Elsevier

Acta Biomaterialia

Volume 121, February 2021, Pages 103-118
Acta Biomaterialia

Review article
Atomic layer deposition on dental materials: Processing conditions and surface functionalization to improve physical, chemical, and clinical properties - A review

https://doi.org/10.1016/j.actbio.2020.11.024Get rights and content

Abstract

Surface functionalization is an effective approach to improve and enhance the properties of dental materials. A review of atomic layer deposition (ALD) in the field of dental materials is presented. ALD is a well-established thin film deposition technique. It is being used for surface functionalization in different technologies and biological related applications. With film thickness control down to Ångström length scale and uniform conformal thin films even on complex 3D substrates, high quality thin films and their reproducibility are noteworthy advantages of ALD over other thin film deposition methods. Low temperature ALD allows temperature sensitive substrates to be functionalized with high quality ultra-thin films too. In the current work, ALD is elaborated as a promising method for surface modification of dental materials. Different aspects of conventional dental materials that can be enhanced using ALD are discussed. Also, the influence of different ALD thin films and their microstructure on the surface properties, corrosion-resistance, antibacterial activity, biofilm formation, and osteoblast compatibility are addressed. Depending on the stage of advancement for the studied materials reported in the literature, these studies are then categorized into four stages: fabrication & characterization, in vitro studies, in vivo studies, and human tests. Materials coated with ALD thin films with potential dental applications are also presented here and they are categorized as stage 1. The purpose of this review is to organize and present the up to date ALD research on dental materials. The current study can serve as a guide for future work on using ALD for surface functionalization and resulting property tuning of materials in real world dental applications.

Introduction

There are different ways to categorize dental materials, the main three ways being: (1) based on the nature of the dental material; (2) based on their interaction with the body, i.e., either they are bioinert when they are implanted in the body or they are bioactive; and (3) based on the shape and form of the dental materials [1]. There are reports in the literature on the failure of conventional dental materials earlier than expected which increase the risk of second surgeries, and significantly higher costs for the patients. Also, simple dental materials cannot meet all clinical expectations. Studies in dental materials are actively proceeding in different aspects such as design, material and technique so that we come up with more suitable effective materials [2,3]. Therefore, there are several studies either on fabricating new materials or enhancing the properties of available dental materials. Property enhancement of current materials can be performed with known modification methods such as microstructural modification, conventional functionalization methods, e.g., adding nanoscopic fillers to dental material compounds [4], [5], [6] or performing novel functionalization techniques, e.g., surface functionalization [7], [8], [9].

Surface functionalization is indeed an increasingly promising approach for property enhancement of dental materials [10]. Due to the importance of the interface region in biological environments, surface modification has several advantages over bulk functionalization. The interface of the biomaterial and the biological environment has a major role in the effectiveness of the biomaterial. Therefore, instead of mixing nanomaterial with the matrix that eventually yields to random distribution of nanomaterial at the interface of the biomaterial and its biological environment, focusing on the surface modification can result in an efficient distribution of the functionalizing agents at that interface. There are several chemical nanofabrication techniques (alone or combination of them) used for dental material fabrication and modification: (i) anodic oxidation (anodization), (ii) acid treatment, (iii) alkali treatment, (iv) chemical etching with hydrogen peroxide, (v) sol-gel treatment, (vi) chemical vapor deposition (CVD), and (vii) atomic layer deposition (ALD) [11], [12], [13], [14], [15], [16], [17].

ALD has several advantages over other thin film deposition methods [18,19]. CVD and ALD are both vapor phase thin film deposition techniques. In CVD both precursors are introduced into the reactor at the same time while in ALD precursors are sequentially introduced to the reactor each followed by an inert gas purge. This sequential process is a key difference between CVD and ALD, which consequently makes ALD a self-limiting reaction without gas phase reactions and gives unique characteristics to this method [20]. A detailed comparison of ALD and other thin film deposition methods is discussed in Ovirah et. al [21]. Outstanding advantages of ALD thin films over those from other techniques include high quality, high density, excellent reproducibility of the results, and control over the thickness down to sub-nm length scale.

The motivation of the current work originated in part from the shape and microstructure complexity of dental materials. Most of the modern dental materials are porous and/or have complex physical shapes. Also, at a smaller scale, these materials show 3D surface microstructure, which makes it hard to get them conformally coated and functionalized with other techniques. Other dental materials are resorbable in solutions, which makes it impossible to functionalize them via methods which include solvents (acid treatment, sol-gel treatment, chemical etching with hydrogen peroxide, or anodic oxidation). ALD is a unique and powerful approach for surface functionalization of substrates which results in uniform and conformal thin films, especially for surfaces with high aspect ratios, porous surfaces, and complex microstructures [17]. Further, processing conditions of ALD are tunable for the functionalization of materials with low degradation temperature.

ALD consists of sequential cycles. Each cycle typically consists of four consecutive steps with designated time durations, under vacuum, i) precursor pulse, ii) precursor purge, iii) oxidizer (or co-reactant) pulse, iv) oxidizer (or co-reactant) purge:

  • (i)

    precursor pulse into the reactor to react/interact with the substrate surface,

  • (ii)

    unreacted precursor molecules purge out of the reactor with only one monolayer of precursor covering the substrate surface,

  • (iii)

    oxidizer (or co-reactant) pulse into the reactor to react with the monolayer of the precursor,

  • (iv)

    oxidizer (or co-reactant) purge to remove the unreacted co-reactant and byproducts

Once the oxidizer (or co-reactant) is pulsed into the reactor, reaction between chemisorbed precursor molecules and pulsed oxidizer molecules takes place. One cycle of a typical ALD is illustrated in Fig. 1.

On the other hand, limitations of ALD are the slow deposition rate, sometimes expensive precursors, and the ALD of many metals and metal compounds have not yet been studied and developed well. Yet, the slow ALD rate has been increasingly addressed effectively with Spatial ALD (SALD) systems in which precursors are continuously supplied in different locations and kept apart by an inert gas region or zone [22], [23], [24]. Film growth is achieved by exposing the substrate to the locations containing the different precursors. Because the purge step is eliminated, the process becomes faster, being indeed compatible with fast-throughput techniques such as roll-to-roll, and much more versatile, easier and cheap to scale up [25]. Due to its higher throughput and growth rate, SALD is of interest for fast commercialized production. ALD on dental materials is still at the lab-scale research level but hopefully moving forwards from laboratory environment to commercialized production.

Precursors play a key role in the ALD reaction. Precursors must be volatile, chemisorb on the surface, and be thermally stable [26]. Precursors are mostly commercially available. An inert gas like nitrogen (N2) or Argon (Ar) can be used as carrier and purging gas [17].

By adjusting the number of cycles, one can tune the final thickness of the thin film. Each cycle of ALD includes chemisorption and self-limiting reaction, which means the entire surface gets exposed to the flow of the pulsed materials and therefore at the end of each cycle (depending on the growth rate), the entire surface can be covered with the targeted thin film. That is why ALD results in uniform, pinhole free, and conformal thin films, which are important advantages of this technique over other vapor phase thin film deposition methods. The final thin film is in the nanometer length scale and allows control over the thickness down to a few Ångstrӧm. The invention and introduction of the first ALD dated back to 1960 [27]. It was first used in the microelectronic and semiconductor industry. For each ALD process there is a temperature window, where the growth rate is constant and saturated [19]. For the fabrication of semiconductor devices via thermal ALD, this temperature window is wide and not suitable for heat sensitive polymeric and biological materials.

However after the discovery of processes and precursors for thin film deposition below 100°C, ALD has been increasingly used in the field of biomedical-advanced materials [28], [29], [30]. Biosensors, biomedical implants, and biomaterials are some of the examples that make use of ALD in the biomedical industry [28,31]. The present work provides a detailed overview of dental materials, which have been functionalized with ALD so far.

Section snippets

Methodology

For this literature review, an electronic search was conducted for papers in the databases Google Scholar, Pubmed, Scopus, Web of Science and SciFinder, using the keywords: atomic layer deposition, dental material, and dentistry. The notable published researches in the area of ALD on dental materials were reviewed first. Next, the search was expanded to their relevant references and citations. Among those references and citations, in the case of any relevant work, again its references and

ALD of metal oxides on metal and metal alloys dental materials

One of the challenges handling restorative dental materials is the unpredictable adherence of those materials to the instruments used in clinical work upon pull out from the cavity. Therefore, development of non-stick dental restorative instruments can be an answer to this challenge. Doped diamond like carbon coating (DLC) and Polytetrafluoroethylene (PTFE) coatings are two of the conventional methods to solve such unpredictable adherence problems. Leppaniemi et al. compared these two

Summary, perspectives, and future works

The translation of newly developed dental material can be categorized as the following four stages [101]:

  • Stage 1: fabrication of the material, microstructure characterizations, physical and mechanical properties.

  • Stage 2: In vitro tests for different cell types, cytotoxicity, genotoxicity.

  • Stage 3: In vivo implantation to study tissue viability, histology, and inflammatory effects.

  • Stage 4: Human trials for clinical feasibility and efficiency.

The ALD-fabricated materials, which were designed for

Conclusion

The current work covers how the promising ALD method can be used in the functionalization of dental material surfaces including metal and ceramic implants, dentures, maxillofacial prostheses, and orthodontic materials. The majority of works were done on TiO2 ALD; however, studies on the ALD of Ag, ZnO, ZrO2, Al2O3, and CaCO3 have also been reported. For removable dental materials, like dentures, challenges are easier: physical and mechanical tests have shown improvement in corrosion resistance,

Declaration of Competing Interest

None.

Acknowledgment

Partial support by the National Science Foundation, NSF 1309114, is gratefully acknowledged. Also, the authors would like to express gratitude for support from the Coordination for the Improvement of Higher Education Personnel (CAPES) in the PrINTProgram (#88887.373422/2019-00), through a scholarship to the author Faverani, L.P. Dove Medical Press is highly acknowledged as the original publisher of Fig. 4 of this manuscript and authors would like to thank them for giving permission to use Fig. 4

References (101)

  • M. Putkonen et al.

    Atomic layer deposition and characterization of biocompatible hydroxyapatite thin films

    Thin Solid Films

    (2009)
  • R.A. Gittens et al.

    The roles of titanium surface micro/nanotopography and wettability on the differential response of human osteoblast lineage cells

    Acta Biomaterialia

    (2013)
  • R. Olivares-Navarrete et al.

    Direct and indirect effects of microstructured titanium substrates on the induction of mesenchymal stem cell differentiation towards the osteoblast lineage

    Biomaterials

    (2010)
  • M. Padial-Molina et al.

    Role of wettability and nanoroughness on interactions between osteoblast and modified silicon surfaces

    Acta Biomaterialia

    (2011)
  • M. Basiaga et al.

    Evaluation of physicochemical properties of surface modified Ti6Al4V and Ti6Al7Nb alloys used for orthopedic implants

    Mater. Sci. Eng.

    (2016)
  • S. Patel et al.

    Novel functionalization of Ti-V alloy and Ti-II using atomic layer deposition for improved surface wettability

    Colloids. Surf. B

    (2014)
  • H. Kang et al.

    Photocatalytic effect of thermal atomic layer deposition of TiO2 on stainless steel

    Appl. Catal. B

    (2011)
  • H.N. Pantaroto et al.

    Antibacterial photocatalytic activity of different crystalline TiO2 phases in oral multispecies biofilm

    Dent. Mater.

    (2018)
  • E. Marin et al.

    Multilayer Al2O3/TiO2 atomic layer deposition coatings for the corrosion protection of stainless steel

    Thin Solid Films

    (2012)
  • P.A. Radi et al.

    Tribocorrosion behavior of TiO2/Al2O3 nanolaminate, Al2O3, and TiO2 thin films produced by atomic layer deposition

    Surf. Coat. Technol.

    (2018)
  • C.-X. Shan et al.

    Corrosion resistance of TiO2 films grown on stainless steel by atomic layer deposition

    Surf. Coat. Technol.

    (2008)
  • Q. Yang et al.

    Atomic layer deposited ZrO2 nanofilm on Mg-Sr alloy for enhanced corrosion resistance and biocompatibility

    Acta Biomaterialia

    (2017)
  • Y. Zhu et al.

    Biofunctionalization of carbon nanotubes/chitosan hybrids on Ti implants by atom layer deposited ZnO nanostructures

    Appl. Surf. Sci.

    (2017)
  • M. Kemell et al.

    Surface modification of thermoplastics by atomic layer deposition of Al2O3 and TiO2 thin films

    Eur. Polym. J.

    (2008)
  • M. Vähä-Nissi et al.

    Antibacterial and barrier properties of oriented polymer films with ZnO thin films applied with atomic layer deposition at low temperatures

    Thin Solid Films

    (2014)
  • K.-H. Park et al.

    Antibacterial activity of the thin ZnO film formed by atomic layer deposition under UV-A light

    Chem. Eng. J.

    (2017)
  • K. Zhang et al.

    Sr/ZnO doped titania nanotube array: an effective surface system with excellent osteoinductivity and self-antibacterial activity

    Mater. Des.

    (2017)
  • R.S. Pessoa et al.

    TiO2 coatings via atomic layer deposition on polyurethane and polydimethylsiloxane substrates: Properties and effects on C. albicans growth and inactivation process

    Appl. Surf. Sci.

    (2017)
  • A.K. Bishal et al.

    Color stability of maxillofacial prosthetic silicone functionalized with oxide nanocoating

    J. Prosthetic Dentistry

    (2019)
  • K. Rezwan et al.

    Biodegradable and bioactive porous polymer/inorganic composite scaffolds for bone tissue engineering

    Biomaterials

    (2006)
  • R.S. Pessoa et al.

    Biomedical applications of ultrathin atomic layer deposited metal oxide films on polymeric materials

    Front. Nanosci.

    (2019)
  • L. Yao et al.

    Atomic layer deposition of zinc oxide on microrough zirconia to enhance osteogenesis and antibiosis

    Ceram. Int.

    (2019)
  • B. Müller et al.

    Atomic layer deposited TiO2 protects porous ceramic foams from grain boundary corrosion

    Corros. Sci.

    (2016)
  • R. Rasouli et al.

    A review of nanostructured surfaces and materials for dental implants: surface coating, patterning and functionalization for improved performance

    Biomater. Sci.

    (2018)
  • L. Gaviria et al.

    Current trends in dental implants

    J. Korean Assoc. Oral Maxillofac. Surg.

    (2014)
  • U. Kadiyala et al.

    Unexpected insights into antibacterial activity of zinc oxide nanoparticles against methicillin resistant Staphylococcus aureus (MRSA)

    Nanoscale

    (2018)
  • M.I. Din et al.

    Green adeptness in the synthesis and stabilization of copper nanoparticles: catalytic, antibacterial, cytotoxicity, and antioxidant activities

    Nanoscale Res. Lett.

    (2017)
  • C.T. Rodrigues et al.

    Antibacterial properties of silver nanoparticles as a root canal irrigant against Enterococcus faecalis biofilm and infected dentinal tubules

    Int. Endod. J.

    (2018)
  • C. Yao et al.

    Enhanced osteoblast functions on anodized titanium with nanotube-like structures

    J. Biomed. Mater. Res. Part A

    (2008)
  • R. Bosco et al.

    Surface engineering for bone implants: a trend from passive to active surfaces

    Coatings

    (2012)
  • P. Roy et al.

    TiO nanotubes: synthesis and applications

    Angewandte Chemie Int. Ed.

    (2011)
  • B.-H. Lee et al.

    In vivo behavior and mechanical stability of surface-modified titanium implants by plasma spray coating and chemical treatments

    J. Biomed. Mater. Res. Part A

    (2004)
  • M. Baryshnikova et al.

    Formation of hydroxylapatite on CVD deposited titania layers

    Physica Status Solidi C

    (2015)
  • A.Y. Arbenin et al.

    Characteristics of the synthesis of TiO2 films on a titanium surface by the sol-gel technique

    Russian J. Gen. Chem.

    (2014)
  • X. Chen et al.

    Titanium dioxide nanomaterials:  synthesis, properties, modifications, and applications

    Chem. Rev.

    (2007)
  • S.M. George

    Atomic layer deposition: an overview

    Chem. Rev.

    (2010)
  • G.L. Doll et al.

    Chemical vapor deposition and atomic layer deposition of coatings for mechanical applications

    J. Therm. Spray Technol.

    (2010)
  • M. Fraga et al.

    Progresses in synthesis and application of SiC films: from CVD to ALD and from MEMS to NEMS

    Micromachines

    (2020)
  • P.O. Oviroh et al.

    New development of atomic layer deposition: processes, methods and applications

    Sci. Technol. Adv. Mater.

    (2019)
  • P. Poodt et al.

    Spatial atomic layer deposition: a route towards further industrialization of atomic layer deposition

    J. Vacuum Sci. Technol. A

    (2011)
  • Cited by (24)

    • Atomic layer deposition: An efficient tool for corrosion protection

      2023, Current Opinion in Colloid and Interface Science
      Citation Excerpt :

      At present, it is applied in microelectronics for the fabrication of DRAM, MIM capacitors and high-K metal gates transistors or used during the device production processes to grow spacers, masking layers or interconnects [5, 6]. It is implemented as well in OLEDs encapsulation [7, 8] and it is envisioned in many other fields: energy storage and production (photovoltaics, batteries, fuel cells, thermoelectric, catalysis) [9, 10, 11, 12], sensors [13, 14], filtration membranes [15, 16], biomaterials [17] and corrosion protection [18]. Surprisingly, the matter does not appear among the topmost investigated fields.

    • Corrosion in Mg-alloy biomedical implants- the strategies to reduce the impact of the corrosion inflammatory reaction and microbial activity

      2022, Journal of Magnesium and Alloys
      Citation Excerpt :

      Such films typically have a uniform microstructure free from any secondary phase. ALD is already an established technique for manufacturing antibacterial dental implant materials [269]. Controlling bacterial invasion at the implant site can lower the inflammation in the host body.

    • Fabrication of patterned polymer brushes using programmable modulated light-excited controllable radical polymerization

      2022, European Polymer Journal
      Citation Excerpt :

      Surface functionalization of material is of great importance for the development of functional materials and advanced technologies [1,2]. Various approaches have been presented to engineer surfaces with a variety of surface properties, topography and functional groups [3–7]. In particular, polymer brushes could be exploited as an effective mean to impart the desired surface performance [8–10], including tunable wettability, biocompatibility and stimulus response, which have triggered immense research interest in various important fields ranging from anti-biofouling coating [11,12], energy device [13] to biomimetic and smart surfaces [14,15].

    • Dental Implants: Enhancing Biological Response Through Surface Modifications

      2022, Dental Clinics of North America
      Citation Excerpt :

      However, the modifications also altered cellular behavior in vitro and bone physiology in vivo.4,32,33 Osseointegration is considered a type of bone healing with an inflammatory response,22,34 and a dental implant surface has been modified in its nano-topography, surface chemistry, and surface energy to enhance the healing.2,27,29,35–37 A dental implant system inserted into a patient’s mouth comprises five interfaces associated with a biological response.

    View all citing articles on Scopus
    View full text