Collapse of arbitrary-shaped soft microfluidics

Soft epidermal microfluidics gain momentum because of their unique capabilities to collect and analyze the sweat or interstitial fluid for health monitoring and disease diagnostics. However, they are susceptible to structural instability or self-collapse due to their high mechanical compliance and strong adhesion between layers. Here, a generic mechanical stability model that combines a geometric optimization approach and superelliptical plate theory is established to analyze the structural stability of arbitrary-shaped soft microfluidic components. The established model not only reduces to the existing models for circle chambers and infinite channels, but also results in a simplified anti-collapse criterion to evaluate the stability of soft microfluidic devices. The result from the model indicates that there exists a shape-specific upper bounds critical value for the normalized work of adhesion to ensure mechanical stability, which combines the effects of the minimum enclosed geometry, interfacial work of adhesion, uniform height and effective bending stiffness of top and bottom plates in microfluidic components. The obtained design theory validated by extensive experimental data provides essential guidelines to design epidermal microfluidic devices free of self-collapse issues.