Special Issue "Ion-Substituted Calcium Phosphates Coatings"

A special issue of Coatings (ISSN 2079-6412). This special issue belongs to the section "Surface Coatings for Biomedicine and Bioengineering".

Deadline for manuscript submissions: closed (31 August 2020) | Viewed by 19968

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Special Issue Editors

Dr. Gabriela Graziani
E-Mail Website
Guest Editor
Laboratory of NanoBiotechnology (NaBi) - IRCCS Istituto Ortopedico Rizzoli (Rizzoli Orthopaedic Institute) - Bologna, Italy
Interests: Calcium phosphates; nanostructured coatings; biomaterials; infection; 3D printing and bioprinting; orthopaedics; orthopaedic oncology; tissue models; cultural heritage; stone consolidants
Special Issues, Collections and Topics in MDPI journals
Dr. Enrico Sassoni
E-Mail Website1 Website2
Guest Editor
Department of Civil, Chemical, Environmental and Materials Engineering (DICAM) – University of Bologna, Bologna, Italy
Interests: calcium phosphates; hydroxyapatite; stone; mortar; masonry; consolidation; mechanical properties; durability; composite materials; hemp
Special Issues, Collections and Topics in MDPI journals

Special Issue Information

Dear Colleagues,

Coatings based on hydroxyapatite and calcium phosphates have a significant relevance in several research fields, such as biomaterials, cultural heritage and water treatment, due to their characteristic properties.

Hydroxyapatite can easily accommodate foreign ions, which can either be incorporated into the lattice, thanks to its specific lattice characteristics, or be adsorbed on its surface. All these substitutions significantly alter the morphology, lattice parameters and crystallinity of hydroxyapatite, so they influence its main properties. These ion substitutions can be desired or can derive from substrate contaminations, which is an important aspect to be evaluated. Finally, this capability can be used to obtain hydroxyapatites with specific properties, such as, among others, antibacterial characteristics.

For these reasons, the aim of this Special Issue is to document current advances in the field of ion-substituted hydroxyapatites and highlight possible future perspectives regarding their use. Contributions in the form of original articles and review articles are encouraged, covering different areas of application.

In particular, the topics of interest include, but are not limited to, the following:

  • Synthesis or deposition of ion-substituted calcium phosphate coatings.
  • Nucleation of calcium phosphate coatings in the presence of substrate contaminations.
  • Antibacterial ion-substituted hydroxyapatites.
  • Ion-substituted hydroxyapatites for different applications.
  • Relevance of specific ion substitutions (e.g., magnesium, strontium, sodium) on the properties and/or the behavior of substituted hydroxyapatites.
  • Novel techniques to improve the control over ion-doping of calcium phosphates.
  • Advanced characterization techniques to investigate the properties of the coatings (composition, morphology, mechanical properties, solubility, crystallinity, ion release in different media etc…).

Dr. Gabriela Graziani
Dr. Enrico Sassoni
Guest Editors

Manuscript Submission Information

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Please visit the Instructions for Authors page before submitting a manuscript. The Article Processing Charge (APC) for publication in this open access journal is 2000 CHF (Swiss Francs). Submitted papers should be well formatted and use good English. Authors may use MDPI's English editing service prior to publication or during author revisions.

Published Papers (9 papers)

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Research

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Article
A Comprehensive Microstructural and Compositional Characterization of Allogenic and Xenogenic Bone: Application to Bone Grafts and Nanostructured Biomimetic Coatings
Coatings 2020, 10(6), 522; https://doi.org/10.3390/coatings10060522 - 29 May 2020
Cited by 8 | Viewed by 1293
Abstract
Bone grafts and bone-based materials are widely used in orthopedic surgery. However, the selection of the bone type to be used is more focused on the biological properties of bone sources than physico-chemical ones. Moreover, although biogenic sources are increasingly used for deposition [...] Read more.
Bone grafts and bone-based materials are widely used in orthopedic surgery. However, the selection of the bone type to be used is more focused on the biological properties of bone sources than physico-chemical ones. Moreover, although biogenic sources are increasingly used for deposition of biomimetic nanostructured coatings, the influence of specific precursors used on coating’s morphology and composition has not yet been explored. Therefore, in order to fill this gap, we provided a detailed characterization of the properties of the mineral phase of the most used bone sources for allografts, xenografts and coating deposition protocols, not currently available. To this aim, several bone apatite precursors are compared in terms of composition and morphology. Significant differences are assessed for the magnesium content between female and male human donors, and in terms of Ca/P ratio, magnesium content and carbonate substitution between human bone and different animal bone sources. Prospectively, based on these data, bone from different sources can be used to obtain bone grafts having slightly different properties, depending on the clinical need. Likewise, the suitability of coating-based biomimetic films for specific clinical musculoskeletal application may depend on the type of apatite precursor used, being differently able to tune surface morphology and nanostructuration, as shown in the proof of concepts of thin film manufacturing here presented. Full article
(This article belongs to the Special Issue Ion-Substituted Calcium Phosphates Coatings)
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Article
Comparative Study Between Ammonium Phosphate and Ethyl Silicate Towards Conservation of Prehistoric Paintings in the Magura Cave (Bulgaria)
Coatings 2020, 10(3), 250; https://doi.org/10.3390/coatings10030250 - 09 Mar 2020
Cited by 4 | Viewed by 1449
Abstract
This study aimed at evaluating the effectiveness and the compatibility of two alternative treatments, in view of their possible use for conservation of prehistoric paintings in the Magura cave (Bulgaria). The paintings are made of bat guano applied over limestone; therefore, two sets [...] Read more.
This study aimed at evaluating the effectiveness and the compatibility of two alternative treatments, in view of their possible use for conservation of prehistoric paintings in the Magura cave (Bulgaria). The paintings are made of bat guano applied over limestone; therefore, two sets of laboratory specimens were considered: stone specimens and stone specimens covered with a layer of sterilized bat guano. The two investigated treatments were a commercial product based on ethyl silicate (“ES”) and a solution of diammonium hydrogen phosphate (“DAP”), aimed at forming calcium phosphates. The results of the study indicated that both treatments were able to increase the mechanical properties of stone, the increase being higher for “DAP”. Both consolidants caused acceptable color changes, but the “ES” treatment significantly decreased stone wettability, water absorption, and water vapor permeability, while the “DAP” treatment slightly affected those properties. In the stone + guano specimens, the presence of the guano layer affected the penetration of the consolidants, thus partly reducing their effectiveness. Compared to the stone samples, the guano layer experienced a more intense color change, alongside visible cracking. However, the adopted methodology to replicate the cave paintings was not completely successful, as the so-deposited guano layer was very prone to detachment when dry, unlike cave paintings. Future work will be dedicated to assessing the consolidant performance onto samples that resemble even more closely the conditions of the cave paintings, by improving the methodology for the guano layer deposition and by contaminating specimens with soluble salts before consolidant application. Full article
(This article belongs to the Special Issue Ion-Substituted Calcium Phosphates Coatings)
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Article
Ion-Substituted Carbonated Hydroxyapatite Coatings for Model Stone Samples
Coatings 2019, 9(4), 231; https://doi.org/10.3390/coatings9040231 - 02 Apr 2019
Cited by 16 | Viewed by 2340
Abstract
Carbonated hydroxyapatite derivatives (CHAp) and its metallic derivatives (Ag, Sr, Ba, K, Zn) have been prepared and characterized in this paper and their coating capacity on some model stone samples have been evaluated and discussed. These compounds were characterized by using several analytical [...] Read more.
Carbonated hydroxyapatite derivatives (CHAp) and its metallic derivatives (Ag, Sr, Ba, K, Zn) have been prepared and characterized in this paper and their coating capacity on some model stone samples have been evaluated and discussed. These compounds were characterized by using several analytical tools, including X-ray diffraction analysis (XRD), thermogravimetric analysis (TGA), Fourier transform infrared spectroscopy (FTIR), to determine the purity of the CHAp sample. The XRD and FTIR results confirmed the presence of AB-carbonated type CHAp. The thermal analysis (TGA) established two stages of weight loss that occured during the heating process: The first weight loss between 30–225 °C corresponding to the partial carbonate release from OH-channel and the second one between 226–700 °C, corresponding to some thermal reactions, possibly to the generation of calcium phosphate. The efficiency and suitability of these products on model stone samples were evaluated by monitoring the resistance to artificial weather (freeze–thaw), and pore structure changes (surface area, pore volume, pore diameter). Meanwhile, optical microscopy (OM) and Scanning Electron Microscopy with Energy Dispersive Spectroscopy (SEM–EDS) techniques showed the particles size and surface morphology of the samples, as well as information on its chemical composition. Also, the compressive strength of these new compounds as coatings revealed a homogeneity and strengthen of these model stone samples. Full article
(This article belongs to the Special Issue Ion-Substituted Calcium Phosphates Coatings)
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Article
Glancing Angle Deposition of Zn-Doped Calcium Phosphate Coatings by RF Magnetron Sputtering
Coatings 2019, 9(4), 220; https://doi.org/10.3390/coatings9040220 - 28 Mar 2019
Cited by 21 | Viewed by 2706
Abstract
Zn-substituted hydroxyapatite with antibacterial effect was used in radiofrequency (RF) magnetron deposition of calcium phosphate coating onto Ti- and Si-inclined substrates. The development of surface nanopatterns for direct bacteria killing is a growing area of research. Here, we combined two approaches for possible [...] Read more.
Zn-substituted hydroxyapatite with antibacterial effect was used in radiofrequency (RF) magnetron deposition of calcium phosphate coating onto Ti- and Si-inclined substrates. The development of surface nanopatterns for direct bacteria killing is a growing area of research. Here, we combined two approaches for possible synergetic antibacterial effect by manufacturing a patterned surface of Zn-doped calcium phosphate using glancing angle deposition (GLAD) technique. A significant change in the coating morphology was revealed with a substrate tilt angle of 80°. It was shown that an increase in the coating crystallinity for samples deposited at a tilt angle of 80° corresponds to the formation of crystallites in the bulk structure of the thin film. The variation in the coating thickness, uniformity, and influence of sputtered species energy on Si substrates was analyzed. Coatings deposited on tilted samples exhibit higher scratch resistance. The coating micro- and nano-roughness and overall morphology depended on the tilt angle and differently affected the rough Ti and smooth Si surfaces. GLAD of complex calcium phosphate material can lead to the growth of thin films with significantly changed morphological features and can be utilized to create self-organized nanostructures on various types of surfaces. Full article
(This article belongs to the Special Issue Ion-Substituted Calcium Phosphates Coatings)
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Article
Electrodeposition of Hydroxyapatite Coatings for Marble Protection: Preliminary Results
Coatings 2019, 9(3), 207; https://doi.org/10.3390/coatings9030207 - 23 Mar 2019
Cited by 5 | Viewed by 1658
Abstract
Surface coatings made of hydroxyapatite (HAP) have been proposed to protect marble artworks from dissolution in rain, originated by the aqueous solubility of calcite. However, HAP coatings formed by wet chemistry exhibit incomplete coverage of marble surface, which results in limited protective efficacy. [...] Read more.
Surface coatings made of hydroxyapatite (HAP) have been proposed to protect marble artworks from dissolution in rain, originated by the aqueous solubility of calcite. However, HAP coatings formed by wet chemistry exhibit incomplete coverage of marble surface, which results in limited protective efficacy. In this study, electrodeposition was explored as a new route to possibly form continuous coatings over the marble surface, leaving no bare areas. Electrodeposition was performed by placing marble samples in poultices containing the electrolyte (an aqueous solution with calcium and phosphate precursors) and the electrodes. The influence of several parameters was investigated, namely the role of the working electrode (cathode or anode), the distance between the marble sample and the working electrode, the deposition conditions (potentiostatic or galvanostatic), the electrolyte composition and concentration, the applied voltage, and time. The coating morphology and composition were assessed by SEM/EDS and FT-IR. The protective ability of the most promising formulations was then evaluated, in all cases comparing electrodeposition with traditional wet synthesis methods. The results of the study suggest that electrodeposition is able to accelerate and improve formation of HAP coatings over the marble surface, even though the obtained protective efficacy is not complete yet. Full article
(This article belongs to the Special Issue Ion-Substituted Calcium Phosphates Coatings)
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Article
Diammonium Hydrogenphosphate Treatment on Dolostone: The Role of Mg in the Crystallization Process
Coatings 2019, 9(3), 169; https://doi.org/10.3390/coatings9030169 - 04 Mar 2019
Cited by 7 | Viewed by 1348
Abstract
The diammonium hydrogenphosphate (DAP, (NH4)2HPO4) reaction with calcite has been extensively investigated. The availability of free calcium ions in the reaction environment has been acknowledged as a crucial factor in the crystallization of calcium phosphates with a [...] Read more.
The diammonium hydrogenphosphate (DAP, (NH4)2HPO4) reaction with calcite has been extensively investigated. The availability of free calcium ions in the reaction environment has been acknowledged as a crucial factor in the crystallization of calcium phosphates with a high (hydroxyapatite, Ca/P 1.67) or low Ca/P molar ratio (dicalcium phosphate dihydrate, Ca/P 1.00; octacalcium phosphate, Ca/P 1.33). On the contrary, no data are available on the DAP interaction at room temperature with dolomite in terms of reaction mechanism and composition of the reaction products. Here, a multi-analytical approach based on scanning electron microscopy (SEM) coupled with energy dispersive X-ray spectrometry (EDS) and X-ray powder diffraction before and after heating treatments is proposed to explore how the formation of calcium phosphates occur on Mg-enriched substrates and if the presence of magnesium ions during the reaction influences the crystallization process of calcium phosphates. The DAP reaction with polycrystalline dolomite gives rise to the formation of struvite and of poorly crystalline hydroxyapatite. Calcium and magnesium ions mutually interfered in the crystallization of magnesium and calcium phosphates, respectively, whose effects influenced the properties (size, micro-morphology, composition and crystallinity) of the newly-formed phases. Full article
(This article belongs to the Special Issue Ion-Substituted Calcium Phosphates Coatings)
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Article
Zinc Doped Hydroxyapatite Thin Films Prepared by Sol–Gel Spin Coating Procedure
Coatings 2019, 9(3), 156; https://doi.org/10.3390/coatings9030156 - 28 Feb 2019
Cited by 18 | Viewed by 2392
Abstract
In this study, ZnHAp layers deposited on a Si substrate were obtained by a sol–gel spin-coating procedure. The ZnHAp solutions used to obtain the ZnHAp coatings were investigated by dynamic light scattering (DLS) analysis, ζ-potential, ultrasound measurements, and flame atomic absorption spectrometry (AAS). [...] Read more.
In this study, ZnHAp layers deposited on a Si substrate were obtained by a sol–gel spin-coating procedure. The ZnHAp solutions used to obtain the ZnHAp coatings were investigated by dynamic light scattering (DLS) analysis, ζ-potential, ultrasound measurements, and flame atomic absorption spectrometry (AAS). The average measured hydrodynamic diameter from the DLS analysis, ζ-potential, and ultrasound measurements were analyzed so as to characterize and estimate the stability of the ZnHAp nanoparticles. The AAS results confirmed the presence of zinc in the gels used in the preparation of the ZnHAp layers. The layers were investigated by X-ray diffraction (XRD) and scanning electron microscopy (SEM). The XRD results revealed the diffraction peaks of the hexagonal hydroxyapatite in all of the investigated samples. The morphology of the ZnHAp coatings annealed at 500 °C (ZnHAp-500) and 700 °C (ZnHAp-700), which evidenced that no fissures or cracks formed on the surface of the coatings. The biocompatibility assays indicated that the ZnHAp coatings did not present any toxicity towards the HeLa cells. Furthermore, the study regarding the cytotoxicity of the ZnHAp layers against microorganisms emphasized that ZnHAp coatings exhibited an inhibitory effect towards S. aureus bacterial cells and also towards C. albicans fungal cells. Full article
(This article belongs to the Special Issue Ion-Substituted Calcium Phosphates Coatings)
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Article
Pulsed Laser Deposited Biocompatible Lithium-Doped Hydroxyapatite Coatings with Antimicrobial Activity
Coatings 2019, 9(1), 54; https://doi.org/10.3390/coatings9010054 - 17 Jan 2019
Cited by 11 | Viewed by 2346
Abstract
Simple and lithium-doped biological-origin hydroxyapatite layers were synthesized by Pulsed Laser Deposition technique on medical grade Ti substrates. Cytotoxic effects of lithium addition and the biocompatibility of obtained coatings were assessed using three cell lines of human origin (new initiated dermal fibroblasts, immortalized [...] Read more.
Simple and lithium-doped biological-origin hydroxyapatite layers were synthesized by Pulsed Laser Deposition technique on medical grade Ti substrates. Cytotoxic effects of lithium addition and the biocompatibility of obtained coatings were assessed using three cell lines of human origin (new initiated dermal fibroblasts, immortalized keratinocytes HaCaT, and MG-63 osteosarcoma). Antimicrobial properties of obtained coatings were assessed on two strains (i.e., Staphylococcus aureus and Candida albicans), belonging to species representative for the etiology of medical devices biofilm-associated infections. Our findings suggest that synthesized lithium-doped coatings exhibited low cytotoxicity on human osteosarcoma and skin cells and therefore, an excellent biocompatibility, correlated with a long-lasting anti-staphylococcal and -fungal biofilm activity. Along with low fabrication costs generated by sustainable resources, these biological-derived materials demonstrate their promising potential for future prospective solutions—viable alternatives to commercially available biomimetic HA implants—for the fabrication of a new generation of implant coatings. Full article
(This article belongs to the Special Issue Ion-Substituted Calcium Phosphates Coatings)
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Review

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Review
A Review on Ionic Substitutions in Hydroxyapatite Thin Films: Towards Complete Biomimetism
Coatings 2018, 8(8), 269; https://doi.org/10.3390/coatings8080269 - 31 Jul 2018
Cited by 69 | Viewed by 3788
Abstract
Plasma sprayed coatings composed of stoichiometric hydroxyapatite have been extensively used to improve integration of metallic implants in the host bone, as hydroxyapatite (HA) is normally regarded as similar to the mineralized phase of bone. However, these coatings exhibited several drawbacks that limited [...] Read more.
Plasma sprayed coatings composed of stoichiometric hydroxyapatite have been extensively used to improve integration of metallic implants in the host bone, as hydroxyapatite (HA) is normally regarded as similar to the mineralized phase of bone. However, these coatings exhibited several drawbacks that limited their success. On the one hand biological apatite is a carbonated-HA, containing significant amounts of foreign ions, having low crystallinity and a small crystals size. This means that it differs from stoichiometric HA in terms of composition, stoichiometry, crystallinity degree, crystal size/morphology and, as a direct consequence, solubility, and ions release in the peri-implant environment. On the other hand, thick plasma sprayed coatings can undergo cracking and delamination and are scarcely uniform. For these reasons, research is pushing into two directions: (i) Increasing the similarity of apatite coatings to real bone, and (ii) exploring deposition by alternative plasma assisted techniques, allowing to achieve thin films, and having superior adhesion and a better control over the coating composition. In this article, we review the latest advances in the field of plasma-assisted deposition of ion-substituted hydroxyapatite thin films, highlighting the state of the art, the limitations, potentialities, open challenges, and the future scenarios for their application. Full article
(This article belongs to the Special Issue Ion-Substituted Calcium Phosphates Coatings)
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