts preserved by either glycerolisation or cryopreservation (with or without the cryoprotectant DMSO). Stress relaxation was used to assess mechanical properties, whilst histological analysis allowed for evaluation of structural integrity. Preservation of tissue, whether by freezing or glycerolisation, altered the relaxation behaviours of skin. Young's modulus upon initial loading significantly decreased for skin frozen without cryoprotectant, but remained unchanged for skin frozen with cryoprotectant and skin preserved with glycerol. After 1.5h of stress relaxation, both fresh skin and skin frozen without DMSO displayed similar relaxation rates. Samples frozen with DMSO or preserved with glycerol had increased relaxation rate and had not reached load equilibrium within this time. To understand the structural basis for the biomechanical changes, samples were histologically assessed. All preservation protocols resulted in a similar degree of visible damage, but cryopreservation appeared particularly damaging to the extracellular matrix, whereas glycerolisation caused dramatic separation of the epidermis from the underlying dermis. The mechanical property alterations reveal that preservation results in laxity, which clinically could hinder contact dependent healing properties, but alternatively may increase capacity for coverage. The structural changes confirm that preservation techniques do not conserve grafts in an in vivo state.