Single-Step Process toward Achieving Superhydrophobic Reduced Graphene Oxide

Fabricating low-cost, robust superhydrophobic coatings with re-entrant topology for self-cleaning, corrosion inhibition, and oil-water separation

HYPOTHESIS

The superhydrophobic surfaces with re-entrant microstructures are known to provide robust superhydrophobicity by enhancing the energy barrier for Cassie-Baxter to Wenzel transition. However, the fabrication of such structured surfaces often involves sophisticated techniques and expensive ingredients.

EXPERIMENTS

Herein, a multifunctional, low-cost, and fluorine-free superhydrophobic coating with re-entrant surface topology was fabricated using fly ash (FA) and room-temperature-vulcanizing silicone. A systematic study was performed to evaluate the coating properties and durability. The robustness was evaluated as a function of particle size and inter-particle spacing. The performance in self-cleaning, corrosion inhibition and oil-water separation has been presented.

FINDINGS

The synthesized coatings are substrate-versatile and demonstrate superhydrophobic behavior. The close-packed coating of re-entrant FA particles attained via vibration compaction was seen to provide high robustness. The coatings retain their superhydrophobicity after multiple cycles of tape-peeling and exposure to environmental factors including temperature, pH, and UV radiation. These coatings exhibit excellent corrosion inhibition (corrosion efficiency > 99.999%), outperforming the majority of the previously reported superhydrophobic coatings. It also displays excellent self-cleaning property and high separation efficiencies in oil-water separation (>99%). We envision that such FA-based superhydrophobic coatings can solve the issues of synthesizing cheaper, sustainable, and robust superhydrophobic surfaces while simultaneously opening new avenues for FA utilization.

Graphene oxide-functionalized nanocomposites promote osteogenesis of human mesenchymal stem cells via enhancement of BMP-SMAD1/5 signaling pathway

Biomaterials that can harness the intrinsic osteogenic potential of stem cells offer a promising strategy to accelerate bone regeneration and repair. Previously, we had used methacrylated gelatin (GelMA)-based scaffolds to achieve bone formation from human mesenchymal stem cells (hMSCs). In this study, we aimed to further enhance hMSC osteogenesis by incorporating graphene oxide (GO)-based nanosheets into GelMA. In vitro results showed high viability and metabolic activities in hMSCs encapsulated in the newly developed nanocomposites. Incorporation of GO markedly increased mineralization within hMSC-laden constructs, which was further increased by replacing GO with silica-coated graphene oxide (SiGO). Mechanistic analysis revealed that the nanosheet enhanced the production, retention, and biological activity of endogenous bone morphogenetic proteins (BMPs), resulting in robust osteogenesis in the absence of exogenous osteoinductive growth factors. Specifically, the osteoinductive effect of the nanosheets was abolished by inhibiting the BMP signaling pathway with LDN-193189 treatment. The bone formation potential of the technology was further tested in vivo using a mouse subcutaneous implantation model, where hMSCs-laden GO/GelMA and SiGO/GelMA samples resulted in bone volumes 108 and 385 times larger, respectively, than the GelMA control group. Taken together, these results demonstrate the biological activity and mechanism of action of GO-based nanosheets in augmenting the osteogenic capability of hMSCs, and highlights the potential of leveraging nanomaterials such as GO and SiGO for bone tissue engineering applications.

Hydrothermal formation of controllable hexagonal holes and Er2O3/Er2O3-RGO particles on silicon wafers toward superhydrophobic surfaces

In this work, controllable hexagonal holes and distributed Er₂O₃/Er₂O₃- graphene particles are fabricated on silicon wafers using a straightforward, hydrofluoric, acid-free, and strong alkali-free hydrothermal method. As long as erbium nitrate hydrate and urea coexist in the reaction mixture, silicon wafers can be synthesized successfully using controllable hexagonal hole structures that are regulated by hydrothermal temperature and the addition of graphene oxide and hexadecyl trimethyl ammonium bromide to the reaction mixture. Correspondingly, the wettability of these silicon wafers also is controllable due to the structure that can be changed from hydrophilic (89.3°) to superhydrophobic (153.1°). In short, this work not only provides a simple and nontoxic approach for preparing hexagonal hole structured silicon wafers, but also produces superhydrophobic silicon wafers that potentially can be applied for corrosion-resistant coatings, oil-water separation, and other fields.

Incorporating silica-coated graphene in bioceramic nanocomposites to simultaneously enhance mechanical and biological performance

The applications of a variety of bioactive ceramics such as hydroxyapatite (HA) in orthopedics are limited by their insufficient mechanical properties, especially poor fracture toughness. Thus, further extending the clinical applications of these materials warrants the enhancement of their mechanical properties. Although the reinforcement of ceramics by 2D nanomaterials has been well recognized, integrated structural, mechanical, and functional considerations have been neglected in the design and synthesis of such composite materials. Herein, we report the first use of silica-coated reduced graphene oxide (S-rGO) hybrid nanosheets to create bioceramic-based composites with simultaneously enhanced mechanical and biological properties. In the representative HA-based bioceramic systems prepared by spark plasma sintering, S-rGO incorporation was found to be more effective for increasing the Young's modulus, hardness, and fracture toughness than the incorporation of uncoated reduced GO (rGO). Furthermore, when assessed with osteoblast-like MG-63 cells, such novel materials led to faster cell proliferation and higher cell viability and alkaline phosphatase activity than are generally observed with pure HA; additionally, cells demonstrate stronger affinity to S-rGO/HA than to rGO/HA composites. The S-rGO/bioceramic composites are therefore promising for applications in orthopedic tissue engineering, and this research provides valuable insights into the fabrication of silica-coated hybrid nanosheet-reinforced ceramics.

A sintered graphene/titania material as a synthetic keratoprosthesis skirt for end-stage corneal disorders

An artificial cornea or keratoprosthesis requires high mechanical strength, good biocompatibility, and sufficient wear and corrosion resistance to withstand the hostile environment. We report a reduced graphene oxide-reinforced titania-based composite for this application. Graphene oxide nanoparticles (GO) and liquid crystalline graphene oxide (LCGO) were the graphene precursors and mixed with titanium dioxide (TiO₂) powder. The composites reinforced with reduced GO or LCGO were produced through spark plasma sintering (SPS). The mechanical properties (Young's modulus and hardness), wear behaviour and corrosion resistance were studied using nanoindentation, anoidic polarization, long-term corrosion assay in artificial tear fluid and tribology assay in corroboration with atomic force microscopy and scanning electron microscopy. Biocompatibility was assessed by human corneal stromal cell attachment, survival and proliferation, and DNA damages. Sintered composites were implanted into rabbit corneas to assess for in vivo stability and host tissue responses. We showed that reduced graphene/TiO₂ hybrids were safe and biocompatible. In particular, the 1% reduced LCGO/TiO₂ (1rLCGO/TiO₂) composite was mechanically strong, chemically stable, and showed better wear and corrosion resistance than pure titania and other combinations of graphene-reinforced titania. Hence the 1rLCGO/ TiO₂ bioceramics can be a potential skirt biomaterial for keratoprosthesis to treat end-stage corneal blindness. STATEMENT OF SIGNIFICANCE: The osteo-odonto-keratoprosthesis (OOKP) is an artificial cornea procedure used to restore vision in end-stage corneal diseases, however it is contraindicated in young subjects, patients with advanced imflammatory diseases and posterior segment complications. Hence, there is a need of an improved keratoprosthesisskirt material with high mechanical and chemical stability, wear resistance and tissue integration ability. Our study characterized a reduced graphene oxide-reinforced titania-based biomaterial, which demonstrated strong mechanical strength, wear and corrosion resistance, and was safe and biocompatible to human corneal stromal cells. In vivo implantation to rabbit corneas did not cause any immune and inflammation outcomes. In conclusion, this invention is a potential keratoprosthesis skirt biomaterial to withstand the hostile environment in treating end-stage corneal blindness.

Rapid-response, reversible and flexible humidity sensing platform using a hydrophobic and porous substrate

A hydrophobic and porous liquid crystal polymer platform is developed to boost the humidity sensing performance of carbon materials.

Effect of thermal annealing on the physico-chemical and tribological performance of hydrophobic alkylated graphene sheets

Modulating physico-chemical and structural evolution of thermally treated functionalized graphitic nanolubricants for effective control of metallic sliding contact friction.

Optimization of spark plasma sintered titania for potential application as a keratoprosthesis skirt

The manufacture of mechanically strong and biocompatible titania (TiO₂ ) materials is of vital importance for their application as corneal implant skirts. This study was aimed at optimizing the selection of raw powder and sintering conditions for TiO₂ ceramics. TiO₂ compacts were synthesized from five raw powders, denoted as Altair, Inframat, Alfa, Materion, and Amperit, respectively, by spark plasma sintering using different sintering parameters. The XRD and Raman results confirmed that the anatase TiO₂ phase in the Inframat powder had converted completely to rutile TiO₂ phase after sintering at 900°C and above. The nanoindentation results indicated that among the five types of TiO₂ samples sintered at 1100°C, the Inframat pellets possessed the highest Young's modulus and hardness. Additionally, when Materion samples were employed to study the effects of SPS parameters, a higher sintering temperature in the range of 1100-1300°C decreased the mechanical properties of sintered pellets probably due to the generation of more structural defects. Culture of human corneal stromal fibroblasts on the sintered sample surfaces showed that comparably high cell viability and proliferation were observed on all TiO₂ samples except Amperit compared to positive control. Furthermore, cells cultured on Inframat TiO₂ sintered in the temperature range of 900-1300°C exhibited viability and formation of focal adhesion complex similar to those on control, and those prepared at 1100°C had significantly higher cell proliferation indices than control. In conclusion, Inframat TiO₂ consolidated at 1100°C by SPS was the best formulation for the preparation of mechanically strong and biocompatible Keratoprosthesis skirt. © 2017 Wiley Periodicals, Inc. J Biomed Mater Res Part A: 105A: 3502-3513, 2017.

Water-repellent and corrosion-resistance properties of superhydrophobic and lubricant-infused super slippery surfaces

Inspired by lotus leaves and pitcher plants, superhydrophobic surfaces and super slippery surfaces have been fabricated to improve the characteristics of AZ31 magnesium alloy surfaces.

Hierarchical flower like double-layer superhydrophobic films fabricated on AZ31 for corrosion protection and self-cleaning

The designed sample is prepared by self-assembly of octadecyltrichlorosilane and deposition of ferric stearate, and the contact angle is 160°.