Fabrication of polydopamine-modified cellulose hydrogel for controlled release of α-mangostin

Hydrogels are notable for their outstanding absorbent qualities, satisfactory compatibility with biological systems, ability to degrade, and inherent safety, all of which contribute to their high demand in the field of biomedicine. This study focuses on the fabrication of hydrogels using environmentally friendly cellulosic material. Cellulose hydrogel beads were prepared by physical cross-linking in a NaOH/urea medium. Furthermore, nano polydopamine was integrated into the hydrogel matrix as functional polymers and α-mangostin was employed as an active pharmaceutical ingredient. The physicochemical properties were comprehensively analyzed using Fourier-transform infrared spectrometer, 13C cross-polarization/magic angle spinning nuclear magnetic resonance, thermogravimetric analysis, and scanning electron microscope. The drug delivery properties, including water content, swelling ratio, and drug release profiles, were evaluated. In vitro cytotoxicity against MC3T3-E1 cells was assessed using sulforhodamine B staining. All test hydrogels exhibited inhibitory activity against the growth of MC3T3-E1 cells. These results indicated the potential use of these hydrogels as a drug delivery carrier for α-mangostin in the treatment of ankylosing spondylitis.

Mussel-Inspired Self-Adhesive and Tough Hydrogels for Effectively Cooling Solar Cells and Thermoelectric Generators

Adhesive hydrogel-based evaporative cooling, which necessitates no electricity input, holds promise for reducing energy consumption in thermal management. Herein, inspired by the surface attachment of mussel adhesive proteins via abundant dynamic covalent bonds and noncovalent interactions, we propose a facile strategy to fabricate a self-adhesive cooling hydrogel (Li-AA-TA-PAM) using a copolymer of acrylamide (AM) and acrylic acid (AA) as the primary framework. The monomers formed hydrogen bonds between their carboxyl and amide groups, while tannic acid (TA), rich in catechol groups, enhances the adhesion of the hydrogel through hydrogen bonding. The hydrogel demonstrated strong adhesion to various material surfaces, including plastic, ceramic, glass, and metal. Even under high-speed rotation, it still maintains robust adhesion. The adhesion strength of the Li-AA-TA-PAM hydrogel to aluminum foil reached an impressive value of 296.875 kPa. Interestingly, the excellent contact caused by robust adhesion accelerates heat transfer, resulting in a rapid cooling performance, which mimics the perspiration of mammals. Lithium bromide (LiBr) with hydroactively sorptive sites is introduced to enhance sorption kinetics, thereby extending the effective cooling period. Consequently, the operation temperature of commercial polycrystalline silicon solar cells was reduced by 16 °C under an illumination of 1 kW m-2, and the corresponding efficiency of energy conversion was increased by 1.14%, thereby enhancing the output properties and life span of solar cells. The strategy demonstrates the potential for refrigeration applications using viscous gels.

Magneto-Induced Janus Adhesive-Tough Hydrogels for Wearable Human Motion Sensing and Enhanced Low-Grade Heat Harvesting

Janus hydrogels with different properties on the two surfaces have considerable potential in the field of material engineering applications. Various Janus hydrogels have been developed, but there are still some problems, such as stress mismatch caused by the double-layer structure and Janus failure caused by material diffusion in the gradient structure. Here, we report a Janus adhesive-tough hydrogel with polydopamine-decorated Fe3O4 nanoparticles (Fe3O4@PDA) at one side induced by magnetic field to avoid uncontrollable material diffusion in the cross-linking polymerization of acrylamide with alginate-calcium. The magneto-induced Janus (MIJ) hydrogel has an adhesive surface and a tough bulk without an obvious interface to avoid stress mismatch. Due to the intrinsic dissipative matrix and the abundant catechol groups on the adhesive surface, it shows strong adhesion onto various substrates. The MIJ hydrogel has high sensitivity (GF = 0.842) in detecting tiny human motion. Owing to the synergy of Fe3O4@PDA-enhanced interfacial adhesion and heat transfer, it is possible to quickly generate effective temperature differences when adhering to human skin. The MIJ hydrogel achieves a Seebeck coefficient of 13.01 mV·K-1 and an output power of 462.02 mW·m-2 at a 20 K temperature difference. This work proposes a novel strategy to construct Janus hydrogels for flexible wearable devices in human motion sensing and low-grade heat harvesting.

Development of Biocompatible Mussel-Inspired Cellulose-Based Underwater Adhesives

Conventional adhesives have poor underwater adhesion and harm to human health and the environment during their use, which largely limits their practical applications. Herein, we synthesized cellulose-based adhesives with underwater adhesion and biocompatibility by grafting N-(3,4-dihydroxyphenethyl)methacrylamide into the cellulose chain via atom transfer radical polymerization (ATRP). FTIR, 1H NMR, and XPS analyses ensured the successful preparation of the cellulose-based adhesive polymers. The different properties of the prepared adhesives, including swelling ratio, adhesion strength, and biocompatibility are examined. Results found that the lap shear strength is enhanced by increasing the catechol content. When catechol content is 27.2 mol %, cellulose-based adhesive with the addition of Fe3+ possesses a strong lap shear strength of 2.13 MPa in a dry environment, 0.10 MPa underwater, and 0.16 MPa under seawater for iron substrate, respectively. In addition, the cell culture test demonstrated that the prepared adhesives have outstanding biocompatibility. The cellulose-based adhesives with underwater adhesion and biocompatibility have potential applications in biomedicine, electronic engineering, and construction fields.

Mussel-inspired adhesive and anti-swelling hydrogels for underwater strain sensing

The application of hydrogels in an underwater environment is limited due to their swelling behavior and the existence of a hydration layer. In this study, a hydrogel based on poly(sulfobetaine methacrylate) (PSBMA), tannic acid (TA) and montmorillonite (MMT) was prepared with excellent anti-swelling properties and underwater self-adhesion properties. The PSBMA hydrogel has excellent anti-swelling properties due to the strong electrostatic interaction between charged groups of PSBMA chains. Inspired by marine mussels, tannic acid modified montmorillonite (TA@MMT) was introduced. Natural polyphenol tannic acid, as a catechol donor, provides a large number of catechol groups for hydrogels. Montmorillonite acts as the physical cross-linking point of PSBMA chains through electrostatic interaction to improve the cohesion of the hydrogel. By combining the adhesion mechanism of zwitterions and catechol, the hydrogel maintains adhesion in air and underwater environments. In addition, a strain sensor was prepared based on the PSBMA/TA@MMT hydrogel, which can closely fit the human skin and stably monitor different movements in air and in underwater environments. Through a Bluetooth communication system, long-distance information transmission can be achieved. Therefore, the PSBMA/TA@MMT hydrogel broadens the application prospect of wearable devices in the underwater environment.

Oxidized sodium alginate/polyacrylamide hydrogels adhesive for promoting wheat growth

Chemical modification of sodium alginate (SA) polymer chains can increase its functional group species. Sodium periodate (SP) was usually used to oxidize the hydroxyl groups on the chain of SA to aldehyde groups, the preparation of oxidized sodium alginate (OSA) using SP is not only complicated, also limits the variety of functional groups on the chain of OSA. By contrast, we have developed an innovative strategy for OSA, in which ammonium persulfate (APS) was used to oxidize SA, providing a clear elucidation of the oxidizing process and mechanism. OSA/PAM hydrogels were synthesized using OSA, the hydrogels possess excellent adhesion properties to various non-metallic and metallic substrates. Tensile and compression tests show that the cross-linked OSA/PAM hydrogels have superior mechanical properties. We exploit OSA/PAM hydrogels as soil adhesive and water-retaining agents for wheat growth. OSA/PAM hydrogels significantly improve the survival time of wheat grown in brown loam soil under a water-shortage environment, and slow down the wilting of wheat in a water-shortage environment and prolong the survival time of wheat in sandy soils. Our trials should make hydrogels important for wheat cultivation in brown loam soils and the development of desert areas.

Mussel-Inspired Calcium Alginate/Polyacrylamide Dual Network Hydrogel: A Physical Barrier to Prevent Postoperative Re-Adhesion

Intrauterine adhesions (IUA) has become one of the main causes of female infertility. How to effectively prevent postoperative re-adhesion has become a clinical challenge. In this study, a mussel-inspired dual-network hydrogel was proposed for the postoperative anti-adhesion of IUA. First, a calcium alginate/polyacrylamide (CA-PAM) hydrogel was prepared via covalent and Ca2+ cross-linking. Benefiting from abundant phenolic hydroxyl groups, polydopamine (PDA) was introduced to further enhance the adhesion ability and biocompatibility. This CA-PAM hydrogel immersed in 10 mg/mL dopamine solution possessed remarkable mechanical strength (elastic modulus > 5 kPa) and super stretchability (with a breaking elongation of 720%). At the same time, it showed excellent adhesion (more than 6 kPa). Surprisingly, the coagulation index of the hydrogel was 27.27 ± 4.91, demonstrating attractive coagulation performance in vitro and the potential for rapid hemostasis after surgery.

Photochemically induced formation of adhesive hydrogels from sodium alginate, acrylamide, and iron sandwich complexes

Visible light irradiation of an aqueous solution of sodium alginate and organometallic complex [(C5H5)Fe(toluene)]BF4 transforms it into a rigid hydrogel due to crosslinking of the carboxylate groups by the iron ions. Irradiation of the same iron complex together with K2S2O8 initiates the polymerization of acrylamide, which provides an efficient method for light-controlled one-step preparation of alginate-polyacrylamide double network hydrogels, which are capable of gluing wet glass with 100-200 kPa shear strength.

Amyloid Fibers Increase Free Radicals of Synthetic Melanin

Functional amyloid fibers are crucial in melanogenesis, but their roles are incompletely understood. In particular, their relationship with intrinsic spin characters of melanin remains unexplored. Here, we show that adding an amyloid scaffold greatly augments the spin density in synthetic melanin. It also brings about concurrent alterations in water dispersibility, bandgaps, and radical scavenging properties of the synthetic melanin, which facilitates its applications in solar water remediation and protection of human keratinocytes from UV irradiation. This work provides implications in the unrevealed role of functional amyloid in melanogenesis and in the origin of the superiority of natural melanin toward its synthetic variants in terms of the spin-related properties.

Alginate/polyacrylamide host-guest supramolecular hydrogels with enhanced adhesion

Although injectable hydrogels with minimally invasive delivery have garnered significant interest, their potential applications have been restricted by a singular property. In this study, a supramolecular hydrogel system with improved adhesion was constructed through host-guest interactions between alginate and polyacrylamide. The maximum tensile adhesion strength between the β-cyclodextrin and dopamine-grafted alginate/adamantane-grafted polyacrylamide (Alg-βCD-DA/PAAm-Ad, namely AβCDPA) hydrogels and pigskin reached 19.2 kPa, which was 76 % stronger than the non-catechol-based control hydrogel (β-cyclodextrin-grafted alginate/adamantane-grafted polyacrylamide, Alg-βCD/PAAm-Ad). Moreover, the hydrogels demonstrated excellent self-healing, shear-thinning, and injectable properties. The required pressure to extrude the AβCDPA2 hydrogel from a 16G needle at a rate of 2.0 mL/min was 67.4 N. As the polymer concentration and adamantane substitution degree increased, the hydrogels exhibited higher modulus, stronger network structure, and lower swelling ratio and degradation rate. Encapsulating and culturing cells within these hydrogels demonstrated good cytocompatibility. Therefore, this hydrogel can serve as a viscosity extender or bioadhesive, and as a carrier material to deliver encapsulated therapeutic substances into the body through minimally invasive injection methods.

Gelatin hydrogel reinforced with mussel-inspired polydopamine-functionalized nanohydroxyapatite for bone regeneration

Developing high-strength hydrogels with biocompatibility and bone conductibility is still desirable for bone regeneration. The nanohydroxyapatite (nHA) was incorporated into a dopamine-modified gelatin (Gel-DA) hydrogel system to create a highly biomimetic native bone tissue microenvironment. In addition, to further increase the cross-linking density between nHA and Gel-DA, nHA was functionalized by mussel-inspired polydopamine (PDA). Compared with nHA, adding polydopamine functionalized nHA (PHA) increased the compressive strength of Gel-Da hydrogel from 449.54 ± 180.32 kPa to 611.18 ± 211.86 kPa without affecting its microstructure. Besides, the gelation time of Gel-DA hydrogels with PHA incorporation (GD-PHA) was controllable from 49.47 ± 7.93 to 88.11 ± 31.18 s, contributing to its injectable ability in clinical applications. In addition, the abundant phenolic hydroxyl group of PHA was beneficial to the cell adhesion and proliferation of Gel-DA hydrogels, leading to the excellent biocompatibility of Gel-PHA hydrogels. Notably, the GD-PHA hydrogels could accelerate the bone repair efficiency in the rat model of the femoral defect. In conclusion, our results suggest the Gel-PHA hydrogel with osteoconductivity, biocompatibility, and enhanced mechanical properties is a potential bone repair material.

A Mechanically Reinforced Super Bone Glue Makes a Leap in Hard Tissue Strong Adhesion and Augmented Bone Regeneration

Existing bone tissue engineering strategies aim to achieve minimize surgical trauma, stabilize the injured area, and establish a dynamic osteogenic microenvironment. The cutting-edge bone glue developed in this study satisfies these criteria. Inspired by the excellent adhesive properties of mussels, herein, a super osteogenic glue (L-DPZ) that integrates poly(vinyl alcohol), L-dopa amino acid, and zeolitic imidazolate framework-8 characterized by catechol-metal coordination is used to successfully adhere to hard tissue with a maximum adhesive strength of 10 MPa, which is much higher than those of commercial and previously reported bone glues. The stable hard tissue adhesion also enables it to adhere strongly to luxated or broken teeth, Bio-Oss (a typical bone graft material), and splice fragments from comminuted fractures of the rabbit femur. Then, it is testified that the L-DPZ hydrogels exhibit satisfactory biocompatibility, stable degradability, and osteogenic ability in vitro. Moreover, the ability to anchor Bio-Oss and sustained osteogenesis of L-DPZ result in satisfactory healing in calvarial bone defect models in rabbits, as observed by increased bone thickness and the ingrowth of new bone tissue. These results are expected to demonstrate solutions to clinical dilemmas such as comminuted bone fracture fixation, bone defect reconstruction, and teeth dislocation replantation.

Advances of Mussel-Inspired Nanocomposite Hydrogels in Biomedical Applications

Hydrogels, with 3D hydrophilic polymer networks and excellent biocompatibilities, have emerged as promising biomaterial candidates to mimic the structure and properties of biological tissues. The incorporation of nanomaterials into a hydrogel matrix can tailor the functions of the nanocomposite hydrogels to meet the requirements for different biomedical applications. However, most nanomaterials show poor dispersion in water, which limits their integration into the hydrophilic hydrogel network. Mussel-inspired chemistry provides a mild and biocompatible approach in material surface engineering due to the high reactivity and universal adhesive property of catechol groups. In order to attract more attention to mussel-inspired nanocomposite hydrogels, and to promote the research work on mussel-inspired nanocomposite hydrogels, we have reviewed the recent advances in the preparation of mussel-inspired nanocomposite hydrogels using a variety of nanomaterials with different forms (nanoparticles, nanorods, nanofibers, nanosheets). We give an overview of each nanomaterial modified or hybridized by catechol or polyphenol groups based on mussel-inspired chemistry, and the performances of the nanocomposite hydrogel after the nanomaterial's incorporation. We also highlight the use of each nanocomposite hydrogel for various biomedical applications, including drug delivery, bioelectronics, wearable/implantable biosensors, tumor therapy, and tissue repair. Finally, the challenges and future research direction in designing mussel-inspired nanocomposite hydrogels are discussed.

Specimen Geometry Effect on Experimental Tensile Mechanical Properties of Tough Hydrogels

Synthetic tough hydrogels have received attention because they could mimic the mechanical properties of natural hydrogels, such as muscle, ligament, tendon, and cartilage. Many recent studies suggest various approaches to enhance the mechanical properties of tough hydrogels. However, directly comparing each hydrogel property in different reports is challenging because various testing specimen shapes/sizes were employed, affecting the experimental mechanical property values. This study demonstrates how the specimen geometry-the lengths and width of the reduced section-of a tough double-network hydrogel causes differences in experimental tensile mechanical values. In particular, the elastic modulus was systemically compared using eleven specimens of different shapes and sizes that were tensile tested, including a rectangle, ASTM D412-C and D412-D, JIS K6251-7, and seven customized dumbbell shapes with various lengths and widths of the reduced section. Unlike the rectangular specimen, which showed an inconsistent measurement of mechanical properties due to a local load concentration near the grip, dumbbell-shaped specimens exhibited a stable fracture at the reduced section. The dumbbell-shaped specimen with a shorter gauge length resulted in a smaller elastic modulus. Moreover, a relationship between the specimen dimension and measured elastic modulus value was derived, which allowed for the prediction of the experimental elastic modulus of dumbbell-shaped tough hydrogels with different dimensions. This study conveys a message that reminds the apparent experimental dependence of specimen geometry on the stress-strain measurement and the need to standardize the measurement of of numerous tough hydrogels for a fair comparison.

Biomass-based hydrogels with high ductility, self-adhesion and conductivity inspired by starch paste for strain sensing

Currently, hydrogel sensors for health monitoring require external tapes, bandages or adhesives to immobilize them on the surface of human skin. However, these external fixation methods easily lead to skin allergic reactions and the decline of monitoring accuracy. A simple strategy to solve this problem is to endow hydrogel sensors with good adhesion. Inspired by the starch paste adhesion mechanism, a biomass-based hydrogel with good conductivity and high repetitive adhesion strength was prepared by introducing modified starch into polyacrylic acid hydrogel system. The properties of biomass-based hydrogels could be controlled by changing the proportion of amylose and amylopectin. The biomass-based hydrogel exhibited a variety of excellent properties, including good stretchability (1290 %), high adhesion strength (pig skin: 46.51 kPa) and conductivity (2.3 S/m). Noticeably, the repeated adhesive strength of biomass-based hydrogel did not decrease with the increase of adhesion times. The strain sensor based on the biomass-based hydrogel could accurately monitor the large-scale and small movements of the human body, and had broad application prospects in the field of flexible wearable devices.

Adhesive Gelatin-Catechol Complex Reinforced Poly(Acrylic Acid) Hydrogel with Enhanced Toughness and Cell Affinity for Cartilage Regeneration

The repair of cartilage damage caused by trauma, wear, or degenerative deformation remains a major challenge in modern medicine. Therefore, it is essential to develop a mechanically compatible and bioactive scaffold for cartilage tissue regeneration. In this study, a mussel-inspired, tough, adhesive polydopamine/gelatin-poly(acrylic acid) (PDA/Gel-PAA) composite hydrogel was developed for cartilage regeneration. The hydrogel achieved a high compressive strength of up to 0.67 MPa and a toughness of 420 J/m2 because of the unique chemical-physical cross-linking structure by introducing the PDA/Gel complex into the PAA network. PAA chains with rich carboxyl groups mimic the negatively charged glycosaminoglycans (GAGs) in the natural cartilage extracellular matrix (ECM), leading to strong water retention in the hydrogel. The incorporation of the PDA/Gel complex with catechol groups on PDA and arginine-glycine-aspartic acid (RGD) sequences on gelatin chains provided abundant adhesive motifs to improve the cell affinity and tissue adhesiveness of PAA, thereby facilitating the adhesion and proliferation of bone marrow stromal cells (BMSCs). In addition, transforming growth factor-β3 (TGFβ3) was stably immobilized and released from the PDA/Gel-PAA hydrogel. Thus, adhesive hydrogels can provide a suitable microenvironment to promote cell migration in the defect area and induce chronogenesis for cartilage regeneration.

Well-Distributed Polysilsesquioxane-Modified Carbon Nanotubes for Thermal Conductive Insulating Silicone Rubbers

Despite carbon nanotubes (CNTs) have garnered tremendous research interests for enhancing the electrical and thermal conductivity of polymers, it is still a considerable challenge to achieve the uniform dispersion of carbon nanotubes in polymer matrix. Herein, inspired by the mussel-inspired chemistry, we adopted the strategy of coating CNTs with polydopamine. And the polysilsesquioxane-modified CNTs (CNTs-PSQ) were obtained based on the click chemistry reaction. The FT-IR, Raman, XRD, and TGA collectively demonstrated the successful modification of PSQ on the surface of CNTs. The incorporation of PSQ could significantly improve the dispersion of CNTs in the silicon rubbers, and a strong interfacial interaction was formed between CNTs-PSQ and silicon rubber matrix, as observed from TEM images of silicon rubber/CNTs-PSQ nanocomposites. Meanwhile, compared with the nanocomposites with neat CNTs, the ones with CNTs-PSQ exhibited simultaneously improved electrical conductivity and insulating performance. This strategy proposed for the preparation of PSQ-modified CNTs provides insights toward highly insulating and thermal conducting polymers.

Dual photothermal nanocomposites for drug-resistant infectious wound management

Management of antibiotic-resistant bacteria-induced skin infections for rapid healing remains a critical clinical challenge. Photothermal therapy, which uses mediated hyperthermia to combat such problems, has recently been recognised as a promising approach to take. In this study, bacterial cellulose-based photothermal membranes were designed and developed to combat bacterial infections and promote rapid wound healing. Polydopamine was incorporated into gold nanoparticles to produce superior dual-photothermal behaviour. The in vitro antibacterial efficacy of the prepared composite membranes against S. aureus, E. coli and methicillin-resistant Staphylococcus aureus (MRSA) could reach 99% under near-infrared (NIR) irradiation. In addition, the synthesised nanocomposite exhibited good biocompatibility in vitro as demonstrated by a cell survival ratio of >85%. The effectiveness of the composite membranes on wound healing was further investigated in a murine model of MRSA-infected wounds, focusing on the effect of photothermal temperature. According to the detailed therapeutic mechanism study undertaken, the composite membranes cause bacterial killing initially and promote the transition from the inflammatory phase to proliferation by suppressing pro-inflammatory cytokine production, promoting collagen deposition, and stimulating angiogenesis. Considering their remarkable effectiveness and facile fabrication process, it is expected that these novel materials could serve as competitive multifunctional dressings in the management of infectious wounds and accelerate the regeneration of damaged tissues related to abnormal immune responses.

Robust Natural Polyphenolic Adhesives against Various Harsh Environments

Although adhesive hydrogels have been extensively explored, the development of adhesives with long-term strong adhesion capacity under various harsh environments is still met with profound challenges such as sophisticated preparation, long-term curing, and low bonding strength. Herein, a series of robust adhesive hydrogels have been developed via the polyphenol-epoxy-cross-linking (PEC) reactions between natural polyphenols (extracts) and epoxy glycidyl ethers. The as-prepared natural polyphenolic adhesive hydrogels could induce strong adhesion onto several kinds of typical substrates (i.e., wood, glass, paper, PET, PMMA, and Fe) under both dry and wet conditions based on multi-interactions. Moreover, those natural polyphenolic adhesives exhibited good low-temperature and solvent resistance performances, which could be widely used in different kinds of device repairment (i.e., chemical, petroleum, wood, metal, glass, plastic, rubber, and other industries) under different conditions. This work could provide new opportunities toward natural-inspired robust adhesives in various fields ranging from chemical transportation, industrial manufacturing, architectural design, and marine engineering to daily life.

Polydopamine Biomaterials for Skin Regeneration

Designing biomaterials capable of biomimicking wound healing and skin regeneration has been receiving increasing attention recently. Some biopolymers behave similarly to the extracellular matrix (ECM), supporting biointerfacial adhesion and intrinsic cellular interactions. Polydopamine (PDA) is a natural bioadhesive and bioactive polymer that endows high chemical versatility, making it an exciting candidate for a wide range of biomedical applications. Moreover, biomaterials based on PDA and its derivatives have near-infrared (NIR) absorption, excellent biocompatibility, intrinsic antioxidative activity, antibacterial activity, and cell affinity. PDA can regulate cell behavior by controlling signal transduction pathways. It governs the focal adhesion behavior of cells at the biomaterials interface. These features make melanin-like PDA a fascinating biomaterial for wound healing and skin regeneration. This paper overviews PDA-based biomaterials' synthesis, properties, and interactions with biological entities. Furthermore, the utilization of PDA nano- and microstructures as a constituent of wound-dressing formulations is highlighted.

An antibacterial biomimetic adhesive with strong adhesion in both dry and underwater situations

Adhesives have attracted extensive attention in biomedical applications in recent years. However, the development of adhesives with strong adhesion in both dry and underwater conditions and antibacterial properties is still a challenge. Herein, a biomimetic adhesive (DP@TA/Gel) was developed based on the adhesion mechanism of mussel in water, from adhesion and solidification to avoiding excessive oxidization processes. DP@TA/Gel exhibited rapid strong nonspecific adhesiveness to diverse materials including wood (485 kPa) metal (507 kPa), plastic (74 kPa), and even fresh biological tissue (39 kPa) in dry conditions. Specially, owing to its biomimetic design, DP@TA/Gel could imitate the mussel adhesion mechanism underwater, endowing it with robust (38 kPa), highly repeatable (at least 15 times) and long-term (at least 120 h) stable adhesion even in underwater conditions. Remarkably, DP@TA/Gel also exhibited high adhesiveness in various water environments, including seawater, and a wide range of pH (3-11) and NaCl concentration (0.9-10%) solutions without any stimulus. In addition, DP@TA/Gel showed excellent biocompatibility and antibacterial properties. Thus, the DP@TA/Gel adhesive has appealing potential biomedical applications such as sutureless wound closure and as a tissue adhesive.

Hydrogel Adhesive Formed via Multiple Chemical Interactions: From Persistent Wet Adhesion to Rapid Hemostasis

Thus far, robust and durable adhesion capability of hydrogel adhesive in wet environment remains a huge challenge. Here, a chemically-physically double-network cross-linked hydrogel matrix was prepared by first mixing acrylic...

A review of recent advances in metal ion hydrogels: mechanism, properties and their biological applications

The mechanisms, common properties and biological applications of different types of metal ion hydrogels are summarized.

In situ self-assembly of polydopamine inside injectable hydrogels: antibacterial activity and photothermal therapy for superbug-infected wound healing

Ideal antibacterial hydrogel wound dressing triggered by the in situ self-assembly of the PDA NPs inside the gel.

High-Strength Hydrogel Adhesive Formed via Multiple Interactions for Persistent Adhesion under Saline

Hydrogel adhesives have been widely used in wet environments. Nonetheless, strong and stable persistent adhesion remains a challenge. Here, we report a facile yet powerful strategy to construct high-strength hydrogel adhesives for durable adhesion in a saline environment. Such a hydrogel consists of two polymer networks: a hydrophobic-associated polyacrylamide network of covalent and noncovalent cross-links and an alginate network cross-linked by divalent cations in saline. Meanwhile, polydopamine nanoparticles formed through in-situ self-polymerization are distributed evenly throughout the system to provide underwater adhesion. A low and controllable swelling rate and high compressive strength of hydrogels can be achieved via this multiple interaction strategy. Ultimately, this strategy contributes to the persistent underwater adhesion of hydrogels, and the decreasing rate of lap-shear adhesion strength of hydrogels is only 24.79 ± 8.01% after saline immersion for up to 21 days. Moreover, good cytocompatibility of hydrogels is helpful for their application in the biomedical field.

Enhancing Tissue Adhesion and Osteoblastic Differentiation of MC3T3-E1 Cells on Poly(aryl ether ketone) by Chemically Anchored Hydroxyapatite Nanocomposite Hydrogel Coating

Tissue adhesion to bone implant and osteoblastic differentiation are the key factors to achieve poly(aryl ether ketone) (PAEK) implant osseointegration. However, physical interaction of implant with tissue and hydroxyapatite coating suffers from slow implant tissue integration and lack of long-term stability. In this study, a novel poly(phthalazinone ether sulfone ketone) containing allyl groups (APPBAESK) is coated onto PPBESK sheet for reacting with the allyl groups of the hydrogel coating to enhance its stability. N-Succinimidyl (NHS)-ester activated group and nano-hydroxyapatite (nano-HA) are introduced into the hydrogel synthesized from gelatin methacrylate (GelMA) and acrylic acid to construct a nanocomposite hydrogel coating on PPBESK which is a promising PAEK implant material. The hydrophilicity of the PPBESK sheet is improved by the hydrogel coating. The chemical components of the nanocomposite hydrogel coating are confirmed by X-ray photoelectron spectroscope, Attenuated total reflection infrared, and X-ray powder diffraction. The tissue shear adhesion strength of the hydrogel coating toward pig skin is enhanced due to the synergism of NHS-ester activated group and nano-HA. The osteogenic differentiation of MC3T3-E1 preosteoblasts is promoted by nano-HA in nanocomposite hydrogel coating. Therefore, the bifunctional nanocomposite hydrogel coating provides a great application prospect in the surface modification of PAEK implants in bone tissue engineering.

Bioinspired Self-Healable Polyallylamine-Based Hydrogels for Wet Adhesion: Synergistic Contributions of Catechol-Amino Functionalities and Nanosilicate

Recently, many studies have been reported on functional adhesives that are applicable in wet conditions as well as in air conditions. In this study, a novel polymer hydrogel that mimics the mussel foot proteins (Mfps) was designed as an adhesive that can adhere strongly to various substrates in wet conditions. Polyallylamine-hydrocaffeic acid (PAA-CA) conjugates were synthesized to introduce the catechol moiety into the PAA backbone. The PAA-CA hydrogels were simply prepared by controlling the pH to enable the formation of a dynamic imine bond via the Schiff base reaction without any additional cross-linking agents. Owing to its residual amino groups, the PAA-CA hydrogel showed improved adhesive strength in wet conditions, which was found to be ∼4.7 times higher than in dry conditions. In addition, dual-cross-linked PAA-CA hydrogels were prepared by the addition of laponite (LP). The synergistic effect of the dynamic imine bonds and ionic bonds of the PAA-CA/LP nanocomposite hydrogels led to improved mechanical and self-healing properties. PAA-based hydrogels have great potential for more diverse applications than those of the commercial adhesives.

Polydopamine-modified collagen sponge scaffold as a novel dermal regeneration template with sustained release of platelet-rich plasma to accelerate skin repair: A one-step strategy

Although employed to release growth factors (GFs) for regenerative medicine, platelet-rich plasma (PRP) has been hindered by issues like burst effect. Based on collagen sponge scaffolds (CSSs) modified with polydopamine (pDA), a novel dermal regeneration template (DRT) was designed. However, whether it could efficiently deliver PRP and even foster wound healing remained unclear. In this work, after PRP was prepared and pDA-modified CSSs (pDA-CSSs) were fabricated, microscopic observation, GFs release assay and in-vitro biological evaluations of pDA-CSSs with PRP (pDA-CSS@PRP) were performed, followed by BALA-C/nu mice full-thickness skin defects implanted with pDA-CSS@PRP covered by grafted skins (termed as a One-step strategy). As a result, scanning electron microscope demonstrated more immobilized platelets on pDA-CSS' surface with GFs' controlled release via enzyme-linked immunosorbent assay, compared with CSSs. In line with enhanced in-vitro proliferation, adhesion and migration of keratinocytes & endothelial cells, pDA-CSS@PRP were histologically revealed to accelerate wound healing with less scar via rapid angiogenesis, arrangement of more mature collagen, guiding cells to spread, etc. In conclusion, pDA-CSSs have potential to serve as a novel DRT capable of delivering PRP, which may foster full-thickness skin defect healing by means of a One-step strategy.

Crucial roles of graphene oxide in preparing alginate/nanofibrillated cellulose double network composites hydrogels

In this study, a novel strategy to prepare sodium alginate (SA)/nano fibrillated cellulose (NFC) double network (DN) hydrogel beads with the aid of graphene oxide (GO) was developed. In comparison with the multi-step freezing-thawing method, this study employs a facile one-step freeze drying method with the presence of GO sheets. The crucial roles of GO were highlighted as an efficient nucleating agent of NFC and a reinforcer for the hydrogel. The adsorption property of the DN hydrogel towards crystal violet (CV) was also studied. Results indicated that the introduction of GO could greatly facilitate the formation of double networks. Furthermore, the as-prepared DN hydrogel beads exhibited an efficacious adsorption property towards CV. The maximum adsorption capacity of the hydrogels for CV was observed as 665 mg g^-1. Therefore, our approach here represents a facile method for the preparation of crystalline polymer based DN hydrogels to replace the awkward freezing-thawing process, giving inspiration for DN hydrogels design and preparation. Moreover, due to its efficient adsorption capacity, the hydrogels hold great promise for the water pollution control materials.