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Surface Modification of Implants by Sol-Gel Coating Technology: Advantages and Applications
Flavia Bollino, Elisabetta Tranquillo
Published: 13 May 2020 by MDPI AG in 2nd Coatings and Interfaces Web Conference session Posters

Nowadays, approximately 1.5 million joint replacements are performed annually in Europe, while 7 million in the United States. Despite the advances made in the biomaterials field over the last 50 years, still today the average lifetime of an implant is about 20 years. his entails the need for subsequent prosthetic device replacement, especially in young patients, resulting in an increase in patients’ health risks as well as clinical and economic burdens for the public health service.

The failure of the implants can be caused by several reasons, such as adverse immune system reaction, biofilm formation or mechanical, chemical, tribological, surgical, manufacturing and biocompatibility problems. An alternative and useful strategy used to overcome this limitation is the modification of the implants' surface by sol-gel coating technology. It allows the production of coatings with a wide range of properties on substrates of different nature and shape, due to the fine control of the coating composition and microstructure.

Sol-gel coatings were successfully proposed to inhibit wear, reduce corrosion and ion release, modify lubricity, hydrophilicity/hydrophobicity, and functionality of several substrates. Moreover, many works report the application of sol-gel coatings on bio-inert implants to improve their bioactivity and biocompatibility, leading to the enhancement of the integration process. This is ascribable to the presence of residual hydroxyl groups on coating materials' surface, able to induce easier nucleation of the hydroxyapatite, to their mesoporosity and, thus, the large specific surface area. Further, the low processing temperatures allows easy coating functionalization by embedding suitable molecules such as anti-inflammatory and antibacterial agents leading to coatings preventing biofilm formation and inflammatory pathway activation.

Therefore, the application of the sol-gel coatings provides an excellent chemical modification of the materials' surface allowing protective barrier layers production.

References: Xiao-Yu Yang, Nidhi Chauhan. Photoenergy and Thin Film Materials, Advanced Materials Series. Chapter 8. WILEY-Scrivener, USA.

  • Open access
  • 12 Reads
N-Type Thermoelectric Textile Fabrics Based on Vapor Grown Carbon Nanofibers
S. Machado, E. M. F. Vieira, A. M. Rocha, A. J. Paleo
Published: 13 May 2020 by MDPI AG in 2nd Coatings and Interfaces Web Conference session Posters

Thermoelectric (TE) devices that convert a heat gradient directly to electricity are considered as a clean technology for energy harvesting. Both hole-transporting (p-type) and electron-transporting (n-type) materials are required in order to fabricate a thermoelectric module. Carbon nanotube (CNT) based textile fabrics are relevant in this context for the production of wearable TE modules due to the combination of the high electrical conductivity and thermopower (Seebeck coefficient) from the CNT and the low thermal conductivity and flexibility provided by the textile fabric [1]. Nevertheless, most as-produced CNT are p-type materials due to their inherent oxygen doping, and therefore the production of air- and thermally stable n-type CNT based textile fabrics remains a challenge nowadays [2]. On the other hand, vapor grown carbon nanofibers (VGCNF), produced by chemical vapor deposition (CVD), have similar structures to multiwall carbon nanotubes (MWCNT), which make them valuable for electronic applications. For instance, by adjusting process variables during their CVD and post growth heat treatment, VGCNF can be tailored to have a wide range of thermal conductivity and electrical conductivity at room temperature. In particular, the unexpected n-type character at room temperature that they supply to dip-coated cotton fabrics will be the issue of this presentation [3].

[1] R. Torah, J. Lawrie-Ashton, Y. Li, S. Arumugam, H.A. Sodano, S. Beeby, Energy-harvesting materials for smart fabrics and textiles, MRS Bulletin 43(3) (2018) 214-219.

[2] L. Brownlie, J. Shapter, Advances in carbon nanotube n-type doping: Methods, analysis and applications, Carbon 126 (2018) 257-270.

[3] A.J. Paleo, E.M.F. Vieira, K. Wan, O. Bondarchuk, M.F. Cerqueira, L.M. Goncalves, E. Bilotti, P. Alpuim, A.M. Rocha, Negative thermoelectric power of melt mixed vapor grown carbon nanofiber polypropylene composites, Carbon 150 (2019) 408-416.

  • Open access
  • 11 Reads
Influence of the Size of Coal Ash FAU Zeolites Used as Dopants on the Sensing Properties of Nb2O5 Thin Films

FAU (faujasite) is a rare natural zeolite which has its synthetic counterpart zeolite X. The sodium form of the synthetic zeolite X - Na-X, is widely used because of its structural supercage with large pore size and high specific surface area. It usually finds application for gas adsorption, separation, ion-exchange, etc.

In this study solid waste from coal combustion in thermal power plants (TPP) was used for synthesis of zeolite Na-X samples. They were prepared by long-term alkaline atmospheric conversion of coal ash collected from the electrostatic precipitators in TPP “AES Galabovo” supplied by lignite coal from the “Maritza East” basin. When used in form of thin films/layers, optical detection of VOCs (Volatile organic compounds) is possible due to change of color of the sample. In order to improve the sensing properties of synthesized zeolites, they were wet-milled for 60 seconds and both, milled and not milled, were used as a dopant for the niobium oxide matrix in form of thin film deposited by the spin-coating method on silicon substrate.

The surface morphology and structure of both zeolites powders were studied by scanning electron microscopy, while their size is determined from DLS (Dynamic Light Scattering) spectra. Optical constants (refractive index, n and extinction coefficient, k) and thickness of the films were calculated. The change in the reflection coefficient ∆R of the films was determined from measured reflectance spectra prior to and after exposure to probe acetone molecules. An increase in the reaction of the films with milled zeolites to acetone compared to the samples with not milled zeolites is demonstrated.

Acknowledgments

The financial support of Bulgarian National Science Fund (BNSF) under the project DN 17/18 (12.12.2017) is highly appreciated. Research equipment of distributed research infrastructure INFRAMAT (part of Bulgarian National roadmap for research infrastructures) supported by Bulgarian Ministry of Education and Science under contract D01-284/17.12.2019 was used in this investigation.

  • Open access
  • 10 Reads
Synthesis of Silica Particles from Sugarcane Bagasse ash for its Application in Hydrophobic Coatings
Jesús Pérez, Juan Ruíz, Antonio Zaldivar, Anabel Álvarez, Salomé de la Parra, Astrid Sánchez

Wastes like sugarcane bagasse ash (SCBA) can be used as raw material in the ceramics, by the elaboration of bricks and tiles, and glass industry due its high amount of silica in its composition (>70 %). Another application for the SCBA is the synthesis of metallic silicates. In this work is studied the synthesis of sodium silicate with SCBA as main raw material and the future application of the sodium silicate for the preparation of silica particles to create hydrophobic surfaces for ceramic materials to prevent its erosion. The sodium silicate synthesis was carried out by the thermochemical method with batches of ash and sodium carbonate in a 1:1 sodium oxide-silicon oxide molar ratio. The thermal treatment was in a electric furnace at 800 °C for 8 hours, then for the synthesis of the silica particles, the sodium silicate was dissolved in water and there was added methanol in a 3:2 water methanol volume ratio, the solution was aging for an hour to create the bond Si-OH, finally TEOS was added and the solution was stirred for 2 hours to originate a hydrophobic and hydrolytically resistant siloxane by the displacement of the H in the Si-OH bond. The application of the solution was by the spray-coating method over substrates of concrete and red clay with an application of 10, 15 and 20 layers. The hydrophobicity was evaluated with the water contact angle test, with results of contact angles above the 110°, thus demonstrating the capacity of a waste for the generation of coatings to prolong the useful life of building materials.

  • Open access
  • 12 Reads
Fabrication of Transparent ITO/Ga-Doped ZnO Coating as a Front Panel Electrode toward Efficient Thin Film Solar Cells
Mariya Aleksandrova, Tsvetozar Tsanev, Tatyana Ivanova, Kostadinka Gesheva, Velichka Strijkova, Jai Singh, Ajaya Kumar Singh

Bi-layer coatings from sputtered indium tin oxide (ITO) and gallium doped zinc oxide (Ga:ZnO) were investigated for transparency in the visible range of the electromagnetic spectrum, optical rejection ability in the near infrared spectrum and conductivity for the novel quantum dot based solar cells. The multilayer stack with optimized films thickness and surface roughness exhibit improved optical properties without to worsen the electrical ones, especially after additional oxidation during reactive sputtering of the metal-oxides. With an average optical transmittance of 90.7% over the visible region, average optical rejection greater than 65 % in the infrared range and resistivity lower than 100 Ω.cm, this coating is good candidate for front panel in CdS/ZnS core-shell quantum dots based solar cells. The efficiency of the cell increased with approximately 3 % as compared to the case with ITO only electrode. The results might be ascribed to the relatively low surface roughness and to the narrowed transmittance spectrum after ITO/Ga:ZnO interface has been established, targeting absorption of visible light only.

  • Open access
  • 13 Reads
Natural Rubber Composites for Paper Coating Applications
Pieter Samyn, Frank Driessen, Dirk Stanssens

Natural rubbers are characterized by extremely high molecular weight that might be beneficial in the formation of a protective barrier layer on paper substrates, providing good cohesive properties but limited adhesion. In parallel, the thermal properties of natural rubber with extremely low glass transition temperature might give the opportunity for good sealability. Therefore, natural rubbers can be good candidates to serve as an alternative ecological binder in paper coatings for water and grease barrier resistance. In order to be able to tune the surface properties of the paper coating, the effect of different additives are evaluated on rheological properties, thermo-mechanical properties and final surface properties of a paper coating. The additives are selected in parallel with common practice for paper industry, including talc, kaolinite clay and a type of organic nanoparticles, which are all added in the range of 5 to 20 wt.-%. Depending on the selected type of natural rubber, the dispersibility range (i.e., dispersive and distributive mixing) of the additives in the latex phase highly varies and is mainly determined by the molecular weight profile of the rubber. However, an optimum selection of viscosity range allows to obtain homogeneous mixtures without the need of surface modification of the additives. After bar-coating the latex mixtures on paper substrates, the drying properties of the composite coatings are followed by thermo-analytical evaluation and spectroscopy illustrating the influences of selected additives on the vulcanization process of the coating. In particular, the latter most efficiently improves in presence of nanoparticle fillers and highly increases the mechanical properties of the coating: the coating hydrophobicity can be successfully increased while in parallel reducing the adhesive surface properties.

  • Open access
  • 90 Reads

Properties of Thin Film-Covered GaN(0001) Surfaces

Gallium nitride (GaN), a wide band gap semiconductor (Eg=3.4 eV) has unique physical properties which opened up the door to widespread applications in modern electronic devices. The semiconductor is used as a base for fabrication of visible and UV lasers, light-emitting diodes, high temperature and frequency detectors, and transistors. In all these devices the electronic properties of bare and thin-covered GaN surfaces have impacts on their efficiencies.

Herein surface sensitive techniques with an emphasis on ultraviolet and X-ray photoelectron spectroscopies (UPS and XPS) are used to understand physical and chemical properties of bare and film-covered GaN(0001) surfaces. Thin films of several elements: nickel, palladium, manganese, arsenic and antimony (Ni, Pd, Mn, As, Sb) are included. The properties of bare GaN surfaces [1] as well as various adsorbate/GaN phase boundary are reported [2-7]. Different types of thin films behavior under an influence of annealing in ultrahigh vacuum conditions are distinguish. Metal films form surface alloys with gallium (NiGa, PdGa) while semi-metals layers easy evaporate from GaN surface, however, the layer in direct contact with the substrate can react with it causing a change in the surface properties of GaN(0001).

[1] M. Grodzicki, P. Mazur, A. Ciszewski, Appl. Surf. Sci. 440, 547 (2018)
[2] M. Grodzicki, P. Mazur, et al., Appl. Phys. A 120, 1443 (2015)
[3] M. Grodzicki, P. Mazur, et al., Appl. Surf. Sci. 304, 24 (2014)
[4] M. Grodzicki, P. Mazur, J. Brona, A. Ciszewski, Appl. Surf. Sci. 481, 790 (2019)
[5] M. Grodzicki, P. Mazur, A. Sabik, Sur. Sci. 689, 121460 (2019)
[6] M. Grodzicki, J. Rousset, et al., Appl. Surf. Sci. 493, 384 (2019)
[7] M. Grodzicki, P. Mazur, A. Sabik, Appl. Surf. Sci. 512, 145643, (2020)

  • Open access
  • 15 Reads
Encapsulated Microbial Propionic Acid as Additive for Texture-Defined Bread
Monica Trif, Ann-Kristin Schwarze, Malte Bethke, Berta Alvarez Penedo, Alexandru Rusu
Published: 14 May 2020 by MDPI AG in 2nd Coatings and Interfaces Web Conference session Posters

The main goal of ELBE-NH project funded by Federal Ministry of Education and Research (BMBF) Germany, is the utilization of the by-products of lignocellulosic biorefinery into high valuable compounds. One of such targeted compounds selected is propionic acid (PA) (obtained by microbiological conversion of the hydrolysates). PA is particularly suitable for use in industrially produced bread and baked goods, for preservation (antifungal abilities) as free acid or as sodium/calcium salts. Because of its astringent smell and strong acid taste, PA is rarely used in the food industry as free acid. Our aim is to test the possibility of (a) using encapsulated hydrophilic PA (0.3% w/v) into β-cyclodextrin (β-CD)/maltodextrin blends as the wall materials (19:1 or 17:3% w/v) spray-dried as additives incorporated direct into texture-defined bread product; and (b) into polysaccharide-based (e.g. carboxymethylcellulose (2% w/v) or chitosan (2% w/v)) biodegradation-resistant edible film (as carriers of PA antimicrobial agent (1.5-15% w/v)) with\without addition of β-CD (5% w/v) to the film matrix, as packaging material to enhance the safety and shelf life of texture-defined bread product., The benefit of adding β-CD, during film preparation, consists in the forming of hydrogen bond interactions with PA, resulting in high amounts of PA encapsulation due to the “fully immersed” complexation phenomenon. The texture-defined bread is a soft gel-like structure bread, easy to swallow and can be consumed without chewing, for people suffering from swallowing and chewing disorders. The texture-defined bread will have a high protein content up to 15 % higher than that of conventional bread and can thus make an important contribution to combating malnutrition.

  • Open access
  • 23 Reads
Natural Coatings on Titanium Surfaces to Improve Their Biological Response
Sara Ferraris, Enrica Vernè, Gissur Örlygsson, Paulo Tambasco, Felipe Sehn, Chuen How Ng, Hilmar Janusson, Giuliana Banche, Valeria Allizond, Cinzia Bertea, Lia Rimondini, Andrea Cochis, Vincenzo Guarino, Alessio Varesano, Claudia Vineis, Giovanna Gautier di Confiengo, Silvia Spriano

Biomolecules and extracts from natural products are gaining increasing interest due to their beneficial properties for human health, low toxicity, environmental compatibility and sustainability.

In this work, keratin, chitosan and peppermint essential oil have been used for the preparation of coatings on titanium substrates for biomedical implants/devices. All these coatings were obtained from local natural products/byproducts: keratin from discarded wool, chitosan from shrimps shells and peppermint essential oils from a local production. This approach supports a sustainable use of the resources and the sustainment of local economies with transformation of byproducts in high added values products.

Keratin was chosen for its ability to stimulate soft tissue adhesion and to be easily doped with metal ions in order to confer antibacterial activity. Keratin coatings were realized as electrospun oriented/random submicrometric fibres or continuous films.

Chitosan was selected for its anti-inflammatory and antibacterial properties. Continuous coatings were obtained with different grafting strategies (direct grafting, tresyl chloride activation or polydopamine addition).

Peppermint essential oil was chosen for its antibacterial activity and used for the obtainment of continuous coatings based on the self polymerizing ability of terpenes.

The coatings were characterized by means of SEM-EDS, FTIR, zeta potential, wettability, tape and scratch tests, cell and bacteria cultures.

Coatings were successfully obtained for all the considered natural substances. Good adhesion to titanium substrates was reached through the optimization of the surface preparation/grafting process. All the coatings were chemically stable in water and the continuous coating were mechanically resistant and protective for the metallic substrates. The keratin coatings were hydrophilic while mint oil and chitosan coatings were hydrophobic. At physiological pH, keratin and mint oil coatings were negatively charged while chitosan ones were positively charged. The oriented keratin fibres were able to drive fibroblast alignment. Ag-doped keratin fibres and mint coating showed antibacterial properties.

  • Open access
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Surface X-Ray Diffraction study of a bi-layer junction based on Cu and Cd sulphides for photovoltaic applications

The development of new-generation photovoltaic devices through more sustainable production techniques and materials is driven by the need of containing the threats to the biosphere while guaranteeing the safety of the supply, accounting for the limited availability of fossil fuels. This study investigates the crystal structure of thin films of chalcogenides, in particular a junction with a p-type (Cu2S) and a n-type (CdS) layer deposited one on top of the other on a Ag(111) substrate, starting from aqueous solution and by means of Electrochemical Atomic Layer Deposition (E-ALD) (the system is denoted by (Cu2S)60/(CdS)60/Ag(111)). The experiment highlights the profound epitaxial relationship existing between the films and the bulk, consequent to the homogenisation of the metrics of the CdS and the Cu2S structures to values commensurate to the surface periodicity of the substrate. Cadmium sulphide develops an elementary cell with crystallographic axes parallel to those of the Ag(111) and parameters |a|, |b| and |c| never found in any of the known mineral phases. The comparison with the wurtzite-type structure of greenockite shows a compensation mechanism related to the strain imposed by the film growth on the crystallographic Ag(111) surface.
The positions in the reciprocal space of the Cu2S reflections is compatible with a pseudo-hexagonal pattern rotated by 30 ° with respect to the Ag, as already noticed in relation to a Cu2S/Ag(111) E-ALD deposit (1). The Cu2S c axis results parallel to the direction [111] of the Ag substrate and its structure is characterized by the strong occurrence of the 3.963 Å periodicity, which corresponds to the interatomic distance S-S in the triangular CuS3 groups, basis of all the mineral Cu2-xS group structures. These data suggest a pseudo-hexagonal chalcocite-like structure with a planarization of S layers (1), as a result of the strong epitaxial relationship existing with the CdS below. This study confirms E-ALD as an energy efficient method for the growth of semiconducting heterostructures with tailored properties.

  • Giaccherini et al. (2017), Scientific Reports | 7: 1615 | DOI:10.1038/s41598-017-01717-0
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