Flow by design: a guided review of microfluidics for wearable biosensors

The integration of microfluidics into wearable biosensors has enabled real-time, non-invasive access to physiological information through biofluids such as sweat, saliva, tears, and interstitial fluid (ISF). However, the successful design and fabrication of microfluidic systems for wearables requires interdisciplinary expertise in fluid dynamics, materials science, microfabrication, and device integration. These significant barriers can hinder rapid innovation and adoption. This review aims to serve as a guide for researchers and engineers developing microfluidic systems for wearable applications. We provide a step-by-step overview of microfluidic design principles, material selection, fabrication methods, and strategies for fluid handling and sampling. Attention is given to the constraints and opportunities unique to wearable formats, such as flexibility, biocompatibility, and integration with sensors and electronics. We also highlight future trends in the field, including the integration with artificial intelligence (AI), design automation, and novel flow control technologies. By providing clear guidance on the design and implementation process, this review seeks to accelerate the development of microfluidic platforms for continuous health monitoring.