Reliable magnetic reversible assembly of complex microfluidic devices: fabrication, characterization, and biological validation

Current standard procedures for fabrication of microfluidic devices combine polydimethylsiloxane (PDMS) replica molding with subsequent plasma treatment to obtain an irreversible sealing onto a glass/silicon substrate. However, irreversible sealing introduces several limitations to applications and internal accessibility of such devices as well as to the choice of materials for fabrication. In the present work, we describe and characterize a reliable, flexible and cost effective approach to fabricate devices that reversibly adhere to a substrate by taking advantage of magnetic forces. This is shown by implementing a PDMS/iron micropowder layer aligned onto a microfluidic layer and coupled with a histology glass slide, in union with either temporary or continuous use of a permanent magnet. To better represent the complexity of microfluidic devices, a Y-shaped configuration including lower scale parallel channels on each branch has been employed as reference geometry. To correctly evaluate our system, current sealing methods have been reproduced on the reference geometry. Sealing experiments (pressure control, flow control and hydraulic characterization) have been carried out, showing consistent increases in terms of maximum achievable flow rates and pressures, as compared to devices obtained with other available reversible techniques. Moreover, no differences were detected between cells cultured on our magnetic devices as compared to cells cultured on permanently sealed devices. Disassembly of our devices for analyses allowed to stain cells by hematoxylin and eosin and for F-actin, following traditional histological processes and protocols. In conclusion, we present a method allowing reversible sealing of microfluidic devices characterized by compatibility with: (i) complex fluidic layer configurations, (ii) micrometer sized channels, and (iii) optical transparency in the channel regions for flow visualization and inspection.