Dual-crosslinked Hydrogel Research Articles

Dual Cross-linked HHA Hydrogel Supplies and Regulates MΦ2 for Synergistic Improvement of Immunocompromise and Impaired Angiogenesis to Enhance Diabetic Chronic Wound Healing.

Immunocompromise and impaired angiogenesis of diabetes lead to chronic inflammation when wounds occur, which is the primary reason for the long-term incurable nature of diabetic chronic wounds. Herein, a high-molecular-weight hyaluronic acid (HHA) hydrogel is developed to supply and regulate M2 phenotype macrophages (MΦ2) for synergistic improvement of immunocompromise and impaired angiogenesis. MΦ2 are seeded on the Cu-HHA/PVA hydrogels prepared by Cu2+ cross-linking of low degree and physical cross-linking (one freeze-thaw cycle and unique lyophilization) to form Cu-HHA/PVA@MΦ2 hydrogels. The Cu-HHA/PVA@MΦ2 hydrogel can directly supply the MΦ2 in the wound site, maintain the consistent phenotype of loaded MΦ2, and transform the M1 phenotype macrophages (MΦ1) in the wound bed to MΦ2 by HHA. Furthermore, Cu2+ could be released from the hydrogels to further stimulate angiogenesis, thus accelerating the wound-healing phase transition from inflammation to proliferation and remodeling. The average wound area after the 0.5Cu-HHA/PVA@MΦ2 (ionic cross-linking degree 0.5%) treatment was much smaller than that of other diabetic groups at day 12 and close to that of the wild nondiabetic control group. Therefore, this facile hydrogel strategy with multiple modulation mechanisms of immunocompromise and angiogenesis may act as a safe and effective treatment strategy for a diabetic chronic wound.

Dual alginate crosslinking for local patterning of biophysical and biochemical properties

Hydrogels with patterned biophysical and biochemical properties have found increasing attention in the biomaterials community. In this work, we explore alginate-based materials with two orthogonal crosslinking mechanisms: the spontaneous Diels-Alder reaction and the ultraviolet light-initiated thiol-ene reaction. Combining these mechanisms in one material and spatially restricting the location of the latter using photomasks, enables the formation of dual-crosslinked hydrogels with patterns in stiffness, biomolecule presentation and degradation, granting local control over cell behavior. Patterns in stiffness are characterized morphologically by confocal microscopy and mechanically by uniaxial compression and microindentation measurement. Mouse embryonic fibroblasts seeded on stiffness-patterned substrates attach preferably and attain a spread morphology on stiff compared to soft regions. Human mesenchymal stem cells demonstrate preferential adipogenic differentiation on soft surfaces and osteogenic differentiation on stiff surfaces. Patterns in biomolecule presentation reveal favored attachment of mouse pre-osteoblasts on stripe regions, where thiolated cell-adhesive biomolecules have been coupled. Patterns in degradation are visualized by microindentation measurement following collagenase exposure. Patterned tissue infiltration into degradable regions on the surface is discernible in n=5/12 samples, when these materials are implanted subcutaneously into the backs of mice. Taken together, these results demonstrate that our hydrogel system with patterns in biophysical and biochemical properties enables the study of how environmental cues affect multiple cell behaviors in vitro and could be applied to guide endogenous tissue growth in diverse healing scenarios in vivo. Statement of SignificanceHydrogels with patterns in biophysical and biochemical properties have been explored in the biomaterials community in order to spatially control or guide cell behavior. In our alginate-based system, we demonstrate the effect of local substrate stiffness and biomolecule presentation on the in vitro cell attachment, morphology, migration and differentiation behavior of two different mouse cell lines and human primary cells. Additionally, the effect of degradation patterns on the in vivo tissue infiltration is analyzed following subcutaneous implantation into a mouse model. The achievement of patterned tissue infiltration following the hydrogel template represents an important step towards guiding endogenous healing responses, thus inviting application in various tissue engineering contexts.

Effect of Hydration on Tensile Response of a Dual Cross-linked PVA Hydrogel

Little is known about the effect of water content on the mechanical properties of dual cross-linked hydrogels. To quantify the changes in the mechanical response and equilibrium modulus in a PVA hydrogel as a function of the hydration level. A dual cross-linked hydrogel was tested in tension to a stretch of 1.3 at two stretch rates and in a stress relaxation test. The equilibrium modulus was calculated using the final relaxation stress value. The stiffness of the hydrogel increases significantly as the gel dries. The equilibrium modulus is found to be linear with the hydration level and approximately 2 × stiffer at 60% hydration relative to 90%.

Injectable and Cytocompatible Dual Cross-Linking Hydrogels with Enhanced Mechanical Strength and Stability.

Injectable hydrogels have become increasingly important in the fields of tissue engineering and drug delivery. However, their biological applications are greatly limited by the weak mechanics and poor stability under a physiological environment. Herein, we developed a stable, strong, and injectable hydrogel by linking strong micelle cross-linking with tetra-armed PEG. This dual cross-linking strategy has not only made hydrogels nonswelling but also maintained the relative integrity of the gel network during the degradation process, both of which work together to ensure the mechanical strength and stability of our hydrogel under a physiological environment. A compressive stress of 40 MPa was achieved at 95% strain, and the mechanical properties could remain stable even after immersion into a physiological environment for two months. Besides, it also showed outstanding antifatigue properties, good tissue adhesion, and good cytocompatibility. On the basis of these characteristics, these dual cross-linking injectable hydrogels would find appealing application in biomedicine especially for the repair of load-bearing soft tissues.

Dual-crosslinked methylcellulose hydrogels for 3D bioprinting applications

Thermo-sensitive methylcellulose (MC) hydrogel has been widely used as a scaffold material for biomedical applications. However, due to its poor mechanical properties, the MC-based hydrogel has rarely been employed in 3D bioprinting for tissue engineering scaffolds. In this study, the dual crosslinkable tyramine-modified MC (MC-Tyr) conjugate was prepared via a two-step synthesis, and its hydrogel showed excellent mechanical properties and printability for 3D bioprinting applications. The MC-Tyr conjugate formed a dual-crosslinked hydrogel by modulating the temperature and/or visible light. A combination of reversible physical crosslinking (thermal crosslinking) and irreversible chemical crosslinking (photocrosslinking) was used in this dual crosslinked hydrogel. Also, the photocrosslinking of MC-Tyr solution was facilitated by visible light exposure in the presence of biocompatible photoinitiators (riboflavin, RF and riboflavin 5’-monophophate, RFp). The RF and RFp were used to compare the cytotoxicity and salting-out effect of MC-Tyr hydrogel, as well as the initiation ability, based on the difference in chemical structure. Also, the influence of the printing parameters on the printed MC hydrogel was investigated. Finally, the cell-laden MC-Tyr bioink was successfully extruded into stable 3D hydrogel constructs with high resolution via a dual crosslinking strategy. Furthermore, the MC-Tyr scaffolds showed excellent cell viability and proliferation.

Self-recovering dual cross-linked hydrogels based on bioorthogonal click chemistry and ionic interactions.

The biocompatible, injectable and high water-swollen nature of hydrogels makes them a popular candidate to imitate the extracellular matrix (ECM) for tissue engineering both in vitro and in vivo. However, commonly used covalently cross-linked hydrogels, despite their stability and tunability, are elastic and deteriorate as bulk material degrades which would impair proper cell function. To improve these deficiencies, here, we present a self-recovering cross-linked hydrogel formed instantaneously with functionalized poly(ethylene glycol) as a basis. We combine covalent cross-links introduced via a strain-promoted azide-alkyne cycloaddition (SPAAC) click reaction and non-covalent links between phosphonate groups and calcium ions. By adjusting the ratios of non-covalent and covalent cross-links, we synthesized these dual cross-linked (DC) hydrogels that displayed storage moduli below ∼2000 Pa and relaxation times from seconds to minutes. The gels recovered to 41-96% of their initial mechanical properties after two subsequent strain failures. Cryo-scanning electron microscopy revealed that DC hydrogels containing approximately equal amounts of covalent and non-covalent cross-links displayed phase separation. Finally, we functionalized the DC hydrogels by incorporating an integrin binding motif, RGDS, to provide a biocompatible environment for human mesenchymal stem cells (HMSCs) by facilitating adhesion inside the gel network. Inside these DC gels HSMCs displayed a viability up to 73% after five days of cell culture.

Injectable dual cross-linked adhesive hyaluronic acid multifunctional hydrogel scaffolds for potential applications in cartilage repair

A double crosslinked hydrogels was designed and prepared by combining the Diels–Alder click reaction and possessed good mechanical strength, injectability and adhesion.

Injectable, Tough and Cytocompatible Dual Cross-Linking Hydrogels with Enhanced Mechanical Stability

Injectable, Tough and Cytocompatible Dual Cross-Linking Hydrogels with Enhanced Mechanical Stability

Effects of surfactant and ionic concentration on properties of dual physical crosslinking self-healing hydrogels by hydrophobic association and ionic interactions

Two kinds of dual crosslinking hydrogels have adjustable mechanical properties, self-healing and self-recovery performances.

Role of a high calcium ion content in extending the properties of alginate dual-crosslinked hydrogels

Dual-crosslinked alginate hydrogels with a high Ca2+ content were successfully prepared, which extended their properties, and showed potential application as a skin strain sensor.

Physically and chemically dual-crosslinked hydrogels with superior mechanical properties and self-healing behavior

Using SDS-C18 micelle as a physical crosslinker and SiPU as a multifunctional chemical crosslinker, a new type of dual-crosslinked self-healing hydrogel with excellent stretchability, strength and resilience was synthesized.

Dual-crosslinked alginate/carboxymethyl chitosan hydrogel containing in situ synthesized calcium phosphate particles for drug delivery application

Dual-crosslinked alginate/carboxymethyl chitosan (CMC) based hydrogels containing in situ synthesized calcium phosphate (CaP) particles were developed by combining two physical crosslinking, the ionic crosslinking of alginate with divalent cation (Ca2+), and the electrostatic interaction between cation of amino groups on CMC and anion of carboxyl groups on alginate. The calcium phosphate particles were in situ synthesized by using the excess Ca2+ of ionic crosslinking. The developed hydrogels were investigated the rheological properties, swelling behavior, degradation, and drug released performance in both water-soluble and insoluble drug models. The results showed that the viscoelasticity and swelling capacity of dual-crosslinked hydrogels were enhanced comparing the single-crosslinked alginate-based hydrogel. The in situ gelation of the developed hydrogel provided the injectable ability and drug-encapsulated capacity. Beside, calcium phosphate, including hydroxyapatite (HAp) was in situ synthesized during the gelation. Biocompatibility of this injectable hydrogel was studied by encapsulation behavior of human adipose-derived stem cells (ASCs). With these qualities, the developed hydrogel may have potential for medical providers such as hydrogel injections and drug providers.

Nucleic Acid-Based Dual Cross-Linked Hydrogels for in Situ Tissue Repair via Directional Stem Cell Migration.

In situ tissue repair holds great potential as a cell-free regenerative strategy. A critical aspect of this approach is the selection of cell instructive materials that can efficiently regulate the defect microenvironment via the release of chemoattractant factors to mobilize and recruit endogenous stem cells toward the site of implantation. Here we report the design of a DNA-based hydrogel as a drug delivery platform for the sustained release of a promising chemoattractant, SDF-1α. The hydrogel is composed of chemically cross-linked DNA strands, which are bridged via silicate nanodisks (nSi). Silicate nanodisks electrostatically interact with the negatively charged DNA backbone resulting in the formation of a dual cross-linked nanocomposite hydrogel with a combination of chemical and physical cross-link points. The formulated nanocomposites display enhanced elasticity and mechanical toughness as compared to their nonsilicate containing counterparts. Moreover, the electrostatic interaction between nSi and SDF-1α leads to sustained release of the chemokine from the hydrogels. The in vitro bioactivity assays confirm the retention of chemotactic properties of the protein after its release. Overall, the dual cross-linked DNA-based hydrogel platform could be potentially used as a cell-instructive material for the recruitment of host stem cells to guide the process of in situ tissue repair.

Dual Cross-Linked Hydrogels That Undergo Structural Transformation via Selective Triggered Depolymerization

This study demonstrates the preparation of dual cross-linked hydrogels capable of selective, spontaneous de-cross-linking behavior triggered by head-to-tail depolymerization. A primary covalent structure of the materials was established on a thermoresponsive network containing pendant functional moieties that could induce noncovalent interaction when combined with a macro-cross-linker. The incorporation of the macro-cross-linker not only reinforced the entire structure while providing secondary physical cross-linking but also caused the resulting materials to show autonomous responses via depolymerization. As a result, transformation of the material was achieved without structural collapse, as the noncovalent network in the materials was rapidly, selectively, and completely removed through the depolymerization reaction of the polymer cross-linker when initiated by a trace (<0.01 wt %) stimulus. Thus, the macroscopic changes in the physical and chemical properties of the hydrogels were investigated. Furthe...

Probing Enhanced Site Activity of Co–Fe Bimetallic Subnanoclusters Derived from Dual Cross-Linked Hydrogels for Oxygen Electrocatalysis

Great efforts have been devoted to unveiling structural contributions of transition heterometallic materials to enhanced catalysis, while effective in situ approaches are still urgently demanded to...

Injectable in situ dual-crosslinking hyaluronic acid and sodium alginate based hydrogels for drug release

A series of injectable in situ dual-crosslinking hydrogels (HA/ALG) based on oxidized sodium alginate (oxi-ALG) and hyaluronic acid modified with thiol and hydrazide (HA-SH/CDH) were prepared via hydrazone bonds and disulfide bonds. The chemical structures, morphologies, rheological properties, gelling time, swelling ratio, degradation rate and drug release behavior of hydrogels were investigated. HA/ALG hydrogels exhibited tunable gelling time, rheological properties, swelling ratio and degradation rate with varying precursor concentrations. The gelling time of HA/ALG hydrogels ranged from 157 s to 955 s, the values of yield stress of HA2/ALG2, HA3/ALG3 and HA4/ALG4 hydrogels were 1724, 4349 and 5306 Pa, and the degradation percentage of HA2/ALG2, HA3/ALG3 and HA4/ALG4 hydrogels were about 64%, 51% and 42% after incubating 35 days, respectively. Bovine serum albumin (BSA) was used as a model drug to investigate the drug controlled release properties, and the in vitro cumulative release percentage of BSA from HA2/ALG2, HA3/ALG3 and HA4/ALG4 drug-loaded hydrogels were about 79%, 72% and 69% after 20 days. The series of injectable in situ dual-crosslinking HA/ALG hydrogels could be an attractive candidate for drug delivery system, tissue engineering and regenerative medicine.

High strength dual-crosslinked hydrogels with photo-switchable color changing behavior

Herein, high strength dual-crosslinked hydrogels with photo-switchable color changing behavior were designed and fabricated. In the mixture solution of α-cyclodextrin (α-CD), α-cyclodextrin-spiropyran (α-CD-SP), and poly(ethylene glycol) diacrylate (PEGDA), the PEGDA chains first threaded into the cavity of α-CD/α-CD-SP and form inclusion complexes to generate the physical gel; then, the as-prepared physical gels were subjected to photopolymerization to form a covalently crosslinked network. With the contribution of both no-covalent and covalent bond, the dual-crosslinked hydrogels possess high tensile strength, which is about fifteen times that of the pure PEG hydrogel. And due to the sacrifice of no-covalent bond, hydrogels showed high energy dissipation ratio, up to 75.3% and high fatigue resistance during loading-unloading tests. While the ingenious introduction of SP moieties, enables the as-prepared gels photo-switchable spatiotemporal color changing behavior reversibly. Erasable patterns on hydrogels could be written using UV light and erased by Vis light for multiple cycles. This flexible hydrogel with good physical performance shows high potential in photochromic flexible wearable devices.

A Dual Cross-Linked Strategy to Construct Moldable Hydrogels with High Stretchability, Good Self-Recovery, and Self-Healing Capability.

Most conventional synthetic hydrogels suffer from poor mechanical properties; despite recent significant progress in fabricating tough hydrogels, it is still a challenge to simultaneously realize high stretchability, self-recovery, and self-healing capability in a hydrogel. In this work, a new type of starch/PVA/borax hybrid dual cross-linked (DC) hydrogel was synthesized by a one-pot method. The as-prepared DC hydrogels exhibited mechanical properties of remarkable extensibility (ca. 2485%), excellent toughness (ca. 290.5 kJ m-3), high compression strength (ca. 547.8 kPa), rapid recoverability (81.9% energy recovery after 30 min), and free-shapeable behavior. More impressively, the DC gels sustained approximately 300 times their own weight and exhibited an outstanding self-healing capability at room temperature both in air and underwater. Furthermore, the adsorption amount of methylene blue onto the anionic DC gel (144.68 mg/g) was much higher than that of corn starch gel. Consequently, the eco-friendly, stable, and biodegradable hydrogels will have a great potential application in removing anionic dyes from the wastewater produced by agriculture and industry.

A mechanically durable and device-level tough Zn-MnO2 battery with high flexibility

Practical application of flexible energy storage devices has not been realized despite the booming of experimental researches. One major concern is their poor mechanical durability, which has seldom been investigated in literatures. On one hand, their flexibility is not good enough to accommodate arbitrary deformations, which was merely demonstrated by statically bending at certain angles. Thus, stability against dynamic mechanical stimuli is highly desired. On the other hand, these devices are not strong enough to endure severe mechanical stimuli including large shear forces and impacts, which greatly limits their practicability. Therefore, device-level toughness to ensure long-term usability is also needed. Here, a mechanically durable Zn-MnO2 battery is developed based on a dual-crosslinked hydrogel electrolyte without the usage of separator. Due to the effective energy dissipation of the hydrogel, the as-fabricated battery maintains a stable energy output when being dynamically deformed under severe mechanical stimuli. It can be vastly deformed into various shapes without electrochemical performance decay, showing excellent flexibility. It also exhibits super toughness that can endure two days' treading pressure and survive 20 times of random run-over by cars on road. These demonstrations reveal its outstanding mechanical stability and durability, suggesting great potential in truly flexible and wearable applications.

Mussel-inspired, robust and self-healing nanocomposite hydrogels: Effective reusable absorbents for removal both anionic and cationic dyes

Polydopamine (PDA) composited LAPONITE® cross-linked hydrophobically associated (PLHA) hydrogels were facilely constructed by in situ polymerization. The PLHA hydrogel exerted improved mechanical properties and excellent stability with an additional cross-linking agent LAPONITE®, which guaranteed the hydrogel could be utilized for long-time and reusable application. Notably, the self-healing property of PLHA gels could be achieved easily by the hereinafter three factors: hydrophobic association, LAPONITE® and PDA. Compared with the pristine hydrophobic associated (HA) gel, excellent dye adsorption capacity towards both anionic and cationic dyes came out in PLHA gels owing to the negative charges on LAPONITE and abundant functional groups on PDA nanoparticles such as amine groups, catechol groups and aromatic moieties. The PLHA gels could bind organic dyes via various ways, including coordination, electrostatic interaction, hydrogen bonding or π-π stacking interaction. Compared with the reported works, our proposed method provided the opportunity to prepare a novel robust, self-healing physically dual cross-linked hydrogels, which have the potential to be applied in tissue engineering and the reusable adsorbents of organic colorants.