Annette Andrieu-Brunsen

Owing to their hydrophilicity and pronounced capillary pressures, mesoporous platforms enable isotropic or multidirectional fluid transport. Based on aqueous salt solution droplets, we investigate nanopore‐driven ion transport control for tailorable droplet communication via a mesoporous surface. Droplets were placed on a mesoporous silica thin film, separated by a polyelectrolyte (PEL) barrier. The PEL‐barrier was incorporated into the mesoporous matrix by automated direct‐laser‐writing and a grafting‐from SI‐PET‐RAFT polymerization. Permselective transport‐regulated barrier breakthrough times were used to compare aqueous BaCl ₂ , MgSO ₄ , MgCl ₂ , and NaCl solutions. By tuning the barrier widths, the full range of the polyelectrolyte barrier functions from ion‐selective flow regulation to complete fluid retention becomes attainable. Ion‐specific barrier interactions lead to characteristic imbibition dynamics beyond the barrier, involving advancing imbibition toward a steady state in the case of favored barrier permeation, or hindered and oscillating imbibition in the case of disfavored barrier permeation. The ionic selectivity further allows the emergence of control of chemical events such as precipitation reactions in nanopores by the spatial localization of droplets according to the barrier site. The insights into polyelectrolyte‐regulated ion transport during imbibition processes bring new tools for the development of compartmentalized and reconfigurable communication between distant fluid reservoirs through nanostructured coatings.

Confined spaces at the nanoscale ─ pores, channels, and cavities that alter molecular affinities and restrict molecular motion, orientation and local distribution ─ are emerging as a powerful design principle for next-generation materials. By tailoring the structure and functionality of these confined spaces, it is possible to control reactivity, transport, and material properties in ways that are unattainable in bulk systems. This Perspective highlights nanoconfinement as a unifying principle for programming function and addressing major societal challenges in energy, water, health and sustainability. Drawing inspiration from nature’s remarkable precision in bio-molecular control, we showcase six representative areas in which confined spaces are transforming technology: chromatography, catalysis, nanofluidics, bioinspired pore design, confinement-programmed material states, and data-driven material development. Together, these examples illustrate the power of nanoconfinement as an enabling unifying concept. By integrating orthogonal functionalization strategies, advanced characterization, modeling, and digitalization, programmable nanoconfinement will become a versatile framework for engineering materials and processes that meet the demands of a sustainable and technologically advanced society.

Enhancing nanopore functionalization precision is relevant to advance future‐relevant technologies such as molecular sensing, separation, catalysis, and energy conversion. An interesting approach for high‐resolution polymerization is to use nanoscale light sources like surface plasmons. To design polymer functionalization in artificial mesopores, Au nanospheres (AuNSs) are implemented into mesoporous silica thin films, harnessing their plasmon for visible‐light near‐field‐induced polymerization initiation. AuNSs are incorporated at defined layer height, pursuing local placement of polymer along the pore depth. Using photoiniferter as photoreactive initiator for reversible‐addition‐fragmentation chain‐transfer (RAFT) polymerization requires demarcated photoreactivity of both moieties, the AuNSs and the photoiniferter. A high reactivity of AuNSs concomitant to the photostability of the photoiniferter is observed. The wavelength‐dependence of the polymerization initiation is investigated, focusing on wavelength separation of iniferter absorption and plasmon generation. Wavelength‐dependent cooperativity effects between AuNSs, the photoiniferter, and the photocatalyst are explored to understand potential radiative and nonradiative polymerization induction mechanisms of the plasmon‐induced polymerization. Ultimately, plasmon‐selective polymerization is integrated into direct laser writing, affording precise lateral polymer functionalization of mesoporous membranes. Aiming at further miniaturized polymer functionalization, a strategy to attain spatial control over polymer placement in an automated process, paving the way to directed ionic movement through mesoporous membranes, is provided.

Controlling the size‐exclusion driven localized placement of polymer chains within nanopores is essential for improving nanopore performance and bridging the gap between artificial and biological pores. While surface‐initiated reversible‐deactivation radical polymerizations are successfully employed for polymerization within nanopores, achieving simultaneous spatial control over polymer placement and minimizing catalyst usage remains a challenge. The study presents an example of enzyme‐catalyzed surface‐initiated atom transfer radical polymerization (SI‐bioATRP) conducted within mesoporous particles requiring only minimal catalyst amounts. It is demonstrated that the mesostructure of the host material can be utilized to guide the polymer placement. Hemoglobin serves as the catalyst for the polymerization of the negatively charged monomer potassium 3‐sulfopropyl methacrylate (KSPMA). The amount of grafted polymer is controlled by adjusting the density of silanol groups and the diameter of the mesopores. By employing mesoporous particles with pore neck diameters of 3.7 nm, polymer growth is predominantly restricted to the outer surface of the particles due to restricted accessibility of the catalyst and small molecules toward the mesoporous structure after initiator grafting, an effect confirmed by confocal laser scanning microscopy (CLSM). This work highlights the potential of SI‐bioATRP for polymer grafting and the size‐exclusion driven local polymer formation in mesoporous particles.

Infiltration of liquids into three-dimensionally ordered macroporous structures, such as inverse replicas of colloidal crystals called inverse opals, is highly sensitive to the geometry of the interconnecting necks between adjacent pores. Here, we demonstrate that the neck angle connecting the individual pores of an inverse opal can be rationally controlled by adjusting the softness of the templating colloidal particles via their glass transition temperature and the oven temperature during the self-assembly process. This allows systematic tuning of the critical contact angle of a liquid that is the threshold to enable spontaneous infiltration into the porous network of the inverse opal. We experimentally determine this critical contact angle as a function of their neck angle. We rationalize these finding via a geometric model that predicts the critical contact angle as a function of the neck angles. Importantly, our results show that the wetting transition is surprisingly robust to neck irregularities and surface roughness of the inverse opals. Finally, we study the dynamics of the wetting process by measuring imbibition and evaporation rate of a water droplet sitting on inverse opal-based thin films with varying neck angles. Our results provide a comprehensive understanding of how the pore geometry of inverse opals controls both static and dynamic liquid transport, offering a design strategy for tailored wetting and transport properties such well-defined porous materials.

Fluid water imbibition into nanoscale porous materials is important in nature and technology and has been shown to follow the Lucas-Washburn behavior. Looking at drop imbibition into nanoscale porous films, the imbibition reaches a steady state governed by capillary imbibition and evaporation, which is reflected in a constant imbibition length. This imbibition length in a steady state depends on the porous structure as well as on the material's wettability and the fluid evaporation rate, for example. As the presence of salts affects these parameters, the imbibition length is expected to be influenced by the solutes present in the drop. Here, we show the influence of salt presence, salt concentration, and ion type on the fluid imbibition of an aqueous salt solution into mesoporous silica films. We observe that salts affect the Lucas-Washburn imbibition occurring directly after drop positioning on mesoporous films. Interestingly, the presence of salts also causes a continuous increase of the characteristic imbibition length at longer time scales, preventing the formation of a steady state after the initial Lucas-Washburn-like imbibition. We identified a self-amplified fluid pumping mechanism using mesoporous silica films. We attribute this continuous fluid pumping and, thus, the continuous increase of the imbibition length to the increasing osmotic pressure within mesoporous materials upon constant fluid flow and fluid evaporation. Understanding aqueous salt solution imbibition into mesoporous films is an important aspect, e.g., in the context of material exchange between drops through mesoporous films.

A material that was able to simultaneously sense a bacterial presence and to release antimicrobial peptides (AMP) on demand in a tunable amount was developed. Simultaneous sensing and release were achieved by the combination of a bacteria-sensing hydrogel with antimicrobial-peptide-carrying mesoporous silica particles or coatings. The mesoporous silica with a mesopore diameter of 22 nm was functionalized with a covalently grafted green light-sensitive linker, to which antimicrobial peptides were covalently attached. The gelatin-based hydrogel, which contains C14R-functionalized mesoporous silica particles, is designed to respond to bacterial presence as it may occur, e.g., in a wound's microbiological environment. In the presence of bacteria and 0.1% trypsin, a protease enzyme simulating bacterial presence, the hydrogel, deposited in a donut shape, undergoes a shape loss as the bacteria cleave cross-linking bonds within the hydrogel. When observing hydrogel shape loss after 2 h as a readout of a bacterial infection, subsequent irradiation triggers the release of antimicrobial peptides on demand with adjustable concentration-time profiles. The sensing and on-demand release are integrated into commercially available wound dressing fabrics, demonstrating an application proof-of-concept. Characterization using ATR-IR spectroscopy, TGA, and BCA validates the successful fabrication and release. The H1.6P composite released antimicrobial agents, reaching concentrations of up to 298 μg/mL at pH 7.4 from a 300 μL sample. The efficacy of the released C14R against E. coli BL21(DE3) is illustrated. Overall, the multifunctionality of this approach presents a promising step toward on-demand wound care and thus for reducing side effects and antibiotic resistance.

2H nuclear magnetic resonance (NMR) field-cycling relaxometry and broadband dielectric spectroscopy (BDS) studies show that water dynamics in silica pores with similar diameters (∼6 nm) strongly depend on the functionalization of the inner surfaces. In all studied confinements, we observe two prominent changes in the temperature dependence of water reorientation. Specifically, the activation energy of Ea ∼ 0.3 eV in the fully liquid state more than triples to Ea ∼ 1.0 eV upon partial crystallization at Tm ∼ 258 K. Furthermore, in the partially crystallized state, the liquid fraction shows a dynamical crossover at ∼185 K, where the common low-temperature behavior of confined water with Ea = 0.4–0.5 eV is established. However, the correlation times of water reorientation are up to two orders of magnitude longer in amino-acid functionalized silica pores than in pristine ones. Comparing the results for different functional groups, NMR and BDS consistently show that the slowdown is strongest for basic lysine followed by neutral alanine and, finally, acidic glutamic acid. Based on this order, one may speculate that the changed dynamics are a consequence of different pH values of water in confinements with different functional groups. Although pH measurements confirm that the pH value strongly depends on the amino-acid functionalization, this speculation must be rejected due to the observation that water with very different pH values does not show diverse reorientation dynamics when enclosed in identical pores.