In the past decade, 3D printing technologies have been adopted for the fabrication of microfluidic devices. Extrusionbased approaches including fused filament fabrication (FFF), jetting technologies including inkjet 3D printing, and vat photopolymerization techniques including stereolithography (SLA) and digital light projection (DLP) are the 3D printing methods most frequently adopted by the microfluidic community. Each printing technique has merits toward the fabrication of microfluidic devices. Inkjet printing offers a good selection of materials and multimaterial printing, and the large build space provides manufacturing throughput, while FFF offers a great selection of materials and multimaterial printing but at lower throughput compared to inkjet 3D printing. Technical and material developments adopted from adjacent research fields and developed by the microfluidic community underpin the printing of sub-100 μm enclosed microchannels by DLP, but challenges remain in multimaterial printing throughput. With the feasibility of 3D printed microfluidics established, we look ahead at trends in 3D printing to gain insights toward the future of this technology beyond the sole prism of being an alternative fabrication approach. A shift in emphasis from using 3D printing for prototyping, to mimic conventionally manufactured outputs, toward integrated approaches from a design perspective is critically developed.

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The combination of microfluidics and material science has led to a breakthrough in ordered porous materials. [1] Singlephase porous materials with a large surface area confined within small volumes facilitate physical exclusion or selective adsorption of unwanted contaminants or chemical species. However, several necessary fields of applications, such as energy storage, fluid filtration, and especially in tissue engineering, require spatially varying porosity or pore size with well-defined gradients. [2,3] Porous materials can be created synthetically or microfabricated using lithographic and/or advanced additive/subtractive approaches, providing various degrees of control over the morphological and chemical properties. [4,5] 3D printing, also referred to as additive manufacturing (AM), offers unprecedented opportunities to design and produce complex architectures. Moreover, custom-designed geometries can be fabricated rapidly and cost effectively, including layouts

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