@article{22218, abstract = {Physiological void spaces exist at every scale of the human body, from organs to molecules, facilitating transport, signal propagation, and localized biochemical activity. Constriction of these spaces (e.g., arterial occlusion, fibrosis) highlights their importance, making their mimicry essential in tissue engineering (TE). This review examines four key strategies for introducing porosity into hydrogels across multiple length scales: templating, microgels, phase separation, and 3D printing. The first three methods enable the engineering of physiological environments at the nano‐ to micro‐scale, mimicking tissue‐ and extracellular matrix (ECM)‐level spaces. Templating involves embedding and removal of gas, liquid, or solid phases, leaving behind pores. Microgel annealing generates inherent interstitial voids. Liquid–liquid phase separation (LLPS) creates biphasic networks reminiscent of native ECM. The fourth approach, extrusion‐ and light‐based 3D printing techniques, enables the fabrication of larger‐scale spaces, such as luminal structures (e.g., vasculature, airways, and ducts). Combining these methods enables the creation of hierarchical architectures from the nano‐ to centimeter scale. The review also highlights Filamented Light (FLight) technology, which creates internal microstructural voids relevant to anisotropic tissues. This review offers insights into current methods and their convergence for generating biomimetic void spaces to meet the physiological demands of cells, tissues, and organs.}, author = {Puiggalí‐Jou, Anna and Hui, Isabel B. and Fernández-Rico, Carla and Zenobi‐Wong, Marcy}, issn = {1521-4095}, journal = {Advanced Materials}, number = {7}, publisher = {Wiley}, title = {{The space within: How architected voids promote tissue formation}}, doi = {10.1002/adma.202507385}, volume = {38}, year = {2026}, } @article{22215, abstract = {Elastic MicroPhase separation (EMPS) provides a simple route to create soft materials with homogeneous microstructures by leveraging the supersaturation of crosslinked polymer networks with liquids. At low supersaturation, network elasticity stabilizes a uniform mixture, but beyond a critical threshold, metastable microphase-separated domains emerge. While previous theories have focused on describing qualitative features about the size and morphology of these domains, they do not make quantitative predictions about EMPS phase diagrams. In this work, we extend Flory–Huggins theory to quantitatively capture EMPS phase diagrams by incorporating strain-stiffening effects. This model requires no fitting parameters and relies solely on independently measured solubility parameters and large-deformation mechanical responses. Our results confirm that strain-stiffening enables metastable microphase separation within the swelling equilibrium state and reveal why the microstructures can range from discrete droplets to bicontinuous networks. This works highlights the critical role of nonlinear elasticity in controlling phase-separated morphologies in polymer gels.}, author = {Fernández-Rico, Carla and Style, Robert W. and Heyden, Stefanie and Wang, Shichen and Olmsted, Peter D. and Dufresne, Eric R.}, issn = {1744-6848}, journal = {Soft Matter}, number = {2}, pages = {330--342}, publisher = {Royal Society of Chemistry}, title = {{Thermodynamics of microphase separation in a swollen, strain-stiffening polymer network}}, doi = {10.1039/d5sm00594a}, volume = {22}, year = {2026}, } @article{22213, abstract = {Unlike biological active matter that constantly adapt to their environment, the motors of synthetic active particles are typically agnostic to their surroundings and merely operate at constant force. Here, we design colloidal active rods capable of modulating their inner activity in response to crowding, thereby enforcing a primitive form of quorum sensing interactions. Through experiments, simulations, and theory we elucidate the impact of these interactions on the phase behavior of isotropic active matter. We demonstrate that, when conditioned to density, motility regulation can either lead to an absorbing phase transition, where all particles freeze their dynamics, or to atypical phase separation, where flat interfaces supporting a net pressure drop are in mechanical equilibrium. Fully active and fully arrested particles can then form heterogeneous patterns ruled by the competition between quorum sensing and mechanical interactions. Beyond the specifics of motile colloids, we expect our findings to apply broadly to adaptive active matter assembled from living or synthetic units.}, author = {Lefranc, Thibault and Dinelli, Alberto and Fernández-Rico, Carla and Dullens, Roel P. A. and Tailleur, Julien and Bartolo, Denis}, issn = {2160-3308}, journal = {Physical Review X}, number = {3}, publisher = {American Physical Society}, title = {{Synthetic quorum sensing and absorbing phase transitions in colloidal active matter}}, doi = {10.1103/8csn-71jk}, volume = {15}, year = {2025}, } @article{22214, abstract = {Highly interconnected percolated networks are interesting structures for materials with enhanced transport and mechanical properties. While percolated networks of anisotropic particles have been explored at the nanoscale, achieving highly interconnected structures at the microscale remains challenging. In this work, we explore the controlled assembly of rod-like polymer colloids under external fields leading to reversible quasi-2D networks. By varying voltage and frequency, we modulate the pore size and thickness of the network. We find that field-driven attractive interactions enable percolation at lower area fractions than predicted for non-interacting rods. Monte Carlo simulations incorporating dipolar interactions and electrostatic boundary conditions confirm the field-induced transition from isotropic to aligned rod configurations, supporting the emergence of percolated networks. This work presents a simple and robust approach for assembling reconfigurable colloidal networks with controlled connectivity, offering new strategies for designing adaptive soft materials.}, author = {Fojo, José and Subert, Rodolfo and Rodríguez-Arco, Laura and López-López, Modesto T. and Dijkstra, Marjolein and Fernández-Rico, Carla and Alvarez, Laura}, issn = {1744-6848}, journal = {Soft Matter}, number = {23}, pages = {4596--4605}, publisher = {Royal Society of Chemistry}, title = {{Field-driven reversible networks from colloidal rods}}, doi = {10.1039/d5sm00218d}, volume = {21}, year = {2025}, } @article{22209, abstract = {The curvature of elongated microscopic building blocks plays a crucial role on their self-assembly into orientationally ordered phases. While rod-like molecules form a handful of liquid crystal (LC) phases, curved or banana-shaped molecules show more than fifty phases, with fascinating physical properties, such as chirality or polarity. Despite the fundamental and technological importance of these so-called ‘banana-shaped liquid crystals’, little is known about their microscopic details at the single-molecule level. Curved colloidal liquid crystals—liquid crystals formed by curved colloidal rods—are excellent model systems to optically resolve the structure and dynamics of curved building blocks within these condensed phases. Recent advances in the synthesis of curved rod-like particles have unlocked the potential for studying—at the single-particle level—the intimate relationship between shape and phase symmetry, and even confirmed the stability of elusive LC phases. Further developments in this nascent field promise exciting findings, such as the first observation of the colloidal twist-bend nematic phase or the fabrication of functional materials with curvature-dependent properties. In this Report on Progress, we will highlight recent advances in the synthesis and assembly of curved colloidal liquid crystals and discuss the upcoming challenges and opportunities of this field.}, author = {Fernández-Rico, Carla and Dullens, Roel P A}, issn = {1361-6633}, journal = {Reports on Progress in Physics}, number = {9}, publisher = {IOP Publishing}, title = {{Liquid crystals from curved colloidal rods: Waves, twists and more}}, doi = {10.1088/1361-6633/ad627b}, volume = {87}, year = {2024}, } @article{22219, abstract = {Bicontinuous microstructures are essential to the function of diverse natural and synthetic systems. Their synthesis has been based on two approaches: arrested phase separation or self-assembly of block copolymers. The former is attractive for its chemical simplicity and the latter, for its thermodynamic robustness. Here we introduce elastic microphase separation (EMPS) as an alternative approach to make bicontinuous microstructures. Conceptually, EMPS balances the molecular-scale forces that drive demixing with large-scale elasticity to encode a thermodynamic length scale. This process features a continuous phase transition, reversible without hysteresis. Practically, EMPS is triggered by simply supersaturating an elastomeric matrix with a liquid, resulting in uniform bicontinuous materials with a well-defined microscopic length scale tuned by the matrix stiffness. The versatility of EMPS is further demonstrated by fabricating bicontinuous materials with superior mechanical properties and controlled anisotropy and microstructural gradients. Overall, EMPS presents a robust alternative for the bulk fabrication of homogeneous bicontinuous materials.}, author = {Fernández-Rico, Carla and Schreiber, Sanjay and Oudich, Hamza and Lorenz, Charlotta and Sicher, Alba and Sai, Tianqi and Bauernfeind, Viola and Heyden, Stefanie and Carrara, Pietro and Lorenzis, Laura De and Style, Robert W. and Dufresne, Eric R.}, issn = {1476-4660}, journal = {Nature Materials}, pages = {124--130}, publisher = {Springer Nature}, title = {{Elastic microphase separation produces robust bicontinuous materials}}, doi = {10.1038/s41563-023-01703-0}, volume = {23}, year = {2024}, } @article{22212, abstract = {Anisotropic colloidal particles exhibit complex dynamics which play a crucial role in their functionality, transport, and phase behavior. In this Letter, we investigate the two-dimensional diffusion of smoothly curved colloidal rods—also known as colloidal bananas—as a function of their opening angle α. We measure the translational and rotational diffusion coefficients of the particles with opening angles ranging from 0◦ (straight rods) to nearly 360◦(closed rings). In particular, we find that the anisotropic diffusion of the particles varies nonmonotonically with their opening angle and that the axis of fastest diffusion switches from the long to the short axis of the particles when α> 180◦. We also find that the rotational diffusion coefficient of nearly closed rings is approximately an order of magnitude higher than that of straight rods of the same length. Finally, we show that the experimental results are consistent with slender body theory, indicating that the dynamical behavior of the particles arises primarily from their local drag anisotropy. These results highlight the impact of curvature on the Brownian motion of elongated colloidal particles, which must be taken into account when seeking to understand the behavior of curved colloidal particles.}, author = {Ulbrich, Justin-Aurel and Fernández-Rico, Carla and Rost, Brian and Vialetto, Jacopo and Isa, Lucio and Urbach, Jeffrey S. and Dullens, Roel P. A.}, issn = {2470-0053}, journal = {Physical Review E}, number = {4}, publisher = {American Physical Society}, title = {{Effect of curvature on the diffusion of colloidal bananas}}, doi = {10.1103/physreve.107.l042602}, volume = {107}, year = {2023}, } @article{22221, author = {Fernández-Rico, Carla}, issn = {1945-0699}, journal = {Physics Today}, number = {5}, pages = {10--11}, publisher = {AIP Publishing}, title = {{Commentary: Researching around Europe: A personal reflection}}, doi = {10.1063/pt.3.4991}, volume = {75}, year = {2022}, } @article{22207, abstract = {Phase separation is a ubiquitous process and finds applications in a variety of biological, organic, and inorganic systems. Nature has evolved the ability to control phase separation to both regulate cellular processes and make composite materials with outstanding mechanical and optical properties. Striking examples of the latter are the vibrant blue and green feathers of many bird species, which are thought to result from an exquisite control of the size and spatial correlations of their phase-separated microstructures. By contrast, it is much harder for material scientists to arrest and control phase separation in synthetic materials with such a high level of precision at these length scales. In this Perspective, we briefly review some established methods to control liquid–liquid phase separation processes and then highlight the emergence of a promising arrest method based on phase separation in an elastic polymer network. Finally, we discuss upcoming challenges and opportunities for fabricating microstructured materials via mechanically controlled phase separation.}, author = {Fernández-Rico, Carla and Sai, Tianqi and Sicher, Alba and Style, Robert W. and Dufresne, Eric R.}, issn = {2691-3704}, journal = {JACS Au}, keywords = {phase separation, arrest, bird feathers, elasticity, polymer networks, microstructured materials}, number = {1}, pages = {66--73}, publisher = {American Chemical Society}, title = {{Putting the squeeze on phase separation}}, doi = {10.1021/jacsau.1c00443}, volume = {2}, year = {2021}, } @article{22211, abstract = {Hierarchically self-assembled materials—structures with order at multiple length scales—can be found everywhere. Examples range from collagen structures in human bones to engineered photonic materials. These structures usually assemble from monodisperse microscopic building blocks that interact via complex directional interactions. In this work, we show that hierarchical materials can, in fact, also be assembled from polydisperse building blocks and by entropic interactions alone. Our simple yet powerful assembly mechanism opens up avenues toward rationally exploiting the often undesired polydispersity of colloidal building blocks for programming entropy-driven self-assembly of hierarchical materials.}, author = {Fernández-Rico, Carla and Dullens, Roel P. A.}, issn = {1091-6490}, journal = {Proceedings of the National Academy of Sciences}, number = {33}, publisher = {National Academy of Sciences}, title = {{Hierarchical self-assembly of polydisperse colloidal bananas into a two-dimensional vortex phase}}, doi = {10.1073/pnas.2107241118}, volume = {118}, year = {2021}, } @article{22217, abstract = {Surface roughness plays an important role in determining the mechanical properties, wettability, and self-assembly in colloidal systems. In this work, we develop a simple and fast method to produce rough colloidal SU-8 rods, bananas, and spheres, via the nanoprecipitation of SU-8 in water. During this process, SU-8 nanospheres are absorbed onto the surface of the colloidal SU-8 particles and then cross-linked using UV-light. The size of the spherical asperities and the asperity density are controlled by the concentration of SU-8 used during the nanoprecipitation reaction. Fluorescent labeling of the rough SU-8 colloidal particles allows for their confocal imaging, which demonstrates their stability at high packing fractions. With these newly developed rough particles, we provide a colloidal model system that allows for studies addressing the impact of surface roughness on materials composed of anisotropic particles.}, author = {Fernández-Rico, Carla and Urbach, Jeffrey S. and Dullens, Roel P. A.}, issn = {1520-5827}, journal = {Langmuir}, number = {9}, pages = {2900--2906}, publisher = {American Chemical Society}, title = {{Synthesis of rough colloidal SU-8 rods and bananas via nanoprecipitation}}, doi = {10.1021/acs.langmuir.0c03361}, volume = {37}, year = {2021}, } @article{22216, abstract = {Understanding the impact of curvature on the self-assembly of elongated microscopic building blocks, such as molecules and proteins, is key to engineering functional materials with predesigned structure. We develop model “banana-shaped” colloidal particles with tunable dimensions and curvature, whose structure and dynamics are accessible at the particle level. By heating initially straight rods made of SU-8 photoresist, we induce a controllable shape deformation that causes the rods to buckle into banana-shaped particles. We elucidate the phase behavior of differently curved colloidal bananas using confocal microscopy. Although highly curved bananas only form isotropic phases, less curved bananas exhibit very rich phase behavior, including biaxial nematic phases, polar and antipolar smectic-like phases, and even the long-predicted, elusive splay-bend nematic phase.}, author = {Fernández-Rico, Carla and Chiappini, Massimiliano and Yanagishima, Taiki and de Sousa, Heidi and Aarts, Dirk G. A. L. and Dijkstra, Marjolein and Dullens, Roel P. A.}, issn = {1095-9203}, journal = {Science}, number = {6506}, pages = {950--955}, publisher = {American Association for the Advancement of Science}, title = {{Shaping colloidal bananas to reveal biaxial, splay-bend nematic, and smectic phases}}, doi = {10.1126/science.abb4536}, volume = {369}, year = {2020}, } @article{22208, abstract = {The bulk synthesis of fluorescent colloidal SU‐8 polymer rods with tunable dimensions is described. The colloidal SU‐8 rods are prepared by shearing an emulsion of SU‐8 polymer droplets and then exposing the resulting non‐Brownian rods to ultrasonic waves, which breaks them into colloidal rods with typical lengths of 3.5–10 µm and diameters of 0.4–1 µm. The rods are stable in both aqueous and apolar solvents, and by varying the composition of apolar solvent mixtures both the difference in refractive index and mass density between particles and solvent can be independently controlled. Consequently, these colloidal SU‐8 rods can be used in both 3D confocal microscopy and optical trapping experiments while carefully tuning the effect of gravity. This is demonstrated by using confocal microscopy to image the liquid crystalline phases and the isotropic–nematic interface formed by the colloidal SU‐8 rods and by optically trapping single rods in water. Finally, the simultaneous confocal imaging and optical manipulation of multiple SU‐8 rods in the isotropic phase is shown.}, author = {Fernández-Rico, Carla and Yanagishima, Taiki and Curran, Arran and Aarts, Dirk G. A. L. and Dullens, Roel P. A.}, issn = {1521-4095}, journal = {Advanced Materials}, number = {17}, publisher = {Wiley}, title = {{Synthesis of colloidal SU‐8 polymer rods using sonication}}, doi = {10.1002/adma.201807514}, volume = {31}, year = {2019}, } @article{22210, abstract = {We disclose a method for the synthesis of chiral colloids from spontaneously formed hollow sugar-surfactant microtubes with internally confined mobile colloidal spheres. Key feature of our approach is the grafting of colloid surfaces with photoresponsive coumarin moieties, which allow for UV-induced, covalent clicking of colloids into permanent chains, with morphologies set by the colloid-to-tube diameter ratio. Subsequent dissolution of tube confinement yields aqueous suspensions that comprise bulk quantities of a variety of linear chains, including single helical chains of polystyrene colloids. These colloidal equivalents of chiral (DNA) molecules are intended for microscopic study of chiral dynamics on a single-particle level.}, author = {Ouhajji, Samia and van Ravensteijn, Bas G. P. and Fernández-Rico, Carla and Lacina, Kanvaly S. and Philipse, Albert P. and Petukhov, Andrei V.}, issn = {1936-086X}, journal = {ACS Nano}, number = {12}, pages = {12089--12095}, publisher = {American Chemical Society}, title = {{Wet-chemical synthesis of chiral colloids}}, doi = {10.1021/acsnano.8b05065}, volume = {12}, year = {2018}, }