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- Herausgeber: John Wiley & Sons
- Kategorie: Fachliteratur
- Sprache: Englisch
Understand the core materials that create biomedical innovation
Some of the greatest medical advances in recent decades have come in the form of biomedical implants. Whether in the form of traditional orthopedic implants, medical devices for the cardiovascular system, or polymer-based ocular implants, biomedical implants can be lifesaving or life-transforming interventions. The biomaterials which comprise these implants are a vital area of ongoing research, but no prior volume has ever taken comprehensive stock of this subject and its growing applications.
An Overview of Biomedical Implants fills this gap with a thorough overview of all major biomaterials and their role in biomedical implants. Composed for an interdisciplinary audience, the book addresses all scales and areas of application. The result is an essential resource in this critical ongoing area of biomedical research.
An Overview of Biomedical Implants readers will also find:
- Description of the relationship between every specific biomaterial and its role in each major implant category
- Detailed discussion of nanoscale to molecular-scale to industrial-scale biomaterials
- Concrete examples in every chapter, along with a list of pertinent references
An Overview of Biomedical Implants is ideal for physicians, scientists, and engineers—those working in the area of biomaterials, medical, biological and chemical and applied physics, pharmaceutical science and as a reference for professors and students in these areas.
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Veröffentlichungsjahr: 2025
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Table of Contents
Cover
Table of Contents
Title Page
Copyright
Dedication
Preface
Acknowledgments
1 Biomaterials for Dental Implants
1.1 Introduction: Dental Implants and Current Materials
1.2 Ceramic Dental Implants
1.3 Polyetheretherketone (PEEK)
1.4 Peptide Coatings for Dental Implants
1.5 Functionally Graded Dental Implants
1.6 Looking to the Future: State‐of‐the‐Art Biomaterials for Dental Implants
1.7 Conclusion
References
2.1 Biomaterials for Total Hip Implants
2.1.1 Introduction
2.1.2 History of THA Development
2.1.3 Metallic Materials
2.1.4 Exploited Materials for Bearing Surface
2.1.5 Orthopedic Wear Debris
2.1.6 Conclusion
References
2.2 Biomaterials for Total Knee Replacement (TKR) and Total Hip Replacement (THR) and Next‐Generation Advancements
2.2.1 Introduction
2.2.2 Ultra‐High Molecular Weight Polyethylene (UHMWPE) and Polyethylene (PE)
2.2.3 Polyetheretherketone (PEEK)
2.2.4 Polymethylmethacrylate (PMMA)
2.2.5 Metal Implants
2.2.6 Ceramics and New Generation Surface Treatments
2.2.7 Advancements in Biomedicine and Nanotechnology: Titanium, Silver Nanoparticles, and More
2.2.8 Summary and Conclusion
References
2.3 Biomaterials for Shoulder Implants
2.3.1 Introduction
2.3.2 Titanium Alloys
2.3.3 Cobalt–Chrome Alloys
2.3.4 Ceramics
2.3.5 Pyrolytic Carbon
2.3.6 Comparison of Shoulder Implants with Different Class Materials
2.3.7 Conclusion
References
3 Biomaterials for Spinal Implants
3.1 Introduction
3.2 Overview of Implants and Corresponding Material Design Requirements
3.3 Metals
3.4 Ceramics
3.5 Polymers
3.6 3D‐Printed Spinal Implants: Applications and Relevant Materials
3.7 Degradable Implants
3.8 Discussion
3.9 Conclusion
References
4 Biomaterials in Cochlear Implants
4.1 Introduction
4.2 Biological Requirements
4.3 Electrical Requirements
4.4 Mechanical Requirements
4.5 New Electrode Biomaterials
4.6 Nanoscale Coatings
4.7 New Potential Implant Materials
4.8 Drug Delivery
4.9 Summary and Conclusion
References
5 Biomaterials for Cardiovascular Implants
5.1 Introduction
5.2 Different Applications
5.3 Summary and Conclusions
References
6 Biomaterials for Liver and Kidney Implants
6.1 Introduction
6.2 Liver Biomaterials
6.3 Kidney Biomaterials
6.4 Conclusions
References
7 Biomaterials for Brain Implants
7.1 Introduction
7.2 Brain Implants Classification
7.3 Causes of Failure
7.4 Materials for Neural Electrodes
7.5 Conclusions
References
8 Biomaterials for Bionic Implants
8.1 Introduction
8.2 Biomaterials in Bionic Eye and Neural Systems
8.3 Biomaterials in Bionic Limbs
8.4 Summary Conclusion
References
9 Final Remarks
Index
End User License Agreement
List of Tables
Chapter 2a
Table 2.1.1 Advantages and disadvantages of bearing surfaces. (Adapted from ...
Chapter 2b
Table 2.2.1 Typical average physical properties of metals used in hip and k...
Table 2.2.2 Typical average physical properties of ceramics used in hip and...
Chapter 2c
Table 2.3.1 Density and Young’s modulus are shown for metal alloys. (Ref. [...
Chapter 3
Table 3.1 Select data on carbon fiber‐reinforced PEEK. (From Ref. [21], 200...
Table 3.2 Comprehensive examination of PEEK composites augmented with diver...
Chapter 5
Table 5.1 Mechanical properties of the metals that are used for making sten...
List of Illustrations
Chapter 1
Figure 1.1 Osseointegration of dental implants over time.
Figure 1.2 Various aspects of dental implant surfaces viewed by scanning ele...
Figure 1.3 Depiction of a range of nanoscale topography effects. Cellular pr...
Figure 1.4 This schematic highlights the interactions between bone and impla...
Figure 1.5 TEM analysis of nZnO (a and b) and nano‐based HA particulates (c ...
Figure 1.6 Strategies to modify PEEK to enhance the general osseointegration...
Figure 1.7 PEEK/n‐HA/CF biocomposite preparation, biological evaluation, and...
Figure 1.8 Diagram o f a FGM dental implant with graded material composition...
Figure 1.9 Current and potential dental applications of PEKK.
Chapter 2a
Figure 2.1.1 Materials utilized in modern Total Hip Arthroplasty (THA) beari...
Figure 2.1.2 Radiographic images depict acetabular aseptic loosening in a 62...
Chapter 2b
Figure 2.2.1 Examples and biological effects of modifications inspired by bo...
Figure 2.2.2 Scanning electron microscopy (SEM) image of a PMMA‐based bone c...
Figure 2.2.3 The antibiotic release and inhibition patterns of gentamicin‐lo...
Figure 2.2.4 Osseointegration graph on the implant–bone interface over 12‐we...
Figure 2.2.5 Surface morphology of Ti after various surface modification tre...
Figure 2.2.6 Representative attachment patterns of
S. aureus
(left) and
P. a
...
Chapter 2c
Figure 2.3.1 X‐rays of implanted shoulder implants. Plain film right shoulde...
Figure 2.3.2 Schematics of Neer’s third design implant placed in a patient's...
Chapter 3
Figure 3.1 A French bender, employed for shaping spinal rods, exhibited the ...
Figure 3.2 (a) Illustration outlining the process of preparing a tumor cell ...
Figure 3.3 (a–i) Scanning electron microscopy (SEM) images capture the surfa...
Figure 3.4 (a–c) Scanning electron microscopy (SEM) images depict Staphyloco...
Figure 3.5 Immunofluorescence analysis was conducted on MC3T3‐E1 cells cultu...
Figure 3.6 Histological pictures illustrating stained cross‐sections of half...
Figure 3.7 Optical images of half‐coated PEEK screws before (a) and after (b...
Figure 3.8 10%HA‐PEEK composite fracture surface SEM image.
Figure 3.9 Cancellous and cortical bone mechanical property (Young’s modulus...
Chapter 4
Figure 4.1 A graph depicting hearing thresholds (dB SPL) on day 0 before and...
Figure 4.2 The graph depicts the percentage of connective tissue in three gr...
Figure 4.3 The figure illustrates DAB‐stained spiral ganglion neurons (SGN) ...
Figure 4.4 The determination of survival and neuritogenesis of spiral gangli...
Figure 4.5 Maximal insertion forces were measured, and the difference betwee...
Figure 4.6 A biocompatible, degradable Ozurdex implant...
Chapter 5
Figure 5.1 Representation of balloon angioplasty: (a) before procedure, (b) ...
Figure 5.2 Steps of the finite element model to simulate the deployment of t...
Figure 5.3 Shape‐memory diagram of nitinol [32].
Figure 5.4 Stent thrombosis (a) drug‐eluting stent implantation in the proxi...
Figure 5.5 Degradation of magnesium staples under
in vitro
and
in vivo
condi...
Figure 5.6 Four valves of the heart, visible with the atria and great vessel...
Figure 5.7 Frequently used Starr–Edwards valves: aortic models 1000 (a) and ...
Figure 5.8 Smeloff–Cutter ball valve [86].
Figure 5.9 Examples of bioprosthetic degeneration (a) bioprosthetic porcine ...
Chapter 6
Figure 6.1 Schematics of the (a) anterior and (b) posterior views of the hum...
Figure 6.2 Microscopic structure of the liver.
Figure 6.3 Scanning electron microscopy (SEM) images of porous PLLA fiber wi...
Figure 6.4 Scheme of a bioactive liver device also known as HepatAssist bior...
Figure 6.5 Schematic of the renal structure: The black labels denote the nep...
Figure 6.6 Scanning electron microphotographs of decellularized ovarian scaf...
Figure 6.7 The circuit diagram illustrates version 1.0 of the Wearable Artif...
Figure 6.8 Schematic design outlines an implantable artificial kidney device...
Chapter 7
Figure 7.1 ECoG grid and activation thresholds. (a) Optical image of a typic...
Figure 7.2 The Utah Intracortical Electrode Array is depicted in this scanni...
Figure 7.3 The illustration portrays the configuration of a deep brain stimu...
Figure 7.4 The macroelectrode and microelectrode array employed in this stud...
Figure 7.5 PEDOT:PSS‐coated test electrode array.
Figure 7.6 SEM images of Ni‐coated needle electrodes. (a,b) Selective coatin...
Figure 7.7 SEM images of 3D‐GFs at low (a) and high (b) magnification; (c) H...
Chapter 8
Figure 8.1 (a) External and (b) implant part of the Argus II system; (c) ill...
Figure 8.2 Schematic of tissue–electrode interfaces. (A) The electrodes of b...
Figure 8.3 (a) Scanning electron microscopy (SEM) image of...
Figure 8.4 Modulus matching serves as a guiding principle in the design of f...
Figure 8.5 The kinetically controlled printing process provides precise mana...
Figure 8.6 A schematic representation of the proposed two‐degree‐of‐freedom ...
Guide
Cover
Table of Contents
Title Page
Copyright
Dedication
Preface
Acknowledgments
Begin Reading
Index
End User License Agreement
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An Overview of Biomedical Implants
Biomaterials for the Human Body
Tolou Shokuhfar
University of Illinois, Chicago, USA
Copyright © 2025 by John Wiley & Sons, Inc. All rights reserved, including rights for text and data mining and training of artificial technologies or similar technologies.
Published by John Wiley & Sons, Inc., Hoboken, New Jersey.
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Library of Congress Cataloging‐in‐Publication Data Applied for:
Hardback ISBN: 9781119850977
Cover Design: Wiley
To Ryan, my dearest son,
Your curiosity and resilience inspire me every day. This book is for you, with all my love.
To my father,
Prof. Ali Shokuhfar, whose wisdom and dedication continue to guide me, even in his absence.
And to my husband, Prof. Reza Shahbazian,
For your unwavering love, support, and belief in me.
Preface
This book explores instances of innovative biomaterials employed in significant biomedical implants aimed at advancing tissue regeneration and regenerative medicine to enhance human life. These biomaterials may exist in various stages: from laboratory prototypes poised for marketing, to industrially implemented products, or in developmental phases. The cases examined span across all scales, encompassing the nanoscale, molecular level, diverse processes, industrial facilities, regional contexts, and global industries. Each case comprehensively outlines the specific biomaterial's role in the development of the corresponding implant, tracing its evolution from inception to subsequent generations.
It serves as an invaluable resource catering to an interdisciplinary audience, inclusive of medical and dental students, biomedical industry researchers, and students with backgrounds in science and engineering, all of whom harbor an interest in biomaterials. While the primary focus remains on major biomaterials utilized in implants, the book also delves into conventional and emerging biomaterials, illustrating their application in the development of next‐generation implants.
Acknowledgments
The author expresses sincere gratitude to the following individuals for their contributions in shaping certain aspects of this book. Mansi Advani, Jialin He, Alessandro Gozzi, Medha Sesham, Iram Hameeduddin, Francesco Marconi, Danny McDermed, Jimit Kapadia, Kasey Leung, and Silvia Leccabue.
1Biomaterials for Dental Implants
CHAPTER MENU
1.1 Introduction: Dental Implants and Current Materials, 1
1.2 Ceramic Dental Implants, 8
1.3 Polyetheretherketone (PEEK), 15
1.4 Peptide Coatings for Dental Implants, 20
1.5 Functionally Graded Dental Implants, 22
1.6 Looking to the Future: State‐of‐the‐Art Biomaterials for Dental Implants, 26
1.7 Conclusion, 28
References, 29
1.1 Introduction: Dental Implants and Current Materials
1.1.1 The Need for Better Dental Implants
An interdisciplinary approach including surface chemistry, physics, and engineering as well as biomechanics is required to develop successful dental implants [1]. Dental implants have been prevalent throughout the past century; however, evidence of dental implants within ancient Mayan and Egyptian civilizations has been found [2]. This brings us to the first prototype of the modern dental implant, which was created by Greenfield in 1913 and was first described as an implant/prosthetic combination made of an iridium–platinum alloy [2]. In the 1970s, Brånemark’s experimentation led to the general acceptance of oral implants and highlighted the importance of osseointegration [3]. We now understand that the success of a dental implant depends on the chemical, physical, mechanical, and topographic characteristics of its surface [4]. As a result of continuous modifications to implant design and surface topography, dental implant placement is a fairly common treatment procedure with high implant survival rates and limited peri‐implant bone loss [5]. In fact, the survival rate of dental implants has been reported to be above 90% [6]. Nowadays, implant surface modifications focus on stronger and faster bone healing to further limit dental implant failure [5]. Even with great advancements in the field of dental implantology, there is still a relatively significant number of dental implant failures, many of which are caused by compromised bone conditions that promote implant failure. For example, diabetes, osteoporosis, obesity, and the use of drugs can decrease bone healing around dental implants [6]. Furthermore, complications involving osseointegrated dental implants can arise from inflammatory conditions associated with bacteria, more specifically, peri‐implantitis [7].
Peri‐implantitis is a pathological condition that occurs in tissues surrounding dental implants [7]. It is characterized by inflammation of the peri‐implant connective tissues as well as loss of supporting bone [7]. In other words, plaque and its byproducts lead to hard and soft tissue breakdown and eventually implant failure, which is a prevalent issue [8]. Factors such as smoking or a history of periodontal disease increase the prevalence of peri‐implantitis [8]. However, even with the lack of the aforementioned factors, features such as implant placement, material biocompatibility, and material degradation also play important roles in the development of peri‐implantitis or osseointegration breakdown [8]. Osseointegration is the formation of bone tissue around the implant without fibrous tissue growth at the bone–implant interface, resulting in direct anchorage of the implant [1]. The osseointegration process can be visualized in Figure 1.1. In fact, the structural and functional union of the implant and living bone is significantly influenced by the surface characteristics of the dental implant [4]. Thus, proper osseointegration is crucial for the success of the implant and is a research topic of great importance. Presently, researchers are finding ways to optimize implant surfaces by studying specific features such as roughness of the implant surface as well as various materials for dental implants in order to promote proper osseointegration and combat peri‐implantitis [10].
Figure 1.1 Osseointegration of dental implants over time.
(From Ref. [9], 2021, Springer Nature, CC BY 4.0).
Currently, titanium or titanium alloys are the gold standard in dental applications [10]. Most dental implants marketed in the United States are made from either commercially pure titanium (cpTi) or titanium alloys [e.g. Ti6Al4V (TAV)] [4]. Seconds after titanium (Ti) is machined, adsorbed oxygen molecules form a thin oxide layer, which is what body tissues interact with [11]. This oxide layer allows for biocompatibility, while the rest of the implant material plays a role in the implant’s mechanical properties [11]. Chemical processes that occur at the tissue–implant interface include corrosion, adsorption of some biomolecules, denaturing of proteins, and catalytic activity [11]. For instance, TAV implants degrade and result in peri‐implant bone loss [12]. The origins of this degradation were revealed by Chen et al. [12] whose results suggest that the observed bone loss is caused by crevice corrosion and the release of consequential by‐products. These types of issues are driving scientists to find materials and methods to improve dental implants, specifically, the surface of dental implants.
1.1.2 Various Approaches and Biomaterials to Improve Dental Implants
The material composition and surface topography of implants greatly influence the wound healing processes that follow implantation and thus also influence subsequent osseointegration [13]. It has been found that implants with a rough surface allow for better osseointegration; however, excessive roughness can increase the risk of peri‐implantitis and ionic leakage [14]. Thus several methods have been proposed to produce a moderate roughness of 1–2 μm including titanium plasma spraying, particle blasting and acid etching, anodization of the implant surface, and coatings [14]. Examples of these methods are highlighted in Figure 1.2. One method, anodization or anodic oxidation on Ti‐based implants, creates an adherent oxide coating that can have a wide range of stoichiometries as well as microporosities and nanoporosities depending on electrolyte selection and condition manipulation [15].
Figure 1.2 Various aspects of dental implant surfaces viewed by scanning electron microscopy. (a) Original machined implant from Nobel Biocare with a smooth surface. (b) Rough surface of a dental implant system developed by the French company ETK implant that was sandblasted, and acid etched. (c) Surface of a Ti UniteTM implant from Nobel Biocare with a thick layer of titanium creating smooth asperities. (d) High magnification of an implant surface after sandblasting and HF acid etching. (e) Surface of a TA6V implant whose surface was sandblasted with corundum particles. (f) Surface of titanium implant, which was sprayed with titanium beads with a plasma torch.
(From Ref. [14], 2016, Elsevier).
Biomaterials of interest that could be used as a coating or as a Ti implant replacement include hydroxyapatite (HA), ceramic materials [e.g. alumina, calcium phosphate (CP), and zirconia], nanoparticulate zinc oxide (nZnO), and polyetheretherketone (PEEK). Each of these materials has their own promising aspects. Some studies have reported benefits of using HA‐coated dental implants as well as risks including dissolution of the coating (although they have not shown that dissolution leads to implant loss) [16]. Furthermore, HA coatings may be more susceptible to bacteria as compared to titanium implants [16]. Nevertheless, coating dental implants with HA has helped metallic materials to osseointegrate with the local tissue environment and distribute load stress [17]. Zirconia is a possible alternative to the traditional Ti‐based implant systems as it has superior biological, aesthetic, mechanical, and optical properties [18]. However, more long‐term and comparative clinical trials are necessary in order to validate zirconia as a viable alternative to titanium implants [18].
There are many other dental implant biomaterials that clinicians may not be familiar with. For example, bioactive dental glass‐ceramics (BDGCs) have shown bone–tooth bonding capabilities as well as positive biological reactions at the material–tissue interface [19]. This makes them an attractive implant coating biomaterial. Nanoparticulate zinc oxide is of great interest because of its integration with antimicrobial nanoparticles (NPs) resulting in a coating material that is antibacterial and promotes osteoblast growth, which would help prevent implant failure from aseptic loosening and infection [20]. PEEK possesses excellent mechanical characteristics and may be used in dentistry with surface modification to enhance its osseointegrative characteristics [10]. Another interesting approach to modifying dental implants is using functionally graded materials (FGMs). FGMs are heterogeneous composite materials that have a compositional gradient with continuously varying properties in the thickness direction [21]. Ultimately, these more “novel” biomaterials must be researched in more depth if they are to be used more frequently in the clinic.
An important aspect of biomaterials for dental implants is the stabilization of dental implants with materials such as bioceramic granules and cements. Occasionally, when an implant is placed, there is not enough bone surrounding it [22]. This issue is solved by using bioceramics to fill in the implant–bone gap; however, these materials have poor mechanical properties and cannot stabilize the implant well [22]. Furthermore, it is important to consider the biological interactions that dental cement composition has as it plays significant roles in the host cellular response and the degree of surface degradation from bacterial attack [23]. A group of materials that are of great interest as they can be used as bone substitutes or even as implant‐coating materials are calcium phosphate cements (CPCs) [24, 25]. More specifically, CPCs can be used as alternatives/complements to autogenous bone grafting in implant dentistry as well as coating materials to enhance the osteoinductivity of Ti implants [25]. CPCs can carry growth factors and are also scaffolds for cell proliferation, differentiation, and penetration [25]. Surprisingly, even though the mechanical strength of CPCs is generally low, this is not a critical issue when used for bone repair [24]. Schickert et al. developed CPC reinforced with fibers which improved flexural strength and toughness and, when molded into the implant–bone gap, stabilized the implants, and allowed for a direct connection between the implant and bone [22]. Overall, strategies using materials containing calcium phosphates (CaPs) aim to enhance dental implant osseointegration in the context of immediate loading and to alter the formation of surrounding bone to allow for long‐term success [25].
1.1.3 Working at the Nanoscale to Improve Dental Implants
Another possible approach to altering dental implants is utilizing nanoscale materials. Nanoscale materials take into account that tissue responses are usually dictated by processes that occur at the nanoscale, so by controlling interfacial reactions at the nano level, we can develop new implant surfaces that eliminate rejection while promoting adhesion and integration with the surrounding tissue environment [15]. The effects of nanoscale features are demonstrated in Figure 1.3. An example of this type of nanoscale engineering is using peptides that are bioactive motifs as coatings. For example, the arginine–glycine–aspartate (RGD) peptide is a cell‐adhesive sequence and has been shown to improve the adherence of human gingival fibroblasts and epithelial cells to Ti dental implants [27]. Zhao et al. grafted the bioactive RGD peptide on cpTi and showed that more fibroblasts and epithelial cells adhered onto the RGD‐grafted titanium as compared to CP titanium [27]. Furthermore, Raphel et al. designed an elastin‐like protein (ELP) that includes an extended RGD sequence, and they found that ELP coatings withstand surgical implantation and promote rapid osseointegration [28]. This allows for earlier implant loading and may prevent micromotion that could lead to aseptic loosening and implant failure [28].
Figure 1.3 Depiction of a range of nanoscale topography effects. Cellular protein adsorption is altered by nanoscale modification of bulk material. Cell specificity and extent of cell adhesions are both altered. Cell spreading may increase or decrease depending on the nano‐architecture. By currently undefined mechanisms, cell proliferation appears to be enhanced by nanoscale topography. Several investigators have shown that nanoscale topography enhances osteoblast differentiation.
(From Ref. [26], 2008, Elsevier).
Another example of working at the nanoscale is nanopatterned surfaces. In vitro and in vivo studies have shown that nanoscale topographies on titanium surfaces promote cell adhesion, osteogenic differentiation, and bone formation [29]. Shiozawa et al. created smaller, standardized, and controlled nanosized structures on titanium surfaces, providing a design basis for effective nanostructures that optimize the osseointegration of dental implants [29]. Additionally, they observed directional cell growth for some line and groove patterns, and they found that the grain structure controls the cell proliferation rate [29]. Researchers are also using NPs or nanofiber reinforcements in polymer matrices to manipulate the mechanical properties of biomaterials. One application is the use of tetracycline (TCH)‐incorporated polymer nanofibers as a potential antimicrobial surface modifier and osteogenic inducer for Ti dental implants [30]. In fact, Shahi et al. found that there was complete inhibition of biofilm formation by peri‐implantitis‐associated pathogens on fibers containing TCH at 10 and 25 wt% [31].
Besides nanofibers, researchers are also studying nanotubes (NTs) to advance dental implant technology. Carbon nanotubes (CNTs) have a unique structure made of rolled graphene sheets that enhances the shear, compression, and tensile strain resistance of dental implants and are also biocompatible [32]. CNTs have been applied to Ti and zirconia implants as well as with HA nanocomposites [32]. CNT nanocomposite materials have great potential in supporting the weaknesses of current commercial dental implant materials, but there still have some challenges to overcome such as controlling the surface properties of CNTs [32]. One example of a CNT application is the development of a multi‐walled carbon nanotubes‐hydroxyapatite (MWCNTs‐HA) nanocomposite. Park et al. produced MWCNTs‐HA nanocomposites with various MWCNT concentrations which coated Ti surfaces [33]. They showed that HA NPs bonded to the surface of the MWCNTs, and cell tests showed that cell proliferation increased regardless of the MWCNT concentration [33]. Furthermore, the filopodia of cells developed in the presence of MWCNTs, and cytodifferentiation was greatest on the 0.5 wt% MWCNTs‐HA surface. Another type of NT is titanium dioxide (TiO2) NTs. Zhao et al. modified the surface of Ti substrates by doping TiO2 NTs on the Ti surface with silicon (Si) [34]. They compared TiO2 NTs and Ti alone with the Si‐doped TiO2 NTs and found that the Si‐doped TiO2 NTs significantly enhanced gene expression for osteogenic differentiation in mouse pre‐osteoblastic cells as well as mineral matrix deposition [34]. Furthermore, in vivo studies of Zhao et al. showed improved implant fixation strength with the use of Si‐doped TiO2 NTs [34]. From these findings, it is clear that Si‐doped TiO2 NTs promote osteogenic differentiation of osteoblastic cells and improve bone–Ti integration, which may have a large impact on Ti implant surface modification [34].
Overall, dental implants are commonplace and improve the quality of life for many patients. However, some implants do fail as a result of several possible reasons such as peri‐implantitis, lack of osseointegration, and mechanical shortcomings. Therefore, it is important to develop biomaterials that will promote osseointegration, fend off infection, and stand up to mechanical forces to decrease the chance of dental implant failure. In this review, I will further explore the wide range and recent advances of biomaterials developed to improve dental implants from novel implant materials to nanoscale strategies.
1.2 Ceramic Dental Implants
Modern ceramic biomaterials often meet or exceed experimental requirements [35]. Structural and mechanical properties of bioceramics can be changed by the composition of the raw material, manufacturing methods, processing parameters, implantation techniques, and engineering variables [35]. Bioceramics used in various medical applications (e.g. total hip and knee replacements) have seen improved wear resistance and long‐term biocompatibility [35]. Ceramic dental implants, particularly zirconia, have much potential for replacing classic titanium dental implants in the future.
1.2.1 Zirconia
Zirconia implants are made from the strong transition metal zirconium, and zirconia is the oxide form of zirconium [18]. Even though titanium implants have shown long‐term reliability, some disadvantages of this material are allergies or sensitivity to titanium, gingival shrinkage and translucency, and the electrical conductivity and corrosive properties of titanium [36]. Lately, there has been an increase in demand for zirconia‐based implants for aesthetic reasons, but zirconia‐based implants also have a superior soft‐tissue response, are biocompatible, and have comparable osseointegration to traditional titanium implants [18]. Even though zirconia is biocompatible, it is also bioinert meaning that osseointegration can be comprised since bone cannot naturally grow on zirconia surfaces [37]. Thus, it is important to study how surface modifications of zirconia dental implants can promote osseointegration. There are two main approaches to improving the surface properties of implant materials: optimizing roughness and applying a bioactive coating [38]. Furthermore, many physiochemical methods have been used to modify the surface of zirconia‐based implants including acid etching, gritblasting, laser treatment, ultra violet (UV) light, CVD, and PVD [39]. Additionally, coatings such as those made of silica, magnesium, graphene, dopamine, and bioactive molecules have been developed [39]. It is necessary to conduct more long‐term studies on zirconia implants in order to validate these good characteristics so that they may be used more frequently in the clinic [40].
1.2.1.1 Surface Roughness Optimization of Zirconia‐Based Implants
It is known that surface modifications that create micro‐rough implant surfaces on titanium implants accelerate the osseointegration process [41]. Sandblasting, also known as airborne particle abrasion, produces a homogenous and gentle anisotropic abrasion on a hard surface using particles such as alumina particles [38]. A drawback of sandblasting is that alumina contamination can alter the implant surface chemistry, but this can be solved using an acid etching treatment [38]. Acid etching, performed using hydrofluoric acid, nitric acid, or sulfuric acid, homogenously roughens the material regardless of size and shape and has been shown to remove alumina residue from sandblasting [38]. By understanding that implant surface roughness plays a critical role in osseointegration, the method of sandblasting and subsequent acid etching has been developed to obtain a desirable dental implant surface.
At this time, sandblasting followed by acid etching may be the “gold standard” technique for creating micro‐rough surfaces [41]. Fischer et al. analyzed the effect of this method on surface morphology and mechanical strength of zirconia implants. They found that sandblasting with 105‐μm alumina followed by one hour of HF etching at room temperature and one hour of heat treatment at 1250°C (heat treatment smoothens sharp edges caused by the acid etching process) created a surface roughness of about 1.2 μm on zirconia implants and is also a reliable and tolerant process [38, 42].
Interestingly, adding microgrooves to the intraosseous portion of zirconia implants immediately followed by loading has shown that the thickness of soft tissues remains stable and that crestal bone preservation is related to insertion depth [36]. Furthermore, higher bone‐to‐implant contact percentages and increased bone density around microgrooved implants can be expected three months following implant insertion and immediate loading [36].
1.2.1.2 Coating Alternatives for Zirconia‐Based Implants
Implant coatings such as HA and beta‐tricalcium phosphate (β‐TCP) are used to improve the bond between the tissue and implant [37]. However, contact shear stresses can cause the coatings to detach from the zirconia surface, which compromises their osseointegration function and can lead to implant failure [37]. As an alternative to coatings, Faria et al. designed an integrated bioactive zirconia outer composite layer on a zirconia substrate to avoid the aforementioned coating issue. This novel material involves a bioactive zirconia–calcium phosphate composite outer layer on a zirconia bulk material that provides mechanical strength [37]. More specifically, the proposed implant has a gradated design with a bioactive outer composite layer (zirconia reinforced by 10 vol% of HAp or 10 vol% of β‐TCP). Faria et al. tested the potential of the gradated composites by evaluating materials, mechanical resistance, fatigue resistance, and biological performance. This design ensures no bioactive detachment when implanted and is a promising material for zirconia‐based dental implants [37].
1.2.1.3 Using Nanotechnology to Modify Zirconia‐Based Implants
With the increasing interest in nanotechnology, new materials and methods have been developed that aid in the osseointegration of dental implants. We can appreciate the importance of nano interactions by examining Figure 1.4. Proteins and cell membrane receptors fall within the nanoscale; thus, surface nanoscale roughness plays crucial roles in osteoblast differentiation and tissue regeneration [43].
Figure 1.4 This schematic highlights the interactions between bone and implant surfaces at different scales.
(From Ref. [43], 2011, Elsevier).
Typically, Ti implants are modified at the nano level, while zirconia implants are modified using subtractive methods such as sandblasting and acid etching, but now there is much interest in modifying ceramic implant surfaces at the nanoscale level [44]. Generally, research focus is on either modifying zirconia implants by patterning the implant surface or by applying novel ceramic coatings [44]. One idea that takes advantage of nanoscale interactions is mimicking the surface topography of extracellular matrix (ECM) components [44]. This may allow implant surfaces to be more conducive to recruiting bone‐forming cells and therefore new bone formation since ECM components are nanosized by nature and influence tissue response [44]. Another example is anodizing the zirconia surface to form a nanostructured surface filled with NTs that can be loaded with different compounds or drugs that can speed up osseointegration or perhaps even be loaded with antibacterial factors [44]. Forming NTs in zirconia is technically challenging, but from this, we can tell that research is geared toward matching surface treatments between titanium and zirconia [44].
A continuous theme is the importance of osseointegration for successful implants. Thus, it follows that research has been conducted concerning roughening of zirconia implants to promote successful osseointegration at the nanoscale. Rezaei et al. investigated the biological and bone integration capabilities of a zirconia surface with distinct mesoscale, microscale, and nanoscale morphology [45]. They found that the unique hierarchical morphology of the rough zirconia surface showed an increase in osseointegration and accelerated osteoblast differentiation as compared to machine‐smooth zirconia [45]. Interestingly, while cell attachment and proliferation were compromised on rough titanium, these events were not compromised on the rough zirconia surface [45]. Overall, this study provides an effective strategy to improve zirconia implants [45]. Furthermore, these findings demonstrate how we can apply ideas typically used to study and improve Ti implants to zirconia implants.
1.2.1.4 Disadvantages and Advantages of Zirconia‐Based Implants
One of the main disadvantages to zirconia is that it is bioinert, which may compromise osseointegration [37]. To solve this issue, researchers have studied ways to modify the surface of zirconia dental implants including sandblasting. The downside of sandblasting is that it can change the implant surface chemistry due to alumina contamination [38]. This disadvantage can be minimized using acid etching treatment [38]. Even though coatings (e.g. HA) on zirconia dental implants may promote osseointegration, contact shear stresses can cause the coatings to detach from the implant surface, compromising the osseointegration function of the coatings [37]. Despite these issues, zirconia is still of interest to the dental implant research community due to zirconia’s superior soft‐tissue response, biocompatibility, and comparable osseointegration as compared to traditional titanium implants [18]. Zirconia dental implants also act as an alternative to titanium implants should a patient have a titanium allergy. To determine whether or not zirconia‐based dental implants should be more widely used in the future, it is important that we conduct more long‐term studies involving zirconia implants [40].
1.2.2 Hydroxyapatite
HA is a calcium‐phosphate‐based ceramic material that can be found in nature such as in bovine bones, fish bones, oyster shells, and corals but can also be synthesized in the lab [46]. HA is biocompatible and osteophilic and easily incorporates into bone tissues [46]. In fact, HA has been used to replace and augment bone tissues for many years as it plays a large role in the inorganic phase in teeth [46]. Furthermore, HA has been used as a bioactive implant coating to improve osseointegration [47]. It has the capacity to absorb proteins, improve osteoblast proliferation, enhance bone formation, and reduce bone loss, all of which allow for a more rapid fixation and stronger bonding between the implant and host bone [47]. More specifically, these properties allow for uniform bone ingrowth at the bone–implant interface, and as a coating, HA limits fibrous membrane formation and can convert a motion‐induced fibrous membrane into a bony anchorage [47]. Creative applications of HA are currently under investigation. For example, hydroxyapatite nanorods have been grafted onto titanium disk implants to improve strong interactions between implants and teeth [48]. HA does not necessarily have to act as a “stand‐alone” dental implant coating; it can be combined with other materials. For instance, a micro‐nanostructured HA coating was prepared on a titanium surface and then chitosan (CS), an antibacterial agent, was loaded onto the HA surface [49]. This HA/CS composite coating demonstrated improved biological and antibacterial properties, showing promise as a material for dental implants [49]. HA is a tried‐and‐true biomaterial that can help improve existing dental implants and be utilized in novel applications.
1.2.2.1 Antimicrobial Properties of Hydroxyapatite‐Containing Materials
When bacteria come in contact with dental implants, they form a biofilm [50]. Approaches such as coatings or embedding implants with antimicrobial agents have been unsuccessful and contribute to antimicrobial resistant [50]. To combat the negative consequences of using antimicrobial agents, Abdulkareem et al. studied the use of metal‐based antimicrobial NPs to control biofilm formation [50]. More specifically, they investigated zinc oxide NPs (nZnO) as well as nanoscale HA (nHA). The shape of zinc oxide NPs is rod and square‐based structures with sharp edges, as shown in Figure 1.5, and these structures may play a role in the antimicrobial capabilities of nZnO [50]. Additionally, nHA particles are mostly rod‐shaped and possess tiny nano‐sized holes that increase their surface area, indicated in Figure 1.5[50]. Abdulkareem et al. found that by combining nZnO and nHA to form a coating on Ti disks, the NPs worked together to provide an antimicrobial effect against opportunistic pathogens while increasing osseointegration [50].
Figure 1.5 TEM analysis of nZnO (a and b) and nano‐based HA particulates (c and d). ZnO NPs show rod‐like and square‐based structures with sharp edges (indicated by red arrows). nHA particulates are mostly rod‐shaped with nano‐sized holes (indicated by green arrows).
(From Ref. [50], 2015, Elsevier).
Furthermore, silver NPs (Ag NPs) are known to be antimicrobial but can be toxic to mammalian cells when used alone [51]. Salaie et al. aimed to enhance the biocompatibility of Ag NPs as a coating on Ti dental implants with HA applied to the surface. They coated Ti‐6Al‐4V disks with Ag NPs, Ag NPs with HA NPs (Ag + nHA), or Ag NPs with HA microparticles (Ag + mHA). They found that implants coated with Ag + nHA maintained a higher degree of biocompatibility compared to the other two groups, promoting the potential use of Ag + nHA in dental implants as a way to increase the antimicrobial activity of dental implants with HA applied to the surface [51].
1.2.2.2 Combination Dental Materials Using Hydroxyapatite
In recent years, HA has been combined with other materials to further improve it as a coating for dental implants. There are many possibilities and potential combinations of dental implant materials. One such example involves Mg‐containing HA. Mg is present in naturally formed HA, and Mg affects osteoblast and osteoclast activity as well as bone growth [52]. In fact, Mg in bone stimulates the transformation of immature (amorphic) bone into mature bone, which would potentially improve the activity between dental implants and bone [52].
Another example is incorporating HA into PEEK. PEEK has been investigated as a potential alternative to current endosseous dental implants due to its low elastic modulus, biocompatibility, and low customization cost [53]. Traditional Ti implants have a high elastic modulus, allowing for stress shielding and therefore bone regeneration inhibition and bone resorption enhancement [53]. PEEK may act as an alternative to this concerning issue. However, the main limitation of PEEK is its poor osseointegration property [53]. To remedy this problem, HA has been incorporated with PEEK, and Geng et al. found that bone formation was improved with HA‐incorporated PEEK in canine tibia [53]. They also stated that HA‐incorporated PEEK implants may serve as an alternative material for dental implants [53].
A unique combination of materials is HA with silk. Silk material has not only been widely used as a suture material but also been used in membranes for guided bone regeneration as well as for increasing new bone formation around dental implants [54]. Kweon et al. examined the clinical potential of silk and HA‐coated implants by comparing bone formation after installation of uncoated, HA‐coated, collagen and HA‐coated, and silk and HA‐coated implants. They found that the silk and HA‐coated implants demonstrated greater new bone formation and bone‐to‐implant contact as compared to the other three groups [54]. Even though HA‐coated dental implants are often successful and produce an acceptable long‐term survival rate, scientists are always looking for ways to improve various aspects of implants and coatings, demonstrated by the discussed examples.
1.2.2.3 Nano‐Hydroxyapatite
Many research fields have expanded into studying nanotechnology, and dental implants are no exception. Nano‐hydroxyapatite (nano‐HA) presents 50–1000 nm crystals [55]. Furthermore, nano‐HA in toothpaste has a strong ability to bind with proteins as well as plaque and bacteria fragments [55]. The NPs have a relatively large surface area that proteins can bind to, and nano‐HA can act as a filler for small holes and depressions on the enamel surface [55]. When considering oral implantology, nano‐HA has been a widely used as a coating material for Ti implants, and this is an established practice since nano‐HA has an excellent osteoinductive capacity and improves bone‐to‐implant integration [55, 56]. Nanoscale structure modification is an achievable strategy to improve surface bioactivity of dental implants.
Hu et al. designed nanorod‐structured HA coatings on Ti‐6Al‐4V implants, which promoted adhesion and proliferation of DM‐rBMSCs and enhanced osteogenic differentiation of these stem cells in vitro[57]. Interestingly, in the context of an in vivo diabetic model, enhanced osseointegration between the nanorod‐structured HA coatings and Ti–6Al–4V implants was observed [57]. These findings demonstrate the potential use of nanorod‐structured HA coatings on Ti–6Al–4V implants to target pathological bone loss by strengthening osteogenesis and angiogenesis [57]. Furthermore, this coating has the potential to be used as a therapeutic coating to promote diabetic osseointegration [57].
A different method of using HA involves sinus augmentation using nanocrystalline HA as a synthetic bone substitute. Ghanaati et al. reported on a three‐year clinical and radiologic follow‐up investigation of dental implants that were placed three and six months after the augmentation [58]. They wanted to determine how the integration of the nanocrystalline HA after three and six months influenced implant integration [58]. Ghanaati et al. concluded that augmentation with the synthetic bone substitute forms a sufficient implantation bed three months after augmentation, allowing for long‐term, stable, implant‐retained restoration [58]. This is favorable for both patients and clinicians and highlights the wide applicability HA has in the dental field.
1.2.2.4 Disadvantages and Advantages of HA‐based Biomaterials
HA is known to be biocompatible and has a highly porous structure, indicating its great potential as a coating for dental implants since HA can facilitate osseointegration [59]. However, some studies have shown concern about whether defects that may appear when doping can cause impurities that can lead to cytotoxicity and thus material rejection [59]. A different study suggests that a HA–protein composite correlates to the development of some chronic diseases [59]. Despite these potential disadvantages, HA continues to be used as a bioactive implant coating to improve osseointegration. The advantages of HA, such as the ability to absorb proteins, improve osteoblast proliferation, enhance bone formation, and reduce bone loss, outweigh the few concerns about HA [47]. HA is also a biomaterial that can be manipulated and combined with other biomaterials, making it a versatile biomaterial in the lab and clinic. HA’s impressive properties allow for quicker fixation and stronger bonding between dental implants and host bone [47].
1.3 Polyetheretherketone (PEEK)
PEEK is a synthetic polymer material that is tooth colored [60]. It has been used in orthopedics for many years due to its Young’s elastic modulus, which is close to that of human bone [60]. Even though titanium and its alloys and zirconia are biocompatible, their largest shortcoming is their relatively large elastic modulus, which is 5–14 times greater than that of compact bone and causes stress shielding [61]. Furthermore, PEEK has tensile properties that are analogous to those of bone, enamel, and dentin [60]. Unlike titanium, PEEK has low osteoconductive properties; thus, much effort has been geared toward improving the bioactivity of PEEK implants [60]. There have been controversial studies regarding unmodified PEEK and cell proliferation, protein turnover, osseointegration, and bioinertness as well as other properties [60]. Therefore, researchers have attempted to modify PEEK to improve its mechanical and biological properties. Two general approaches to enhance PEEK bioactivity are composite preparations and surface modifications, both of which are highlighted in Figure 1.6[10]. There are many different strategies that have been explored, particularly when it comes to surface modifications [10]. PEEK dental implants have not been used extensively in the clinic, so there is not enough data to determine the long‐term effects in human subjects [60].
Figure 1.6 Strategies to modify PEEK to enhance the general osseointegration of PEEK in cementless applications.
(From Ref. [10], 2019/John Wiley & Sons/CC BY 4.0).
1.3.1 PEEK Composites to Improve Mechanical Properties
Modified PEEK has high‐quality mechanical properties as compared to unmodified PEEK [61]. PEEK can be modified by incorporating other materials such as carbon fibers (CFs) to increase the elastic modulus to 18 GPa which is comparable to cortical bone and dentin [60]. This allows for a more appropriate level of stress shielding as compared to titanium implants. Han et al. were able to incorporate CFs into PEEK using fused deposition modeling (FDM), which is a 3D printing technology. They fabricated pure PEEK as well as carbon fiber‐reinforced PEEK (CFR‐PEEK) and characterized them using mechanical tests [62]. Han et al. found that the printed CFR‐PEEK samples had significantly higher mechanical strength as compared to pure PEEK samples [62]. They also modified the sample surfaces using polishing and sandblasting methods to analyze how surface roughness and topography influenced biocompatibility and cell adhesion [62]. This revealed that PEEK and CFR‐PEEK materials demonstrated good biocompatibility with and without surface modification [62]. However, cell densities were significantly greater on the “as‐printed” sample surfaces of both PEEK and CFR‐PEEK as compared to the surface modified samples [62]. Overall, the FDM‐printed CFR‐PEEK composite has appropriate mechanical strengths and has potential in the dental implant field.
1.3.2 PEEK Bioactivity
Dental implant surface interactions are incredibly important to consider as the surface is what comes into contact with blood in the human body first during implantation [10]. As such, water and protein contact must be considered. Surface protein adsorption is controlled by hydrophobicity, charge, and chemical properties, so surface wettability may play a role in protein adsorption [10]. A favorable surface allows for sufficient protein adsorption and optimally good protein orientation and receptor–ligand accessibility [10]. Furthermore, the surface topography regulates cellular adhesion, migration, proliferation, and differentiation [10].
Caballé‐Serrano et al. were interested in the soft tissue response to dental implant closure caps made of PEEK as compared to Ti [63]. Significantly more multinucleated giant cells (MNGCs) were in contact with PEEK closure caps as compared to Ti closure caps [63]. MNGCs on dental biomaterials may be part of the normal wound healing process; however, MNGCs have been implicated in the development of biological complications that lead to the loss of osseointegration [63]. Thus, it is important to find ways to improve the bioactivity of PEEK without adverse effects in the context of dental implants.
1.3.3 Working at the Nanoscale and With Composites to Enhance PEEK Bioactivity
Studies with PEEK composites have shown promising results in improving bioactivity. Some examples of PEEK composites include PEEK with CNTs, TiO2−, and bioglass [10]. These composites have shown better in vitro compatibility when compared to pure PEEK. As previously discussed, PEEK composites containing HA improve bone formation on implants in canine tibia [53]. Other studies using PEEK‐HA composites with different volume fractions have shown increased presence of fibroblasts at implant surfaces, which stimulates vascularization [10]. However, PEEK‐HA composites may not have as great of a load‐carrying capacity when compared to other PEEK composites [10].
By creating PEEK composites, scientists can introduce new properties to the material. For instance, Wang et al. analyzed the adhesion of Streptococcus mutans on the surface of fluorine‐containing nano‐fluorohydroxyapatite (n‐FHA)‐PEEK composite material [64]. They found that apatite components, especially those that contain fluorine, can reduce the amount of bacterial adhesion on the surface of PEEK and also increase the number of dead bacteria in the biofilm [64]. These properties can reduce the risk of peri‐implantitis and may be a good prospect as a dental implant material [64]. Lu et al. used another method to incorporate antibacterial characteristics into PEEK. They used dual zinc and oxygen plasma immersion ion implantation (Zn/O‐PIII) to modify CF‐reinforced PEEK (CFRPEEK) [65]. CFRPEEK is nontoxic, has good chemical resistance, and possesses excellent mechanical properties but is bioinert [65]. By using the aforementioned method, special micro‐/nano‐pits with Zn incorporation were created on the CFRPEEK surface, which demonstrated antibacterial activity and also increased cell adhesion, proliferation, and osteodifferentiation of mouse osteoblasts [65].
Another interesting PEEK composite incorporates strontium (Sr), which plays a useful role in stimulating bone formation and decreasing bone resorption [66]. Additionally, adiponectin (APN) may have a relationship with bone metabolism [66]. To improve PEEK bioactivity, Wang et al. incorporated Sr into a 3D porous PEEK substrate and then deposited the APN protein membrane [66]. Nanostructures formed on sulfonated PEEK‐SR‐APN surfaces, and APN coatings on the substrate could alter the Sr release rate and also mediate cell–material interactions [66]. Furthermore, Sr/APN coordinate regulation significantly increased cellular proliferation and differentiation [66]. Overall, the incorporation of Sr and APN on nano‐topographic PEEK greatly improved the cellular responses and overall bioactivity on PEEK substrates and may be a promising strategy for dental applications [66].
Binary composites involving PEEK have been studied; however, the simple reinforcements can impair some of PEEK’s mechanical properties such as tensile strength and work‐to‐failure limit and can have adverse effects on surrounding tissues [67]. An approach to solve this problem is using ternary composites, which can compensate for the shortcomings of conventional binary composites and also promote advanced mechanical properties and biocompatibility [67]. Deng et al. used PEEK, n‐HA, and CFs to create a ternary biocomposite through compounding and an injection‐molding process [67]. This process can be visualized in Figure 1.7. HA is used for bone regeneration and to improve bone integration, while CFs have excellent mechanical attributes, are nontoxic, and have a low cost [67]. Deng et al. evaluated the mechanical and biological properties of the PEEK/n‐HA/CF composite in vitro and in vivo and showed that the composite displayed similar mechanical properties (elastic modulus and ultimate tensile strength) to human cortical bone [67]. The composite also promoted cell attachment and proliferation and osteogenic differentiation [67]. Furthermore, in vivo preclinical evaluation showed that the newly formed bone volume of the PEEK/n‐HA/CF biocomposite was higher than that of pure PEEK [67]. A summary of the findings can be visualized in Figure 1.7. By using ternary PEEK composites rather than binary composites, the biological properties of PEEK can be improved without impairing PEEK’s mechanical properties.
Figure 1.7 PEEK/n‐HA/CF biocomposite preparation, biological evaluation, and effects.
(From Ref. [67], 2015, Elsevier).
Altering surface morphology is a method to develop implants with superior properties. Micro‐ and nano‐textured implants are favorable for initial cell fixation and exhibit enhanced osteoblast attachment and differentiation as compared to smooth‐textured implants [68]. Furthermore, nanostructures such as nanopores, NTs, and nanorods can alter cell behavior [68]. Ouyang et al. [68] used argon PIII followed by hydrogen peroxide treatment to create nanostructures on the PEEK surface, which provided a preferable surface for bone regeneration as compared to PEEK treated with only argon PIII. Xu et al. [69] demonstrated the effects of altering the surface topography of PEEK/n‐HA/CF. They used oxygen plasma and sandblasting to generate micro‐/nano‐topographical structures on the surface of the PEEK/n‐HA/CF ternary biocomposite. Results of Xu et al. highlighted that the micro‐/nano‐topographical ternary biocomposite promoted the proliferation and differentiation of MG‐63 cells in vitro and also boosted the osseointegration between the implant and bone in vivo[69]. It is apparent that there are many ways to improve PEEK bioactivity whether that is by altering the biomaterial surface morphology or creating composites or both.
1.3.4 Disadvantages and Advantages of PEEK
The main advantage to using PEEK is that its Young’s elastic modulus is close to that of human bone, and it has tensile properties similar to that of bone, enamel and dentin [60]. A major disadvantage of using PEEK is that it has low osteoconductive properties [60]. For this reason, research has been focused on modifying PEEK to improve its mechanical properties and bioactivity. An approach to combat PEEK’s low osteoconductive properties is to use PEEK in composites, which have been shown to improve bioactivity. However, composites such as PEEK‐HA composites may have a lower load‐carrying capacity compared to other PEEK composites [10]. Furthermore, binary composites using PEEK may impair some of PEEK’s properties such as tensile strength and work‐to‐failure limit [67]. Thus, there is much give‐and‐take when it comes to finding a PEEK composite that is suitable for dental implants. The main challenge when it comes to working with PEEK is finding the right method, modification, or composite makeup that will allow for osteoconduction without sacrificing PEEK’s advantages.
1.4 Peptide Coatings for Dental Implants
The lack of bioactive interactions between the inert dental implant surface and surrounding natural tissues is one of the main reasons for implant failure [70]. Surface functionalization by using biological approaches is a method to combat this issue [70]. Materials such as titanium and zirconia have been functionalized with biomolecules [70]. A method to covalently immobilize biomolecules on inorganic materials is silane‐chemistry which involves using silanes as coupling agents between metal implant materials and biomolecules [70]. Various biomolecules with different levels of complexity that have been tethered to metal surfaces include the RGD sequence, other oligopeptides, proteins, and even multiple peptides with cooperative activities [70].
Fernandez‐Garcia et al. have extended this approach to develop thermochemically and mechanically stable biofunctional coatings on titanium, which as a result, can resist surgical shear stresses during implantation as well as the challenging bioenvironment after implantation [70]. Titanium has been biologically functionalized to either influence physiological paths involved in bone regeneration or prevent bacterial colonization on the implant surface [70]. However, methodologies of biofunctionalization on implant surfaces for other materials such as zirconia have not yet been developed. Using their already‐developed biofunctionalization method for titanium surfaces, Fernandez‐Garcia et al. developed stable and functional biocoatings made up of oligopeptides on zirconia [70]. By incorporating signaling oligopeptides and thus bioactivating zirconia‐containing components for dental implant applications, clinical performance can be improved [70]. The oligopeptides help accelerate osseointegration, improve permucosal sealing, and/or possess antimicrobial properties [70].
Various antimicrobial dental implant coatings have been studied. Chen et al. developed an antimicrobial peptide, GL13K, which contains a modified 13‐amino acid sequence that is derived from the parotid secretory protein (BPIFA2) [71]. GL13K has shown anti‐inflammatory and bactericidal activity and is bactericidal in solution against several species such as Pseudomonas aeruginosa and
