Chitosan is one of the most widely used natural biopolymers for a great variety of biomedical applications owing to its biocompatibility, biodegradability, and antibacterial activity, being generally ...regarded as a safe material. It can be employed as a dispersant, binder, and surface charge agent for particles in suspension. Electrophoretic deposition (EPD) of chitosan, especially in combination with other materials, is receiving increasing attention for biomedical applications. This article presents a comprehensive review of the field of EPD of chitosan-based composite coatings by highlighting their microstructural, mechanical, surface, and biological properties. Since suspension characteristics have significant influences on the deposition mechanisms, kinetics, and on the overall properties of the electrophoretically deposited coatings, suspension parameters such as concentration, viscosity, and zeta potential are discussed, including chitosan-based suspensions with hydroxyapatite, bioactive glass particles, carbonaceous materials and other inorganic and organic materials. The deposition mechanisms proposed for each composite system are highlighted. Moreover, the effects of key EPD process parameters on the microstructural homogeneity, mechanical properties as well as surface and biological characteristics of the coatings are emphasised, and specific approaches for future research are proposed based on the state-of-the-art and considering EPD produced chitosan-based coatings in applications such as tissue engineering and drug delivery systems.
Ti6Al4V alloy was shot peened by using stainless-steel shots with different sizes (0.09–0.14 mm (S10) and 0.7–1.0 mm (S60)) for two durations (5 and 15 min) using a custom-designed peening system. ...The shot size was the main parameter modifying the roughness (0.74 µm for S10 vs. 2.27 µm for S60), whereas a higher peening time slightly increased roughness. Hardness improved up to approximately 35% by peening with large shots, while peening time was insignificant in hardness improvement. However, longer peening duration with large shots led to an unwanted formation of micro-cracks and delamination on the peened surfaces. After dry sliding wear tests, the mass loss of peened samples (S60 for 15 min) was 25% higher than that of un-peened samples, while the coefficient of friction decreased by 12%. Plastically deformed regions and micro-scratches were observed on the worn surfaces, which corresponds to mostly adhesive and abrasive wear mechanisms. The present study sheds light on how surface, subsurface and tribological properties of Ti6Al4V vary with shot peening and peening parameters, which paves the way for the understanding of the mechanical, surface, and tribological behavior of shot peened Ti6Al4V used in both aerospace and biomedical applications.
For the first time, the present review critically evaluates biodegradable polymer matrix composites containing graphene-related materials (GRMs) for antibacterial applications while discussing their ...development, processing routes, mechanical properties, and antibacterial activity. Due to its suitable biological properties and processability, chitosan has been the most widely used biodegradable polymer for the fabrication of GRM-containing composites with antibacterial properties. The majority of biodegradable polymers (including cellulose-, gelatine-, PVA-, PCL-, and PHA-based polymers) exhibit little to no antibacterial effect alone; however, they show significant antibacterial activity (>70%) when combined with GRMs. In vitro and in vivo studies indicate that GRMs functionalization with biodegradable polymers also reduces potential GRM cytotoxicity. Overall, GRMs in biodegradable polymer matrices provide attractive antibacterial activity against a broad spectrum of bacteria (>30 different bacteria) along with improved mechanical properties over pristine polymers, where the type and the degree of improvement provided by GRMs depend on the specific matrix. For example, the addition of GRMs into chitosan, PVA, and PCL matrices increases their tensile strength by 80%, 180%, and 40%, respectively. Challenges remain in understanding the effects of processing routes and post-processing methods on the antibacterial activity and biocompatibility of biodegradable polymer/GRM composites. Given their promising properties and functionality, research on these composites is expected to further increase along with the implementation of new composite systems. These would include a wide range of applications, e.g., wound dressings, tissue engineering, drug delivery, biosensing, and photo-thermal therapy, as well as non-medical use, e.g., antibacterial food packaging, water treatment, and antibacterial fabrics.
Graphene-related materials (GRMs) in polymer matrices can provide excellent antibacterial activity against a broad spectrum of bacteria together with improved mechanical properties (e.g., tensile strength and elastic modulus) over pristine polymers; thus, research efforts and applications of biodegradable polymer matrix composites containing GRMs have increased notably in the last ten years. For the first time, the present review critically evaluates biodegradable polymer matrix composites containing GRMs for antibacterial applications while discussing their development, processing routes, mechanical properties, and antibacterial activity. Future research directions for each composite system are proposed to shed light on overcoming the existing challenges in composite performance (e.g., mechanical properties, toxicity) reported in the literature.
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The objectives of this study were to compare the fracture strength of endocrown restorations fabricated with different preparation depth and various CAD/CAM ceramics, and to assess the fracture ...types. Endodontically treated 100 extracted human permanent maxillary centrals were divided into two preparation depth groups as short (S: 3-mm-deep) and long (L: 6-mm-deep), then five ceramic subgroups, namely: feldspathic-ceramic (Vita Mark II-VM2), lithium-disilicate glass-ceramic (IPS e.max CAD-E.max), resin-ceramic (LAVA Ultimate-LU), polymer infiltrated ceramic (Vita Enamic-VE) and monoblock zirconia (inCoris TZI-TZI) (n=10/subgroup). The endocrowns were fabricated by CAD/CAM and were cemented with resin cement (RelyX U200). The teeth were thermally cycled (5,000cycles) and fracture tests were performed at 45º angle to the teeth. The data were statistically analyzed (Kruskal-Wallis, Mann Whitney U), failure modes were evaluated with stereomicroscopy. Zirconia group provided the statistically highest fracture strength, but also exhibited non-repairable failures. Preparation depth has an effect on the fracture strength only for feldspathic ceramic.
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•Chitosan-based composite coatings are deposited by EPD on grit-blasted substrates.•The coatings exhibit a complex and rough topography owing to grit blasting.•A deposition mechanism ...is proposed for coatings deposited on grit-blasted surfaces.•Effects of surface features of substrates on the wettability of coatings are shown.•Grit blasting could be convenient to tailor the surface features of EPD coatings.
Chitosan, chitosan/45S5 bioactive glass (mBG), chitosan/nanobioglass (nBG), and chitosan/mBG/nBG coatings were deposited on grit-blasted and mirror-polished Ti6Al4 V alloy substrates by electrophoretic deposition (EPD). This study discusses how the surface characteristics of the substrates influence the 3D surface topography, areal surface roughness, morphology, and wettability of chitosan-based thin composite coatings while focusing on tuning the surface characteristics by grit-blasting. The surfaces of coated and uncoated specimens were characterised by SEM analysis with EDX, image analysis, contact angle measurements, 3D surface topography analysis, FTIR analysis, and in-vitro bioactivity studies. The coatings deposited on grit-blasted substrates presented rougher surface topography, higher areal surface roughness values and wettability compared to the mirror-polished surfaces. A deposition mechanism was suggested to clarify the deposition of chitosan/mBG coatings on grit-blasted substrates. Apatite crystals were formed on chitosan/mBG coatings after immersion in SBF for three days. A robust image analysis method was applied to reveal the distribution and area coverage percent of deposited mBG, which demonstrated the increase of mBG coverage with the increases in voltage. The present study shows that grit blasting could be a favourable surface treatment to tailor the surface characteristics of organic-inorganic composite coatings by influencing their surface topography, roughness, and wettability.
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•Polyetheretherketone/hydroxyapatite coatings were deposited via EPD.•Coatings were optimized regarding the bioactivity and adhesion of the coating.•The increase of hydroxyapatite ...amount in suspension increased the zeta potential.•The increase in voltage increased polyetheretherketone content in the coating.•There is a tradeoff between the adhesion strength and bioactivity of the coatings.
This study focuses on the optimization of electrophoretic deposition (EPD) and suspension parameters for producing PEEK-hydroxyapatite (HA) coatings with feasible microstructure, adhesion strength, and in-vitro bioactivity. Nanostructured hydroxyapatite (HA) micro-granules were incorporated with PEEK to form PEEK-hydroxyapatite composite coatings via EPD. After EPD, a heat-treatment at 375 °C was applied for densification of the coatings and for enhancing the adhesion between the coatings and the substrates. It was found that both adhesion strength and in-vitro bioactivity of the coatings were dependent on the PEEK and HA relative contents. Thus, increasing the amount of HA improved the bioactivity while decreased the adhesion strength of the coatings. Apatite-like layer formation was observed on coatings with high HA content after incubation for three days in simulated body fluid (SBF). Finally, a deposition mechanism was proposed for the EPD of the PEEK-hydroxyapatite composite system.
The present study aims to reveal the effectiveness of grit blasting when modifying the surface properties of a Ti6Al4V alloy deteriorated due to shot peening. Ti6Al4V samples shot-peened under ...different parameters were grit-blasted (at impingement angles of 30° and 90°, blasting pressures of 1.5 bar and 3 bar). Grit blasting proved to be an effective way of tailoring the surface topography as the surface roughness of shot-peened samples (approx. 10 µm) declined to approx. 2 µm. The surface modifications mainly occurred via micro-ploughing and micro-cutting wear mechanisms, indicating that grit blasting at 30° was more favourable than at 90° for modifying the deteriorated surface properties after shot peening. Shot-peened samples behaved similarly to mirror-polished unpeened samples during grit blasting, showing that the modified surface and subsurface properties obtained via shot peening have an insignificant effect on grit blasting of the alloy. A quantitative analysis of the area covering the embedded particles on the surface of the alloy due to grit blasting showed that the area almost doubled when the alloy was grit blasted at 90° compared to 30°, highlighting an excessive amount of embedding, which would be critical when surface decontamination is important.
Thermal barrier coatings (TBCs) are commonly applied specifically for aerospace applications in which they are subjected to air-borne particles. Therefore, solid particle erosion behavior of all ...coating layer has been an important phenomenon and erosion behavior of various TBCs has been widely investigated in literature. In the present study, CoNiCrAlY and yttria stabilized zirconia (ZrO
2
+ 8% Y
2
O
3
) powders were deposited on Inconel 718 nickel based super alloy substrate. Atmospheric plasma spraying technique was applied for the deposition of the metallic bond coat and the ceramic top coats. Erosion tests were carried out under various particle impingement angles with an air jet erosion tester. Afterwards, eroded surfaces of the specimens were investigated with a three-dimensional (3D) optical surface profilometer (noncontact) and scanning electron microscope. The erosion rates, the areal surface roughness values, the 3D surface topographies, and the surface morphology of the specimens were evaluated based on the particle impingement angle to understand the solid particle erosion behavior of the produced coatings. The maximum erosion rates occurred at 60° impingement angle which is an indication of semi-ductile/semi-brittle erosion behavior. Furthermore, the surface roughness values and surface topographies also dramatically varied depending on the impingement angle. Deeper and wider erosion craters formed at 60° impact angle and the erosion craters were visualized by profilometer analysis.
High-velocity air fuel (HVAF) coating processes have advantages over conventional high-velocity oxygen fuel (HVOF) processes, resulting in coatings with superior properties. The present review first ...provides a concise overview of HVAF coatings, highlighting their advantages over HVOF coatings. Then, the fundamentals of solid particle, slurry, and cavitation erosion are briefly introduced. Finally, the performance of HVAF coatings for erosion-resistant applications is discussed in detail. The emerging research consistently reports HVAF-coatings having higher erosion resistance than HVOF-coatings, which is attributed to their elevated hardness and density and improved microstructural features that inhibit the surface damages caused by erosion. The dominant wear mechanisms are mainly functions of particle impact angle. For instance, the removal of the binder phase at high impact angles causes the accumulation of plastic strain on hard particles (e.g., WC particles) in the matrix, forming micro-cracks between the hard particles and the matrix, eventually decreasing the erosion resistance of HVAF coatings. The binder phase of HVAF-coatings significantly affects erosion resistance, primarily due to their inherent mechanical properties and bearing capacity of hard particles. Optimizing spraying parameters to tailor the microstructural characteristics of these coatings appears to be the key to enhancing their erosion resistance. The relationship between microstructural features and erosion mechanisms needs to be clarified to process coatings with tailored microstructural features for erosion-resistant applications.
The present study aims to examine the effects of operational parameters on the surface topography and wear mechanisms of monolithic and conventional yttria‐stabilized zirconia (Y‐TZP) ceramics in the ...micro blasting process, performed under various acceleration pressures (1.5–3 bar), particle impact angles (30°–90°), and erodent particle sizes (50–460 μm). Three‐dimensional (3D) surface topography, surface roughness, and surface morphology of micro‐blasted specimens were analyzed by using non‐contact optical profilometry and SEM‐EDS. The micro blasting characteristics of both Y‐TZP were similar that increased blasting pressure and erodent particle size increased surface roughness. Erosion rate increased with increasing blasting pressure, whereas it decreased with increasing erodent particle size. Particle size was the most effective parameter on changing surface topography, while the particle impact angle had no distinct effect on the erosion rate, surface roughness, and surface topography of Y‐TZP ceramics. SEM‐EDS analyses showed that the primary wear mechanism during micro blasting was micro‐cutting with a substantial amount of embedded particles on the material's surface.
The present study aims to: (1) examine the effects of operational parameters on the surface topography of yttria‐stabilized zirconia (Y‐TZP) ceramics in micro blasting process, and to (2) investigate wear and deformation mechanisms affecting surface topography during roughening of monolithic and conventional Y‐TZP ceramics via micro blasting process, which was performed under various acceleration pressures (1.5–3 bar), particle impact angles (30°–90°), and erodent particle sizes (50 –460 μm) via a micro blasting test rig. The micro blasting characteristics of both Y‐TZP were similar that increased blasting pressure and erodent particle size lead to increase in surface roughness, and erosion rate rises with increasing blasting pressure, whereas it decreases with increasing erodent particle size. Particle size is the most effective parameter on changing surface topography while particle impact angle had no distinct effect on the erosion rate, surface roughness, and surface topography of Y‐TZP ceramics.
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