Two- and Three-Dimensional All-Carbon Nanomaterial Assemblies for Tissue Engineering and Regenerative Medicine

VMT/ACP/Dextran composite nanosheets against dental caries through promoting mineralization of dentin tubules, pH buffering, and antibacterial

Dental caries is a worldwide public healthcare concern, and is closely related to the acidic environment that caused by bacterial decomposition of food. In this study, a two-step ion exchange liquid-phase stripping method was applied to strip out vermiculite (VMT) nanosheets, then amorphous calcium phosphate (ACP) and dextran were inserted between the VMT nanosheets interlayer to obtain a composite two-dimension nanosheets (VMT/ACP/Dextran). VMT/ACP/Dextran composite nanosheets exhibited excellent biocompatibility and could provide exogenous Ca2+and PO43- from ACP, provide SiO44-, Mg2+, Fe2+ and obtain buffering pH and antibacterial properties from VMT, as well as improve suspension stability and targeting Streptococcus mutans through glucan. The in vitro study showed that the composite materials could promote the mineralization and sealing of dentin tubules by releasing active ions, buffer pH 4.5 (a value close to the pH in the dental plaque environment) to pH 6.6-7.1 (values close to the pH in human saliva) through ion exchange, and exert antibacterial effects by targeting Streptococcus mutans and exerting oxidase like and peroxidase like activities to produce reactive oxygen species (ROS). The in vivo animal study showed that daily cleaning teeth using VMT/ACP/Dextran composite nanosheets could effectively reduce the incidence rate and severity of dental caries in rats. Taking together, the developed VMT/ACP/Dextran composite nanosheets, which integrated the excellent properties of VMT, ACP and dextran, can effectively prevent dental caries through a combination of factors such as buffering acids, antibacterial properties, and promoting calcification, and may be used as an active ingredient for daily oral hygiene or filling materials to prevent and treat dental caries.

Recent advances in biological molecule detection based on a three-dimensional graphene structure

Graphene has become an attractive material in the field of electrochemical detection owing to its unique electrical properties. Although the simple stacking structures of two-dimensional (2D) graphene sheets can provide excellent detection properties, a macroscopic three-dimensional (3D) structure needs to be constructed to enhance its functional properties. Graphene with a 3D structure has elegant functions, unlike graphene with a 2D structure. These properties include a large specific surface area, easy loading of nanomaterials with electrocatalytic and redox functions, and so on. Herein, we outline the preparation methods (self-assembly, chemical vapor deposition, templates, and 3D printing) for 3D graphene structures for obtaining excellent detection performance and applications in detecting biological molecules, bacteria, and cells. Furthermore, this review focuses on the improvement of the detection performance and enhancement of the applicability of graphene-based electrochemical sensors. We hope that this article will provide a reference for the future development of electrochemical sensors based on 3D graphene composites.

Synthesis and Characterization of Carbon Microbeads

We report a microfluidic-based droplet generation platform for synthesizing micron-sized porous carbon microspheres. The setup employs carbon materials such as graphite, carbon nanotubes, graphene, fullerenes, and carbon black as starting materials. Custom composition, structure, and function are achieved through combinations of carbon materials, cross-linkers, and additives along with variations in process parameters. Carbon materials can be assembled into spheres with a mean diameter of units to hundreds of μm with relatively tight size distribution (<25% RSD). Pore structure and size (tens to hundreds of angstrom) can be modulated by incorporating porogen/coporogen dilutants during synthesis. The microbeads have excellent mechanical stability with an elastic modulus of hundreds of MPa. They can sustain high dynamic fluid flow pressures of up to 9000 psi. This work lays the foundation for synthesizing novel tailorable and customizable carbon microbeads. It opens avenues for applying these novel materials for composite and additive manufacturing, energy, life science, and biomedical applications.

Recent advances and trends in the applications of MXene nanomaterials for tissue engineering and regeneration

MXene, as a new two-dimensional nanomaterial, is endowed with lots of particular properties, such as large surface area, excellent conductivity, biocompatibility, biodegradability, hydrophilicity, antibacterial activity, and so on. In the past few years, MXene nanomaterials have become a rising star in biomedical fields including biological imaging, tumor diagnosis, biosensor, and tissue engineering. In this review, we sum up the recent applications of MXene nanomaterials in the field of tissue engineering and regeneration. First, we briefly introduced the synthesis and surface modification engineering of MXene. Then we focused on the application and development of MXene and MXene-based composites in skin, bone, nerve and heart tissue engineering. Uniquely, we also paid attention to some research on MXene with few achievements at present but might become a new trend in tissue engineering and regeneration in the future. Finally, this paper will also discuss several challenges faced by MXene nanomaterials in the clinical application of tissue engineering.

Extrapolating neurogenesis of mesenchymal stem/stromal cells on electroactive and electroconductive scaffolds to dental and oral-derived stem cells

The high neurogenic potential of dental and oral-derived stem cells due to their embryonic neural crest origin, coupled with their ready accessibility and easy isolation from clinical waste, make these ideal cell sources for neuroregeneration therapy. Nevertheless, these cells also have high propensity to differentiate into the osteo-odontogenic lineage. One strategy to enhance neurogenesis of these cells may be to recapitulate the natural physiological electrical microenvironment of neural tissues via electroactive or electroconductive tissue engineering scaffolds. Nevertheless, to date, there had been hardly any such studies on these cells. Most relevant scientific information comes from neurogenesis of other mesenchymal stem/stromal cell lineages (particularly bone marrow and adipose tissue) cultured on electroactive and electroconductive scaffolds, which will therefore be the focus of this review. Although there are larger number of similar studies on neural cell lines (i.e. PC12), neural stem/progenitor cells, and pluripotent stem cells, the scientific data from such studies are much less relevant and less translatable to dental and oral-derived stem cells, which are of the mesenchymal lineage. Much extrapolation work is needed to validate that electroactive and electroconductive scaffolds can indeed promote neurogenesis of dental and oral-derived stem cells, which would thus facilitate clinical applications in neuroregeneration therapy.

Effect of Length of Cellulose Nanofibers on Mechanical Reinforcement of Polyvinyl Alcohol

Cellulose nanofibers (CNF), representing the nano-structured cellulose, have attained an extensive research attention due to their sustainability, biodegradability, nanoscale dimensions, large surface area, unique optical and mechanical performance, etc. Different lengths of CNF can lead to different extents of entanglements or network-like structures through van der Waals forces. In this study, a series of polyvinyl alcohol (PVA) composite films, reinforced with CNF of different lengths, were fabricated via conventional solvent casting technique. CNF were extracted from jute fibers by tuning the dosage of sodium hypochlorite during the TEMPO-mediated oxidation. The mechanical properties and thermal behavior were observed to be significantly improved, while the optical transparency decreased slightly (Tr. > 75%). Interestingly, the PVA/CNF20 nanocomposite films exhibited higher tensile strength of 34.22 MPa at 2 wt% filler loading than the PVA/CNF10 (32.55 MPa) while displayed higher elastic modulus of 482.75 MPa than the PVA/CNF20 films (405.80 MPa). Overall, the findings reported in this study provide a novel, simple and inexpensive approach for preparing the high-performance polymer nanocomposites with tunable mechanical properties, reinforced with an abundant and renewable material.

Theoretical analysis of the electrochemical systems used for the application of direct current/voltage stimuli on cell cultures

Endogenous electric fields drive many essential functions relating to cell proliferation, motion, differentiation and tissue development. They are usually mimicked in vitro by using electrochemical systems to apply direct current or voltage stimuli to cell cultures. The many studies devoted to this topic have given rise to a wide variety of experimental systems, whose results are often difficult to compare. Here, these systems are analysed from an electrochemical standpoint to help harmonize protocols and facilitate optimal understanding of the data produced. The theoretical analysis of single-electrode systems shows the necessity of measuring the Nernst potential of the electrode and of discussing the results on this basis rather than using the value of the potential gradient. The paper then emphasizes the great complexity that can arise when high cell voltage is applied to a single electrode, because of the possible occurrence of anode and cathode sites. An analysis of two-electrode systems leads to the advice to change experimental practices by applying current instead of voltage. It also suggests that the values of electric fields reported so far may have been considerably overestimated in macro-sized devices. It would consequently be wise to revisit this area by testing considerably lower electric field values.

Mesoporous bioactive glass combined with graphene oxide scaffolds for bone repair

Recently there has been an increasing interest in bioactive factors with robust osteogenic ability and angiogenesis function to repair bone defects. However, previously tested factors have not achieved satisfactory results due to low loading doses and a short protein half-life. Finding a validated stable substitute for these growth factors and apply it to the construction of porous scaffolds with the dual function of osteogenesis and angiogenesis is therefore vital for bone tissue regeneration engineering. Graphene oxide (GO) has attracted increasing attention due to its good biocompatibility, osteogenic, and angiogenic functions. This study aims to design a scaffold composed of mesoporous bioactive glasses (MBG) and GO to investigate whether the composite porous scaffold promotes local angiogenesis and bone healing. Our in vitro studies demonstrate that the MBG-GO scaffolds have better cytocompatibility and higher osteogenesis differentiation ability with rat bone marrow mesenchymal stem cells (rBMSCs) than the purely MBG scaffold. Moreover, MBG-GO scaffolds promote vascular ingrowth and, importantly, enhance bone repair at the defect site in a rat cranial defect model. The new bone was fully integrated not only with the periphery but also with the center of the scaffold. From these results, it is believed that the MBG-GO scaffolds possess excellent osteogenic-angiogenic properties which will make them appealing candidates for repairing bone defects. The novelty of this research is to provide a new material to treat bone defects in the clinic.

Development of medical-grade, discrete, multi-walled carbon nanotubes as drug delivery molecules to enhance the treatment of hematological malignancies

Carbon nanotubes (CNTs) hold great potential as drug delivery transporters given their large drug-binding surface area. Herein, we designed novel, multi-walled, discrete CNTs (dMWCNTs), PEGylated dMWCNTs (PEG-dMWCNTs), and bone-targeting (BT), alendronate-conjugated PEG-dMWCNTs (BT-PEG-dMWCNTs). Using zeta potential, thermogravimetric analysis, TEM, SEM, and FTIR, dMWCNTs were characterized as individual, uniform, and stable. Drug binding and release assays validated dMWCNTs as effective doxorubicin (DOX) transporters. The mass ratio of DOX loading onto dMWCNTs was 35% wt/wt with a ~95% wt/wt efficiency. DOX release was ~51% w/w after 48 hours. Neoplastic transformation, chromosomal aberration, and cytotoxicity assays, confirmed biocompatibility for all dMWCNTs. PEG-dMWCNTs were well tolerated and modulated drug pharmacokinetics in mice. In mice with Burkitt's lymphoma, DOX-loaded PEG-dMWCNTs and BT-PEG-dMWCNTs reduced tumor burden and increased survival similarly to free drug. Importantly, DOX toxicity was abrogated when DOX was loaded onto PEG-dMWCNTs or BT-PEG-dMWCNTs. Overall, PEG-dMWCNTs and BT-PEG-dMWCNTs represent a promising new nanocarrier platform.

Enhanced Osteogenesis by Molybdenum Disulfide Nanosheet Reinforced Hydroxyapatite Nanocomposite Scaffolds

The advances in the arena of biomedical engineering enable us to fabricate novel biomaterials that provide a suitable platform for rapid bone regeneration. Herein, we have investigated the in vitro and in vivo osteogenic differentiation, proliferation, and bone regeneration capability of molybdenum disulfide nanosheets (MoS₂NSs) reinforced HAP nanocomposite scaffolds. The MG-63 cells were incubated with HAP and HAP/MoS₂NSs nanocomposite and followed for various cellular activities. The cells incubated with HAP@2 shows higher cell adhesion, cell proliferation, and alkaline phosphatase activity (ALP) in contrast to HAP. The in vivo and in vitro results of the increased ALP level confirm that HAP@2 promotes osteogenic differentiation. This improved osteogenesis was validated with upregulation of osteogenic marker viz. transcription factor, RUNX-2 (∼34 fold), collagen-1 (∼15 fold), osteopontin (∼11 fold), osteocalcin (∼20 fold), and bone morphogenetic protein-2 (∼12 fold) after 12 week postimplantation in comparison to drilled. The X-ray imaging demonstrates that HAP@2 implants promote rapid osteogenesis and bioresorbability than HAP and drilled. The outcomes of the present study provide a promising tool for the regeneration of bone deformities, without using any external growth factor.

Two-dimensional graphene oxide-reinforced porous biodegradable polymeric nanocomposites for bone tissue engineering

This study investigates the mechanical properties and in vitro cytotoxicity of two-dimensional (2D) graphene oxide nanoribbons and nanoplatelets (GONRs and GONPs) reinforced porous polymeric nanocomposites. Highly porous poly(propylene fumarate) (PPF) nanocomposites were prepared by dispersing 0.2 wt % single- and multiwalled SONRs (SWGONRs and MWGONRs) and GONPs. The mechanical properties of scaffolds were characterized using compression testing and in vitro cytocompatibility was assessed using QuantiFlour assay for cellularity and PrestoBlue assay for cell viability. Immunofluorescence was used to assess collagen-I expression and deposition in the extracellular matrix. Porous PPF scaffolds were used as a baseline control and porous single and multiwalled carbon nanotubes (SWCNTs and MWCNTs) reinforced nanocomposites were used as positive controls. Results show that incorporation of 2D graphene nanomaterials leads to an increase in the mechanical properties of porous PPF nanocomposites with following the trend: MWGONRs > GONPs > SWGONRs > MWCNTs > SWCNTs > PPF control. MWGONRs showed the best enhancement of compressive mechanical properties with increases of up to 26% in compressive modulus (i.e., Young's modulus), ~60% in yield strength, and ~24% in the ultimate compressive strength. Addition of 2D nanomaterials did not alter the cytocompatibility of porous PPF nanocomposites. Furthermore, PPF nanocomposites reinforced with SWGONRs, MWGONRs, and GONPs show an improvement in the adsorption of collagen-I compared to PPF baseline control. The results of this study show that 2D graphene nanomaterial reinforced porous PPF nanocomposites possess superior mechanical properties, cytocompatibility, and increased protein adsorption. The favorable cytocompatibility results opens avenues for in vivo safety and efficacy studies for bone tissue engineering applications. © 2019 Wiley Periodicals, Inc. J Biomed Mater Res Part A: 107A: 1143-1153, 2019.

Effects of thermal treatment on the adhesion strength and osteoinductive activity of single-layer graphene sheets on titanium substrates

In recent years, dental implants have become the preferred approach for the restoration of missing teeth. At present, most dental implants are made of pure titanium, and are affected by peri-implantitis and bone resorption, which usually start from the implant neck, due to the complex environment in this region. To address these issues, in this study we modified the surface of titanium (Ti) implants to exploit the antibacterial and osteoinductive effects of single-layer graphene sheets. Chemical vapor deposition (CVD)-grown single-layer graphene sheets were transferred to titanium discs, and a method for improving the adhesion strength of graphene on Ti was developed due to compromised adhesion strength between graphene and titanium surface. A thermal treatment of 2 h at 160 °C was found to enhance the adhesion strength of graphene on Ti to facilitate clinical transformation. Graphene coatings of Ti enhanced cell adhesion and osteogenic differentiation, and imparted antibacterial activity to Ti substrate; these favorable effects were not affected by the thermal treatment. In summary, the present study elucidated the effects of a thermal treatment on the adhesion strength and osteoinductive activity of single-layer graphene sheets on titanium substrates.

Conjugated systems of porphyrin–carbon nanoallotropes: a review

This review summarizes the synthesis and applications of various porphyrin–carbon nanoallotrope conjugates.

Nanotechnology for Neuroscience: Promising Approaches for Diagnostics, Therapeutics and Brain Activity Mapping

Unlocking the secrets of the brain is a task fraught with complexity and challenge - not least due to the intricacy of the circuits involved. With advancements in the scale and precision of scientific technologies, we are increasingly equipped to explore how these components interact to produce a vast range of outputs that constitute function and disease. Here, an insight is offered into key areas in which the marriage of neuroscience and nanotechnology has revolutionized the industry. The evolution of ever more sophisticated nanomaterials culminates in network-operant functionalized agents. In turn, these materials contribute to novel diagnostic and therapeutic strategies, including drug delivery, neuroprotection, neural regeneration, neuroimaging and neurosurgery. Further, the entrance of nanotechnology into future research arenas including optogenetics, molecular/ion sensing and monitoring, and piezoelectric effects is discussed. Finally, considerations in nanoneurotoxicity, the main barrier to clinical translation, are reviewed, and direction for future perspectives is provided.

Effects of intermolecular interactions on the stability of carbon nanotube-gold nanoparticle conjugates in solution

This work deals with the role of intermolecular interactions in the stability of a carbon nanotube (CNT) capped by functionalized gold nanoparticles (AuNPs). The importance of such a system is due to its potential application as a pH-controlled drug carrier. Our preliminary experimental studies showed that fabrication of such a nanobottle/nanocontainer is feasible and it is possible to encapsulate the anticancer drug cisplatin inside the inner space of a CNT and seal its ends by functionalized AuNPs. The expected behavior, that is, detachment of AuNPs at acidic pH and the release of cisplatin, was, however, not observed. On the other hand, our theoretical studies of chemically identical system led to the conclusion that the release of cisplatin at acidic pH should be observed. Therefore, in this work, a deeper theoretical analysis of various factors that could be responsible for the disagreement between experimental and theoretical results were performed. The study found that the major factor is a large dispersion interaction component acting between CNT and AuNP in solution in the case of the experimental system. This factor can be controlled to some extent by tuning the system size or the ratio between AuNP diameter and CNT diameter. Thus, such kind of a pH-sensitive drug carrier is still of great interest, but its structural parameters need to be properly adjusted.

Toxicology of graphene-based nanomaterials

Graphene based nanomaterials possess remarkable physiochemical properties suitable for diverse applications in electronics, telecommunications, energy and healthcare. The human and environmental exposure to graphene-based nanomaterials is increasing due to advancements in the synthesis, characterization and large-scale production of graphene and the subsequent development of graphene based biomedical and consumer products. A large number of in vitro and in vivo toxicological studies have evaluated the interactions of graphene-based nanomaterials with various living systems such as microbes, mammalian cells, and animal models. A significant number of studies have examined the short- and long-term in vivo toxicity and biodistribution of graphene synthesized by variety of methods and starting materials. A key focus of these examinations is to properly associate the biological responses with chemical and morphological properties of graphene. Several studies also report the environmental and genotoxicity response of pristine and functionalized graphene. This review summarizes these in vitro and in vivo studies and critically examines the methodologies used to perform these evaluations. Our overarching goal is to provide a comprehensive overview of the complex interplay of biological responses of graphene as a function of their physiochemical properties.

Spinal cord fusion with PEG-GNRs (TexasPEG): Neurophysiological recovery in 24 hours in rats

BACKGROUND

The GEMINI spinal cord fusion protocol has been developed to achieve a successful cephalosomatic anastomosis. Here, for the first time, we report the effects of locally applied water-soluble, conductive PEG(polyethylene glycol)ylated graphene nanoribbons (PEG-GNRs) on neurophysiologic conduction after sharp cervical cord transection in rats. PEG-GNRs were produced by the polymerization of ethylene oxide from anion-edged graphene nanoribbons. These combine the fusogenic potential of PEG with the electrical conducting properties of the graphene nanoribbons.

METHODS

Laminectomy and transection of cervical spinal cord (C5) was performed on Female Sprague-Dawley (SD) rats. After applying PEG-GNR on the severed part, electrophysiological recovery of the reconstructed cervical spinal cord was confirmed by somatosensory evoked potentials (SSEPs) at 24 h after surgery.

RESULTS

While no SSEPs were detected in the control group, PEG-GNR treated group showed fast recovery of SSEPs at 24 h after the surgery.

CONCLUSION

In this preliminary dataset, for the first time, we report the effect of a novel form of PEG with the goal of rapid reconstruction of a sharply severed spinal cord.

Three-dimensional macroporous graphene scaffolds for tissue engineering

The assembly of carbon nanomaterials into three-dimensional (3D) porous scaffolds is critical to harness their unique physiochemical properties for tissue engineering and regenerative medicine applications. In this study, we report the fabrication, characterization, and in vitro cytocompatibility of true 3D (>1 mm in all three dimensions), macroscopic (3-8 mm in height and 4-6 mm in diameter), chemically cross-linked graphene scaffolds prepared via radical initiated thermal cross-linking of single- and multiwalled graphene oxide nanoribbons (SWGONRs and MWGONRs). SWGONR and MWGONR scaffolds possess tunable porosity (∼65-80%) and interconnected macro-, micro-, and nanoscale pores. Human adipose derived stem cells (ADSCs) and murine MC3T3 preosteoblast cells show good cell viability on SWGONR and MWGONR scaffolds after 1, 3, and 5 days comparable to 3D poly(lactic-co-glycolic) acid (PLGA) scaffolds. Confocal live-cell imaging showed that cells were metabolically active and could spread on SWGONR and MWGONR scaffolds. Immunofluorescence imaging showed the presence of focal adhesion protein vinculin and expression of cell proliferation marker Ki-67 suggesting that cells could attach and proliferate on SWGONR and MWGONR scaffolds. These results indicate that cross-linked SWGONR and MWGONR scaffolds are cytocompatible and opens-avenues toward the development of 3D multifunctional graphene scaffolds for tissue engineering applications. © 2016 Wiley Periodicals, Inc. J Biomed Mater Res Part A: 105A: 73-83, 2017.