Glycidyl methacrylate-modified gum arabic mediated graphene exfoliation and its use for enhancing mechanical performance of hydrogel

Highly conductive, stretchable, and biocompatible graphene oxide biocomposite hydrogel for advanced tissue engineering

The importance of hydrogels in tissue engineering cannot be overemphasized due to their resemblance to the native extracellular matrix. However, natural hydrogels with satisfactory biocompatibility exhibit poor mechanical behavior, which hampers their application in stress-bearing soft tissue engineering. Here, we describe the fabrication of a double methacrylated gelatin bioink covalently linked to graphene oxide (GO) via a zero-length crosslinker, digitally light-processed (DLP) printable into 3D complex structures with high fidelity. The resultant natural hydrogel (GelGOMA) exhibits a conductivity of 15.0 S m-1as a result of the delocalization of theπ-orbital from the covalently linked GO. Furthermore, the hydrogel shows a compressive strength of 1.6 MPa, and a 2.0 mm thick GelGOMA can withstand a 1.0 kg ms-1momentum. The printability and mechanical strengths of GelGOMAs were demonstrated by printing a fish heart with a functional fluid pumping mechanism and tricuspid valves. Its biocompatibility, electroconductivity, and physiological relevance enhanced the proliferation and differentiation of myoblasts and neuroblasts and the contraction of human-induced pluripotent stem cell-derived cardiomyocytes. GelGOMA demonstrates the potential for the tissue engineering of functional hearts and wearable electronic devices.

Multifunctioning of carboxylic-cellulose nanocrystals on the reinforcement of compressive strength and conductivity for acrylic-based hydrogel

Simultaneously having competitive compressive properties, fatigue-resistant stability, excellent conductivity and sensitivity has still remained a challenge for acrylic-based conductive hydrogels, which is critical in their use in the sensor areas where pressure is performed. In this work, an integrated strategy was proposed for preparing a conductive hydrogel based on acrylic acid (AA) and sodium alginate (SA) by addition of carboxylic-cellulose nanocrystals (CNC-COOH) followed by metal ion interaction to reinforce its compressive strength and conductivity simultaneously. The CNC-COOH played a multifunctional role in the hydrogel by well-dispersing SA and AA in the hydrogel precursor solution for forming a uniform semi-interpenetrating network, providing more hydrogen bonds with SA and AA, more -COOH for metal ion interactions to form uniform multi-network, and also offering high modulus to the final hydrogel. Accordingly, the as-prepared hydrogels showed simultaneous excellent compressive strength (up to 3.02 MPa at a strain of 70 %) and electrical conductivity (6.25 S m-1), good compressive fatigue-resistant (93.2 % strength retention after 1000 compressive cycles under 50 % strain) and high sensitivity (gauge factor up to 14.75). The hydrogel strain sensor designed in this work is capable of detecting human body movement of pressing, stretching and bending with highly sensitive conductive signals, which endows it great potential for multi-scenario strain sensing applications.

Effective reinforcement of plasticized starch by the incorporation of graphene, graphene oxide and reduced graphene oxide

Plasticized starch (PLS) nanocomposite films using glycerol and reinforced with graphene (G) and graphene oxide (GO) were prepared by solvent casting procedure. On one hand, the influence of adding different G contents into the PLS matrix was analyzed. In order to improve the stability of G nanoflakes in water, Salvia extracts were added as surfactants. The resulting nanocomposites presented improved mechanical properties. A maximum increase of 287 % in Young's modulus and 57 % in tensile strength was achieved for nanocomposites with 5 wt% of G. However, it seemed that Salvia acted as co-plasticizer for the PLS. Moreover, the addition of the highest G content led to an improvement of the electrical conductivity close to 5 × 10-6 S/m compared to the matrix. On the other hand, GO was also incorporated as nanofiller to prepare nanocomposites. Thus, the effect of increasing the GO content in the final behavior of the PLS nanocomposites was evaluated. The characterization of GO containing PLS nanocomposites showed that strong starch/GO interactions and a good dispersion of the nanofiller were achieved. Moreover, the acidic treatment applied for the reduction of the GO was found to be effective, since the electrical conductivity was 150 times bigger than its G containing counterpart.

Recent Trends in Graphene/Polymer Nanocomposites for Sensing Devices: Synthesis and Applications in Environmental and Human Health Monitoring

Graphene-based nanocomposites are largely explored for the development of sensing devices due to the excellent electrical and mechanical properties of graphene. These properties, in addition to its large specific surface area, make graphene attractive for a wide range of chemical functionalization and immobilization of (bio)molecules. Several techniques based on both top-down and bottom-up approaches are available for the fabrication of graphene fillers in pristine and functionalized forms. These fillers can be further modified to enhance their integration with polymeric matrices and substrates and to tailor the sensing efficiency of the overall nanocomposite material. In this review article, we summarize recent trends in the design and fabrication of graphene/polymer nanocomposites (GPNs) with sensing properties that can be successfully applied in environmental and human health monitoring. Functional GPNs with sensing ability towards gas molecules, humidity, and ultraviolet radiation can be generated using graphene nanosheets decorated with metallic or metal oxide nanoparticles. These nanocomposites were shown to be effective in the detection of ammonia, benzene/toluene gases, and water vapor in the environment. In addition, biological analytes with broad implications for human health, such as nucleic bases or viral genes, can also be detected using sensitive, graphene-based polymer nanocomposites. Here, the role of the biomolecules that are immobilized on the graphene nanomaterial as target for sensing is reviewed.

Effect of chitin nanowhiskers on mechanical and swelling properties of Gum Arabic hydrogels nanocomposites

Hydrogels based on biopolymers like Gum Arabic (GA) usually show low applicability due to weak mechanical properties. To overcome this issue, (nano)fillers are utilized as reinforcing agents. Here, GA hydrogels were reinforced by chitin nanowhiskers (CtNWs, aspect ratio of 14) isolated from the biopolymer chitin through acid hydrolysis. Firstly, GA was chemically modified with glycidyl methacrylate (GMA), which allowed its crosslinking by free radical reactions. Next, hydrogel samples containing different concentrations of CtNWs (0-10 wt%) were prepared and fully characterized. Mechanical characterization revealed that 10 wt% of CtNWs promoted an increase of 44% in the Young's modulus and 96% the rupture force values compared to the pristine hydrogel. Overall, all nanocomposites were stiffer and more resistant to elastic deformation. Due to this feature, the swelling capacity of the nanocomposites decreased. GA hydrogel without CtNWs exhibited a swelling degree of 975%, whereas nanocomposites containing CtNWs exhibited swelling degrees under 725%.

Stabilization of Polymer Nanocomposites in High-Temperature and High-Salinity Brines

Stabilization of polymer nanocomposites in aqueous environment with high salinity has been a constant challenge for their applications. This work aimed to improve the stability of graphene oxide (GO) polyacrylamide nanocomposites at high-temperature and high-ionic-strength brines. GO was synthesized via a modified Hummers' method and the copolymer of acrylamide (COPAM) was obtained via free-radical polymerization. The covalent functionalization of COPAM with the partially reduced GO (rGO) was successfully achieved. 1,3-Propane sultone was used to further functionalize the obtained rGO-COPAM composites to accomplish the zwitterionic character on the rGO-COPAM surface to get a material with excellent temperature stability and dispersibility in the presence of high ionic strength brines. The synthesized materials were characterized by 1H NMR, gel permeation chromatography, X-ray photoelectron spectroscopy, scanning electron microscopy, transmission electron microscopy analysis, and so forth. The thermal stability of the dispersion at 80 °C for 120 days was observed by visual inspection and spectroscopic analysis. The results showed that the zwitterionic polymer produced excellent brine stability with GO nanosheets and suggested promising applications of zwitterionic polyacrylamide-GO systems especially for enhanced oil recovery.

Graphene hybrid materials? The role of graphene materials in the final structure of hydrogels

Graphene (G), graphene oxide (GO) and graphene quantum dots (GQDs) have been introduced into a three-dimensional polymeric network based on polyacrylamide in order to ascertain the role of each nanomaterial in hydrogels. The hydrogel structure is not affected by the introduction of GQDs, since these nanoparticles do not form part of the polymeric network. G and GO modify the structure of the hydrogels but in a different way. GO seems to interact by hydrogen bonding to form non-homogeneous gels in which the mechanical properties are not markedly improved. However, G takes an active part in the formation of the polymeric network, which leads to improved mechanical properties and stability of the final material to give rise to truly hybrid hydrogels and not mere two-phase composite materials.

Graphene Improves the Biocompatibility of Polyacrylamide Hydrogels: 3D Polymeric Scaffolds for Neuronal Growth

In tissue engineering strategies, the design of scaffolds based on nanostructures is a subject undergoing intense research: nanomaterials may affect the scaffolds properties, including their ability to interact with cells favouring cell growth and improving tissue performance. Hydrogels are synthetic materials widely used to obtain realistic tissue constructs, as they resemble living tissues. Here, different hydrogels with varying content of graphene, are synthesised by in situ radical polymerization of acrylamide in aqueous graphene dispersions. Hydrogels are characterised focusing on the contribution of the nanomaterial to the polymer network. Our results suggest that graphene is not a mere embedded nanomaterial within the hydrogels, rather it represents an intrinsic component of these networks, with a specific role in the emergence of these structures. Moreover, a hybrid hydrogel with a graphene concentration of only 0.2 mg mL-1 is used to support the growth of cultured brain cells and the development of synaptic activity, in view of exploiting these novel materials to engineer the neural interface of brain devices of the future. The main conclusion of this work is that graphene plays an important role in improving the biocompatibility of polyacrylamide hydrogels, allowing neuronal adhesion.

Biomolecule-assisted exfoliation and dispersion of graphene and other two-dimensional materials: a review of recent progress and applications

Direct liquid-phase exfoliation of layered materials by means of ultrasound, shear forces or electrochemical intercalation holds enormous promise as a convenient, cost-effective approach to the mass production of two-dimensional (2D) materials, particularly in the form of colloidal suspensions of high quality and micrometer- and submicrometer-sized flakes. Of special relevance due to environmental and practical reasons is the production of 2D materials in aqueous medium, which generally requires the use of certain additives (surfactants and other types of dispersants) to assist in the exfoliation and colloidal stabilization processes. In this context, biomolecules have received, in recent years, increasing attention as dispersants for 2D materials, as they provide a number of advantages over more conventional, synthetic surfactants. Here, we review research progress in the use of biomolecules as exfoliating and dispersing agents for the production of 2D materials. Although most efforts in this area have focused on graphene, significant advances have also been reported with transition metal dichalcogenides (MoS2, WS2, etc.) or hexagonal boron nitride. Particular emphasis is placed on the specific merits of different types of biomolecules, including proteins and peptides, nucleotides and nucleic acids (RNA, DNA), polysaccharides, plant extracts and bile salts, on their role as efficient colloidal dispersants of 2D materials, as well as on the potential applications that have been explored for such biomolecule-exfoliated materials. These applications are wide-ranging and encompass the fields of biomedicine (photothermal and photodynamic therapy, bioimaging, biosensing, etc.), energy storage (Li- and Na-ion batteries), catalysis (e.g., catalyst supports for the oxygen reduction reaction or electrocatalysts for the hydrogen evolution reaction), or composite materials. As an incipient area of research, a number of knowledge gaps, unresolved issues and novel future directions remain to be addressed for biomolecule-exfoliated 2D materials, which will be discussed in the last part of this review.

Graphene oxide linked sulfonate-based polyanionic nanogels as biocompatible, robust and versatile modifiers of ultrafiltration membranes

A GO linked sulfonate-based polyanionic nanogel as a membrane modifier has application potential in clinical hemodialysis and other biomedical therapies.

Highly swellable and biocompatible graphene/heparin-analogue hydrogels for implantable drug and protein delivery

The GO/heparin-analogue hydrogels with hemo- and cyto-compatibility could be used in various biomedical fields, such as drug and protein delivery, tissue regeneration scaffold, and other biomedical systems.

Polysaccharide-assisted rapid exfoliation of graphite platelets into high quality water-dispersible graphene sheets

High quality graphene has been obtained by polysaccharide-assisted ultrasonication in aqueous medium. This approach provides an economical, solvent-free, high-yield, and industrially scalable route for new applications of graphene-based nanocomposites.

Epoxy/graphene nanocomposites – processing and properties: a review

Graphene, a 2D fullerene, is a unique material because of its exceptional set of properties. This review has been focused on the processing methods and mechanical, electrical, thermal, and fire retardant properties of epoxy/graphene nanocomposites.

Rheology and morphology of pristine graphene/polyacrylamide gels

Enhancement of toughness in nanomaterial-based hydrogels is a critical metric for many of their engineering applications. Pristine graphene-polyacrylamide (PAM) hydrogels are synthesized via in situ polymerization of acrylamide monomer in PAM-stabilized graphene dispersion. In-situ polymerization leads to the uniform dispersion of the graphene sheets in the hydrogel. The graphene sheets interact with the elastic chains of the hydrogel through physisorption and permit gelation in the absence of any chemical cross-linker. This study represents the first report of pristine graphene as a physical cross-linker in a hydrogel. The properties of the graphene-polymer hydrogel are characterized by rheological measurements and compressive tests, revealing an increase in the storage modulus and toughness of the hydrogels compared to the chemically cross-linked PAM analogues. The physically cross-linked graphene hydrogels also exhibit self-healing properties. These hydrogels prove to be efficient precursors for graphene-PAM aerogels with enhanced electrical conductivity and thermal stability.