Network Structure Of Hydrogels Research Articles

Multifunctional graft-IPN hydrogels of cellulose nanofibers and poly(N-isopropyl acrylamide) via silver-promoted decarboxylative radical polymerization

Interpenetrating polymer networks (IPNs) have emerged as innovative materials for a wide range of applications. Owing to the crosslinked structure of their polymer components, IPNs exhibit superior properties relative to their single component counterparts. Here, we report a new class of multifunctional graft-interpenetrating polymer network (graft-IPN) hydrogel composites of poly(N-isopropylacrylamide) (PNIPAM) grafted onto cellulose nanofibers (CNFs) via silver(I)-promoted decarboxylative polymerization. This novel approach involves the Ag-promoted graft polymerization and the crosslinking of PNIPAM in the CNF network, forming a hybrid of semi-IPN and graft-copolymer hydrogel. Different from conventional PNIPAM-CNF IPNs, the CNFs in graft-IPN hydrogels form an interconnected network as a result of crosslinking between neighboring grafted PNIPAM. Silver nanoparticles (AgNPs) are also formed in situ in the graft-IPN hydrogel matrix, demonstrating the dual functionality of silver as both a catalyst in the polymerization and an eventual antibacterial agent in the hydrogel. The network structure of graft-IPN hydrogels can be controlled by crosslinker and Ag(I) concentration, therefore modulating their thermo-responsive, mechanical, and swelling properties. The grafting of PNIPAM from CNFs shifts the volume phase transition to 36 °C and significantly improves the mechanical strength and swelling capacity of the hydrogels. Ultimately, this work demonstrates the excellent potential of these multifunctional graft-IPN hydrogels with controllable thermosensitivity, mechanical strength and anti-microbial activity as engineered biomaterials for advanced applications in biomedicine, engineering, and industry.

An ultrasound-triggered injectable sodium alginate scaffold loaded with electrospun microspheres for on-demand drug delivery to accelerate bone defect regeneration

Biological processes, such as bone defects healing are precisely controlled in both time and space. This spatiotemporal characteristic inspires novel therapeutic strategies. The sustained-release systems including hydrogels are commonly utilized in the treatment of bone defect; however, traditional hydrogels often release drugs at a consistent rate, lacking temporal precision. In this study, a hybrid hydrogel has been developed by using sodium alginate, sucrose acetate isobutyrate, and electrospray microspheres as the base materials, and designed with ultrasound response, and on-demand release properties. Sucrose acetate isobutyrate was added to the hybrid hydrogel to prevent burst release. The network structure of the hybrid hydrogel is formed by the interconnection of Ca2+ with the carboxyl groups of sodium alginate. Notably, when the hybrid hydrogel is exposed to ultrasound, the ionic bond can be broken to promote drug release; when ultrasound is turned off, the release returned to a low-release state. This hybrid hydrogel reveals not only injectability, degradability, and good mechanical properties but also shows multiple responses to ultrasound. And it has good biocompatibility and promotes osteogenesis efficiency in vivo. Thus, this hybrid hydrogel provides a promising therapeutic strategy for the treatment of bone defects.

Thermally Reversible Gel-Sol Transition of Hydrogels via Dissociation and Association of an Artificial Protein Nanocage.

Oligomeric protein nanocages often disassemble into their subunits and reassemble by external stimuli. Thus, using these nanocages as cross-linkers for hydrogel network structures is a promising approach to allow hydrogels to undergo stimuli-responsive gel-sol transitions or self-healing. Here, we report hydrogels that show a reversible gel-sol transition resulting from the heat-induced dissociation and reassociation of protein nanocages. The hydrogel contained the 60-mer artificial protein nanocage, TIP60, as a supramolecular cross-linker for polyethylene glycol network structures. The hydrogel showed a gel-to-sol transition upon heating at a temperature above the melting point of TIP60 and immediately returned to a gel state upon cooling to room temperature. During the heating and cooling treatment of the hydrogel, small-angle X-ray scattering analysis suggested the dissociation and reassociation of TIP60. Furthermore, we demonstrated redox-responsive cargo release from TIP60 in the hydrogel. These results showed the potential of TIP60 as a component of multi-stimuli-responsive hydrogels.

Construction and tribological properties of poly acrylic acid‐poly(3‐(methacryloylamino)propyl) dimethyl(3‐sulfopropyl)ammonium hydroxide hydrogel coatings embedded with SiO2 nanoparticles on Ti6Al4V substrate

AbstractThe development of highly effective bio‐lubricant coatings for arthritis treatment is extremely demanded. Herein, inspired by the efficient lubrication of articular cartilage, acrylic acid (AA) with (3‐(methacryloylamino) propyl) dimethyl (3‐sulfopropyl) ammonium hydroxide (MPDSAH) hydrogel coatings containing nanoparticles on Ti6Al4V substrate were designed and fabricated via UV grafting technology. SiO2 and SiO2 grafted with PAA polymer brushes (SiO2‐g‐PAA) were separately doped into the PAA‐PMPDSAH hydrogel. The PAA‐PMPDSAH/SiO2‐g‐PAA exhibits good tensile and compressive properties compared with PAA‐PMPDSAH/SiO2 hydrogel, with an enhancement of 183.4% in tensile modulus and 60.8% in compressive modulus. The PAA‐PMPDSAH/SiO2‐g‐PAA hydrogel coatings exhibit a low wear volume, 2.9 ± 0.16 × 106 μm3, representing a decline of 32.1% and 61.3% compared with the PAA‐PMPDSAH and PAA‐PMPDSAH/SiO2 hydrogel coatings, respectively. The antiwear performance has obviously improved. The hydrophilic PAA polymer brushes prevent the agglomeration of nanoparticles and promote homogeneously dispersion within the hydrogel. The three‐dimensional crosslinked network structure of hydrogel effectively protects the structural integrity of the polymer brushes, thereby facilitating enduring lubrication properties. This work provides a strategy for promising artificial joint lubrication in biomedical fields.

Hybridized cellulose nanocrystals enhanced the temperature resistance and viscoelasticity of the fracturing fluid network

This study aimed to fabricate a novel, low-cost, and environmental-friendly cellulose composite hydrogels based on cellulose nanocrystals (CNCs) and carboxymethyl cellulose (CMC-Na) via hybridizing methods. The performance of composite hydrogels was characterized and the nanocrystals enhancing hydrogels performance mechanism was analyzed, which showed that the apparent viscosity, temperature tolerance, elastic modulus, and tensile strength of cellulose hydrogels were improved by CNCs. Compared with the cellulose hydrogels, the viscosity of the cellulose composite hydrogels at 120 °C reached 195 mPa·s, with an increase of 200 %, and the elastic modulus was 30 Pa, with an increase of about 253 %. Furthermore, the microscopic analysis revealed that CNCs can play the role of nucleus and skeleton in the network structure of cellulose composite hydrogels and obviously enhanced the strength of the network structure. It is obvious to improve the performance of cellulose hydrogels by adding CNCs into the cellulose composite hydrogels. This method provides a new idea for the development of fracturing fluids suitable for unconventional reservoirs.

Low solid content mouldable chitin physical hydrogel prepared by atypical rupture-free swelling.

In this study, the atypical swelling gelation of chitin physical hydrogels was investigated. Just by tuning the amount of the N-acetylation reagent, the degree of acetylation varied and mouldable chitin hydrogels with a wide variety of gel concentrations (0.2-6.4 wt%) were obtained. In response to the gel concentration, the mechanical properties ranged from swollen soft gels to shrunken rigid gels (compressive moduli of 4-310 kPa). The thus-prepared chitin hydrogels, which were composed of only chitin and water, exhibited high transparency and integrity. The swelling gelation of chitin physical hydrogels was achieved owing to both the positive charges of the amino groups inducing the osmotic pressure and the toughness of the crystalline nanofibrous network structure of the chitin hydrogels that endured the large volume change. These previously unnoticed advantageous aspects of chitin have pioneered a novel area of swellable physical gels that has been exclusive to chemical gels so far.

New insights into pure zwitterionic hydrogels with high strength and high toughness.

Zwitterionic hydrogels are electrically neutral materials with both cationic and anionic groups that impart excellent anti-fouling properties and ion channel orientations. However, pure zwitterionic hydrogels generally exhibit low strength and toughness. In this study, it has been discovered that polymerizable zwitterionic monomers in aqueous solution exhibit a unique liquid-liquid phase separation phenomenon at a high monomer concentration of ≥50 wt%, resulting in pure and commercial zwitterionic hydrogels with high compressive strength (6.5 MPa) and high toughness (2.12 kJ m-2). This phase separation and the corresponding aggregations might be caused by strong dipole-dipole interactions among residual zwitterionic monomers under the lack of free-water condition. The synergistic effect of liquid-liquid phase separation and polymer entanglement enhances the mechanical strength, toughness, self-recovery, and anti-freezing properties of pure polyzwitterionic hydrogels. Moreover, the high fracture energy of highly elongated yet tough polyzwitterionic hydrogels facilitates the development of high crack propagation resistance, which supports an expanded role in tissue engineering, soft flexible devices, and electronics applications with improved durability. A wide range of applications for the proposed polyzwitterionic hydrogels is demonstrated by the development and testing of a strain sensor and a triboelectric nanogenerator device. Our findings provide novel insights into the network structure of pure polyzwitterionic hydrogels.

Tuning network structures of hydrophobic hydrogels by controlling polymerization solvent

Hydrophobic hydrogels with various copolymer sequences and network structures are prepared by tuning the solvent condition of the reaction solution, which exhibit different appearance and properties under the same monomer composition.

Humidity-adjustable functional gelatin hydrogel/ethyl cellulose bilayer films for active food packaging application

A sustainable functional bilayer film composed of gelatin hydrogel/ethyl cellulose was fabricated using a simple LBL casting method. The outer layer was hydrophobic ethyl cellulose (EC), while the inner layer was hydrophilic gelatin (GEL) hydrogel. Tannic acid (TA) served as a green cross-linker for GEL hydrogel preparation and as a reductant for AgNPs synthesis in-situ within the hydrogel network. Physicochemical and functional properties of the bilayer films containing different TA content were studied. When 3 wt% TA was added, the AgNPs@GT-3/EC bilayer film exhibited superior UV-light barrier, possessed desirable humidity-adjustable capability and oxygen barrier due to denser hydrogel network structure, and effectively inactivated foodborne pathogens S. aureus and E. coli with bacteriostatic rates of 99 %. The application results indicated that this bilayer film effectively maintained the postharvest quality of white button mushrooms and prolonged their shelf-life to 7 days under ambient storage, demonstrating its promising potential for fresh food packaging.

Controlled release of dual food functional ingredients from octenyl succinic anhydride/β-cyclodextrin nanoparticles integrated carrageenan/polyvinyl alcohol hydrogels

A novel nanohybrid polysaccharide hydrogel was prepared using octenyl succinic anhydride/β-cyclodextrin nanoparticles (OS-β-CD NPs) crosslinked with polyvinyl alcohol (PVA) and κ-carrageenan (κ-CRG) via cascade self-assembly. FTIR and1HNMR confirmed that the formation of NPs/PVA/κ-CRG hydrogels was mainly by hydrogen bonds and electron forces. Results of SEM showed that the NPs/PVA/κ-CRG hydrogels had a well-developed porous structure with interconnected pores of about 4.22 μm. Measurements of rheological, swelling, and thermogravimetric revealed that the NPs/PVA/κ-CRG hydrogels had a good solid-like properties and enhanced mechanical strength due to the participation of OS-β-CD NPs in the formation of hydrogel network structure. In vitro release of the NPs/PVA/κ-CRG hydrogels loaded with vitamin E (VE) and proanthocyanidins (PC) simultaneously in PBS showed that the hydrogels could commendably control the explosive releaseof VE and PC and prolong release period during co-delivery. Moreover, the double active compounds loadedNPs/PVA/κ-CRG hydrogels were beneficial in enhancing synergistic antioxidant capacity.

Conductive 3D Ti3C2Tx MXene-Matrigel hydrogels promote proliferation and neuronal differentiation of neural stem cells

Neural stem cells (NSCs) transplantation has great potential in the field of central nervous system injury repair, but the limited differentiation efficiency of transplanted NSCs often affects the therapeutic effect. In this paper, we present a stable three-dimensional (3D) conductive hydrogel prepared by cross-linking MXenes to Matrigel hydrogel. Benefiting from 3D microporous network structure of hydrogel, the conductive hydrogel can provide an extracellular matrix-like substrate for NSCs growth. Moreover, with the addition of Ti3C2Tx MXenes, the composite has excellent electrical conductivity and biocompatibility. It is demonstrated that MXene-Matrigel hydrogels can effectively promote the proliferation and differentiation of NSCs. These findings provide experimental evidence for understanding the regulatory role of conductive hydrogels on NSCs and provides new strategies for neural tissue engineering.

Multimaterial Hydrogel 3D Printing

AbstractIn recent years, hydrogels have emerged as quintessential 3D printing materials. Coupled with their inherent printability, the unique mechanical properties, network structure, and biocompatibility of hydrogels make them ideal for a wide range of 3D printing applications. Also in recent years, the rise of multimaterial 3D printing, an additive manufacturing technology which involves at least two different materials in the fabrication process, has been witnessed. Advanced multimaterial 3D printing protocols have brought the field closer than ever before to a new industrial revolution. In this review, the use of hydrogels in multimaterial 3D printing is investigated. The review is sectioned by discussing three major multimaterial 3D printing methods: direct‐ink‐writing, vat‐switching, and coaxial extrusion. Subsections detail three common domains of multimaterial hydrogel 3D printing: bioprinting, 4D printing, and particle‐polymer composite printing. In the second part of the review, recent advancements in both multimaterial 3D printing hardware and hydrogel inks which are expected to steer the field in exciting new directions are explored. Finally, a case is made for coaxial extrusion and light‐responsive printers being the best choice for multimaterial hydrogel 3D printing in the long run, due to their gradient and greyscale printing capabilities.

Evaluation of the Effect of Honey-Containing Chitosan/Hyaluronic Acid Hydrogels on Wound Healing.

The 3D polymeric network structure of hydrogels imitates the extracellular matrix, thereby facilitating cell growth and differentiation. In the current study, chitosan/hyaluronic acid/honey coacervate hydrogels were produced without any chemicals or crosslinking agents and investigated for their wound-healing abilities. Chitosan/hyaluronic acid/honey hydrogels were characterized by FTIR, SEM, and rheology analysis. Moreover, their water content, water uptake capacities, and porosity were investigated. In FT-IR spectra, it was discovered that the characteristic band placement of chitosan with hyaluronic acid changed upon interacting with honey. The porosity of the honey-containing hydrogels (12%) decreased compared to those without honey (17%). Additionally, the water-uptake capacity of honey-containing hydrogels slightly decreased. Also, it was observed that hydrogels' viscosity increased with the increased hyaluronic acid amount and decreased with the amount of honey. The adhesion and proliferation of fibroblast cells on the surface of hydrogel formulations were highest in honey-containing hydrogels (144%). In in vivo studies, wound healing was accelerated by honey addition. It has been demonstrated for the first time that honey-loaded chitosan-hyaluronic acid hydrogels, prepared without the use of toxic covalent crosslinkers, have potential for use in wound healing applications.

Bioinspired multi-crosslinking and solid–liquid composite lubricating MXene/PVA hydrogel based on salting out effect

Due to the unique synergistic lubrication mechanisms, solid–liquid composite lubrication has received widespread attention in tribology. However, the cumbersome preparation process and solid–liquid separated service conditions limit its practical application. Inspired by the phenomenon of cell dehydration in electrolyte solutions, a simple salting out method is employed to develop multi-crosslinked and salted out MXene/polyvinyl alcohol (PVA) (MS-MP) hydrogels that can release water controllably for achieving solid–liquid composite lubrication in a single material. In this work, zinc ions (Zn2+) with both multi-crosslinking effect and salting out effect are incorporated into MXene/PVA hydrogels. These effects not only induce the formation of crystalline domains and the strengthening of network structure of hydrogels, but also release the water in hydrogels to realize the solid–liquid composite lubrication. Furthermore, the structure and tribological properties of MS-MP hydrogels can be regulated by adjusting the salting out degree, resulting in the acquisition of a structurally stable hydrogel with exceptional load-bearing capacity and superior lubrication performance. In brief, this work provides a novel and simple strategy for the fabrication of solid–liquid composite lubricating hydrogels, which shows great potential in fabricating liquid-containing lubrication materials.

Photo and temperature responsive novel surface active ionic liquid-based polymeric hydrogel

Integrating more than two properties into a single polymeric hydrogel to introduce the multi-functionality has been a challenge for the scientific community in recent times. In order to impart photo and temperature responsive characteristics added with adjustable mechanical properties into the polymeric hydrogel, herein we have added newly synthesized photo-responsive ionic liquid (IL) into the polymeric (κ-carrageenan) hydrogel. The IL used is having morpholine-based ester functionalized long chain cation and azobenzene based anion that exhibited trans to cis transformation when irradiated by light of 465 nm for 50 min and show surface-active properties with CMC of 6.83 mM. IL with such photo and temperature responsive properties when mixed with the hydrogel of κ-carrageenan in KCl solution gives the photo and thermo-responsive hybrid hydrogel. The three-dimensional network structure of hydrogel made up of the ellipsoidal aggregates with major and minor axis radius of 9.3 A0 and 1.6 A0, respectively is made up of a fibrous porous structure and gets disrupted through the light irradiation and initiated the gel to sol transition, studied through the SEM images, DLS data and rheological measurements. The (IL) based hydrogel gets disrupted after light irradiation as the anion of the IL starts transforming from trans to cis isomerization. Also, the thermo-reversible transition of hydrogel within room temperature to 54 °C is also shown by rheology. Kinetics of the trans to cis transformation, controlled strain and stress measurement and thermal stability of the hydrogel are assessed here. The studied photo and temperature responsive hydrogel could start a new range of smart materials.

Regulated the Swelling Properties of Poly(acrylamide‐co‐acrylic acid) Hydrogel by Changing the Charge Density

AbstractHydrogels can swell without dissolving in water and are widely used in water treatment and biomedicine. The swelling rate of hydrogels is closely related to the network structure and charge density of hydrogels, but there are few detailed studies in this area. In this work, poly(acrylamide‐co‐acrylic acid) anionic hydrogel with acrylic acid (AA) as anionic monomer is prepared. By changing the monomer ratio, or changing the pH value of hydrogels, the internal charge density can be adjusted, and then the swelling rate can be controlled. With the increase of AA monomer content, the content of carboxylate in hydrogel increases, resulting in higher charge density. A high charge density corresponds to a high swelling rate. On the other hand, the swelling rate is closely related to the pH value, which is because the concentration of proton affects the ionization of carboxylic acid, which leads to the change of charge density. It is worth noting when pH increases to 10, the charge shielding effect of the counter‐ion (Na+) gradually increases, thus limiting the swelling of the hydrogel and reducing the swelling rate. This work has reference value for the practical application of hydrogels.

Preparation and sustained release bacteriostatic performance of pH-responsive complex hydrogel bacteriostatic microspheres for oral drug delivery

pH-responsive hydrogel antibacterial microspheres were prepared by complex coacervation method and used as drug carriers to load the antibiotic substitute potassium diformate (KDF). The results showed that the three-dimensional network structure of the composite hydrogel was formed among the polysaccharide components, and Zeolite A loaded with KDF was uniformly dispersed in it. The results of drug release behavior and kinetics in vitro showed that the drug release rate was higher and the release mechanism followed the Ritger-Peppas model, which indicated that the antibacterial microspheres had a good pH response. In vitro, the carrier showed broad-spectrum antibacterial activity, good biocompatibility, and degradability.

Structurally decoupled stiffness and solute transport in multi-arm poly(ethylene glycol) hydrogels

Synthetic hydrogels are widely used as artificial 3D environments for cell culture, facilitating the controlled study of cell-environment interactions. However, most hydrogels are limited in their ability to represent the physical properties of biological tissues because stiffness and solute transport properties in hydrogels are closely correlated. Resultingly, experimental investigations of cell-environment interactions in hydrogels are confounded by simultaneous changes in multiple physical properties. Here, we overcame this limitation by simultaneously manipulating four structural parameters to synthesize a library of multi-arm poly (ethylene glycol) (PEG) hydrogel formulations with robustly decoupled stiffness and solute transport. This structural design approach avoids chemical alterations or additions to the network that might have unanticipated effects on encapsulated cells. An algorithm created to statistically evaluate stiffness-transport decoupling within the dataset identified 46 of the 73 synthesized formulations as robustly decoupled. We show that the swollen polymer network model accurately predicts 11 out of 12 structure-property relationships, suggesting that this approach to decoupling stiffness and solute transport in hydrogels is fundamentally validated and potentially broadly applicable. Furthermore, the unprecedented control of hydrogel network structure provided by multi-arm PEG hydrogels confirmed several fundamental modeling assumptions. This study enables nuanced hydrogel design for uncompromised investigation of cell-environment interactions.

Characterization of structural and functional properties of soy protein isolate and sodium alginate interpenetrating polymer network hydrogels.

This study used enzymatic and Ca2+ cross-linking methods to prepare edible soy protein isolate (SPI) and sodium alginate (SA) interpenetrating polymer network hydrogels to overcome the disadvantages of traditional interpenetrating polymer network (IPN) hydrogels, such as poor performance, high toxicity, and inedibility. The influence of changes in SPI and SA mass ratio on the performance of SPI-SA IPN hydrogels was investigated. Fourier transform infrared spectroscopy (FTIR) and scanning electron microscopy (SEM) were used to characterize the structure of the hydrogels. Texture profile analysis (TPA), rheological properties, swelling rate, and Cell Counting Kit-8 (CCK-8) were used to evaluate physical and chemical properties and safety. The results showed that, compared with SPI hydrogel, IPN hydrogels had better gel properties and structural stability. As the mass ratio of SPI-SA IPN changed from 1:0.2 to 1:1, the gel network structure of hydrogels also tended to be dense and uniform. The water retention and mechanical properties of these hydrogels, such as storage modulus (G'), loss modulus (G"), and gel hardness increased significantly and were greater than those of the SPI hydrogel. Cytotoxicity tests were also performed. The biocompatibility of these hydrogels was good. This study proposes a new method to prepare food-grade IPN hydrogels with mechanical properties of SPI and SA, which may have strong potential for the development of new foods. © 2023 Society of Chemical Industry.

Enzymatically cross-linked hyaluronic acid hydrogels as in situ forming carriers of platelet-rich plasma: Mechanical properties and bioactivity levels evaluation

New studies have shown the great potential of the combination of in situ enzymatically cross-linked hydrogels based on tyramine derivative of hyaluronic acid (HA-TA) with platelet-rich plasma (PRP) and platelet lysate in regenerative medicine. This study describes how the presence of PRP and platelet lysate affects the kinetics of gelation, viscoelastic properties, swelling ratio, and the network structure of HA-TA hydrogels and how the encapsulation of PRP in hydrogels affects the bioactivity of released PRP determined as the ability to induce cell proliferation. The properties of hydrogels were tuned by a degree of substitution and concentration of HA-TA derivatives. The addition of platelet derivatives to the reaction mixture slowed down the cross-linking reaction and reduced elastic modulus (G′) and thus cross-linking efficiency. However, low-swellable hydrogels (7–190%) suitable for soft tissue engineering with G’ 200–1800 Pa were prepared with a gelation time within 1 min. It was confirmed that tested cross-linking reaction conditions are suitable for PRP incorporation because the total bioactivity level of PRP released from HA-TA hydrogels was ≥87% and HA-TA content in the hydrogels and thus mesh size (285–482 nm) has no significant effect on the bioactivity level of released PRP.