3D Printing of a Graphene-Modified Photopolymer Using Stereolithography for Biomedical Applications: A Study of the Polymerization Reaction.

Additive manufacturing is gaining importance thanks to its multiple advantages. Stereolithography (SLA) shows the highest accuracy and the lowest anisotropy, which has facilitated the emergence of new applications as dentistry or tissue engineering. However, the availability of commercial photopolymers is still limited, and there is an increasing interest in developing resins with properties adapted for these new applications. The addition of graphene-based nanomaterials (GBN) may provide interesting advantages, such as improved mechanical properties and bioactivity. However, there is a lack of knowledge regarding the effect of GBNs on the polymerization reaction. A photopolymerizable acrylic resin has been used, and the effect of the addition of 0.1wt% of graphene (G); graphene oxide (GO) and graphite nanoplatelets (GoxNP) on printability and polymerization have been investigated. It was observed that the effect depended on GBN type, functionalization and structure (e.g., number of layers, size, and morphology) due to differences in the extent of dispersion and light absorbance. The obtained results showed that GO and GoxNP did not significantly affect the printability and quality of the final structure, whilst the application of G exhibited a negative effect in terms of printability due to a reduction in the polymerization degree. GO and GoxNP-loaded resins showed a great potential to be used for manufacturing structures by SLA.

Graphene Oxide and Graphene Reinforced PMMA Bone Cements: Evaluation of Thermal Properties and Biocompatibility.

The incorporation of well-dispersed graphene oxide (GO) and graphene (G) has been demonstrated as a promising solution to improve the mechanical performance of polymethyl methacrylate (PMMA) bone cements in an attempt to enhance the long-term survival of the cemented orthopaedic implants. However, to move forward with the clinical application of graphene-based PMMA bone cements, it is necessary to ensure the incorporation of graphene-based powders do not negatively affect other fundamental properties (e.g., thermal properties and biocompatibility), which may compromise the clinical success of the implant. In this study, the effect of incorporating GO and G on thermal properties, biocompatibility, and antimicrobial activity of PMMA bone cement was investigated. Differential scanning calorimetry studies demonstrated that the extent of the polymerisation reaction, heat generation, thermal conductivity, or glass transition temperature were not significantly (p > 0.05) affected by the addition of the GO or G powders. The cell viability showed no significant difference (p > 0.05) in viability when MC3-T3 cells were exposed to the surface of G- or GO-PMMA bone cements in comparison to the control. In conclusion, this study demonstrated the incorporation of GO or G powder did not significantly influence the thermal properties or biocompatibility of PMMA bone cements, potentially allowing its clinical progression.

Graphene and graphene oxide functionalisation with silanes for advanced dispersion and reinforcement of PMMA-based bone cements.

The reinforcement of PMMA bone cements using carbon based nanomaterials has demonstrated to be a potential solution to their poor mechanical properties. The achievement of an optimal dispersion of the nanoparticles within the polymeric matrix is a crucial but not easy stage in the production of high-quality reinforced materials. In this work, a useful route for the graphene (G) functionalisation, via silanisation with (3-methacryloxypropyl) trimethoxy silane (MPS), has been developed, providing a remarkable enhancement in dispersibility and mechanical properties. With the purpose to define the critical graphene surface oxidation parameters for an optimal silanisation, different routes were thoroughly analysed using infrared spectroscopy (FTIR), thermogravimetric analysis (TGA), X-ray photoelectron spectroscopy (XPS) and scanning electron microscopy (SEM). The results showed that the silanisation significantly improved the G dispersibility: whereas the pristine G dispersion fell down within the first 24 h, the silanised G showed an adequate stability after 5 days. Additionally, this improved dispersibility produced a notable increase in the mechanical properties of the G-reinforced bone cements: in comparison with the pristine G, the compression and bending strength of silanised G increased by 12% and by 13.7% respectively and the fracture toughness by 28%. These results provide very useful information on the relevance that the characteristics of the superficial oxidation of graphene have on the effectiveness of the silanisation process, besides an interesting functionalisation procedure for advanced dispersion and reinforcement of G-PMMA bone cements.

Mechanical and thermal behaviour of an acrylic bone cement modified with a triblock copolymer.

The basic formulation of an acrylic bone cement has been modified by the addition of a block copolymer, Nanostrength(®) (NS), in order to augment the mechanical properties and particularly the fracture toughness of the bone cement. Two grades of NS at different levels of loading, between 1 and 10 wt.%, have been used. Mechanical tests were conducted to study the behaviour of the modified cements; specific tests measured the bend, compression and fracture toughness properties. The failure mode of the fracture test specimens was analysed using scanning electron microscopy (SEM). The effect of NS addition on the thermal properties was also determined, and the polymerisation reaction using differential scanning calorimetry. It was observed that the addition of NS produced an improvement in the fracture toughness and ductility of the cement, which could have a positive contribution by reducing the premature fracture of the cement mantle. The residual monomer content was reduced when the NS was added. However this also produced an increase in the maximum temperature and the heat delivered during the polymerisation of the cement.

Determination of linuron in soil by stripping voltammetry with a carbon fiber microelectrode.

A carbon fiber microelectrode was used for the electroanalytical determination of Linuron (LIN) in soil extracts. The microelectrode was subjected to an electrochemical pretreatment in order to improve the herbicide adsorption on the electrode surface. With this preconcentration step, detection limits of 80 ng ml(-1) and determination limits of 260 ng ml(-1) were reached. Optimal conditions with respect to accumulation time and potential, scan rate and pH were established. The LIN was determined in a soil sample with the method proposed and the results found were comparable to those obtained by HPLC.

Determination of carbendazim in soil samples by anodic stripping voltammetry using a carbon fiber ultramicroelectrode.

A method for the determination of carbendazim (MBC) by anodic stripping voltammetry using a carbon fiber ultramicroelectrode was developed. The ultramicroelectrode was made in our laboratory and its electrochemical behavior was characterized by measuring the electrochemical response with a solution of potassium ferricyanide. The optimum parameters used for the determination of MBC are the following: 0.05 M phosphate buffer at pH 2.0 as supporting electrolyte; a scan rate of v = 10.00 V s(-1) and an accumulation potential of Eac = 0.00 V. The MBC was determined in a soil sample with the method proposed and the results found were comparable to those obtained by HPLC.

Rapid identification of carbendazim and linuron by adsorptive stripping on a carbon fiber ultramicroelectrode.

A method is described for the identification of a mixture of carbendazim and linuron. It is based on adsorptive stripping voltammetry at a carbon fiber ultramicroelectrode. Conditions for the determination of carbendazim in a mixture were optimized and the method was applied to soil samples. It was compared to HPLC with spectrophotometric detection, where similar results were obtained.

Determination of abscisic acid by cathodic stripping square wave voltammetry.

In this paper a study is accomplished on behavior in a mercury electrode, of the phytohormone abscisic acid and of the conditions of accumulation in a HMDE. A mechanism is proposed of reduction based on its electrochemical behavior and proving the product of the reduction through mass spectrometry of bulks. A method is proposed for the determination of Abscisic acid (ABA) with a quantification limit of 58 ng ml(-1). The procedure is applied wing determination of ABA in pears through the combination of high performance liquid chromatography (HPLC) with electrochemical quantification.