Supramolecular structures with strain-stiffening properties are ubiquitous in nature but remain rare in the lab. Herein, we report on strain-stiffening supramolecular hydrogels that are entirely produced through the self-assembly of synthetic molecular gelators. The involved gelators self-assemble into semi-flexible fibers, which thereby crosslink into hydrogels. Interestingly, these hydrogels are capable of stiffening in response to applied stress, resembling biological intermediate filaments system. Furthermore, strain-stiffening hydrogel networks embedded with liposomes are constructed through orthogonal self-assembly of gelators and phospholipids, mimicking biological tissues in both architecture and mechanical properties. This work furthers the development of biomimetic soft materials with mechanical responsiveness and presents potentially enticing applications in diverse fields, such as tissue engineering, artificial life, and strain sensors.

@en

Supramolecular assemblies are promising building blocks for the fabrication of functional soft devices for high-tech applications. However, there is a lack of effective methods for large-scale manipulation and integration of nano-sized supramolecular structures on soft substrate. Now, functional soft devices composed of micellar filaments and hydrogels can be created through a versatile approach involving guided dewetting, transfer-printing, and laser-assisted patterning. Such an approach enables unprecedented control over the location and alignment of the micellar filaments on hydrogel substrates. As examples, freely suspended micellar fishnets immobilized on hydrogels are formed, showing the capability of trapping and releasing micro-objects and the piconewton force sensitivity. By incorporating responsive moieties into hydrogels, shape-morphing actuators with micelle-controlled rolling directionality are constructed.

@en

Micropillar adhesives have gained increasing attention because they generate high pull-off forces. The generation of high friction, however, has been proven difficult with such geometries, because micropillars tend to buckle under shear loading. Here, we fabricated orthogonal arrays of composite poly-dimethoxysiloxane (PDMS) micropillars with a stiff core and spin-coated them with PDMS solutions to form a soft coating, as well as bridges between neighboring micropillars. We used 10 wt% and 5 wt% PDMS solution to obtain thick or thin bridges, respectively. The micropillars had an average height of about 60 µm and a diameter of 40 µm. Adhesion and friction measurements were performed with three types of adhesives (i.e., without bridges and with either thin or thick bridges) as well as unpatterned samples as reference, on stiff glass substrates and on deformable PDMS substrates. We found that, on PDMS substrates, bridging resulted in increased friction, compared to non-bridged micropillars. Friction increased with increasing bridge thickness, presumably due to buckling prevention. The adhesives were also subjected to 99 repeating friction cycles to test the effect of micropillar bridging on the durability of the adhesives. The results showed that adhesives with thick micropillar bridges preserved their friction performance over the cycles, whereas adhesives with no bridges or thin bridges exhibited a gradual decay of friction.@en

Introduction of dynamic thiol-alkynone double addition cross-links in a polymer network enable the formation of a self-healing injectable polymer hydrogel. A four-arm polyethylene glycol (PEG) tetra-thiol star polymer is cross-linked by a small molecule alkynone via the thiol-alkynone double adduct to generate a hydrogel network under ambient aqueous conditions (buffer pH = 7.4 or 8.2, room temperature). The mechanical properties of these hydrogels can be easily tuned by varying the concentration of polymer precursors. Through the dynamic thiol-alkynone double addition cross-link, these hydrogels are self-healing and shear thinning, as demonstrated by rheological measurements, macroscopic self-healing, and injection tests. These hydrogels can be injected through a 20G syringe needle and recover after extrusion. In addition, good cytocompatibility of these hydrogels is confirmed by cytotoxicity test. This work shows the application of the thiol-alkynone double addition dynamic covalent chemistry in the straightforward preparation of self-healing injectable hydrogels, which may find future biomedical applications such as tissue engineering and drug delivery.@en

Hydrogel microparticles are important in materials engineering, but their applications remain limited owing to the difficulties associated with their manipulation. Herein, we report the self-orientation of crescent-shaped hydrogel microparticles and elucidate its mechanism. Additionally, the microparticles were used, for the first time, as micro-buckets to carry living cells. In aqueous solution, the microparticles spontaneously rotated to a preferred orientation with the cavity facing up. We developed a geometric model that explains the self-orienting behavior of crescent-shaped particles by minimizing the potential energy of this specific morphology. Finally, we selectively modified the particles’ cavities with RGD peptide and exploited their preferred orientation to load them with living cells. Cells could adhere, proliferate, and be transported and released in vitro. These micro-buckets hold a great potential for applications in smart materials, cell therapy, and biological engineering.

@en

Herein, the micropatterning of supramolecular gels with oriented growth direction and controllable spatial dimensions by directing the self-assembly of small molecular gelators is reported. This process is associated with an acid-catalyzed formation of gelators from two soluble precursor molecules. To control the localized formation and self-assembly of gelators, micropatterned poly(acrylic acid) (PAA) brushes are employed to create a local and controllable acidic environment. The results show that the gel formation can be well confined in the catalytic surface plane with dimensions ranging from micro- to centimeter. Furthermore, the gels show a preferential growth along the normal direction of the catalytic surface, and the thickness of the resultant gel patterns can be easily controlled by tuning the grafting density of PAA brushes. This work shows an effective “bottom-up” strategy toward control over the spatial organization of materials and is expected to find promising applications in, e.g., microelectronics, tissue engineering, and biomedicine.

@en

The last decade has witnessed great progress in understanding and manipulating self-assembly of block copolymers in solution. A wide variety of micellar structures can be created and many promising applications in bioscience have been reported. In particular, nano-fibrous micelles provide a great platform to mimic the filamentous structure of native extracellular matrix (ECM). However, the evaluation of this kind of filomicellar system with potential use in tissue engineering is virtually unexplored. The question behind it, such as if the block copolymer nano-fibrous micelles can regulate cellular response, has lingered for many years because of the difficulties in preparation and 3D manipulation of these tiny objects. Here, by using a combination approach of self-assembly of block copolymers and soft lithography, we establish a novel and unique nano-fibrous 2D platform of organized micelles and demonstrate that patterned micelles enable control over the cellular alignment behavior. The area density and orientation of fibrous micelles determine the alignment degree and directionality of cells, respectively. Furthermore, when cells were cultured on multi-directionally aligned micelles, a competitive response was observed. Due to the virtually infinite possibilities of functionalization of the micelle corona, our work opens a new route to further mimic the native fibrous networks with artificial micelles containing various functionalities.

@en

Self-assembly of amphiphilic block copolymers in aqueous solution provides a versatile tool to create complex and functional micelles with various nanostructures, such as spherical, cylindrical and bilayer structures. As an important class in these structures, nanofibrillar micelles have attracted growing interest due to their unique properties that can potentially mimic biological analogues. For example, a great number of nanofibrillar structures, such as actin filaments and collagen gels with filamentous structures, were found in nature systems and have greatly motivated researchers to mimic these systems with synthetic materials. Besides, precise spatiotemporal control and integration of these nanofibrillar structures will offer a powerful strategy for construction of new soft devices in the future. Therefore, in this thesis, we explore the ultra-long, stiff and quenched micelles of diblock copolymers and develop a hybrid approach combining self-assembly of block copolymers and micro-fabrication methods to manipulate these micelles for building soft devices.@en

While the formation of (tri)block copolymer hydrogels has been extensively investigated, such studies mostly focused on equilibrium self-assembling whereas the use of preformed structures as building blocks such as out of equilibrium, quenched, nanofibrillar micelles is still a challenge. Here, we demonstrate that quenched, ultralong polystyrene-b-poly(ethylene oxide) (PS-b-PEO) micelles can be used as robust precursors of hydrogels. Two cross-linking strategies, (i) thermal fusion of micellar cores and (ii) chemical cross-linking of preformed micellar coronas were studied. The gelation process and the structure of the micellar networks were investigated by in situ rheological measurements, confocal microscopy and transmission electron microscopy. Direct observation of core fusion of preformed quenched micelles is provided validating this method as a robust gelation route. Using time sweep rheological experiments, it was found for both cross-linking methods that these 3D "mikado" gels are formed in three different stages, containing (1) initiation, (2) transition (growth), and (3) stabilization regimes.@en

Self-assembly of biomolecules catalytically controls the formation of natural supramolecular structures, giving highly ordered complex materials. Such desirable hybrid systems are very difficult to design and construct synthetically. A hybrid double-network hydrogel with a maximum storage modulus (G′_max) of up to 55 kPa can be synthesized by using a self-assembled hydrogel that catalyses the formation of another kinetically arrested hydrogel network. Tuning of the catalytic efficiency of the first network allowed spatiotemporal control over the evolution of the second network and the resulting mechanical properties. The distribution of active catalytic sites was optimal for catalytic fibres prepared at the minimum gelation concentration (MGC) to give the double-network hydrogel with highest storage modulus. This approach could be very useful in preparing complex hierarchical structures with tailor-made properties.

@en

By equipping mutually incompatible carboxylic acid and proline catalytic groups with different self-assembling motives we have achieved self-sorting of the resulting catalytic gelators, namely SucVal8 and ProValDoc, into different supramolecular fibers, thus preventing the acidic and basic catalytic groups from interfering with each other. The resulting spatial separation of the incompatible catalytic functions is found to be essential to achieve one-pot deacetalization–aldol tandem reactions with up to 85% efficiency and 90% enantioselectivity. On the contrary, when SucVal8 was co-assembled with a structurally similar catalytically active hydrogelator (ProVal8), self-sorting was precluded and no tandem catalysis was observed.@en

A novel and facile approach to fabricating well-organized macroscopic 2D networks of cylindrical micelles is reported, based on transfer printing and thermal welding of aligned supramolecular micelles of block copolymers. This versatile approach provides a new strategy for fabricating functional 2D superstructures with a higher level of order.

@en