Sonsma1, J., Grin1, P.C., Jorritsma1, P.A., Bronneberg2, D., Bouten2, C.V.C., Oomens2, C.W.J., and Baaijens2, F.P.T. 1VHall Instituut Leeuwarden, Unit Life Sciences, Biotechnology. 2Eindhoven University of Technology, Department of Biomedical Engineering, Section Soft Tissue Biomechanics and Engineering.

As stated in the “Conclusions” section, the main experiment in this study by researchers at Eindhoven University of Technology was performed to determine whether urine makes the skin more susceptible for mechanical loading, and that to make this determination, an experimental setup was successfully developed that made use of (MatTek’s) EpiDerm, s-urine and a custom-built loading device. Decubitus wounds, also known as pressure ulcers, are areas of soft tissue breakdown that result from sustained mechanical loading of the skin and underlying tissue. Today little is known with respect to the etiology of these ulcers, making prevention complicated. Several subjective risk assessment calculators are currently used which do not predict pressure ulcer development satisfactorily. Therefore, there is need for objective prevention strategies that identify people at risk for developing pressure ulcers before the physiological signs of tissue damage occur. Eindhoven University of Technology is evaluating the use of early damage markers to distinguish people at risk of developing pressure ulcers from people who are not at risk. Urine is defined as an important risk factor for developing pressure ulcers. Nevertheless, until now the nursing staff makes a clear distinction between wounds inflicted by pressure and wounds inflicted by urine. Upon prolonged exposure, urine is known to chemically irritate the skin and impair its structure and function. Urine consists of various irritating components. The urine of urine incontinent patients tends to be alkaline due to the formation of ammonia by urease producing micro-organisms. Normal urine pH ranges between pH 6.0-6.5, but the urine pH of incontinent people increases to pH 8.0 – 9.0. It is known that these high pH levels, just like moisture, increase skin permeability and thus make the skin more vulnerable to noxious substances. The aim of the present study was to determine whether urine makes the skin (in particular the epidermis) more susceptible to mechanical loading. It was hypothesized that urine makes the skin more susceptible for mechanically induced skin damage and thus for developing pressure ulcers. The epidermal susceptibility to loading was evaluated by assessing tissue damage in an in vitro model (EpiDerm™) of the epidermis. Epidermal equivalents were first chemically irritated by topical application of synthetic urine during 4 hours, followed by mechanical irritation with different clinically relevant pressures for an additional 24 hours. Damage progression in the epidermis was assessed by looking at the tissue structure (histology), the tissue viability (MTT and LDH assay) and by measuring the release of early damage markers (Interleukin-1alpha, Interleukin-1 receptor antagonist and Interleukin-8) by ELISA. Prior to the current study, different pilot experiments were performed to determine the effect of urine itself on the epidermal damage progression. Pilot results indicated that synthetic urine seemed to have a damaging effect on the epidermis when exposure was prolonged (24 hours). Furthermore, this effect seemed to be pH dependent; damage progression in the epidermis seemed to be more pronounced when synthetic urine was more alkaline. 4 Hours exposure to synthetic urine did not seem to have any visible effects, although an increased damage marker release could be observed. It could not be confirmed statistically whether chemical irritation by synthetic urine makes the epidermis more susceptible for mechanical loading. However, results seemed very promising to continue further research. Although no clear visible tissue damage could be observed by histology and MTT assay, chemical irritation of the epidermis by topical application of s-urine seemed to make the epidermis more susceptible for mechanical loading of 50mmHg and 75mmHg. This susceptibility was based on increased IL-1á and IL-1ra levels. Furthermore visible tissue damage could be observed when EpiDerm samples were mechanically irritated with 100mmHg. This tissue damage seemed to be more intensified when samples were not only mechanically irritated but also chemically. MTT, LDH, IL-1á and IL-1ra results seemed to confirm this increased tissue damage as a result of the combination of chemical and mechanical irritation, making it very likely to assume that s-urine has an additional effect on the damage progression in the epidermis.


Damage, Decubitus wounds, EPI-200, EpiDerm, Histology, IL-1a, IL-1ra, IL-8, LDH assay, MTT, Mechanically induced skin damage, Pressure ulcers, Structural, Urine

Materials Tested

Mechanical loading, Urine, pH

Request a copy of this paper, click here.