Self-healing Nanocomposite Hydrogels Research Articles

Silica-based Janus nanosheets for self-healing nanocomposite hydrogels

As functional nanocomposites, Janus nanomaterials can play an important role due to their asymmetric structure and different components on the same surface. In this manuscript, hollow silicon spheres (SiO2 JHs) with an asymmetric structure were prepared by an emulsion interfacial self-organized sol-gel process. Inspired by mussel chemistry, the exposed surfaces of the SiO2 JHs were modified chemically by polydopamine (PDA). 2-(3-(6-Methyl-4-oxo-1,2,3,4-tetrahydropyrimidin-2-yl)ureido)ethyl methacrylate (MAUPy) containing multiple hydrogen bond groups were grafted to obtain SiO2@PDA/PMAUPy Janus Nanosheets (SiO2@PDA/PMAUPy JNs) by Pickering emulsion. The prepared SiO2@PDA/PMAUPy JNs were further applied to prepare nanocomposite self-healing hydrogels. As a result of the synergy of reversible non-covalent metal-ligand and hydrogen bonding, hydrogels with dual self-healing feature were successfully fabricated. The obtained hydrogels maintain preferable mechanical properties (strain of about 411.0% and stress of about 4.1 MPa) and excellent healing ratio (92.6%), which may have broad application prospects in smart flexible sensor and biomedical application.

Fabrication of self-healing nanocomposite hydrogels with the cellulose nanocrystals-based Janus hybrid nanomaterials

Janus nanomaterials possess remarkable prospects in the design of a series of smart materials with unique asymmetric properties. In this work, surface functionalized Janus cellulose nanocrystalline-type (CNCs-type) nanomaterials were manufactured by Pickering emulsion template and the construction of self-healing nanocomposite hydrogels has been realized. During emulsification, the mussel-inspired chemistry was employed to develop Janus nanocomposites. The extension of molecular chain of poly-lysine (PLL) and the polydopamine (PDA) coating were grafted on different sides of CNCs. Afterwards, the prepared nanocomposites were added to poly (acrylic acid) (PAA)-based hydrogels which formed by in-situ polymerization. The collaborative effect of metal-ligand coordination between the molecular chain of PLL, PDA coating, PAA chains and metal ions endowed the nanocomposite hydrogels with excellent mechanical properties (8.8 MPa) and self-healing efficiency (88.9%). Therefore, the synthesized Janus CNCs-PDA/PLL nanocomposites are expected to have diverse application in the development of smart materials with self-healing ability.

Self-healing and toughness cellulose nanocrystals nanocomposite hydrogels for strain-sensitive wearable flexible sensor

Recently, self-healing and high mechanical strength hydrogels have aroused much research due to their potential future in strain-sensitive flexible sensors. In this manuscript, we successfully designed self-healing and toughness cellulose nanocrystals (CNCs) nanocomposite hydrogels by grafted polypyrrole (PPy) on the surface of CNCs to enhance electrical conductivity. The obtained nanocomposite hydrogels exhibit outstanding self-healing and mechanical behaviors, and the optimal mechanical strength, toughness and self-healing efficiency can be up to 5.7 MPa, 810% and 89.6%, respectively. Using these functional nanocomposite hydrogels, strain-sensitive wearable flexible sensors were designed to monitor finger joint motions, bending of knee, and even the slight pulse beating. Surprisingly, the flexible sensors could evidently perceive body motions from large movements (knee bending) to tiny signals (pulse beating). In addition, it exhibited excellent durability after repeated cycles. This method of prepared self-healing nanocomposite hydrogels will have a potential prospect in the design of biomedical, biosensors, and flexible electronic devices.

Injectable and self-healing nanocomposite hydrogel loading needle-like nano-hydroxyapatite and graphene oxide for synergistic tumour proliferation inhibition and photothermal therapy.

Non-chemotherapeutic tumour treatment has received extensive attention due to its having fewer side effects as compared to chemotherapy. However, nanomaterials-based non-chemotherapy still faces limitations such as poor targeting and low retention. Therefore, a Schiff base cross-linked hydrogel was designed and prepared using aldehyde-modified polyethylene glycol (PEG) and carboxymethyl chitosan (CMC). This hydrogel has good injectable and self-healing properties and can carry graphene oxide (GO) as a photothermal agent and needle-like nano-hydroxyapatite (HAP) as a tumour inhibitor. Combined with tumour proliferation inhibition therapy and photothermal therapy, the nanocomposite hydrogel system can avoid the side effects of chemotherapy and improve the accuracy of tumour treatment. The PEG-CMC/HAP/GO nanocomposite hydrogel system has a porous structure, good injectability and self-healing properties to meet the mechanical requirements. In vitro cell characterization showed that GO is phototoxic to tumour cells, HAP can inhibit the proliferation of tumour cells, the nanocomposite hydrogel remained in the tumour site, and the encapsulated GO and HAP did not transfer to the normal site and cause cell damage. In the in vivo investigation, the breast cancer tumour-bearing mice, the model animals for tumour treatment, were treated with an intratumoral injection of the PEG-CMC/HAP/GO nanocomposite hydrogel. This functional self-healing hydrogel loaded with GO and HAP effectively inhibited tumour cell proliferation and realized the synergistic effect of photothermal therapy, which is expected to become a new effective treatment approach for tumours.

A fast on-demand preparation of injectable self-healing nanocomposite hydrogels for efficient osteoinduction

Injectable hydrogels have been considered as promising materials for bone regeneration, but their osteoinduction and mechanical performance are yet to be improved. In this study, a novel biocompatible injectable and self-healing nano hybrid hydrogel was on-demand prepared via a fast (within 30 s) and easy gelation approach by reversible Schiff base formed between −CH=O of oxidized sodium alginate (OSA) and −NH2 of glycol chitosan (GCS) mixed with calcium phosphate nanoparticles (CaP NPs). Its raw materials can be ready in large quantities by a simple synthesis process. The mechanical strength, degradation and swelling behavior of the hydrogel can be readily controlled by simply controlling the molar ratio of −CH=O and −NH2. This hydrogel exhibits pH responsiveness, good degradability and biocompatibility. The hydrogel used as the matrix for mesenchymal stem cells can significantly induce the proliferation, differentiation and osteoinduction in vitro. These results showed this novel hydrogel is an ideal candidate for applications in bone tissue regeneration and drug delivery.

The effect of print speed and material aging on the mechanical properties of a self-healing nanocomposite hydrogel

A UV-curable nanoclay-zwitterionic hydrogel is synthesised and evaluated though rheological and mechanical testing. The results show that aging time of the pre-gel has a big impact on storage and loss of modulus which both increases with increasing aging time, particularly in the first 48 h. The pre-gel is successfully printed and is shown to be able to support itself making it possible to fully print structures before curing. Compression and tensile samples are printed and compared to cast samples. The pre-gel aging time showed that an increased time resulted in a lower strain at failure for both cast and extruded samples. However, when printing with a speed of 10 mm/s with UV-curing during printing, a significant increase in strain at failure is achieved. Furthermore, the compressed samples display self-healing abilities at room temperature and almost completely returns to its original state before compression occurred.

Injectable and Self-Healing Nanocomposite Hydrogels with Ultrasensitive pH-Responsiveness and Tunable Mechanical Properties: Implications for Controlled Drug Delivery.

Injectable, self-healing, and pH-responsive hydrogels are great intelligent drug delivery systems for controlled and localized therapeutic release. Hydrogels that show pH-sensitive behaviors in the mildly acidic range are ideal to be used for the treatment of regions showing local acidosis like tumors, wounds and infections. In this work, we present a facile preparation of an injectable, self-healing, and supersensitive pH-responsive nanocomposite hydrogel based on Schiff base reactions between aldehyde-functionalized polymers and amine-modified silica nanoparticles. The hydrogel shows fast gelation within 10 s, injectability, and rapid self-healing capability. Moreover, the hydrogel demonstrates excellent stability under neutral physiological conditions, while a sharp gel-sol transition is observed, induced by a faintly acidic environment, which is desirable for controlled drug delivery. The pH-responsiveness of the hydrogel is ultrasensitive, where the mechanical properties, hydrolytic degradation, and drug release behaviors can alter significantly when subjected to a slight pH change of 0.2. Additionally, the hydrogel's mechanical and pH-responsive properties can be readily tuned by its composition. Its excellent biocompatibility is confirmed by cytotoxicity tests toward human dermal fibroblast cells (HDFa). The novel injectable, self-healing, and sensitive pH-responsive hydrogel serves as a promising candidate as a localized drug carrier with controlled delivery capability, triggered by acidosis, holding great promise for cancer therapy, wound healing, and infection treatment.

Conductive adhesive self-healing nanocomposite hydrogel wound dressing for photothermal therapy of infected full-thickness skin wounds

Bacteria-infected wounds and antibiotics abuse have become significant burdens to patients and medical systems. Thus, designing a non-antibiotic-dependent multifunctional wound dressing for treating bacteria-infected wounds is urgently desired. Herein, a series of conductive self-healing and adhesive nanocomposite hydrogels with a remarkable photothermal antibacterial property based on N-carboxyethyl chitosan (CEC) and benzaldehyde-terminated Pluronic F127/carbon nanotubes (PF127/CNT) were developed, and their great potential as agents for photothermal therapy (PTT) of infected wounds was demonstrated in vivo. The hydrogels exhibited a suitable gelation time, stable mechanical properties, hemostatic properties, high water absorbency, and good biodegradability. After loading the antibiotic moxifloxacin hydrochloride, the hydrogels showed a pH-responsive release profile and good antibacterial activity. The tissue adhesive property of the hydrogels allowed them to have a good hemostatic effect in a mouse liver trauma model, mouse liver incision model, and mouse tale amputation model. The addition of CNTs endowed the hydrogel with in vitro/in vivo photothermal antimicrobial activity and good conductivity. An in vivo experiment in a mouse full-thickness skin wound-infected model indicated that the hydrogels had an excellent treatment effect leading to significantly enhanced wound closure healing, collagen deposition, and angiogenesis. In summary, these conductive photothermal self-healing nanocomposite hydrogels as multifunctional wound dressing exhibit great potential for the treatment of infected wounds.

Surface-initiated photoinduced electron transfer ATRP and mussel-inspired chemistry: Surface engineering of graphene oxide for self-healing hydrogels

In this manuscript, self-healable nanocomposite hydrogels were successfully fabricated by combining surface-initiated photoinduced electron transfer-atom transfer radical polymerization (PET-ATRP) with mussel-inspired chemistry. Using these efficient and eco-friendly methods, poly(4-vinylpyridine) (P4VP) was initiated on the surface of graphene oxide (GO) via PET-ATRP with polydopamine (PDA) as the anchor and 10-phenylphenothiazine (PhPTZ) as organic photocatalyst, respectively. After in-situ polymerization of acrylic acid, self-healing nanocomposite hydrogels were successfully obtained, and they had excellent tensile strength (about 6.94 MPa), toughness (605%) performance as well as self-healing efficiency (94.9% after 8 h).

Eco-friendly extraction of cellulose nanocrystals from grape pomace and construction of self-healing nanocomposite hydrogels

Extensive grape pomace from red-winemaking may seriously pollute the environment and cause the waste of resources. Cellulose after fermentation in grape pomace is suitable as the source of extract outstanding cellulose nanocrystals (CNCs). Herein, CNCs were successfully extracted from grape pomace with an eco-friendly and facile deep eutectic solvent (DES). The green DES with the composition of lactic acid/choline chloride (the molar ratio was 2:1), were used to fabricate CNCs. Importantly, the obtained CNCs as a robust nanocomposite can be successfully utilized to prepare the self-healing nanocomposite hydrogels. After added of Fe(III) and borax, the excellent self-healing performance of the guar gum-based hydrogels were achieved by the reversible noncovalent bonding interaction. Specifically, the hydrogels showed good mechanical properties (the stress was about 0.95 MPa, the strain was about 170%) and self-healing ability (the self-healing efficiency was about 90.0%). These biologically self-healing nanocomposite hydrogels can greatly broaden the recycling and utilization of grape pomace.

Sustained protein therapeutics enabled by self-healing nanocomposite hydrogels for non-invasive bone regeneration.

Bone tissue engineering based on stem cells, growth factors and bioactive scaffolds presents an appealing but challenging approach for rehabilitation of patients with bone defects. A versatile system with the capability for easy operation and precise protein delivery in specific locations is attractive for enhancing bone regeneration. Here, we develop a non-invasive delivery system based on injectable and self-healing nanocomposite hydrogels for sustained protein release, which has the potential to improve the current orthopedic strategy. Specifically, LAPONITE® (LAP) nanoplatelets are able to accelerate the gelation process through hydrogen bonds with polysaccharide matrices, endowing hydrogels with superior mechanical and rheological behaviors, along with better injectability and self-healing ability. Attractively, the strong static binding between LAP nanoplatelets and bone morphogenetic protein-2 (BMP-2) can form stable LAP@BMP-2 complexes. The results indicate that the complexes effectively preserve the intrinsic bioactivity of BMP-2 and prolong the release period for more than four weeks. Moreover, hydrogels incorporating with the LAP@BMP-2 complexes synergistically boost cell spreading, proliferation activity and osteogenesis, both in vitro and in vivo, compared with LAP or BMP-2 alone. Overall, this study proposes a valid platform for protein therapeutics and non-invasive bone repair.

Fabrication of Janus graphene oxide hybrid nanosheets by Pickering emulsion template for self-healing nanocomposite hydrogels

Janus nanomaterials can be highlighted to design a series of smart materials with the remarkable characteristic of two different properties or constituents. In this manuscript, functional Janus graphene oxide-type (GO-type) nanomaterials were fabricated by Pickering emulsion template and successfully applied to develop of dual self-healing nanocomposite hydrogels. Asymmetric functionalization of Janus nanosheets were achieved in typical oil-in-water Pickering emulsion by atom transfer radical polymerization (ATRP) and mussel-inspired chemistry. Poly(2-(acryloyloxy)ethyl ferrocenecarboxylate) (PMAEFc) and polydopamine (PDA) were unsymmetrically grafted on the two sides of GO (Janus GO-PMAEF/PDA (JGNs)), which successfully applied in self-healing nanocomposite hydrogels. The collaborative effect of metal-ligand coordination and host-guest interaction make the dual self-healing hydrogels have excellent self-healing properties (self-healing efficiency can reach to 93.4% within 1 h) and mechanical strength (tensile strength of 0.94 MPa and strain of 508.5%). Therefore, these chemical asymmetric JGNs have outstandingly application prospect in the development of smart materials.

Conductive Self-Healing Nanocomposite Hydrogel Skin Sensors with Antifreezing and Thermoresponsive Properties.

With growing interest in flexible and wearable devices, the demand for nature-inspired soft smart materials, especially intelligent hydrogels with multiple perceptions toward external strain and temperatures to mimic the human skin, is on the rise. However, simultaneous achievement of intelligent hydrogels with skin-compatible performances, including good transparency, appropriate mechanical properties, autonomous self-healing ability, multiple mechanical/thermoresponsiveness, and retaining flexibility at subzero temperatures, is still challenging and thus limits their application as skinlike devices. Here, conductive nanocomposite hydrogels (NC gels) were delicately designed and prepared via gelation of oligo(ethylene glycol) methacrylate (OEGMA)-based monomers in a glycerol-water cosolvent, where inorganic clay served as the physical cross-linker and provided conductive ions. The resultant NC gels exhibited good conductivity (∼3.32 × 10-4 S cm-1, akin to biological muscle tissue) and an autonomously self-healing capacity (healing efficiency reached 84.8%). Additionally, such NC gels displayed excellent flexibility and responded well to multiple strain/temperature external stimuli and subtle human motions in a wide temperature range (from -20 to 45 °C). These distinguished properties would endow such NC gels significant applications in fields of biosensors, human-machine interfaces, and soft robotics.

Surface-initiated PET-ATRP and mussel-inspired chemistry for surface engineering of MWCNTs and application in self-healing nanocomposite hydrogels.

A green strategy by integrating surface-initiated metal-free photoinduced electron transfer-atom transfer radical polymerization (PET-ATRP) with mussel-inspired polydopamine (PDA) chemistry, was used to fabricate multi-walled carbon nanotubes (MWCNTs)/poly(4-vinylpyridine) (P4VP) nanocomposites. Self-healing nanocomposite hydrogels were facilely designed with these nanocomposites through dynamic supramolecular interactions. Using mussel-inspired PDA chemistry from MWCNTs, nanocomposites (MWCNTs@PDA-P4VP) were successfully prepared by metal-free PET-ATRP with MWCNTs@PDA-Br as an initiator, rhodamine B as photocatalyst, 4-vinylpyridine (4VP) as monomer, respectively. Importantly, the obtained nanocomposite hydrogels had high mechanical strength (2.9MPa), prior fracture strain (633.8%) and excellent self-healing property (90.6%). These methodologies will provide opportunities for the design of eco-functional materials or flexible biosensors.

Surface Engineering of Porous Carbon for Self-Healing Nanocomposite Hydrogels by Mussel-Inspired Chemistry and PET-ATRP.

In this work, surface-functionalized microcapsules from porous carbon nanospheres (PCNs) were successfully prepared by mussel-inspired chemistry with polydopamine (PDA) and metal-free photoinduced electron transfer-atom transfer radical polymerization (PET-ATRP). These functional microcapsules are introduced into self-healing hydrogels to enhance their mechanical strength. The PCNs synthesized by a simple soft template method are mixed with linseed oil for loading of the biomass healing agent, and the microcapsules are first prepared by coating PDA. PDA coatings were used to immobilize the ATRP initiator for initiating 4-vinylpyridine on the surface of microcapsules by PET-ATRP. Using these functional microcapsules, the self-healing efficiency was about 92.5% after 4 h at ambient temperature and the healed tensile strength can be held at 2.5 MPa with a fracture strain of 625.2%. All results indicated that the surface-functionalized microcapsules for self-healing hydrogels have remarkable biocompatibility and mechanical properties.

Self-healing graphene oxide-based nanocomposite hydrogels serve as near-infrared light-driven valves

Light-driven hydrogel actuators show increasing advantages in flowing control, soft robot and microreactor. Herein, we proposed one photothermal responsive and self-healing nanocomposite hydrogel containing poly(N-isopropylacrylamide) (PNIPAM) and poly(N,N-dimethylacrylamide) (PDMAA) to serve as light-driven valves by stimulating the bilayer and “hinge-type” hydrogel composites. With graphene oxide (GO) and clay, the hydrogels possess good mechanical property and near-infrared (NIR)-driven self-healing behavior because of the non-covalent bonding between the polymer chains and clay. Such bilayer-type hydrogels present local folding with the guide of NIR laser and can realize solid/liquid transportation and controllable trigger of the reaction. We proposed the integration of inhomogeneous structure via NIR light healing to form “hinge-type” hydrogel, consisting of one bilayer hydrogel as the “hinge” section and two PDMAA hydrogels as the “blade” section. The “hinge-type” hydrogel presents repeatable and obvious deformation with irradiation. Thus, the photothermal responsive and self-healing hydrogel may have potential applications in soft actuator, microfluidic, and microreactor.

An injectable self-healing hydrogel-cellulose nanocrystals conjugate with excellent mechanical strength and good biocompatibility

In this work, a novel strategy for the construction of injectable self-healing nanocomposite (NC) hydrogels dominated by reversible boronic ester bonds was demonstrated. Specifically, NC hydrogels were constructed by the solution-mixing of N,N-dimethylacrylamide-stat-3-acrylamidophenylboronicacid statistical copolymers (PDMA-stat-PAPBA) and poly(glycerolmonomethacrylate) (PGMA) chains grafted cellulose nanocrystals (CNC-g-PGMA). Rheology analysis indicated the as-constructed NC hydrogel displayed about 7-fold increase in the storage modulus with a low CNCs loading level of 1.43 wt% in comparison with PGMA/PDMA-stat-PAPBA hydrogel without CNCs. Furthermore, the mechanical strength of the CNC-g-PGMA/PDMA-stat-PAPBA hydrogel was far superior to that of its PGMA/PDMA-stat-PAPBA/CNCs hydrogel counterpart, in which PGMA chains were not covalently grafted on the surfaces of CNCs. Due to reversible boronic ester bonds cross-linking networks, CNC-g-PGMA/PDMA-stat-PAPBA NC hydrogel exhibited excellent self-healing and injectable properties as well as pH/glucose responsive sol-gel transitions. Good biocompatibility was also demonstrated through in vitro cytotoxicity tests.

Self-healing nanocomposite hydrogels based on modified cellulose nanocrystals by surface-initiated photoinduced electron transfer ATRP

Self-healing hydrogels with excellent toughness and mechanical strength are particularly desirable for practical application. In this paper, green and environmentally friendly cellulose nanocrystals (CNCs) were successfully modified on the surface via metal-free photoinduced electron transfer atom transfer radical polymerization (PET-ATRP). Surface-initiated PET-ATRP was achieved by using 4-vinylpyridine (4VP) as functional monomer, 10-phenylphenothiazine (Ph-PTZ) as photocatalyst and ultraviolet light (365 nm) as light source, respectively. The prepared P4VP-CNCs hybrid materials (CNCs@P4VP) were used as green reinforcement to obtain self-healing nanocomposite hydrogels by electrostatic interactions. As a result, the nanocomposite hydrogels displayed outstanding mechanical (6.6 MPa at a strain of 921.6%) and self-healing (85.9% after repairing 6 h) properties. This work provides a promising green method for designing novel self-healing nanocomposite hydrogels with high strength.

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

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

Stimuli-Responsive Conductive Nanocomposite Hydrogels with High Stretchability, Self-Healing, Adhesiveness, and 3D Printability for Human Motion Sensing.

Self-healing, adhesive conductive hydrogels are of great significance in wearable electronic devices, flexible printable electronics, and tissue engineering scaffolds. However, designing self-healing hydrogels with multifunctional properties such as high conductivity, excellent mechanical property, and high sensitivity remains a challenge. In this work, the conductive self-healing nanocomposite hydrogels based on nanoclay (laponite), multiwalled carbon nanotubes (CNTs), and N-isopropyl acrylamide are presented. The presented nanocomposite hydrogels displayed good electrical conductivity, rapid self-healing and adhesive properties, flexible and stretchable mechanical properties, and high sensitivity to near-infrared light and temperature. These excellent properties of the hydrogels are demonstrated by the three-dimensional (3D) bulky pressure-dependent device, human activity monitoring device, and 3D printed gridding scaffolds. Good cytocompatibility of the conductive hydrogels was also evaluated with L929 fibroblast cells. These nanocomposite hydrogels have great potential for applications in stimuli-responsive electrical devices, wearable electronics, and so on.