Mariana Ionita

Sodium alginate/graphene oxide composite films with enhanced thermal and mechanical properties

Sodium alginate/graphene oxide (Al/GO) nanocomposite films with different loading levels of graphene oxide were prepared by casting from a suspension of the two components. The structure, morphologies and properties of Al/GO films were characterized by Fourier transform infrared (FT-IR) spectroscopy, X-ray diffraction (XRD), scanning (SEM) and transmission electron microscopy (TEM), thermal gravimetric (TG) analysis, and tensile tests. The results revealed that hydrogen bonding and high interfacial adhesion between GO filler and Al matrix significantly changed thermal stability and mechanical properties of the nanocomposite films. The tensile strength (σ) and Youngs modulus (E) of Al films containing 6 wt% GO increased from 71 MPa and 0.85 GPa to 113 MPa and 4.18 GPa, respectively. In addition, TG analysis showed that the thermal stability of Al/GO composite films was better than that of neat Al film.

Synthesis, characterization, and in vitro studies of graphene oxide/chitosan-polyvinyl alcohol films.

Nanocomposites based on chitosan-polyvinyl alcohol (CS-PVA) and graphene oxide (GO) were prepared by casting the stable aqueous mixture of the components. SEM, TEM and X-ray diffraction showed that graphene oxide is largely dispersed on molecular scale within CS-PVA matrix. FTIR investigation indicated the occurrence of some interaction between graphene oxide nanosheets and CS-PVA. The obtained composites are mechanically strong and exhibit improved thermal stability. By addition of 6 wt.% GO within CS-PVA blend, the elastic modulus increased over 200%. The cell viability and proliferation results showed that MC3T3-E1 mouse osteoblastic cells can adhere and developed on the CS-PVA/GO composite films. A significant proliferation potential was displayed by the cells in contact with CS-PVA/GO 6 wt.%. Graphene oxide reinforced CS-PVA with high mechanical and bioactive properties are potential candidates for tissue engineering.

In vitro cytocompatibility evaluation of chitosan/graphene oxide 3D scaffold composites designed for bone tissue engineering

Extensively studied nowadays, graphene oxide (GO) has a benefic effect on cell proliferation and differentiation, thus holding promise for bone tissue engineering (BTE) approaches. The aim of this study was not only to design a chitosan 3D scaffold improved with GO for optimal BTE, but also to analyze its physicochemical properties and to evaluate its cytocompatibility and ability to support cell metabolic activity and proliferation. Overall results show that the addition of GO in the scaffolds composition improved mechanical properties and pore formation and enhanced the bioactivity of the scaffold material for tissue engineering. The new developed CHT/GO 3 wt% scaffold could be a potential candidate for further in vitro and in vivo osteogenesis studies and BTE approaches.

Gelatin–poly(vinyl alcohol) porous biocomposites reinforced with graphene oxide as biomaterials

The present work aims to develop new biocomposites based on gelatin (Gel) and poly(vinyl alcohol) (PVA) reinforced with graphene oxide (GO). On the one hand, the model is designed with consideration of the high performance of the aforementioned biopolymers as biomaterials; on the other hand, the original component of the system, GO, is expected to improve structural stability and boost mechanical strength. Porous Gel-PVA/GO materials with GO content ranging from 0.5 to 3 wt% are obtained by freeze-drying. Structural analysis by Fourier transform infrared spectrometry (FT-IR), X-ray diffraction (XRD) and transmission electron microscopy (TEM) revealed the ability of well-dispersed GO nanosheets to form interactions with the polymers, leading to a unique molecular structuration. 3D analysis by X-ray microtomography (microCT) and scanning electron microscopy (SEM) suggests that GO has an influence on pore adjustment. According to mechanical tests, GO undoubtedly exhibits a beneficial effect on the polymer resistance against compressive stress, improving their compressive strengths by 97-100% with the addition of 0.5-3 wt% GO. Moreover, biological assessment using the MC3T3-E1 preosteoblast murine cell line indicated the fabrication of a cytocompatible composite formula, with potential for further in vivo testing and tissue engineering applications.

Preparation and characterization of polysulfone/ammonia-functionalized graphene oxide composite membrane material

The study highlights the first use of ammonia-functionalized graphene oxide (GO-NH2) as an additive to enhance the features of polysulfone (PSF) matrix. Composite membrane materials with different ratios of GO-NH2 (0.25, 0.5, 1, and 1.5 wt%) were obtained by phase inversion method. Subsequently structural and morphological characteristics were investigated by Raman spectroscopy, X-ray diffraction (XRD), scanning, and transmission electron microscopy (TEM). Lastly, mechanical and thermogravimetric studies were performed in order to establish whether GO-NH2 addition influenced PSF/GO-NH2 composite material performance. Raman spectroscopy, XRD, and TEM revealed evenly dispersed GO-NH2 within PSF/GO-NH2 composite membrane material forming exfoliated structures for lower concentration of GO-NH2. An enhancement in both mechanical and thermal characteristics was attained. The decomposition temperature at which the mass loss is 3%, of the composite membrane material with 1 wt% GO-NH2 was increased with 7°C. Conversely, an increase in Young’s modulus from 246 MPa to 285 MPa was achieved with the addition of 1 wt% GO-NH2 within the PSF matrix.

Chitosan-Graphene Oxide 3D scaffolds as Promising Tools for Bone Regeneration in Critical-Size Mouse Calvarial Defects

Limited self-regenerating capacity of human skeleton makes the reconstruction of critical size bone defect a significant challenge for clinical practice. Aimed for regenerating bone tissues, this study was designed to investigate osteogenic differentiation, along with bone repair capacity of 3D chitosan (CHT) scaffolds enriched with graphene oxide (GO) in critical-sized mouse calvarial defect. Histopathological/histomorphometry and scanning electron microscopy(SEM) analysis of the implants revealed larger amount of new bone in the CHT/GO-filled defects compared with CHT alone (pu2009<u20090.001). When combined with GO, CHT scaffolds synergistically promoted the increase of alkaline phosphatase activity both in vitro and in vivo experiments. This enhanced osteogenesis was corroborated with increased expression of bone morphogenetic protein (BMP) and Runx-2 up to week 4 post-implantation, which showed that GO facilitates the differentiation of osteoprogenitor cells. Meanwhile, osteogenesis was promoted by GO at the late stage as well, as indicated by the up-regulation of osteopontin and osteocalcin at week 8 and overexpressed at week 18, for both markers. Our data suggest that CHT/GO biomaterial could represent a promising tool for the reconstruction of large bone defects, without using exogenous living cells or growth factors.

Effect of morphological state of graphene on mechanical properties of nanocomposites

In the last decade, graphene has emerged as one of the best-performing reinforcement materials for nanocomposites. Incorporation of graphene into polymer results in a nanocomposite with a new microstructure responsible for its enhanced features. A morphological state of graphene flakes is one of the factors that govern formation of this microstructure. Studies showed that graphene oxide (GO) flakes can be found either as fully exfoliated or intercalated in polymer-based nanocomposites. While traditional parameters are commonly taken into consideration in theoretical assessment of properties of composites by means of micromechanical models, the morphological state is often ignored. This research aims to investigate the effect of morphological state of GO flakes on stiffness of nanocomposites with widely used micromechanical models, e.g. rule of mixtures, Hui–Shia and Halpin–Tsai. Pure sodium alginate and nanocomposites on its basis reinforced with 1.0 and 2.5 wt% GO were used in the study. Parameters required for modelling were quantified with microstructural characterisation. Micromechanical models were adapted to account for the morphological state of intercalation observed in the characterisation study. Tensile experiments were employed to assess the adopted models, and the effect matrix stiffness, GO thickness, spacing of intercalates as well as the Poisson’s ratio and stiffness of inter-flake polymer layers were studied.

Enhanced X-ray absorption for micro-CT analysis of low density polymers

Abstract X-ray microtomography (micro-CT), one of the most resourceful instruments for high resolution 3D analysis, can provide qualitative and quantitative accurate structural and compositional information for a broad range of materials. Yet its contribution to the field of biopolymeric materials science is often limited by low imaging contrast due to scarce X-ray attenuation features, particularly for sponges and foam-like structures. This limitation can be overcome to some extent by adjusting the working parameters of micro-CT equipment. However, such approach also facilitates noise and artefacts, and solving the signal-to-noise trade-off has been always problematic. Searching for alternatives turns one’s attention towards the improvement of X-ray attenuation features. While several studies report the use of contrast agents for biological materials, studies to integrate multiple micro-CT approaches for biopolymers were not conducted so far. This method paper is thus aimed to serve as a platform for micro-CT analysis of low X-ray absorptive polymers. Here, several contrast enhancing artifices were developed and trialled on gelatin and poly(vinyl alcohol) biopolymer composites (GP). Accordingly, GP were modified with iodine, barium, silver-based chemicals and hexa(methyl disilazane) by two different methods, i.e. addition of high atomic number chemicals during materials synthesis and post-synthesis staining, respectively. Consequently, cross-sectional scanning electron microscopy emerged as complementary characterization, aimed to confirm the reproducibility of samples morphological features. The most versatile methods were barium chloride additive incorporation and iodine staining coupled with hexa(methyl disilazane) chemical drying. Both methods significantly improved the X-ray absorbance of our polymeric samples, providing better contrast of micro-CT tomograms.

The Impact of Graphene Oxide on Bone Regeneration Therapies

Currently, there are several tissue engineering strategies meant to overcome the incomplete or insufficient bone regeneration conditions offered by autologous bone graft or surgery approaches. In the last decade, attention has been focused toward finding the equilibrium between a suitable scaffold with osteoinductive properties, a cell source with evident potential to develop bone tissue and the appropriate proosteogenic factors to condition the differentiation process after cell-scaffold implanta‐ tion. Consequently, this chapter aims to discuss the benefits that graphene and its derivatives, graphene oxide (GO), bring both to the scaffold biomaterial and to the interaction between the material and the cellular component in order to create a favorable micro-environment for efficient osteogenic differentiation process. Several advantages of including GO in the composition of the materials are shown in relation to cell viability, proliferation, attachment, and osteogenic differentiation.

Optical properties of graphene-based materials in transparent polymer matrices

Different aspects of graphene-based materials (GBMs) and GBM-nanocomposites have been investigated due to their intriguing features; one of these features is their transparency. Transparency of GBMs has been of an interest to scientists and engineers mainly with regard to electronic devices. In this study, optical transmittance of structural, purpose-made nanocomposites reinforced with GBMs was analyzed to lay a foundation for optical microstructural characterization of nanocomposites in future studies. Two main types of GBM reinforcements were studied, graphene oxide (GO) and graphite nanoplates (GNPs). The nanocomposites investigated are GO/poly(vinyl alcohol), GO/sodium alginate, and GNP/epoxy with different volume fractions of GBMs. Together with UV-visible spectrophotometry, image-processing-assisted micro and macro photography were used to assess the transparency of GBMs embedded in the matrices. The micro and macro photography methods developed were proven to be an alternative way of measuring ligh...