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Polymerization-induced self-assembly (PISA) with (in situ) encapsulation of (therapeutic) cargo has proven to be an efficient preparation method for loaded polymeric micelles and polymersomes, thereby presenting significant opportunities in the field of drug delivery. However, despite extensive research efforts, no significant advances toward systematic in vivo studies or clinical applications have been achieved to date. In this Review, we outline the current state-of-the-art of cargo encapsulation via PISA with a specific focus on developments achieved in the past 5 years. Considering the general requirements for functional drug delivery systems, we identify the major hurdles that still need to be overcome in order to push PISA-derived systems from a promising academic exercise to viable candidates for clinical translation.

In the past decade, stimuli-responsive hydrogels are increasingly studied as biomaterials for tissue engineering and regenerative medicine purposes. Smart hydrogels can not only replicate the physicochemical properties of the extracellular matrix but also mimic dynamic processes that are crucial for the regulation of cell behavior. Dynamic changes can be influenced by the hydrogel itself (isotropic vs anisotropic) or guided by applying localized triggers. The resulting swelling-shrinking, shape-morphing, as well as patterns have been shown to influence cell function in a spatiotemporally controlled manner. Furthermore, the use of stimuli-responsive hydrogels as bioinks in 4D bioprinting is very promising as they allow the biofabrication of complex microstructures. This perspective discusses recent cutting-edge advances as well as current challenges in the field of smart biomaterials for tissue engineering. Additionally, emerging trends and potential future directions are addressed.

The influence of homopolymer architecture on the properties of polyion complex micelles is reported. Using a combination of dynamic and static light scattering, the authors show how the architecture is only relevant in kinetically trapped states of micelles formed by the electrostatic assembly of poly(N-isopropyl acrylamide-block-styrene sulfonate) (p(NIPAM-b-SS) and linear, 4-arm, 8-arm star quaternized poly(dimethyl amino ethyl acrylate) (PDMAEA) homopolymers or poly(amidoamine) (PAMAM) dendrimers. Interestingly, the micellar size and the aggregation number in these kinetically arrested states follow a clear trend with the number of arms but differ in the case of dendrimers possibly due to the distinct chemical nature of the monomers. The authors show that if the micelles are prepared in a weak polyelectrolyte pairing regime (i.e., high ionic strength), they all converge into similar structures. The presented findings represent a new way of controlling the properties of polyion complex micelles through kinetically trapped states.

We report a switchable, templated polymerization system where the strength of the templating effect can be modulated by solution pH and/or ionic strength. The responsiveness to these cues is incorporated through a dendritic polyamidoamine-based template of which the charge density depends on pH. The dendrimers act as a template for the polymerization of an oppositely charged monomer, namely sodium styrene sulfonate. We show that the rate of polymerization and maximum achievable monomer conversion are directly related to the charge density of the template, and hence the environmental pH. The polymerization could effectively be switched “ON” and “OFF” on demand, by cycling between acidic and alkaline reaction environments. These findings break ground for a novel concept, namely harnessing co-assembly of a template and growing polymer chains with tunable association strength to create and control coupled polymerization and self-assembly pathways of (charged) macromolecular building blocks.

Efficient and cheap storage of energy from renewable resources presents a key technology to facilitate the ongoing energy transition. Storing heat in thermochemical materials (TCMs), such as salt hydrates, provides a promising concept to meet this demand. TCMs can capture heat reversibly and loss-free by relying on equilibrium hydration reactions of the salts. Persistent bottlenecks in the full-scale application of this technology are the low mechanical resilience of salt grains and their tendency to coagulate or dissolve when in contact with water vapor. To overcome this, the salt grains can be encapsulated by a stabilizing polymer coating. Ideal coatings combine high water vapor permeability with reversible deformability to minimize the resistance for water transport and to accommodate the volumetric changes of the TCM during repetitive (de)hydration, respectively. Here, a systematic study into the applicability of commercially available polymers as coating materials is presented. Mechanical analysis and wet-cup experiments on freestanding polymer films revealed that cellulose-based coatings successfully combine permeability and ductility and meet the engineering demands for domestic TCM-based heat storage applications. The validity of using freestanding films as model system was confirmed by encapsulating granular TCMs in ethyl and hydroxyl propyl cellulose using fluidized bed coating. The permeability was retained and an enhanced structural integrity of the TCM grains during (de)hydration cycles was observed.

The fuel-driven assembly of colloids has opened a route to new, biologically inspired active materials.

Macroscopic material properties are ultimately determined by the microstructural arrangement of building blocks. Bottom-up material fabrication routes exploit this central dogma by reverse-engineering the required building blocks from a targeted structure or property. Despite the plethora of available building blocks, bridging the gap between the microscopic and macroscopic world remains a formidable task. Recently, Macfarlane and co-workers approached this challenge by developing sintering-inspired processing strategies for nanoparticles, allowing the production of centimeter-scale objects while maintaining order on a single-particle level.

Transient assembled structures play an indispensable role in a wide variety of processes fundamental to living organisms including cellular transport, cell motility, and proliferation. Typically, the formation of these transient structures is driven by the consumption of molecular fuels via dissipative reaction networks. In these networks, building blocks are converted from inactive precursor states to active (assembling) states by (a set of) irreversible chemical reactions. Since the activated state is intrinsically unstable and can be maintained only in the presence of sufficient fuel, fuel depletion results in the spontaneous disintegration of the formed superstructures. Consequently, the properties and behavior of these assembled structures are governed by the kinetics of fuel consumption rather than by their thermodynamic stability. This fuel dependency endows biological systems with unprecedented spatiotemporal adaptability and inherent self-healing capabilities. Fascinated by these unique material characteristics, coupling the assembly behavior to molecular fuel or light-driven reaction networks was recently implemented in synthetic (supra)molecular systems. In this invited feature article, we discuss recent studies demonstrating that dissipative assembly is not limited to the molecular world but can also be translated to building blocks of colloidal dimensions. We highlight crucial guiding principles for the successful design of dissipative colloidal systems and illustrate these with the current state of the art. Finally, we present our vision on the future of the field and how marrying nonequilibrium self-assembly with the functional properties associated with colloidal building blocks presents a promising route for the development of next-generation materials.

We report the (spontaneous) formation of colloidal strings, Bernal spiral-like, and tubular clusters comprising spherical, isotropically functionalized colloidal particles in an aqueous environment. The formation of colloidal strings and Bernal spiral-like clusters is guided by an interplay between short-ranged hydrophobic attraction and relatively longer-ranged electrostatic repulsion acting between the colloids. When a dispersion of these colloids is densifiedviacentrifugation, well-defined tubular aggregates were observed.

Transient assembled structures play an indispensable role in a wide variety of processes fundamental to living organisms including cellular transport, cell motility, and proliferation. Typically, the formation of these transient structures is driven by the consumption of molecular fuels via dissipative reaction networks. In these networks, building blocks are converted from inactive precursor states to active (assembling) states by (a set of) irreversible chemical reactions. Since the activated state is intrinsically unstable and can be maintained only in the presence of sufficient fuel, fuel depletion results in the spontaneous disintegration of the formed superstructures. Consequently, the properties and behavior of these assembled structures are governed by the kinetics of fuel consumption rather than by their thermodynamic stability. This fuel dependency endows biological systems with unprecedented spatiotemporal adaptability and inherent self-healing capabilities. Fascinated by these unique material characteristics, coupling the assembly behavior to molecular fuel or light-driven reaction networks was recently implemented in synthetic (supra)molecular systems. In this invited feature article, we discuss recent studies demonstrating that dissipative assembly is not limited to the molecular world but can also be translated to building blocks of colloidal dimensions. We highlight crucial guiding principles for the successful design of dissipative colloidal systems and illustrate these with the current state of the art. Finally, we present our vision on the future of the field and how marrying nonequilibrium self-assembly with the functional properties associated with colloidal building blocks presents a promising route for the development of next-generation materials., ChemE/Advanced Soft Matter

Colloidal structures and lattices made of patchy particles with chemically distinct lobes are formed by exploring site-specifc depletion forces. This approach introduces a simple route to assemble colloidal superlattices.

Bifunctional Janus particles with patches carrying orthogonal surface functionalities that can be independently modified are widely seen as promising building blocks for the bottom-up assembly of functional materials due to their full compositional and geometrical programmability. However, synthesis of these colloids remains an elusive task as current scalable procedures are generally limited to monofunctional particles only. Herein, a scalable bulk wet-chemical synthetic method for fabricating bifunctional Janus particles following a two-step dispersion polymerization is developed. Patch formation on these colloids is driven by the spontaneous phase separation between a brominated outer shell and poly(propargyl acrylate) (p(PA)), formed after the seed particles were swollen with the corresponding monomer. The size ratio between the two patches is readily tunable by controlling the volumetric ratio between the feeding monomers. The distinct patches of these Janus particles carry chemical handles facilitating independent and orthogonal surface modification using Atom Transfer Radical Polymerization (ATRP) and thiol-yne Click chemistry for the brominated and alkyne-containing patches, respectively. The presented route toward bifunctional patchy spheres provides a versatile starting point for the development of bifunctional colloidal particles with tailored directional properties.

Fuel-driven assembly operates under the continuous influx of energy and results in superstructures that exist out of equilibrium. Such dissipative processes provide a route toward structures and transient behavior unreachable by conventional equilibrium self-assembly. Although perfected in biological systems like microtubules, this class of assembly is only sparsely used in synthetic or colloidal analogues. Here, we present a novel colloidal system that shows transient clustering driven by a chemical fuel. Addition of fuel causes an increase in hydrophobicity of the building blocks by actively removing surface charges, thereby driving their aggregation. Depletion of fuel causes reappearance of the charged moieties and leads to disassembly of the formed clusters. This reassures that the system returns to its initial, equilibrium state. By taking advantage of the cyclic nature of our system, we show that clustering can be induced several times by simple injection of new fuel. The fuel-mediated assembly of colloidal building blocks presented here opens new avenues to the complex landscape of nonequilibrium colloidal structures, guided by biological design principles.

In this article, we report the synthesis and physical characterization of colloidal polystyrene particles that carry water-soluble supramolecular N,N′,N″,-trialkyl-benzene-1,3,5-tricarboxamides (BTAs) on their surface. These molecules are known to assemble into one-dimensional supramolecular polymers via noncovalent interactions. By tethering the BTAs to charge-stabilized particles, the clustering behavior of the resulting colloids was dictated by a balance between interparticle electrostatic repulsion and the BTA-mediated attractions. Through careful tuning of the dispersing medium's ionic strength, a regime was found in which particle aggregation could be reversibly induced upon heating the dispersion. These findings clearly indicate that hydrophobic interactions, which become stronger upon heating, play an important role during the clustering process. Besides the thermoreversible nature of the generated hydrophobic interparticle attractions, we found the clustering to be selective, that is, the BTA-functionalized colloids do not interact with nonfunctionalized hydrophobic polystyrene particles. This selectivity in the association process can be rationalized by the preferred stacking of the surface-tethered BTAs. These selective intermolecular/particle bonds are likely stabilized by the formation of hydrogen bonds, as previously observed for analogous molecular BTA assemblies. The resulting driving force responsible for particle clustering is therefore dual in nature and depends on both hydrophobic attractions and hydrogen bonding.