Numerical modeling of a flat microdialysis probe for skin wound analysis

Skin wound is the state at which the outer most skin layer (epidermis) is broken. Chemokines and cytokines are generated as the inflammatory response to wounding. Researchers have used various techniques to explore inflammatory effects of the skin, including skin blister, ultra-filtration and microdialysis [1]. Microdialysis is a diffusion-based sampling technique that is widely used in vivo in different clinical areas [2]. Microdialysis is a continuous sampling technique based on controlling the mass transfer rate of small molecules across a semipermeable membrane while excluding the larger ones. For biochemical monitoring, microdialysis systems are usually placed (inserted or implanted) inside the tissue of interest with an isotonic perfusion fluid flowing through the system and diffusional exchange occurring between the perfusate and the surrounding interstitial fluid (ISF). Because the dialysis process has a minimal effect on the surrounding fluid, it is viewed as a tool for continuous monitoring. Microdialysis probes consist of a very small membrane where solutes of a certain size can diffuse through. The membrane is implanted in the tissue and perfused with a saline solution matching the tissue physiological fluid. The fluid inside and outside the membrane equilibrates following the principle of diffusion, recovering the substances of interest. Skin microdialysis is preferred to other technique due to its minimal invasion during probe placement. However, this minimal invasion causes stress to an already damaged area, increasing the inflammatory response further [3]. In this study we have designed a new flat microdialysis probe geometry, which eliminates perforation and hence ideal for use on skin wound tissue, using COMSOL Multiphysics as modeling software. Flow rate plays and important role in microdialysis recovery and needs to be considered in designing an efficient microdialysis probe [4]. Typically, microdialysis flow rates range between 0.5 and 6 μ1/min [2]. The probe design was developed varying the degree of bifurcation for both sharp corners and rounded corners. Velocity field was simulated at different angles (20 to 60°) and constant pressure, and in the case of rounded corners, at different radius of curvature as shown in Figure 1(a-b). Our results show that as the angle is decreased, the velocity increases, presenting a maximum velocity at 20 degrees. As for rounded angles our results show that larger radius leads to higher velocity at constant pressure.