Materials: Advances in Surface Coatings

Materials, Vol. 3, Pages 4607-4625: Creating Surface Properties Using a Palette of Hydrophobins

Filippo Zampieri — Mon, 06 Sep 2010 00:00:00 CEST

Small secreted proteins called hydrophobins play diverse roles in the life cycle of filamentous fungi. For example, the hydrophobin SC3 of Schizophyllum commune is involved in aerial hyphae formation, cell-wall assembly and attachment to hydrophobic surfaces. Hydrophobins are capable of self-assembly at a hydrophilic-hydrophobic interface, resulting in the formation of an amphipathic film. This amphipathic film can make hydrophobic surfaces of a liquid or a solid material wettable, while a hydrophilic surface can be turned into a hydrophobic one. These properties, among others, make hydrophobins of interest for medical and technical applications. For instance, hydrophobins can be used to purify proteins from complex mixtures; to reduce the friction of materials; to increase the biocompatibility of medical implants; to increase the solubility of water insoluble drugs; and to immobilize enzymes, for example, biosensor surfaces.

Materials, Vol. 3, Pages 4109-4141: Thin Film Deposition Using Energetic Ions

Darina Manova — Thu, 29 Jul 2010 00:00:00 CEST

One important recent trend in deposition technology is the continuous expansion of available processes towards higher ion assistance with the subsequent beneficial effects to film properties. Nowadays, a multitude of processes, including laser ablation and deposition, vacuum arc deposition, ion assisted deposition, high power impulse magnetron sputtering and plasma immersion ion implantation, are available. However, there are obstacles to overcome in all technologies, including line-of-sight processes, particle contaminations and low growth rates, which lead to ongoing process refinements and development of new methods. Concerning the deposited thin films, control of energetic ion bombardment leads to improved adhesion, reduced substrate temperatures, control of intrinsic stress within the films as well as adjustment of surface texture, phase formation and nanotopography. This review illustrates recent trends for both areas; plasma process and solid state surface processes.

Materials, Vol. 3, Pages 3994-4050: Functional Coatings or Films for Hard-Tissue Applications

Wang — Fri, 09 Jul 2010 00:00:00 CEST

Metallic biomaterials like stainless steel, Co-based alloy, Ti and its alloys are widely used as artificial hip joints, bone plates and dental implants due to their excellent mechanical properties and endurance. However, there are some surface-originated problems associated with the metallic implants: corrosion and wear in biological environments resulting in ions release and formation of wear debris; poor implant fixation resulting from lack of osteoconductivity and osteoinductivity; implant-associated infections due to the bacterial adhesion and colonization at the implantation site. For overcoming these surface-originated problems, a variety of surface modification techniques have been used on metallic implants, including chemical treatments, physical methods and biological methods. This review surveys coatings that serve to provide properties of anti-corrosion and anti-wear, biocompatibility and bioactivity, and antibacterial activity.

Materials, Vol. 3, Pages 3948-3964: Imaging Analysis of Carbohydrate-Modified Surfaces Using ToF-SIMS and SPRi

Bolles — Wed, 07 Jul 2010 00:00:00 CEST

Covalent modification of surfaces with carbohydrates (glycans) is a prerequisite for a variety of glycomics-based biomedical applications, including functional biomaterials, glycoarrays, and glycan-based biosensors. The chemistry of glycan immobilization plays an essential role in the bioavailability and function of the surface bound carbohydrate moiety. However, the scarcity of analytical methods to characterize carbohydrate-modified surfaces complicates efforts to optimize glycan surface chemistries for specific applications. Time-of-Flight Secondary Ion Mass Spectrometry (ToF-SIMS) is a surface sensitive technique suited for probing molecular composition at the biomaterial interface. Expanding ToF-SIMS analysis to interrogate carbohydrate-modified materials would increase our understanding of glycan surface chemistries and advance novel tools in the nascent field of glycomics. In this study, a printed glycan microarray surface was fabricated and subsequently characterized by ToF-SIMS imaging analysis. A multivariate technique based on principal component analysis (PCA) was used to analyze the ToF-SIMS dataset and reconstruct ToF-SIMS images of functionalized surfaces. These images reveal chemical species related to the immobilized glycan, underlying glycan-reactive chemistries, gold substrates, and outside contaminants. Printed glycoarray elements (spots) were also interrogated to resolve the spatial distribution and spot homogeneity of immobilized glycan. The bioavailability of the surface-bound glycan was validated using a specific carbohydrate-binding protein (lectin) as characterized by Surface Plasmon Resonance Imaging (SPRi). Our results demonstrate that ToF-SIMS is capable of characterizing chemical features of carbohydrate-modified surfaces and, when complemented with SPRi, can play an enabling role in optimizing glycan microarray fabrication and performance.

Materials, Vol. 3, Pages 3845-3866: Sintering of Fine Particles in Suspension Plasma Sprayed Coatings

Latka — Thu, 01 Jul 2010 00:00:00 CEST

Suspension plasma spraying is a process that enables the production of finely grained nanometric or submicrometric coatings. The suspensions are formulated with the use of fine powder particles in water or alcohol with some additives. Subsequently, the suspension is injected into plasma jet and the liquid additives evaporate. The remaining fine solids are molten and subsequently agglomerate or remain solid, depending on their trajectory in the plasma jet. The coating’s microstructure results from these two groups of particles arriving on a substrate or previously deposited coating. Previous experimental studies carried out for plasma sprayed titanium oxide and hydroxyapatite coatings enabled us to observe either a finely grained microstructure or, when a different suspension injection mode was used, to distinguish two zones in the microstructure. These two zones correspond to the dense zone formed from well molten particles, and the agglomerated zone formed from fine solid particles that arrive on the substrate in a solid state. The present paper focuses on the experimental and theoretical analysis of the formation process of the agglomerated zone. The experimental section establishes the heat flux supplied to the coating during deposition. In order to achieve this, calorimetric measurements were made by applying experimental conditions simulating the real coatings’ growth. The heat flux was measured to be in the range from 0.08 to 0.5 MW/m2,depending on the experimental conditions. The theoretical section analyzes the sintering during the coating’s growth, which concerns the fine particles arriving on the substrate in the solid state. The models of volume, grain boundary and surface diffusion were analyzed and adapted to the size and chemistry of the grains, temperature and time scales corresponding to the suspension plasma spraying conditions. The model of surface diffusion was found to best describe the sintering during suspension plasma spraying. The formation of necks having the relative size equal to 10% of particle diameter was found to be possible during the thermal cycles occurring at the coatings’ deposition. Transmission electron microscopic observations of the agglomerated zone hydroxyapatite coating confirm the sintering of some of the fine grains.

Materials, Vol. 3, Pages 3369-3384: Thin film of Poly(acrylic acid-co-allyl acrylate) as a Sacrificial Protective Layer for Hydrophilic Self Cleaning Glass

Lejnieks — Tue, 25 May 2010 00:00:00 CEST

Poly(acrylic acid-co-allyl acrylate) statistical copolymers were synthesized in a controlled manner in two steps: first tert.butyl acrylate and allyl acrylate were polymerized via atom transfer radical polymerization (ATRP) and afterwords the tert.butyl protective groups were removed via hydrolysis. Samples of self cleaning glass (SCG) were coated with thin films of poly(acrylic acid-co-allyl acrylate) and cross-linked afterwards by UV irradiation (in the presence of a photoinitiator and an accelerator). Solution cast thin films were transparent and homogeneous before and after UV cross-linking. The irradiated samples were found to be hydrophilic (Θ < 20°) and water insoluble. The coating prevented the spontaneous hydrophobization of the SCG by residual silicon exhaled from the sealing material. The TiO2 photocatalyst that covers the glass surface was found to strip the protective coating. The rate of the photooxidation process was measured by IR spectroscopy. The real field performance of the protective coating was also tested.