Rapid Fabrication of Round Flexdym Microchannels via Direct PDMS (Thermoset)-to-Flexdym (Thermoplastic) Thermal Replication

Round microchannels provide physiologically relevant flow environments and improved fluidic performance compared with conventional rectangular geometries; however, their scalable fabrication in potentially biocompatible thermoplastic substrates remains challenging. Here, we present a rapid and low-cost PDMS-to-Flexdym thermal replication strategy to directly transform round microchannel architectures from a reusable compliant thermoset PDMS mold into a thermoplastic microfluidic platform. Round PDMS convex molds generated by thermal air expansion followed by PDMS double casting were used for heat-assisted conformal replication to transform spatially varying complex round microchannels into Flexdym. The method successfully transferred complex serpentine, branched, and interconnected channel architectures while preserving continuous flow paths and curved geometries. Temperature-dependent framework and experimentation revealed improved vertical feature recovery with increasing embossing temperature, while lateral dimensions remained highly conserved. Across representative channel widths of ~37–249 µm, replicated Flexdym channels achieved width and height transfer ratios of approximately 99–103% and 93–105%, respectively. Sequential dimensional analysis among concave PDMS, convex PDMS, and Flexdym replicas showed no statistically significant differences in channel width or height (p > 0.05), confirming high geometric fidelity throughout the replication process. AFM, SEM, and stylus profilometry results further verified the preservation of surface characteristics, rounded cross-sectional morphology, and reproducible channel profiles, with Flexdym surface roughness reduced from ~84.1 nm (PDMS mold) to ~25.1 nm in Flexdym after replication. Finally, integration of the replicated round channels into a multilayer microvalve demonstrated functional fluidic control through syringe-assisted compressed air actuation, supported by two-phase moving-mesh simulation and analytical air compression modeling. This strategy provides a practical route for translating PDMS-based round microchannel prototyping into scalable, more biocompatible thermoplastic microfluidic platforms for building next-generation microphysiological systems and bioengineering applications.