Biomedical Engineering Reference
In-Depth Information
widely used as dental implant materials due to their good mechanical properties, excellent corrosion
resistance, and biocompatibility. The long-term normal functions of dental implants are related to
their early and rigid osseointegration. Although the spontaneously formed thin TiO
2
passive layer
provides some corrosion resistance and biocompatibility for the Ti implant, it is not able to induce
bone formation effectively. Providing that the natural extracellular matrix (ECM) has a hierarchical
nanostructure
[1]
, the formation of a nanostructured surface on an implant is a good strategy to
achieve enhanced osseointegration. Grit blasting, anodization, acid etching, chemical grafting,
and ion implantation are some common techniques used to modify Ti implants to enhance bone
implant contact (BIC) and improve their clinical performance. Anodization is a newly developed
method to form an oxide nanotube (NT) coating on metals including Ti
[2
5]
. By adjusting the
anodization conditions such as the voltage and time, nanoscale properties can be controlled
[2,3]
.
The nanotubular topography mimics the dimensions of collagen fibril in bones to some extent
[6]
and has elasticity similar to that of bones
[7]
. The NT coatings on Ti have been found to foster the
growth of nanostructured hydroxyapatite in simulated body fluids (SBF)
[8,9]
, enhance ECM secre-
tion, mineralization, and other functionalities of osteoblasts, and even induce the commitment of
mesenchymal stem cells (MSCs) toward bone lineage in the absence of extra osteogenic supple-
ments (OS)
[2,3,10
12]
. Emerging in vivo evidence also suggests the ability of the NT coatings
to enhance osseointegration
[13
16]
.
Implant-associated infection which is another issue impairing the normal function of dental
implants is usually difficult to treat and sometimes requires implant removal and repeated revi-
sion of surgeries
[17]
. Various means such as thorough sterilization and stringent aseptic surgical
protocols have been proposed to mitigate bacterial contamination. However, bacterial invasion
usually occurs after surgery, and complications can arise from infection of nearby tissues or a
hematogenous source at a later time
[18]
. Infections associated with dental implants are character-
ized by bacterial colonization and biofilm formation on the implanted device and infection of the
adjacent tissues (periimplantitis). Bacteria in the biofilm are far more resistant to antibiotics
resulting in persistent infection despite aggressive antibiotic therapy
[19]
. As emerging antibiotic
resistance becomes more challenging, developing novel implants or surface modification methods
with dual functions of excellent bone-bonding ability and long-lasting antibacterial ability
through a procedure ready for industrial production and clinical application is the need for the
hour in implant dentistry.
NTs on dental Ti implants not only provide a nanotopographical surface to induce bone forma-
tion effectively but also serve as a good drug loading and delivering platform for various targeted
agents to attain extra functions. Many kinds of agents including antibacterial agents, bone growth
favoring agents, and anti-inflammatory agents have been incorporated into NTs to enhance the
implants in clinical applications. It is our belief that NTs are more suitable for loading and delivery
of the inorganic agents that are stable and have very low effective doses. Hence, we have loaded
silver
[5]
, strontium
[20]
, zinc and so on into the NTs to achieve long-term functions concerning
antibacterial ability and osteogenesis induction.
In this chapter, we summarize the latest progress on TiO
2
NT coatings and review the factors
influencing the NT bioactivity, the effects of the NTs on bone cell functionalities in vitro, osseoin-
tegration in vivo, and drug loading and delivery. This chapter will not describe in detail the prepa-
ration and mechanism of TiO
2
NT by anodization because there are already some reviews in the
literature regarding the fabrication of anodized NT arrays on Ti implants.
