Surface plasma functionalization influences macrophage behavior on carbon nanowalls

Advancements in tailoring PEDOT: PSS properties for bioelectronic applications: A comprehensive review

In the field of bioelectronics, the demand for biocompatible, stable, and electroactive materials for functional biological interfaces, sensors, and stimulators, is drastically increasing. Conductive polymers (CPs) are synthetic materials, which are gaining increasing interest mainly due to their outstanding electrical, chemical, mechanical, and optical properties. Since its discovery in the late 1980s, the CP Poly(3,4-ethylenedioxythiophene):poly(styrene sulfonic acid) (PEDOT:PSS) has become extremely attractive, being considered as one of the most capable organic electrode materials for several bioelectronic applications in the field of tissue engineering and regenerative medicine. Main examples refer to thin, flexible films, electrodes, hydrogels, scaffolds, and biosensors. Within this context, the authors contend that PEDOT:PSS properties should be customized to encompass: i) biocompatibility, ii) conductivity, iii) stability in wet environment, iv) adhesion to the substrate, and, when necessary, v) (bio-)degradability. However, consolidating all these properties into a single functional solution is not always straightforward. Therefore, the objective of this review paper is to present various methods for acquiring and improving PEDOT:PSS properties, with the primary focus on ensuring its biocompatibility, and simultaneously addressing the other functional features. The last section highlights a collection of designated studies, with a particular emphasis on PEDOT:PSS/carbon filler composites due to their exceptional characteristics.

Plasma modification of carbon nanowalls induces transition from superhydrophobic to superhydrophilic

Graphene-based materials play an essential role in a wide range of modern technologies due to their surface properties such as adsorption capacity and controllable wettability, which depend on the production methods. For practical applications, it is crucial to control the surface properties to achieve the desired wetting characteristics, which can be described with the contact angle (CA). Here, we experimentally investigate the wettability properties of the carbon nanowalls and show how to manage a wetting transition from superhydrophobic to superhydrophilic states. A CA of 170° was reached with direct plasma synthesis, while an angle smaller than 20° was achieved during the atmosphere plasma modification. Combining the formation of the surface groups due to the plasma treatment results and the macroscale wetting behavior in terms of the Cassie-Baxter model, we qualitatively explain how the observed wetting enhancement is induced by both controlled chemical and geometrical surface-heterogeneity.

Review of Vertical Graphene and its Applications

Vertical graphene (VG) is a thin-film complex material featuring hierarchical microstructures: graphene-containing carbon nanosheets growing vertically on its deposition substrate, few-layer graphene basal layers, and chemically active atomistic defect sites and edges. Thanks to the fundamental characteristics of graphene materials, e.g. excellent electrical conductivity, thermal conductivity, chemical stability, and large specific surface area, VG materials have been successfully implemented into various niche applications which are strongly associated with their unique morphology. The microstructure of VG materials can be tuned by modifying growth methods and the parameters of growth processes. Multiple growth processes have been developed to address faster, safer, and mass production methods of VG materials, as well as accommodating various applications. VG's successful applications include field emission, supercapacitors, fuel cells, batteries, gas sensors, biochemical sensors, electrochemical analysis, strain sensors, wearable electronics, photo trapping, terahertz emission, etc. Research topics on VG have been more diversified in recent years, indicating extensive attention from the research community and great commercial value. In this review article, VG's morphology is briefly reviewed, and then various growth processes are discussed from the perspective of plasma science. After that, the most recent progress in its applications and related sciences and technologies are discussed.

Biological responses to physicochemical properties of biomaterial surface

Biomedical scientists use chemistry-driven processes found in nature as an inspiration to design biomaterials as promising diagnostic tools, therapeutic solutions, or tissue substitutes. While substantial consideration is devoted to the design and validation of biomaterials, the nature of their interactions with the surrounding biological microenvironment is commonly neglected. This gap of knowledge could be owing to our poor understanding of biochemical signaling pathways, lack of reliable techniques for designing biomaterials with optimal physicochemical properties, and/or poor stability of biomaterial properties after implantation. The success of host responses to biomaterials, known as biocompatibility, depends on chemical principles as the root of both cell signaling pathways in the body and how the biomaterial surface is designed. Most of the current review papers have discussed chemical engineering and biological principles of designing biomaterials as separate topics, which has resulted in neglecting the main role of chemistry in this field. In this review, we discuss biocompatibility in the context of chemistry, what it is and how to assess it, while describing contributions from both biochemical cues and biomaterials as well as the means of harmonizing them. We address both biochemical signal-transduction pathways and engineering principles of designing a biomaterial with an emphasis on its surface physicochemistry. As we aim to show the role of chemistry in the crosstalk between the surface physicochemical properties and body responses, we concisely highlight the main biochemical signal-transduction pathways involved in the biocompatibility complex. Finally, we discuss the progress and challenges associated with the current strategies used for improving the chemical and physical interactions between cells and biomaterial surface.

Multi-linear antenna microwave plasma assisted large-area growth of 6 × 6 in.2 vertically oriented graphenes with high growth rate

Vertically oriented graphenes (VGs) are promising for many emerging energy and environmental applications, while their mass production still remains a critical challenge. This note reports a multi-linear antenna microwave plasma device for fabricating VGs on a large-scale. Eight coaxial linear plasma antennas are parallelly arrayed to produce large-area plasma, depositing 6 × 6 in.² VGs on nickel foil at a high rate of 160 nm min^-1. In supercapacitor applications, the potential of VGs for AC line filtering (an RC time of 0.43 ms) and decreasing the interfacial contact resistance within commercial activated carbon supercapacitors is demonstrated.

Current Advances in Immunomodulatory Biomaterials for Bone Regeneration

Biomaterials with suitable surface modification strategies are contributing significantly to the rapid development of the field of bone tissue engineering. Despite these encouraging results, utilization of biomaterials is poorly translated to human clinical trials potentially due to lack of knowledge about the interaction between biomaterials and the body defense mechanism, the "immune system". The highly complex immune system involves the coordinated action of many immune cells that can produce various inflammatory and anti-inflammatory cytokines. Besides, bone fracture healing initiates with acute inflammation and may later transform to a regenerative or degenerative phase mainly due to the cross-talk between immune cells and other cells in the bone regeneration process. Among various immune cells, macrophages possess a significant role in the immune defense, where their polarization state plays a key role in the wound healing process. Growing evidence shows that the macrophage polarization state is highly sensitive to the biomaterial's physiochemical properties, and advances in biomaterial research now allow well controlled surface properties. This review provides an overview of biomaterial-mediated modulation of the immune response for regulating key bone regeneration events, such as osteogenesis, osteoclastogenesis, and inflammation, and it discusses how these strategies can be utilized for future bone tissue engineering applications.

Oriented Carbon Nanostructures by Plasma Processing: Recent Advances and Future Challenges

Carbon, one of the most abundant materials, is very attractive for many applications because it exists in a variety of forms based on dimensions, such as zero-dimensional (0D), one-dimensional (1D), two-dimensional (2D), and-three dimensional (3D). Carbon nanowall (CNW) is a vertically-oriented 2D form of a graphene-like structure with open boundaries, sharp edges, nonstacking morphology, large interlayer spacing, and a huge surface area. Plasma-enhanced chemical vapor deposition (PECVD) is widely used for the large-scale synthesis and functionalization of carbon nanowalls (CNWs) with different types of plasma activation. Plasma-enhanced techniques open up possibilities to improve the structure and morphology of CNWs by controlling the plasma discharge parameters. Plasma-assisted surface treatment on CNWs improves their stability against structural degradation and surface chemistry with enhanced electrical and chemical properties. These advantages broaden the applications of CNWs in electrochemical energy storage devices, catalysis, and electronic devices and sensing devices to extremely thin black body coatings. However, the controlled growth of CNWs for specific applications remains a challenge. In these aspects, this review discusses the growth of CNWs using different plasma activation, the influence of various plasma-discharge parameters, and plasma-assisted surface treatment techniques for tailoring the properties of CNWs. The challenges and possibilities of CNW-related research are also discussed.

Bioelectronics with nanocarbons

Characterizing the electrical activity of cardiomyocytes and neurons is crucial in understanding the complex processes in the heart and brain tissues, both in healthy and diseased states. Micro- and nanotechnologies have significantly improved the electrophysiological investigation of cellular networks. Carbon-based nanomaterials or nanocarbons, such as carbon nanotubes (CNTs), nanodiamonds (NDs) and graphene are promising building blocks for bioelectronics platforms owing to their outstanding chemical and physical properties. In this review, we discuss the various bioelectronics applications of nanocarbons and their derivatives. Furthermore, we touch upon the challenges that remain in the field and describe the emergence of carbon-based hybrid-nanomaterials that will potentially address those limitations, thus improving the capabilities to investigate the electrophysiology of excitable cells, both as a network and at the single cell level.

Nanochannelar Topography Positively Modulates Osteoblast Differentiation and Inhibits Osteoclastogenesis

Based on previously reported findings showing reduced foreign body reactions on nanochannelar topography formed on TiZr alloy, this study explores the in vitro effects of such a nanostructured surface on cells relevant for implant osseointegration, namely osteoblasts and osteoclasts. We show that such nanochannelar surfaces sustain adhesion and proliferation of mouse pre-osteoblast MC3T3-E1 cells and enhance their osteogenic differentiation. Moreover, this specific nanotopography inhibits nuclear factor kappa-B ligand (RANKL)-mediated osteoclastogenesis. The nanochannels’ dual mode of action on the bone-derived cells could contribute to an enhanced bone formation around the bone implants. Therefore, these results warrant further investigation for nanochannels’ use as surface coatings of medical implant materials.

Nanostructured Graphene Surfaces Promote Different Stages of Bone Cell Differentiation

Nanostructured graphene films were used as platforms for the differentiation of Saos-2 cells into bone-like cells. The films were grown using the plasma-enhanced chemical vapor deposition method, which allowed the production of both vertically and horizontally aligned carbon nanowalls (CNWs). Modifications of the technique allowed control of the density of the CNWs and their orientation after the transfer process. The influence of two different topographies on cell attachment, proliferation, and differentiation was investigated. First, the transferred graphene surfaces were shown to be noncytotoxic and were able to support cell adhesion and growth for over 7 days. Second, early cell differentiation (identified by cellular alkaline phosphatase release) was found to be enhanced on the horizontally aligned CNW surfaces, whereas mineralization (identified by cellular calcium production), a later stage of bone cell differentiation, was stimulated by the presence of the vertical CNWs on the surfaces. These results show that the graphene coatings, grown using the presented method, are biocompatible. And their topographies have an impact on cell behavior, which can be useful in tissue engineering applications.

Graphene nanoplatelets-sericin surface-modified Gum alloy for improved biological response

In this study a “Gum Metal” titanium-based alloy, Ti-31.7Nb-6.21Zr-1.4Fe-0.16O, was synthesized by melting and characterized in order to evaluate its potential for biomedical applications. The results showed that the newly developed alloy presents a very high strength, high plasticity and a low Young's modulus relative to titanium alloys currently used in medicine. For further bone implant applications, the newly synthesized alloy was surface modified with graphene nanoplatelets (GNP), sericin (SS) and graphene nanoplatelets/sericine (GNP–SS) composite films via Matrix Assisted Pulsed Laser Evaporation (MAPLE) technique. The characterization of each specimen was monitored by scanning electron microscopy (SEM), atomic force microscopy (AFM), contact angle (CA) measurements, and Fourier Transform Infrared Spectroscopy (FTIR). The materials' surface analyses suggested the successful coating of GNP, SS and GNP–SS onto the alloy surface. Additionally, the activities of pre-osteoblasts such as cell adhesion, cytoskeleton organization, cell proliferation and differentiation potentials exhibited on these substrates were investigated. Results showed that the GNP–SS-coated substrate significantly enhanced the growth and osteogenic differentiation of MC3T3-E1 cells when compared to bare and GNP-coated alloy. Collectively, the results show that GNP–SS surface-modified Gum alloy can modulate the bioactivity of the pre-osteoblasts holding promise for improved biological response in vivo.

GNP–SS functionalized Gum alloy exhibits superior bioactivity in inducing in vitro osteogenesis.

Flexible electrochemical biosensors based on graphene nanowalls for the real-time measurement of lactate

We demonstrate a flexible biosensor for lactate detection based on l-lactate oxidase immobilized by chitosan film cross-linked with glutaraldehyde on the surface of a graphene nanowall (GNW) electrode. The oxygen-plasma technique was developed to enhance the wettability of the GNWs, and the strength of the sensor's oxidation response depended on the concentration of lactate. First, in order to eliminate interference from other substances, biosensors were primarily tested in deionized water and displayed good electrochemical reversibility at different scan rates (20-100 mV s^-1), a large index range (1.0 μM to 10.0 mM) and a low detection limit (1.0 μM) for lactate. Next, these sensors were further examined in phosphate buffer solution (to mimick human body fluids), and still exhibited high sensitivity, stability and flexibility. These results show that the GNW-based lactate biosensors possess important potential for application in clinical analysis, sports medicine and the food industry.

Fibroblast-Cytophilic and HeLa-Cytotoxic Dual Function Carbon Nanoribbon Network Platform

Carbon nanomaterials have emerged as a promising material in cancer diagnosis and therapy. Carbon nanomaterials/nanostructures (C-C molecular structure) act as a carrier/skeleton and require further surface modification through functionalization with chemicals or biomolecules to attain cell response. We report the synthesis of a novel carbon nanoribbon network (CNRN) platform that possesses a combination of C-C and C-O bond architecture. The bioactive CNRN showed enhanced ability for cell adhesion. Most importantly, it induced opposite cell responses from healthy cells and cancerous cells, cytophilic to fibroblasts but cytotoxic to HeLa cells. Ultrafast laser ionization under ambient conditions transforms nonbioresponsive C-C bond of graphite to C-C and C-O bonds, forming a self-assembled CNRN platform. The morphology, nanochemistry, and functionality on modulating fibroblast and HeLa adhesion and proliferation of the fabricated CNRN platforms were investigated. The results of in vitro studies suggested that the CNRN platforms not only attracted but also actively accelerated the adhesion and proliferation of both fibroblasts and HeLa cells. The proliferation rate of fibroblasts and HeLa cells is 91 and 98 times greater compared with that of a native graphite substrate, respectively. The morphology of the cells over a period of 24 to 48 h revealed that the CNRN platform induced an apoptosis-like cytotoxic function on HeLa cells, whereas fibroblasts experienced a cytophilic effect and formed a tissuelike structure. The degree of cytotoxic or cytophilic effect can be further enhanced by adjusting parameters such as the ratio of C-C bonds to C-O bonds, the nanoribbon width, and the nanovoid porosity of the CNRN platforms, which could be tuned by careful control of laser ionization. In a nutshell, for the first time, pristine carbon nanostructures free from biochemical functionalization demonstrate dual function, cytophilic to fibroblast cells and cytotoxic to HeLa cells.

Chitin and carbon nanotube composites as biocompatible scaffolds for neuron growth

The design of biocompatible implants for neuron repair/regeneration ideally requires high cell adhesion as well as good electrical conductivity. Here, we have shown that plasma-treated chitin carbon nanotube composite scaffolds show very good neuron adhesion as well as support of synaptic function of neurons. The addition of carbon nanotubes to a chitin biopolymer improved the electrical conductivity and the assisted oxygen plasma treatment introduced more oxygen species onto the chitin nanotube scaffold surface. Neuron viability experiments showed excellent neuron attachment onto plasma-treated chitin nanotube composite scaffolds. The support of synaptic function was evident on chitin/nanotube composites, as confirmed by PSD-95 staining. The biocompatible and electrically-conducting chitin nanotube composite scaffold prepared in this study can be used for in vitro tissue engineering of neurons and, potentially, as an implantable electrode for stimulation and repair of neurons.