Single Network Hydrogels Research Articles

Environmentally stable, highly stretchable strain sensor based on a conductive single-network hydrogel with non-drying and adhesive properties

Conductive hydrogels inevitably face dehydration, which deteriorates the conductive and tensile properties. Herein, a single-network hydrogel was constructed via the free-radical polymerization of 3-acrylamidopropyl trimethylammonium chloride (ATAC) and 2-hydroxyethyl methacrylate (HEMA) to enhance stretchability and adaptability to the environment. The single-network hydrogel exhibited excellent mechanical properties (fracture strain of 1812.96 %, fracture stress of 124.80 kPa, Young’ s modulus of 73.29 kPa, and toughness of 1426.01 KJ m−3) due to the existence of abundant hydrogen bonds. ATAC can suppress the vaporization of water by breaking the hydrogen bonds between water molecules, endowing the hydrogel with anti-drying performance and greatly broadening its application fields. This work provides a facile strategy for the construction of a single-network hydrogel with high stretchability, ion conductivity, adhesive and non-drying properties and offers new insights into the design of wearable sensors applicable in open environments.

Totally dynamically cross-linked dual-network conductive hydrogel with superb and rapid self-healing ability for motion detection sensors

To overcome the status quo of fragile network and single function in the single-network hydrogel, this work designed and fabricated a dual-network O-CMCS (O-carboxymethyl chitosan)/PVA (polyvinyl alcohol) PBOC conductive hydrogel based on two kinds of totally dynamic reversible cross-linking networks. The PBOC conductive hydrogel combined a flexible O-PT (oxidized pectin)/O-CMCS network with a rigid PVA-borax network, and CNTs (carbon nanotubes) were introduced to improve its toughness and conductivity. Its structural characteristics were investigated through Fourier transform infrared spectroscopy (FT-IR), scanning electron microscope (SEM), X-ray diffractometer (XRD), nuclear magnetic resonance (NMR) and other techniques. Its superb and rapid self-healing property was confirmed through dynamic rheological tests, and its electrical property was studied through an electrochemical workstation. The co-existence of the dual networks endowed the PBOC conductive hydrogel with excellent stretchable property (821% of the maximum elongation at break), and it could quickly self-heal within 60 s after being cut due to the intense interaction of totally reversible multiple dynamic bonding. Notably, the PBOC conductive hydrogel strain sensor exhibited high strain sensitivity with GF (gauge factor) of 8.44 at 800% strain and could accurately detect all kinds of human motions (e.g. finger bending, wrist bending and elbow bending, etc.), confirming its tremendous application potential in the field of wearable sensor devices.

Hybrid Hydrogels with Orthogonal Transient Cross-linking Exhibiting Highly Tunable Mechanical Properties

Compositional changes in the chemical makeup of hydrogels offer a powerful strategy for fine tuning of mechanical properties, enabling specific targeting for different applications. The chemical versatility exhibited by the tunable system introduced here can be leveraged to address a broad range of characteristics across the field of tissue engineering─from blood vessels to cartilage, for example─which demands materials with very different mechanical profiles. Furthermore, we rely exclusively on dynamic, non-covalent cross-linking to provide opportunities for 3D printing and injectability. This work describes a highly tunable system based on hydrogen bonding and ionic interactions. Single network hydrogels were made by exploiting various acrylic monomers including N-acryloyl glycinamide (NAGA) and acrylic acid (AAc). Additionally, hybrid hydrogels were explored by combining these acrylic networks with an ionically cross-linked alginate network. By combining orthogonal cross-linking strategies and altering the ratio between different components in these hybrid gels, a broad range of mechanical properties is demonstrated. The characteristics were extensively investigated using tensile testing, compression testing, and rheological measurements. The final scaffolds were also shown to be non-cytotoxic in preliminary cell viability studies for human dermal fibroblasts.

Injectable Double-Network Hydrogel-Based Three-Dimensional Cell Culture Systems for Regenerating Dental Pulp

The regeneration of dental pulp tissue is very important, but difficult, in dentistry. The biocompatibility, water content, and viscoelastic properties of pulp-like tissue must be optimized to achieve the efficient transfer of metabolites and nutrients, a suitable degradation rate, distribution of encapsulated cells, injectability, and gelation in situ under physiological conditions. As promising materials for pulp regeneration, hydrogel scaffolds have been produced to simulate the extracellular matrix and transmit signaling molecules. It is imperative to develop hydrogels to effectively regenerate pulp tissue for clinical application. Here, two injectable double-network (DN) hydrogel-based three-dimensional (3D) cell culture systems were developed for regenerating dental pulp. The microstructure, mechanical property, rheology property, and degradation behavior of the injectable DN glycol chitosan-based hydrogels in a simulated root canal model were characterized and compared to a single-network (SN) glycol chitosan-based hydrogel. Human dental pulp stem cells (hDPSCs) were then encapsulated into the GC-based hydrogels for the regeneration of pulp tissue, and the biological performance was investigated both in vitro and in vivo. The results showed that the DN hydrogels had ideal injectability under physiological conditions due to the dynamic nature of the crosslinks. Besides, the DN hydrogels exhibited better mechanical properties and longer degradation duration than the corresponding SN hydrogel. As a 3D cell culture system, the characteristics of the DN hydrogel facilitated odontogenic differentiation and mineralization of hDPSCs in vitro. Further in vivo analysis confirmed that the chemical composition, matrix stiffness, and degradation rate of the DN hydrogel matched those of pulp-like fibrous connective tissue, which might be related to Smad3 activation. These findings demonstrate that DN glycol chitosan-based hydrogels are suitable for the regeneration of pulp tissue.

A potential well model for host-guest chemistry in double-network hydrogels toward mechanochemical coupling and toughening

Different from conventional single-network hydrogels, double-network (DN) hydrogels have attracted great research interest due to their ultra-high toughness; however, the working principles behind their complex mechanochemical coupling have not been fully understood. In this study, an extended potential well model is formulated to investigate the host-guest chemistry and the free-energy trap effect, coupled in DN hydrogels undergoing mechanochemical toughening. According to the Morse potential and mean field model, the newly established potential well model can describe the coupled binding of the host brittle network and guest ductile network in the DN hydrogels. A free-energy equation is further proposed to describe the working principles of the mechanochemical coupling and toughening mechanisms using the depth, width, and trap number of potential wells, which determine the barrier energy of the host brittle network, the mesh size of guest ductile network, and the mechanochemical host-guest interactions of these two networks, respectively. Finally, the effectiveness of the proposed model is verified using finite-element analysis (FEA) and experimental results of various DN hydrogels reported in the literature. Using the potential well model, which has host-guest chemistry from both brittle and ductile networks, this study clarifies the linking of mechanochemical coupling and toughening mechanisms in DN hyrdogels.

Recent advances in conductive hydrogels: classifications, properties, and applications.

Hydrogel-based conductive materials for smart wearable devices have attracted increasing attention due to their excellent flexibility, versatility, and outstanding biocompatibility. This review presents the recent advances in multifunctional conductive hydrogels for electronic devices. First, conductive hydrogels with different components are discussed, including pure single network hydrogels based on conductive polymers, single network hydrogels with additional conductive additives (i.e., nanoparticles, nanowires, and nanosheets), double network hydrogels based on conductive polymers, and double network hydrogels with additional conductive additives. Second, conductive hydrogels with a variety of functionalities, including self-healing, super toughness, self-growing, adhesive, anti-swelling, antibacterial, structural color, hydrophobic, anti-freezing, shape memory and external stimulus responsiveness are introduced in detail. Third, the applications of hydrogels in flexible devices are illustrated (i.e., strain sensors, supercapacitors, touch panels, triboelectric nanogenerator, bioelectronic devices, and robot). Next, the current challenges facing hydrogels are summarized. Finally, an imaginative but reasonable outlook is given, which aims to drive further development in the future.

Double-Network Hydrogel Films Based on Cellulose Derivatives and κ-Carrageenan with Enhanced Mechanical Strength and Superabsorbent Properties.

Covalently crosslinked sodium carboxymethyl cellulose (CMC)-hydroxyethyl cellulose (HEC) hydrogel films were prepared using citric acid (CA) as the crosslinking agent. Thereafter, the physically crosslinked κ-carrageenan (κ-CG) polymer was introduced into the CMC-HEC hydrogel structure, yielding κ-CG/CMC-HEC double network (DN) hydrogels. The κ-CG physical network provided sacrificial bonding, which effectively dissipated the stretching energy, resulting in an increase in the tensile modulus, tensile strength, and fracture energy of the DN hydrogels by 459%, 305%, and 398%, respectively, compared with those of the CMC-HEC single network (SN) hydrogel. The dried hydrogels exhibited excellent water absorbency with a maximum water-absorption capacity of 66 g/g in distilled water. Compared with the dried covalent SN gel, the dried DN hydrogels exhibited enhanced absorbency under load, attributed to their improved mechanical properties. The water-absorption capacities and kinetics were dependent on the size of the dried gel and the pH of the water.

Modeling the Additive Effects of Nanoparticles and Polymers on Hydrogel Mechanical Properties Using Multifactor Analysis.

Interpenetrating networks (IPN)s have been conceived as a biomimetic tool to tune hydrogel mechanical properties to the desired target formulations. In this study, the rheological behavior of acrylamide (AAm) [2.5-10%] hydrogels crosslinked with N,N'-methylenebis(acrylamide) (Bis) [0.0625-0.25%] was characterized in terms of the saturation modulus affected by the interaction of silica nanoparticle (SiNP) nanofillers [0-5%] and dextran [0-2%] at a frequency of 1 Hz and strain rate of 1% after a gelation period of 90 min. For single-network hydrogels, a prominent transition was observed at 0.125% Bis for 2.5% AAm and 0.25% Bis for 5% AAm across the SiNP concentrations and was validated by retrospective 3-level factorial design models, as characterized by deviation from linearity in the saturation region (R2 = 0.86). IPN hydrogels resulting from the addition of dextran to the single network in the pre-saturation region, as outlined by the strong goodness of fit (R2= 0.99), exhibited a correlated increase in the elastic (G') and viscous moduli (G"). While increasing the dextran concentrations [0-2%] and MW [100 kDa and 500 kDa] regulated the increase in G', saturation in G" or the loss tangent (tan(δ)) was not recorded within the observed operating windows. Results of multifactor analysis conducted on Han plots in terms of the elastic gains indicate that amongst the factors modulating the viscoelasticity of the IPN hydrogels, dextran concentration is the most important (RDex = 35.3 dB), followed by nanoparticle concentration (RSiNP = 7.7 dB) and dextran molecular weight (RMW = 2.9 dB). The results demonstrate how the Han plot may be systematically used to quantify the main effects of intensive thermodynamic properties on rheological phase transition in interpenetrating networks where traditional multifactor analyses cannot resolve statistical significance.

A Universal and Simple Method to Obtain Hydrogels with Combined Extreme Mechanical Properties and Their Application as Tendon Substitutes.

With the development of biomedical engineering, the preparation of hydrogels with combined extreme mechanical properties similar to those of some biological hydrogels becomes an important research topic for scientists. In this work, a single-network hydrogel with combined extreme mechanical properties is prepared through a simple and universal method, wherein the strength, elongation at break, toughness, and fracture energy of the hydrogel WPU-3PAAm-6PAN are achieved at 24.7 MPa, 544.0%, 68.9 MJ m-3, and 37.2 kJ m-2, respectively. Herein, a series of photosensitive resins in emulsion form are synthesized, and due to the water-oil diphasic characteristic, hydrophobic monomers and high-efficient hydrophobic photo-initiators are adopted into the resins, which can significantly improve the mechanical properties of the hydrogels due to the hydrophobic association effect and solve the biggest barrier of low curing rate in digital light processing (DLP) fabrication of hydrogels, respectively. Moreover, the simple and facile method to obtain robust and tough hydrogels can be universally applied to other polymer systems. Combined with the excellent mechanical properties and printing ability, the hydrogels with optimized structures are fabricated through DLP printing technology and applied as tendon substitutes. The tendon substitutes exhibit superior performance for mechanical connection and regeneration of collagen fibers. Although further clinical research is required, the hydrogels have great potential applications in various biological areas.

A combined enzymatic and ionic cross-linking strategy for pea protein/sodium alginate double-network hydrogel with excellent mechanical properties and freeze-thaw stability

While pea protein (PeaP) is considered to be the plant protein with the most potential for use in plant-based meat products, it is limited by poor gel performance. To overcome this issue, a one-pot method was adopted to prepare a double-network (DN) hydrogel based on a transglutaminase-induced cross-linked network of PeaP and a physically cross-linked network of sodium alginate (SA). As SA concentration increased, the layered structure inside the hydrogel first converted into a porous honeycomb-like structure before forming a dense 3D network structure. Mechanical testing results suggested that the Young's Modulus of hydrogel increased from 2.1 MPa to 8.6 MPa at 80% strain as SA increased from 0% to 0.25%. This dense DN structure endowed the hydrogel with great fatigue resistance as well as excellent textural properties. Low-field nuclear magnetic resonance suggested that the DN hydrogel had a higher binding water content than PeaP single-network hydrogel, and showed good freeze-thaw stability. It is believed that this present work can give some insight into existing PeaP gel systems and inspire the development of more PeaP-based DN hydrogel with desired mechanical strength and freeze-thaw stability. • Double-network hydrogel based on pea protein and sodium alginate was produced. • The Young's Modulus of pea protein-based hydrogel increased from 2.1 to 8.6 MPa. • Hydrogel exhibited great fatigue resistance and self-recovery properties. • Hydrogel showed excellent freeze-thaw stability. • Hydrogel had good mechanical and textural properties after heating treatment.

External Stimuli-Responsive Characteristics of Poly(N,N'-diethylacrylamide) Hydrogels: Effect of Double Network Structure.

Swelling experiments and NMR spectroscopy were combined to study effect of various stimuli on the behavior of hydrogels with a single- and double-network (DN) structure composed of poly(N,N′-diethylacrylamide) and polyacrylamide (PAAm). The sensitivity to stimuli in the DN hydrogel was found to be significantly affected by the introduction of the second component and the formation of the double network. The interpenetrating structure in the DN hydrogel causes the units of the component, which is insensitive to the given stimulus in the form of the single network (SN) hydrogel, to be partially formed as globular structures in DN hydrogel. Due to the hydrophilic PAAm groups, temperature- and salt-induced changes in the deswelling of the DN hydrogel are less intensive and gradual compared to those of the SN hydrogel. The swelling ratio of the DN hydrogel shows a significant decrease in the dependence on the acetone content in acetone–water mixtures. A certain portion of the solvent molecules bound in the globular structures was established from the measurements of the 1H NMR spin–spin relaxation times T2 for the studied DN hydrogel. The time-dependent deswelling and reswelling kinetics showed a two-step profile, corresponding to the solvent molecules being released and absorbed during two processes with different characteristic times.

Double – network hydrogel based on exopolysaccharides as a biomimetic extracellular matrix to augment articular cartilage regeneration

Cartilage regeneration remains a current challenge with no satisfactory strategy in surgery. Hydrogels with structurally and biochemically biomimicking characteristics have been regarded as a promising approach for the success of cartilage regeneration. Naturally sourced hydrogels from exopolysaccharides are ideal candidates for the construction of biomimetic extracellular matrix (ECM) because of their biomimetic networks, high water content, cytocompatibility, and biodegradability. Here, an approach that integrates covalent and ionic bonds in a hydrogel system is shown to form a natural polymeric hydrogel double network (DN) for promoting the adhesion and proliferation of chondrocytes and supporting the formation of matured cartilage tissue. DN hydrogels comprised of chemically crosslinked hyaluronan (HA) and physically crosslinked gellan gum (GG) were developed for potential scaffold fabrication. Compared with HA single network (SN) hydrogel and GG SN hydrogel, the obtained HA/GG DN hydrogel with Young's modulus of 28.6 kPa exhibited adequate compressive strength (208.9 kPa) and high toughness (dissipated energy 2837 J/m3) and thus can be used as a biomimetic extracellular matrix for minimal invasively repairing cartilage. In vitro studies showed that HA/GG DN hydrogel-based ECM promoted the proliferation of chondrocytes. The HA/GG DN hydrogel significantly supported the deposition of cartilage ECM-specific sulfated glycosaminoglycan and type II collagen and facilitated the formation of cartilage tissues. In a rabbit osteochondral defect model, HA/GG DN hydrogel significantly improved cartilage regeneration. The HA/GG DN hydrogel as a biomimetic ECM is a promising candidate as a biomaterial scaffold for cartilage regeneration and repair. Statement of significanceThe fabrication of a biomaterial scaffold as an artificial extracellular matrix (ECM) for cartilage regeneration remains a big challenge. In this work, we fabricated a double-network (DN) hydrogel based on hyaluronan and gellan gum (HA/GG) through a sequential chemical and physical cross-linking process. The HA/GG DN hydrogel exhibited high compressive strength, high toughness, stiffness, and good self-recovery property. The HA/GG DN hydrogel can support chondrocyte proliferation and new ECM deposition correlated with the enhanced mechanical properties, good cytocompatibility, and biodegradability. In vivo animal experiments demonstrated that this HA/GG DN hydrogel facilitates hyaline-like cartilage regeneration. These findings imply that the developed HA/GG DN hydrogel as a biomimetic ECM offers a hopeful new platform for cartilage tissue engineering.

Preparation of double-network hydrogel consisting of chitosan, cellulose and polyacrylamide for enrichment of tetracyclines

A double-network hydrogel was prepared with the chitosan-cellulose composite as the rigid network and polyacrylamide as the flexible network (abbreviated as CCP hydrogel). A deep eutectic solvent synthesized by choline chloride and malic acid was used as the assistant solvent to dissolve cellulose for preparation of the CCP hydrogel. The obtained CCP hydrogel was characterized by scanning electron microscopy, Fourier transform infrared spectroscopy, X-ray diffraction, thermal gravimetric analysis, and stress-strain test. The properties of the CCP hydrogel are obviously better than those of the single network hydrogel. The compressive strength of CCP hydrogel is 2.8 times that of the chitosan-cellulose single network hydrogel. The CCP hydrogel exhibits the favorable swelling performance (swelling ratio of 955 %–1377 %), water-locking ability (water retention value of 40 %), and stability in aqueous system. Moreover, the CCP hydrogel performs the excellent adsorption capacity, fast adsorption efficiency, and good selective towards tetracyclines. The effects of temperature and solution pH on the adsorption properties of CCP hydrogel were assessed. The Langmuir, Freundlich, pseudo-first-order, pseudo-second-order, and thermodynamic models were applied to explore the adsorption characteristics of CCP hydrogel. After multiple adsorption/desorption cycles, the CCP hydrogel still maintains 84.3 %–93.4 % of adsorption capacity. Finally, the CCP hydrogel combined with ultra-performance liquid chromatography-mass spectrometry were used to analyze tetracyclines in food samples. The tetracycline (0.14 μg/mL) and minocycline (0.080 μg/mL) in milk, tetracycline (0.082 μg/mL) and minocycline (0.089 μg/mL) in fish, and tetracycline (0.078 μg/mL) and demeclocycline (0.10 μg/mL) in chicken were detected by CCP-hydrogel method with a high accuracy (recoveries of 75.82 %–108.8 %). Furthermore, for comparison with the CCP-hydrogel method, the traditional precipitation method was also applied to detect the tetracyclines in foods. The CCP-hydrogel method possesses a higher accuracy than traditional method, and can more accurately and satisfactorily detect tetracyclines in foods.

Improving Mechanical Properties of Starch-Based Hydrogels Using Double Network Strategy.

This work aims to improve the mechanical properties of starch-based hydrogels using a double-network (DN) strategy. The single network (SN) starch hydrogel was first prepared using glutaraldehyde as a crosslinker. The compressive properties of the SN hydrogels were influenced by both crosslinker content and crosslinking time. The SN starch hydrogel possessing the best mechanical properties was then fabricated into DN hydrogels. Poly(vinyl alcohol) (PVA) and borax were used as a secondary polymer and a crosslinker, respectively. The PVA–borax complexation partly enhanced the DN hydrogel’s compressive modulus by 30% and its toughness by 39%. DN hydrogels were found to have denser microstructures than SN hydrogels. To be specific, their walls thickened and grew more continuous while their pores shrank. The increased crosslinking density resulted in changes to the microstructure, which were well correlated with their porosity and water uptake capacity. An in vitro cytotoxicity test of the DN hydrogels revealed that they were non-toxic to chondrocytes. This work demonstrated that double networking is a simple but effective strategy for improving mechanical properties of starch-based hydrogels without sacrificing their biocompatibility. This approach can be used to tailor hydrogel properties to fulfill requirements for biomedical applications, such as tissue engineering and other related fields.

Antifouling and antimicrobial cobaltocenium-containing metallopolymer double-network hydrogels.

ABSTRACTCompared with single-network hydrogels, double-network hydrogels offer higher mechanical strength and toughness. Integrating useful functions into double-network hydrogels can expand the portfolios of the hydrogels. We report the preparation of double-network metallopolymer hydrogels with remarkable hydration, antifouling, and antimicrobial properties. These cationic hydrogels are composed of a first network of cationic cobaltocenium polyelectrolytes and a second network of polyacrylamide, all prepared via radical polymerization. Antibiotics were further installed into the hydrogels via ion-complexation with metal cations. These hydrogels exhibited significantly enhanced hydration, compared with polyacrylamide-based hydrogels, while featuring robust mechanical strength. Cationic metallopolymer hydrogels exhibited strong antifouling against oppositely charged proteins. These antibiotic-loaded hydrogels demonstrated a synergistic effect on the inhibition of bacterial growth and antifouling of bacteria, as a result of the unique ion complexation of cobaltocenium cations.

Hysteresis-Free Double-Network Hydrogel-Based Strain Sensor for Wearable Smart Bioelectronics.

Hydrogel-based electronics have attracted substantial attention in the field of biological engineering, energy storage devices, and soft actuators due to their resemblance to living tissues, biocompatibility, tunable softness, and consolidated structures. However, combining the properties of quick resilience, hysteresis-free, and robust mechanical properties in physically cross-linked hydrogels is still a great challenge. Herein, we present a vinyl hybrid silica nanoparticle (VSNPs)/polyacrylamide (PAAm)/alginate double-network hydrogel-based strain sensor with the characteristics of quick resilience, hysteresis-free, and a low limit of detection (LOD). The physical cross-linking among PAAm chains and covalent cross-linking between PAAm, alginate, and N,N-methylenebisacrylamide chains promotes excellent mechanical properties. Moreover, the incorporation of VSNPs reinforces the mechanical strength by the dynamic cross-linking of the PAAm network to maintain the integrity of the hydrogel and works as a stress buffer to dissipate energy. The as-prepared hydrogel-based sensor exhibits a strain sensitivity (i.e., gauge factor) of 1.73 (up to 100% strain), a response time of 0.16 s, an ultra-low electrical hysteresis of 2.43%, and a low LOD of 0.4%. The outstanding properties of the hydrogel are further used to illustrate the utility of the sensor in e-skin, ranging from low-strain applications, such as carotid pulse and artificial sound detection, to large bending applications, such as sign language translations. In addition, an efficient and cost-effective synthesis of double-network hydrogel that can overcome the bottleneck of the electromechanical properties of single network hydrogel has potential prospects in soft actuators, tissue engineering, and various biomedical applications.

Simultaneous One-Pot Interpenetrating Network Formation to Expand 3D Processing Capabilities.

The incorporation of a secondary network into traditional single-network hydrogels can enhance mechanical properties, such as toughness and loading to failure. These features are important for many applications, including as biomedical materials; however, the processing of interpenetrating polymer network (IPN) hydrogels is often limited by their multistep fabrication procedures. Here, a one-pot scheme for the synthesis of biopolymer IPN hydrogels mediated by the simultaneous crosslinking of two independent networks with light, namely: i) free-radical crosslinking of methacrylate-modified hyaluronic acid (HA) to form the primary network and ii) thiol-ene crosslinking of norbornene-modified HA with thiolated guest-host assemblies of adamantane and β-cyclodextrin to form the secondary network, is reported. The mechanical properties of the IPN hydrogels are tuned by changing the network composition, with high water content (≈94%) hydrogels exhibiting excellent work of fracture, tensile strength, and low hysteresis. As proof-of-concept, the IPN hydrogels are implemented as low-viscosity Digital Light Processing resins to fabricate complex structures that recover shape upon loading, as well as in microfluidic devices to form deformable microparticles. Further, the IPNs are cytocompatible with cell adhesion dependent on the inclusion of adhesive peptides. Overall, the enhanced processing of these IPN hydrogels will expand their utility across applications.

Molecular stiffness cues of an interpenetrating network hydrogel for cell adhesion

Understanding cells' response to the macroscopic and nanoscale properties of biomaterials requires studies in model systems with the possibility to tailor their mechanical properties and different length scales. Here, we describe an interpenetrating network (IPN) design based on a stiff PEGDA host network interlaced within a soft 4-arm PEG-Maleimide/thiol (guest) network. We quantify the nano- and bulk mechanical behavior of the IPN and the single network hydrogels by single-molecule force spectroscopy and rheological measurements. The IPN presents different mechanical cues at the molecular scale, depending on which network is linked to the probe, but the same mechanical properties at the macroscopic length scale as the individual host network. Cells attached to the interpenetrating (guest) network of the IPN or to the single network (SN) PEGDA hydrogel modified with RGD adhesive ligands showed comparable attachment and spreading areas, but cells attached to the guest network of the IPN, with lower molecular stiffness, showed a larger number and size of focal adhesion complexes and a higher concentration of the Hippo pathway effector Yes-associated protein (YAP) than cells linked to the PEGDA single network. The observations indicate that cell adhesion to the IPN hydrogel through the network with lower molecular stiffness proceeds effectively as if a higher ligand density is offered. We claim that IPNs can be used to decipher how changes in ECM design and connectivity at the local scale affect the fate of cells cultured on biomaterials.

Formulation of the Polymeric Double Networks (DNs) for Biomedical Applications with Physicochemical Properties to Resemble a Biological Tissue

Single-network hydrogels can have an internal porous structure and biocompatibility, but have lower mechanical properties. Combining these properties with another biocompatible and mechanically strong network can help in mimicking the extracellular matrix of native tissues to make them suitable for tissue scaffolds with desired performance. In the current objective, we combine the properties of poly (ethylene glycol) dimethacrylate (PEGDMA) macromer and polysaccharides as the two components in double networks (DN) for synergistic effects of both components resulting in the interpenetrating polymeric network for making it functional for replacement of injured tissues. The hydrogels were characterized by physical properties like swelling ratio, mechanical properties like tensile and compressive modulus, and rheological behavior. The chemical composition was studied using Fourier transform infrared spectroscopy (FTIR), and the thermal behavior using differential scanning calorimetry (DSC) experiments. Biodegradability and mechanical strength both are gained using double networks (DN), thus making it resemble more like living tissues. DN hydrogels were tested for cell compatibility for possible application in tissue engineering. Furthermore, these properties may allow their application as tissue-engineered scaffolds.

Construction of polysaccharide based physically crosslinked double-network antibacterial hydrogel

Most hydrogels are chemically crosslinked hydrogels, the use of excessive chemical crosslinkers limits their application in biomedicine and other fields. Herein, a completely physically crosslinked double-network hydrogel of sodium alginate/chitosan/zinc ion (SA/CS/Zn2+ PDH) which does not contain toxic chemical reagents was prepared. Compared with the sodium alginate/chitosan single-network hydrogel crosslinked by electrostatic interactions, the mechanical properties of the PDH is significantly improved. Gelation time, swelling behavior, mechanical performance, and antibacterial ability were evaluated with zinc concentration as a variable. It was found that with the increase of zinc content, the gelation rate increased, the swelling rate decreased, and the mechanical properties improved. The PDH exhibited outstanding antibacterial activity against both Staphylococcus aureus and Escherichia coli. Our work provides a new idea for the fabrication of environment-friendly physically crosslinked double-network hydrogels based on natural polysaccharides.