A low-cost, composite collagen-PDMS material for extended fluid retention in the skin-interfaced microfluidic devices

Abstract The advancement of soft, wearable microfluidic devices relies on the microfabrication of polydimethylsiloxane (PDMS) using soft lithography techniques. However, thin 3D microstructures made of PDMS limit long-term storage of aqueous samples and reduce the accuracy of onboard sensing modalities within the platform because of the material's high permeation of water vapor. We studied a composite material of collagen microparticles and PDMS that greatly reduces water evaporation while maintaining the properties of a soft elastomer required for skin-interfaced microfluidics. The collagen-PDMS material is biocompatible, affordable, and non-toxic. We reduced permeability by 80.2% by building a film containing 30 wt% collagen microparticles. Mechanical properties, such as elastic modulus and bonding efficacy, can vary as a function of particle concentration in the films. The skin-interfaced collagen-PDMS microfluidic devices increase sweat retention by 45% through 9 h compared with pure PDMS. This material can greatly improve the long-term sample storage of epidermal devices.