Special Issue "Titanium and Its Alloys for Biomedical Applications"

A special issue of Metals (ISSN 2075-4701). This special issue belongs to the section "Biobased and Biodegradable Metals".

Deadline for manuscript submissions: 1 November 2021.

Special Issue Editor

Dr. Hyun-Do Jung
E-Mail Website
Guest Editor
Department of Biomedical-Chemical Engineering, Catholic University of Korea, Seoul, Korea
Interests: titanium alloys; implants; additive manufacturing; powder metallurgy; porous structure; drug delivery; nanoroughness; plasma electrolytic oxidation

Special Issue Information

Dear Colleagues,

Metallic biomaterials have been widely used as load-bearing implants and internal fixation devices because of their excellent mechanical strength and resilience. Among various biometals, titanium (Ti) and its alloys are one of the most widely used materials in the medical field as orthopedic and dental implants, and even vascular/nonvascular stents due to their excellent mechanical properties, chemical stability, and good biocompatibility.

Even though Ti and its alloys have been generally used for biomedical applications, there is still room for improvement because of the mechanical mismatch between bone and implant and low bioactivity. In recent years, much attention has been placed on the design of new Ti alloys with a modified process such as heat treatment and severe plastic deformation for fabricating orthopedic and dental implants with lower elastic moduli in combination with higher strength. On the other hand, some researchers have focused on the surface modification of Ti implants for inducing rapid bone ingrowth.

Porous Ti have also attracted increasing interest, because the 3D pore network can provide a favorable environment for bone ingrowth and possess bone-like mechanical properties. Thus far, considerable efforts have been made to develop new manufacturing techniques for producing porous Ti, such as powder metallurgy and the additive manufacturing method.

Hence, this Special Issue proposes novel results on several aspects of titanium and its alloys for biomedical applications. For this purpose, we warmly welcome submissions, including regular research papers, short communications, and reviews describing current research trends and future perspectives in titanium and its alloys for biomedical applications. The following topics, though not exclusively, fall within the scope of the Special Issue:

  • New Ti alloy design for reducing the mechanical mismatch;
  • Heat treatment and plastic deformation processing to enhance mechanical properties;
  • Surface coating to improve biological responses;
  • Manufacturing of porous titanium;
  • Additive manufacturing of titanium and its alloy;
  • Evaluation of antibacterial properties and cytotoxicity of titanium;
  • Characterization of the mechanical behavior of titanium;
  • New trends in titanium and its alloy.
Dr. Hyun-Do Jung
Guest Editor

Manuscript Submission Information

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Keywords

  • titanium alloy design
  • heat treatment
  • plastic deformation processing
  • surface coating
  • additive manufacturing
  • powder metallurgy
  • porous titanium
  • advanced processing
  • biocompatibility
  • mechanical properties

Published Papers (9 papers)

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Research

Article
Electrophoretic Deposition of a Hybrid Graphene Oxide/Biomolecule Coating Facilitating Controllable Drug Loading and Release
Metals 2021, 11(6), 899; https://doi.org/10.3390/met11060899 - 31 May 2021
Viewed by 457
Abstract
Two-dimensional (2D) graphene oxide (GO) exhibits a high drug loading capacity per unit mass due to its unique structure and hydrophilicity and has been widely researched for drug-delivery systems. Here, we modified the surfaces of metal implants; we applied GO-based coatings that controlled [...] Read more.
Two-dimensional (2D) graphene oxide (GO) exhibits a high drug loading capacity per unit mass due to its unique structure and hydrophilicity and has been widely researched for drug-delivery systems. Here, we modified the surfaces of metal implants; we applied GO-based coatings that controlled drug loading and release. We used electrophoretic deposition (EPD) to apply the coatings at room temperature. The EPD coatings were analyzed in terms of their components, physical properties such as hardness and hydrophilicity, and in vitro cell tests of their biological properties. Uniform GO-EPD coatings improved surface hydrophilicity and hardness and greatly improved the bone differentiation properties of the metal substrate. Drug loading and release increased greatly compared to when the drug was adsorbed to only the surface of a coating. GO facilitated deposition of a drug-containing coating via EPD, and the surface modification, and drug loading and release, were controlled by the thickness of the coating. Full article
(This article belongs to the Special Issue Titanium and Its Alloys for Biomedical Applications)
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Article
Characterization of Titanium Surface Modification Strategies for Osseointegration Enhancement
Metals 2021, 11(4), 618; https://doi.org/10.3390/met11040618 - 11 Apr 2021
Cited by 1 | Viewed by 520
Abstract
As biocompatible metallic materials, titanium and its alloys have been widely used in the orthopedic field due to their superior strength, low density, and ease of processing. However, further improvement in biological response is still required for rapid osseointegration. Here, various Ti surface-treatment [...] Read more.
As biocompatible metallic materials, titanium and its alloys have been widely used in the orthopedic field due to their superior strength, low density, and ease of processing. However, further improvement in biological response is still required for rapid osseointegration. Here, various Ti surface-treatment technologies were applied: hydroxyapatite blasting, sand blasting and acid etching, anodic oxidation, and micro-arc oxidation. The surface characteristics of specimens subjected to these techniques were analyzed in terms of structure, elemental composition, and wettability. The adhesion strength of the coating layer was also assessed for the coated specimens. Biocompatibility was compared via tests of in vitro attachment and proliferation of pre-osteoblast cells. Full article
(This article belongs to the Special Issue Titanium and Its Alloys for Biomedical Applications)
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Article
Discovery of New Ti-Based Alloys Aimed at Avoiding/Minimizing Formation of α” and ω-Phase Using CALPHAD and Artificial Intelligence
Metals 2021, 11(1), 15; https://doi.org/10.3390/met11010015 - 24 Dec 2020
Cited by 2 | Viewed by 757
Abstract
In this work, we studied a Ti-Nb-Zr-Sn system for exploring novel composition and temperatures that will be helpful in maximizing the stability of β phase while minimizing the formation of α” and ω-phase. The Ti-Nb-Zr-Sn system is free of toxic elements. This system [...] Read more.
In this work, we studied a Ti-Nb-Zr-Sn system for exploring novel composition and temperatures that will be helpful in maximizing the stability of β phase while minimizing the formation of α” and ω-phase. The Ti-Nb-Zr-Sn system is free of toxic elements. This system was studied under the framework of CALculation of PHAse Diagram (CALPHAD) approach for determining the stability of various phases. These data were analyzed through artificial intelligence (AI) algorithms. Deep learning artificial neural network (DLANN) models were developed for various phases as a function of alloy composition and temperature. Software was written in Python programming language and DLANN models were developed utilizing TensorFlow/Keras libraries. DLANN models were used to predict various phases for new compositions and temperatures and provided a more complete dataset. This dataset was further analyzed through the concept of self-organizing maps (SOM) for determining correlations between phase stability of various phases, chemical composition, and temperature. Through this study, we determined candidate alloy compositions and temperatures that will be helpful in avoiding/minimizing formation of α” and ω-phase in a Ti-Zr-Nb-Sn system. This approach can be utilized in other systems such as ω-free shape memory alloys. DLANN models can even be used on a common Android mobile phone. Full article
(This article belongs to the Special Issue Titanium and Its Alloys for Biomedical Applications)
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Article
Histomorphometric Analysis of Osseointegrated Grade V Titanium Mini Transitional Implants in Edentulous Mandible by Backscattered Scanning Electron Microscopy (BS-SEM)
Metals 2021, 11(1), 2; https://doi.org/10.3390/met11010002 - 22 Dec 2020
Viewed by 531
Abstract
The purpose of this study is to assess the use of grade V titanium mini transitional implants (MTIs) immediately loaded by a temporary overdenture. For this, a histomorphometric analysis of the bone area fraction occupancy (BAFO) was performed by backscattered scanning electron microscopy [...] Read more.
The purpose of this study is to assess the use of grade V titanium mini transitional implants (MTIs) immediately loaded by a temporary overdenture. For this, a histomorphometric analysis of the bone area fraction occupancy (BAFO) was performed by backscattered scanning electron microscopy (BS-SEM). Four female patients were submitted to surgery in which two MTIs were installed and immediately loaded with a temporary acrylic prosthesis. During the same surgery, two regular diameter implants were placed inside the bone and maintained without mechanical load. After 8 months, the MTIs were extracted using a trephine and processed for ultrastructural bone analysis by BS-SEM, and the regular-diameter implants were loaded with an overdenture device. A total of 243 BAFOs of MTIs were analyzed, of which 94 were mainly filled with cortical bone, while 149 were mainly filled with trabecular bone. Bone tissue analysis considering the total BAFOs with calcified tissues showed 72.13% lamellar bone, 26.04% woven bone, and 1.82% chondroid bone without significant differences between the samples. This study revealed that grade V titanium used in immediately loaded MTI was successfully osseointegrated by a mature and vascularized bone tissue as assessed from the BAFO. Full article
(This article belongs to the Special Issue Titanium and Its Alloys for Biomedical Applications)
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Article
Effects of Ti6Al4V Surfaces Manufactured through Precision Centrifugal Casting and Modified by Calcium and Phosphorus Ion Implantation on Human Osteoblasts
Metals 2020, 10(12), 1681; https://doi.org/10.3390/met10121681 - 16 Dec 2020
Cited by 1 | Viewed by 786
Abstract
(1) In order to enable a more widespread use of uncemented titanium-based endoprostheses to replace cobalt-containing cemented endoprostheses for joint replacement, it is essential to achieve optimal osseointegrative properties and develop economic fabrication processes while retaining the highest biomedical quality of titanium materials. [...] Read more.
(1) In order to enable a more widespread use of uncemented titanium-based endoprostheses to replace cobalt-containing cemented endoprostheses for joint replacement, it is essential to achieve optimal osseointegrative properties and develop economic fabrication processes while retaining the highest biomedical quality of titanium materials. One approach is the usage of an optimized form of Ti6Al4V-precision casting for manufacturing. Besides the chemical and physical properties, it is necessary to investigate possible biological influences in order to test whether the new manufacturing process is equivalent to conventional methods. (2) Methods: Primary human osteoblasts were seeded on discs, which were produced by a novel Ti6Al4V centrifugal-casting process in comparison with standard machined discs of the same titanium alloy. In a second step, the surfaces were modified by calcium or phosphorus ion beam implantation. In vitro, we analyzed the effects on proliferation, differentiation, and apoptotic processes. (3) Results: SEM analysis of cells seeded on the surfaces showed no obvious differences between the reference material and the cast material with or without ion implantation. The MTT (3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide) proliferation assay also did not reveal any significant differences. Additionally, the osteogenic differentiation process tested by quantitative polymerase chain reactions (PCR), Alizarin red S assay, and C-terminal collagen type I propeptide (CICP) Elisa was not significantly modified. No signs of induced apoptosis were observed. (4) Conclusions: In this study, we could show that the newly developed process of centrifugal casting generated a material with comparable surface features to standard machined Ti6Al4V material. In terms of biological impact on primary human osteoblasts, no significant differences were recognized. Additional Ca- or P-ion implantation did not improve or impair these characteristics in the dosages applied. These findings indicate that spin casting of Ti6Al4V may represent an interesting alternative to the production of geometrically complex orthopedic implants. Full article
(This article belongs to the Special Issue Titanium and Its Alloys for Biomedical Applications)
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Article
In Situ Synchrotron X-ray Diffraction Investigations of the Nonlinear Deformation Behavior of a Low Modulus β-Type Ti36Nb5Zr Alloy
Metals 2020, 10(12), 1619; https://doi.org/10.3390/met10121619 - 02 Dec 2020
Cited by 2 | Viewed by 538
Abstract
The low modulus β-type Ti alloys usually have peculiar deformation behaviors due to their low phase stability. However, the study of the underlying mechanisms is challenging since some physical mechanisms are fully reversible after the release of the load. In this paper, [...] Read more.
The low modulus β-type Ti alloys usually have peculiar deformation behaviors due to their low phase stability. However, the study of the underlying mechanisms is challenging since some physical mechanisms are fully reversible after the release of the load. In this paper, the deformation behavior of a low modulus β-type Ti36Nb5Zr alloy was investigated with the aid of in situ synchrotron X-ray diffraction (SXRD) during tensile loading. The evolution of lattice strains and relative integrated diffraction peak intensities of both the β and α” phases were analyzed to determine the characteristics of the potential deformation mechanisms. Upon loading, the α” diffraction spots appeared at specific azimuth angles of the two-dimensional SXRD patterns due to the <110> fiber texture of original β grains and the selection of favorable martensitic variants. The nonlinear deformation behavior originated from a reversible stress-induced martensitic transformation (SIMT). However, the SIMT contributed a little to the large recoverable strain of over 2.0%, which was dominated by the elastic deformation of the β phase. Various deformation mechanisms were activated successively at different applied strains, including elastic deformation, SIMT and plastic deformation. Our investigations provide in-depth understandings of the deformation mechanisms in β-type Ti alloys with low elastic modulus. Full article
(This article belongs to the Special Issue Titanium and Its Alloys for Biomedical Applications)
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Article
Effect of Environmentally Friendly Oil on Ni-Ti Stent Wire Using Ultraprecision Magnetic Abrasive Finishing
Metals 2020, 10(10), 1309; https://doi.org/10.3390/met10101309 - 30 Sep 2020
Cited by 1 | Viewed by 571
Abstract
Nickel-titanium (Ni-Ti) has been widely used to make shape-memory actuator wire for numerous medical industrial applications, with the result that it frequently comes into contact with the human body. High-quality and nontoxic surfaces of this material are therefore in high demand. We used [...] Read more.
Nickel-titanium (Ni-Ti) has been widely used to make shape-memory actuator wire for numerous medical industrial applications, with the result that it frequently comes into contact with the human body. High-quality and nontoxic surfaces of this material are therefore in high demand. We used a rotating magnetic field for an ultraprecision finishing of Ni-Ti stent wire biomaterials and evaluated the finishing technique’s efficacy with different processing oils. To create nontoxic Ni-Ti stent wire, the industrial processing oils that are generally used in the surface improvement process were exchanged for oils with low environmental impacts, and processed under rotating magnetic fields at different speeds and processing times. The processing performance of the different oils was compared and verified. The results show that ultraprecision magnetic abrasive finishing that uses olive and castor oil improves surface roughness by 66.67%, and 45.83%, respectively. SEM and energy-dispersive X-ray spectroscopy (EDX) analyses of the finished components (before and after processing) showed that the material composition of the Ni-Ti stent wire was not changed. Additionally, the magnetic abrasive tool composition was not found on the surface of the finished Ni-Ti stent wire. In conclusion, the environmentally friendly oil effectively improved the diameter of the Ni-Ti stent wire, demonstrating the utility of olive and castor oil in ultraprecision finishing of Ni-Ti stent wire biomaterials. Full article
(This article belongs to the Special Issue Titanium and Its Alloys for Biomedical Applications)
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Article
Fabrication of a Novel Ta(Zn)O Thin Film on Titanium by Magnetron Sputtering and Plasma Electrolytic Oxidation for Cell Biocompatibilities and Antibacterial Applications
Metals 2020, 10(5), 649; https://doi.org/10.3390/met10050649 - 18 May 2020
Viewed by 1051
Abstract
Pure titanium (Ti) and titanium alloys are widely used as artificial implant materials for biomedical applications. The excellent biocompatibility of Ti has been attributed to the presence of a natural or artificial surface layer of titanium dioxide. Zinc oxide and tantalum oxide thin [...] Read more.
Pure titanium (Ti) and titanium alloys are widely used as artificial implant materials for biomedical applications. The excellent biocompatibility of Ti has been attributed to the presence of a natural or artificial surface layer of titanium dioxide. Zinc oxide and tantalum oxide thin films are recognized due to their outstanding antibacterial properties. In this study, high power impulse magnetron sputtering (HiPIMS) was used for the deposition of tantalum oxide and zinc-doped Ta(Zn)O thin films on Ti with rough and porous surface, which was pretreated by plasma electrolytic oxidation (PEO). Surface morphology, antibacterial property as well as cell biocompatibility were analyzed. The antibacterial effect was studied individually for the Gram-positive and Gram-negative bacteria Staphylococcus aureus (S. aureus) and Actinobacillus actinomycetemcomitans (A. actinomycetemcomitans). The deposited Ta (Zn)O coating was composed of amorphous tantalum oxide and crystalline ZnO. The antibacterial results on the tantalum oxide and Ta(Zn)O coated Ti indicated a significant inhibition of both S. aureus and A. actinomycetemcomitans bacteria when compared with the uncoated Ti samples. The deposited Ta(Zn)O showed the best antibacterial performance. The Ta(Zn)O coated Ti showed lower level of the cell viability in MG-63 cells compared to other groups, indicating that Zn-doped Ta(Zn)O coatings may restrict the cell viability of hard tissue-derived MG-63 cells. However, the biocompatibility tests demonstrated that the tantalum oxide and Ta(Zn)O coatings improved cell attachment and cell growth in human skin fibroblasts. The cytotoxicity was found similar between the Ta2O5 and Ta(Zn)O coated Ti. By adopting a first PEO surface modification and a subsequent HiPIMS coating deposition, we synthetized amorphous tantalum oxide and Ta(Zn)O coatings that improved titanium surface properties and morphologies, making them a good surface treatment for titanium-based implants. Full article
(This article belongs to the Special Issue Titanium and Its Alloys for Biomedical Applications)
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Article
Microstructure and Mechanical Properties of Titanium–Equine Bone Biocomposites
Metals 2020, 10(5), 581; https://doi.org/10.3390/met10050581 - 29 Apr 2020
Cited by 1 | Viewed by 1025
Abstract
Microstructure and mechanical properties of Ti-6Al-4V/equine bone (EB) composites fabricated by ball milling and spark plasma sintering (SPS) have been investigated. Ti-6Al-4V/EB composites were successfully fabricated by a planetary ball-milling of spherical Ti6Al4V powder and natural EB powder and SPS at 1000 °C [...] Read more.
Microstructure and mechanical properties of Ti-6Al-4V/equine bone (EB) composites fabricated by ball milling and spark plasma sintering (SPS) have been investigated. Ti-6Al-4V/EB composites were successfully fabricated by a planetary ball-milling of spherical Ti6Al4V powder and natural EB powder and SPS at 1000 °C within 15 min under 50 MPa. EB was uniformly dispersed in the Ti6Al4V matrix owing to ball-milling, and beta phase transformation temperature of 1000 °C provided phase stability. The composites containing 0.5 wt.% EB exhibit Vickers hardness and elastic modulus of 540.6 HV and 130.5 GPa, respectively. The microstructures and mechanical properties of the composites were observed using scanning electron micrograph and nanoindentation. Full article
(This article belongs to the Special Issue Titanium and Its Alloys for Biomedical Applications)
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Planned Papers

The below list represents only planned manuscripts. Some of these manuscripts have not been received by the Editorial Office yet. Papers submitted to MDPI journals are subject to peer-review.

Title: Discovery of nontoxic Ti-based biomedical alloys having minimum amount of α” and ω-phases using CALPHAD and artificial intelligence
Authors: Rajesh Jha and George S. Dulikravich
Affiliation: Department of Mechanical and Materials Engineering, Multidisciplinary Analysis, Inverse Design, Robust Optimization and Control (MAIDROC) Laboratory, Florida International University, Miami, FL 33174, USA
Abstract: Titanium based alloys have been widely accepted for biomedical applications due to comparatively superior biocompatibility and anticorrosion properties. Efforts are being made to explore new alloys containing elements that are not toxic, as well as developing alloys with Young’s modulus comparable to human bone for avoiding stress shielding. Titanium alloys containing β-phase as the predominant phase is helpful in lowering the Young’s modulus. During development/heat-treatment of Titanium alloys, β-phase can transform into ω-phase. In Ti-based metallic alloys, α” and ω-phases are responsible for degradation of mechanical properties and causing their embrittlement. In this work, we have studied Ti-Zr-Nb-Sn system computationally for exploring novel compositions and temperatures that will be helpful in avoiding/minimizing formation of α” and ω-phases. We studied this alloy system under the framework of CALPHAD approach used for determining phase stability of various phases. Thereafter, we analyzed this phase stability dataset through the application of Artificial Intelligence (AI) algorithms for determining correlation between phase stability of various phases and chemical composition and temperature. We developed artificial neural network models through deep learning approach for various phases and studied correlations within the dataset using Self Organizing Maps (SOM) approach. Through this study, we determined several compositions and temperatures that will be helpful in minimizing and even avoiding formation of α” and ω-phase in Ti-Zr-Nb-Sn system, which is free of toxic elements.

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