Special Issue "Advances in Enhancing Degradation Resistance of Metallic Implants by Surface Engineering"

A special issue of Metals (ISSN 2075-4701).

Deadline for manuscript submissions: closed (31 January 2018)

Special Issue Editor

Guest Editor
Assoc. Prof. Bobby Kannan Mathan

Biomaterials and Engineering Materials (BEM) Laboratory, College of Science, Technology and Engineering, James Cook University, Townsville, Queensland 4811, Australia
Website | E-Mail
Interests: Electrochemical Engineering; Biomaterials; Corrosion; Wastewater Treatment

Special Issue Information

Dear Colleagues,

In today’s society, the use of metallic implants to assist in the repair or replacement of damaged tissue and bone structure has become very common. There are a wide range of specifically designed devices that are intended to be implanted within the body to assist in healing process. Generally, it is a prerequisite for the implant materials to have high biocompatibility. In addition, it is desirable to have load bearing capacity in order to support the weight of the body during service. These implants can be broadly classified into two categories, i.e., permanent implants and temporary implants. Titanium alloys, cobalt-chrome alloys and stainless steels are the commonly used materials for permanent implants in applications such as hip and long-bone replacements. These materials are designed to have high degradation resistance and good mechanical properties. However, long-term exposure of these metallic materials causes degradation and eventually failure of implants. A significant amount of work has been done to improve the degradation resistance of these materials. Minor factures generally require mini-implants in the form of screws, pins and small plates for bone repair. These implants are only required for a short-period of time, hence, they are termed temporary implants. Use of permanent implant materials for this purpose would require an addition surgery to remove the implants after the healing process. Metallic magnesium is an attractive material for this purpose since it is biocompatible and biodegradable. However, the high degradation rate of magnesium is a major issue. Hence, the research focus has been towards improving the degradation performance of metallic magnesium.

For this Special Issue on “Advances in Enhancing Degradation Resistance of Metallic Implant by Surface Engineering”, we are interested in original and review articles on advanced methods, e.g., surface treatments, ceramic and polymer coatings, and ion implantation, for improving the degradation resistance of metallic biomaterials such as titanium-based alloys, stainless steels, cobalt-chromium, and magnesium alloys.

Prof. Dr. M. Bobby Kannan
Guest Editor

Manuscript Submission Information

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Keywords

  • Biomaterials
  • Biodegradation
  • Corrosion
  • Coatings
  • Surface Engineering
  • Calcium Phosphates
  • Anodisation
  • Plasma Electrolytic Oxidation
  • Polymer Coating

Published Papers (10 papers)

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Open AccessArticle
TiO2 Nanotubes on Ti Dental Implant. Part 3: Electrochemical Behavior in Hank’s Solution of Titania Nanotubes Formed in Ethylene Glycol
Metals 2018, 8(7), 489; https://doi.org/10.3390/met8070489
Received: 8 June 2018 / Revised: 22 June 2018 / Accepted: 23 June 2018 / Published: 27 June 2018
Cited by 2 | PDF Full-text (2689 KB) | HTML Full-text | XML Full-text
Abstract
Anodic oxidation is an easy and cheap surface treatment to form nanostructures on the surface of titanium items for improving the interaction between metallic implants and the biological environment. The long-term success of the devices is related to their stability. In this work, [...] Read more.
Anodic oxidation is an easy and cheap surface treatment to form nanostructures on the surface of titanium items for improving the interaction between metallic implants and the biological environment. The long-term success of the devices is related to their stability. In this work, titanium nanotubes were formed on a dental screw, made of titanium CP2, through an anodization process using an “organic” solution based on ethylene glycol containing ammonium fluoride and water. Then, the electrochemical stability in the Hank’s solution of these “organic” nanotubes has been investigated for 15 days and compared to that of titanium nanotubes on a similar type of sample grown in an inorganic solution, containing phosphoric and hydrofluoridric acids. Morphological and crystallographic analysis were performed by using scanning electron microscopy (SEM) and X-Ray diffractometry (XRD) tests. Electrochemical measurements were carried out to study the stability of the nanotubes when are in contact with the biological environment. The morphological measurements revealed long nanotubes, small diameters, smooth side walls, and a high density of “organic” nanotubes if compared to the “inorganic” ones. XRD analysis demonstrated the presence of rutile form. An appreciable electrochemical stability has been revealed by Electrochemical Impedance Spectroscopy (EIS) analysis, suggesting that the “organic” nanotubes are more suitable for biomedical devices. Full article
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Open AccessArticle
Finite Element Analysis of Surface Integrity in Deep Ball-Burnishing of a Biodegradable AZ31B Mg Alloy
Metals 2018, 8(2), 136; https://doi.org/10.3390/met8020136
Received: 29 December 2017 / Revised: 3 February 2018 / Accepted: 12 February 2018 / Published: 16 February 2018
Cited by 1 | PDF Full-text (12911 KB) | HTML Full-text | XML Full-text
Abstract
As an effective and affordable technique, deep ball-burnishing has been applied to induce the plastic deformation of material, thus resulting in an increased surface hardness, compressive residual stress, and finish quality. Recent research shows that the fast degradation of an Mg alloy implant [...] Read more.
As an effective and affordable technique, deep ball-burnishing has been applied to induce the plastic deformation of material, thus resulting in an increased surface hardness, compressive residual stress, and finish quality. Recent research shows that the fast degradation of an Mg alloy implant is a prime limiting factor for its success in in vivo human trials. This paper presents a comprehensive investigation into deep ball-burnishing of a biodegradable AZ31B Mg alloy, in order to improve the alloy’s surface integrity. A series of experiments using an in-house built burnishing tool with a 10-mm steel ball have been conducted, with a key focus of exploring the influence of the major process parameters—e.g., burnishing force (750–2650 N), feed rate (150–500 mm/min), and step-over (0.05–0.15 mm)—on hardness and finish quality. With the aim of performing a parametric sensitivity study, a three-dimensional (3D) finite element (FE) model is developed to predict the deformation mechanics, plastic flow, hardness, and residual stress. The FE model agrees with the experiment, hence validating the reliability of the model. Results show that while burnishing significantly improves surface integrity compared to the untreated surface, burnishing force and step-over are shown to be dominant. The net material movement dictates generated residual stress (tensile or compressive), often negatively affecting the surface integrity (e.g., surface cracks), which may be responsible for the onset of corrosion. An appropriate burnishing strategy must therefore be planned, in order to achieve the intended process outcome. The resulting surface properties, enhanced by the deep ball-burnishing, are expected to potentially increase the corrosion resistance of AZ31B Mg alloy implants. Full article
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Open AccessArticle
Influence of Heat Treatment and UV Irradiation on the Wettability of Ti35Nb10Ta Nanotubes
Metals 2018, 8(1), 37; https://doi.org/10.3390/met8010037
Received: 18 November 2017 / Revised: 21 December 2017 / Accepted: 29 December 2017 / Published: 7 January 2018
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Abstract
The implant osseointegration rate depends on the surface’s topography and chemical composition. There is a growing interest in the anodic oxidation process to obtain an oxide layer with a nanotube morphology on beta titanium alloys. This surface treatment presents large surface area, nanoscale [...] Read more.
The implant osseointegration rate depends on the surface’s topography and chemical composition. There is a growing interest in the anodic oxidation process to obtain an oxide layer with a nanotube morphology on beta titanium alloys. This surface treatment presents large surface area, nanoscale rugosity and electrochemical properties that may increase the biocompatibility and osseointegration rate in titanium implants. In this work, an anodic oxidation process was used to modify the surface on the Ti35Nb10Ta alloy to obtain a titanium nanotubes topography. The work focused on analyzing the influence of some variables (voltage, heat treatment and ultraviolet irradiation) on the wettability performance of a titanium alloy. The morphology of the nanotubes surfaces was studied by Field Emission Scanning Electron Microscopy (FESEM), and surface composition was analyzed by Energy Dispersive Spectroscopy (EDS). The measurement of contact angle for the TiO2 nanotube surfaces was measured by a video contact angle system. The surface with the non photoinduced nanotubes presented the largest contact angles. The post-heat treatment lowered the F/Ti ratio in the nanotubes and decreased the contact angle. Ultraviolet (UV) irradiation of the TiO2 nanotubes decrease the water contact angle. Full article
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Open AccessFeature PaperArticle
Ion Implantation of Calcium and Zinc in Magnesium for Biodegradable Implant Applications
Metals 2018, 8(1), 30; https://doi.org/10.3390/met8010030
Received: 8 December 2017 / Revised: 29 December 2017 / Accepted: 29 December 2017 / Published: 3 January 2018
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Abstract
In this study, magnesium was implanted with calcium-ion and zinc-ion at fluences of 1015, 1016, and 1017 ion·cm−2, and its in vitro degradation behaviour was evaluated using electrochemical techniques in simulated body fluid (SBF). Rutherford backscattering [...] Read more.
In this study, magnesium was implanted with calcium-ion and zinc-ion at fluences of 1015, 1016, and 1017 ion·cm−2, and its in vitro degradation behaviour was evaluated using electrochemical techniques in simulated body fluid (SBF). Rutherford backscattering spectrometry (RBS) revealed that the implanted ions formed layers within the passive magnesium-oxide/hydroxide layers. Electrochemical impedance spectroscopy (EIS) results demonstrated that calcium-ion implantation at a fluence of 1015 ions·cm−2 increased the polarisation resistance by 24%, but higher fluences showed no appreciable improvement. In the case of zinc-ion implantation, increase in the fluence decreased the polarisation resistance. A fluence of 1017 ion·cm−2 decreased the polarisation resistance by 65%, and fluences of 1015 and 1016 showed only marginal effect. Similarly, potentiodynamic polarisation results also suggested that low fluence of calcium-ion decreased the degradation rate by 38% and high fluence of zinc-ion increased the degradation rate by 61%. All the post-polarized ion-implanted samples and the bare metal revealed phosphate and carbonate formation. However, the improved degradative behaviour in calcium-ion implanted samples can be due to a relatively better passivation, whereas the reduction in degradation resistance in zinc-ion implanted samples can be attributed to the micro-galvanic effect. Full article
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Open AccessArticle
TiO2 Nanotubes on Ti Dental Implant. Part 2: EIS Characterization in Hank’s Solution
Metals 2017, 7(6), 220; https://doi.org/10.3390/met7060220
Received: 18 May 2017 / Revised: 6 June 2017 / Accepted: 12 June 2017 / Published: 14 June 2017
Cited by 6 | PDF Full-text (3551 KB) | HTML Full-text | XML Full-text
Abstract
Titania nanotubes are widely studied for their potential applications in several fields. In this paper, the electrochemical characterization of a dental implant, made of commercially pure titanium grade 2, covered by titania nanotubes, when immersed in Hank’s solution, is proposed. Few papers were [...] Read more.
Titania nanotubes are widely studied for their potential applications in several fields. In this paper, the electrochemical characterization of a dental implant, made of commercially pure titanium grade 2, covered by titania nanotubes, when immersed in Hank’s solution, is proposed. Few papers were found in the scientific literature regarding this topic, so a brief review is reported, concerning the use of some equivalent circuits to model experimental data. The analysis of results, obtained by using Electrochemical Impedance Spectroscopy, showed that: (i) a good correlation exists between the variation of Ecorr and the estimated values of the charge transfer resistance for both the bare- and the nanotube-covered samples, (ii) the nanostructured surface seems to possess a more active behaviour, while the effect could be over-estimated due to the real extent of the surface covered by nanotubes, (iii) the analysis of the “n” parameter, used to fit the experimental data, confirms the complex nature of nanostructured layer as well as that the nanotubes are partially filled by compounds containing Ca, P and Mg, when immersed in Hank’s solution. The results obtained in this work give a better understanding of the electrochemical behaviour of the nanotubes layer when immersed in Hank’s solution and could help to design a surface able to improve the implant osseointegration. Full article
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Open AccessArticle
Preparation and Characterization of Aminated Hydroxyethyl Cellulose-Induced Biomimetic Hydroxyapatite Coatings on the AZ31 Magnesium Alloy
Metals 2017, 7(6), 214; https://doi.org/10.3390/met7060214
Received: 13 April 2017 / Revised: 15 May 2017 / Accepted: 6 June 2017 / Published: 8 June 2017
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Abstract
The purpose of this work is to improve the cytocompatibility and corrosion resistance of magnesium alloy in the hope of preparing a biodegradable medical material. The aminated hydroxyethyl cellulose-induced biomimetic hydroxyapatite coating was successfully prepared on AZ31 magnesium alloy surface with a sol-gel [...] Read more.
The purpose of this work is to improve the cytocompatibility and corrosion resistance of magnesium alloy in the hope of preparing a biodegradable medical material. The aminated hydroxyethyl cellulose-induced biomimetic hydroxyapatite coating was successfully prepared on AZ31 magnesium alloy surface with a sol-gel spin coating method and biomimetic mineralization. Potentiodynamic polarization tests and electrochemical impedance spectroscopy showed that the hydroxyapatite/aminated hydroxyethyl cellulose (HA/AHEC) coating can greatly improve the corrosion resistance of AZ31 magnesium alloy and reduce the degradation speed in simulated body fluid (SBF). The MTT [3-(4,5-dimethylthiazol-2-yl)-2,5-Diphenyltetrazolium bromide] method and cell morphology observation results showed that the HA/AHEC coating on AZ31 magnesium alloy has excellent cytocompatibility and biological activity. Full article
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Open AccessArticle
Investigation of the Effectiveness of Dental Implant Osseointegration Characterized by Different Surface Types
Metals 2017, 7(6), 203; https://doi.org/10.3390/met7060203
Received: 6 April 2017 / Revised: 17 May 2017 / Accepted: 25 May 2017 / Published: 2 June 2017
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Abstract
Different surfaces were obtained by Plasma Electrolytic Oxidation (PEO) of the Ti–6Al–4V alloy; followed by hydrothermal treatment (HT). The surfaces were studied by scanning electron microscopy (SEM); Energy Dispersive Spectroscopy (EDS); X-ray Diffraction (XRD); Brunauer–Emmett–Teller (BET) absorption and abrasion wear tests. The resulting [...] Read more.
Different surfaces were obtained by Plasma Electrolytic Oxidation (PEO) of the Ti–6Al–4V alloy; followed by hydrothermal treatment (HT). The surfaces were studied by scanning electron microscopy (SEM); Energy Dispersive Spectroscopy (EDS); X-ray Diffraction (XRD); Brunauer–Emmett–Teller (BET) absorption and abrasion wear tests. The resulting surface contains hydroxyapatite (HA); which contributes to superior implant osseointegration. Treated implants were introduced into rabbits and their osseointegration was studied after two and six months. It was established that implant surface area increases due to pore formation. Pore formation and hydroxyapatite on the surface of the implant qualitatively change contact osseogenesis processes with reduced duration of osseointegration of implants. The treatment of the surface of the implants by the combination of PEO and HT provided better results in the medico-biological investigations than PEO alone. Abrasion tests demonstrated that the HA will be preserved after the procedure of implantation; ensuring effective osseointegration. Full article
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Open AccessArticle
TiO2 Nanotubes on Ti Dental Implant. Part 1: Formation and Aging in Hank’s Solution
Metals 2017, 7(5), 167; https://doi.org/10.3390/met7050167
Received: 11 April 2017 / Revised: 4 May 2017 / Accepted: 8 May 2017 / Published: 11 May 2017
Cited by 8 | PDF Full-text (2235 KB) | HTML Full-text | XML Full-text
Abstract
Self-organized TiO2 nanotube layer has been formed on titanium screws with complex geometry, which are used as dental implants. TiO2 nanotubes film was grown by potentiostatic anodizing in H3PO4 and HF aqueous solution. During anodizing, the titanium screws [...] Read more.
Self-organized TiO2 nanotube layer has been formed on titanium screws with complex geometry, which are used as dental implants. TiO2 nanotubes film was grown by potentiostatic anodizing in H3PO4 and HF aqueous solution. During anodizing, the titanium screws were mounted on a rotating apparatus to produce a uniform structure both on the peaks and on the valleys of the threads. X-ray diffraction (XRD), Scanning electron microscopy (SEM), Energy dispersive X-ray (EDX) and electrochemical characterization were used to evaluate the layer, chemical composition and electrochemical properties of the samples. Aging in Hank’s solution of both untreated and nanotubes covered screw, showed that: (i) samples are covered by an amorphous oxide layer, (ii) the nanotubes increases the corrosion resistance of the implant, and (iii) the presence of the nanotubes catalyses the formation of chemical compounds containing Ca and P. Full article
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Open AccessArticle
Primary Stability of Temporary Screws after Dentary and Orthopedic Forces under Static and Dynamic Load Cycles
Metals 2017, 7(3), 80; https://doi.org/10.3390/met7030080
Received: 28 December 2016 / Accepted: 16 February 2017 / Published: 3 March 2017
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Abstract
The objective was to analyze the influence of dentary and orthopedic forces under static and dynamic loads in temporary screw stability. Self-drilling titanium (Ti6Al4V) screws (6 × 1.5 mm) were inserted and removed from pig ribs. Screws were loaded by static loads of [...] Read more.
The objective was to analyze the influence of dentary and orthopedic forces under static and dynamic loads in temporary screw stability. Self-drilling titanium (Ti6Al4V) screws (6 × 1.5 mm) were inserted and removed from pig ribs. Screws were loaded by static loads of 2 N and 5 N for 5 weeks. Dynamic force was applied during 56,000 cycles for simulations of a patient’s opening–closing mouth movements. Dynamic applied loads ranged from 2 to 5 N and from 5 to 7 N under a frequency of 1 Hz. Torque peak values at placement and removal were measured before and after static and dynamic cycles. Similarities in torque peaks (p = 0.3139) were identified at placement (12.54 Ncm) and removal (11.2 Ncm) of screws after a static load of 2 N. Statistical comparisons showed significant stability loss after dynamic cycles under loads of 2 N (64.82% at p = 0.0005) and 5 N (64.63% at p = 0.0026). Limited stability loss occurred in temporary screws submitted to 2 N static forces (p = 0.3139). The detrimental effects of dynamic cycles in temporary screws stability was attested after the simulation of dentary and skeletal forces, being intermittent forces more relevant in the loss of mechanical stability. Full article
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Other

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Open AccessOpinion
Osseoconductive and Corrosion-Inhibiting Plasma-Sprayed Calcium Phosphate Coatings for Metallic Medical Implants
Metals 2017, 7(11), 468; https://doi.org/10.3390/met7110468
Received: 25 August 2017 / Revised: 21 October 2017 / Accepted: 22 October 2017 / Published: 1 November 2017
Cited by 4 | PDF Full-text (2934 KB) | HTML Full-text | XML Full-text
Abstract
During the last several decades, research into bioceramic coatings for medical implants has emerged as a hot topic among materials scientists and clinical practitioners alike. In particular, today, calcium phosphate-based bioceramic materials are ubiquitously used in clinical applications to coat the stems of [...] Read more.
During the last several decades, research into bioceramic coatings for medical implants has emerged as a hot topic among materials scientists and clinical practitioners alike. In particular, today, calcium phosphate-based bioceramic materials are ubiquitously used in clinical applications to coat the stems of metallic endoprosthetic hips as well as the surfaces of dental root implants. Such implants frequently consist of titanium alloys, CoCrMo alloy, or austenitic surgical stainless steels, and aim at replacing lost body parts or restoring functions to diseased or damaged tissues of the human body. In addition, besides such inherently corrosion-resistant metals, increasingly, biodegradable metals such as magnesium alloys are being researched for osseosynthetic devices and coronary stents both of which are intended to remain in the human body for only a short time. Biocompatible coatings provide not only vital biological functions by supporting osseoconductivity but may serve also to protect the metallic parts of implants from corrosion in the aggressive metabolic environment. Moreover, the essential properties of hydroxylapatite-based bioceramic coatings including their in vitro alteration in contact with simulated body fluids will be addressed in this current review paper. In addition, a paradigmatic shift is suggested towards the development of transition metal-substituted calcium hexa-orthophosphates with the NaSiCON (Na superionic conductor) structure to be used for implant coatings with superior degradation resistance in the corrosive body environment and with pronounced ionic conductivity that might be utilized in novel devices for electrical bone growth stimulation. Full article
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