PDMS MICROSTRUCTURES 3D-NANOPRINTED INSIDE UNCOATED, ENCLOSED PDMS-ON-GLASS MICROCHANNELS VIA IN SITU DIRECT LASER WRITING

Polydimethylsiloxane (PDMS) is one of the most commonly used materials for soft lithography protocols and microfluidics research.Yet, for emerging applications that rely on "in situ Direct Laser Writing (isDLW)"-approaches in which microstructures are additively manufactured directly inside of enclosed microfluidic channels-PDMS has presented a number of challenges as a microchannel material, primarily stemming from difficulties in facilitating sufficient adhesion between printed structures and the channel wall.To address such issues and enable the facile fabrication of PDMSbased isDLW-printed microfluidic technologies, here we introduce a novel strategy for printing PDMS microstructures directly onto and fluidically sealed to uncoated PDMS sidewalls of enclosed PDMS-on-glass microfluidic channels.We investigated microchannel geometry (e.g., rectangular, trapezoidal, and semi-ovular cross sections) as a determinant in microfluidic print-to-wall sealing efficacy for 10 μm-thick fluidic barrier microstructures printed in channels with heights and widths of 50 μm.Microfluidic burstpressure results revealed that semi-ovular channels yielded superior sealing integrity with pressure tolerances up to 350 kPa (i.e., >5× that of our prior work), suggesting that the presented strategy offers unique promise to enable new classes of PDMS-based 3D microfluidic structures for biomedical and soft robotic applications.