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

Stiffness-tunable biomaterials provide a good extracellular matrix environment for axon growth and regeneration

Neuronal growth, extension, branching, and formation of neural networks are markedly influenced by the extracellular matrix-a complex network composed of proteins and carbohydrates secreted by cells. In addition to providing physical support for cells, the extracellular matrix also conveys critical mechanical stiffness cues. During the development of the nervous system, extracellular matrix stiffness plays a central role in guiding neuronal growth, particularly in the context of axonal extension, which is crucial for the formation of neural networks. In neural tissue engineering, manipulation of biomaterial stiffness is a promising strategy to provide a permissive environment for the repair and regeneration of injured nervous tissue. Recent research has fine-tuned synthetic biomaterials to fabricate scaffolds that closely replicate the stiffness profiles observed in the nervous system. In this review, we highlight the molecular mechanisms by which extracellular matrix stiffness regulates axonal growth and regeneration. We highlight the progress made in the development of stiffness-tunable biomaterials to emulate in vivo extracellular matrix environments, with an emphasis on their application in neural repair and regeneration, along with a discussion of the current limitations and future prospects. The exploration and optimization of the stiffness-tunable biomaterials has the potential to markedly advance the development of neural tissue engineering.

Advanced Hydrogels: Enhancing Tissue Bioengineering with RGD Peptides and Carbon Nanomaterials

The advancement of tissue engineering (TE) is driven by the development of scaffolds that mimic the mechanical, spatial, and biological environment of the extracellular matrix (ECM), crucial for regulating cell behavior and tissue repair. Hydrogels, 3D networks of polymer chains, are particularly suited for TE due to their high biocompatibility, ability to mimic tissue water content, facilitate cell migration, sustain growth factor release, and offer controllable physical properties. However, hydrogels mimicking the ECM often face challenges related to cell adhesion due to the absence of specific receptors. This issue can be addressed by incorporating ECM components into the polymer matrix, such as the peptide sequence arginine-glycine-aspartic acid (RGD), known for its role in cell adhesion. Additionally, carbon nanomaterials (CNMs) offer unique physicochemical properties that can improve scaffold-cell interactions. Despite the potential benefits, there are limited reports on their combination. RGD-CNM hydrogels enable a more accurate emulation of the natural cellular environment, enhancing tissue engineering applications. This hybrid approach may promote robust cell adhesion along with exceptional mechanical and electrical properties. This review outlines the potential benefits of these hybrid scaffolds and their synergistic potential, aiming to inspire new research directions in this innovative field.

Fundamentals and Applications of Raman-Based Techniques for the Design and Development of Active Biomedical Materials

Raman spectroscopy is an analytical method based on light-matter interactions that can interrogate the vibrational modes of matter and provide representative molecular fingerprints. Mediated by its label-free, non-invasive nature, and high molecular specificity, Raman-based techniques have become ubiquitous tools for in situ characterization of materials. This review comprehensively describes the theoretical and practical background of Raman spectroscopy and its advanced variants. The numerous facets of material characterization that Raman scattering can reveal, including biomolecular identification, solid-to-solid phase transitions, and spatial mapping of biomolecular species in bioactive materials, are highlighted. The review illustrates the potential of these techniques in the context of active biomedical material design and development by highlighting representative studies from the literature. These studies cover the use of Raman spectroscopy for the characterization of both natural and synthetic biomaterials, including engineered tissue constructs, biopolymer systems, ceramics, and nanoparticle formulations, among others. To increase the accessibility and adoption of these techniques, the present review also provides the reader with practical recommendations on the integration of Raman techniques into the experimental laboratory toolbox. Finally, perspectives on how recent developments in plasmon- and coherently-enhanced Raman spectroscopy can propel Raman from underutilized to critical for biomaterial development are provided.

Integrating Graphene Oxide-Hydrogels and Electrical Stimulation for Controlled Neurotrophic Factor Encapsulation: A Promising Approach for Efficient Nerve Tissue Regeneration

Nerve growth factor (NGF) plays a crucial role in cellular growth and neurodifferentiation. To achieve significant neuronal regeneration and repair using in vitro NGF delivery, spatiotemporal control that follows the natural neuronal processes must be developed. Notably, a challenge hindering this is the uncontrolled burst release from the growth factor delivery systems. The rapid depletion of NGF reduces treatment efficacy, leading to poor cellular response. To address this, we developed a highly controllable system using graphene oxygen (GO) and GelMA hydrogels modulated by electrical stimulation. Our system showed superior control over the release kinetics, reducing the burst up 30-fold. We demonstrate that the system is also able to sequester and retain NGF up to 10-times more efficiently than GelMA hydrogels alone. Our controlled release system enabled neurodifferentiation, as revealed by gene expression and immunostaining analysis. The increased retention and reduced burst release from our system show a promising pathway for nerve tissue engineering research toward effective regeneration.

Influence of Graphene-Based Nanocomposites in Neurogenesis and Neuritogenesis: A Brief Summary

Graphene is a prospective candidate for various biomedical applications, including drug transporters, bioimaging agents, and scaffolds for tissue engineering, thanks to its superior electrical conductivity and biocompatibility. The clinical issue of nerve regeneration and rehabilitation still has a major influence on people's lives. Nanomaterials based on graphene have been exploited extensively to promote nerve cell differentiation and proliferation. Their high electrical conductivity and mechanical robustness make them appropriate for nerve tissue engineering. Combining graphene with other substances, such as biopolymers, may transmit biochemical signals that support brain cell division, proliferation, and regeneration. The utilization of nanocomposites based on graphene in neurogenesis and neuritogenesis is the primary emphasis of this review. Here are some examples of the many synthetic strategies used. For neuritogenesis and neurogenesis, it has also been explored to combine electrical stimulation with graphene-based materials.

Micro- and Nanostructured Fibrous Composites via Electro-Fluid Dynamics: Design and Applications for Brain

The brain consists of an interconnected network of neurons tightly packed in the extracellular matrix (ECM) to form complex and heterogeneous composite tissue. According to recent biomimicry approaches that consider biological features as active components of biomaterials, designing a highly reproducible microenvironment for brain cells can represent a key tool for tissue repair and regeneration. Indeed, this is crucial to support cell growth, mitigate inflammation phenomena and provide adequate structural properties needed to support the damaged tissue, corroborating the activity of the vascular network and ultimately the functionality of neurons. In this context, electro-fluid dynamic techniques (EFDTs), i.e., electrospinning, electrospraying and related techniques, offer the opportunity to engineer a wide variety of composite substrates by integrating fibers, particles, and hydrogels at different scales-from several hundred microns down to tens of nanometers-for the generation of countless patterns of physical and biochemical cues suitable for influencing the in vitro response of coexistent brain cell populations mediated by the surrounding microenvironment. In this review, an overview of the different technological approaches-based on EFDTs-for engineering fibrous and/or particle-loaded composite substrates will be proposed. The second section of this review will primarily focus on describing current and future approaches to the use of composites for brain applications, ranging from therapeutic to diagnostic/theranostic use and from repair to regeneration, with the ultimate goal of providing insightful information to guide future research efforts toward the development of more efficient and reliable solutions.

Optimization of 3D Synthetic Scaffolds for Neuronal Tissue Engineering Applications

The increasing prevalence of neurodegenerative diseases has spurred researchers to develop advanced 3D models that accurately mimic neural tissues. Hydrogels stand out as ideal candidates as their properties closely resemble those of the extracellular matrix. A critical challenge in this regard is to comprehend the influence of the scaffold's mechanical properties on cell growth and differentiation, thus enabling targeted modifications. In light of this, a synthesis and comprehensive analysis of acrylamide-based hydrogels incorporating a peptide has been conducted. Adequate cell adhesion and development is achieved due to their bioactive nature and specific interactions with cellular receptors. The integration of a precisely controlled physicochemical hydrogel matrix and inclusion of the arginine-glycine-aspartic acid peptide sequence has endowed this system with an optimal structure, thus providing a unique ability to interact effectively with biomolecules. The analysis fully examined essential properties governing cell behavior, including pore size, mechanical characteristics, and swelling ability. Cell-viability experiments were performed to assess the hydrogel's biocompatibility, while the incorporation of grow factors aimed to promote the differentiation of neuroblastoma cells. The results underscore the hydrogel's ability to stimulate cell viability and differentiation in the presence of the peptide within the matrix.

Graphene derivative based hydrogels in biomedical applications

Graphene and its derivatives are widely used in tissue-engineering scaffolds, especially in the form of hydrogels. This is due to their biocompatibility, electrical conductivity, high surface area, and physicochemical versatility. They are also used in tissue engineering. Tissue engineering is suitable for 3D printing applications, and 3D printing makes it possible to construct 3D structures from 2D graphene, which is a revolutionary technology with promising applications in tissue and organ engineering. In this review, the recent literature in which graphene and its derivatives have been used as the major components of hydrogels is summarized. The application of graphene and its derivative-based hydrogels in tissue engineering is described in detail from different perspectives.

Fast Visible-Light 3D Printing of Conductive PEDOT:PSS Hydrogels

Functional inks for light-based 3D printing are actively being searched for being able to exploit all the potentialities of additive manufacturing. Herein, a fast visible-light photopolymerization process is showed of conductive PEDOT:PSS hydrogels. For this purpose, a new Type II photoinitiator system (PIS) based on riboflavin (Rf), triethanolamine (TEA), and poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) is investigated for the visible light photopolymerization of acrylic monomers. PEDOT:PSS has a dual role by accelerating the photoinitiation process and providing conductivity to the obtained hydrogels. Using this PIS, full monomer conversion is achieved in less than 2 min using visible light. First, the PIS mechanism is studied, proposing that electron transfer between the triplet excited state of the dye (3 Rf*) and the amine (TEA) is catalyzed by PEDOT:PSS. Second, a series of poly(2-hydroxyethyl acrylate)/PEDOT:PSS hydrogels with different compositions are obtained by photopolymerization. The presence of PEDOT:PSS negatively influences the swelling properties of hydrogels, but significantly increases its mechanical modulus and electrical properties. The new PIS is also tested for 3D printing in a commercially available Digital Light Processing (DLP) 3D printer (405 nm wavelength), obtaining high resolution and 500 µm hole size conductive scaffolds.

Enhanced Stability of Dopamine Delivery via Hydrogel with Integrated Graphene

The synthesis of graphene-based materials for drug delivery represents an area of active research, and the use of graphene in drug delivery systems is promising due to its unique properties. Thus, in the present work, we discuss the potential of few-layer graphene in a hydrogel system for dopamine release. The hydrogels are frequently used for these systems for their special physico-chemical properties, which can ensure that the drug is effectively released in time. However, the release from such structures is mostly determined by diffusion alone, and to overcome this restriction, the hydrogel can be "improved" with nanoscale fillers like graphene. The release kinetics of the composite obtained were analyzed to better understand how the use of graphene, instead of the more common graphene oxide (GO) and reduced graphene oxide (rGO), affects the characteristics of the system. Thus, the systems developed in this study consist of three main components: biopolymer, graphene, and dopamine. The hydrogels with graphene were prepared by combining two different solutions, one with polyacrylic acid and agarose and one with graphene prepared by the exfoliation method with microwave irradiation. The drug delivery systems were developed by adding dopamine to the obtained hydrogels. After 24 h of release, the presence of dopamine was observed, demonstrating that the system developed can slow down the drug's degradation because of the interactions with the graphene nanoplates and the polymer matrix.

Mimicking the extracellular matrix by incorporating functionalized graphene into hybrid hydrogels

The efficient functionalization of graphene with sulfonic groups using a sustainable approach facilitates the interaction of biomolecules with its surface. The inclusion of these graphene sheets inside a photopolymerized acrylamide-based hydrogel provides a 3D scaffold with viscoelastic behaviour closer to that found in natural tissues. Cell-culture experiments and differentiation assays with SH-SY5Y cells showed that these hybrid hydrogels are non-cytotoxic, thus making them potentially useful as scaffold materials mimicking the extracellular environment.

Reinforcement of Acrylamide Hydrogels with Cellulose Nanocrystals Using Gamma Radiation for Antibiotic Drug Delivery

In this paper, we report the synthesis of acrylamide hydrogels (net-AAm) reinforced with cellulose nanocrystals (CNCs) using gamma radiation, a powerful tool to obtain crosslinked polymers without the use of chemical initiators and crosslinking agents. Some slight changes in the chemical structure and crystallinity of CNCs took place during gamma irradiation without affecting the nanofiller function. In fact, cellulose nanocrystals had a notable influence over the swelling and mechanical properties on the reinforced hydrogels (net-AAm/CNC), obtaining more rigid material since the Young compression modulus increased from 11 kPa for unreinforced net-AAm to 30 kPa for net-AAm/CNC (4% w/w). Moreover, the studies of retention and release of ciprofloxacin (Cx), a quinolone antibiotic drug, showed that reinforced hydrogels were able to load large amounts of ciprofloxacin (1.2-2.8 mg g-1) but they distributed 100% of the drug very quickly (<100 min). Despite this, they exhibited better mechanical properties than the control sample, allowing their handling, and could be used as wound dressings of first response because they can absorb the exudate and at the same time deliver an antibiotic drug directly over the injury.

Physical mechanisms of emerging neuromodulation modalities

One of the ultimate goals of neurostimulation field is to design materials, devices and systems that can simultaneously achieve safe, effective and tether-free operation. For that, understanding the working mechanisms and potential applicability of neurostimulation techniques is important to develop noninvasive, enhanced, and multi-modal control of neural activity. Here, we review direct and transduction-based neurostimulation techniques by discussing their interaction mechanisms with neurons via electrical, mechanical, and thermal means. We show how each technique targets modulation of specific ion channels (e.g. voltage-gated, mechanosensitive, heat-sensitive) by exploiting fundamental wave properties (e.g. interference) or engineering nanomaterial-based systems for efficient energy transduction. Overall, our review provides a detailed mechanistic understanding of neurostimulation techniques together with their applications toin vitro, in vivo, and translational studies to guide the researchers toward developing more advanced systems in terms of noninvasiveness, spatiotemporal resolution, and clinical applicability.

Plasma-Derived Fibrin Hydrogels Containing Graphene Oxide for Infections Treatment

Wound infection is inevitable in most patients suffering from extensive burns or chronic ulcers, and there is an urgent demand for the production of bactericidal dressings to be used as grafts to restore skin functionalities. In this context, the present study explores the fabrication of plasma-derived fibrin hydrogels containing bactericidal hybrids based on graphene oxide (GO). The hydrogels were fully characterized regarding gelation kinetics, mechanical properties, and internal hydrogel structures by disruptive cryo scanning electron microscopies (cryo-SEMs). The gelation kinetic experiments revealed an acceleration of the gel formation when GO was added to the hydrogels in a concentration of up to 0.2 mg/mL. The cryo-SEM studies showed up a decrease of the pore size when GO was added to the network, which agreed with a faster area contraction and a higher compression modulus of the hydrogels that contained GO, pointing out the critical structural role of the nanomaterial. Afterward, to study the bactericidal ability of the gels, GO was used as a carrier, loading streptomycin (STREP) on its surface. The loading content of the drug to form the hybrid (GO/STREP) resulted in 50.2% ± 4.7%, and the presence of the antibiotic was also demonstrated by Raman spectroscopy, Z-potential studies, and thermogravimetric analyses. The fibrin-derived hydrogels containing GO/STREP showed a dose-response behavior according to the bactericidal hybrid concentration and allowed a sustained release of the antibiotic at a programmed rate, leading to drug delivery over a prolonged period of time.

TEGylated Double-Walled Carbon Nanotubes as Platforms to Engineer Neuronal Networks

In the past two decades, important results have been obtained on the application of carbon nanotubes (CNTs) as components of smart interfaces promoting neuronal growth and differentiation. Different forms of CNTs have been employed as scaffolds, including raw CNTs and functionalized CNTs, characterized by a different number of walls, mainly single-walled CNTs (SWCNTs) or multiwalled CNTs (MWCNTs). However, double-walled carbon nanotubes (DWCNTs), which present interesting electronic and transport properties, have barely been studied in the field. Apart from the electrical conductivity, the morphology, shape, porosity, and corresponding mechanical properties of the scaffold material are important parameters when dealing with neuronal cells. Thus, the presence of open porous and interconnected networks is essential for cell growth and differentiation. Here, we present an easy methodology to prepare porous self-standing and electrically conductive DWCNT-based scaffolds and study the growth of neuro/glial networks and their synaptic activity. A cross-linking approach with triethylene glycol (TEG) derivatives is applied to improve the tensile performance of the scaffolds while neuronal growth and differentiation are promoted. By testing different DWCNT-based constructs, we confirm that the manufactured structures guarantee a biocompatible scaffold, while favoring the design of artificial networks with high complexity.

Functional Two-Dimensional Materials for Bioelectronic Neural Interfacing

Realizing the neurological information processing by analyzing the complex data transferring behavior of populations and individual neurons is one of the fast-growing fields of neuroscience and bioelectronic technologies. This field is anticipated to cover a wide range of advanced applications, including neural dynamic monitoring, understanding the neurological disorders, human brain-machine communications and even ambitious mind-controlled prosthetic implant systems. To fulfill the requirements of high spatial and temporal resolution recording of neural activities, electrical, optical and biosensing technologies are combined to develop multifunctional bioelectronic and neuro-signal probes. Advanced two-dimensional (2D) layered materials such as graphene, graphene oxide, transition metal dichalcogenides and MXenes with their atomic-layer thickness and multifunctional capabilities show bio-stimulation and multiple sensing properties. These characteristics are beneficial factors for development of ultrathin-film electrodes for flexible neural interfacing with minimum invasive chronic interfaces to the brain cells and cortex. The combination of incredible properties of 2D nanostructure places them in a unique position, as the main materials of choice, for multifunctional reception of neural activities. The current review highlights the recent achievements in 2D-based bioelectronic systems for monitoring of biophysiological indicators and biosignals at neural interfaces.

Recent progress of electroactive interface in neural engineering

Neural tissue is an electrical responsible organ. The electricity plays a vital role in the growth and development of nerve tissue, as well as the repairing after diseases. The interface between the nervous system and external device for information transmission is called neural electroactive interface. With the development of new materials and fabrication technologies, more and more new types of neural interfaces are developed and the interfaces can play crucial roles in treating many debilitating diseases such as paralysis, blindness, deafness, epilepsy, and Parkinson's disease. Neural interfaces are developing toward flexibility, miniaturization, biocompatibility, and multifunctionality. This review presents the development of neural electrodes in terms of different materials for constructing electroactive neural interfaces, especially focus on the piezoelectric materials-based indirect neuromodulation due to their features of wireless control, excellent effect, and good biocompatibility. We discussed the challenges we need to consider before the application of these new interfaces in clinical practice. The perspectives about future directions for developing more practical electroactive interface in neural engineering are also discussed in this review. This article is categorized under: Implantable Materials and Surgical Technologies > Nanomaterials and Implants Implantable Materials and Surgical Technologies > Nanotechnology in Tissue Repair and Replacement.

Polyacrylamide/poly(2-(dimethylamino) Ethyl Methacrylate) Interpenetrating Polymer Networks as Drug Delivery Systems for Diclofenac Sodium

Nowadays, modern pharmaceutical investigations are directed toward the design and production of drug delivery systems for achieving prolonged and controlled drug delivery. In this respect, the use of interpenetrating polymer networks (IPNs) is an opportunity in the preparation of polymer drug delivery systems with desired characteristics. This paper describes the synthesis and characterization of novel poly(2-(dimethylamino) ethyl methacrylate) (PDMAEMA) and polyacrylamide (PAAm)-based IPNs with different compositions and their application as diclofenac sodium delivery systems. The prepared IPNs were shown to possess phase-separated structures at the nano level, as revealed by SEM and TM-DSC. The IPNs' composition was shown to determine the swelling behavior of these novel materials, and the inclusion of the charged IPN component (PDMAEMA) has changed the water molecules type diffusion from Fickian to non-Fickian, as revealed by the swelling kinetics study. Loading efficiency of diclofenac sodium and diclofenac sodium content in the polymer network was evaluated, and in vitro drug release experiments were carried out in order to estimate the ability of the obtained IPNs to control the release of the water-soluble drug.

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.

Application of Graphene Oxide-Based Hydrogels in Bone Tissue Engineering

As an important derivative of graphene-based materials, graphene oxide (GO) not only plays an important role not only in optoelectronics and sensing but also in biology due to its unique mechanical, electronic, and optical properties. This article reviews the application of GO-based hydrogels in bone tissue engineering. Whether it is a hydrogel synthesized with natural polymer compounds, synthetic polymer chemicals, bioceramics, bioactive factors, or other materials, the addition of GO can significantly improve various properties of the hydrogel. We also introduce some high-performance GO-based hydrogels in this paper, proposing some insights into materials that may be applied to bone tissue engineering in the future.

Natural-clay-reinforced hydrogel adsorbent: Rapid adsorption of heavy-metal ions and dyes from textile wastewater

In this study, two natural clay minerals were combined with hydrogels to study the influence of natural adsorbents on the adsorption performance of hydrogels. Here, we separately doped bentonite and vermiculite and discussed their mechanical properties and adsorption properties. It was found that the compressive performance of the hydrogel added with clay increased by 21.6% and the swelling performance decreased or increased to varying degrees. Regarding the adsorption performance of hydrogels, it can be seen from the adsorption Langmuir isotherm model that the adsorption capacity of clay-hydrogels is improved to varying degrees (6.6%-15.8%) compared with non-clay-hydrogels, and clay-hydrogels have different degrees of improvement (6.6%-15.8%). The hydrogel has a removal efficiency of more than 95% for low concentrations of heavy-metal ions and dyes. In addition, the clay-hydrogel has low cost and is easy to prepare, and can be recycled many times. Therefore, the material is of great significance for the treatment of pollutants. PRACTITIONER POINTS: The effect of natural clay on the adsorption performance of hydrogels was studied. Clay can enhance the compression and adsorption properties of hydrogels. The adsorption mechanism and adsorption capacity of clay hydrogels were evaluated.

Engineering Tissues of the Central Nervous System: Interfacing Conductive Biomaterials with Neural Stem/Progenitor Cells

Conductive biomaterials provide an important control for engineering neural tissues, where electrical stimulation can potentially direct neural stem/progenitor cell (NS/PC) maturation into functional neuronal networks. It is anticipated that stem cell-based therapies to repair damaged central nervous system (CNS) tissues and ex vivo, "tissue chip" models of the CNS and its pathologies will each benefit from the development of biocompatible, biodegradable, and conductive biomaterials. Here, technological advances in conductive biomaterials are reviewed over the past two decades that may facilitate the development of engineered tissues with integrated physiological and electrical functionalities. First, one briefly introduces NS/PCs of the CNS. Then, the significance of incorporating microenvironmental cues, to which NS/PCs are naturally programmed to respond, into biomaterial scaffolds is discussed with a focus on electrical cues. Next, practical design considerations for conductive biomaterials are discussed followed by a review of studies evaluating how conductive biomaterials can be engineered to control NS/PC behavior by mimicking specific functionalities in the CNS microenvironment. Finally, steps researchers can take to move NS/PC-interfacing, conductive materials closer to clinical translation are discussed.

3D Neuronal Cell Culture Modeling Based on Highly Porous Ultra-High Molecular Weight Polyethylene

Cell culturing methods in its classical 2D approach have limitations associated with altered cell morphology, gene expression patterns, migration, cell cycle and proliferation. Moreover, high throughput drug screening is mainly performed on 2D cell cultures which are physiologically far from proper cell functions resulting in inadequate hit-compounds which subsequently fail. A shift to 3D culturing protocols could solve issues with altered cell biochemistry and signaling which would lead to a proper recapitulation of physiological conditions in test systems. Here, we examined porous ultra-high molecular weight polyethylene (UHMWPE) as an inexpensive and robust material with varying pore sizes for cell culturing. We tested and developed culturing protocols for immortalized human neuroblastoma and primary mice hippocampal cells which resulted in high rate of cell penetration within one week of cultivation. UHMWPE was additionally functionalized with gelatin, poly-L-lysine, BSA and chitosan, resulting in increased cell penetrations of the material. We have also successfully traced GFP-tagged cells which were grown on a UHMWPE sample after one week from implantation into mice brain. Our findings highlight the importance of UHMWPE use as a 3D matrix and show new possibilities arising from the use of cheap and chemically homogeneous material for studying various types of cell-surface interactions further improving cell adhesion, viability and biocompatibility.

Application of Graphene in Tissue Engineering of the Nervous System

Graphene is the thinnest two-dimensional (2D), only one carbon atom thick, but one of the strongest biomaterials. Due to its unique structure, it has many unique properties used in tissue engineering of the nervous system, such as high strength, flexibility, adequate softness, electrical conductivity, antibacterial effect, and the ability to penetrate the blood-brain barrier (BBB). Graphene is also characterized by the possibility of modifications that allow for even wider application and adaptation to cell cultures of specific cells and tissues, both in vitro and in vivo. Moreover, by using the patient's own cells for cell culture, it will be possible to produce tissues and organs that can be re-transplanted without transplant rejection, the negative effects of taking immunosuppressive drugs, and waiting for an appropriate organ donor.

An Update on Graphene-Based Nanomaterials for Neural Growth and Central Nervous System Regeneration

Thanks to their reduced size, great surface area, and capacity to interact with cells and tissues, nanomaterials present some attractive biological and chemical characteristics with potential uses in the field of biomedical applications. In this context, graphene and its chemical derivatives have been extensively used in many biomedical research areas from drug delivery to bioelectronics and tissue engineering. Graphene-based nanomaterials show excellent optical, mechanical, and biological properties. They can be used as a substrate in the field of tissue engineering due to their conductivity, allowing to study, and educate neural connections, and guide neural growth and differentiation; thus, graphene-based nanomaterials represent an emerging aspect in regenerative medicine. Moreover, there is now an urgent need to develop multifunctional and functionalized nanomaterials able to arrive at neuronal cells through the blood-brain barrier, to manage a specific drug delivery system. In this review, we will focus on the recent applications of graphene-based nanomaterials in vitro and in vivo, also combining graphene with other smart materials to achieve the best benefits in the fields of nervous tissue engineering and neural regenerative medicine. We will then highlight the potential use of these graphene-based materials to construct graphene 3D scaffolds able to stimulate neural growth and regeneration in vivo for clinical applications.

X-ray tomography analysis reveals the influence of graphene on porous morphology of collagen cryogels

X-ray micro-tomography based analysis of porous hydrogel has gained a wide attention recently. It provides an advantage in three-dimensional analysis of pore morphometric and interconnection within the hydrogel network. We have fabricated highly elastic graphene crosslinked collagen hydrogel using cryogelation technique. The influence of graphene as a nano-crosslinker on the overall porosity and inter-connections between the pores in collagen cryogels was determined using X-ray micro-tomography. We have evaluated the effect of different concentration of amino-functionalized graphene nano-crosslinker on collagen cryogels porosity, pore volume, interconnectivity density, fractal dimensions and pore wall thickness. This study, reveals that the use of graphene as a nano-crosslinker have improved micro-architecture as compare to collagen cryogels in the absence of graphene for tissue engineering applications.

Tissue-like skin-device interface for wearable bioelectronics by using ultrasoft, mass-permeable, and low-impedance hydrogels

Hydrogels consist of a cross-linked porous polymer network and water molecules occupying the interspace between the polymer chains. Therefore, hydrogels are soft and moisturized, with mechanical structures and physical properties similar to those of human tissue. Such hydrogels have a potential to turn the microscale gap between wearable devices and human skin into a tissue-like space. Here, we present material and device strategies to form a tissue-like, quasi-solid interface between wearable bioelectronics and human skin. The key material is an ultrathin type of functionalized hydrogel that shows unusual features of high mass-permeability and low impedance. The functionalized hydrogel acted as a liquid electrolyte on the skin and formed an extremely conformal and low-impedance interface for wearable electrochemical biosensors and electrical stimulators. Furthermore, its porous structure and ultrathin thickness facilitated the efficient transport of target molecules through the interface. Therefore, this functionalized hydrogel can maximize the performance of various wearable bioelectronics.

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.

Electrophysiology Read-Out Tools for Brain-on-Chip Biotechnology

Brain-on-Chip (BoC) biotechnology is emerging as a promising tool for biomedical and pharmaceutical research applied to the neurosciences. At the convergence between lab-on-chip and cell biology, BoC couples in vitro three-dimensional brain-like systems to an engineered microfluidics platform designed to provide an in vivo-like extrinsic microenvironment with the aim of replicating tissue- or organ-level physiological functions. BoC therefore offers the advantage of an in vitro reproduction of brain structures that is more faithful to the native correlate than what is obtained with conventional cell culture techniques. As brain function ultimately results in the generation of electrical signals, electrophysiology techniques are paramount for studying brain activity in health and disease. However, as BoC is still in its infancy, the availability of combined BoC-electrophysiology platforms is still limited. Here, we summarize the available biological substrates for BoC, starting with a historical perspective. We then describe the available tools enabling BoC electrophysiology studies, detailing their fabrication process and technical features, along with their advantages and limitations. We discuss the current and future applications of BoC electrophysiology, also expanding to complementary approaches. We conclude with an evaluation of the potential translational applications and prospective technology developments.

On-Demand Hydrophobic Drug Release Based on Microwave-Responsive Graphene Hydrogel Scaffolds

Electromagnetically driven drug delivery systems stand out among stimulus-responsive materials due to their ability to release cargo on demand by remote stimulation, such as light, near infrared (NIR) or microwave (MW) radiation. MW-responsive soft materials, such as hydrogels, generally operate at 2.45 GHz frequencies, which usually involves rapid overheating of the scaffold and may affect tissue surrounding the target location. In contrast, 915 MHz MW penetrate deeper tissues and are less prone to induce rapid overheating. In order to circumvent these limitations, we present here for the first time a graphene-based hydrogel that is responsive to MW irradiation of ν=915 MHz. This system is a candidate soft scaffold to deliver a model hydrophobic drug. The graphene present in the hydrogel acts as a heat-sink and avoids overheating of the scaffold upon MW irradiation. In addition, the microwave trigger stimulates the in vitro delivery of the model drug, thus suggesting a remote and deep-penetrating means to deliver a drug from a delivery reservoir. Moreover, the MW-triggered release of drug was observed to be enhanced under acidic conditions, where the swelling state is maximum due to the swelling-induced pH-responsiveness of the hydrogel. The hybrid composite described here is a harmless means to deliver remotely a hydrophobic drug on demand with a MW source of 915 MHz. Potential use in biomedical applications were evaluated by cytotoxicity tests.

Composite Hydrogel of Poly(acrylamide) and Starch as Potential System for Controlled Release of Amoxicillin and Inhibition of Bacterial Growth

Novel composite hydrogels of poly(acrylamide) (PAAm) and starch, at different ratios, were studied as potential platforms for controlled release of amoxicillin. The composite hydrogels were characterized by Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDX), and swelling kinetic measurements. The morphology analysis revealed the presence of starch granules well embedded within the PAAm network. The increase in starch content increased the rate of water uptake and the swelling degree at equilibrium. The amoxicillin release kinetics was sensitive to pH and temperature conditions. The in vitro bacterial growth inhibition of antibiotic-loaded hydrogels was tested though disc diffusion assays with Escherichia coli ATCC 25922, Staphylococcus aureus ATCC 25923, and a carbapenemase producer Pseudomonas aeruginosa strain. The optimal release profile at physiological conditions and the powerful bacteria growth inhibition effects of amoxicillin-loaded hydrogels evidenced its potential for biomedical applications, particularly in oral administration and the local treatment of bacterial infections.

Novel carbon film induces precocious calcium oscillation to promote neuronal cell maturation

Different types of carbon materials are biocompatible with neural cells and can promote maturation. The mechanism of this effect is not clear. Here we have tested the capacity of a carbon material composed of amorphous sp³ carbon backbone, embedded with a percolating network of sp² carbon domains to sustain neuronal cultures. We found that cortical neurons survive and develop faster on this novel carbon material. After 3 days in culture, there is a precocious increase in the frequency of neuronal activity and in the expression of maturation marker KCC2 on carbon films as compared to a commonly used glass surface. Accelerated development is accompanied by a dramatic increase in neuronal dendrite arborization. The mechanism for the precocious maturation involves the activation of intracellular calcium oscillations by the carbon material already after 1 day in culture. Carbon-induced oscillations are independent of network activity and reflect intrinsic spontaneous activation of developing neurons. Thus, these results reveal a novel mechanism for carbon material-induced neuronal survival and maturation.

Near-infrared stimulated hydrogel patch for photothermal therapeutics and thermoresponsive drug delivery

Nanotechnology driven cancer theranostics hold potential as promising future clinical modalities. Currently, there is a strong emphasis on the development of combinational modalities, especially for cancer treatment. In this study, we present a topical hydrogel patch for nanomaterial-assisted photothermal therapeutics as well as for on-demand drug delivery application. The patch was derived from interpenetrating networks (IPNs) of alginate (Alg) and polyacrylamide (PAAm) in weight ratio 8:1 by free radical polymerization. The patch interiors were composed of hybrid nanostructures derived from gold nanorods (AuNRs) anchored onto polyvinylpyrrolidone (PVP) functionalized graphene oxide (PVP-nGO) to form PVP-nGO@AuNRs hybrids. Field emission scanning electron microscopy (FE-SEM) images revealed the porous nature of the hybrid hydrogel patch with an average pore size of ~28.60 ± 3.10 μm. Besides, functional characteristics of the hybrid patch, such as mechanical strength, viscoelastic and swelling behavior, were investigated. Under near-infrared (NIR) radiation exposure, the hybrid patch exhibited photothermal properties such as surface temperature rise to 75.16 ± 0.32 °C, sufficient to ablate cancer cells thermally. Besides, the heat generated in the hybrid patch could be transmitted to an underlying hydrogel (mimicking skin tissue) when stacked together without much loss. Under cyclic photothermal heating, the patch could retain its photothermal stability for four cycles. Furthermore, the hybrid patch demonstrated NIR stimulated drug release, which was evaluated using methotrexate (MTX, water-insoluble anticancer drug) and rhodamine B (RhB, water-soluble dye). Taken together, this work provides a new dimension towards the development of externally placed hydrogel patches for thermal destruction of localized solid tumors and tunable delivery of chemotherapeutic drugs at the target site.

Stimuli-responsive graphene-based hydrogel driven by disruption of triazine hydrophobic interactions

The study reported here concerns the preparation of a novel graphene-diaminotriazine (G-DAT) nanocomposite hydrogel for application in the drug delivery field. The hybrid nature of this material is founded on two key elements: the presence of the DAT backbone induced the formation of hydrophobic regions that allowed efficient loading of a series of drugs of increasing hydrophobicity (Metronidazole, Benzocaine, Ibuprofen, Naproxen and Imipramine), while simultaneously endowing swelling-induced pH-responsiveness to the hydrogel. Additionally, the incorporation of graphene was found to interfere with these hydrophobic domains through favourable non-covalent interactions, thus leading to the partial disruption of these aggregates. As a consequence, graphene facilitated and enhanced the release of model hydrophobic drug Imipramine in a synergistic manner with the pH trigger, and increased the swelling capacities and improved mechanical performance. This hybrid hydrogel can therefore be envisaged as a proof-of-concept system for the release of hydrophobic compounds in the field of drug delivery.

Electrospun poly(vinyl alcohol)/reduced graphene oxide nanofibrous scaffolds for skin tissue engineering

Graphene is composed of a two-dimensional (2D) layer of carbon atoms arranged in a honeycomb lattice configuration. In this paper, we adopted a green synthetic method of producing reduced graphene oxide using glucose as a reducing and stabilizing agent. We also investigated the fabrication of electrospun nanofibers of glucose-reduced graphene oxide (GRGO) (0-1.0 wt%) reinforced with polyvinyl alcohol (PVA) as (PG) scaffolds, and chemically crosslinked with acidic glutaraldehyde (GA) in acetone medium to mimic the extracellular matrix (ECM) for skin tissue engineering applications. These PG scaffolds were evaluated for morphology, mechanical strength, surface wettability, thermal properties, hemocompatibility, and biocompatibility. Field emission-scanning electron microscopy (FE-SEM) revealed an increase in the thickness of nanofibers in PG scaffolds with an increase in the concentration of GRGO. X-ray diffraction and attenuated total reflectance-infrared and Raman spectra showed the GRGO was incorporated in the PVA nanofibrous matrix. As the concentration of GRGO was increased in PG scaffolds, tensile strengths and elongations at break decreased, whereas thermal properties increased. The biological activities of PG scaffolds were evaluated using in vitro hemolysis, using CCD-986Sk (a human skin fibroblast cell line) viability and proliferation assays, and by live/dead cell imaging. Results showed GRGO inclusion in PVA nanofibers caused a slight hydrophilic to hydrophobic shift. PG scaffolds did not cause hemolysis of red blood cells even at a GRGO loading of 1.0 wt%, and PG-1.0 scaffold (with a GRGO loading of 1.0 wt%) exhibited excellent compatibility with fibroblasts and significantly increased metabolic activity after culture for 21 days as compared with PG-0 controls. DAPI staining and live/dead imaging assays showed that all PG scaffolds increased fibroblast proliferation and viability, indicating the potential for skin tissue engineering applications.

Synthesis of a polyacrylamide hydrogel using CO2 at room temperature

Carbon dioxide (CO2) is an environmentally harmful “greenhouse gas” that is present in abundant quantities in the earth’s atmosphere. Thus, the sequestration and conversion of CO2 to value-added organic chemicals is of environmental and economical importance. In this proof-of-concept study, amine groups of acrylamide compounds were found to react with CO2 under ambient conditions to form a polyacrylamide hydrogel. This composite was characterized using scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), transmission electron microscopy (TEM), Fourier-transform infrared spectroscopy (FTIR) and electrospray ionization mass spectrometry (ESI–MS), which confirmed successful synthesis and demonstrated all characteristics representative of a typical hydrogel material. Rheology analyses further proved the formation of the hydrogel, as well as its self-healing nature. The novel approach proposed in this work can potentially be used in the construction of versatile amine-based gel materials for efficient CO2 utilization applications.

Chemically Cross-Linked Carbon Nanotube Films Engineered to Control Neuronal Signaling

In recent years, the use of free-standing carbon nanotube (CNT) films for neural tissue engineering has attracted tremendous attention. CNT films show large surface area and high electrical conductivity that combined with flexibility and biocompatibility may promote neuron growth and differentiation while stimulating neural activity. In addition, adhesion, survival, and growth of neurons can be modulated through chemical modification of CNTs. Axonal and synaptic signaling can also be positively tuned by these materials. Here we describe the ability of free-standing CNT films to influence neuronal activity. We demonstrate that the degree of cross-linking between the CNTs has a strong impact on the electrical conductivity of the substrate, which, in turn, regulates neural circuit outputs.

Do biomedical engineers dream of graphene sheets?

During the past few years, graphene has outstandingly emerged as a key nanomaterial for boosting the performance of commercial, industrial and scientific related technologies. The popularity of this novel nanomaterial in biomedical engineering is due to its excellent biological, electronic, optical and thermal properties that, as a whole, surpass the features of commonly used biomaterials and consequently open a wide range of applications so far within the reach of science fiction. In this minireview, the potential of graphene and its based materials in the expanding biomedical field is highlighted with focus on groundbreaking diagnostic, monitoring and therapeutic strategies. Some of the major challenges related to the synthesis and safety of graphene-based materials are also briefly discussed because of their critical importance in bringing this class of carbon materials closer to the clinic.

Biofabrication of Lysinibacillus sphaericus-reduced graphene oxide in three-dimensional polyacrylamide/carbon nanocomposite hydrogels for skin tissue engineering

The biological synthesis of reduced graphene oxide (rGO) from graphene oxide (GO) is an emerging phenomenon for developing biocompatible nanomaterials for its potential applications in nanomedicine. In this study, we demonstrated a simple, green, and non-toxic method for graphene synthesis using the live biomass of Lysinibacillus sphaericus as the reducing and stabilizing agent under ambient conditions. Ultraviolet-visible spectroscopic analysis confirmed the formation of graphene from GO suspension. X-ray diffraction studies showed the disappearance of the GO peak and the appearance of characteristic graphene broad peak at 2θ = 22.8°. Infrared analysis showed the decrease/disappearance of peaks corresponding to the oxygen-containing functionalities, and appearance of a peak at 1620 cm^-1 from unoxidized graphitic domains. Scanning electron microscopic images showed that L. sphaericus-reduced graphene oxide (L-rGO) contains aggregated graphene nanoflakes. Evaluation of the in vitro cytotoxicity of L-rGO nanosheets on human skin fibroblasts using the WST-1 assay did not show any significant effects after 24 h of exposure, which is indicative of biocompatibility. Polyacrylamide hydrogels with L-rGO were synthesized and used as scaffolds to support the growth and proliferation of skin fibroblasts. Cell viability assays and DAPI staining showed proliferation of fibroblasts and exhibited 83% of cell viability even after 28 days. Biofilm formation by Pseudomonas aeruginosa and Staphylococcus aureus was enhanced in nanocomposite hydrogels in the presence of 0.25 mg/mL GO and L-rGO in 48 h. Overall, this study showed that microbially-synthesized L-rGO can be used as a dopant in polymeric scaffolds for tissue engineering and highlighted their role in biofilm formation.

Biocompatibility and biodegradability of 2D materials: graphene and beyond

The potential risks associated with two-dimensional (2D) nanomaterials may cause serious concerns about their real applications and impact in biological systems. In addition, the demonstration of biodegradability of these flat nanomaterials is essential in living organisms. Here, we summarise the state-of-the-art in the field of biocompatibility and biodegradability of graphene-related materials (such as 2D materials like MoS2, BN or WS2). The impact of chemical functionalisation on the potential control of the biodegradability profile of these structures is also discussed.