Academic literature on the topic 'Self-regenerating coatings'

: Self-healing coatings are intended to increase long-term durability and reliability and can be prepared by the use of microcapsules containing a self-healing agent capable of interacting with the matrix and regenerating the system. This review article provides an overview of the stateof- the-art patents published in the field of microcapsule-based self-healing organic coatings since the early 2000s. A discussion regarding coatings for corrosion protection is presented and the different self-healing approaches and mechanisms are also addressed, as well as future challenges and expectations for this kind of coatings.

The construction of optimized biological fuel cells requires a cathode which combines the longevity of a microbial catalyst with the current density of an enzymatic catalyst. Laccase-secreting fungi were grown directly on the cathode of a biological fuel cell to facilitate the exchange of inactive enzymes with active enzymes, with the goal of extending the lifetime of laccase cathodes. Directly incorporating the laccase-producing fungus at the cathode extends the operational lifetime of laccase cathodes while eliminating the need for frequent replenishment of the electrolyte. The hybrid microbial–enzymatic cathode addresses the issue of enzyme inactivation by using the natural ability of fungi to exchange inactive laccases at the cathode with active laccases. Finally, enzyme adsorption was increased through the use of a functionally graded coating containing an optimized ratio of titanium dioxide nanoparticles and single-walled carbon nanotubes. The hybrid microbial–enzymatic fuel cell combines the higher current density of enzymatic fuel cells with the longevity of microbial fuel cells, and demonstrates the feasibility of a self-regenerating fuel cell in which inactive laccases are continuously exchanged with active laccases.

ABSTRACTIn recent years, considerable effort has been devoted to the design and controlled fabrication of structured materials with functional properties. The layer by layer buildup of polyelectrolyte multilayer films (PEM films) from oppositely charged polyelectrolytes1 offers new opportunities for the preparation of functionalized biomaterial coatings. This technique allows the preparation of supramolecular nano-architectures exhibiting specific properties in terms of control of cell activation and may also play a role in the development of local drug delivery systems. Peptides, proteins or DNA, chemically bound to polyelectrolytes, adsorbed or embedded in PEM films, have been shown to retain their biological activities. Recently, tissue engineering has merged with stem cell technology with interest to develop new sources of transplantable material for injury or disease treatment. Eminently interesting, are bone and joint injuries disorders because of the low self-regenerating capacity of the matrix secreting cells. We present here for the first time that embedded BMP-2 and TGFβ1 in a multilayered polyelectrolyte film can drive embryonic stem cells to the cartilage or bone differentiation depending on supplementary co-factors. We selected a model system made from layer by layer poly-ℓ-glutamic acid (PℓGA) and poly-ℓ-lysine succinylated (PℓLs) films into which BMP-2 and TGFβ1 have been embedded. Our results demonstrate clearly that we are able to induce osteogenesis in embryonic stem cells mediated by growth factors embedded in a polyelectrolyte multilayer film.

ABSTRACTWe demonstrate a versatile class of nanoscale sensors based on single-stranded DNA (ss-DNA) as the chemical recognition site and single-walled carbon nanotube field effect transistors (swCN-FETs) as the electronic readout component. Coating swCN-FETs with ss-DNA causes a current change when exposed to gaseous analytes, whereas bare swCN-FETs show no detectable change. The responses differ in sign and magnitude depending both on the type of gaseous analyte and the sequence of DNA. Our results suggest that the conformation of ss-DNA on swCN-FET plays a role in determining the sensor response to gaseous analytes. The conformation depends not only on the base content of the oligomer, but also on the specific arrangement of the bases in the ss-DNA. We compare our results with the molecular dynamic simulations for understanding of the sensing mechanisms. SsDNA/swCN-FETs possess rapid recovery and self-regenerating ability, which could lead to realization of large arrays for sensitive electronic olfaction and disease diagnosis.

La sélection des matériaux utilisés dans les parties chaudes des moteurs aéronautiques ou dans les centrales de production d’énergie est devenue un enjeu crucial au vu des impératifs écologiques et économiques. L’un des composants critiques de ces systèmes sont les aubes de turbine dont la tenue mécanique est assurée par la nature des substrats employés (aciers et superalliages à base nickel). Cependant, leur tenue environnementale nécessite l’application de revêtements protecteurs source d’Al capables de former de barrières d’oxyde (Al2O3) imperméables à l’attaque externe par oxydation et corrosion aux hautes températures. L’épuisement de l’Al pour former l’oxyde et par interdiffusion avec le substrat conduit inexorablement à la perte de protection. Ainsi, des structures spécifiques de revêtement telles les barrières de diffusion peuvent alors être mises en place pour augmenter la durée des vies des aubes au détriment de leurs propriétés mécaniques et de coûts élevés de fabrication et environnementaux. Durant cette étude, des nouvelles voies originales de synthèse des revêtements de diffusion d’aluminium « autorégénérants » ont été étudiées. Ces revêtements disposent d’une structure composite, avec une matrice de phases intermétallique (NixAly) renforcée par des microréservoirs constitués d’un cœur (NixAly) et d'une paroi en Al2O3 à travers laquelle l’Al du cœur peut ravitailler la matrice et maintenir une concentration globale en Al suffisamment élevée dans la matrice capable de former la couche externe protectrice d’Al2O3.Nos études démontrent que les réactions aluminothermiques entre du NiO et l’Al permettent de former un tel revêtement autorégénerant avec une barrière de diffusion à l’interface substrat/revêtement lorsque le Ni est initialement pré-oxydé à 1100°C pendant 2h. Néanmoins, aucun compromis n’a été trouvé pour former des revêtements sans NiO résiduel qui pourrait compromettre l’adhérence du revêtement au substrat. En revanche, une voie électrochimique permet d’incorporer de microparticules d’Al3Ni2 dans des électrodépots de Ni. A la suite d’un traitement d’aluminisation par barbotine, les microparticules préoxydées s’incorporent de manière homogène dans un revêtement de β-NiAl. Après traitement d’oxydation isotherme à 1000°C durant 48h, ce revêtement par voie électrodéposition + aluminisation présente une teneur en aluminium supérieure à 40 at%, ce qui est supérieur à un revêtement de diffusion absent de microréservoirs démontrant ainsi le caractère autorégénerant des nouveaux revêtements
The selection of materials used in the hot parts of aeronautical turbines or in power plants has become a crucial issue in view of ecological and economic imperative. Turbine blades are amongst the most critical components. Their mechanical resistance is ensured by the substrate itself (steels and Ni alloys and superalloys). However, their low environmental resistance requires the application of protective coatings delivering Al to form oxide barriers blocking the external oxidative and corrosive attack. Upon exposure at high temperatures, Al depletes from the coating by oxidation to grow the oxide scale and by interdiffusion with the substrate’s elements resulting in the loss of protection. Some specific coating structures like the diffusion barriers have been investigated in the past but the overall mechanical properties are lowered and the fabrication and environmental costs are high. Therefore, a pioneering and original investigation has been conducted to synthesize “self-regenerating” aluminum diffusion coatings. These coatings are characterized by a composite structure whereby the matrix made of NixAly intermetallic phases is strengthened with microreservoirs made of NixAly core and an Al2O3 shell through which Al diffuses out to maintain the adequate Al concentration in the matrix, hence to stabilize the external protective Al2O3 scale.Our studies demonstrate that the aluminothermic reactions between NiO and Al lead to the formation of such a self-regenerating coating with an interdiffusion barrier at the coating/substrate interface whenever Ni is preoxidized at 1100°C for 2h beforehand. However, all the coatings sintered through this method possess residual NiO, which may compromise their adherence to the substrate. In contrast, the use of electrochemical methods allows to incorporate Al3Ni2 microparticles in the NI electrodeposits. With a subsequent slurry aluminizing treatment, the preoxidized particles incorporate homogeneously in a β-NiAl coating matrix. After exposure at 1100°C for 48h in air, the Al content in the self-regenerating coatings is greater than 40 at% as opposed to the micro-reservoirs-free aluminide coating allowing to demonstrate the self-regenerating property of these new coatings