Feasibility of using low pressure cold gas spray for the spraying of thick ceramic hydroxyapatite coatings

This article deals with the production of thick ceramic hydroxyapatite coatings obtained by Low Pressure Cold Gas Spray (LPCGS) system. Several factors such as powder microstructure, surface roughness and cold gas spray system are here discussed in the build‐up process. The use of nanocrystalline powder composed by fine agglomerates and needle‐like shape microstructure allows the realignment and compaction of individual crystallites to form thick deposits. In addition, the activation of the substrate surface results convenient for the first impinging particles anchored properly. Then, layer by layer, particles can remain attached leading to coating build‐up. Additionally, the use of low shock pressure as well as constant feeding system provided by LPCGS system lead to homogeneous coatings in comparison with High Pressure Cold Gas Spray (HPCGS) system. The successful coating build‐up has been achieved not only by the use of an agglomerated feedstock powder, but also by previous surface treatment and the use of the low pressure system. The obtaining of HA components by LPCGS is promising within biomedical field. An improvement of component strength is also suggested by means of thermomechanical analysis of the powder. The performance of a post heat‐treatment leads to an increase in HA strength, as well as crystal size

Effect of Heat Treatment on Osteoblast Performance and Bactericidal Behavior of Ti6Al4V(ELI)-3at.%Cu Fabricated by Laser Powder Bed Fusion

Cu addition to alloys for biomedical applications has been of great interest to reduce bac-terial growth. In situ-alloyed Ti6Al4V(ELI)-3at.%Cu was successfully manufactured by laser pow-der bed fusion (L-PBF). Even so, post-heat treatments are required to avoid distortions and/or achieve required/desired mechanical and fatigue properties. The present study is focused on the investigation of microstructural changes in L-PBF Ti6Al4V(ELI)-3at.%Cu after stress relieving and annealing treatments, as well as their influence on osteoblast and bactericidal behavior. After the stress relieving treatment, a homogenously distributed β phase and CuTi2 intermetallic precipitates were observed over the αʹ matrix. The annealing treatment led to the increase in amount and size of both types of precipitates, but also to phase redistribution along α lamellas. Although microstruc-tural changes were not statistically significant, such increase in β and CuTi2 content resulted in an increase in osteoblast proliferation after 14 days of cell culture. A significant bactericidal behavior of L-PBF Ti6Al4V(ELI)-3at.%Cu by means of ion release was found after the annealing treatment, provably due to the easier release of Cu ions from β phase. Biofilm formation was inhibited in all on Cu-alloyed specimens with stress relieving but also annealing treatment

In-vitro comparison of hydroxyapatite coatings obtained by cold spray and conventional thermal spray technologies

Hydroxyapatite (HA) coatings onto Ti6Al4V alloy substrates were obtained by several thermal spray technologies: atmospheric plasma spray (APS) and high velocity oxy fuel (HVOF), together with the cold spray (CS) technique. A characterization study has been performed by means of surface and microstructure analyses, as well as biological performance. In-vitro tests were performed with primary human osteoblasts at 1, 7 and 14 days of cell culture on substrates. Cell viability was tested by MTS and LIVE/DEAD assays, cell differentiation by alkaline phosphatase (ALP) quantification, and cell morphology was analyzed by scanning electron microscopy. The HA coatings showed an increase of HA crystallinity from 62,4% to 89%, but also an increase of hydrophilicity from ∼32° to 0°, with the decrease of the operating temperature of the thermal spray techniques (APS > HVOF > CS). Additionally, APS HA coatings showed more surface micro-features than HVOF and CS HA coatings; cells onto APS HA coatings showed faster attachment by acquiring osteoblastic morphology in comparison with the rounded cell morphology observed onto CS HA coatings at 1 day of cell culture. HVOF HA coatings also showed proper cell adherence but did not show extended filopodia as cells onto APS HA coatings. However, at 14 days of cell culture, higher cell proliferation and differentiation was detected on HA coatings with higher crystallinity (HVOF and CS techniques). Cell attachment is suggested to be favoured by surface micro-features but also moderate surface wettability whereas cell proliferation and differentiation is suggested to be highly influenced by HA crystallinity and crystal size

Functionalized coatings by cold spray: an in vitro study of micro- and nanocrystalline hydroxyapatite compared to porous titanium

Three different surface treatments on a Ti6Al4V alloy have been in vitro tested for possible application in cementless joint prosthesis. All of them involve the novelty of using the Cold Spray technology for their deposition: (i) an as-sprayed highly rough titanium and, followed by the deposition of a thin hydroxyapatite layer with (ii) microcrystalline or (iii) nanocrystalline structure. Primary human osteoblasts were extracted from knee and seeded onto the three different surfaces. Cell viability was tested by MTS and LIVE/DEAD assays, cell differentiation by alkaline phosphatase (ALP) quantification and cell morphology by Phalloidin staining. All tests were carried out at 1, 7 and 14 days of cell culture. Different cell morphologies between titanium and hydroxyapatite surfaces were exhibited. At 1 day of cell culture, cells on the titanium coating were spread and flattened, expanding the filopodia actin filaments in all directions, while cells on the hydroxyapatite coatings showed round like-shape morphology due to slower attachment. Higher cell viability was detected at all times of cell culture on titanium coating due to a better attachment at 1 day. However, from 7 days of cell culture, cells on hydroxyapatite showed good attachment onto surfaces and highly increased their proliferation, mostly on nanocrystalline, achieving similar cell viability levels than titanium coatings. ALP levels were significantly higher in titanium, in part, because of greatest cell number. Overall, the best cell functional results were obtained on titanium coatings whereas microcrystalline hydroxyapatite presented the worst cellular parameters. However, results indicate that nanocrystalline hydroxyapatite coatings may achieve promising results for the faster cell proliferation once cells are attached on the surface

X-ray microtomographic characterization of highly rough titanium cold gas sprayed coating for identification of effective surfaces for osseointegration

A highly rough titanium coating obtained by Cold Gas Spray (CGS) has been characterized by means of high-resolution 3D microtomography (micro-CT) with the aim to evaluate its open and close porosity for possible use in orthopaedic implants to promote osseointegration. Micro-CT allowed a qualitative and quantitative description of the main features, morphology of the pores and surface roughness of the coating. Several numerical values were obtained to describe size, form and distribution of the closed/inner and open/outer pores. Additionally, surface roughness and open porosity were image-analyzed to find the effective surface for osseointegration

Hierarchical structures of anodised cold gas sprayed titanium coatings

Three different surface treatments on a Ti6Al4V alloy have been in vitro tested for possible application in cementless joint prosthesis; all of them involve the novelty of using the Cold Spray technology for their deposition: (i) an as-sprayed highly rough titanium and, followed by the deposition of a thin hydroxyapatite layer with (ii) microcrystalline or (iii) nanocrystalline structure. Primary human osteoblasts extracted from knee were seeded onto surfaces and cell viability using MTS and LIFE/DEAD assays, osteoblasts differentiation by alkaline phosphatase (ALP) quantification as well as cell morphology were tested at 1, 7 and 14 days of cell culture. Different cell morphologies between titanium and hydroxyapatite surfaces were exhibited; at 1 day of cell culture, cells on the titanium coating were spread and flattened, expanding the filopodia actin filaments in all directions, while cells on the hydroxyapatite coatings showed round like-shape morphology due to a slower attachment. Higher cell viability was detected at all times of cell culture on titanium coating due to a better attachment at 1 day. However, from 7 days of cell culture, cells on hydroxyapatite showed good attachment onto surfaces and highly increased their proliferation, mostly on nanocrystalline, achieving similar cell viability levels than titanium coatings. ALP levels were significantly higher in titanium, in part, because of greatest cell number. Overall, the best cell functional results were obtained on titanium coatings whereas microcrystalline hydroxyapatite presented the worst cellular parameters. However, results indicate that nanocrystalline hydroxyapatite coatings may achieve promising results for the faster cell proliferation once cells are attached on the surface

A new alternative for obtaining nanocrystalline bioactive coatings: study of hydroxyapatite deposition mechanisms by cold gas praying

The present article is intended to study the deposition mechanisms of bioactive hydroxyapatite (HA) particles by means of Cold Gas Spraying (CGS). A comparison of the deposition on two different substrates (Ti6Al4V and Al7075T6) and different particle sizes is presented. Although this is a more specific deposition technique for ductile materials, it is here shown that, in certain conditions, ceramic deposition is possible despite the inherent low ductility. The resulting internal structure and the features at the particle-substrate interface are discussed in view of Transmission Electron Microscopy examinations of a Focused Ion Beam lift-out prepared sample. Mainly, under shock compressive loading, the porous sintered powder proceeds through pore collapse, fragmentation and densification as well as grain refinement. The process is described through different plastic mechanisms in ceramics. This opens a new alternative route to produce nanocrystalline HA coatings through a cost-effective proces

In-vitro study of hierarchical structures: Anodic oxidation and alkaline treatments onto highly rough titanium cold spray coatings for biomedical applications

Hierarchical structures were obtained applying two different nanotexturing surface treatments onto highly rough commercial pure titanium coatings by cold spray: (i) anodic oxidation and (ii) alkaline treatments. An extended surface characterization in terms of topography, composition, and wettability has been performed to understand how those parameters affect to cell response. Primary human osteoblasts extracted from knee were seeded onto the as-sprayed titanium surface before and after the nanotexturing treatments. Cell viability was tested by using MTS and LIVE/DEAD assays, as well as osteoblasts differentiation by alkaline phosphatase (ALP) quantification at 3 and 10 days of cell culture. The combination of micro-/nano-roughness results in a significantly increase of cell proliferation, as well as cell differentiation after 10 days of cell culture in comparison with the non-treated coatings

Dense nanostructured calcium phosphate coating on titanium by cold spray

This article deals with the understanding of building-up mechanisms of bioactive nanocrystalline hydroxyapatite coatings by Cold Spray, revealing very promising results in contrast to more conventional techniques such as Plasma Spray. A full characterization of feedstock and coatings is provided. The agglomerated structure of the powder proved to be suitable to obtain successfully thick hydroxyapatite coatings. A crystallite size below similar to 20 nm in the powder and the as-sprayed coatings is calculated by the Rietveld X-ray refinement method and agreed by Transmission Electron Microscopy. Some wipe tests were carried out on Ti6Al4V substrates in order to study the deposition of single particles and the nanoscale features were evaluated. The resulting structure indicates that there is no delimitation of particle boundaries and the overall coating has been formed by effective compaction of the original nanocrystallites, leading to consistent and consolidated layers

Isolo : a new concept of privacy

Isolo es un conjunto de cuatro productos interactivos, diseñados por los estudiantes del Grado de Diseño de EINA, que exploran y aplican el concepto “privacidad”. Los proyectos ofrecen diferentes formas de aislamiento respetando los hábitos de los usuarios y recreando atmósferas de intimidad, desde el individuo hasta el colectivo. Los proyectos presentados son: Köllen Eget es un espacio de trabajo adaptado a los nuevos hábitos de trabajo y al uso de las de las nuevas tecnologías. La interactividad del producto permite reorganizar el espacio y generar un ambiente personalizado, adaptándose a cada usuario gracias a la iluminación, la acústica y la presencia de diferentes elementos móviles. Còdol es un separador de espacios que contempla el contraste entre el vacío y la plenitud. Consigue crear un ambiente privado dentro de un entorno interior y concurrido gracias a su estructura envolvente de paneles móviles con propiedades acústicas y tonalidades suaves. Petal es una silla versátil y adaptable al usuario, inspirada en las formas orgánicas de las flores. En cada lateral hay un panel flexible que permite ser regulado en diferentes posiciones y de esta manera convertirlo en un espacio del almacenamiento personalizado acorde con las necesidades del usuario. Kodama es un panel decorativo, que se presenta como una arboleda de influencia oriental coronada por los elementos más distintivos de todo el conjunto: los asientos, que están colocados aleatoriamente por toda la estructura a disposición del usuario.Isolo és un conjunt de quatre productes interactius, dissenyats pels estudiants del Grau de Disseny d’EINA, que exploren i apliquen el concepte “privacitat”. Els projectes ofereixen diferents formes d’aïllament respectant els hàbits dels usuaris i recreant atmosferes d’intimitat, des de l’individu fins al col·lectiu. Els projectes presentats són: Köllen Eget és un espai de treball adaptat als nous hàbits de treball i a l’ús de les noves tecnologies. La interactivitat del producte permet reorganitzar l’espai i generar un ambient personalitzat, adaptant-se a cada usuari a través de la il·luminació, l’acústica i la presència de diferents elements mòbils. Còdol és un separador d’espais que contempla el contrast entre el buit i el ple. Aconsegueix crear un ambient privat dins d’un entorn interior i concorregut gràcies a la seva estructura envoltant de panells mòbils amb propietats acústiques i tonalitats suaus. Petal és una cadira versàtil i adaptable a l’usuari, inspirada en les formes orgàniques de les flors. A cada lateral hi ha un panell flexible que permet ser regulat en diferents posicions i d’aquesta manera convertir-lo en un espai d’emmagatzematge personalitzat d’acord amb les necessitats de l’usuari. Kodama és un panell decoratiu, que es presenta com una arbreda d’influència oriental, coronada pels elements més distintius de tot el conjunt: els seients, que estan disposats aleatòriament per tota l’estructura a disposició de l’usuari.Isolo is a set of four interactive products, designed by students on the EINA Bachelor’s Degree in Design, that explore and apply the concept of “privacy”. The projects offer different forms of isolation, respecting users’ habits and recreating atmospheres of intimacy, from the individual to the group. The projects presented are: Köllen Eget is a workspace adapted to new working habits and the use of new technologies. The interactivity of the product allows users to reorganise their space and create a personalised ambience, adapting to each user through light, sound and the presence of different mobile elements. Còdol is a space divider that considers the contrast between empty and full. It manages to create a private ambience in an interior and busy environment thanks to its structure, surrounded by moveable panels with sound properties and soft tones. Petal is a versatile chair that is adaptable to the user, inspired by the organic shapes of flowers. On each side is a flexible panel that can be regulated in different positions, so turning it into a personalised storage space in line with your needs. Kodama is a decorative panel displayed as an Oriental-influenced woodland crowned by the most distinctive elements of the entire piece: the seats, which are placed at random throughout the whole structure for use by the user