Metal–organic framework nanoparticles self-assemble at coacervate interfaces to form semipermeable, rigid membranes that stabilize protocells and enable compartmentalized reactivity. By integrating porosity, coordination chemistry, and mechanical robustness, metal–organic framework membranes regulate molecular transport, protein localization, and inter-compartment communication, advancing biomimetic tissue-like assemblies and interfacial porous materials design. Metal–organic frameworks (MOFs) have long been highly regarded for their crystalline order, structural modularity, and precisely defined porosity. Metal nodes and organic linkers form ordered lattices with defined pores, enabling predictable adsorption and transport processes. Traditionally, research on MOFs has primarily focused on established fields such as molecular adsorption and heterogeneous catalysis 1, 2. In these studies, MOFs are typically regarded as static, rigid, and isolated solids operating within relatively simple chemical environments, where interfaces exert only a minor role. Performance is usually judged under equilibrium or near-equilibrium conditions. As materials chemistry moves toward complex systems, many emerging functionalities cannot be understood solely through bulk properties. Recently, there has been growing interest in introducing MOFs into chemically complex, soft, and dynamic systems, including aqueous media, biomolecular environments, and multicomponent assemblies. A critical question arises: can porous crystalline materials retain functional relevance when removed from rigid, solid-state settings and embedded into fluctuating soft-matter interfaces? It is critical that MOFs transition from isolated functional solids toward components of adaptive chemical systems. However, research into MOFs as interfacial materials remains largely unexplored, particularly concerning their behavior at liquid–liquid interfaces. Given concerns over the mechanical brittleness, hydrolytic stability, and uncontrolled aggregation of MOFs, their use as interfacial building blocks remains relatively uncommon. Nevertheless, it is precisely the porosity, surface chemical reactivity, and coordination flexibility of MOFs that constitute the core characteristics of their interfacial properties, representing the domain where they can be most effectively transformed into functional applications. Qiao's research team has directly addressed this gap by positioning MOF nanoparticles as active interfacial materials and placing them at the center of an interfacial system 3. By assembling MOFs at the boundary of complex coacervate droplets, these membranized coacervates can be further engineered into primitive cells containing artificial organelles, as well as tissue-like assemblies possessing signal processing capabilities and intercellular communication functions. This research demonstrates the potential for designing artificially controlled biomolecular systems to mimic natural cellular functions, providing crucial insights for assembling membranized coacervates into primitive tissues. The preparation of conventional MOF films relies on templating methods, involving direct film formation or growth on rigid substrates 4. In this research, the MOF layer is not prefabricated but rather self-assembles at the liquid–liquid interface. This assembly process is driven by coordination interactions and surface forces, with electrostatic interactions also playing a role. While these principles are well established in colloid science, they are relatively uncommon in the study of MOFs. This interfacial membrane changes system behavior. Membraneless coacervates are unstable, prone to fusion where multiple molecules merge and lose their independence 5. Inspired by the layered structures and intricate functions of cell membranes, cytoplasm, and organelles (Figure 1A), Qiao and colleagues achieved functional organization of coacervate microdroplets using a MOF protective layer (Figure 1B). The interfacial membrane is primarily formed by a zeolitic imidazolate framework (ZIF-8), constructed from Zn2+ nodes coordinated with 2-methylimidazolate linkers. The fast coordination kinetics and moderate stability of this Zn–imidazolate network enable in situ nucleation on the coacervate interface, while its intrinsic microporosity provides size-selective permeability and a chemically addressable surface for biomolecular organization. The ZIF-8 shell constructs a protective layer featuring an intrinsic cavity and distinctive surface chemistry, enabling the coacervate microdroplets to maintain their independence over time. This stability permits sustained chemical processes and enables controlled comparisons between distinct compartments. The MOF membrane establishes a functional platform, transforming fragile soft phases into editable systems. The membrane formed by the MOF coating is typically not sufficiently dense. Its internal pores remain accessible and continuous across the interface, allowing molecular exchange between interior and exterior solutions. Transport is selective, but not in a simplistic, size-exclusive sense. Transport across the MOF-coated interface is governed by a combination of electrostatic interactions, coordination affinity, and interfacial adsorption effects. The Zn–imidazolate surface presents charged and polar sites capable of transiently interacting with guest molecules, allowing species with favorable charge states or binding propensity to partition into or traverse the membrane preferentially. Furthermore, molecular passage depends on a combination of pore dimensions, membrane thickness, particle packing, and local adsorption at exposed metal sites. Crucially, the transport process is not solely governed by porosity. Surface chemistry also plays a decisive role. Metal nodes and organic linkers remain exposed on the membrane surface, creating interaction sites for biomolecules. Proteins and enzymes achieve selective adsorption through coordination tendencies and electrostatic interactions rather than artificially designed binding motifs. In many biological contexts, such non-specific adsorption would be considered detrimental. However, within this system, as illustrated in Figure 1C, integrating proteins into the MOF membrane mimics the localization of transmembrane and periplasmic proteins. This locally enhanced adsorption alters the behavioral patterns of enzymes, exhibiting characteristics of heterogeneous catalysis (Figure 1D). The effective local concentration increases, diffusion distances shorten, and consequently, reaction rates are modified. Activity is no longer solely determined by molecular properties but is increasingly regulated by the spatial environment. Therefore, the membrane structure functions as a reaction-regulating interface rather than a passive barrier. Particularly noteworthy is its interaction mechanism, which can be achieved through universal coordination chemistry without requiring complex, customized surface modifications. This approach not only demonstrates the robustness of the system but, more importantly, its underlying principles can be extended beyond the specific experiments conducted herein. Individual MOF coacervate droplets do not exist in isolation, and they form collective organizations when interfacial transport and reactivity establish connections. Under controlled ionic conditions, they adhere to one another and assemble into tissue-like structures. Each compartment remains distinct, with fusion phenomena suppressed. At this stage, the mechanical rigidity of the MOF membrane becomes a critical factor. Unlike fluid lipid bilayers, this membrane resists rearrangement. This rigidity stabilizes contacts between compartments, enabling the maintenance of persistent higher-order structures. In many soft matter systems, fluidity promotes fusion and leads to the loss of compartmental characteristics. This study highlights the vital role of stability within soft matter systems. Despite the absence of membrane fluidity, inter-compartmental communication persists. Small molecules diffuse through the porous membrane, enabling chemical signals to propagate throughout the assembly. This connectivity arises not from lateral diffusion within the membrane, but through transmembrane transport. This demonstrates that predictable mechanical responses and controllable permeability can replace the dynamic properties typically relied upon by soft interfaces. By regulating molecular transport through pore structure, localizing and modulating reactivity at the surface, and stabilizing cellular compartments through membrane architecture, this system demonstrates the synthesis of functional MOF membranes through cross-scale coordination, thereby achieving collective behavior in the assembly. By assembling intrinsically porous MOF nanoparticles into semipermeable membranes co-precipitated onto protocell surfaces, the authors presented a strategy integrating porosity, surface chemistry, and mechanical rigidity at the mesoscale. Within this system, MOFs evolve beyond their traditional roles as containers or filters, instead functioning as organizing units that regulate molecular positioning, stabilize compartment boundaries, and enable controlled chemical communication. This transition from static structure-function relationships to environmentally responsive interfacial functionality marks a significant advancement in the field of porous materials research. Systematic control over membrane thickness, particle packing, and exposed coordination sites offers a route to predictable tuning of transport and adsorption behaviors across biologically relevant length scales. Equally important, the compatibility of MOF membranes with coacervate interiors and embedded organelle-like components suggests that productive interactions with biomolecules can be achieved without elaborate molecular programming. This reveals that universal coordination chemistry and electrostatic interactions suffice to generate robust and transferable functionality. The implications of this research extend the field to encompass studies of primordial cells and tissues. It demonstrates that compartmentalization, signal processing, and collective organization functions can be achieved through carefully designed material properties. Membrane structures based on MOFs simultaneously prevent fusion, regulate biomolecular distribution, and facilitate communication between adjacent compartments. Consequently, they bridge the longstanding gap between bottom-up material design and systems-level biological modelling. This work positions MOFs and related porous materials as core components for constructing biomimetic cells, prototypical tissues, and other hierarchical assemblies. It holds significant potential for exploring life-like organizational structures and designing functional material-driven biological models. At the same time, extending this interfacial strategy beyond controlled model environments raises several important questions. Most experiments so far have been conducted in relatively simplified buffer systems, and it remains unclear how these MOF-membranized assemblies will behave in chemically complex physiological media, where competing ions, proteins, and dynamic exchange processes may influence interfacial growth, stability, and permeability. In addition, the durability of the crystalline–soft matter boundary over extended periods, especially under continuous gradients or mechanical disturbance, also requires further examination. Addressing these questions will be essential for assessing whether such systems can develop from well-defined protocell models into dependable platforms for studying compartmentalization, communication, and emergent biological behavior. The authors declare no conflicts of interest. Data sharing not applicable to this article as no datasets were generated or analysed during the current study.
Li et al. (Sun,) studied this question.