In microfluidics, bonding techniques are as varied as the number of materials used. Polydimethylsiloxane (PDMS) is probably the most common adhesive that offers a stick-and-play concept for device integration, allowing increased functionality. But reversible bonding is weak so researchers are looking for more secure materials.
Adhesive abilities of geckos are the result of one key factor: Van der Waals forces. On their own, these forces are weak, but they exhibit significant adhesion capacities when acting over large areas. Inspired by that concept, Dan Sameoto and Abdul Wasay, from the University of Alberta, designed and manufactured a reversible system over 10 times stronger than PDMS. The difference with current techniques is in the design of the channels, which involves creating a gasket to contain the fluidics.
Dry adhesive fibres of styrene ethylene butylene styrene surround this gasket, generating a mushroom shaped geometry and act as a sweep to define the path of the desired channel. Apart from acting as sidewalls, these fibres enhance net adhesion and contribute to make the whole geometry tolerant to defects and surface variation.
‘From a technical standpoint, the development of a process to make reliable mushroom shaped fibres was the biggest challenge,’ admits Sameoto. ‘The infrastructure needed to apply this work is not that onerous at all and can permit very high quality structures to be produced at quite low costs.’
‘This new adhesive technology will make complex microfluidic patterns much simpler to assemble,’ says Ali Dhinojwala, from the University of Akron, US, who is also interested in mimicking the sticking power of geckos. ‘By incorporating mushroom-shape tips in the fabrication of the device, they demonstrate reversible seals with larger burst pressures than PDMS-based devices.’
Sameoto is now exploring the full potential of this study, stressing how significant this advance is for resource-limited projects. He is confident that microfluidics processes and materials will be cheap enough someday that disposable devices could be distributed ‘almost like Band-Aids, sealed and sterilised, and ready to implement in point-of-care settings at a price point affordable to nearly anyone in the world.’