Pressure-sensitive microfluidic gates fabricated by patterning surface free energies inside microchannels

A series of pressure-sensitive microfluidic gates to regulate liquid flow have been successfully fabricated by patterning surface free energies inside microchannels using self-assembled monolayers in combination with either multistream laminar flow or photolithography. The designs are based on the principles of surface-directed liquid flow previously reported. Aqueous liquids, including protein solutions, are confined to the hydrophilic pathways (or the most hydrophilic pathway) under spontaneous flow conditions and flow into the hydrophobic regions or the less hydrophilic pathways when pressures exceed critical values. A programmable pressure-sensitive liquid delivery device is demonstrated. We have also investigated the initial rate of liquid flow in surface-patterned microchannels under spontaneous flow conditions from both analytical and experimental approaches. The methods described here provide an alternative to the conventional approaches to control liquid flow in the fast-developing field of microfluidic systems.