Morphing out-of-surface channels enable strain-based control over fluid flow in skin-mountable patches

Area of Science:

• Materials Science
• Biomedical Engineering
• Fluid Mechanics

Background:

• Conventional biomechanical pumps rely on compression for pressure generation due to natural material expansion under tension.
• Microfluidic devices often require external power sources for fluid actuation.

Purpose of the Study:

• To introduce and characterize out-of-surface microchannels (OSMiCs) that generate pressure from tensile strain.
• To investigate the relationship between microchannel geometry, mechanical strain, and fluid flow.
• To demonstrate a novel, power-free fluid control element for strain-based applications.

Main Methods:

• Fabrication of monolithic polydimethylsiloxane (PDMS) patches with OSMiCs.
• Characterization of OSMiC behavior under uniaxial tensile strain.
• Investigation of wrinkling, buckling, and snap-back phenomena.
• Measurement of fluid flow pressure generation.
• Numerical simulations to validate experimental observations.

Main Results:

• OSMiCs exhibit negative volumetric strain, generating pressure under tensile strain.
• Tunable, asymmetrical pressure generation achieved through shape-changing (morphing) properties.
• Maximum forward (backward) flow pressure of 10 (-14) kPa measured at 20% uniaxial strain.
• Demonstrated discrete strain-actuated flow control by integrating OSMiCs with different Q values.
• Successful demonstration of a power-free OSMiC skin patch for liquid administration.

Conclusions:

• OSMiCs offer a novel mechanism for biomechanical fluid actuation based on tensile strain.
• The developed technology enables tunable, power-free fluid control for wearable and implantable devices.
• OSMiCs present a versatile platform for strain-responsive microfluidic applications, including drug delivery.