Pipette aspiration is widely used to probe the mechanics of viscoelastic materials such as vesicles, emulsions, and living cells. Here, we implement micropipette aspiration rheometry based on piezoelectric pressure control in a conventional glass-pipette setup. We characterize its dynamic response over a wide range of pressures and frequencies. We describe the aspiration of viscoelastic liquids and solids using theoretical formulations based on modified Kelvin-Voigt models that combine springs and dashpots. The corresponding elastic and dissipative parameters are derived from scaling laws in polymer physics and viscoelasticity. This enables measurement of elastic moduli of gels from 0.1 kPa to 3 MPa and interfacial tensions in aqueous two-phase systems down to 20 mu N m-1. Computer control of pressure also allows programming of arbitrary pressure sweeps. Using oscillatory pressures, we also extract frequency-dependent elastic and viscous properties. The piezoelectric control of pressure hence allows dynamic micropipette aspiration rheometry, broadening the applicability of pipette aspiration.

A combination of biomedical imaging and photodynamic therapy (PDT) in a single nanomaterial would be a breakthrough in nanomedicine. However, devising a single photosensitizer capable of efficient PDT without requiring an external oxygen source under typically hypoxic tumor conditions, combined with high photostability, biocompatibility, and renal clearance, remains a challenge. Atomically precise ultrasmall (<2 nm) gold nanoclusters (AuNCs) are emerging as potential multifunctional biomedicines, encompassing imaging, diagnosis, and therapy in a single nanoplatform. Herein, we report bioderived cellulose nanocrystal-supported gold nanoclusters (CNC-AuNCs) with selective mono or multiheteroatom (Ag, Pd, and Pt) substitution at the core of the nanoclusters. The replacement of one or more gold atoms significantly modulates their emission wavelengths, photoluminescence quantum yields, as well as excited-state relaxation kinetics. These materials can easily penetrate the cells, accumulating in the cytoplasm and emitting bright luminescence. While the nanocomposites are highly biocompatible, they can produce reactive oxygen species (ROS) through the formation of free radicals (O2-· and ·OH) upon exposure of light. The synergistic effect of the light absorption by the matrix and the diverse excited-state relaxation pathways of the nanoclusters results in the efficient generation of ROS in variable concentrations, ultimately leading to the complete destruction of targeted cancer cells via Type-I photodynamic effect. The optimal ROS efficacy combined with minimal cytotoxicity suggests a universal strategy for developing strong PDT-I agents, paving the way for versatile nanomaterials in theranostic applications.

The assembly of synthetic systems with the ability for protein-mediated division remains a challenge in bottom-up synthetic biology. Here, the reconstitution of an active Drs2p-Cdc50p lipid flippase in polymer lipid hybrid vesicles (HVs) made from phospholipids and 1 or 2.5 mol% amphiphilic block copolymers, with poly(carboxyethyl acrylate) or poly(6-O-methacryloyl-d-galactopyranose) as the hydrophilic extension and either cholesteryl methacrylate or butyl methacrylate or combinations thereof as the hydrophobic blocks is demonstrated. The reconstitution of Drs2p-Cdc50p in HVs flip 2-dioleoyl-sn-glycero-3-phospho-l-serine (DOPS) lipids from the inner to the outer leaflet, leading to transmembrane asymmetry. Importantly, the chemical nature of the hydrophobic block in the amphiphilic block copolymers used to assemble the HVs is crucial to support changes in the spontaneous curvature of the bilayers due to translocation of DOPS lipids that results in HV constriction and division. Taken together, this effort is a step forward in imitating cell division in synthetic assemblies toward potentially bottom-up assembled self-replicating units.

We review recent theoretical and experimental advances in understanding the mechanical tension of porous vesicles. Focusing on three key deformation processes, aspiration, spreading, and tube extrusion, we show how membrane porosity introduces novel timescales and feedback mechanisms that alter vesicle behavior. In particular, we highlight how tube extrusion from porous membranes demonstrates the vesicle's ability to regulate internal volume and dynamically modulate membrane tension. This regulation enables the sustained elongation of membrane tubes under milder mechanical conditions than those required for nonporous vesicles. These findings provide new insight into biologically relevant processes such as organelle shaping, intracellular transport, and mechanosensitive remodeling, emphasizing the crucial role of membrane permeability in cellular morphodynamics.

Biological tissues exhibit complex behaviors with their dynamics often resembling inert soft matter such as liquids, polymers, colloids, and liquid crystals. These analogies enable physics-based approaches for investigations of emergent behaviors in biological processes. A well-studied case is the spreading of cellular aggregates on solid surfaces, where they display dynamics similar to viscous droplets. In vivo, however, cells and tissues are in a confined environment with varying geometries and mechanical properties to which they need to adapt. In this work, we compressed cellular aggregates between two solid surfaces and studied their dynamics using microscopy, and computer simulations. The confined cellular aggregates transitioned from compressed spheres into dynamic living capillary bridges exhibiting bridge thinning and a convex-to-concave meniscus curvature transition. We found that the stability of the bridge is determined by the interplay between cell growth and cell spreading on the confining surfaces. This interaction leads to bridge rupture at a critical length scale determined by the distance between the plates. The force distributions, formation and stability regimes of the living capillary bridges were characterized with full 3D computer simulations that included cell division, migration and growth dynamics, directly showing how mechanical principles govern the behavior of the living bridges; cellular aggregates display jamming and stiffening analogously to granular matter, and cell division along the long axis enhances thinning. Based on our results, we propose a new class of active soft matter behavior, where cellular aggregates exhibit liquid-like adaptation to confinement, but with self-organized rupturing driven by biological activity.

3D printing has emerged as a transformative technology in several manufacturing processes, being of particular interest in biomedical research for allowing the creation of 3D structures that mimic native tissues. The process of tissue 3D printing entails the construction of functional, 3D tissue structures. In this article, the integration of ferrofluid consisting of iron oxide nanoparticles into muscle cell-laden bioink is presented to obtain a 3D printed magnetically responsive muscle tissue, i.e., the ferromuscle. Using extrusion-based methods, the seamless integration of biocompatible ferrofluids are achieved to cell-laden hydrogels. The resulting ferromuscle tissue exhibits improved tissue differentiation demonstrated by the increased force output upon electrical stimulation compared to muscle tissue prepared without ferrofluid. Moreover, the magnetic component originating from the iron oxide nanoparticles allows magnetic guidance, as well as good cytocompatibility and biodegradability in cell culture. These findings offer a new versatile fabrication approach to integrate magnetic components into living constructs, with potential applications as bioactuators and for future integration in smart, functional muscle implants.

Cancer is a leading cause of death globally. Early detection of tumors can be an effective way to reduce mortality, however, traditional cancer diagnostic methods are based on the detection of organ dysfunction, which generally occurs at advanced stages of the disease. The first signs of disease initiation appear much earlier as molecular abnormalities yet are challenging to detect. An advanced design of microbubbles is reported that allows molecular targeting for subsequent binding to tumor cells. The microbubbles consist of perfluorocarbon gas encapsulated in a functional and stable shell made of a surface-active protein (hydrophobin HFBI from Trichoderma reesei) and corresponding fusion protein (HFBI-domZ) onto which antibodies can be easily grafted. The functionality of the bubbles is investigated, among others, using cryogenic transmission electron microscopy (cryo-TEM), confocal microscopy, and in vitro experiments. The results show the potential of the microbubbles as a probe to be used as a targeting contrast agent in ultrasound molecular imaging (MI) for cancer diagnostics.

There is an increasing understanding that condensation is a crucial intermediate step in the assembly of biological materials and for a multitude of cellular processes. To apply and to understand these mechanisms, in vitro biophysical characterisation techniques are central. The formation and biophysical properties of protein condensates depend on a multitude of factors, such as protein concentration, pH, temperature, salt concentration, and presence of other biomolecules as well as protein purification and storage conditions. Here we show how critical the procedures for preparing protein samples for in vitro studies are. We compare two purification methods of the recombinant spider silk protein CBM-AQ12-CBM and study the effect of background molecules, such as DNA, on the formation and properties of the condensates. We characterize the condensates using aggregation induced emitters (AIEs), coalescence studies, and micropipette aspiration. The condensated sample containing background molecules exhibit a lower threshold concentration for condensate formation accompanied by a lower surface tension and longer coalescence time when compared to the pure protein condensates. Furthermore, the partitioning of small AIEs is enhanced in the presence of background molecules. Our results highlight that the purification method and remaining background molecules strongly affect the biophysical properties of spider silk condensates. Using the acquired knowledge about spider silk protein purification we derive guidelines for reproducible condensate formation that will foster the use of spider silk proteins as adhesives or carriers for biomedical applications.

Numerous biomolecular shell-forming condensates are reported in cells and bioengineered in vitro. The relationship between the molecular structure of shell-forming condensates and their biophysical properties remains largely unexplored. To fill this gap, we characterize shell-forming condensates of bioengineered spider silk proteins based on Araneus diadematus major ampulla gland silk fibroin 3 (ADF3) using micropipette aspiration. We observe that condensates can burst during aspiration like soap bubbles or polymersomes, demonstrating the formation of a dense protein layer (shell) at the condensate interface. The tendency to burst is more pronounced for condensates formed from proteins with weakly dimerizing terminal blocks. We develop a model to analyse the aspiration and bursting of the condensates, to obtain the surface and bulk viscosity, and to estimate the shell thickness and viscosity. Understanding and controlling the bursting of condensates will open avenues for their use in materials, as compartments for reactions or drug delivery systems. Condensates with a shell can be formed by liquid-liquid phase separation and can burst like viscous bubbles by nucleation and growth of a hole in the shell surrounded by a rim. The authors develop a model to extract a broad range of rheological properties for spherical shells to understand the conditions for bursting.

Gas vesicles used as contrast agents for noninvasive ultrasound imaging must be formulated to be stable, and their mechanical properties must be assessed. We report here the formation of perfluoro-n-butane microbubbles coated with surface-active proteins that are produced by filamentous fungi (hydrophobin HFBI from Trichoderma reesei). Using pendant drop and pipette aspiration techniques, we show that these giant gas vesicles behave like glassy polymersomes, and we discover novel gas extraction regimes. We develop a model to analyze the micropipette aspiration of these compressible gas vesicles and compare them to incompressible liquid-filled vesicles. We introduce a sealing parameter to characterize the leakage of gas under aspiration through the pores of the protein coating. Utilizing this model, we can determine the elastic dilatation modulus, surface viscosity, and porosity of the membrane. These results demonstrate the engineering potential of protein-coated bubbles for echogenic and therapeutic applications and extend the use of the pipette aspiration technique to compressible and porous systems.

Near-infrared (NIR) fluorophores with pH-responsive properties suggest merits in biological analyses. This work establishes a general and effective method to obtain pH-responsive NIR emissive gold nanoclusters by introducing aliphatic tertiary amine (TA) groups into the ligands. Computational study suggests that the pH-responsive NIR emission is associated with electronic structure change upon protonation and deprotonation of TA groups. Photo-induced electron transfer between deprotonated TA groups and the surface Au-S motifs of gold nanoclusters can disrupt the radiative transitions and thereby decrease the photoluminescence intensity in basic environments (pH=7-11). By contrast, protonated TA groups curb the electron transfer and restore the photoluminescence intensity in acidic environments (pH=4-7). The pH-responsive NIR-emitting gold nanoclusters serve as a specific and sensitive probe for the lysosomes in the cells, offering non-invasive emissions without interferences from intracellular autofluorescence.

We study the fusion of homogeneous cell aggregates and of hybrid aggregates combining cells and microparticles. In all cases, we find that the contact area does not vary linearly over time, as observed for liquid drops, but rather it follows a power law in t2/3. This result is interpreted by generalizing the fusion model of soft viscoelastic solid balls to viscoelastic liquid balls, akin to jelly pearls. We also explore the asymmetric fusion between a homogeneous aggregate and a hybrid aggregate. This latter experiment allows the determination of the self-diffusion coefficient of the cells in a tissue by following the spatial distribution of internalized particles in the cells.

Ferrofluids are magnetic liquids known for the patterns they form in external magnetic fields. Typically, the patterns form at the interface between a ferrofluid and another immiscible non-magnetic fluid with a large interfacial tension γ ∼ 10 −2 N m −1 , leading to large pattern periodicities. Here we show that it is possible to reduce the interfacial tension several orders of magnitude down to ca. γ ∼ 10 −6 N m −1 by using two immiscible aqueous phases based on spontaneous phase separation of dextran and polyethylene glycol and the asymmetric partitioning of superparamagnetic maghemite nanoparticles into the dextran-rich phase. The system exhibits classic Rosensweig instability in a uniform magnetic field with a periodicity of ∼200 μm, significantly lower than in traditional systems (∼10 mm). This system paves the way towards the science of pattern formation at the limit of vanishing interfacial tension and ferrofluid applications driven by small external magnetic fields.

β-1,3-Glucans are ubiquitously observed in various biological systems with diverse physio-ecological functions, yet their underlying assembly mechanism and multiscale complexation in vitro remains poorly understood. Here, we provide for the first-time evidence of unidentified β-1,3-glucan supramolecular complexation into intricate hierarchical architectures over several length scales. We mediated these unique assemblies using a recombinantly produced β-1,3-glucan phosphorylase (Ta1,3BGP) by fine-tuning solution conditions during particle nucleation and growth. We report a synthesis of interconnected parallel hexagonal lamellae composed of 8 nm thick sheets of highly expanded paracrystals. The architecture consists of β-1,3-glucan triple-helices with considerable inter-intra hydrogen bonding within, as well as in between adjacent triple-helices. The results extend our understanding of β-1,3-glucan molecular organization and shed light on different aspects of the crystallization processes of biomolecules into structures unseen by nature. The presented versatile synthesis yields new materials for diverse medical and industrial applications.

Recombinant expression of proteins destined to form biological materials often results in poor production yields or loss of their function due to premature aggregation. Recently, liquid-liquid phase separation has been proposed as a mechanism to control protein solubility during expression and accumulation in the cytoplasm. Here, we investigate this process in vivo during the recombinant overexpression of the mimetic spider silk mini-spidroin NT2RepCT in Escherichia coli. The protein forms intracellular liquid-like condensates that shift to a solid-like state triggered by a decrease in their microenvironmental pH. These features are also maintained in the purified sample in vitro both in the presence of a molecular crowding agent mimicking the bacterial intracellular environment, and during a biomimetic extrusion process leading to fiber formation. Overall, we demonstrate that characterization of protein condensates inside E. coli could be used as a basis for selecting proteins for both materials applications and their fundamental structure-function studies.

While both active and granular matter have been extensively studied, here we investigate what happens when we mix the two of them, in a model system combining microparticles and cell assemblies. On a substrate covered with polystyrene or silica microparticles, we notice two regimes in the spreading of a cell aggregate: light particles are pushed by the cells and form a ring, which bonds to the substrate by adhesion forces that oppose spreading, while for heavy particles, the cell monolayer spreads above the particle bed. In both cases, cell activity is transmitted to inert beads, leading to the formation of cell-microparticle aggregates, which flicker and diffuse. We then study the formation and the spreading of hybrid aggregates of microparticles and living cells and observe phase separations and jamming transitions. Our study may have implications on processes such as cancer metastasis and development, and may guide cancer therapies based on inert particles. Interaction of active matter with geometrical and topological constraints is a topic of intense research in the recent few years due to its potential for design and control of active flow patterns. Here, the authors experimentally study the growth and expansion of cell aggregates interleaved by passive colloidal particles, showing that inert particles can reshape the collective pattern formation in cellular aggregates.

Ferrofluids exhibit a unique combination of liquid properties and strong magnetic response, which leads to a rich variety of interesting functional properties. Here, the magnetic‐field‐induced splitting of ferrofluid droplets immersed in an immiscible liquid is presented, and related fascinating dynamics and applications are discussed. A magnetic field created by a permanent magnet induces instability on a mother droplet, which divides into two daughter droplets in less than 0.1 s. During the splitting process, the droplet undergoes a Plateau–Rayleigh‐like instability, which is investigated using high‐speed imaging. The dynamics of the resulting satellite droplet formation is shown to depend on the roughness of the supporting surface. Further increasing the field results in additional splitting events and self‐assembly of microdroplet populations, which can be magnetically actuated. The effects of magnetization and interfacial tension are systematically investigated by varying magnetic nanoparticles and surfactant concentrations, and a variety of outcomes from labyrinthine patterns to discrete droplets are observed. As the splitting process depends on interfacial tension, the droplet splitting can be used as a measure for interfacial tension as low as 0.1 mN m −1 . Finally, a population‐based digital microfluidics concept based on the self‐assembled microdroplets is presented.

Recent developments suggest that the phase transition of natural and synthetic biomacromolecules represents an important and ubiquitous mechanism underlying structural assemblies toward the fabrication of high-performance materials. Such a transition results in the formation of condensed liquid droplets, described as condensates or coacervates. Being able to effectively control the assembly of such entities is essential for tuning the quality and their functionality. Here we describe how self-coacervation of genetically engineered spidroin-inspired proteins can be preceded by a wide range of kosmotropic salts. We studied the kinetics and mechanisms of coacervation in different conditions, from direct observation of initial phase separation to the early stage of nucleation/growth and fusion into large fluid assemblies. We found that coacervation induced by kosmotropic salts follows the classical nucleation theory and critically relies on precursor clusters of few weak-interacting protein monomers. Depending on solution conditions and the strength of the supramolecular interaction as a function of time, coacervates with a continuum of physiochemical properties were observed. We observed similar characteristics in other protein-based coacervates, which include having a spherical-ellipsoid shape in solution, an interconnected bicontinuous network, surface adhesion, and wetting properties. Finally, we demonstrated the use of salt-induced self-coacervates of spidroin-inspired protein as a cellulosic binder in dried condition.

The generation of highly reactive oxygen species (ROS) at room temperature for application in organic synthesis and wastewater treatment represents a great challenge of the current chemical industry. In fact, the development of biodegradable scaffolds to support ROS-generating active sites is an important prerequisite for the production of environmentally benign catalysts. Herein, the electrostatic cocrystallization of a cationic phthalocyanine (Pc) and negatively charged tobacco mosaic virus (TMV) is described, together with the capacity of the resulting crystals to photogenerate ROS. To this end, a novel peripherally crowded zinc Pc (1) is synthesized. With 16 positive charges, this photosensitizer shows no aqueous aggregation, and is able to act as a molecular glue in the unidimensional assembly of TMV. A step-wise decrease of ionic strength in mixtures of both components results in exceptionally long fibers, constituted by hexagonally bundled viruses thoroughly characterized by electron and confocal microscopy. The fibers are able to produce ROS in a proof-of-concept microfluidic device, where they are immobilized and irradiated in several cycles, showing a resilient performance. The bottom-up approach also enables the light-triggered disassembly of fibers after use. This work represents an important example of a biohybrid material with projected application in light-mediated heterogeneous catalysis.