Single Network Hydrogels Research Articles

Dye removal by eco-friendly physically cross-linked double network polymer hydrogel beads and their functionalized composites

Hydrogels have attracted large attention in wastewater treatment fields due to their low-cost and good interaction with pollutants, among which novel double network hydrogel is an outstanding class. To expand the application of double network hydrogel in water treatment, in this study, eco-friendly physically cross-linked double network polymer hydrogel beads (DAP) are prepared and studied in depth on the mechanism of Methylene Blue (MB) adsorption; and then the polymer hydrogels are further functionalized by inorganic materials. MB adsorption on DAP favors alkaline condition which is due to the increase of electrostatic attraction and adsorption site, and it reaches equilibrium within 10 hr, which is faster than that of the single network hydrogel beads (SAP). Through thermodynamics study, the process shows to be an exothermic and spontaneous process. The adsorption isotherms are well fitted by Langmuir model, with a maximum monolayer adsorption capacity of 1437.48 mg/g, which is larger than SAP (1255.75 mg/g). After being functionalized with common inorganic materials including activated carbon, Fe3O4 and graphene oxide (GO), the composites show to have larger pore sizes and have obvious increases in adsorption capacity especially the one contains GO. Then the composites contains Fe3O4 are used as heterogeneous Fenton catalyst which shows to have excellent performance in MB degradation. The results indicate the potential of polymer double network to be functionalized in environmental areas.

Design of a tunable nanocomposite double network hydrogel based on gellan gum for drug delivery applications

The design of an efficient drug delivery platform relies on the fabrication of a suitable polymeric network that can modulate the release of therapeutic molecules. In this study, we aimed to reach this goal by fabricating a novel nanocomposite double network (nDN) hydrogel, which contains the synthetic clay Laponite as the nanofiller necessary to influence the mechanical, physical and releasing properties of the designed carrier. Laponite concentration was varied from 0.5% up to 1.5% w/v to modulate the mechanical and swelling behavior of a hydrogel made of a methacrylate derivate of gellan gum (GG-MA), which served as the first brittle network of the nDN system. Additionally, polyethylene glycol dimethacrylate (PEG-DMA) was chosen as the second soft and elastic network. The inclusion of the clay at a concentration as low as 0.5% w/v positively influenced the single network (SN) hydrogel properties by increasing the stiffness and reducing the swelling ratio of the GG-MA hydrogels. The presence of Laponite® affected the amount of PEG-DMA diffused within the SN of GG-MA. The resulting stretchable and tough nDN system presented a higher swelling ratio in deionized water, and elasticity when compared to the DN hydrogels without any Laponite. Finally, the nDN system showed increased drug adsorption and displayed a better control in modulating the release kinetics of the model drug ofloxacin. Overall, these findings suggest the possible use of the designed nDN system as a novel drug delivery platform for the sustained release of therapeutic molecules.

Tough, Swelling-Resistant, Self-Healing, and Adhesive Dual-Cross-Linked Hydrogels Based on Polymer–Tannic Acid Multiple Hydrogen Bonds

We demonstrate a facile and universal strategy in the fabrication of dual-cross-linked (DC) single network hydrogels with high toughness, “nonswellability”, rapid self-healing, and versatile adhesiveness based on polymer–tannic acid (TA) multiple hydrogen bonds. Two widely used hydrogels, physically cross-linked poly(vinyl alcohol) and chemically cross-linked polyacrylamide, have been transformed to TA-based DC hydrogels by dipping the corresponding aerogels into TA solution. The second cross-link via multiple polymer–TA hydrogen bonds effectively suppresses the crack propagation, resulting in both DC gels with high mechanical strength. But these two TA-based DC hydrogels go through different deformation mechanisms during the stretching based on analyzing their stress–strain curves using the Mooney–Rivlin equation. Moreover, these DC hydrogels are swelling-resistant, with strong toughness, good self-recoverability, rapid self-healing, and versatile adhesiveness. This work provides a simple route to fabric...

Highly Elastic Biodegradable Single-Network Hydrogel for Cell Printing.

Cell printing is becoming a common technique to fabricate cellularized printed scaffold for biomedical application. There are still significant challenges in soft tissue bioprinting using hydrogels, which requires live cells inside the hydrogels. Moreover, the resilient mechanical properties from hydrogels are also required to mechanically mimic the native soft tissues. Herein, we developed a visible-light cross-linked, single-network, biodegradable hydrogel with high elasticity and flexibility for cell printing, which is different from previous highly elastic hydrogel with double-network and two components. The single-network hydrogel using only one stimulus (visible light) to trigger gelation can greatly simplify the cell printing process. The obtained hydrogels possessed high elasticity, and their mechanical properties can be tuned to match various native soft tissues. The hydrogels had good cell compatibility to support fibroblast growth in vitro. Various human cells were bioprinted with the hydrogels to form cell–gel constructs, in which the cells exhibited high viability after 7 days of culture. Complex patterns were printed by the hydrogels, suggesting the hydrogel feasibility for cell printing. We believe that this highly elastic, single-network hydrogel can be simply printed with different cell types, and it may provide a new material platform and a new way of thinking for hydrogel-based bioprinting research.

Dynamic covalent bond-based hydrogels with superior compressive strength, exceptional slice-resistance and self-healing properties

A novel dynamic-covalent bond-based single network hydrogel was developed, of which the failure compressive stress and strain as well as the failure tensile stress and strain could exceed 27.3 MPa and 98.4% as well as 0.23 MPa and 282.3%, respectively. In addition, the gel shows remarkable slice-resistance and self-healing properties.

Fabrication of tough poly(ethylene glycol)/collagen double network hydrogels for tissue engineering.

In this study, a series of poly(ethylene glycol)/collagen (PEG/Col) double network (DN) hydrogel is fabricated from PEG and Col. Results of the compressive strength test indicate that the strength and toughness of these DN hydrogels are significantly enhanced. The fracture strength of PEG/Col DN hydrogels increases by 9- to 12-fold compared with that of PEG single network (SN) hydrogel, and by 36- to 48-fold compared with that of Col SN hydrogel. Taking advantage of both PEG and Col building blocks, the PEG/Col DN hydrogels possess a strengthened skeleton. Moreover, the water-storage capability and favorable biocompatibility of Col are effectively maintained. Given that the DN hydrogels can provide the appropriate environment for the adhesion, growth, and proliferation of MC3T3-E1 cells, PEG/Col DN hydrogels have potential as a load-bearing tissue repair material. © 2017 Wiley Periodicals, Inc. J Biomed Mater Res Part A: 106A: 192-200, 2018.

One-pot fabrication of triple-network structure hydrogels with high-strength and self-healing properties

We recently proposed and demonstrated a novel strategy to improve mechanical strength by designing triple-network (TN) structure. The hydrogel composed of polyacrylamide (PAM), gelatin (Gela) and polyvinyl alcohol (PVA) was prepared by a simple one-pot method of copolymerization, cooling and freezing/thawing. The PAM/Gela/PVA hydrogels with 2% Gela and 8% PVA could achieve high mechanical properties, the strain and stress at break were 256% and 500kPa, respectively, and the compression strength could reach 4.6MPa under the deformation of 85% which exhibited superior mechanical properties than those of single network (SN) and double network (DN) hydrogels. What’s more, the hydrogels exhibited self-healing property. Thus, the TN concept should be applicable to developing tough hydrogels which provided insight into how these polymers played a role as structural components in cartilage and other tissues.

Construction of Injectable Double-Network Hydrogels for Cell Delivery.

Herein we present a unique method of using dynamic cross-links, which are dynamic covalent bonding and ionic interaction, for the construction of injectable double-network (DN) hydrogels, with the objective of cell delivery for cartilage repair. Glycol chitosan and dibenzaldhyde capped poly(ethylene oxide) formed the first network, while calcium alginate formed the second one, and in the resultant DN hydrogel, either of the networks could be selectively removed. The moduli of the DN hydrogel were significantly improved compared to that of the parent single-network hydrogels and were tunable by changing the chemical components. In situ 3D cell encapsulation could be easily performed by mixing cell suspension to the polymer solutions and transferred through a syringe needle before sol-gel transition. Cell proliferation and mediated differentiation of mouse chondrogenic cells were achieved in the DN hydrogel extracellular matrix.

Tough, self-healable and tissue-adhesive hydrogel with tunable multifunctionality

An ideal hydrogel for biomedical engineering should mimic the intrinsic properties of natural tissue, especially high toughness and self-healing ability, in order to withstand cyclic loading and repair skin and muscle damage. In addition, excellent cell affinity and tissue adhesiveness enable integration with the surrounding tissue after implantation. Inspired by the natural mussel adhesive mechanism, we designed a polydopamine–polyacrylamide (PDA–PAM) single network hydrogel by preventing the overoxidation of dopamine to maintain enough free catechol groups in the hydrogel. Therefore, the hydrogel possesses super stretchability, high toughness, stimuli-free self-healing ability, cell affinity and tissue adhesiveness. More remarkably, the current hydrogel can repeatedly be adhered on/stripped from a variety of surfaces for many cycles without loss of adhesion strength. Furthermore, the hydrogel can serve as an excellent platform to host various nano-building blocks, in which multiple functionalities are integrated to achieve versatile potential applications, such as magnetic and electrical therapies.

Diverse rheological properties, mechanical characteristics and microstructures of corn fiber gum/soy protein isolate hydrogels prepared by laccase and heat treatment

Two types of corn fiber gums (CFGs) were extracted from corn fibers (CFs) obtained from wet or dry corn milling processing. Both CFGs could form hydrogels induced via laccase, but CFGs isolated from wet milling CFs exhibited higher storage modulus (G′) and better mechanical strength as obtained from rheological testings. Afterwards, CFGs from wet milling CFs and soy protein isolate (SPI) were used to fabricate CFG-SPI double network (DN) hydrogel using laccase and heat treatment processes, in which CFG solution formed the first gel network through laccase oxidation, while SPI formed the second network through heating. When compared with single network (SN) CFG-SPI hydrogel, the DN CFG-SPI hydrogel looked more firm and complete with better elasticity. The rheological testings showed that both the storage modulus (G′) and loss modulus (G″) of DN hydrogel were higher than SN hydrogels of CFGs or SPI. Moreover, the CFG-SPI DN hydrogels exhibited more applicable hardness compared to SPI hydrogels and better deformation ability compared to CFG hydrogels. The results from scanning electron microscopy indicated that these CFG-SPI DN hydrogels had more regular, denser inner structure and smoother surface than SN hydrogels.

Double network hydrogels with highly enhanced toughness based on a modified first network.

A novel double network (DN) hydrogel with highly enhanced toughness has been prepared using reversible addition-fragmentation transfer (RAFT)-modified poly(2-acrylamide-2-methylpropane sulfonic acid) (PAMPS) as the first network, and polyacrylamide (PAM) as the second network. The mechanical properties of the first-network-modified PAMPS/PAM DN hydrogels have been studied and the new DN hydrogel shows remarkably high fracture energy (3.3 MJ m-3) in tensile deformation, which is nearly 9 times larger than that of the unmodified PAMPS/PAM DN hydrogel. Synchrotron radiation small-angle X-ray scattering (SAXS) was used to study the microstructures of the first-network single network (SN) and DN hydrogels. It was demonstrated by the SAXS results that the introduction of the RAFT agent into the first network enlarges the size of the ordered cross-linked domains in the SN hydrogel. The large ordered domains are beneficial for entanglement and interpenetration between the first and the second networks to dissipate concentrated stress more efficiently, resulting in the enhanced toughness of the first-network-modified DN hydrogels.

Dual Physically Cross-Linked Double Network Hydrogels with High Mechanical Strength, Fatigue Resistance, Notch-Insensitivity, and Self-Healing Properties.

Double-network (DN) hydrogels with high strength and toughness have been developed as promising materials. Herein, we explored a dual physically cross-linked polyacrylamide/xanthan gum (PAM/XG) DN hydrogel. The nonchemically cross-linked PAM/XG DN hydrogels exhibited fracture stresses as high as 3.64 MPa (13 times higher than the pure PAM single network hydrogel) and compressive stresses at 99% strain of more than 50 MPa. The hydrogels could restore their original shapes after continuously loading-unloading tensile and compressive cyclic tests. In addition, the PAM/XG DN hydrogels demonstrated excellent fatigue resistance, notch-insensitivity, high stability in different harsh environments, and remarkable self-healing properties, which might result from their distinctive physical-cross-linking structures. The attenuated total reflectance infrared spectroscopy (ATR-IR) and dynamic thermogravimetric analysis (TGA) results indicated that there were no chemical bonds (only hydrogen bonds) between the XG and PAM networks. The PAM/XG DN hydrogel synthesis offers a new avenue for the design and construction of DN systems, broadening current research and applications of hydrogels with excellent mechanical properties.

Facile Synthesis of Tough Double Network Hydrogel

ABSTRACTIn this paper, a facile and novel method was developed to fabricate high toughness and stiffness double network hydrogels made of ionical-linked natural hydrogel and synthetic hydrogel. The synthetic hydrogel network is formed firstly, and then the gel is soaked in the ionic solution to build second network to form double network hydrogel with high toughness and stiffness. Two different natural polymers, alginate and chitosan, are employed to build rigid and brittle network and poly(acrylamide) is used as soft network in double network hydrogel. The compressive strength of Calcium alginate/poly(acrylamide) double network hydrogels is increased twice than that of poly(acrylamide) single network hydrogels, and the Ca2+ ionically cross-linked alginate is the key to improve the compressive property of double network hydrogels as a sacrificial bond. However, the chitosan/poly(acrylamide) double network hydrogels exhibit no enhancement of compressive strength comparing to poly(acrylamide) single network hydrogels.

Bio-inspired effective and regenerable building cooling using tough hydrogels

Innovative thermal regulation technologies could provide great potential for reducing energy consumption in buildings. In this work, we report, for the first time, the application of highly stretchable and tough double network hydrogels (DN-Gels) as durable and reusable ‘sweating skins’ for cooling buildings. These DN-Gels demonstrate outstanding cooling performance, reducing the top roof surface temperature of wooden house models by 25–30°C for up to 7h after only a single water hydration charge. More importantly, compared with single network hydrogels (SN-Gels) previously studied for cooling applications, these DN-Gels exhibit extraordinary toughness and cyclability due to their interpenetrated ionically and covalently cross-linked networks, as demonstrated by constant cooling performance over more than 50 cycles. This excellent cyclability is further demonstrated by the unaltered mechanical properties and charging capability of the hydrogels after many cycles, compared to fresh ones. By coating a 100m2 roof of a single house with tough DN-Gels, it is estimated that the annual electricity consumption needed for air conditioning can be reduced by ∼290kWh with associated CO2 emission reductions of 160kg. Our results suggest that bio-inspired sweat cooling, specifically using tough DN-Gel coatings, represents a promising energy-efficient technology for cooling buildings as well as other devices and systems.

Fully injectable hydrazone-thiosuccinimide and hydrazone-disulfide interpenetrating polymer network (IPN) hydrogels by kinetically orthogonal cross-linking of functionalized poly(N-isopropylacrylamide) (PNIPAM) and poly(1-vinyl-2-pyrrolidone) (PVP) precur

Event Abstract Back to Event Fully injectable hydrazone-thiosuccinimide and hydrazone-disulfide interpenetrating polymer network (IPN) hydrogels by kinetically orthogonal cross-linking of functionalized poly(N-isopropylacrylamide) (PNIPAM) and poly(1-vinyl-2-pyrrolidone) (PVP) precur Trevor Gilbert1 and Todd R. Hoare1* 1 McMaster University, Chemical Engineerin, Canada Introduction: IPNs are produced by interlocking two chemically distinct networks in each other’s free volume fraction. This interlocking and the potential for segregation of the IPNs into inhomogeneous domains can cause mechanical properties and microstructures distinct from single network controls. Prior IPNs reported as injectable (desired for minimally invasive delivery) were polymerized in situ with cross-linkers[1], raising potential concerns of high temperature / UV initiation / chemical toxicity[2]. Networks may instead be formed by simple mixing of injected functionalized polymers[2]. To thus produce an IPN, the two bonding reactions must be highly specific, such as hydrazide-aldehyde with thiol-maleimide[3] or the slower thiol to disulfide reaction. Materials and Methods: Hydrogel IPNs were based on thermosensitive PNIPAM functionalized to produce hydrazones and hydrophilic networks produced from PVP-thiol and -maleimide (Figure 1). Samples were characterized by shear rheometry, freeze-fracture SEM and small-angle neutron scattering (SANS). Thermoresponsive swelling, network degradation and model drug release were evaluated. Results and Discussion: Polymer concentrations were chosen to match storage moduli of single network PNIPAM and PVP controls. IPNs showed enhanced (p<0.05) G’ relative both to the sum of the single networks and to semi-IPN controls with one linear polymer embedded in the other network (Figure 2), attributed to elastic interlocking of the two distinct networks, and suggesting IPN hydrogels as potential reinforced tissue engineering scaffolds. SEM and SANS studies showed differences in IPN microstructure, particularly dependent on the cross-linking rate of the PVP network relative to hydrazone formation in the PNIPAM one, with slower gelling disulfides permitting more phase separation than the faster thiosuccinimide cross-linking. The IPN reflects the PNIPAM component’s LCST behaviour, but with slower transitions and reduced hysteresis after the initial thermal cycle (Figure 3a,b), attributed to the PVP phase’ elastic contribution to re-swelling. Hydrolytic degradation in the IPN is also both slower and less extensive overall (Figure 3c,d), with IPNs retaining their shape and at least half their initial mass weeks longer than the single network controls in an accelerated hydrolysis model. Conclusions: Distinctive mechanical and thermoresponsive behaviour and degradation kinetics between IPN, semi-IPN and single network hydrogels clearly demonstrate the effects of network interpenetration on biomaterial properties. Interlocking also modulates the hydrogel microstructure, dependent on rates of crosslinking between the constitutive networks. We anticipate utility for these hydrogels as reinforced tissue engineering scaffolds, and for reducing burst release in hydrogel drug loading[4],[5], wherein the initial de-swelling typically elutes a large proportion of stored drug by convection.

Ion-linked double-network hydrogel with high toughness and stiffness

In this paper, a facile one-pot method was developed to fabricate ion cross-linked calcium-alginate/poly(acrylamide) (PAAm) double-network hydrogels with excellent toughness and stiffness. In comparison to the sodium alginate/PAAm hybrid gel, the as-fabricated calcium-alginate/PAAm gel demonstrated superior mechanical properties. After soaking in calcium chloride (CaCl2) solution, the size of the as-synthesized hybrid gel can be well controlled without observable volumetric swelling through manipulating the equilibrium between shrinkable elastic energy from ionic (Ca2+) bonds and swelling osmotic energy. This material design and processing technology are promising to fabricate complicated-shaped cartilage with high geometric fidelity. After soaking in 8 wt% CaCl2 solution for 2 h, compressive strength of calcium-alginate/PAAm gel was significantly improved by 92 % compared to PAAm single network hydrogel, meanwhile the size and shape of calcium-alginate/PAAm gel were nearly changed and deformed, respectively.

Swelling and mechanical behavior of nanoclay reinforced hydrogel: single network vs. full interpenetrating polymer network

Despite the various uses of hydrogels, one of their weaknesses is the poor gel strength. To overcome this restriction, the current study has focused on simultaneously employing an interpenetrating polymer network (IPN) structure and nanocomposite hydrogels. Through this approach, the influence of nanofiller in the single network and IPN hydrogel properties was also studied in detail. For this purpose, a novel full interpenetrating polymer network (IPN) hydrogel nanocomposite based on 2-acrylamido-2-methylpropane sulfonic acid (AMPS)/acrylic acid (AA)–sodium acrylate (AANa) was synthesized in two steps through a facile solution polymerization with incorporation of modified bentonite (MBE) as nanofiller. The prepared modified nanoplatelets, MBE, were characterized by XRD and FT-IR. The effect of MBE content on the chemical structure of single network and full IPN hydrogels was studied by FT-IR, XRD and DSC. The obtained swelling capacity for these IPN hydrogel nanocomposites was generally decreased by incorporation of MBE nanosheets. So that the lowest water absorbency (about 25 g/g) was obtained for the nanocomposite hydrogels containing 10 wt% of MBE. Moreover, rheological method and tensile test were used to investigate the mechanical properties of hydrogels. The results indicated that by increasing the MBE content in the IPN hydrogel network, the storage modulus of the prepared nanocomposite showed a totally different behavior compared to that of single network hydrogel. It is worth noting that IPN hydrogel containing only 1 % nanoclay showed the highest Young’s modulus in comparison to that of other prepared hydrogels. On the other hand, the highest elongation (about 600 %) was observed for MBE-free IPN hydrogel matrix. Thus, fascinating elastic responses and full recovery after a few minutes of unloading indicate that the synthesized IPN nanocomposite hydrogel exhibits admissible mechanical strength, which makes it a promising candidate for various applications.

Injectable Hydrogels with In Situ Double Network Formation Enhance Retention of Transplanted Stem Cells.

Stem cell transplantation via direct injection is a minimally invasive strategy being explored for treatment of a variety of injuries and diseases. Injectable hydrogels with shear moduli &lt;50 Pa can mechanically protect cells during the injection process; however, these weak gels typically biodegrade within 1–2 weeks, which may be too fast for many therapeutic applications. To address this limitation, an injectable hydrogel is designed that undergoes two different physical crosslinking mechanisms. The first crosslinking step occurs ex vivo through peptide‐based molecular recognition to encapsulate cells within a weak gel that provides mechanical protection from injection forces. The second crosslinking step occurs in situ to form a reinforcing network that significantly retards material biodegradation and prolongs cell retention time. Human adipose‐derived stem cells are transplanted into the subcutaneous space of a murine model using hand‐injection through a 28‐gauge syringe needle. Cells delivered within the double‐network hydrogel are significantly protected from mechanical damage and have significantly enhanced in vivo cell retention rates compared to delivery within saline and single network hydrogels. These results demonstrate that in situ formation of a reinforcing network within an already existing hydrogel can greatly improve transplanted cell retention, thereby enhancing potential regenerative medicine therapies.

Mechanical Properties of the ‘Stretchable’ Polyacrylamide-Gelatin Double Network Hydrogel

Double network (DN) hydrogels have drawn considerable attention as innovative materials possessing both high water content as well as improved mechanical properties. In this study, DN hydrogels were formed from a combination of two hydrogel networks. The first network composed of acrylamide (AAm) and N’,N’-methylenebisacrylamide (MBAAm). AAm and MBAAm were covalently crosslinked via photopolymerization simultaneously with/without the presence of the second network pre-gel mixture; physically crosslinked gelatin-calcium carbonate (GCa). The mechanical properties characterization of the hydrogels revealed that tensile strength, Young’s modulus and elongation at break increased with the increasing amount of second network component; i.e. GCa. These data could confirmed that the polyacrylamide (PAAm)-GCa DN hydrogels possessed ‘stretchability’ character. Overall, PAAm-GCa DN hydrogels had shown better mechanical strength than the PAAm single network hydrogels. We foreseen that DN hydrogels are highly potential to be developed as artificial muscles.

Advances in interpenetrating polymer network hydrogels and their applications

Abstract Interpenetrating polymer network (IPN) hydrogels brought distinct benefits compared to single network hydrogels like more widely controllable physical properties, and (frequently) more efficient drug loading/release. However, IPN strategy is not sufficient to design hydrogels with enhanced mechanical properties required for regenerative medicine like replacement of natural cartilage or artificial cornea. Some of the novel techniques promoted last decade for the preparation of IPN hydrogels which fulfill these requirements are discussed in the review. Among them, “double network” strategy had a strong contribution in the development of a large variety of hydrogels with spectacular mechanical properties at water content up to 90 %. Using cryogelation in tandem with IPN strategy led to composite cryogels with high mechanical properties and high performances in separation processes of ionic species. Highly stretchable and extremely tough hydrogels have been obtained by combining a covalently cross-linked synthetic network with an ionically cross-linked alginate network. IPN hydrogels with tailored mesh size have been also reported.