The Pulsed Electron Deposition Technique for Biomedical Applications: A Review

Synthetic or Natural (Bio-Based) Hydroxyapatite? A Systematic Comparison between Biomimetic Nanostructured Coatings Produced by Ionized Jet Deposition

Calcium phosphate (CaP)-based materials are largely explored in orthopedics, to increase osseointegration of the prostheses and specifically in spine surgery, to permit better fusion. To address these aims, nanostructured biogenic apatite coatings are emerging, since they better mimic the characteristics of the host tissue, thus potentially being better candidates compared to their synthetic counterpart. Here, we compare hydroxyapatite (HA) nanostructured coatings, obtained by ionized jet deposition, starting from synthetic and natural sources. The starting materials and the corresponding films are characterized and compared from a compositional and morphological point of view, then their stability is studied after post-treatment annealing. Although all the films are formed by globular aggregates and show morphological features at different scales (from nano to micro), significant differences are found in composition between the synthetic and naturally derived HA in terms of magnesium and sodium content, carbonate substitution and Ca/P ratio, while differences between the coatings obtained by the different natural HA sources are minor. In addition, the shape of the aggregates is also target-dependent. All coatings have a good stability after over 14 days of immersion in medium, with natural apatite coatings showing a better behavior, as no cracking and detachments are observed during immersion. Based on these results, both synthetic and naturally derived apatitic materials appear promising for applications in spine surgery, with coatings from natural sources possessing physiochemical properties more similar to the mineral phase of the human bone tissue.

Simple Non-Equilibrium Atmospheric Plasma Post-Treatment Strategy for Surface Coating of Digital Light Processed 3D-Printed Vanillin-Based Schiff-Base Thermosets

A simple non-equilibrium atmospheric plasma post-treatment strategy was developed for the surface coating of three-dimensional (3D) structures produced by digital light processing 3D printing. The influence of non-equilibrium atmospheric plasma on the chemical and physical properties of vanillin-derived Schiff-base thermosets and the dip-coating process was investigated and compared to the influence of traditional post-treatment with UV-light. As a comparison, thermosets without post-treatment were also subjected to the coating procedure. The results document that UV post-treatment can induce the completion of the curing of the printed thermosets if complete curing is not reached during printing. Conversely, the plasma post-treatment does not contribute to the curing of the thermoset but causes some opening of the imine bonds and the regeneration of aldehyde functions. As a consequence, no great differences are observed between the not post-treated and plasma post-treated samples in terms of mechanical, thermal, and solvent-resistant properties. In contrast to the UV post-treatment, the plasma post-treatment of the thermosets induces a noticeable increase of the thermoset hydrophilicity ascribed to the reformation of amines on the thermoset surface. The successful coating process and the greatest uniformity of the lignosulfonate coating on the surface of plasma post-treated samples are considered to be due to the presence of these amines and aldehydes. The investigation of the UV shielding properties and antioxidant activities documents the increase of both properties with the increasing amount and uniformity of the formed coating. Interestingly, evident antioxidant properties are also shown by the noncoated thermosets, which are deduced to their chemical structures.

Silver-Containing Biomaterials for Biomedical Hard Tissue Implants

Bacterial infection caused by biomaterials is a very serious problem in the clinical treatment of implants. The emergence of antibiotic resistance has prompted other antibacterial agents to replace traditional antibiotics. Silver is rapidly developing as an antibacterial candidate material to inhibit bone infections due to its significant advantages such as high antibacterial timeliness, high antibacterial efficiency, and less susceptibility to bacterial resistance. However, silver has strong cytotoxicity, which can cause inflammatory reactions and oxidative stress, thereby destroying tissue regeneration, making the application of silver-containing biomaterials extremely challenging. In this paper, the application of silver in biomaterials is reviewed, focusing on the following three issues: 1) how to ensure the excellent antibacterial properties of silver, and not easy to cause bacterial resistance; 2) how to choose the appropriate method to combine silver with biomaterials; 3) how to make silver-containing biomaterials in hard tissue implants have further research. Following a brief introduction, the discussion focuses on the application of silver-containing biomaterials, with an emphasis on the effects of silver on the physicochemical properties, structural properties, and biological properties of biomaterials. Finally, the review concludes with the authors' perspectives on the challenges and future directions of silver in commercialization and in-depth research.

Recent Progress of Organic Semiconductor Materials in Spintronics

Spintronics, a new discipline focusing on the spin-dependent transport process of electrons, has been developing rapidly. Spin valves are the most significant carriers of spintronics utilizing the spin freedom of electrons. It is expected to pierce "Moore's Law" and become the core component in processors of the next generation. Organic semiconductors advance in their adjustable band gap, weak spin-orbit coupling and hyperfine interaction, excellent film-forming property, having enormous promise for spin valves. Here, the principle of spin valves is introduced, and the history and progress in organic spin injection and transport materials are summarized. Then we analyze the influence of spinterface on device performance and introduce reliable methods of constructing organic spin valves. Finally, the challenges for spin valves are discussed, and the future is proposed. We aim to draw the attention of researchers to organic spin valves and promote further research in spintronics through this paper.

Electrospun fibers coated with nanostructured biomimetic hydroxyapatite: A new platform for regeneration at the bone interfaces

Reconstruction of gradient organic/inorganic tissues is a challenging task in orthopaedics. Indeed, to mimic tissue characteristics and stimulate bone regeneration at the interface, it is necessary to reproduce both the mineral and organic components of the tissue ECM, as well as the micro/nano-fibrous morphology. To address this goal, we propose here novel biomimetic patches obtained by the combination of electrospinning and nanostructured bone apatite. In particular, we deposited apatite on the electrospun fibers by Ionized Jet Deposition, a plasma-assisted technique that allows conformal deposition and the preservation in the coating of the target's stoichiometry. The damage to the substrate and fibrous morphology is a polymer-dependent aspect, that can be avoided by properly selecting the substrate composition and deposition parameters. In fact, all the tested polymers (poly(l-lactide), poly(D,l-lactide-co-glycolide, poly(ε-caprolactone), collagen) were effectively coated, and the morphological and thermal characterization revealed that poly(ε-caprolactone) suffered the least damage. The coating of collagen fibers, on the other hand, destroyed the fiber morphology and it could only be performed when collagen is blended with a more resistant synthetic polymer in the nanofibers. Due to the biomimetic composition and multiscale morphology from micro to nano, the poly(ε-caprolactone)-collagen biomimetic patches coated with bone apatite supported MSCs adhesion, patch colonization and early differentiation, while allowing optimal viability. The biomimetic coating allowed better scaffold colonization, promoting cell spreading on the fibers.

Microstructure and Properties of Hydroxyapatite Coatings Made by Aerosol Cold Spraying–Sintering Technology

Hydroxyapatite is a widely used material used for the bioactivation of an implant’s surface. A promising hydroxyapatite coating approach is the kinetic deposition of powder particles. The possibility of solid-state deposition improvement through the merging of Aerosol Deposition and Low Pressure Cold Spraying techniques is a promising prospect for improving the deposition efficiency and the quality of coatings. The objective of the paper is to study the possibilities of hydroxyapatite coating structure modification through changes in the coating process and post-heat treatment. The novel Aerosol Cold Spraying system joining Low Pressure Cold Spraying and Aerosol Deposition was used for the deposition of coatings. The coating’s post-processing was conducted using two techniques: Spark Plasma Sintering and Pressureless Sintering. The coating’s structure was examined using scanning, transmission, and light microscopy, and X-ray diffraction. Substrate–coating bond strength was assessed using a tensile test. Homogenous buildup using Aerosol Cold Spraying of hydroxyapatite was achieved. Various pores and microcracks were visible in the sprayed coatings. The deposition process and the thermal post-processing did not lead to significant degradation of the hydroxyapatite phase. As a result of the Spark Plasma Sintering and Pressureless Sintering at 800 °C, an increase in tensile adhesion bond strength and crystal size was obtained.

Ionized jet deposition of antimicrobial and stem cell friendly silver-substituted tricalcium phosphate nanocoatings on titanium alloy

Orthopedic infections pose severe societal and economic burden and interfere with the capability of the implanted devices to integrate in the host bone, thus significantly increasing implants failure rate. To address infection and promote integration, here nanostructured antibacterial and bioactive thin films are proposed, obtained, for the first time, by Ionized Jet Deposition (IJD) of silver-substituted tricalcium phosphate (Ag-TCP) targets on titanium. Coatings morphology, composition and mechanical properties are characterized and proof-of-concept of biocompatibility is shown. Antimicrobial efficacy is investigated against four Gram positive and Gram negative bacterial strains and against C. albicans fungus, by investigating the modifications in planktonic bacterial growth in the absence and presence of silver. Then, for all bacterial strains, the capability of the film to inhibit bacterial adhesion is also tested. Results indicate that IJD permits a fine control over films composition and morphology and deposition of films with suitable mechanical properties. Biological studies show a good efficacy against Escherichia coli, Staphylococcus aureus, Pseudomonas aeruginosa, Enterococcus faecalis and against fungus Candida albicans, with evidences of efficacy against planktonic growth and significant reduction of bacterial cell adhesion. No cytotoxic effects are evidenced for equine adipose tissue derived mesenchymal stem cells (ADMSCs), as no reductions are caused to cells viability and no interference is assessed in cells differentiation towards osteogenic lineage, in the presence of silver. Instead, thanks to nanostructuration and biomimetic composition, tricalcium phosphate (TCP) coatings favor cells viability, also when silver-substituted. These findings show that silver-substituted nanostructured coatings are promising for orthopedic implant applications.

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Silver-substituted TCP films on titanium are prepared by Ionized Jet Deposition

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Films are nanostructured, hard, with submicron thickness

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Adipose mesenchymal stem cells differentiate into osteogenic lineage on the surface of films

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Films show antimicrobial and anti-adhesive activity against several microorganisms

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Films are promising for application in orthopedic titanium implants

A Comprehensive Review of Bioactive Glass Coatings: State of the Art, Challenges and Future Perspectives

Bioactive glasses are promising biomaterials for bone and tissue repair and reconstruction, as they were shown to bond to both hard and soft tissues stimulating cells towards a path of regeneration and self-repair. Unfortunately, due to their relatively poor mechanical properties, such as brittleness, low bending strength and fracture toughness, their applications are limited to non-load-bearing implants. However, bioactive glasses can be successfully applied as coatings on the surface of metallic implants to combine the appropriate mechanical properties of metal alloys to bioactivity and biocompatibility of bioactive glasses. In this review, several available coating techniques to coat metal alloys using bioactive glasses are described, with a special focus on thermal spraying, which nowadays is the most used to deposit coatings on metallic implants.

Biomimetic Coatings Obtained by Combinatorial Laser Technologies

The modification of implant devices with biocompatible coatings has become necessary as a consequence of premature loosening of prosthesis. This is caused mainly by chronic inflammation or allergies that are triggered by implant wear, production of abrasion particles, and/or release of metallic ions from the implantable device surface. Specific to the implant tissue destination, it could require coatings with specific features in order to provide optimal osseointegration. Pulsed laser deposition (PLD) became a well-known physical vapor deposition technology that has been successfully applied to a large variety of biocompatible inorganic coatings for biomedical prosthetic applications. Matrix assisted pulsed laser evaporation (MAPLE) is a PLD-derived technology used for depositions of thin organic material coatings. In an attempt to surpass solvent related difficulties, when different solvents are used for blending various organic materials, combinatorial MAPLE was proposed to grow thin hybrid coatings, assembled in a gradient of composition. We review herein the evolution of the laser technological process and capabilities of growing thin bio-coatings with emphasis on blended or multilayered biomimetic combinations. These can be used either as implant surfaces with enhanced bioactivity for accelerating orthopedic integration and tissue regeneration or combinatorial bio-platforms for cancer research.

Nanodecoration of electrospun polymeric fibers with nanostructured silver coatings by ionized jet deposition for antibacterial tissues

Silver-based nanomaterials are used as antibacterial agents in a number of applications, including wound dressing, where electrospun materials can effectively promote wound healing and tissue regeneration thanks to their biomimicry, flexibility and breathability. Incorporation of such nanomaterials in electrospun nonwovens is highly challenging if aiming at maximizing stability and antibacterial efficacy and minimizing silver detachment, without neglecting process straightforwardness and scalability. In this work nanostructured silver coatings were deposited by Ionized Jet Deposition (IJD) on Polylactic acid, a medical grade polyester-urethane and Polyamide 6,6 nanofibers. The resulting materials were thoroughly characterized to gain an in-depth view of coating morphology and substrate resistance to the low-temperature deposition process used. Morphology of silver coatings with well-cohesive grains having dimensions from a few tens to a few hundreds of nanometers was analyzed by SEM, TEM and AFM. TGA, DSC, FTIR and GPC showed that the polymers well withstand the deposition process with negligible effects on their properties, the only exception being the polylactic acid that resulted more susceptible to degradation. Finally, the efficacy against S. aureus and E. coli bacterial strains was demonstrated, indicating that electrospun fibers decorated with nanostructured silver by IJD represent a breakthrough solution in the field of antibacterial devices.