Hydrogel Architecture Research Articles

Self-assembled MoS2-GO Framework as an Efficient Cocatalyst of CuInZnS for Visible-Light Driven Hydrogen Evolution

A ternary heterostructured CuInZnS/MoS2-GO (graphene oxide) photocatalyst was constructed by a simple two-step hydrothermal method. The three-dimensional hierarchical architecture of MoS2-GO hydrogel was first synthesized through a facile hydrothermal method. The obtained MoS2-GO hydrogel with ultralow density and high surface area was redispersed into water and composite with CuInZnS. The resulting catalysts were analyzed by systematic characterizations including X-ray diffraction (XRD), transmission electron microscopy (TEM), field emission scanning electron microscopy (FESEM), Raman, and UV–vis diffuse reflectance spectra (DRS), et al. The noble metal-free composite exhibited dramatically enhanced photocatalytic performance toward hydrogen evolution. The enhanced solar water splitting performance could be ascribed to the synergetic effect of GO and MoS2. GO served as an electron acceptor and transporter while MoS2 provided abundant active sites for hydrogen evolution. We hope this work may give some pe...

Two-photon lithography and microscopy of 3D hydrogel scaffolds for neuronal cell growth

3D fabrication techniques are rapidly expanding in the field of scaffold development for cell culture and tissue engineering. Herein we report the realization of free-standing PEGDA hydrogel architectures by using two-photon lithography. The morphological and immunofluorescence characterization of neuro2A cells revealed a tridimensional colonization featuring multiple neuritic extensions per cell as well as the expression of β-tubulin neuronal marker and actin microfilaments. The results open new perspectives in the continuous quest for structured biomaterials able to provide a favorable environment to cells and at the same time not interfering with imaging protocols necessary for a clear scenario of the cell seeding.

Multi-scale characterisation of deuterated cellulose composite hydrogels reveals evidence for different interaction mechanisms with arabinoxylan, mixed-linkage glucan and xyloglucan

The interactions of cellulose with other major plant cell wall polysaccharides - arabinoxylan (AX), xyloglucan (XG) and mixed linkage glucans (MLG) - have been investigated by characterising the architecture of composite deuterated cellulose hydrogels by means of SAXS and SANS, combined with XRD, NMR and microscopy. The results indicate that cellulose-AX interactions, limited to the ribbons' surface, take place via a non-specific adsorption mechanism. In contrast, XG and MLG interact specifically with cellulose, forming two different fractions: (i) interfibrillar domains interacting with the cellulose microfibrils and (ii) surface domains, responsible for the cross-linking of ribbons. XG co-crystallises with cellulose, promoting the formation of Iβ-richer microfibrils and forming intercalated amorphous regions. On the other hand, MLG interacts with cellulose forming a paracrystalline coating layer. This structural role of XG and MLG in preventing microfibril aggregation may help explain their key function in the cell expansion process of growing plant tissues.

Collagen Fiber Architecture Regulates Hypoxic Sarcoma Cell Migration.

Collagen is prevalent in the microenvironment of many cancer types and has been demonstrated to play an important role during disease progression. We previously showed the importance of hypoxic gradients in sarcoma cell migration. Here, we utilized an oxygen gradient collagen gel platform to determine the impact of collagen fiber density and hypoxic gradient on sarcoma cell migration. The oxygen gradient was created by regulating the oxygen diffusion coefficient along with the cellular oxygen consumption rate. Collagen fiber density in the hydrogels is modified by changing the preincubation period of the collagen gel solution at 4 °C, controlling fiber density independently of collagen concentration and oxygen tension. High fiber density gels have wider and longer fibers but a similar microscale pore size with a larger nanoscale pore size and quicker stress relaxation time, compared to the low fiber density gel. Both gels have the same Young's modulus. We analyzed responses of sarcoma cells encapsulated in the different hydrogels for 3 days. In the nonhypoxic low fiber density constructs, sarcoma cells exhibit a larger aspect ratio, and the matrix has less fiber alignment compared to the nonhypoxic high fiber density constructs. Interestingly, we found a minimal effect of fiber density on cell migration and the ability of the cells to degrade the matrix in nonhypoxic constructs. When compared with hypoxic constructs, we observed the opposite trend, where cells in low fiber density constructs exhibit a lower aspect ratio and the matrix has more aligned fibers compared to hypoxic high fiber density constructs. Sarcoma cells encapsulated in high fiber density hypoxic gels migrated faster and degraded the matrix more rapidly compared to the low fiber density hypoxic constructs. Overall, we show that hypoxic cell migration and matrix degradation are enhanced in high fiber density gels, while hypoxic matrix alignment is prominent in low fiber density gels. Our results suggest that the differences in cellular responses under hypoxic gradients are due to the hydrogel architecture including fiber density, size (length and width), and stress relaxation.

Shape-Memory Hydrogels: Evolution of Structural Principles To Enable Shape Switching of Hydrophilic Polymer Networks.

The ability of hydrophilic chain segments in polymer networks to strongly interact with water allows the volumetric expansion of the material and formation of a hydrogel. When polymer chain segments undergo reversible hydration depending on environmental conditions, smart hydrogels can be realized, which are able to shrink/swell and thus alter their volume on demand. In contrast, implementing the capacity of hydrogels to switch their shape rather than volume demands more sophisticated chemical approaches and structural concepts. In this Account, the principles of hydrogel network design, incorporation of molecular switches, and hydrogel microstructures are summarized that enable a spatially directed actuation of hydrogels by a shape-memory effect (SME) without major volume alteration. The SME involves an elastic deformation (programming) of samples, which are temporarily fixed by reversible covalent or physical cross-links resulting in a temporary shape. The material can reverse to the original shape when these molecular switches are affected by application of a suitable stimulus. Hydrophobic shape-memory polymers (SMPs), which are established with complex functions including multiple or reversible shape-switching, may provide inspiration for the molecular architecture of shape-memory hydrogels (SMHs), but cannot be identically copied in the world of hydrophilic soft materials. For instance, fixation of the temporary shape requires cross-links to be formed also in an aqueous environment, which may not be realized, for example, by crystalline domains from the hydrophilic main chains as these may dissolve in presence of water. Accordingly, dual-shape hydrogels have evolved, where, for example, hydrophobic crystallizable side chains have been linked into hydrophilic polymer networks to act as temperature-sensitive temporary cross-links. By incorporating a second type of such side chains, triple-shape hydrogels can be realized. Considering the typically given light permeability of hydrogels and the fully hydrated state with easy permeation by small molecules, other types of stimuli like light, pH, or ions can be employed that may not be easily used in hydrophobic SMPs. In some cases, those molecular switches can respond to more than one stimulus, thus increasing the number of opportunities to induce actuation of these synthetic hydrogels. Beyond this, biopolymer-based hydrogels can be equipped with a shape switching function when facilitating, for example, triple helix formation in proteins or ionic interactions in polysaccharides. Eventually, microstructured SMHs such as hybrid or porous structures can combine the shape-switching function with an improved performance by helping to overcome frequent shortcomings of hydrogels such as low mechanical strength or volume change upon temporary cross-link cleavage. Specifically, shape switching without major volume alteration is possible in porous SMHs by decoupling small volume changes of pore walls on the microscale and the macroscopic sample size. Furthermore, oligomeric rather than short aliphatic side chains as molecular switches allow stabilization of the sample volumes. Based on those structural principles and switching functionalities, SMHs have already entered into applications as soft actuators and are considered, for example, for cell manipulation in biomedicine. In the context of those applications, switching kinetics, switching forces, and reversibility of switching are aspects to be further explored.

Fabrication of nanozyme@DNA hydrogel and its application in biomedical analysis

Nanozymes have received great attention owing to the advantages of easy preparation and low cost. Unlike natural enzymes that readily adapt to physiological environments, artificial nanozymes are apt to passivate in complex clinical samples (e.g., serum), which may damage the catalytic capability and consequently limit the application in biomedical analysis. To conquer this problem, in this study, we fabricated novel nanozyme@DNA hydrogel architecture by incorporating nanozymes into a pure DNA hydrogel. Gold nanoparticles (AuNPs) were adopted as a model nanozyme. Results indicate that AuNPs incorporated in the DNA hydrogel retain their catalytic capability in serum as they are protected by the hydrogel, whereas AuNPs alone totally lose the catalytic capability in serum. The detection of hydrogen peroxide and glucose in serum based on the catalysis of the AuNPs@DNA hydrogel was achieved. The detection limit of each reaches 1.7 and 38 μM, respectively, which is equal to the value obtained using natural enzymes. Besides the mechanisms, some other advantages, such as recyclability and availability, have also been explored. This nanozyme@DNA hydrogel architecture may have a great potential for the utilization of nanozymes as well as the application of nanozymes for biomedical analysis in complex physiological samples.

High-performance symmetric supercapacitors based on carbon nanosheets framework with graphene hydrogel architecture derived from cellulose acetate

Abstract Three-dimensional nitrogen-doped carbon nanosheets framework (N-CNF) has been obtained starting with cellulose acetate. The product is prepared through a so-called one-step method that carbonization, activation and nitrogen-doping occur simultaneously. The resultant N-CNF shows an architecture like graphene hydrogel with interconnected hierarchical porous structure, N-doping with high nitrogen content (8.7 wt%) and high specific surface area (1003.6 m 2 g −1 ). The N-CNF electrode displays excellent electrochemical performances due to the unique architecture and pseudocapacitance contribution from heteroatoms. In the three-electrode configuration, the N-GNF achieves a high specific capacitance of 242 F g −1 at 1 A g −1 and displays ultrahigh rate capability (83.4% capacitance retention at 100 A g −1 ) in 6 mol L −1 KOH electrolyte. The symmetric supercapacitor (SSC) based N-CNF exhibits energy density as high as 60.4 Wh kg −1 (at a power density of 1750 W kg −1 ) and 17.9 Wh kg −1 (at 850 W kg −1 ) in ionic liquid and aqueous electrolytes, respectively. It is surprised that the single device filled by ionic liquid electrolyte is able to light easily 60 red light-emitting diodes (LEDs, 2.2 V) in parallel after charging for only 10 s, showing an excellent energy storage/release performance.

Dual-responsive and Multi-functional Plasmonic Hydrogel Valves and Biomimetic Architectures Formed with Hydrogel and Gold Nanocolloids.

We present a straightforward approach with high moldability for producing dual-responsive and multi-functional plasmonic hydrogel valves and biomimetic architectures that reversibly change volumes and colors in response to temperature and ion variations. Heating of a mixture of hybrid colloids (gold nanoparticles assembled on a hydrogel colloid) and hydrogel colloids rapidly induces (within 30 min) the formation of hydrogel architectures resembling mold shapes (cylinder, fish, butterfly). The biomimetic fish and butterfly display reversible changes in volumes and colors with variations of temperature and ionic conditions in aqueous solutions. The cylindrical plasmonic valves installed in flow tubes rapidly control water flow rate in on-off manner by responding to these stimuli. They also report these changes in terms of their colors. Therefore, the approach presented here might be helpful in developing new class of biomimetic and flow control systems where liquid conditions should be visually notified (e.g., glucose or ion concentration changes).

Electrophoretic hydrogel adhesion for fabrication of three-dimensional materials

The adhesion of hydrogels has attracted substantial attention for use in building three-dimensional constructs such as scaffolds for cell culture, carriers of drug release system and soft actuators. This review article summarizes our group’s research on electrophoretic hydrogel adhesion, a novel strategy for the adhesion of hydrogels. This technique involves the electrophoretic manipulation of a polyelectrolyte to form an adhesive layer at the interface of the two hydrogels and is a powerful method for fabrication of free-form hydrogel constructs through the adhesion of microgels. The adhesion of hydrogels has attracted attention for use in building three-dimensional (3D) constructs, such as scaffolds for cell culture, carriers of drug release system and soft actuators. Electrophoretic hydrogel adhesion, which is the electrophoretic manipulation of a polyelectrolyte to form an adhesive layer at the interface of two gels, was developed. To apply this adhesive method to build 3D materials, rapid and free-form fabrication of hydrogel constructs was achieved by the electrophoretic adhesion of microgels. The development of a novel adhesion strategy will be useful for the fabrication of novel 3D hydrogel architectures.

Investigation of the micro- and nano-scale architecture of cellulose hydrogels with plant cell wall polysaccharides: A combined USANS/SANS study

The structure of protiated, deuterated and composite cellulose hydrogels with plant cell wall (PCW) polysaccharides has been investigated by combined USANS/SANS experiments, complemented with spectroscopy and microscopy. The broad size range covered by the USANS/SANS experiments enabled the identification of cellulose architectural features in the cross-sectional and longitudinal directions. In the cross-sectional direction, cellulose ribbons are modelled as core-shell structures. Xyloglucan and mixed linkage glucans interfere with the cellulose crystallisation process, reducing the crystallinity and establishing cross-bridges between ribbons. However, only xyloglucan is able to establish strong interactions with the cellulose microfibrils, affecting the properties of the ribbons’ core. Longitudinally, the ribbons are hypothesised to present a ca. 1.4–1.5 μm periodic twist with a crystallite length of ca. 140–180 nm for the individual microfibrils. These results highlight the potential of USANS/SANS techniques to investigate the multi-scale architecture of cellulose hydrogels as well as the interaction mechanism between cellulose and PCW polysaccharides.

Multi-scale model for the hierarchical architecture of native cellulose hydrogels

The structure of protiated and deuterated cellulose hydrogels has been investigated using a multi-technique approach combining small-angle scattering with diffraction, spectroscopy and microscopy. A model for the multi-scale structure of native cellulose hydrogels is proposed which highlights the essential role of water at different structural levels characterised by: (i) the existence of cellulose microfibrils containing an impermeable crystalline core surrounded by a partially hydrated paracrystalline shell, (ii) the creation of a strong network of cellulose microfibrils held together by hydrogen bonding to form cellulose ribbons and (iii) the differential behaviour of tightly bound water held within the ribbons compared to bulk solvent. Deuterium labelling provides an effective platform on which to further investigate the role of different plant cell wall polysaccharides in cellulose composite formation through the production of selectively deuterated cellulose composite hydrogels.

Biocompatible Double-Membrane Hydrogels from Cationic Cellulose Nanocrystals and Anionic Alginate as Complexing Drugs Codelivery.

A biocompatible hydrogel with a double-membrane structure is developed from cationic cellulose nanocrystals (CNC) and anionic alginate. The architecture of the double-membrane hydrogel involves an external membrane composed of neat alginate, and an internal composite hydrogel consolidates by electrostatic interactions between cationic CNC and anionic alginate. The thickness of the outer layer can be regulated by the adsorption duration of neat alginate, and the shape of the inner layer can directly determine the morphology and dimensions of the double-membrane hydrogel (microsphere, capsule, and filmlike shapes). Two drugs are introduced into the different membranes of the hydrogel, which will ensure the complexing drugs codelivery and the varied drugs release behaviors from two membranes (rapid drug release of the outer hydrogel, and prolonged drug release of the inner hydrogel). The double-membrane hydrogel containing the chemically modified cellulose nanocrystals (CCNC) in the inner membrane hydrogel can provide the sustained drug release ascribed to the "nano-obstruction effect" and "nanolocking effect" induced by the presence of CCNC components in the hydrogels. Derived from natural polysaccharides (cellulose and alginate), the novel double-membrane structure hydrogel material developed in this study is biocompatible and can realize the complexing drugs release with the first quick release of one drug and the successively slow release of another drug, which is expected to achieve the synergistic release effects or potentially provide the solution to drug resistance in biomedical application.

A Minimalistic in Vitro 3D Model to Study F98 Rat Brain Tumor Growth

Classical in vitro methods for studying cell behavior, mainly 2D cell cultures on Petri dishes, suffer from many biases (simple dimensionality, absence of biochemical gradients, rigidity⋯). On the other hand, in vivo studies involve very complex systems and do not allow separating the role of each component. Alternative strategies inspired from in vivo tissue's architecture and composition, have been under development for years, in order to mimic extracellular 3D matrix (ECM). Among them, synthetic hydrogels are good in vitro minimalistic models, allowing fine tuning of their composition as well as their structural and functional features.In this context, we manufactured an original PEG-based hydrogel grafted with poly-L-lysine moieties in order to: i) validate this substrate as an artificial 3D ECM; ii) follow the growth (proliferation, migration) of a population of the F98 rat glioma cell line in this minimalistic tissue-like structure.First, we studied the hydrogel physical properties when varying the size and concentration of PEG and poly-L-lysine, using rheology and FRAP. In particular, we explored a range of rigidities, including that of brain ECM (1kPa), and diffusivities following different polymer mesh size. In a second step, we examined how the gel properties and its composition (PEG and poly-L-lysine) influence the organization and growth rate of the cell population.In our 3D substrate, cells have rounded shape different from 2D form. They organize as aggregates for which growth rate and shape varies as a function of hydrogel composition: the higher is the density of PEG and poly-L-lysine, the smaller is the size of the aggregates.Finally, our data clearly give an insight on how spatial constraints in the 3D hydrogel architecture limit tumor's progression into the polymer network. Correlation with in vivo characteristics would be further investigated.

Biomimetic 4D printing.

Shape-morphing systems can be found in many areas, including smart textiles, autonomous robotics, biomedical devices, drug delivery and tissue engineering. The natural analogues of such systems are exemplified by nastic plant motions, where a variety of organs such as tendrils, bracts, leaves and flowers respond to environmental stimuli (such as humidity, light or touch) by varying internal turgor, which leads to dynamic conformations governed by the tissue composition and microstructural anisotropy of cell walls. Inspired by these botanical systems, we printed composite hydrogel architectures that are encoded with localized, anisotropic swelling behaviour controlled by the alignment of cellulose fibrils along prescribed four-dimensional printing pathways. When combined with a minimal theoretical framework that allows us to solve the inverse problem of designing the alignment patterns for prescribed target shapes, we can programmably fabricate plant-inspired architectures that change shape on immersion in water, yielding complex three-dimensional morphologies.

Hierarchical architecture of bacterial cellulose and composite plant cell wall polysaccharide hydrogels using small angle neutron scattering.

Small angle neutron scattering (SANS) has been applied to characterise the structure of pure bacterial cellulose hydrogels, and composites thereof, with two plant cell wall polysaccharides (arabinoxylan and xyloglucan). Conventional published models, which assume that bacterial cellulose ribbons are solid one-phase systems, fail to adequately describe the SANS data of pure bacterial cellulose. Fitting of the neutron scattering profiles instead suggests that the sub-structure of cellulose microfibrils contained within the ribbons results in the creation of regions with distinct values of neutron scattering length density, when the hydrogels are subjected to H2O/D2O exchange. This may be represented within a core-shell formalism that considers the cellulose ribbons to comprise a core containing impermeable crystallites surrounded by a network of paracrystalline cellulose and tightly bound water, and a shell containing only paracrystalline cellulose and water. Accordingly, a fitting function comprising the sum of a power-law term to account for the large scale structure of intertwined ribbons, plus a core-shell cylinder with polydisperse radius, has been applied; it is demonstrated to simultaneously describe all SANS contrast variation data of pure and composite bacterial cellulose hydrogels. In addition, the resultant fitting parameters indicate distinct interaction mechanisms of arabinoxylan and xyloglucan with cellulose, revealing the potential of this approach to investigate the role of different plant cell wall polysaccharides on the biosynthesis process of cellulose.

Nanostructured Surface with Tunable Contact Angle Hysteresis for ConstructingIn VitroTumor Model

Contact angle hysteresis (CAH) is an important phenomenon in surface chemistry. In this paper, we fabricated nanostructured substrates and investigated the relationship between roughness and CAH. We demonstrated that by patterning well-tuned CAH in superhydrophobic background, we can pattern droplets with controlled sizes. We further showed that our system could be used in fabricating complex hydrogel architecture, allowing coculture of different types of cells in three-dimensional way. This CAH-based patterning strategy would providein vitromodels for tissue engineering and drug delivery.

Semi‐Egg‐Like Heterogeneous Compartmentalization of Cells Controlled by Contact Angle Hysteresis

Precise control of liquid inside compartments is critically important in bioreactors, combinatorial analysis, and tissue engineering. A contact angle hysteresis (CAH)‐based strategy is demonstrated to construct a semi‐egg‐like hydrogel architecture, leading to spatial heterogeneous compartmentalization of cells. The semi‐egg‐like architecture is fabricated by successively capturing and gelling prehydrogel liquids using a substrate with controlled‐CAH pattern and ultralow‐CAH background. The controlled‐CAH pattern could capture liquid with tunable size, while ultralow‐CAH background prevents liquid sticking. It is envisioned that this CAH‐based strategy would be promising in designing functional surface for engineering complicated architectures of either biomedical or nonbiomedical systems.

Hybrid cross-linking characteristics of hydrogel control stem cell fate.

Controlling hydrogel structures by combination of physical and chemical cross-links provides a novel system to regulate (stem) cell fate. In this study, we designed a polyethylene glycol (PEG)-based hydrogel where the polymer chains contain both physical and chemical cross-linking units in the same chain with self-assembling L-tyrosine-based dipeptides and photopolymerizable polyacrylate groups, respectively. It is shown that hydrogel architectures derived from this polymer are correlated to the cross-linking mechanisms. Combination of these cross-links controls three-dimensional gel architecture to regulate stem cell behavior in these hydrogels. Particularly, interaction of mesenchymal stem cells with the hydrogel enabled cellular aggregation to enhance chondrogenic differentiation as observed from the deposition of chondrogenic matrix. Increased chondrogenesis was due to enhanced cell-cell adhesion, which was mediated by gel morphology. This study shows the interplay of physical and chemical cross-links in hydrogels to regulate stem cell function and provides a novel molecular engineering tool for controlling hydrogel properties.

Three-dimensional plasmonic hydrogel architecture: facile synthesis and its macroscale effective space

A facile strategy was developed to fabricate a 3D hydrogel decorated with Ag nanoparticles as a SERS substrate. The macro effective depth in this 3D network was confirmed. The substrate produced satisfactory results in the analysis of trace environmental molecules.

Hierarchical Si hydrogel architecture with conductive polyaniline channels on sulfonated-graphene for high-performance Li ion battery anodes having a robust cycle life

A hierarchical Si hydrogel architecture with conductive polyaniline channels on sulfonated-graphene gives high capacity, in addition to excellent capacity retention and robust cycle life.