Diffusion measurements in epidermal tissues with fluorescent recovery after photobleaching

Background: Pressure ulcers are areas of soft tissue breakdown, resulting from sustained mechanical loading of the skin and underlying tissues. Measuring biochemical markers that are released upon mechanical loading by the epidermis seems a promising method for objective risk assessment of the development of pressure ulcers. This risk assessment method will better determine the risk of a patient to develop pressure ulcers than the risk score lists currently used. So far, experimental studies have been performed that measure the tissue response in the culture supernatant. To elucidate the transport of the biochemical markers within the epidermis, the diffusion coefficient needs to be established. Methods: In the current study, fluorescent recovery after photobleaching (FRAP) is used to determine the diffusion coefficient of fluorescent-labeled dextran molecules in human epidermis, porcine epidermis and engineered epidermal equivalents. These dextran molecules have a similar weight to the biochemical markers. Results: Similar diffusion coefficients were found for human and porcine epidermal samples (6.2 x 10(-5)+/- 1.2 x 10(-5) and 5.9 x 10(-5)+/- 6.1 x 10(-6) mm(2)/s, respectively), whereas the diffusion coefficient of the engineered epidermal equivalent was significantly lower (2.3 x 10(-5)+/- 1.0 x 10(-5) mm(2)/s). Conclusion: The diffusion could be measured in epidermal tissues using FRAP. In the future, the diffusion coefficients obtained in the current study will be used to study the difference between the transport in EpiDerm cultures and in human epidermis.