Abstract Recent progress in polymer chemistry and microfluidic fabrication has enabled the synthesis of soft hydrogel microparticles with precisely controlled anisotropic shapes, moving beyond simple spheres to complex architectures like ribbons, rods, bowls, and others. This morphological control is not merely aesthetic; achieving a specific particle shape directly unlocks new functional applications by dictating the particle mechanics, interactions, and responses to external stimuli. For instance, ribbon-shaped microgels can undergo a cyclic twisting and untwisting motion when subjected to external fields such as temperature changes or magnetic fields, allowing them to operate as synthetic microswimmers in low Reynolds number environments. In another example, rod-shaped microgels, particularly those integrating magnetic nanoparticles, can be aligned within an injectable hydrogel matrix to create anisotropic scaffolds. This alignment provides critical contact guidance, effectively directing the growth of the nerve tissue for regenerative medicine. Finally, bowl-shaped microgels introduce a unique concavity that transforms them into effective microcontainers capable of stably encapsulating therapeutic cargo and enabling targeted, site-specific drug delivery. This review highlights recent advances in the synthesis, properties, and applications of hydrogel microparticles of various nonspherical shapes.

Single amphiphilic network-like polymer particles with random distribution of hydrophilic (A) and hydrophobic (B) segments in the polymer network and internal cavity were studied at an oil-water interface by means of mesoscopic computer simulations. Effects of the cavity size, interfacial tension between the liquids, their selectivity as solvents toward species A and B, and the degree of incompatibility between the A and B units on the internal microgel structure and distribution of the liquids are considered. Similar to the regular (cavity-free) counterparts, the intrashell mixing of two immiscible liquids was found for the hollow particles. However, the presence of a cavity filled with one of the liquids caused some unique differences, and for the symmetric composition (equal fractions of A and B segments), the adsorption pathway of the hollow microgels appeared to predefine their position with respect to the interface and the sort of the liquid inside the cavity. In turn, the machine learning has been used to establish structure-property relationships of the simulated systems. As a result, most notable parameters and their combinations affecting (i) lateral and normal sizes of the adsorbed microgels, (ii) their position along the normal to the interface, and (iii) the integrity of the cavity were established. Subsequently, the developed framework was used to predict the presented values of the microgels suitable for different interfacial scenarios. Notably, a boundary case with a periodically collapsing cavity has been found.

Poly(butyl cyanoacrylate) microbubbles (PBCA MB) are clinically investigated ultrasound-responsive materials whose formation is governed by surfactant-mediated interfacial templating. Here, we used a chemically diverse panel of 14 commercially designated greener non-ionic surfactants to clarify how surfactant chemistry governs PBCA MB formation and performance. By combining physicochemical analysis, dissipative particle dynamics simulations, microscopy, drug-loading experiments, and acoustic characterization, we determined how the architecture of the hydrophobic moiety, PEG chain length, and hydrophilic-lipophilic balance shape MB yield, shell composition, morphology, and function. The hydrophobic tail structure primarily influenced MB yield, while increasing PEG chain length shifted the morphology toward asymmetric particles. Surfactant incorporation into PBCA MB shells depended on surfactant hydrophilic-lipophilic balance, and dissipative particle dynamics simulations indicated preferential surfactant enrichment at the polymer-water interface. Brij O20 and Ecosurf SA-9 increased drug loading by 6.2- and 4.8-fold relative to conventional Triton X-100-generated MB, while acoustic performance could be tuned toward either greater stability or stronger non-linear, disruption-prone behavior. Together, these findings clarify the role of surfactant chemistry in PBCA MB synthesis and promote surfactant design as a practical route to tailor MB morphology, shell composition, drug loading, and acoustic performance.

We investigated the self-assembly capabilities of comb-shaped macromolecules with alternating side chains of different chemical types (A and B) in melts using dissipative particle dynamics. Due to the variety in the number of parameters controlling architecture/composition, the molecular structure of such objects can be finely tuned, thereby programming their self-assembly in melts. In the current work, we confine ourselves by considering two macromolecular architectures: (i) equal fractions of A and B side chains so that the elementary "building block" (segment) of the brush represents a linear triblock copolymer (A-d-B, d being a dimer from the backbone) and (ii) unequal fractions of A and B side chains so that the elementary segment corresponds to a branched (star-like) motif (one arm of a minor component (A) and few arms of the major component (B), all being connected by the backbone fragment). In the linear elementary segment regime, the presence of a long backbone enables stabilization of not only conventional morphologies like lamellae, perforated lamellae, and cylinders, but also structures with three-dimensional percolation: the double gyroid with bicontinuous percolation and the novel cocontinuous M15 morphology. In the star-like elementary segment regime, molecular brushes tend to form morphologies with spherical domain types. We observed the conventional spheres ordered with the symmetry of the body-centered cubic lattice as well as Frank-Kasper sigma-type spheres. It was also shown that the backbone directly influences Frank-Kasper sphere packing types, since individual star-like macromolecules not connected by a backbone can form Frank-Kasper A15-type spheres. Furthermore, materials based on molecular brushes with star-like elementary segments can exhibit microphase separation with unique viscoelastic properties due to polymer bridge formation between the domains.

Block copolymers have been known for more than a half-century. In contrast to their statistical counterparts, such macromolecules can form aggregates of various, well-defined shapes in solutions and at the interfaces. Meanwhile, due to a significant progress in polymer synthesis, gradient copolymers are gaining more and more interest as a potentially cheaper alternative to the simplest case of block structures – the diblock copolymers. Because of relative novelty of such macromolecules, the new properties of respective polymer systems are being continuously discovered. This review highlights the recent advances in the study of gradient and diblock copolymer assemblies in solution and at various interfaces and provides by a direct comparison of properties of the latter and the former.

Microbubbles (MB) are widely used as contrast agents for ultrasound (US) imaging and US‐enhanced drug delivery. While the majority of studies utilize commercial MB formulations, increasing experimental evidence indicates that distinct MB features critically determine their diagnostic and therapeutic performance. Here, it is shown that shell stiffness engineering of poly(alkyl cyanoacrylate) (PACA) MB, via introducing monomers with varying alkyl chain lengths and glass transition temperatures, preserves a narrow size distribution ≈2–3 µm, while enhancing MB drug loading, in vitro sonoporation capability, and in vitro and in vivo acoustic responses. All‐atom molecular dynamics simulations and spectroscopic experiments demonstrate that MB shell engineering increases drug diffusion rates in the shell, maximizing the loading capacity of the formulations. Atomic force microscopy demonstrates that the stiffness of the MB shell can be tailored by more than ten‐fold, boosting sonoporation and imaging performance. Altogether, the work provides new insights into the control of polymeric MB structure and performance via dedicated shell engineering, promoting applications in US imaging and therapy.

Arborescent (dendrigraft) polymers are high-molecular-weight dendritic macromolecules with a regular, multilevel branched topology and a high density of functional end groups in their periphery. Their well-defined architecture, devoid of cross-links or loops, imparts a particle-macromolecule duality that becomes particularly pronounced at interfaces. However, the underlying mechanisms governing their interfacial behavior remain largely unexplored. Here, we elucidate how the unique topology dictates the interfacial organization of water-soluble arborescent polymers. Using an iterative grafting-from approach via single-electron transfer living radical polymerization, we synthesized narrowly dispersed polymers with controlled branching and ultra-high molecular weight of 6.2 x 106 g mol-1. These polymers transition from spherical rigid particles in solution, to highly flexible, two-dimensional conformations upon interfacial adsorption. At solid interfaces, increasing segment density shifts surface morphologies from quasi-2D discs to fried-egg-like structures, as observed by atomic force microscopy and corroborated by dissipative particle dynamics simulations. At liquid-liquid interfaces, the absence of substrate constraints facilitates complete spreading into uniform 2D discs, driven by the energy gain due to polymer-segment adsorption. Furthermore, we uncover that macromolecular crowding and topological constraints inherent to the arborescent architecture dictate the response to compression of the adsorbed polymer layer, contrasting sharply with the behavior of conventional flexible linear or star polymers. The combination of high interfacial activity, spatially adaptable end groups, and extreme molecular flexibility will enable arborescent polymers to adapt to complex interfaces, acting as versatile platforms for multivalent and superselective interactions. These properties open new avenues for designing multivalent nanocarriers and adaptive interfacial materials with cooperative binding effects.

Understanding the adsorption features of polymer microgels with different chemical compositions and structures is crucial in studying the mechanisms of respective emulsion stabilization. Specifically, the use of stimuli-responsive particles can introduce new properties and broaden the application range of such complex systems. Recently, we demonstrated that emulsions stabilized by microgels composed of interpenetrating networks (IPNs) of poly-N-isopropylacrylamide (PNIPAM) and polyacrylic acid (PAA) exhibit higher colloidal stability upon heating compared to PNIPAM homopolymer and other relevant PNIPAM-based copolymer counterparts. In the present work, using pendant drop tensiometry, we studied the evolution of water–tetradecane interfacial tension during the adsorption of PNIPAM-PAA IPN particles, comparing them with single-network P-(NIPAM-co-AA) and PNIPAM microgels. The results showed that, despite having the same chemical composition, copolymer particles exhibit completely different adsorption behavior in comparison to other microgel architectures. The observed disparity can be attributed to the nonuniform distribution of charged acrylic acid groups within the P-(NIPAM-co-AA) network obtained through precipitation polymerization. Oppositely, the presence of IPN architecture provides a uniform distribution of different monomers inside respective microgels. Additionally, hydrogen bonding between PNIPAM and PAA subchains appears to reduce the electrostatic energy barrier, enhancing the ability of IPN particles to successfully cover the liquid interface. Overall, our findings confirm the efficiency of using PNIPAM-PAA IPN microgels for the preparation of oil-in-water emulsions and their stability, even when the temperature rises above the lower critical solution temperature of PNIPAM.

Microbubbles (MB) are widely used as contrast agents for ultrasound (US) imaging and US-enhanced drug delivery. Polymeric MB are highly suitable for these applications because of their acoustic responsiveness, high drug loading capability, and ease of surface functionalization. While many studies have focused on using polymeric MB for diagnostic and therapeutic purposes, relatively little attention has thus far been paid to improving their inherent imaging and drug delivery features. This study here shows that manipulating the polymer chemistry of poly(butyl cyanoacrylate) (PBCA) MB via temporarily mixing the monomer with the monomer-mimetic butyl cyanoacetate (BCC) during the polymerization process improves the drug loading capacity of PBCA MB by more than twofold, and the in vitro and in vivo acoustic responses of PBCA MB by more than tenfold. Computer simulations and physisorption experiments show that BCC manipulates the growth of PBCA polymer chains and creates nanocavities in the MB shell, endowing PBCA MB with greater drug entrapment capability and stronger acoustic properties. Notably, because BCC can be readily and completely removed during MB purification, the resulting formulation does not include any residual reagent beyond the ones already present in current PBCA-based MB products, facilitating the potential translation of next-generation PBCA MB.

Emulsions have become a crucial product form in various industries in modern times. Expanding the class of substances used to stabilize emulsions can improve their stability or introduce new properties. Particularly, the use of stimuli-responsive microgels makes it possible to create "smart" emulsions whose stability can be controlled by changing any of the specified stimuli. Thus, finding new ways to stabilize emulsions may broaden their application. In this work, for the first time, we applied microgels based on interpenetrating polymeric networks (IPNs) of poly(N-isopropylacrylamide) (PNIPAM) and poly(acrylic acid) (PAA) as stabilizing agents for "oil-in-water" emulsions. We have demonstrated that emulsions stabilized by such soft particles can remain colloidally stable for an extended period, even after being heated up to 40 degrees C, which is above the lower critical solution temperature (LCST) of PNIPAM. On the contrary, the emulsions stabilized by PNIPAM homopolymer microgels were broken upon heating. To understand the stabilization mechanism of the emulsions, mesoscopic computer simulations were performed to study the IPN microgels at the liquid-liquid interface. The simulations demonstrated that when the first subnetwork (PNIPAM) collapses, the particle adopts a flattened core-shell morphology with a highly swollen PAA-rich shell and a collapsed PNIPAM-rich core. Unlike its PNIPAM homopolymer counterpart, the IPN microgel maintains its three-dimensional shape, which provides stability to the microgel-based emulsions over a wide range of temperatures. Our combined findings could be useful in developing new approaches to emulsions' storage, biphasic catalysis, and lubrication of mechanisms in various operating and climatic conditions.

The swelling and collapse of responsive nanogels on a planar lipid bilayer are studied by means of mesoscopic computer simulations. The effects of molecular weight, cross-linking density, and adhesion strength are examined. The conditions for collapse-mediated engulfing by the bilayer are found. In particular, the results show that at low hydrophobicity level the increase in the nanogel softness decreases the engulfing rate. On the contrary, for stronger hydrophobicity level the trend changes to the opposite one. At the same time, when the cross-linking density is too low or the adhesion strength is too high the nanogel deformation at the membrane suppresses the engulfing regardless of the network swelling ratio. Finally, for comparative reasons, the behavior of the nanogels is also studied at the solid surface. These results may be useful in the design of soft particles capable of tuning of their elasticity and porosity for successful intracellular drug delivery.

Effect of the architecture and composition of a hydrophilic microgel catalyst on the rate of interfacial catalytic reaction proceeding at the water/oil interface and involving reagents dissolved in opposite phases is studied using dissipative particle dynamics simulations. It is shown that a decrease in the crosslinking density of the microgel, the existence of a cavity in its architecture, an increase in its size, the incorporation the hydrophobic comonomers into a macromolecule, and a rise in the degree of solubility of a network macromolecule in oil contribute to acceleration of the catalytic reaction due to increase of the area of the water–oil–microgel contact and growth of the number of contacts between reagents and catalytic groups. However, in the case of amphiphilic microgels and microgels soluble in both phases, the acceleration of the reaction is restrained by a low rate of reagents diffusion and a rapid reduction in the concentration of reagents in the vicinity of catalytic sites.

The reaction of a biphasic catalysis with microgels bearing catalytic groups adsorbed at liquid interface was simulated for the first time using dissipative particle dynamics. It was shown that the rate of the catalytic process increases with the degree of deformation of the polymer network, which depends on the fraction of the crosslinker and the solubility of the polymer in both phases. It was found that the highest reaction rate was observed when the microgel was soluble in both phases due to an increase in its porosity (in comparison with amphiphilic microgels) and in the water–microgel–oil contact area with a simultaneous decrease in the time for the reagents to reach the catalytic groups due to the flattening of the microgel. The results obtained can be useful for increasing the efficiency of a wide range of catalytic reactions of the type considered through the use of network-like macromolecules.

Polymer microgels have proven to be highly promising macromolecular objects for a wide variety of applications. In particular, the soft particles of an anisotropic (rod-like) shape are of special interest because of their potential use in tissue engineering or materials design. However, a little is known about the physical behavior of such microgels in solution, which inspired us to study them using mesoscopic computer simulations. For single networks, depending on the solvent quality, the dimensional characteristics were obtained for microgels of different molecular weight, crosslinking density and aspect ratio. In particular, the conditions for the rod-to-rod (preserving the nonspherical shape) and rod-to-sphere collapse were found. In addition, the effect of the liquid-crystalline (LC) ordering was demonstrated for the ensemble of rod-like microgels at different swelling ratios, and the influence of microgel aspect ratio on the volume fraction of the LC transition was shown.

Monolayers of polymer microgels with a spherical cavity adsorbed at the liquid-liquid interface were studied using mesoscopic computer simulations. One liquid, named water, was always considered as a good solvent, while the microgel solubility in the second liquid, named oil, was varied. The symmetric and asymmetric cases of vanishing and the strong differences in solubility between the network particles and the liquids were considered. The simulations provided us with an insight into the shape and volume changes of the microgels upon compression, making it possible to relate the response of the individual network with the collective order and structure of the monolayer. Similar to regular microgels, the compression of the monolayer of hollow particles led to a decrease in lateral sizes accompanied by shape transformation from a flattened to a nearly spherical shape. However, the presence of a cavity filled with solvent caused some unique differences in the behavior of the system. The adsorption pathway of hollow microgels at the liquid interface predefines: (a) the position of the particles with respect to the interface and (b) the structure of the monolayer. A striking discovery is that in the symmetric case of similar solubility of the microgel in both liquids, it is possible to produce a monolayer in which one part of the network faces the aqueous phase and the other part faces the oil phase. The polymer concentration profiles plotted along the normal to the interface reveal a redistribution of polymeric mass of the microgels relative to the interface, distinguishing between the microgels whose cavities are filled with water and oil, respectively. Moreover, the ratio between the microgels faced in water and oil does not change upon compression and predetermines the response and order of the monolayer.

Hollow soft nanoparticles possess both the high absorption capacity and the ability to change their shape.

Densely grafted comb-like macromolecules (bottlebrushes) with alternating solvophobic and solvophilic side chains were studied in a selective solvent and at the liquid interface using mesoscopic computer simulations. The effects of backbone length and copolymer composition were considered. While self-assembly in solution revealed only spherical aggregates for all ar-chitectures studied, adsorption onto the liquid interface in particular cases resulted in morpho-logical changes, with worm-like aggregates or a continuous monolayer observed. In turn, the compression of macromolecules at the interface also leads to morphological transitions, includ-ing the formation of a mesh-like percolated structure. The obtained results may be useful for the preparation of solid nanoparticles of anisotropic shape or nanostructured ultra-thin copolymer films.

Correction for 'Effect of network topology and crosslinker reactivity on microgel structure and ordering at liquid-liquid interface' by Rustam A. Gumerov et al., Soft Matter, 2022, 18, 3738-3747, https://doi.org/10.1039/D2SM00269H.