Injectable Shear-Thinning Fluorescent Hydrogel Formed by Cellulose Nanocrystals and Graphene Quantum Dots

Recent advances in synergistic use of GQD-based hydrogels for bioimaging and drug delivery in cancer treatment

Graphene quantum dot (GQD) integration into hydrogel matrices has become a viable approach for improving drug delivery and bioimaging in cancer treatment in recent years. Due to their distinct physicochemical characteristics, graphene quantum dots (GQDs) have attracted interest as adaptable nanomaterials for use in biomedicine. When incorporated into hydrogel frameworks, these nanomaterials exhibit enhanced stability, biocompatibility, and responsiveness to external stimuli. The synergistic pairing of hydrogels with GQDs has created new opportunities to tackle the problems related to drug delivery and bioimaging in cancer treatment. Bioimaging plays a pivotal role in the early detection and monitoring of cancer. GQD-based hydrogels, with their excellent photoluminescence properties, offer a superior platform for high-resolution imaging. The tunable fluorescence characteristics of GQDs enable real-time visualization of biological processes, facilitating the precise diagnosis and monitoring of cancer progression. Moreover, the drug delivery landscape has been significantly transformed by GQD-based hydrogels. Because hydrogels are porous, therapeutic compounds may be placed into them and released in a controlled environment. The large surface area and distinct interactions of graphene quantum dots (GQDs) with medicinal molecules boost loading capacity and release dynamics, ultimately improving therapeutic efficacy. Moreover, GQD-based hydrogels' stimulus-responsiveness allows for on-demand medication release, which minimizes adverse effects and improves therapeutic outcomes. The ability of GQD-based hydrogels to specifically target certain cancer cells makes them notable. Functionalizing GQDs with targeting ligands minimizes off-target effects and delivers therapeutic payloads to cancer cells selectively. Combined with imaging capabilities, this tailored drug delivery creates a theranostic platform for customized cancer treatment. In this study, the most recent advancements in the synergistic use of GQD-based hydrogels are reviewed, with particular attention to the potential revolution these materials might bring to the area of cancer theranostics.

From Nature-Sourced Polysaccharide Particles to Advanced Functional Materials

Polysaccharides constitute over 90% of the carbohydrate mass in nature, which makes them a promising feedstock for manufacturing sustainable materials. Polysaccharide particles (PSPs) are used as effective scavengers, carriers of chemical and biological cargos, and building blocks for the fabrication of macroscopic materials. The biocompatibility and degradability of PSPs are advantageous for their uses as biomaterials with more environmental friendliness. This review highlights the progresses in PSP applications as advanced functional materials, by describing PSP extraction, preparation, and surface functionalization with a variety of functional groups, polymers, nanoparticles, and biologically active species. This review also outlines the fabrication of PSP-derived macroscopic materials, as well as their applications in soft robotics, sensing, scavenging, water harvesting, drug delivery, and bioengineering. The paper is concluded with an outlook providing perspectives in the development and applications of PSP-derived materials.

Electrochemical Regeneration of Highly Stable and Sustainable Cellulose/Graphene Adsorbent Saturated with Dissolved Organic Dye

Electrochemical regeneration of adsorbents presents a cost-effective and environmentally friendly approach. Yet, its application to 3D structured adsorbents such as cellulose/graphene-based aerogels remains largely unexplored. This study introduces a method for producing these aerogels, highlighting their significant adsorption capacity for dissolved organic pollutants and resilience during electrochemical regeneration. By adjusting the ratio of hydrophobized cellulose nanofibers to graphene, the aerogels demonstrate a tunable adsorption capacity, ranging from 56 to 228 mg/g. Hydrophobization using oleic acid is vital for maintaining the aerogels' structural stability in water. Notably, the aerogels maintain structural integrity and efficiency over at least 18 electrochemical regeneration cycles, underscoring their potential for long-term environmental applications. The increase in adsorption capacity observed after regeneration cycles, approximately 10-20% by the fifth cycle, is attributed to electrochemical surface roughening and the creation of new adsorption sites. The tunability and durability of these aerogels offer a sustainable solution for adsorption with electrochemical regeneration technology.

Biomedical applications of supramolecular hydrogels with enhanced mechanical properties

Supramolecular hydrogels bound by hydrogen bonding, host-guest, hydrophobic, and other non-covalent interactions are among the most attractive biomaterials available. Supramolecular hydrogels have attracted extensive attention due to their inherent dynamic reversibility, self-healing, stimuli-response, excellent biocompatibility, and near-physiological environment. However, the inherent contradiction between non-covalent interactions and mechanical strength makes the practical application of supramolecular hydrogels a great challenge. This review describes the mechanical strength of hydrogels mediated by supramolecular interactions, and focuses on the potential strategies for enhancing the mechanical strength of supramolecular hydrogels and illustrates their applications in related fields, such as flexible electronic sensors, wound dressings, and three-dimensional (3D) scaffolds. Finally, the current problems and future research prospects of supramolecular hydrogels are discussed. This review is expected to provide insights that will motivate more advanced research on supramolecular hydrogels.

Design, characterization and applications of nanocolloidal hydrogels

Nanocolloidal gels (NCGs) are an emerging class of soft matter, in which nanoparticles act as building blocks of the colloidal network. Chemical or physical crosslinking enables NCG synthesis and assembly from a broad range of nanoparticles, polymers, and low-molecular weight molecules. The synergistic properties of NCGs are governed by nanoparticle composition, dimensions and shape, the mechanism of nanoparticle bonding, and the NCG architecture, as well as the nature of molecular crosslinkers. Nanocolloidal gels find applications in soft robotics, bioengineering, optically active coatings and sensors, optoelectronic devices, and absorbents. This review summarizes currently scattered aspects of NCG formation, properties, characterization, and applications. We describe the diversity of NCG building blocks, discuss the mechanisms of NCG formation, review characterization techniques, outline NCG fabrication and processing methods, and highlight most common NCG applications. The review is concluded with the discussion of perspectives in the design and development of NCGs.

Fibrillar biocompatible colloidal gels based on cellulose nanocrystals and poly(N-isopropylacrylamide) for direct ink writing

HYPOTHESIS

Hydrogels based on cellulose nanocrystals (CNC) have attracted great interest because of their sustainability, biocompatibility, mechanical strength and fibrillar structure. Gelation of colloidal particles can be induced by the introduction of polymers. Existing examples include gels based on CNC and derivatives of cellulose or poly(vinyl alcohol), however, gel structure and their application for extrusion printing were not shown. Hence, we rationalize formation of colloidal gels based on mixture of poly(N-isopropylacrylamide) (PNIPAM) and CNC and control their structure and mechanical properties by variation of components ratio.

EXPERIMENTS

State diagram for colloidal system based on mixture of PNIPAM and CNC were established at 25 and 37 °C. Biocompatibility, fiber diameter and rheological properties of the gels were studied for different PNIPAM/CNC ratio.

FINDINGS

We show that depending on the ratio between PNIPAM and CNC, colloidal system could be in sol or gel state at 25 °C and at gel state or phase separated at 37 °C. Physically crosslinked hydrogels were thermosensitive and could reversibly change it transparency from translucent to opaque in biologically relevant temperature range. These colloidal hydrogels were biocompatible, had fibrillar structure and demonstrate shear-thinning behavior, which makes them a promising material for bioapplications related to extrusion printing.

Hydrogel-Inducing Graphene-Oxide-Derived Core–Shell Fiber Composite for Antibacterial Wound Dressing

The study reveals the polymer–crosslinker interactions and functionality of hydrophilic nanofibers for antibacterial wound coatings. Coaxial electrospinning leverages a drug encapsulation protocol for a core–shell fiber composite with a core derived from polyvinyl alcohol and polyethylene glycol with amorphous silica (PVA-PEG-SiO2), and a shell originating from polyvinyl alcohol and graphene oxide (PVA-GO). Crosslinking with GO and SiO2 initiates the hydrogel transition for the fiber composite upon contact with moisture, which aims to optimize the drug release. The effect of hydrogel-inducing additives on the drug kinetics is evaluated in the case of chlorhexidine digluconate (CHX) encapsulation in the core of core–shell fiber composite PVA-PEG-SiO2-1x-CHX@PVA-GO. The release rate is assessed with the zero, first-order, Higuchi, and Korsmeyer–Peppas kinetic models, where the inclusion of crosslinking silica provides a longer degradation and release rate. CHX medicated core–shell composite provides sustainable antibacterial activity against Staphylococcus aureus.

Doped Carbon Quantum Dots Reinforced Hydrogels for Sustained Delivery of Molecular Cargo

Hydrogels have emerged as important soft materials with numerous applications in fields including biomedicine, biomimetic smart materials, and electrochemistry. Because of their outstanding photo-physical properties and prolonged colloidal stability, the serendipitous findings of carbon quantum dots (CQDs) have introduced a new topic of investigation for materials scientists. CQDs confined polymeric hydrogel nanocomposites have emerged as novel materials with integrated properties of the individual constituents, resulting in vital uses in the realm of soft nanomaterials. Immobilizing CQDs within hydrogels has been shown to be a smart tactic for preventing the aggregation-caused quenching effect and also for manipulating the characteristics of hydrogels and introducing new properties. The combination of these two very different types of materials results in not only structural diversity but also significant improvements in many property aspects, leading to novel multifunctional materials. This review covers the synthesis of doped CQDs, different fabrication techniques for nanostructured materials made of CQDs and polymers, as well as their applications in sustained drug delivery. Finally, a brief overview of the present market and future perspectives are discussed.

A review of graphene quantum dots and their potential biomedical applications

Today, nanobiotechnology is a pioneering technology in biomedicine. Every day, new nanomaterials are synthesized with elevated physiochemical properties for better diagnosis and treatment of diseases. One advancing class of materials is the Graphene family. Among different kinds of graphene derivatives, graphene quantum dots (GQDs) show fantastic optical, electrical, and electrochemical features originating from their unique quantum confinement effect. Due to the distinct properties of GQD, including large surface-to-volume ratio, low cytotoxicity, and easy functionalization, this nanomaterial has gone popular in biomedical field. Herein, a short overview of different strategies developed for GQD synthesis and functionalization is discussed. In the following, the most recent progress of GQD based nanomaterials in different biomedical fields, including bio-imaging, drug/gene delivery, antimicrobial, tissue engineering, and biosensors, are reviewed.

Nanocellulosics in Transient Technology

Envisage a world where discarded electrical/electronic devices and single-use consumables can dematerialize and lapse into the environment after the end-of-useful life without constituting health and environmental burdens. As available resources are consumed and human activities build up wastes, there is an urgency for the consolidation of efforts and strategies in meeting current materials needs while assuaging the concomitant negative impacts of conventional materials exploration, usage, and disposal. Hence, the emerging field of transient technology (Green Technology), rooted in eco-design and closing the material loop toward a friendlier and sustainable materials system, holds enormous possibilities for assuaging current challenges in materials usage and disposability. The core requirements for transient materials are anchored on meeting multicomponent functionality, low-cost production, simplicity in disposability, flexibility in materials fabrication and design, biodegradability, biocompatibility, and environmental benignity. In this regard, biorenewables such as cellulose-based materials have demonstrated capacity as promising platforms to fabricate scalable, renewable, greener, and efficient materials and devices such as membranes, sensors, display units (for example, OLEDs), and so on. This work critically reviews the recent progress of nanocellulosic materials in transient technologies toward mitigating current environmental challenges resulting from traditional material exploration, usage, and disposal. While spotlighting important fundamental properties and functions in the material selection toward practicability and identifying current difficulties, we propose crucial research directions in advancing transient technology and cellulose-based materials in closing the loop for conventional materials and sustainability.

Supramolecular Shear-Thinning Glycopeptide Hydrogels for Injectable Enzyme Prodrug Therapy Applications

Transplantable catalytic reactors have attracted considerable attention as therapeutic biomedical materials. However, existing transplantable reactors such as biocatalytic films are limited by their invasiveness. Here, we report the fabrication of biocatalytic supramolecular hydrogels via self-assembly of amphiphilic glycopeptides. We show that the hydrogels have shear-thinning properties, demonstrating their potential to be administered using a syringe. Enzymes can be loaded into the hydrogels by simply adding enzyme solution, and the enzyme-loaded hydrogels can transform a prodrug into an anticancer drug that inhibits tumor cell growth. This study demonstrates the potential of these biocatalytic hydrogels as injectable therapeutic reactors for enzyme prodrug therapy.

Recent advances in the hybridization of cellulose and carbon nanomaterials: Interactions, structural design, functional tailoring, and applications

Due to the good biocompatibility and flexibility of cellulose and the excellent optical, electronic, as well as mechanical properties of carbon nanomaterials (CNMs), cellulose/CNM hybrid materials have been widely synthesized and used in energy storage, sensors, adsorption, biomedicine, and many other fields. In this review, we present recent advances (2016-current) in the design, structural design, functional tailoring and various applications of cellulose/CNM hybrid materials. For this aim, first the interactions between cellulose and CNMs for promoting the formation of cellulose/CNM materials are analyzed, and then the hybridization between cellulose with various CNMs for tailoring the structures and functions of hybrid materials is introduced. Further, abundant applications of cellulose/CNM hybrid materials in various fields are presented and discussed. This comprehensive review will be helpful for readers to understand the functional design and facile synthesis of cellulose-based nanocomposites, and to promote the high-performance utilization and sustainability of biomass materials in the future.

Cellulose nanocrystals: Fundamentals and biomedical applications

The present review explores the recent developments of cellulose nanocrystals, a class of captivating nanomaterials in variety of applications. CNCs are made by acid hydrolysing cellulosic materials like wood, cotton, tunicate, flax fibers by sonochemistry. It has many desirable properties, including a high tensile strength, wide surface area, stiffness, exceptional colloidal stability, and the ability to be modified. CNCs are colloidally stable, hydrophilic, and rigid rod-shaped bio-based nanomaterials in the form of rigid rods with high strength and surface area that has a diverse set of applications and properties. The intriguing features emerging from numerous fibers studies, such as renewable character and biodegradability, piqued the curiosity of many researchers who worked on lowering the size of these fibers. Physicochemical properties such as rheological, mechanical, thermal, lipid crystalline, swelling capacity, microstructural properties result in affecting surface-area to volume ratio and crystallinity of cellulose nanocrystals. The present article highlights the fundamentals of cellulose nanocrystals such as sources, isolation, fabrication, properties and surface modification with an emphasis on plethora of biomedical applications. Selected nanocellulose studies with significant findings on cellular labelling and bioimaging, tissue engineering, biosensors, gene delivery, anti-viral property, anti-bacterial property, ocular delivery, modified drug release, anti-cancer activity and enzyme immobilization are emphasized.

Research progress of smart response composite hydrogels based on nanocellulose

In recent years, smart-responsive nanocellulose composite hydrogels have attracted extensive attention due to their unique porous substrate, hydrophilic properties, biocompatibility and stimulus responsiveness. At present, the research on smart response nanocellulose composite hydrogel mainly focuses on the selection of composite materials and the construction of internal chemical bonds. The common composite materials and connection methods used for preparation of smart response nanocellulose composite hydrogels are compared according to the different types of response sources such as temperature, pH and so on. The response mechanisms and the application prospects of different response types of nanocellulose composite hydrogels are summarized, and the transformation of internal ions, functional groups and chemical bonds, as well as the changes in mechanical properties such as modulus and strength are discussed. Finally, the shortcomings and application prospects of nanocellulose smart response composite hydrogels are summarized and prospected.

Preparation, Marriage Chemistry and Applications of Graphene Quantum Dots-Nanocellulose Composite: A Brief Review

Graphene quantum dots (GQDs) are zero-dimensional carbon-based materials, while nanocellulose is a nanomaterial that can be derived from naturally occurring cellulose polymers or renewable biomass resources. The unique geometrical, biocompatible and biodegradable properties of both these remarkable nanomaterials have caught the attention of the scientific community in terms of fundamental research aimed at advancing technology. This study reviews the preparation, marriage chemistry and applications of GQDs-nanocellulose composites. The preparation of these composites can be achieved via rapid and simple solution mixing containing known concentration of nanomaterial with a pre-defined composition ratio in a neutral pH medium. They can also be incorporated into other matrices or drop-casted onto substrates, depending on the intended application. Additionally, combining GQDs and nanocellulose has proven to impart new hybrid nanomaterials with excellent performance as well as surface functionality and, therefore, a plethora of applications. Potential applications for GQDs-nanocellulose composites include sensing or, for analytical purposes, injectable 3D printing materials, supercapacitors and light-emitting diodes. This review unlocks windows of research opportunities for GQDs-nanocellulose composites and pave the way for the synthesis and application of more innovative hybrid nanomaterials.

Photoinitiated Polymerization of Hydrogels by Graphene Quantum Dots

As a smart stimulus-responsive material, hydrogel has been investigated extensively in many research fields. However, its mechanical brittleness and low strength have mattered, and conventional photoinitiators used during the polymerization steps exhibit high toxicity, which limits the use of hydrogels in the field of biomedical applications. Here, we address the dual functions of graphene quantum dots (GQDs), one to trigger the synthesis of hydrogel as photoinitiators and the other to improve the mechanical strength of the as-synthesized hydrogel. GQDs embedded in the network effectively generated radicals when exposed to sunlight, leading to the initiation of polymerization, and also played a significant role in improving the mechanical strength of the crosslinked chains. Thus, we expect that the resulting hydrogel incorporated with GQDs would enable a wide range of applications that require biocompatibility as well as higher mechanical strength, including novel hydrogel contact lenses and bioscaffolds for tissue engineering.

Simple ultrasonic-assisted approach to prepare polysaccharide-based aerogel for cell research and histocompatibility study

Salecan, a water-soluble microbial polysaccharide with attractive biocompatible characteristics, is very suitable for aerogel fabrication. However, the practical application of salecan-based aerogels for cell culture was limited by complicated preparation method, lack of cell anchorage signals, and the ability to modulate this properly. Here, a smart aerogel was designed by ultrasonic-assisted self-assembly of salecan and cationic starch (CAS) without any organic and toxic crosslinkers. The ultrasound waves generated a marked impact on self-assemble process by means of ultrasonic cavitation. Aerogel network was produced by strong electrostatic attractions between the polysaccharides. Especially, salecan/CAS ratio can be precisely modulated to tailor the hydrophilicity, mechanical stiffness, and morphologic property. The specific surface area of the aerogels gradually increased with the increase in salecan/CAS ratio. These aerogels were non-cytotoxic, and the incorporation of salecan into them promoted cell-matrix interactions by directionally supporting cell adhesion and proliferation. Most strikingly, in vivo experiment revealed that the histological features in the main organs of the mice were similar to those observed in the PBS-treated control group, and no sign of the histopathological abnormality or tissue destruction was observed, indicating the excellent histocompatibility of the aerogels. This study offered a new and powerful avenue to fabricate functional biomaterial.

Multifunctional 3D-Printed Wound Dressings

Personalized wound dressings provide enhanced healing for different wound types; however multicomponent wound dressings with discretely controllable delivery of different biologically active agents are yet to be developed. Here we report 3D-printed multicomponent biocomposite hydrogel wound dressings that have been selectively loaded with small molecules, metal nanoparticles, and proteins for independently controlled release at the wound site. Hydrogel wound dressings carrying antibacterial silver nanoparticles and vascular endothelial growth factor with predetermined release profiles were utilized to study the physiological response of the wound in a mouse model. Compared to controls, the application of dressings resulted in improvement in granulation tissue formation and differential levels of vascular density, dependent on the release profile of the growth factor. Our study demonstrates the versatility of the 3D-printed hydrogel dressings that can yield varied physiological responses in vivo and can further be adapted for personalized treatment of various wound types.

Rheological Aspects of Cellulose Nanomaterials: Governing Factors and Emerging Applications

Cellulose nanomaterials (CNMs), mainly including nanofibrillated cellulose (NFC) and cellulose nanocrystals (CNCs), have attained enormous interest due to their sustainability, biodegradability, biocompatibility, nanoscale dimensions, large surface area, facile modification of surface chemistry, as well as unique optical, mechanical, and rheological performance. One of the most fascinating properties of CNMs is their aqueous suspension rheology, i.e., CNMs helping create viscous suspensions with the formation of percolation networks and chemical interactions (e.g., van der Waals forces, hydrogen bonding, electrostatic attraction/repulsion, and hydrophobic attraction). Under continuous shearing, CNMs in an aqueous suspension can align along the flow direction, producing shear-thinning behavior. At rest, CNM suspensions regain some of their initial structure immediately, allowing rapid recovery of rheological properties. These unique flow features enable CNMs to serve as rheological modifiers in a wide range of fluid-based applications. Herein, the dependence of the rheology of CNM suspensions on test protocols, CNM inherent properties, suspension environments, and postprocessing is systematically described. A critical overview of the recent progress on fluid applications of CNMs as rheology modifiers in some emerging industrial sectors is presented as well. Future perspectives in the field are outlined to guide further research and development in using CNMs as the next generation rheological modifiers.

Graphene Integrated Hydrogels Based Biomaterials in Photothermal Biomedicine

Recently, photothermal therapy (PTT) has emerged as one of the most promising biomedical strategies for different areas in the biomedical field owing to its superior advantages, such as being noninvasive, target-specific and having fewer side effects. Graphene-based hydrogels (GGels), which have excellent mechanical and optical properties, high light-to-heat conversion efficiency and good biocompatibility, have been intensively exploited as potential photothermal conversion materials. This comprehensive review summarizes the current development of graphene-integrated hydrogel composites and their application in photothermal biomedicine. The latest advances in the synthesis strategies, unique properties and potential applications of photothermal-responsive GGel nanocomposites in biomedical fields are introduced in detail. This review aims to provide a better understanding of the current progress in GGel material fabrication, photothermal properties and potential PTT-based biomedical applications, thereby aiding in more research efforts to facilitate the further advancement of photothermal biomedicine.

Functionalized Graphene Oxide-Reinforced Chitosan Hydrogel as Biomimetic Dressing for Wound Healing

A novel chitosan composite hydrogel by combining functionalized graphene oxide (CGO) is fabricated. The introduction of CGO significantly improves the mechanical property of CS hydrogel owing to the enhanced interaction between chitosan and CGO sheets. In comparison to the CS-GO composite hydrogel, the compressive stress of the CS-CGO composite hydrogel increases from 1.9 MPa at strain of 70.4% to 4.2 MPa at strain of 78.4%, the tensile stress and strain improve from 141.2 kPa and 134.6% to 300.2 kPa and 165.9%, respectively. An interconnected porous structure is formed in the CS-CGO composite hydrogel and the pore size decreases as the CGO loading increases, which is desirable in improving its mechanical property. Furthermore, the cytotoxicity tests indicate that the CS-CGO composite hydrogel possesses an excellent biocompatibility and can promote the adhesion and proliferation of fibroblasts. In vivo evaluation on full-thickness excision wounds in experimental rat shows that the CS-CGO composite hydrogel significantly accelerates wound healing, and the wound closure rate reaches up to 92.2% after 21 days. A feasible strategy to fabricate an enhanced chitosan composite hydrogel for application in wound healing is offered.

Construction of electrochemical immunosensors based on redox hydrogels for ultrasensitive detection of carcinoembryonic antigens

The introduction of cellulose nanocrystals (CNCs) endows a redox hydrogel with a larger specific surface area and better adhesion to an electrode.

Stimulus-responsive luminescent hydrogels: Design and applications

Luminescent hydrogels are emerging soft materials with applications in photoelectric, biomedicine, sensors and actuators, which are fabricated via covalently conjugation of luminophors to hydrogelators or physical loading of luminescent organic/inorganic materials into hydrogel matrices. Due to the intrinsic stimulus-responsiveness for hydrogels such as thermo-, pH, ionic strength, light and redox, luminescent hydrogels could respond to external physical or chemical stimuli through varying the luminescent properties such as colors, fluorescent intensity and so on, affording diverse application potential in addition to the pristine individual hydrogels or luminescent materials. Based on the rapid development of such area, here we systematically summarize and discuss the design protocols, properties as well as the applications of stimulus-responsive luminescent hydrogels. Because of the stimuli-responsiveness, biocompatibility, injectable and controllability of luminescent hydrogels, they are widely used as functional smart materials. We illustrate the applications of luminescent hydrogels. The future developments about luminescent hydrogels are also presented.

Research Progress Review of Preparation and Applications of Fluorescent Hydrogels

The fluorescent gel with good flexibility and biocompatibility has attracted more and more attention due to its excellent optical properties. In this paper, the research progresses in preparation methods and applications of fluorescent gels are reviewed. In addition, the preparation methods of self-assembly and polymerization of fluorescent gel are also introduced. In this paper, it should be noted that some outstanding research about the fluorescent gels used in sensors, bio-imaging probes, drug delivery, and other application fields is summarized. This work provides useful reference information for further exploration and study of fluorescent hydrogels.

Cellulose Composites with Graphene for Tissue Engineering Applications

Tissue engineering is an interdisciplinary field that combines principles of engineering and life sciences to obtain biomaterials capable of maintaining, improving, or substituting the function of various tissues or even an entire organ. In virtue of its high availability, biocompatibility and versatility, cellulose was considered a promising platform for such applications. The combination of cellulose with graphene or graphene derivatives leads to the obtainment of superior composites in terms of cellular attachment, growth and proliferation, integration into host tissue, and stem cell differentiation toward specific lineages. The current review provides an up-to-date summary of the status of the field of cellulose composites with graphene for tissue engineering applications. The preparation methods and the biological performance of cellulose paper, bacterial cellulose, and cellulose derivatives-based composites with graphene, graphene oxide and reduced graphene oxide were mainly discussed. The importance of the cellulose-based matrix and the contribution of graphene and graphene derivatives fillers as well as several key applications of these hybrid materials, particularly for the development of multifunctional scaffolds for cell culture, bone and neural tissue regeneration were also highlighted.

Physical and Chemical Factors Influencing the Printability of Hydrogel-based Extrusion Bioinks

Bioprinting researchers agree that "printability" is a key characteristic for bioink development, but neither the meaning of the term nor the best way to experimentally measure it has been established. Furthermore, little is known with respect to the underlying mechanisms which determine a bioink's printability. A thorough understanding of these mechanisms is key to the intentional design of new bioinks. For the purposes of this review, the domain of printability is defined as the bioink requirements which are unique to bioprinting and occur during the printing process. Within this domain, the different aspects of printability and the factors which influence them are reviewed. The extrudability, filament classification, shape fidelity, and printing accuracy of bioinks are examined in detail with respect to their rheological properties, chemical structure, and printing parameters. These relationships are discussed and areas where further research is needed, are identified. This review serves to aid the bioink development process, which will continue to play a major role in the successes and failures of bioprinting, tissue engineering, and regenerative medicine going forward.

Cellulose Nanocrystals/Graphene Hybrids-A Promising New Class of Materials for Advanced Applications

With the growth of global fossil-based resource consumption and the environmental concern, there is an urgent need to develop sustainable and environmentally friendly materials, which exhibit promising properties and could maintain an acceptable level of performance to substitute the petroleum-based ones. As elite nanomaterials, cellulose nanocrystals (CNC) derived from natural renewable resources, exhibit excellent physicochemical properties, biodegradability and biocompatibility and have attracted tremendous interest nowadays. Their combination with other nanomaterials such as graphene-based materials (GNM) has been revealed to be useful and generated new hybrid materials with fascinating physicochemical characteristics and performances. In this context, the review presented herein describes the quickly growing field of a new emerging generation of CNC/GNM hybrids, with a focus on strategies for their preparation and most relevant achievements. These hybrids showed great promise in a wide range of applications such as separation, energy storage, electronic, optic, biomedical, catalysis and food packaging. Some basic concepts and general background on the preparation of CNC and GNM as well as their key features are provided ahead.

Surface-Initiated Controlled Radical Polymerization Approach to In Situ Cross-Link Cellulose Nanofibrils with Inorganic Nanoparticles

This paper investigates a strategy to convert hydrophilic cellulose nanofibrils (CNF) into a hydrophobic highly cross-linked network made of cellulose nanofibrils and inorganic nanoparticles. First, the cellulose nanofibrils were chemically modified through an esterification reaction to produce a nanocellulose-based macroinitiator. Barium titanate (BaTiO₃, BTO) nanoparticles were surface-modified by introducing a specific monomer on their outer-shell surface. Finally, we studied the ability of the nanocellulose-based macroinitiator to initiate a single electron transfer living radical polymerization of stearyl acrylate (SA) in the presence of the surface-modified nanoparticles. The BTO nanoparticles will transfer new properties to the nanocellulose network and act as a cross-linking agent between the nanocellulose fibrils, while the monomer (SA) directly influences the hydrophilic-lipophilic balance. The pristine CNF and the nanoparticle cross-linked CNF are characterized by FTIR, SEM, and solid-state ¹³C NMR. Rheological and dynamic mechanical analyses revealed a high dregee of cross-linking.

Carbon Dots Conjugated with Vascular Endothelial Growth Factor for Protein Tracking in Angiogenic Therapy

One of the challenges of using growth factors for tissue regeneration is to monitor their biodistributions and delivery to injured tissues for minimally invasive detection. In the present study, tracking of human vascular endothelial growth factor (VEGF) was achieved by chemically linking it to photoluminescent carbon dots (CDs). Carbon dots were synthesized by the hydrothermal method and, subsequently, conjugated with VEGF using carbodiimide coupling. ELISA and western blot analysis revealed that VEGF-conjugated CDs preserve the binding affinity of VEGF to its antibodies. We also show that VEGF-conjugated CDs maintain the functionality of VEGF for tube formation and cell migration. The VEGF-conjugated CDs were also used for in vitro imaging of human umbilical vein endothelial cells. The results of this work suggest that cell-penetrating VEGF-conjugated CDs can be used for growth factor protein tracking in therapeutic and tissue engineering applications.

Cellulose Nanocrystal and Silver Nanobelt Gel: Cooperative Interactions Enabling Dispersion, Colloidal Gels, and Flexible Electronics

Using cellulose nanocrystals (CNCs) as a dispersant and cross-linker, we sought to enable the dispersion of silver nanobelts (AgNBs) in water for use in the manufacture of flexible electronics. In this work, we obtained a colloidal gel relying on contributions from both particles. When dried, particle interactions during gel collapse induced cooperative buckling of the AgNBs, obtaining a desirable spring-like conductive network that was not seen without the presence of CNCs. Thus, exploiting the collapse of bonded colloidal gels may represent a novel method to obtain desirable network buckling behavior for use in flexible electronics, which previously has only been obtained through printing on prestrained substrates.

Injectable Biocompatible Hydrogels from Cellulose Nanocrystals for Locally Targeted Sustained Drug Release

Injectable hydrogels from biocompatible materials are in demand for tissue engineering and drug delivery systems. Here, we produce hydrogels from mere cellulose nanocrystals (CNCs) by salt-induced charge screening. The injectability of CNC hydrogels was assessed by a combination of shear and capillary rheology, revealing that CNC hydrogels are conveyed via plug flow in capillaries allowing injection with minimal impact on mechanical properties. The potential of CNC hydrogels as drug carriers was elaborated by the in vitro release of the model protein bovine serum albumin (BSA), poorly water soluble tetracycline (TC), and readily soluble doxorubicin (DOX) into physiological saline and simulated gastric juice. For TC, a burst release was observed within 2 days, whereas BSA and DOX both showed a sustained release for 2 weeks. Only DOX was released fully from the hydrogels. The different release patterns were attributed to drug size, solubility, and specific drug-CNC interactions. The biocompatibility of CNC hydrogels and maintained bioactivity of released DOX were confirmed in a HeLa cell assay. The drug release was modulated by the incorporation of sucrose or xanthan gum in CNC hydrogels, whereas altering CNC concentration showed minor effects. The release into simulated gastric juice at pH 2 ceased for BSA due to charge inversion and electrostatic complexation, but not for smaller TC. Thus, CNC hydrogels may act as pH-responsive delivery systems that preserve drugs under gastric conditions followed by pH-triggered release in the duodenum.

Gradient Poly(ethylene glycol) Diacrylate and Cellulose Nanocrystals Tissue Engineering Composite Scaffolds via Extrusion Bioprinting

Bioprinting has advanced drastically in the last decade, leading to many new biomedical applications for tissue engineering and regenerative medicine. However, there are still a myriad of challenges to overcome, with vast amounts of research going into bioprinter technology, biomaterials, cell sources, vascularization, innervation, maturation, and complex 4D functionalization. Currently, stereolithographic bioprinting is the primary technique for polymer resin bioinks. However, it lacks the ability to print multiple cell types and multiple materials, control directionality of materials, and place fillers, cells, and other biological components in specific locations among the scaffolds. This study sought to create bioinks from a typical polymer resin, poly(ethylene glycol) diacrylate (PEGDA), for use in extrusion bioprinting to fabricate gradient scaffolds for complex tissue engineering applications. Bioinks were created by adding cellulose nanocrystals (CNCs) into the PEGDA resin at ratios from 95/5 to 60/40 w/w PEGDA/CNCs, in order to reach the viscosities needed for extrusion printing. The bioinks were cast, as well as printed into single-material and multiple-material (gradient) scaffolds using a CELLINK BIOX printer, and crosslinked using lithium phenyl-2,4,6-trimethylbenzoylphosphinate as the photoinitiator. Thermal and mechanical characterizations were performed on the bioinks and scaffolds using thermogravimetric analysis, rheology, and dynamic mechanical analysis. The 95/5 w/w composition lacked the required viscosity to print, while the 60/40 w/w composition displayed extreme brittleness after crosslinking, making both CNC compositions non-ideal. Therefore, only the bioink compositions of 90/10, 80/20, and 70/30 w/w were used to produce gradient scaffolds. The gradient scaffolds were printed successfully and embodied unique mechanical properties, utilizing the benefits of each composition to increase mechanical properties of the scaffold as a whole. The bioinks and gradient scaffolds successfully demonstrated tunability of their mechanical properties by varying CNC content within the bioink composition and the compositions used in the gradient scaffolds. Although stereolithographic bioprinting currently dominates the printing of PEGDA resins, extrusion bioprinting will allow for controlled directionality, cell placement, and increased complexity of materials and cell types, improving the reliability and functionality of the scaffolds for tissue engineering applications.

Methods and applications of nanocellulose loaded with inorganic nanomaterials: A review

Nanocellulose obtained from natural renewable resources has attracted enormous interests owing to its unique morphological characteristics, excellent mechanical strength, biocompatibility and biodegradability for a variety of applications in many fields. The template structure, high specific surface area, and active surface groups make it feasible to conduct surface modification and accommodate various nano-structured materials via physical or chemical deposition. The review presented herein focuses on the methodologies of loading different nano-structured materials on nanocellulose, including metals, nanocarbons, oxides, mineral salt, quantum dots and nonmetallic elements; and further describes the applications of nanocellulose composites in the fields of catalysis, optical electronic devices, biomedicine, sensors, composite reinforcement, photoswitching, flame retardancy, and oil/water separation.

A review on cellulose nanocrystals as promising biocompounds for the synthesis of nanocomposite hydrogels

Hydrogels are hydrophilic cross-linked polymer networks formed via the simple reaction of one or more monomers with the ability to retain a significant extent of water. Owing to an increased demand for environmentally friendly, biodegradable, and biocompatible products, cellulose nanocrystals (CNCs) with high hydrophilicity have emerged as a promising sustainable material for the formation of hydrogels. The cytocompatibility, swellability, and non-toxicity make CNC hydrogels of great interest in biomedical, biosensing, and wastewater treatment applications. There has been a considerable progress in the research of CNC hydrogels, as the number of scientific publications has exponentially increased (>600%) in the last five years. In this paper, recent progress in CNC hydrogels with particular emphasis on design, materials, and fabrication techniques to control hydrogel architecture, and advanced applications are discussed.

The Significance of Graphene Oxide-Polyacrylamide Interactions on the Stability and Microstructure of Oil-in-Water Emulsions

The emulsification of oil in water by nanoparticles can be facilitated by the addition of costabilizers, such as polymers and surfactants. The enhanced properties of the resulting emulsions are usually attributed to nanoparticle/costabilizer synergy; however, the mechanism of this synergistic effect and its impacts on emulsion stability and microstructure remain unclear. Here, we study the synergistic interaction of graphene oxide (GO) and a high molecular weight anionic polyacrylamide (PAM) in stabilization of paraffin oil/water emulsion systems. We show that the addition of PAM reduces the amount of GO required to stabilize an emulsion significantly. In order to probe the synergistic effect of GO and PAM, we analytically analyze the oil-free GO and GO-PAM dispersions and directly image their morphology via Cryo-TEM and atomic force microscopy (AFM). X-ray diffraction results confirm the adsorption of PAM molecules onto GO sheets resulting in the formation of ultimate GO-PAM complexes. The adsorption phenomenon is a consequence of hydrogen bonding and acid-base interactions, conceivably leading to a resilient electron-donor-acceptor complex. The microstructure of emulsions is captured with two-color fluorescent microscopy and Cryo-TEM. The acquired images display the localization of GO-PAM complexes at the interface while large amount of GO-PAM flocs coexist at the interface and in between oil droplets. Localization of such complexes and flocs at the interface is found to be responsible for their slow creaming rates compared to their GO counterparts. Mechanical properties of both dispersions and emulsions are studied by shear rheology. Rheological measurements confirm that GO-PAM complexes have a higher desorption energy from the interface resulting in higher critical shear strain of GO-PAM emulsions. The results, with insights into both structure and rheology, form a foundational understanding for integration of other polymers and nanoparticles in emulsion systems, which enables efficient design of these systems for an application of interest.

Nanofilamentous Virus-Based Dynamic Hydrogels with Tunable Internal Structures, Injectability, Self-Healing, and Sugar Responsiveness at Physiological pH

With expanding applications of hydrogels in diverse fields ranging from biomaterials to sensors, actuators, and soft robotics, there is an urgent need to endow one single gel with multiple physicochemical properties, such as stimuli-responsiveness, injectability, self-healing, and tunable internal structures. However, it is challenging to simultaneously incorporate these highly sought-after properties into one single gel. Herein, a conceptual hydrogel system with all of these properties is presented via combining bioconjugate chemistry, filamentous viruses, and dynamic covalent bonds. Nanofilamentous bioconjugates with diol affinity were prepared by coupling a tailor-synthesized low-p K_a phenylboronic acid (PBA) derivative to a well-defined green nanofiber the M13 virus with a high aspect ratio (PBA-M13). Dynamic hydrogels with tunable mechanical strength were prepared by using multiple diol-containing agents such as poly(vinyl alcohol) to cross-link such PBA-M13 via the classic boronic-diol dynamic bonds. The as-prepared hydrogels exhibit excellent injectability and self-healing behaviors as well as easy chemical accessibility of the PBA moieties on the virus backbone inside the gel matrix. Ordered internal structures were imparted into virus-based hydrogels by simple shear-induced alignment of the virus nanofibers. Furthermore, unique hydrogels with chiral internal structures were fabricated through in situ gelation induced by diffusion of diol-containing molecules to fix the chiral liquid crystal phase of the PBA-M13 virus. Sugar responsiveness of this gel leads to a glucose-regulated release behavior of payloads such as insulin. All of these properties have been implemented at physiological pH, which will facilitate future applications of these hydrogels as biomaterials.

Nanocolloidal Hydrogel for Heavy Metal Scavenging

We report a nanocolloidal hydrogel that combines the advantages of molecular hydrogels and nanoparticle-based scavengers of heavy metal ions. The hydrogel was formed by the chemical cross-linking of cellulose nanocrystals and graphene quantum dots. Over a range of hydrogel compositions, its structure was changed from lamellar to nanofibrillar, thus enabling the control of hydrogel permeability. Using a microfluidic approach, we generated nanocolloidal microgels and explored their scavenging capacity for Hg²⁺, Cu²⁺, Ni²⁺, and Ag⁺ ions. Due to the large surface area and abundance of ion-coordinating sites on the surface of nanoparticle building blocks, the microgels exhibited a high ion-sequestration capacity. The microgels were recyclable and were used in several ion scavenging cycles. These features, in addition to the sustainable nature of the nanoparticles, make this nanocolloidal hydrogel a promising ion-scavenging material.

Ferritin and neuromelanin "quantum dot" array structures in dopamine neurons of the substantia nigra pars compacta and norepinephrine neurons of the locus coeruleus

In this review, the author shows that ferritin has documented quantum dot material properties that have been reported in numerous independent studies, and can enable quantum mechanical electron transport over substantial distances. In addition, neuromelanin is a pi-conjugated polymer, and quantum dot/pi-conjugated polymer combinations have been reported in numerous independent studies to facilitate electron transport for solar photovoltaic and other applications. Both ferritin and neuromelanin are present in large quantities in the dopamine neurons of the substantia nigra pars compactaand the norepinephrine neurons of the locus coeruleus. The unique structure of subgroups of these neurons that have a large number of axon branches and synapses may have evolved to take advantage of this electron transport mechanism, if it is present, such as to coordinate conscious action, or for other purposes. Independent clinical and laboratory studies are also reviewed that corroborate this theory of coordinated action in these neuron groups. Research to validate the theory using charge transport measurements, materials characterization, existing fluorescent probe material and reaction time testing is proposed.