Biological ion channels penetrated through cell membrane form unique transport pathways for selective ionic conductance. Replicating the success of ion selectivity with mixed matrix membranes (MMMs) will enable new separation technologies but remains challenging. Herein, we report a soft substrate‐assisted solution casting method to develop MMMs with penetrating subnanochannels for selective metal ion conduction. The MMMs are composed of penetrating Prussian white (PW) microcubes with subnanochannels in dense polyimide (PI) matrices, achieving selective monovalent metal ion conduction. The ion selectivity of K+/Mg2+ is up to 14.0, and the ion conductance of K+ can reach 45.5 μS with the testing diameter of 5 mm, which can be further improved by increasing the testing area. Given the diversity of nanoporous materials and polymer matrices, we expect that the MMMs with penetrating subnanochannels could be developed into a versatile nanofluidic platform for various emerging applications.

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Achieving efficient separation of mono‐/multivalent metal ions is essential in various fields, yet it remains a significant challenge. In this work, a metal–organic framework (MOF) array with subnanochannels that exhibit high selectivity and ion permeability in the sieving of mono‐/multivalent metal ion was developed. Specifically, we used confined interfacial reaction at room temperature to synthesis the MOF array inside the micrometer through‐pores of a polyethylene terephthalate (PET) membrane. The location of the oil/water interface was regulated by adjusting the surface wettability of the PET membrane. By taking advantage of size sieving effect of the subnanochannels of MOF crystals, we were able to effectively separate monovalent metal ions from multivalent metal ions with selectivity reaching up to 3930±373 (e.g., Li+/Zr4+). The fluxes of Li+ ions were observed to be as high as 1.97 mol h−1 m−2. The MOF array‐based membrane with subnanochannels that we have developed exhibits great promise for applications in wastewater treatment, lithium extraction from salt‐lake brines, and other related fields.

Ultrathin hydrogel films composed of cross-linked polymer networks swollen by water, with soft and moisturized features similar to biological tissue, play a vital role in flexible biosensors and wearable electronics. However, achieving efficient and continuous fabrication of such films remains a challenge. Here, we present a microfluidic-based strategy for the continuous fabrication of free-standing ultrathin hydrogel films by using laminar flow, which can be precisely controlled in the micrometer scale. Compared with conventional methods, the microfluidic-based method shows advantages in producing hydrogel films with a high homogeneity as well as maintaining the structural integrity, without the need of supporting substrates and sophisticated equipment. This strategy allows the precise control over the thickness of the hydrogel films ranging from 15 ± 0.2 to 39 ± 0.5 μm, by adjusting the height of the microfluidic channels, with predictable opportunities for scaling up. Therefore, our strategy provides a facile route to produce advanced thin polymer films in a universal, steerable, and scalable manner and will promote the applications of thin polymer films in biosensors and wearable electronics.