Programmable Porosity in Polymers via Microfluidic Templating and 3D Printing

Polymeric functionally graded porous materials (pFGPMs) enable spatial control over transport and mechanical response in a continuous solid in which porosity is strategically placed rather than uniformly distributed. Early research on the production of pFGPMs has demonstrated that graded architectures can be induced as indirect outcomes of time-evolving temperature, pressure, or concentration fields. Because these gradients emerge from process-driven kinetics, reproducibility and spatiotemporal control remain limited. Fluid templating offers a more direct route: the transient structure of polymerizable/crosslinkable foams or high internal phase emulsions (HIPEs) can be transferred into a solid matrix while controlling compartment size, packing, and film stability during solidification. Microfluidics enhance fluid management by confining interfacial breakup to produce monodisperse bubbles or droplets whose size, volume fraction, and interconnectivity can be tuned independently, transforming liquid templates into programmable solid architectures. This review follows the evolution of microfluidic templating toward its integration with additive manufacturing, with an emphasis on platforms that embed in-line bubble or droplet generation at the printhead. We conclude with an outlook on the opportunity to expand the palette of available materials and discuss the emerging role of data-driven approaches in managing the coupled dynamics of formulation, breakup, and solidification, enabling truly programmable polymeric FGPMs.