Biomedical Engineering Reference
In-Depth Information
is used is the leeching of aluminum (Al) and vanadium (V) ions from the alloy. Thus other Ti alloys
including Ti-6Al-7Nb are under investigation to search for materials with better corrosion properties
[21,26,27] . Table 8.1 shows the mechanical properties and applications of different Ti alloys that are
currently used.
Several modification methods have been developed to create distinct nanotopographic features
because recent studies have shown that nanotopography may affect cell adhesion, growth, and dif-
ferentiation. In addition, different surface structures and chemical functional groups can be added to
the Ti surface so that they can be used to covalently bind to cell growth-promoting factors and bone-
related factors such as fibroblast growth factors, bone morphogenic protein-2 (BMP-2), and Isterix
[5,34] . A few examples of surface modification methods include modification of Ti implants with
inorganic materials such as hydroxyapatite (HA), chromium (Cr), cobalt (Co), and vanadium (V), and
use of nanoparticles or incorporation of Ti powders with polymers such as poly(L-lactic acid) (PLLA)
or poly(L-lactic-co-glycolic) acid (PLGA) to produce distinct indentations and nanoscale features.
The modification techniques commonly used to create nanotopography on Ti implants will be briefly
discussed in the next section.
8.2.1 Surface Modification of Ti Implants with Inorganic Materials/Nanoparticles
Modification of Ti implants in the nanoscale dimension affects the topography and chemistry of the
surface. It is important to note that the surface of an implant possesses three main properties which
are mechanical, topographic, and physicochemical properties, and that changing any of these proper-
ties will have an effect on the other two properties [5] . Although various methods have been devel-
oped to impart nanoscale modification to implant materials as shown in Table 8.2 , there are only a
few methods often used for surface modification due to their ease of use and reproducibility. Physical
approaches for surface modification include compaction of nanoparticles and ion beam deposition. Of
these methods, the compaction of nanoparticles and microparticles of titanium dioxide (TiO 2 ) is often
used, and this modification yields implant surfaces with nanoscale and microscale features [24] . Since
this method physically deposits the micro- and/or nanofeatures onto the implant surface, it has little
impact on the bulk chemical properties of the material [41] .
In addition to physical approaches, chemical methods including treatment of implants with active
chemicals such as acids have also been developed to impart nanotopography onto the implant sur-
faces. Common chemicals used to produce nanostructures on titanium implant surfaces are sodium
hydroxide (NaOH) and hydrogen peroxide (H 2 O 2 ) [42] . NaOH treatment of Ti implants produces a
sodium-titanate gel layer on the surface, whereas H 2 O 2 treatment creates a titania gel layer. These
gel layers can then be used to deposit osteoblast-promoting materials such as HA. Titanium implants
chemically treated with acids and NaOH have been shown to accelerate HA crystal growth in simu-
lated body fluid [27] . Other chemical treatments such as peroxidation or acid oxidation (hydrofluoric
acid) have also been used to create nanotopography [43] . It has been shown that treatment of titanium
implant surfaces with H 2 O 2 /HCl increased adsorption of RGD peptides onto the surface due to cre-
ation of an amorphous nanoscale feature on the implant surface [35] . In general, chemical approaches
to generate nanotopography are popularly used in dental implants which might be due to their ease of
use [41] .
One novel approach to creating nanofeatures on Ti implants is the deposition of nanoparticles
onto the surface [36] . Nanoscale deposition of calcium phosphate has been achieved by the sol-gel
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