Recent Impact of Microfluidics on Skin Models for Perspiration Simulation

Abstract

Skin models offer an in vitro alternative to human trials without their high costs, variability, and ethical issues. Perspiration models, in particular, have gained relevance lately due to the rise of sweat analysis and wearable technology. The predominant approach to replicate the key features of perspiration (sweat gland dimensions, sweat rates, and skin surface characteristics) is to use laser-machined membranes. Although they work effectively, they present some limitations at the time of replicating sweat gland dimensions. Alternative strategies in terms of fabrication and materials have also showed similar challenges. Additional research is necessary to implement a standardized, simple, and accurate model representing sweating for wearable sensors testing.

Wearable Sweat Loss Measuring Devices: From the Role of Sweat Loss to Advanced Mechanisms and Designs

“… An additional challenge is to formulate an accurate and elaborate sweat gland model to describe sweat gland and simulate sweat generation mechanism. [ 53 , 112 ] In terms of biomarker sensing, such a model will improve understanding of each biomarker partitioning and transport, as well as their correlation with blood or ISF levels; this will explore the use of sweat biomarkers for more opportunities in disease diagnostics. The inter‐ and intraindividual variability in a region or entire body is due to differences in the sweat secretion rate per gland instead of the total number of active sweat glands.…”

“…[ 42 , 53 , 111 ] Compared with reducing the dilution effect at a lower SSR, active calibration by measuring sensible sweat rates using a detailed perspiration model for the skin and sweat gland is a better approach to correct the dilution effect in more extensive sweat scenarios (e.g., exercise, sport, and sauna). [ 53 , 112 ] By contrast, the active portioning components in sweat are essentially not affected by the dilution effect because of the active transport mechanisms. [ 53 , 110 ] Nevertheless, the active nature of reabsorption of ions (e.g., sodium, chloride, and bicarbonate) in the sweat gland duct is also confirmed to be flow‐rate‐dependent, such that higher sensible sweat rates are associated with proportionally lower ion reabsorption rates, resulting in higher final concentration.…”

Skin and Artificial Skin Models in Electrical Sensing Applications

“…Using laser-machined membranes is one of the common approaches which provides control over sweat rate and composition, although there are limitations about mimicking the dimensions of the sweat glands. Using bilayer membranes, Hou et al, Eiler et al, and Hansen et al were able to homogeneously control the sweat rate in a perforated film mimicking the perspiration conditions in skin. − Other approaches based on the electronic control of the sweat rate and porous hydrogels have also been developed and summarized in a recent review paper …”

An Integrated 3D Hydrophilicity/Hydrophobicity Design for Artificial Sweating Skin (i‐TRANS) Mimicking Human Body Perspiration

“…For example, microfluidic devices made of layer(s) of membranes with laser cut pores usually require complicated fabrication, and uniform "sweat pore" activation still needs sufficiently high pressure provided. [21][22][23][24] For thermal assessment of textiles during perspiration, the water-fed porous metal plate covered by water-vapor permeable but liquid-water impermeable membrane can only simulate the vapor evaporation of human body, ignoring liquid sweat. [25,26] Supplying water through tiny tubes to holes at the manikin surface was performed, but the manufacturing of the system is very complex and costly.…”