Fluid Flow Control in Cotton Threads with Mesoporous Silica Coatings

Abstract Microfluidic devices are important, e.g. in the field of point of care diagnostics. They are of special importance, if they are fabricated out of cheap and renewable materials. Tackling complex separation or sensing problems profits from modular three‐dimensional fluidic devices. Using cotton threads as renewable material allows the modular design of three‐dimensional fluidic devices and networks. Here, fluidic threads with modular designed and tunable thread wettability are presented. The wettability is gradually adjusted from highly hydrophilic to hydrophobic. The thread wettability directly affects the fluid imbibition velocity as well as the distance, which the fluid imbibes into the thread. The wettability adjustment is based on a simple dense or mesoporous silica coating applied onto the cotton thread using sol‐gel chemistry and evaporation induced self‐assembly. In addition to wettability, the mesoporosity and the pore functionalization are used to tune the fluid velocity within the thread. Connecting different silica functionalized threads into one device by knotting them together, fluids can be guided through this network in a predicted manner, which allows a modular design of 3D microfluidic thread‐based devices.