Mass Production of Biocompatible Graphene Using Silk Nanofibers

Biocompatible 2D Materials via Liquid Phase Exfoliation

2D materials (2DMs), such as graphene, transition metal dichalcogenides (TMDs), and black phosphorus (BP), have been proposed for different types of bioapplications, owing to their unique physicochemical, electrical, optical, and mechanical properties. Liquid phase exfoliation (LPE), as one of the most effective up-scalable and size-controllable methods, is becoming the standard process to produce high quantities of various 2DM types as it can benefit from the use of green and biocompatible conditions. The resulting exfoliated layered materials have garnered significant attention because of their biocompatibility and their potential use in biomedicine as new multimodal therapeutics, antimicrobials, and biosensors. This review focuses on the production of LPE-assisted 2DMs in aqueous solutions with or without the aid of surfactants, bioactive, or non-natural molecules, providing insights into the possibilities of applications of such materials in the biological and biomedical fields.

A bio-inspired approach for the synthesis of few-layer graphene using beetle defensive gland extract

Graphene exhibits remarkable properties and holds substantial promise for diverse applications. Its unique combination of thermal, chemical, physical, and biological properties makes it an appealing material for a wide range of uses. But, the lack of an economical and environmentally friendly approach to synthesize good-quality graphene represents an immense challenge for the scientific community. What makes this research unique is the utilization of the defensive gland extract from the beetle species Luprops tristis (Order: Coleoptera, Family: Tenebrionidae) to synthesize a few layers of graphene (FLG). This innovative incorporation of natural resources and exploration of biologically inspired methods provides an eco-friendly and cost-effective alternative to conventional graphene production techniques. The exfoliated graphene displayed antimicrobial effects against both Gram-positive (Staphylococcus aureus) and Gram-negative (Escherichia coli) bacteria, with particularly potent bactericidal activity. Additionally, the cytotoxicity assay demonstrated the anti-cancer properties of biosynthesized graphene against Daltons Lymphoma Acetic (DLA) cells.

Concurrent Reduction and Stabilization of Graphene Oxide Dispersion by Silk-Inspired Polymer

Silk, a popular biomaterial, is used as a greener alternative of toxic reducing agent in biocompatible graphene synthesis. However, silk often forms gel uncontrollably due to its heavy-chain molecular weight and faces significant challenges in the reduction, stabilization, and dispersion process of graphene. In this contribution, we report a rapid chemical synthesis approach for a low-molecular-weight silk-inspired polymer via ring-opening and microwave-assisted Diels-Alder-aided step-growth polymerizations. This synthetic polymer with periodic sequences of hydrophilic and hydrophobic moieties not only reduces graphene oxide efficiently but also enhances the dispersibility of hydrophobic reduced graphene oxide in aqueous media.

Synthesis and Functionalization of Graphene Materials for Biomedical Applications: Recent Advances, Challenges, and Perspectives

Since its discovery in 2004, graphene is increasingly applied in various fields owing to its unique properties. Graphene application in the biomedical domain is promising and intriguing as an emerging 2D material with a high surface area, good mechanical properties, and unrivalled electronic and physical properties. This review summarizes six typical synthesis methods to fabricate pristine graphene (p-G), graphene oxide (GO), and reduced graphene oxide (rGO), followed by characterization techniques to examine the obtained graphene materials. As bare graphene is generally undesirable in vivo and in vitro, functionalization methods to reduce toxicity, increase biocompatibility, and provide more functionalities are demonstrated. Subsequently, in vivo and in vitro behaviors of various bare and functionalized graphene materials are discussed to evaluate the functionalization effects. Reasonable control of dose (<20 mg kg^-1 ), sizes (50-1000 nm), and functionalization methods for in vivo application are advantageous. Then, the key biomedical applications based on graphene materials are discussed, coupled with the current challenges and outlooks of this growing field. In a broader sense, this review provides a comprehensive discussion on the synthesis, characterization, functionalization, evaluation, and application of p-G, GO, and rGO in the biomedical field, highlighting their recent advances and potential.

Adenine derived reactive dispersant and the enhancement of graphene based composites

HYPOTHESIS

Homogeneous dispersion of graphene is the precondition for constructing high performance graphene based composites. However, most of the current dispersants reported in literature still suffer excess usage to reach a desired graphene concentration. Residual of dispersant in composite may seriously affect its properties. Hence, it is expected to obtain effective dispersant with high reactivity to diminish its adverse impacts on graphene composites.

EXPERIMENTS

A highly reactive graphene dispersant (DSiA) was synthesized by grafting silanol groups (Si-OH) onto adenine. Molecular structure and the performance of the dispersant were systematically characterized. Composites were fabricated by direct writing of the graphene dispersion on various substrates, and their features were evaluated by resistance, solvent erosion and tensile testing.

FINDINGS

Graphene concentration can reach up to 6 mg mL^-1 in the presents of DSiA at the weight ratio of 1:1 (DSiA: graphene). DSiA also exhibited good performance for stabilizing multi-walled carbon nanotubes (MWCNTs). Moreover, the dispersant is highly reactive. The graphene based composites showed good mechanical strength and excellent solvent resistance. Overall, the new dispersant provides an ideal choice to uniformly disperse graphene and suitable for fabricating high performance nanocarbon based composites.

Graphene-Based Materials in Dental Applications: Antibacterial, Biocompatible, and Bone Regenerative Properties

Graphene-based materials have been shown to have advantageous properties in biomedical and dental applications due to their high mechanical, physiochemical, antibacterial, and stem cell differentiating properties. Although graphene-based materials have displayed appropriate biocompatible properties when used in implant materials for orthopedic applications, little research has been performed to specifically test the biocompatibility of graphene for dental applications. The oral environment, compared to the body, varies greatly and must be considered when evaluating biocompatibility requirements for dental applications. This review will discuss in vitro and in vivo studies that assess graphene's cytotoxicity, antibacterial properties, and cell differentiation ability to evaluate the overall biocompatibility of graphene-based materials for dental applications. Particle shape, size, and concentration were found to be major factors that affected overall biocompatibility of graphene.

Ionovoltaic electricity generation over graphene-nanoplatelets: protein-nanofibril hybrid materials

Continuous harvesting of electricity from the ambient environment has attracted great attention as a facile approach to green and sustainable energy. Natural water evaporation-driven electricity generators with active materials from economical and environment-friendly sources are highly sought after. Herein, we present devices made from a combination of protein nanofibrils (PNFs) and low-cost graphene nanoplatelets (GNPs) that can be employed for electricity generation, simply by partly inserting the device into evaporating standing water. The origin of the electricity generation can be explained by the ionovoltaic effect where ionic motion, driven by evaporating water, leads to movement of charge carriers in the electrically conductive GNP-phase. Moreover, the device performance can be improved by adding a small amount of salt to the active layer. A device, composed of GNP:PNF:AlCl₃, produces a sustained voltage of about 0.48 V, and a current of 89 nA. Furthermore, the device can tolerate saline water, with only a modest decrease of voltage, which provides potential for harvesting electricity from both evaporating saline water and fresh water.

Graphene Properties, Synthesis and Applications: A Review

We have evaluated some of the most recent breakthroughs in the synthesis and applications of graphene and graphene-based nanomaterials. This review includes three major categories. The first section consists of an overview of the structure and properties, including thermal, optical, and electrical transport. Recent developments in the synthesis techniques are elaborated in the second section. A number of top-down strategies for the synthesis of graphene, including exfoliation and chemical reduction of graphene oxide, are discussed. A few bottom-up synthesis methods for graphene are also covered, including thermal chemical vapor deposition, plasma-enhanced chemical vapor deposition, thermal decomposition of silicon, unzipping of carbon nanotubes, and others. The final section provides the recent innovations in graphene applications and the commercial availability of graphene-based devices.

Advancements and Applications in the Composites of Silk Fibroin and Graphene-Based Materials

Silk fibroin and three kinds of graphene-based materials (graphene, graphene oxide, and reduced graphene oxide) have been widely investigated in biomedical fields. Recently, the hybrid composites of silk fibroin and graphene-based materials have attracted much attention owing to their combined advantages, i.e., presenting outstanding biocompatibility, mechanical properties, and excellent electrical conductivity. However, maintaining bio-toxicity and biodegradability at a proper level remains a challenge for other applications. This report describes the first attempt to summarize the hybrid composites’ preparation methods, properties, and applications to the best of our knowledge. We strongly believe that this review will open new doors for coming researchers.

Multigraphene Prepared by One-Pot Pyrolysis of Diatomite/Polypropylene Composites

Multigraphene was prepared via a one-pot pyrolysis method using polypropylene (PP) as the carbon source and diatomite (DM) as the catalyst. The obtained graphene had 4–6 layers and a D/G intensity ratio of 0.70 and a 2D/G intensity ratio of 0.72, indicating a high degree of graphitization. When the pyrolysis temperature was higher than 850 °C under argon, the graphene yield was greatly dependent on the DM content. The highest graphene yield of 25.86% was obtained by pyrolysis of PP with 30 wt.% DM at the temperature of 1000 °C. A catalytic effect of DM and infusible cross-linking structure formation were proposed to explain the possible mechanism of graphene growth during the pyrolysis of the DM/PP composites.

Large-Scale Syntheses of 2D Materials: Flash Joule Heating and Other Methods

In the past 17 years, the larger-scale production of graphene and graphene family materials has proven difficult and costly, thus slowing wider-scale commercial applications. The quality of the graphene that is prepared on larger scales has often been poor, demonstrating a need for improved quality controls. Here, current industrial graphene synthetic and analytical methods, as well as recent academic advancements in larger-scale or sustainable synthesis of graphene, defined here as weights more than 200 mg or films larger than 200 cm² , are compiled and reviewed. There is a specific emphasis on recent research in the use of flash Joule heating as a rapid, efficient, and scalable method to produce graphene and other 2D nanomaterials. Reactor design, synthetic strategies, safety considerations, feedstock selection, Raman spectroscopy, and future outlooks for flash Joule heating syntheses are presented. To conclude, the remaining challenges and opportunities in the larger-scale synthesis of graphene and a perspective on the broader use of flash Joule heating for larger-scale 2D materials synthesis are discussed.

Silk Nanocarrier Size Optimization for Enhanced Tumor Cell Penetration and Cytotoxicity In Vitro

Silk nanofibers are versatile carriers for hydrophobic and hydrophilic drugs, but fall short in terms of effective delivery to cells, which is essential for therapeutic benefits. Here, the size of silk nanofibers was tuned by ultrasonic treatment to improve the cell penetration features without impacting the structural features. The gradual decrease in silk nanofiber length from 1700 to 40 nm resulted in improved cell uptake. The internalized silk nanofiber carriers evaded lysosomes, which facilitated retention in cancer cells in vitro. The smaller sizes also facilitated enhanced penetration of tumor spheroids for improved delivery in vitro. The cytotoxicity of paclitaxel (PTX)-laden nanocarriers increased when the length of the silk nanocarriers decreased. Both the drug loading capacity and delivery of silk nanocarriers with optimized sizes suggest potential utility in cell treatments.

Fragile-Tough Mechanical Reversion of Silk Materials via Tuning Supramolecular Assembly

Regenerated silk nanofibers are interesting as protein-based material building blocks due to their unique structure and biological origin. Here, a new strategy based on control of supramolecular assembly was developed to regulate interactions among silk nanofibers by changing the solvent, achieving tough mechanical features for silk films. Formic acid was used to replace water related to charge repulsion of silk nanofibers in solution, inducing interactions among the nanofibers. The films formed under these conditions had an elastic modulus of 3.4 ± 0.3 GPa, an ultimate tensile strength of 76.9 ± 1.6 MPa, and an elongation at break of 3.5 ± 0.1%, while the materials formed from aqueous solutions remained fragile. The mechanical performance of the formic acid-derived nanofiber films was further improved through post-stretching or via the addition of graphene. In addition, the silk nanofiber films could be functionalized with various bioactive ingredients such as curcumin. These new silk nanofiber films with a unique combination of mechanical properties and functions provide new biomaterials achieved using traditional solvents and processes through insight and control of their assembly mechanisms in solution.

Heterogeneous electro-Fenton process for degradation of bisphenol A using a new graphene/cobalt ferrite hybrid catalyst

A simple, efficient, environmentally friendly, and inexpensive synthesis route was developed to obtain a magnetic nano-hybrid (GH) based on graphene and cobalt ferrite. Water with a high content of natural organic matter (NOM) was used as solvent and a source of carbon. The presence of NOM in the composition of GH was confirmed by FTIR and Raman spectroscopy, which evidenced the formation of graphene, as also corroborated by XRD analyses. The diffractograms and TEM images showed the formation of a hybrid nanomaterial composed of graphene and cobalt ferrite, with crystallite and particle sizes of 0.83 and 4.0 nm, respectively. The heterogeneous electro-Fenton process (EF-GH) achieved 100% degradation of bisphenol A (BPA) in 50 min, with 80% mineralization in 7 h, at pH 7, using a current density of 33.3 mA cm^-2. The high catalytic performance was achieved at neutral pH, enabling substantial reduction of the costs of treatment processes. This work contributes to understanding the role of NOM in the synthesis of a magnetic nano-hybrid based on graphene and cobalt ferrite, for use in heterogeneous catalysis. This nano-hybrid has excellent potential for application in the degradation of persistent organic pollutants found in aquatic environments.

Green Preparation of Aqueous Graphene Dispersion and Study on Its Dispersion Stability

The large-scale preparation of stable graphene aqueous dispersion has been a challenge in the theoretical research and industrial applications of graphene. This study determined the suitable exfoliation agent for overcoming the van der Waals force between the layers of expanded graphite sheets using the liquid-phase exfoliation method on the basis of surface energy theory to prepare a single layer of graphene. To evenly and stably disperse graphene in pure water, the dispersants were selected based on Hansen solubility parameters, namely, hydrophilicity, heterocyclic structure and easy combinative features. The graphene exfoliation grade and the dispersion stability, number of layers and defect density in the dispersion were analysed under Tyndall phenomenon using volume sedimentation method, zeta potential analysis, scanning electron microscopy, Raman spectroscopy and atomic force microscopy characterization. Subsequently, the long-chain quaternary ammonium salt cationic surfactant octadecyltrimethylammonium chloride (0.3 wt.%) was electrolyzed in pure water to form ammonium ions, which promoted hydrogen bonding in the remaining oxygen-containing groups on the surface of the stripped graphene. Forming the electrostatic steric hindrance effect to achieve the stable dispersion of graphene in water can exfoliate a minimum of eight layers of graphene nanosheets; the average number of layers was less than 14. The 0.1 wt.% (sodium dodecylbenzene sulfonate: melamine = 1:1) mixed system forms π–π interaction and hydrogen bonding with graphene in pure water, which allow the stable dispersion of graphene for 22 days without sedimentation. The findings can be beneficial for the large-scale preparation of waterborne graphene in industrial applications.

A general strategy for designing NIR-II emissive silk for the in vivo monitoring of an implanted stent model beyond 1500 nm

Silk fibroin-based materials spun by silkworms present excellent biocompatible and biodegradable properties, endowing them with broad applications for use in in vivo implanted devices. Therefore, it is highly desirable to explore functionalized silk with additional optical bioimaging abilities for the direct in situ monitoring of the status of implanted devices in vivo. Herein, a new type of silk material with a second near-infrared (NIR-II, 1000-1700 nm) emission is explored for the real-time observation of a biological stent model using a general route of feeding larval silkworms with lanthanide-based NaYF₄:Gd³⁺/Yb³⁺/Er³⁺@SiO₂ nanocrystals. After being fed lanthanide nanocrystals, the silk spun by silkworms shows efficient NIR-II emission beyond 1500 nm. Moreover, NIR-II bio-imaging guided biological stent model monitoring presents a superior signal-to-noise (S/N) ratio compared to the traditional optical imaging by utilizing the upconversion (UC) region. These findings open up the possibility of designing NIR-II optically functionalized silk materials for highly sensitive and deep-tissue monitoring of the in vivo states of the implanted devices.

Electric field-driven building blocks for introducing multiple gradients to hydrogels

Gradient biomaterials are considered as preferable matrices for tissue engineering due to better simulation of native tissues. The introduction of gradient cues usually needs special equipment and complex process but is only effective to limited biomaterials. Incorporation of multiple gradients in the hydrogels remains challenges. Here, beta-sheet rich silk nanofibers (BSNF) were used as building blocks to introduce multiple gradients into different hydrogel systems through the joint action of crosslinking and electric field. The blocks migrated to the anode along the electric field and gradually stagnated due to the solution-hydrogel transition of the systems, finally achieving gradient distribution of the blocks in the formed hydrogels. The gradient distribution of the blocks could be tuned easily through changing different factors such as solution viscosity, which resulted in highly tunable gradient of mechanical cues. The blocks were also aligned under the electric field, endowing orientation gradient simultaneously. Different cargos could be loaded on the blocks and form gradient cues through the same crosslinking-electric field strategy. The building blocks could be introduced to various hydrogels such as Gelatin and NIPAM, indicating the universality. Complex niches with multiple gradient cues could be achieved through the strategy. Silk-based hydrogels with suitable mechanical gradients were fabricated to control the osteogenesis and chondrogenesis. Chondrogenic-osteogenic gradient transition was obtained, which stimulated the ectopic osteochondral tissue regeneration in vivo. The versatility and highly controllability of the strategy as well as multifunction of the building blocks reveal the applicability in complex tissue engineering and various interfacial tissues.

Natural Nanofiber Shuttles for Transporting Hydrophobic Cargo into Aqueous Solutions

Hydrophobic biomolecules realize their functions in vivo in aqueous environments, often through a delicate balance of amphiphilicity and chaperones. Introducing exogenous hydrophobic biomolecules into in vivo aqueous systems is a challenge in drug delivery and regenerative medicine, where labile linkers, carriers, and fusions or chimeric molecules are often designed to facilitate such aqueous interfaces. Here, we utilize naturally derived silk nanofiber shuttles with the capacity to transport hydrophobic cargos directly into aqueous solutions. These nanofibers disperse in organic solvents and in aqueous solutions because of their inherent amphiphilicity, with enriched hydrophobicity and strategically interspersed negatively charged groups. Hydrophobic molecules loaded on these shuttles in organic solvent-water systems separated from the solvent after centrifugation. These concentrated hydrophobic molecule-loaded nanofibers could then be dispersed into aqueous solution directly without modification. These shuttle systems were effective for different hydrophobic molecules such as drugs, vitamins, and dyes. Improved biological stability and functions of hydrophobic cargos after loading on these nanofibers suggest potential applications in drug delivery, cosmetology, medical diagnosis, and related health fields, with a relatively facile process.

SERS Substrate with Silk Nanoribbons as Interlayer Template

The formation of hot spots is an effective approach to improve the performance of surface-enhanced Raman scattering (SERS). Silk nanoribbons (SNRs), with a height of about 1-2 nm, and Au nanoparticles (AuNPs) were assembled by electrostatic interactions to introduce sandwich hot spot structures. These sandwich structures were optimized by tuning the ratio of SNRs and AuNPs, resulting in strong SERS signals with a sensitivity of 10^-13 M and enhancement factor (EF) of 5.8 × 10⁶. Improved SERS spectrum uniformity with relative standard deviation (RSD) about 11.2% was also achieved due to the homogeneous distribution of these hot spot structures. The inherent biocompatibility of SNRs and facile fabrication processes utilized endowed the SERS substrates significant benefits toward biomedical applications, confirmed by cytocompatibility and improved SERS bioimaging capacity in vitro. The results of this study suggest the feasibility of forming high performance bioimaging systems through the use of naturally derived materials with special nanostructures.

Impact of adding glucose-coated water-soluble silver nanoparticles to the silkworm larval diet on silk protein synthesis and related properties

Biological modifications of the silk fibroin (silk) material have broad applications in textiles, biomedical materials and other industrial materials. It is economical to incorporate nanoparticles to the biosynthesis of silk fibroin by adding them to silkworm larval diets. This strategy may result in the rapid stable production of modified silk. Glucose-coated silver nanoparticles (AgNPs) were used to improve the AgNPs' biocompatibility, and the AgNPs were efficiently incorporated into silk by feeding. Larvae fed with AgNPs produced silk with significantly improved antibacterial properties and altered silk secondary structures. Both positive and negative effects on the growth and synthesis of silk proteins were observed after different AgNPs doses. Larvae feeding with low concentration of 0.02% and medium 0.20% AgNPs have greater transfer efficiencies of AgNPs to silk compared with feeding high concentration of 2.00% AgNPs. In addition, the elongation and tensile strength of the produced silk fibers were also significantly increased, with greater mammalian cell compatibility. The appropriate AgNPs concentration in the diet of silkworms can promote the synthesis of silk proteins, enhance their mechanical properties, improve their antibacterial property and inhibit the presence of Gram-negative bacteria.

The assembly of silk fibroin and graphene-based nanomaterials with enhanced mechanical/conductive properties and their biomedical applications

The assembly of silk fibroin and graphene-based nanomaterials would present fantastic properties and functions via optimizing the interaction between each other, and can be processed into various formats to tailor specific biomedical applications.

Design, Fabrication, and Function of Silk-Based Nanomaterials

Animal silks are built from pure protein components and their mechanical performance, such as strength and toughness, often exceed most engineered materials. The secret to this success is their unique nanoarchitectures that are formed through the hierarchical self-assembly of silk proteins. This natural material fabrication process in sharp contrast to the production of artificial silk materials, which usually are directly constructed as bulk structures from silk fibroin (SF) molecular. In recent years, with the aim of understanding and building better silk materials, a variety of fabrication strategies have been designed to control nanostructures of silks or to create functional materials from silk nanoscale building blocks. These emerging fabrication strategies offer an opportunity to tailor the structure of SF at the nanoscale and provide a promising route to produce structurally and functionally optimized silk nanomaterials. Here, we review the critical roles of silk nanoarchitectures on property and function of natural silk fibers, outline the strategies of utilization of these silk nanobuilding blocks, and we provide a critical summary of state of the art in the field to create silk nanoarchitectures and to generate silk-based nanocomponents. Further, such insights suggest templates to consider for other materials systems.

Safety Assessment of Graphene-Based Materials: Focus on Human Health and the Environment

Graphene and its derivatives are heralded as "miracle" materials with manifold applications in different sectors of society from electronics to energy storage to medicine. The increasing exploitation of graphene-based materials (GBMs) necessitates a comprehensive evaluation of the potential impact of these materials on human health and the environment. Here, we discuss synthesis and characterization of GBMs as well as human and environmental hazard assessment of GBMs using in vitro and in vivo model systems with the aim to understand the properties that underlie the biological effects of these materials; not all GBMs are alike, and it is essential that we disentangle the structure-activity relationships for this class of materials.