Electrically conductive "SMART" hydrogels for on-demand drug delivery

In the current transformative era of biomedicine, hydrogels have established their presence in biomaterials due to their superior biocompatibility, tuneability and resemblance with native tissue. However, hydrogels typically exhibit poor conductivity due to their hydrophilic polymer structure. Electrical conductivity provides an important enhancement to the properties of hydrogel-based systems in various biomedical applications such as drug delivery and tissue engineering. Consequently, researchers are developing combinatorial strategies to develop electrically responsive "SMART" systems to improve the therapeutic efficacy of biomolecules. Electrically conductive hydrogels have been explored for various drug delivery applications, enabling higher loading of therapeutic cargo with on-demand delivery. This review emphasizes the properties, mechanisms, fabrication techniques and recent advancements of electrically responsive "SMART" systems aiding on-site drug delivery applications. Additionally, it covers prospects for the successful translation of these systems into clinical research.

Effect of the molar mass of chitosan and film casting solvents on the properties of chitosan films loaded with Mentha spicata essential oil for potential application as wound dressing

Chitosan based films endowed with antibacterial features have witnessed remarkable progress as potential wound dressings. The current study aimed at appraising the effects of the molar mass of chitosan (MM) and the film casting acids on the properties of unplasticized chitosan films and plasticized MSO-embedded chitosan films in order to provide best suited film formulation as a potential candidate for wound dressing application. The prepared films were functionally characterized in terms of their qualitative assessment, thickness, density, swelling behavior, water vapor barrier, mechanical and antibacterial properties. Overall, all chitosan films displayed thickness lower than the human dermis even though thicker and denser films were produced with lactic acid. Assessment of the swelling behavior revealed that only high molar mass (HMM) chitosan films may be regarded as absorbent dressings. Moreover, unplasticized HMM lactate (HMM-LA) films furnished lower stiffness and higher percent strain break as compared to acetate films, due to the plasticizing effect of the remaining lactic acid as alluded by the FTIR analysis. Meanwhile, they provided suitable level of moisture and indicated substantial antibacterial activity against S. aureus and E. coli, the most commonly opportunistic bacteria found in infected skin wound. Plasticized chitosan films doped with MSO were significantly thicker and more permeable to water compared to unplasticized films. Furthermore, MSO significantly potentiate the antibacterial effect of chitosan-based films. Therefore, plasticized HMM-LA/MSO chitosan film flashing good swelling behavior, adequate WVTR and WVP, suitable mechanical properties and antibacterial performances substantiated to be a promising antibacterial dressing material for moderately exuding wounds.

Hydrogel Films with Impact Resistance by Sacrificial Micelle-Assisted-Alignment

Various strategies are developed to engineer aligned hierarchical architectures in polymer hydrogels for enhanced mechanical performance. However, chain alignment remains impeded by the presence of hydrogen bonds between adjacent chains. Herein, a facile sacrificial micelle-assisted-alignment strategy is proposed, leading to well-aligned, strong and tough pure chitosan hydrogels. The sacrificial sodium dodecyl sulfate micelles electrostatically interact with the protonated chitosan chains, enabling chain sliding and alignment under uniaxial forces. Subsequently, sacrificial micelles can be easily removed via NaOH treatment, causing the reforming of H-bond in the chain networks. The strength of the pure chitosan hydrogels increases 140-fold, reaching 58.9 ± 3.4 MPa; the modulus increases 595-fold, reaching 226.4 ± 42.8 MPa. After drying-rehydration, the strength and modulus further rise to 70.3 ± 2.4 and 403.5 ± 76.3 MPa, marking a significant advancement in high-strength pure chitosan hydrogel films. Furthermore, the designed multiscale architectures involving enhanced crystallinity, well-aligned fibers, strong interfaces, robust multilayer Bouligand assembly contribute to the exact replica of lobster underbelly with impact resistance up to 6.8 ± 1.0 kJ m-1. This work presents a promising strategy for strong, tough, stiff and impact-resistant polymer hydrogels via well-aligned hierarchical design.

Doxorubicin-loaded liposome-like particles embedded in chitosan/hyaluronic acid-based hydrogels as a controlled drug release model for local treatment of glioblastoma

Glioblastoma (GBM) resection and medication treatment are limited, and local drug therapies are required. This study aims to create a hybrid system comprising liposome-like particles (LLP-DOX) encapsulated in chitosan/hyaluronic acid/polyethyleneimine (CHI/HA/PEI) hydrogels, enabling controlled local delivery of doxorubicin (DOX) into the resection cavity for treating GBM. CHI/HA/PEI hydrogels were characterized morphologically, physically, chemically, mechanically, and thermally. Findings revealed a high network and compact micro-network structure, along with enhanced physical and thermal stability compared to CHI/HA hydrogels. Simultaneously, drug release from CHI/HA/PEI/LLP-DOX hydrogels was assessed, revealing continuous and controlled release up to the 148th hour, with no significant burst release. Cell studies showed that CHI/HA/PEI hydrogels are biocompatible with low genotoxicity. Additionally, LLP-DOX-loaded CHI/HA/PEI hydrogels significantly decreased cell viability and gene expression levels compared to LLP-DOX alone. It was also observed that the viability of GBM spheroids decreased over time when interacting with CHI/HA/PEI/LLP-DOX hydrogels, accompanied by a reduction in total surface area and an increase in apoptotic tendencies. In this study, we hypothesized that creating a hybrid drug delivery system by encapsulating DOX-loaded LLPs within a CHI/HA/PEI hydrogel matrix could achieve sustained drug release, improve anticancer efficacy via localized treatment, and effectively mitigate GBM progression for 3D microtissues.

Surface-anchored carbon nanomaterials for antimicrobial surfaces

Carbon nanomaterials (CNMs) are known for their antimicrobial (antibacterial and antiviral) activity when dispersed in a liquid, but whether this can be transferred to the surface of common materials has rarely been investigated. We have compared two typical CNMs (double-walled carbon nanotubes and few-layer graphene) in their non-oxidised and oxidised forms in terms of their antibacterial (Pseudomonas aeruginosa and Staphylococcus aureus) and antiviral (SARS-CoV2) activities after anchoring them onto the surface of silicone. We propose a very simple and effective protocol using the air-brush spray deposition method to entrap CNMs on the surfaces of two different silicone materials and demonstrate that the nanomaterials are anchored within the polymer while still being in contact with bacteria. We also investigated their antiviral activity against SARS-COV2 after deposition on standard surgical respiratory masks. Our results show that while suspensions of double-walled carbon nanotubes had a moderate effect on P. aeruginosa, this was not transferred after anchoring them to the surface of silicone. In contrast, graphene oxide showed a very strong antibacterial effect on P. aeruginosa and oxidised double-walled carbon nanotubes on S. aureus only when anchored to the surface. No significant antiviral activity was observed. This work paves the way for new antibacterial surfaces based on CNMs.

Seamless Integration of Conducting Hydrogels in Daily Life: From Preparation to Wearable Application

Conductive hydrogels (CHs) have received significant attention for use in wearable devices because they retain their softness and flexibility while maintaining high conductivity. CHs are well suited for applications in skin-contact electronics and biomedical devices owing to their high biocompatibility and conformality. Although highly conductive hydrogels for smart wearable devices are extensively researched, a detailed summary of the outstanding results of CHs is required for a comprehensive understanding. In this review, the recent progress in the preparation and fabrication of CHs is summarized for smart wearable devices. Improvements in the mechanical, electrical, and functional properties of high-performance wearable devices are also discussed. Furthermore, recent examples of innovative and highly functional devices based on CHs that can be seamlessly integrated into daily lives are reviewed.

A Novel Cryogenic Approach to 3D Printing Cytocompatible, Conductive, Hydrogel-Based Inks

In the field of tissue engineering and regenerative medicine, developing cytocompatible 3D conductive scaffolds that mimic the native extracellular matrix is crucial for the engineering of excitable cells and tissues. In this study, a custom cryogenic extrusion 3D printer was developed, which afforded control over both the ink and printing surface temperatures. Using this approach, aqueous inks were printed into well-defined layers with high precision. A conductive hydrogel ink was developed from chitosan (CS) and edge-functionalised expanded graphene (EFXG). Different EFXG:CS ratios (between 60:40 and 80:20) were evaluated to determine both conductivity and printability. Using the novel customized cryogenic 3D printer, conductive structures of between 2 and 20 layers were produced, with feature sizes as small as 200 μm. The printed structures are mechanically robust and are electrically conducting. The highest Young's modulus and conductivity in a hydrated state were 2.6 MPa and ∼45 S/m, respectively. Cytocompatibility experiments reveal that the developed material supports NSC-34 mouse motor neuron-like cells in terms of viability, attachment, and proliferation. The distinctive mechanical and electrical properties of the 3D-printed structures would make them good candidates for the engineering of 3D-structured excitable cells. Moreover, this novel printing setup can be used to print other hydrogel-based inks with high precision and resolution.

Three-Dimensional Printing of Hydrogels for Flexible Sensors: A Review

The remarkable flexibility and heightened sensitivity of flexible sensors have drawn significant attention, setting them apart from traditional sensor technology. Within this domain, hydrogels-3D crosslinked networks of hydrophilic polymers-emerge as a leading material for the new generation of flexible sensors, thanks to their unique material properties. These include structural versatility, which imparts traits like adhesiveness and self-healing capabilities. Traditional templating-based methods fall short of tailor-made applications in crafting flexible sensors. In contrast, 3D printing technology stands out with its superior fabrication precision, cost-effectiveness, and satisfactory production efficiency, making it a more suitable approach than templating-based strategies. This review spotlights the latest hydrogel-based flexible sensors developed through 3D printing. It begins by categorizing hydrogels and outlining various 3D-printing techniques. It then focuses on a range of flexible sensors-including those for strain, pressure, pH, temperature, and biosensors-detailing their fabrication methods and applications. Furthermore, it explores the sensing mechanisms and concludes with an analysis of existing challenges and prospects for future research breakthroughs in this field.

Magnesium (Mg2 +), Strontium (Sr2 +), and Zinc (Zn2 +) Co-substituted Bone Cements Based on Nano-hydroxyapatite/Monetite for Bone Regeneration

New bone cement type that combines Sr2 + /Mg2 + or Sr2 + /Zn2 + co-substituted nano-hydroxyapatite (n-HAs) with calcium phosphate dibasic and chitosan/gelatin polymers was developed to increase adhesion and cellular response. The cements were physicochemically described and tested in vitro using cell cultures. All cements exhibited quite hydrophilic and had high washout resistance. Cement releases Ca2 + , Mg2 + , Sr2 + , and Zn2 + in concentrations that are suitable for osteoblast proliferation and development. All of the cements stimulated cell proliferation in fibroblasts, endothelial cells, and osteoblasts, were non-cytotoxic, and produced apatite. Cements containing co-substituted n-HAs had excellent cytocompatibility, which improved osteoblast adhesion and cell proliferation. These cements had osteoinductive potential, stimulating extracellular matrix (ECM) mineralization and differentiation of MC3T3-E1 cells by increasing ALP and NO production. The ions Ca2 + , Mg2 + , Zn2 + , and Sr2 + appear to cooperate in promoting osteoblast function. The C3 cement (HA-SrMg5%), which was made up of n-HA co-substituted with 5 mol% Sr and 5 mol% Mg, showed exceptional osteoinductive capacity in terms of bone regeneration, indicating that this new bone cement could be a promising material for bone replacement.

Hydrogels with electrically conductive nanomaterials for biomedical applications

Hydrogels, soft 3D materials of cross-linked hydrophilic polymer chains with a high water content, have found numerous applications in biomedicine because of their similarity to native tissue, biocompatibility and tuneable properties. In general, hydrogels are poor conductors of electric current, due to the insulating nature of commonly-used hydrophilic polymer chains. A number of biomedical applications require or benefit from an increased electrical conductivity. These include hydrogels used as scaffolds for tissue engineering of electroactive cells, as strain-sensitive sensors and as platforms for controlled drug delivery. The incorporation of conductive nanomaterials in hydrogels results in nanocomposite materials which combine electrical conductivity with the soft nature, flexibility and high water content of hydrogels. Here, we review the state of the art of such materials, describing the theories of current conduction in nanocomposite hydrogels, outlining their limitations and highlighting methods for improving their electrical conductivity.

Recent Advances in 3D Printing of Photocurable Polymers: Types, Mechanism, and Tissue Engineering Application

The conversion of liquid resin into solid structures upon exposure to light of a specific wavelength is known as photopolymerization. In recent years, photopolymerization-based 3D printing has gained enormous attention for constructing complex tissue-specific constructs. Due to the economic and environmental benefits of the biopolymers employed, photo-curable 3D printing is considered an alternative method for replacing damaged tissues. However, the lack of suitable bio-based photopolymers, their characterization, effective crosslinking strategies, and optimal printing conditions are hindering the extensive application of 3D printed materials in the global market. This review highlights the present status of various photopolymers, their synthesis, and their optimization parameters for biomedical applications. Moreover, a glimpse of various photopolymerization techniques currently employed for 3D printing is also discussed. Furthermore, various naturally derived nanomaterials reinforced polymerization and their influence on printability and shape fidelity are also reviewed. Finally, the ultimate use of those photopolymerized hydrogel scaffolds in tissue engineering is also discussed. Taken together, it is believed that photopolymerized 3D printing has a great future, whereas conventional 3D printing requires considerable sophistication, and this review can provide readers with a comprehensive approach to developing light-mediated 3D printing for tissue-engineering applications.

Electrodeposition of chitosan/graphene oxide conduit to enhance peripheral nerve regeneration

Currently available commercial nerve guidance conduits have been applied in the repair of peripheral nerve defects. However, a conduit exhibiting good biocompatibility remains to be developed. In this work, a series of chitosan/graphene oxide (GO) films with concentrations of GO varying from 0–1 wt% (collectively referred to as CHGF-n) were prepared by an electrodeposition technique. The effects of CHGF-n on proliferation and adhesion abilities of Schwann cells were evaluated. The results showed that Schwann cells exhibited elongated spindle shapes and upregulated expression of nerve regeneration-related factors such as Krox20 (a key myelination factor), Zeb2 (essential for Schwann cell differentiation, myelination, and nerve repair), and transforming growth factor β (a cytokine with regenerative functions). In addition, a nerve guidance conduit with a GO content of 0.25% (CHGFC-0.25) was implanted to repair a 10-mm sciatic nerve defect in rats. The results indicated improvements in sciatic functional index, electrophysiology, and sciatic nerve and gastrocnemius muscle histology compared with the CHGFC-0 group, and similar outcomes to the autograft group. In conclusion, we provide a candidate method for the repair of peripheral nerve defects using free-standing chitosan/GO nerve conduits produced by electrodeposition.

Advances and Innovations of 3D Bioprinting Skin

Three-dimensional (3D) bioprinted skin equivalents are highlighted as the new gold standard for alternative models to animal testing, as well as full-thickness wound healing. In this review, we focus on the advances and innovations of 3D bioprinting skin for skin regeneration, within the last five years. After a brief introduction to skin anatomy, 3D bioprinting methods and the remarkable features of recent studies are classified as advances in materials, structures, and functions. We will discuss several ways to improve the clinical potential of 3D bioprinted skin, with state-of-the-art printing technology and novel biomaterials. After the breakthrough in the bottleneck of the current studies, highly developed skin can be fabricated, comprising stratified epidermis, dermis, and hypodermis with blood vessels, nerves, muscles, and skin appendages. We hope that this review will be priming water for future research and clinical applications, that will guide us to break new ground for the next generation of skin regeneration.

Electrically Conductive Hydrogels for Articular Cartilage Tissue Engineering

Articular cartilage is a highly specialized tissue found in diarthrodial joints, which is crucial for healthy articular motion. Despite its importance, articular cartilage has limited regenerative capacities, and the degeneration of this tissue is a leading cause of disability worldwide, with hundreds of millions of people affected. As current treatment options for cartilage degeneration remain ineffective, tissue engineering has emerged as an exciting approach to create cartilage substitutes. In particular, hydrogels seem to be suitable candidates for this purpose due to their biocompatibility and high customizability, being able to be tailored to fit the biophysical properties of native cartilage. Furthermore, these hydrogel matrices can be combined with conductive materials in order to simulate the natural electrochemical properties of articular cartilage. In this review, we highlight the most common conductive materials combined with hydrogels and their diverse applications, and then present the current state of research on the development of electrically conductive hydrogels for cartilage tissue engineering. Finally, the main challenges and future perspectives for the application of electrically conductive hydrogels on articular cartilage repair strategies are also discussed.

Fabrication of Conductive Tissue Engineering Nanocomposite Films Based on Chitosan and Surfactant-Stabilized Graphene Dispersions

Chitosan (CS)/graphene nanocomposite films with tunable biomechanics, electroconductivity and biocompatibility using polyvinylpyrrolidone (PVP) and Pluronic F108 (Plu) as emulsion stabilizers for the purpose of conductive tissue engineering were successfully obtained. In order to obtain a composite solution, aqueous dispersions of multilayered graphene stabilized with Plu/PVP were supplied with CS at a ratio of CS to stabilizers of 2:1, respectively. Electroconductive films were obtained by the solution casting method. The electrical conductivity, mechanical properties and in vitro and in vivo biocompatibility of the resulting films were assessed in relation to the graphene concentration and stabilizer type and they were close to that of smooth muscle tissue. According to the results of the in vitro cytotoxicity analysis, the films did not release soluble cytotoxic components into the cell culture medium. The high adhesion of murine fibroblasts to the films indicated the absence of contact cytotoxicity. In subcutaneous implantation in Wistar rats, we found that stabilizers reduced the brittleness of the chitosan films and the inflammatory response.

Silk-Elastin-Like-Protein/Graphene-Oxide Composites for Dynamic Electronic Biomaterials

Genetically engineered silk-elastin-like-proteins (SELPs) synthesized with the combination of silk and elastin domains are bioengineered to also contain a graphene oxide (GO) binding domain. The conductivity and mechanical stability of graphene, combined with SELP-specific graphene interfaces are pursued as dynamic hybrid materials, toward biomaterial-based electronic switches. The resulting bioengineered proteins with added GO demonstrate cytocompatibility and conductivity that could be modulated by changing hydrogel size in response to temperature due to the SELP chemistry. Upon increased temperature, the gels coalesce and contract, providing sufficient condensed spacing to facilitate conductivity via the graphene domains, a feature that is lost at lower temperatures with the more expanded hydrogels. This thermally induced contraction-expansion is reversible and cyclable, providing an "on-off" conductive switch driven by temperature-driven hydrogel shape-change.

Potentialities of graphene and its allied derivatives to combat against SARS-CoV-2 infection

Graphene is a two-dimensional material with sp2 hybridization that has found its broad-spectrum potentialities in various domains like electronics, robotics, aeronautics, etc.; it has recently gained its utilities in the biomedical domain. The unique properties of graphene and its derivatives of graphene have helped them find their utilities in the biomedical domain. Additionally, the sudden outbreak of SARS-CoV-2 has immensely expanded the research field, which has also benefitted graphene and its derivatives. Currently, the world is facing a global pandemic due to the sudden outbreak of Severe Acute Respiratory Syndrome Coronavirus-2 (SARS-CoV-2), also known as COVID-19, from its major onset in Wuhan city, China, in December 2019. Presently, many new variants and mutants appear, which is more harmful than previous strains. However, researchers and scientists are focused on understanding the target structure of coronavirus, mechanism, causes and transmission mode, treatment, and alternatives to cure these diseases in this critical pandemic situation; many findings are achieved, but much more is unknown and pending to be explored. This review paper is dedicated to exploring the utilities of graphene and its derivatives in combating the SARS-CoV-2 by highlighting their mechanism and applications in the fabrication of biosensors, personal protection equipment (PPE) kits, 3-D printing, and antiviral coatings. Further, the paper also covers the cytotoxicity caused by graphene and its derivatives and highlights the graphene-based derivatives market aspects in biomedical domains. Thus, graphene and graphene-derived materials are our new hope in this pandemic time, and this review helps acquire broad knowledge about them.

Effect of Graphene Addition on Polycaprolactone Scaffolds Fabricated Using Melt-Electrowriting

Melt-electrowriting (MEW) is an emerging method that combines electrospinning and extrusion printing, allowing the fabrication of micron-scale structures suitable for tissue engineering. Compared to other additive fabrication methods, melt-electro written structures can offer more appropriate substrates for cell culture due to filament size and mechanical characteristics of the fabricated scaffolds. In this study, polycaprolactone (PCL)/graphene composites were investigated for fabrication of micron-size scaffolds through MEW. It was demonstrated that the addition of graphene can considerably improve the processability of PCL to fabricate micron-scale scaffolds with enhanced resolution. The tensile strength of the scaffold prepared from PCL/graphene composite (with only 0.5 wt.% graphene) was proved significantly (by more than 270%), better than that of the pristine PCL scaffold. Furthermore, graphene was demonstrated to be a suitable material for tailoring the degradation process to avoid undesirable bulk degradation, rapid mass loss and damage to the internal matrix of the polymer. The findings of this study offer a promising route for the fabrication of high-resolution scaffolds with micron-scale resolution for tissue engineering.

MacGyvered Multiproperty Materials Using Nanocarbon and Jam: A Spectroscopic, Electromagnetic, and Rheological Investigation

As part of a biopolymer matrix, pectin was investigated to obtain an engineered jam, due to its biodegradability. Only a few examples of pectin-based nanocomposites are present in the literature, and even fewer such bionanocomposites utilize nanocarbon as a filler-mostly for use in food packaging. In the present paper, ecofriendly nanocomposites made from household reagents and displaying multiple properties are presented. In particular, the electrical behavior and viscoelastic properties of a commercial jam were modulated by loading the jam with carbon nanotubes and graphene nanoplates. A new nanocomposite class based on commercial jam was studied, estimating the percolation threshold for each filler. The electrical characterization and the rheological measurements suggest that the behavior above the percolation threshold is influenced by the different morphology-i.e., one-dimensional or two-dimensional-of the fillers. These outcomes encourage further studies on the use of household materials in producing advanced and innovative materials, in order to reduce the environmental impact of new technologies, without giving up advanced devices endowed with different physical properties.

Nanoengineered biomimetic hydrogels: A major advancement to fabricate 3D-printed constructs for regenerative medicine

Nanostructured compounds already validated as performant reinforcements for biomedical applications together with different fabrication strategies have been often used to channel the biophysical and biochemical features of hydrogel networks. Ergo, a wide array of nanostructured compounds has been employed as additive materials integrated with hydrophilic networks based on naturally-derived polymers to produce promising scaffolding materials for specific fields of regenerative medicine. To date, nanoengineered hydrogels are extensively explored in (bio)printing formulations, representing the most advanced designs of hydrogel (bio)inks able to fabricate structures with improved mechanical properties and high print fidelity along with a cell-interactive environment. The development of printing inks comprising organic-inorganic hybrid nanocomposites is in full ascent as the impact of a small amount of nanoscale additive does not translate only in improved physicochemical and biomechanical properties of bioink. The biopolymeric nanocomposites may even exhibit additional particular properties engendered by nano-scale reinforcement such as electrical conductivity, magnetic responsiveness, antibacterial or antioxidation properties. The present review focus on hydrogels nanoengineered for 3D printing of biomimetic constructs, with particular emphasis on the impact of the spatial distribution of reinforcing agents (0D, 1D, 2D). Here, a systematic analysis of the naturally-derived nanostructured inks is presented highlighting the relationship between relevant length scales and size effects that influence the final properties of the hydrogels designed for regenerative medicine. This article is protected by copyright. All rights reserved.

The Effect of Graphite Additives on Magnetization, Resistivity and Electrical Conductivity of Magnetorheological Plastomer

Common sensors in many applications are in the form of rigid devices that can react according to external stimuli. However, a magnetorheological plastomer (MRP) can offer a new type of sensing capability, as it is flexible in shape, soft, and responsive to an external magnetic field. In this study, graphite (Gr) particles are introduced into an MRP as an additive, to investigate the advantages of its electrical properties in MRPs, such as conductivity, which is absolutely required in a potential sensor. As a first step to achieve this, MRP samples containing carbonyl iron particles (CIPs) and various amounts of of Gr, from 0 to 10 wt.%, are prepared, and their magnetic-field-dependent electrical properties are experimentally evaluated. After the morphological aspect of Gr-MRP is characterized using environmental scanning electron microscopy (ESEM), the magnetic properties of MRP and Gr-MRP are evaluated via a vibrating sample magnetometer (VSM). The resistivities of the Gr-MRP samples are then tested under various applied magnetic flux densities, showing that the resistivity of Gr-MRP decreases with increasing of Gr content up to 10 wt.%. In addition, the electrical conductivity is tested using a test rig, showing that the conductivity increases as the amount of Gr additive increases, up to 10 wt.%. The conductivity of 10 wt.% Gr-MRP is found to be highest, at 178.06% higher than the Gr-MRP with 6 wt.%, for a magnetic flux density of 400 mT. It is observed that with the addition of Gr, the conductivity properties are improved with increases in the magnetic flux density, which could contribute to the potential usefulness of these materials as sensing detection devices.

Mussel-inspired hydrogels as tough, self-adhesive and conductive bioelectronics: a review

To overcome the wearable sensor's defects and achieve the goal of robust mechanical properties, long-term adhesion, sensitive electrical conductivity, the multifunctional hydrogels were inspired by various mussels on the base of catechol and its analogues. In this review, we review the strategies for improving the mechanical strength, adhesion, conductivity and antibacterial properties of mussel-inspired hydrogels as bioelectronics. Double network structures, nanocomposites, supramolecular block polymers and other strategies were utilized for achieving tough hydrogels to prevent tensile fractures under high deformation. Many mussel-inspired chemistries were incorporated for constructing skin-attachable hydrogel strain sensors and some strategies for controlling the oxidation of catechol were employed to achieve long-term adhesion. In addition, electrolytes, conductive fillers, conductive polymers and their relevant hydrophilic modifications were introduced for fabricating the conductive hydrogel bioelectronics to enhance the conductivity properties. Finally, the challenges and outlooks in this promising field are featured from the perspective of materials chemistry.

Modulation of hydrogel stiffness by external stimuli: soft materials for mechanotransduction studies

Mechanotransduction is an important process in determining cell survival, proliferation, migration and differentiation. The extracellular matrix (ECM) is the component of natural tissue that provides structural support and biochemical signals to adhering cells. The ECM is dynamic and undergoes physical and biochemical changes in response to various stimuli and there is an interest in understanding the effect of dynamic changes in stiffness on cell behaviour and fate. Therefore, stimuli-responsive hydrogels have been developed to mimic the cells' microenvironment in a controlled fashion. Herein, we review strategies for dynamic modulation of stiffness using various stimuli, such as light, temperature and pH. Special emphasis is placed on conducting polymer (CP) hydrogels and their fabrication procedures. We believe that the redox properties of CPs and hydrogels' biological properties make CPs hydrogels a promising substrate to investigate the effect of dynamic stiffness changes and mechanical actuation on cell fate in future studies.

Recent Advances in Chitin and Chitosan/Graphene-Based Bio-Nanocomposites for Energetic Applications

Herein, we report recent developments in order to explore chitin and chitosan derivatives for energy-related applications. This review summarizes an introduction to common polysaccharides such as cellulose, chitin or chitosan, and their connection with carbon nanomaterials (CNMs), such as bio-nanocomposites. Furthermore, we present their structural analysis followed by the fabrication of graphene-based nanocomposites. In addition, we demonstrate the role of these chitin- and chitosan-derived nanocomposites for energetic applications, including biosensors, batteries, fuel cells, supercapacitors and solar cell systems. Finally, current limitations and future application perspectives are entailed as well. This study establishes the impact of chitin- and chitosan-generated nanomaterials for potential, unexplored industrial applications.

Graphene oxide-reinforced pectin/chitosan polyelectrolyte complex scaffolds

Three-dimensional (3D) porous scaffolds based on graphene oxide (GO) incorporated pectin/chitosan polyelectrolyte complex (PCGO) were prepared by the freeze-drying technique. The chemical composition and microstructure of the prepared PCGO scaffolds were studied by FTIR and XRD analysis. The presence of GO and its uniform distribution within the polymer matrix was confirmed by Raman spectroscopy and confocal Raman mapping analysis, respectively. TGA analysis revealed that the addition of GO improves the thermal stability of the pectin/chitosan complex. SEM analysis confirmed the uniform pore distribution of PCGO scaffolds. Moreover, it showed that the pore size of the scaffolds was decreased with the increase in GO content. Among the developed PCGO scaffolds, the scaffolds with 1 wt.% of GO presented the improved hydrophilicity by exhibiting the water swelling degree of 2004%, water retention capacity of 1101% and water contact angle (WCA) of 21°. In addition, these scaffolds presented better compressive strength (∼283 kPa) and resistance towards lysozyme-mediated degradation. The PCGO scaffolds presented an acceptable level of bio-and hemocompatibility and GO concentration-dependent cell attachment ability. These results demonstrate the suitability of PCGO scaffolds for tissue engineering.

Flexible and Conductive Bioelectrodes Based on Chitosan-Carbon Black Membranes: Towards the Development of Wearable Bioelectrodes

Wearable sensors for non-invasive monitoring constitute a growing technology in many industrial fields, such as clinical or sport monitoring. However, one of the main challenges in wearable sensing is the development of bioelectrodes via the use of flexible and stretchable materials capable of maintaining conductive and biocompatible properties simultaneously. In this study, chitosan-carbon black (CH-CB) membranes have been synthesized using a straightforward and versatile strategy and characterized in terms of their composition and their electrical and mechanical properties. In this sense, CH-CB membranes showed good conductivity and mechanical resistance thanks to the presence of carbon black, which decreases the insulating behavior of chitosan, while flexibility and biocompatibility are maintained due to the dual composition of the membrane. Thus, flexible and biocompatible conductive bioelectrodes have been developed by the combined use of CH and CB without the use of toxic reagents, extra energy input, or long reaction times. The membranes were modified using the enzymes Glucose Oxidase and Laccase in order to develop flexible and biocompatible bioelectrodes for enzymatic glucose biofuel cells (BFCs) and glucose detection. A BFC assembled using the flexible bioelectrodes developed was able to deliver 15 µW cm^-2, using just 1 mM glucose as biofuel, and up to 21.3 µW·cm^-2 with higher glucose concentration. Additionally, the suitability of the CH-CB membranes to be used as a glucose sensor in a linear range from 100 to 600 µM with a limit of detection (LOD) of 76 µM has been proven. Such demonstrations for energy harvesting and sensing capabilities of the developed membrane pave the way for their use in wearable sensing and energy harvesting technologies in the clinical field due to their good mechanical, electrical, and biocompatible properties.

A facile approach for the development of high mechanical strength 3D neuronal network scaffold based on chitosan and graphite nanoplatelets

In this work, novel composite microparticles based on chitosan (CHI) and graphite nanoplatelets (GNP) were developed as 3D scaffolds for neuronal cells. The aim is to improve the scaffold strength while maintaining its ability to sustain cell adhesion and differentiation. An air-assisted jetting technique followed by physical crosslinking is employed to obtain CHI/GNP microparticles. Optical and Field Emission Scanning Electron Microscopy micrographs showed a uniform distribution of GNP within the CHI porous matrix. The presence of GNP turned out to improve the strength of the microparticles while conferring good electrical conductivity and ameliorating their stability in aqueous environment. The morphological and immunocytochemical characterization, combined with a preliminary electrophysiological analysis, evidenced the effectiveness of the developed composite microparticles as a scaffold for neuron growth. These scaffolds could be employed for the development of advanced 3D neuronal in vitro models for networks dynamics analysis and drug screening.

Chitosan-based 3D-printed scaffolds for bone tissue engineering

Despite the spontaneous regenerative properties of autologous bone grafts, this technique remains dilatory and restricted to fractures and injuries. Conventional grafting strategies used to treat bone tissue damage have several limitations. This highlights the need for novel approaches to overcome the persisting challenges. Tissue-like constructs that can mimic natural bone structurally and functionally represent a promising strategy. Bone tissue engineering (BTE) is an approach used to develop bioengineered bone with subtle architecture. BTE utilizes biomaterials to accommodate cells and deliver signaling molecules required for bone rejuvenation. Among the various techniques available for scaffold creation, 3D-printing technology is considered to be a superior technique as it enables the design of functional scaffolds with well-defined customizable properties. Among the biomaterials obtained from natural, synthetic, or ceramic origins, naturally derived chitosan (CS) polymers are promising candidates for fabricating reliable tissue constructs. In this review, the physicochemical-biological properties and applications of CS-based 3D-printed scaffolds and their future perspectives in BTE are summarized.

Graphene Oxide-Embedded Extracellular Matrix-Derived Hydrogel as a Multiresponsive Platform for 3D Bioprinting Applications

Decellularized extracellular matrices (dECMs) have shown enormous potential for the biofabrication of tissues due to their biomimetic properties that promote enhanced cellular interaction and tissue regeneration. However, biofabrication schemes requiring electrostimulation pose an additional constraint due to the insulating properties of natural materials. Here, we propose a methacryloyl-modified decellularized small intestine submucosa (SISMA) hydrogel, embedded with graphene oxide (GO) nanosheets, for extrusion-based 3D bioprinting applications that require electrostimulation. Methacryloyl biochemical modification is performed to enhance the mechanical stability of dECM constructs by mediating photo-crosslinking reactions, and a multistep fabrication scheme is proposed to harness the bioactive and hydrophilic properties of GO and electroconductive properties of reduced GO. For this, GO was initially dispersed in SISMA hydrogels by exploiting its hydrophilicity and protein adsorption capabilities, and in situ reduction was subsequently performed to confer electroconductive abilities. SISMA-GO composite hydrogels were successfully prepared with enhanced structural characteristics, as shown by the higher crosslinking degree and increased elastic response upon blue-light exposure. Moreover, GO was homogeneously dispersed without affecting photocrosslinking reactions and hydrogel shear-thinning properties. Human adipose-derived mesenchymal stem cells were successfully bioprinted in SISMA-GO with high cell viability after 1 week and in situ reduction of GO during this period enhanced the electrical conductivity of these nanostructures. This work demonstrates the potential of SISMA-GO bioinks as bioactive and electroconductive scaffolds for electrostimulation applications in tissue engineering and regenerative medicine.

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.

In Situ Formation of 3D Conductive and Cell-Laden Graphene Hydrogel for Electrically Regulating Cellular Behavior

Electroconductive and injectable hydrogels are attracting increasing attention owing to the needs of electrically induced regulation of cell behavior, tissue engineering of electroactive tissues, and achieving minimum invasiveness during tissue repair. In this study, a novel in situ formed 3D conductive and cell-laden hydrogel is developed, which can be broadly used in bioprinting, tissue engineering, neuroengineering etc. An instantaneous, uniform spatial distribution and encapsulation of cells can be achieved as a result of hydrogen bonding induced hydrogel formation. Particularly, the cell-laden hydrogel can be easily obtained by simply mixing and shaking the polydopamine (PDA) functionalized rGO (rGO-PDA) with polyvinyl alcohol (PVA) solution containing cells. Graphene oxide is reduced and functionalized by dopamine to restore the electrical conductivity, while simultaneously enhancing both hydrophilicity and biocompatibility of reduced graphene oxide. In vitro culture of PC12 cells within the cell-laden hydrogel demonstrates its biocompatibility, noncytotoxicity as well as the ability to support long-term cell growth and proliferation. Enhanced neuronal differentiation is also observed, both with and without electrical stimulation. Overall, this 3D conductive, cell-laden hydrogel holds great promise as potential platform for tissue engineering of electroactive tissues.

3D Printable Electrically Conductive Hydrogel Scaffolds for Biomedical Applications: A Review

Electrically conductive hydrogels (ECHs), an emerging class of biomaterials, have garnered tremendous attention due to their potential for a wide variety of biomedical applications, from tissue-engineered scaffolds to smart bioelectronics. Along with the development of new hydrogel systems, 3D printing of such ECHs is one of the most advanced approaches towards rapid fabrication of future biomedical implants and devices with versatile designs and tuneable functionalities. In this review, an overview of the state-of-the-art 3D printed ECHs comprising conductive polymers (polythiophene, polyaniline and polypyrrole) and/or conductive fillers (graphene, MXenes and liquid metals) is provided, with an insight into mechanisms of electrical conductivity and design considerations for tuneable physiochemical properties and biocompatibility. Recent advances in the formulation of 3D printable bioinks and their practical applications are discussed; current challenges and limitations of 3D printing of ECHs are identified; new 3D printing-based hybrid methods for selective deposition and fabrication of controlled nanostructures are highlighted; and finally, future directions are proposed.

Stimuli-Responsive Biomaterials: Scaffolds for Stem Cell Control

Stem cell fate is closely intertwined with microenvironmental and endogenous cues within the body. Recapitulating this dynamic environment ex vivo can be achieved through engineered biomaterials which can respond to exogenous stimulation (including light, electrical stimulation, ultrasound, and magnetic fields) to deliver temporal and spatial cues to stem cells. These stimuli-responsive biomaterials can be integrated into scaffolds to investigate stem cell response in vitro and in vivo, and offer many pathways of cellular manipulation: biochemical cues, scaffold property changes, drug release, mechanical stress, and electrical signaling. The aim of this review is to assess and discuss the current state of exogenous stimuli-responsive biomaterials, and their application in multipotent stem cell control. Future perspectives in utilizing these biomaterials for personalized tissue engineering and directing organoid models are also discussed.

Novel biopolymer-based nanocomposite food coatings that exhibit active and smart properties due to a single type of nanoparticles

We used nanoparticles which possess simultaneously active (antimicrobial, UV-protective and antioxidant) and smart (temperature sensing) properties. The nanoparticles (2Rh = 450 nm, PDI = 0.118 ± 0.014, ζ-potential = 21 mV and T_g = 8 ± 1 °C) are based on polyethylene glycol (PEG)/methyl cellulose (MC) core with anthocyanidin and sodium acetate, and chitosan/gallotannin-based shell. The core of nanoparticles acts as a temperature indicator, changing its color from colorless into deep purple at 8 °C, while the shell provides antimicrobial (due to chitosan), UV-protective and antioxidant (due to gallotannin) effects. We incorporated these nanoparticles into the chitosan matrix. The coatings demonstrated improved mechanical and barrier properties compared with the pure chitosan coating. The elaborated coatings pronouncedly improve the shelf-life of Ricotta cheese. Moreover, they serve as thermo indicators, which warn about cheese storage at an unacceptable temperature. Thus, we developed new coatings in which all properties are enabled by a single type of nanoparticles.

Design Strategies of Conductive Hydrogel for Biomedical Applications

Conductive hydrogel, with electroconductive properties and high water content in a three-dimensional structure is prepared by incorporating conductive polymers, conductive nanoparticles, or other conductive elements, into hydrogel systems through various strategies. Conductive hydrogel has recently attracted extensive attention in the biomedical field. Using different conductivity strategies, conductive hydrogel can have adjustable physical and biochemical properties that suit different biomedical needs. The conductive hydrogel can serve as a scaffold with high swelling and stimulus responsiveness to support cell growth in vitro and to facilitate wound healing, drug delivery and tissue regeneration in vivo. Conductive hydrogel can also be used to detect biomolecules in the form of biosensors. In this review, we summarize the current design strategies of conductive hydrogel developed for applications in the biomedical field as well as the perspective approach for integration with biofabrication technologies.

Biological and structural properties of graphene oxide/curcumin nanocomposite incorporated chitosan as a scaffold for wound healing application

AIMS

The purpose of this research is to fabricate chitosan (CS)/graphene oxide (GO)/curcumin (Cur) 3D scaffolds through the freeze-drying method for wound dressing applications.

MAIN METHODS

GO is produced by Hammer's method; then, it is characterized by X-ray diffraction and TEM analysis. Fabricated scaffolds are characterized by FTIR, FESEM, AFM, water vapor transmission rate, PBS absorption, contact angle, tensile strength, porosity measurement, biodegradability, and drug release methods. The cell viability and morphology of NIH/3 T3 cells are investigated by WST assay kit and FESEM analysis, and the antibacterial activity of scaffolds is determined by the optical density (OD) method. The photothermal antibacterial activity is characterized by NIR irradiation, too.

KEY FINDINGS

The mean pore diameter of scaffolds adjusted by the incorporation of about 0-1.5%wt. of GO/Cur nanocomposite into CS matrix, decreasing from 87 to 40 μm that can be attributed to the intermolecular bonds between CS and GO/Cur nanocomposite. Besides, the PBS absorption of scaffolds enhances by the addition of GO/Cur, especially 1% of it. Furthermore, the overall average of cell viability of nanocomposite scaffolds is about 95%, and the FESEM images show that NIH/3T3 fibroblasts well spread on the nanocomposite scaffolds. GO/Cur has a significant influence on the antibacterial activity of CS scaffolds as CS/GO/Cur 0.5 scaffold diminishes the bacterial growth to about 52% of the control sample's growth.

SIGNIFICANCE

The results evidence the antibacterial CS/GO/Cur scaffolds are excellent supports for cell growth and proliferation, and they could be promising candidates for wound dressing applications.

Bioactive polymeric materials and electrical stimulation strategies for musculoskeletal tissue repair and regeneration

Electrical stimulation (ES) is predominantly used as a physical therapy modality to promote tissue healing and functional recovery. Research efforts in both laboratory and clinical settings have shown the beneficial effects of this technique for the repair and regeneration of damaged tissues, which include muscle, bone, skin, nerve, tendons, and ligaments. The collective findings of these studies suggest ES enhances cell proliferation, extracellular matrix (ECM) production, secretion of several cytokines, and vasculature development leading to better tissue regeneration in multiple tissues. However, there is still a gap in the clinical relevance for ES to better repair tissue interfaces, as ES applied clinically is ineffective on deeper tissue. The use of a conducting material can transmit the stimulation applied from skin electrodes to the desired tissue and lead to an increased function on the repair of that tissue. Ionically conductive (IC) polymeric scaffolds in conjunction with ES may provide solutions to utilize this approach effectively. Injectable IC formulations and their scaffolds may provide solutions for applying ES into difficult to reach tissue types to enable tissue repair and regeneration. A better understanding of ES-mediated cell differentiation and associated molecular mechanisms including the immune response will allow standardization of procedures applicable for the next generation of regenerative medicine. ES, along with the use of IC scaffolds is more than sufficient for use as a treatment option for single tissue healing and may fulfill a role in interfacing multiple tissue types during the repair process.

3D bioprinting of cell-laden electroconductive MXene nanocomposite bioinks

MXenes, a new family of burgeoning two-dimensional (2D) transition metal carbides/nitrides, have been extensively explored in recent years owing to their outstanding properties such as a large specific surface area, high electrical conductivity, low toxicity, and biodegradability. Numerous efforts have been devoted to exploring MXenes for various biomedical applications such as cancer therapy, bioimaging, biosensing, and drug delivery. However, the potential application of MXene nanosheets in tissue engineering has been almost overlooked despite their excellent performance in other biomedical applications. The overarching goal of this paper is to demonstrate the potential of MXene cell-laden bioinks for tissue engineering and their ability to assemble functional scaffolds to regenerate damaged tissue via 3D bioprinting. We formulate a new electroconductive cell-laden bioink composed of Ti3C2 MXene nanosheets dispersed homogeneously within hyaluronic acid/alginate (HA/Alg) hydrogels and showed its performance for extrusion-based 3D bioprinting. The prepared hydrogel bioinks with MXenes display excellent rheological properties, which allows the fabrication of multilayered 3D structures with high resolution and shape retention. Moreover, the introduction of Ti3C2 MXene nanosheets within the HA/Alg hydrogel introduces electrical conductivity to the ink, addressing the poor electrical conductivity of the current bioinks that mismatch with the physico-chemical properties of tissue. In addition, the MXene nanocomposite ink with encapsulated Human Embryonic Kidney 293 (HEK-293) cells displayed high cell viability (>95%) in both bulk hydrogel and 3D bioprinted structures. These results suggest that MXene nanocomposite bioinks and their 3D bioprinting with high electrical conductivity, biocompatibility and degradability can synergize some new applications for tissue and neural engineering.

Three-Dimensional Printing Constructs Based on the Chitosan for Tissue Regeneration: State of the Art, Developing Directions and Prospect Trends

Chitosan (CS) has gained particular attention in biomedical applications due to its biocompatibility, antibacterial feature, and biodegradability. Hence, many studies have focused on the manufacturing of CS films, scaffolds, particulate, and inks via different production methods. Nowadays, with the possibility of the precise adjustment of porosity size and shape, fiber size, suitable interconnectivity of pores, and creation of patient-specific constructs, 3D printing has overcome the limitations of many traditional manufacturing methods. Therefore, the fabrication of 3D printed CS scaffolds can lead to promising advances in tissue engineering and regenerative medicine. A review of additive manufacturing types, CS-based printed constructs, their usages as biomaterials, advantages, and drawbacks can open doors to optimize CS-based constructions for biomedical applications. The latest technological issues and upcoming capabilities of 3D printing with CS-based biopolymers for different applications are also discussed. This review article will act as a roadmap aiming to investigate chitosan as a new feedstock concerning various 3D printing approaches which may be employed in biomedical fields. In fact, the combination of 3D printing and CS-based biopolymers is extremely appealing particularly with regard to certain clinical purposes. Complications of 3D printing coupled with the challenges associated with materials should be recognized to help make this method feasible for wider clinical requirements. This strategy is currently gaining substantial attention in terms of several industrial biomedical products. In this review, the key 3D printing approaches along with revealing historical background are initially presented, and ultimately, the applications of different 3D printing techniques for fabricating chitosan constructs will be discussed. The recognition of essential complications and technical problems related to numerous 3D printing techniques and CS-based biopolymer choices according to clinical requirements is crucial. A comprehensive investigation will be required to encounter those challenges and to completely understand the possibilities of 3D printing in the foreseeable future.

Electrically Conducting Hydrogels for Health care: Concept, Fabrication Methods, and Applications

Electrically conducting hydrogels are gaining increasing attention due to their potential application in smart patches, biosensors, functional tissue engineering scaffolds, wound management, and implants. The current review focuses on these novel materials, their synthesis routes, and their composites. Special attention is paid to fabrication routes to produce functional composites with organic and inorganic components. The design of conductive hydrogels leads to inheritance of the advantages of each component and offers new features from the synergistic effects between the components, thus opening new application areas. The review also discusses the emerging role of 3D printing as an advanced approach toward new design, functionality, and material combination possibilities. The issue of lack of the spatial control with current techniques is highlighted, and possible new routes to solve it are discussed. The review will provide readers with knowledge tool to select appropriate methodology for designing desired hydrogel material composites.

Design and fabrication of clinoptilolite-nanohydroxyapatite/chitosan-gelatin composite scaffold and evaluation of its effects on bone tissue engineering

The aim of this study was to synthesize an innovative composite scaffold, which structured of clinoptilolite-nanohydroxyapatite/chitosan-gelatin (CLN-nHA/CS-G) with enhanced attributes for utilization in the bone tissue engineering. This composite scaffold was prepared by blending the CLN, nHA, chitosan, and gelatin solution followed by a freeze-drying step. The fabricated composite scaffolds were studied using BET, FTIR, XRD, and SEM techniques. The highly porous composite scaffolds with a pore size of 200 ± 100 μm were synthesized. Moreover, the effects of CLN and nHA on the physicochemical features of the scaffold such as density, swelling ratio, biomineralization, biodegradation, and mechanical behavior were studied. Compared with CS-G scaffold, the presence of CLN and nHA leads to an increased surface area, increased biomineralization, and low rate of degradation in simulated body fluid solution (SBF) and mechanical strength. Cytotoxicity of the CLN-nHA/CS-G scaffold was studied by MTT assay on human dental pulp stem cells (h-DPSCs). The biological response of h-DPSCs showed no toxicity and studied cells proliferated and attached on the pore surfaces of the scaffold. Results indicated that introducing CLN and nHA to composite improves the scaffold characteristics in a way that makes it suitable for bone tissue engineering.

From design to applications of stimuli-responsive hydrogel strain sensors

Stimuli-responsive hydrogel strain sensors that synergize the advantages of both hydrogel and smart functional materials have attracted increasing interest from material design to emerging applications in health monitors and human–machine interfaces.