Materials Sciences and Applications, 2010, 1, 118-126
doi:10.4236/msa.2010.13020 Published Online August 2010 (
Copyright © 2010 SciRes. MSA
Development of a Low Temperature Sol-Gel-Derived
Titania-Silica Implant Coating
Virpi Ääritalo1,5, Ville Meretoja1, Teemu Tirri1, Sami Areva2, Timo Jämsä3, Juha Tuukkanen4,
Ari Rosling5, Timo Närhi1
1Department of Prosthetic Dentistry, Institute of Dentistry, University of Turku, Lemminkäisenkatu, Turku, Finland; 2Turku Centre
for Biomaterials, Itäinen Pitkäkatu 4B, Turku, Finland; 3Department of Medical Technology, University of Oulu, Oulu, Finland;
4Department of Anatomy and Cell Biology, University of Oulu, Oulu, Finland; 5Laboratory of Polymer Technology, Åbo Akademi
University, Biskopsgatan, Turku, Finland.
Received May 20th, 2010; revised June 13th, 2010; accepted June 28th, 2010.
Objective of this study was to develope low temperature sol-gel coatings for shape memory metal (NiTi) and evaluate
their biocompatibility on NiTi suture material. A series of low temperature TiO2 and TiO2-SiO2 sol-gel coatings were
prepared on glass substrates. The silica content of TiO2-SiO2 coatings ranged from 0 to 30 mol%. The coatings were
also prepared with polyethyleneglycol (PEG). The contact angle and photocatalytic activity measurements were used to
evaluate the surface properties of the coatings. Stability of the coatings was tested in simulated body fluid (SBF). The
TiO2-SiO2 90/10 film made with PEG was more hydrophilic, showed photocatalytic activity and was crack-free after the
SBF test, thus it was chosen to animal experiment as a new experimental coating. Uncoated NiTi suture and the suture
coated with high temperature TiO2 were used as reference materials. NiTi sutures were inserted subcutaneously on the
back of rat for four weeks. In routine histological examinations all materials showed good biocompatibility with mild
inflammatory cell reaction. No significant differences in the soft tissue response among the materials were observed.
Both the high and new low temperature processed sol-gel coatings remained attached on the sutures confirming the
suitability of the coating technique on thin NiTi sutures.
Keywords: Sol-Gel Technique, Titania-Silica, Thin Film, Bioactive Coating, NiTi, Soft Tissue
1. Introduction
Sol-gel technology is a promising manufacturing method
to produce bioactive materials for biomedical applicati-
ons [1,2]. The growing interest towards sol-gel materials
is based on their ability to form a tight contact with the
surrounding tissues, providing a strong chemical bond
with them [3-5]. The silicon has shown to have several
important roles in material preparation and materials bio-
logical response. The addition of the silicon into the ma-
terials structure has shown positive effect on osteoblast
response on medical implant surfaces, e.g. on hydroxya-
patite [6-8] and sol-gel titania films [9-11]. The TiO2-
SiO2 sol-gel coatings have been shown to be biocompati-
ble in vitro [9] and in vivo [12].
The nickel-titanium shape memory alloys (NiTi, Niti-
nol) are promising materials for surgical implants in rec-
onstructive medicine, because of their unique shape me-
mory effect and super-elasticity [13]. However, some ad-
verse effects such as inferior osteogenesis process, im-
paired osteonectin synthesis and increased cell death rate
have also been reported [14-16]. The biocompatibility of
nikel-titanium alloys may be enhanced by the protective
film e.g. by thickening the natural TiO2 layer at high tem-
peratures [17], by hydroxyapatite coating [18] or by ion
implantation [19]. A sol-gel derived titania-silica coating
has been found to increase the bone to implant contact
and biocompatibility of NiTi intramedullary nails [12].
The sol-gel materials can be processed and applied at
room temperature, but the prepared materials often need
a consolidation and densification step, by which the opt-
imal material structure and surface properties can be tail-
ored [20-22]. The conventional methods to consolidate
the sol-gel titania are heat treatment at above 400˚C and/
or laser densification, but with these techniques the sub-
strate material is limited to ceramics and metals. These
temperatures are far too high for thermally sensitive mat-
erials, such as most polymers, thus there is a striking ne-
ed for bioactive sol-gel coatings prepared at lower tem-
Development of a Low Temperature Sol-Gel-Derived Titania-Silica Implant Coating119
The purpose of this study was to evaluate the possibil-
ity to lower the processing temperature of bioactive sol-
gel derived implant coatings and to explore biologic res-
ponse of the most promising coatings in soft tissue envi-
ronment on NiTi suture materials.
2. Materials and Methods
2.1 Preparation of Coatings
A series of titania and titania-silica coatings were prepa-
red on glass slides by dip-coating method. Before the co-
ating process the glass slides were ultrasonically cleaned
in acetone and in ethanol, five minutes in both solvents.
TiO2-SiO2 sols were prepared by mixing the following
TiO2 and SiO2 sols so that the TiO2-SiO2 molar ratios
100/0, 90/10, 80/20 and 70/30 were obtained. SiO2 sol
was prepared by mixing tetraethyl orthosilicate [TE-OS,
(Si(OC2H5)4], ethanol and water at room temperature
having the EtOH: Si(OR)4 and H2O: Si(OR)4 molar ratios
of 1.9 and 1.0, respectively. The prepared sol was hydr-
olyzed at 40˚C for one hour. TiO2 was prepared by mix-
ing titanium tetraisopropoxide [TIPT, (Ti(OC3H7)4)], eth-
anol, nitric acid (65%), and water at room temperature
and hydrolyzed at 40˚C for 30 min having the EtOH:
Ti(OR)4, H2O: Ti(OR)4 and HNO3: Ti(OR)4 molar ratios
18.0, 1.2 and 0.33, respectively. The prepared sols are
mixed rapidly under stirring. The mixed TiO2-SiO2 sols
were aged at 40˚C for 24 hours and cooled to room temp-
erature before the dipping process. Sols were also prepa-
red with polyethylene glycol PEG (Mw 600 g/mol). PEG
is added into the mixed sol (mPEG = moxides) before aging.
The compositions of the prepared mixed sols are shown
in Table 1. The dipping process was carried out at amb-
ient atmosphere at room temperature. The substrate pl-
ates were dipped into the sol and withdrawn at a speed of
0.3 mm/s. The dip-coated plates were dried at 60˚C for
one hour. The dried coatings were further treated in aut-
oclave, 60 minutes at 121˚C. The TiO2-SiO2 90/10 PEG
containing coatings were also post-treated under UV-lig-
ht (254 nm) for three hours.
Table 1. The compositions of the prepared TiO2-SiO2 sols
Material EtOH/alk H2O/alk HNO3/alk
TiSi 70/30 13.2 1.14 0.23
TiSi 70/30 PEG 13.2 1.14 0.23
TiSi 80/20 14.8 1.16 0.27
TiSi 80/20 PEG 14.8 1.16 0.27
TiSi 90/10 16.4 1.18 0.30
TiSi 90/10 PEG 16.4 1.18 0.30
TiO2 18.0 1.20 0.34
TiO2 PEG 18.0 1.20 0.34
2.2 Surface Characterization
The transmittance through the dip coated glass substrates
was measured using the UV-Vis spectrometer in the wa-
velength range 300-600 nm [Shimadzu UV-1601]. Water
contact angle of the coatings was measured by sessile
drop method at room temperature by using contact angle
meter CAM100 [KSV instruments Ltd., Helsinki, Finland].
The contact angle was established from six parallel
measurements taken from each sample. Photocatalytic
activity of the specimens was given by the degradation of
methylene blue (MB). The coated glass substrates (2.5
cm × 2.5 cm) were immersed into MB aqueous solution
(10-5 M). The substrates were irradiated with UV light
and the changes in concentrations of MB in the aqueous
solution were examined as a function of time from ab-
sorption spectra measured on a UV-Vis spectrophotome-
ter [Shimadzu UV-1601] at a wavelength of 660 nm. The
concentration of methylene blue was measured over a
5-hour period, at intervals of one hour. The reaction rate
constant for photocatalytic degradation of methylene
blue was obtained graphically from the relationship bet-
ween natural logarithm of the normalized absorbance,
ln(A/A0), and reaction time [23]. The kinetic may be ex-
pressed as follow,
where k is the apparent reaction rate constant (1/hours),
A0 and A are the initial absorbance and the reaction abs-
orbance of methylene blue, respectively and t is time.
The initial absorbance value is measured from the meth-
ylene blue solution after one hour immersion in dark. The
rate for the decomposition reaction of the MB aqueous so-
lutions was obtained one time for each coating. An exa-
mple for absorbance curves is shown in Figure 1. The
resulted decomposition rates (1/hours) are given per area
Figure 1. Calculation of the photocatalytic activity (k)
(hour-1cm-2) from methylene blue time-absorbance curves.
Curves are only shown for TiO2-SiO2 90/10 films; original
and PEG containing, though in figure 4 all k-values are
Copyright © 2010 SciRes. MSA
Development of a Low Temperature Sol-Gel-Derived Titania-Silica Implant Coating
(cm2), because the specimens are cut from the glass sli-
des (average size 2.5 cm × 2.5 cm). The stability of the
coatings was tested by immersing the samples (10 × 10
mm2) into 15 ml of simulated body fluid (SBF) [24] at
37˚C for three weeks. Two parallel samples were immer-
sed in closed polyethylene tubes under a shaking water
bath at a constant temperature of 37˚C. After immersion
the samples were removed from the fluid, gently rinsed
with distilled water and dried at 40˚C before the surface
analysis. The surfaces were analysed with optical micros-
3. Animal Experiment
3.1 Implant Materials
The NiTi (Ni 55.5-Ti 44.5 weight %) suture material was
ground by silicon carbide papers having 1200 grits and
the suture was ultrasonically washed 5 min in acetone
and 5 min in ethanol before dipping. Two different sol-
gel coated NiTi sutures were prepared: TiO2 heat treated
at 500˚C and novel low temperature TiO2-SiO2 90/10
prepared with PEG, which exhibited the most suitable
properties for implant coating (see materials characteri-
zation section). The uncoated NiTi suture was used as
reference. The average diameter of NiTi suture is 220 μm.
The conventional TiO2 sol-gel coating was prepared by
sol-gel dip-coating technique as described by Areva and
co-workers [3]. Briefly, titanium tetraisopropoxide [TIPT,
Ti((CH3)2CHO)4] was dissolved into ethanol and mixed
with the solution containing ethyleneglycolmonoethyle-
ther (C2H5OCH2OH), deionized water, fuming hydroch-
loric acid (HCl, 37%) and ethanol. The sol was aged for
24 hours at 0˚C before dipping. The number of coating
layers was five and every layer was heat treated 15 min-
utes at 500˚C. The TiO2-SiO2 90/10 PEG sol was prep-
ared as described in this work. The TiO2-SiO2 film was
used as monolayer. The prepared film was autoclaved 60
minutes at 121˚C and UV-light treated for three hours.
The implant sutures were sterilized with gamma radiation
(minimum, 25 kGy). The morphology of implant surfa-
ces was examined with SEM [JEOL Scanning Electron
Microscope JSM-5500].
3.2 Surgical Procedure
Four adult Sprague-Dawley rats were used for the study.
The experiment was accepted by The Ethical Committee
for Animal Experiments at the Turku University, Finland
(license #1420/04) and national guidelines for the care
and use of laboratory animals were followed. Operations
were performed under general anesthesia induced by sub-
cutaneous injection of fentanyl citrate/fluanisone (Hypn-
orm®, Janssen Pharmaceutica, Beerse, Belgium) and mi-
datzolam (Dormicum®, Roche, Basel, Switzerland). The
operation area was shaved and disinfected with chlorhex-
idine gluconate solution (Klorhexol®, Leiras Ltd, Turku,
The two centimeters long experimental materials were
inserted subcutaneously on the back of each rat via six one
centimeter skin incisions. Skin wound was closed with
individual resorbable sutures (Vicryl 3-0, Johnson & Joh-
nson Intl, Brussels, Belgium). Animals were sacrificed
after four weeks using CO2 suffocation. Implants were
retrieved with 2 to 4 mm soft tissue margin and fixed in
4% buffered formalin at 8˚C for two weeks.
3.3 Histological and Histomorphometrical
Fixed specimens were dehydrated in a graded series of
ethanol and embedded in light curing resin (Technovit
7200, Exakt, Kulzer, Norderstedt, Germany). The specim-
ens were cut and ground down to 20 μm and stained with
haematoxylin and eosin (HE) for light microscope analy-
sis. Sections were histologically evaluated for fibrous tis-
sue capsule formation, inflammatory reaction and foreign
body reaction using light microscope.
Histomorphometrical grading was done according to
the criteria by Jansen and co-workers [25]. Briefly, cap-
sule thickness, tissue morphology and implant to tissue
interface were rated from 0 (the least favorable) to 4 (the
most favourable). The capsule thickness measurement
was based on the observed number of fibroblasts. The qu-
alitative rating of the capsule consisted of rating the tiss-
ue morphology (fibrous tissue, maturity, presence of con-
nective tissue or fat tissue) and cellularity (presence of fi-
broblasts, macrophages, giant cells and other inflamma-
tory cells). Direct contact was evaluated from four cross
sectional sectors of the implants and graded according to
the number of sectors from which immediate implant to
tissue contact was detected. An implant was determined
to be in direct contact if no visible gap could be observed
between the connective tissue and implant surface at
magnification × 200. Statistical analysis was performed
with an SPSS v.11.0 software package (SPSS Inc., IL).
Data were analyzed with one-way ANOVA followed by
Tukey’s post-hoc test. Differences were considered sig-
nificant at 95% confidence level.
4. Results
4.1 Surface Characteristics
TiO2 and TiO2-SiO2 sols with 10, 20 and 30 mol% silica
were successfully prepared and the sols produced clear
crack free coatings on glass substrates (TiSi 70/30, TiSi
80/20, TiSi 90/10 and TiO2). The transmittance curves
for the TiO2-SiO2 90/10 PEG coating after drying and
after autoclaving of dried coating are seen in Figure 2.
The figure shows the general trend seen in all the films
with different compositions and no obvious difference in
transmittance could be observed. All the prepared coat-
ings were hydrophilic, contact angles varying from 60° to
Copyright © 2010 SciRes. MSA
Development of a Low Temperature Sol-Gel-Derived Titania-Silica Implant Coating121
20° (Figure 3). Pure TiO2 coating with PEG and TiO2-
SiO2 90/10 coatings with and without PEG exhibit lowest
water contact angles (Figure 3). The lowest contact an-
gles were measured for pure TiO2 coating prepared with
PEG (~ 25°) and from the coatings containing only 10%
of SiO2. The use of PEG has the strongest influence on
pure TiO2 films, where the contact angle decreased from
55° to 25° by PEG addition.
The photocatalytic activity of TiO2 and TiO2-SiO2 co-
atings is given as the decomposition rate of methylene
blue (Figures 1 and 4). The activity of coatings from ori-
ginal sols without PEG increased with decreasing silica
content, showing the highest photocatalytic activity for
TiO2-SiO2 90/10 coating. The results from the coatings
made with PEG showed all the increased photocatalytic
activities, but the values may be mostly due to the PEG
on the surfaces, rather than the chemistry or morphology
of the material. The UV treatment of PEG containing co-
atings further increased the photocatalytic activity.
Figure 2. UV-Vis transmittance of TiO2 – SiO2 90/10 films
Figure 3. The contact angles of autoclaved films prepared
from original and PEG containing sols
After the SBF test the only crack free surface was ob-
served for TiO2-SiO2 90/10 made with PEG. The optical
microscope pictures from TiO2-SiO2 90/10 coating surfaces
after SBF test are shown in Figure 5. It shows that the
original TiO2-SiO2 90/10 coating was cracked during the
SBF immersion, but the PEG containing was crack free.
The SEM pictures of TiO2-SiO2 90/10 films (Figure 6)
Figure 4. Photocatalytic activity of autoclaved films prepa-
red from original and PEG containing sols and after UV-
treatment of films made with PEG (estimated error 10%)
Figure 5. Optical micrographs of autoclaved films after 3
week immersion in SBF. Original TiO2-SiO2 90/10 film ab-
ove and a film made with PEG below
Copyright © 2010 SciRes. MSA
Development of a Low Temperature Sol-Gel-Derived Titania-Silica Implant Coating
Copyright © 2010 SciRes. MSA
were taken before and after SBF immersion. The films
were consisted of the small granular particles having the
size of 20-50 nanometers. TiO2-SiO2 90/10 coating made
with PEG show smoother structure compared to coating
made without PEG, but after SBF immersion the mor-
phology of coatings was similar.
The TiO2-SiO2 90/10 coating made with PEG was
chosen to the animal experiment. This coating was hydr-
ophilic, showed photocatalytic activity and had the parti-
cle size suitable for biological coatings, thus concluded
to compose the best candidate as implant coating.
4.2 Animal Experiment
All the implanted samples were available for histological
evaluation. In most cases the implants were surrounded
by fibrous connective tissue, but occasionally by adipose
tissue. A connective tissue layer surrounded all the expe-
rimental materials. Also in those cases where an implant
was located in the adipose tissue, a connective tissue lay-
er was observed around the implant (Figure 7). The his-
tological scene was characterized by a mild inflammatory
cell reaction, with no differences among the three mate-
rials. No multinuclear giant cells were noticed in any of
the haematoxyline eosine stained slides. The thickness of
the connective tissue capsule was very thin around the
experimental implants ranging from 2 to 3 cell layers. No
difference among the materials was noticed. Uncoated
NiTi implants scored highest in the qualitative evaluation
of the connective tissue capsule (3.8 ± 0.5 vs 3.3 ± 0.5
for both of the coated implants). TiO2 coated implants ap-
peared to have more areas in direct contact with the con-
nective tissue than uncoated or TiO2-SiO2 coated im-
plants. However, due to high standard deviation this dif-
ference did not reach statistical significance (Figure 8).
Figure 6. SEM pictures of autoclaved TiO2-SiO2 90/10 film without PEG and with it and pictures after SBF immersion. Scale
bar is 200 nm
Figure 7. Histological cross-sections of the implants after 4 weeks. HE stain. (a) Uncoated Niti; (b) coated with TiO2; (c)
coated with TiO2-SiO2 90/10 PEG. The diameter of implant is 220 μm
Development of a Low Temperature Sol-Gel-Derived Titania-Silica Implant Coating123
Figure 8. Fibrous tissue capsule formation (0-4): quality and
thickness of the capsule and direct implant to tissue contact
5. Discussion
In this study a series of low temperature TiO2 and TiO2-
SiO2 sol-gel coatings were first prepared onto microsc-
ope glass slides to optimize the low temperature sol-gel
film for biological applications. The biological response
of sol-gel materials largely depends on their surface pro-
perties: topography, hydrophilicity, electronegativity and
ionic dissolution in body environment. A comparable ev-
aluation between different sol-gel titania and titania-sil-
ica films can be made with contact angle and photocata-
lytic activity measurements; the results of this study ex-
press above mentioned properties all together, thus ena-
bling a ranking according to the surface activity of the
coatings. The contact angle of the surface depends on the
surface porosity and the possible hydroxyl groups on the
surface, while the photocatalytic activity is related to the
chemical state of titania and the surface area of the coat-
ing. TiO2 is a wide bandgap material (Eg 3.2 eV) exhib-
iting photocatalytic activity. The intrinsic photocatalytic
activity of TiO2 is directly related with its crystal proper-
ties and it is widely known that the photo-induced cha-
rges (electrons and holes) are generated in well crystal-
lized phases and preferably in the anatase allotropic form
The sol-gel method allows nanoscale mixing of orga-
nic and inorganic components. The introduction of or-
ganic components into an inorganic sol-gel network usu-
ally improves mechanical properties and leads to an eas-
ier processing of porous thick films [28-30]. A thick sin-
gle pure inorganic crack free sol-gel layer is difficult to
obtain by dip-coating process. The polyethylene glycol
(PEG) can be used to increase the thickness and specific
surface area of the films. Such incorporation of inorganic
elements at the molecular level to organic polymers has
resulted in novel properties such as improved mechanical
strength and thermal stability [31]. The lack of absorp-
tion bands between 300 and 600 nm (Figure 2), indicates
the high transparency of the film in the visible region.
The decreased transmittance after autoclaving is a sign of
condensation and increased thickness of the film. The ad-
dition of PEG into the sol also slows down the hydrolysis
and condensation speed through reducing the free water
in the whole sol-gel system and, e.g. the formed TiO2
will not easily form large agglomerates in the film [32].
The PEG content of the sols was 6.4 g/100 ml. Small
amounts of PEG may be used in sol-gel process without
effect on the roughness and pore structure of sol-gel
films [33]. Thus the role of PEG in this study seems to be
more a processing aid; it does not influence on the parti-
cle formation of oxides (Figure 6).
The addition of PEG into the sol markedly increased
the photocatalytic results of the coatings. Though, the
PEG containing coatings were slightly blue dyed after
the test, thus the colour adsorption may have had an eff-
ect on the results. The test was also performed with the
coatings were preincubated overnight in methylene blue
solution before the photocatalytic test, but the results (not
shown) were similar. However it was evident, that the
activity of TiO2-SiO2 90/10 coating was higher than the
activity of pure TiO2 film, and the activity diminished
with increasing silica content. This indicates that a part
of photocatalytic activity of TiO2-SiO2 90/10 coating is
also chemistry based. In addition, the UV treatment fur-
ther increased the photocatalytic activity of PEG cont-
aining coatings. The trend was same as with the coatings
made from original sols, thus giving additional proof of
real photocatalytic active sites present in the coatings.
The stability test of the coatings was performed in SBF.
The possible dissolution of ions from the surface and the
relaxation of intrinsic tensions in the coatings in liquid en-
vironment may cause crack formation, especially in the
coatings with poor adhesion to the substrate. The TiO2-
SiO2 90/10 coating made with PEG was the only crack
free film after SBF test (Figure 5), which indicates a
better stability and/or adhesion compared to other coat-
ings in this study.
The titania content of TiO2-SiO2 coatings ranged from
100 to 70 mol%. The titania is able to crystallize in ho-
mogeneous, atomically mixed TiO2-SiO2 oxides, but the
amount of TiO2 content is then limited to 20 wt% [34,
35]. At higher Ti contents, TiO2 crystallites tend to form
a separate phase, demonstrating that silica can not favou-
rably accommodate all the Ti atoms in the network above
a certain limit [34 and references therein]. Silicon rel-
easing sol-gel materials can be obtained when Si atoms
are not chemically bonded to the Ti atoms, and there are
separate oxide phases in the structure. It is previously
shown that the TiO2-SiO2 90/10 sol-gel coatings are able
to release silica even though the films are heat-treated at
500˚C [36]. It was concluded that the coatings con- sisted
of isolated TiO2 particles surrounded by an amorphous
SiO2, possibly cross-linked by Ti-O-Si bonds in a con-
tinuous structure. The SEM pictures of TiO2-SiO2 90/10
coatings made in the present study, showed quite smooth
Copyright © 2010 SciRes. MSA
Development of a Low Temperature Sol-Gel-Derived Titania-Silica Implant Coating
granular structures for coatings made with and without
PEG (Figure 6). The slightly smoother structure of the
PEG containing coating may derive from the applied
PEG, because the original granular structure was re-
vealed after a three week immersion in SBF. The coating
structure consisted mainly of those granular particles
having the size from 20 to 50 nm, thus exhibiting the
morphology shown to favour bioactivity of sol-gel mate-
rials (2-50 nm) [37-39].
The crystallinity of the studied materials was not ana-
lysed in this work. X-ray diffraction (XRD) is a prefer-
able method to analyse crystallinity of sol-gel films, but
the sensitivity of the equipment is insufficient for analy-
sing thin coatings with very small crystallites. It is shown
that the incorporation of the silica onto the titania net-
work can effectively inhibit the crystallite growth of tita-
nia or even disrupt the phase transformation from amor-
phous to anatase or rutile form [40-42].
In the present study different sol-gel derived coatings
were fabricated on shape memory alloy sutures. Subcu-
taneous implantation is often used method to examine bi-
ocompatibility of new biomaterials. In terms of biocom-
patibility both the test and control materials performed
equally well in rat subcutaneous environment after a 4
weeks implantation period. The high temperature sol-gel
titania coating studied in this work is previously shown
to bond to the connective tissue [3,43]. In light of this,
the new low temperature TiO2-SiO2 coating is a promi-
sing implant coating material. Longer implantation time
in more demanding conditions would be needed in order
to be able to detect real differences in the biological res-
ponse, e.g. in terms of the unwanted dissolution of nickel,
from these experimental materials.
6. Conclusions
Based on this study it can be concluded that biocompati-
ble sol-gel derived coatings can be applied on memory
metal sutures. The comparable study of different sol-gel
surfaces by contact angle and photocatalytic activity
measurements may be used to evaluate the surface activ-
ity of the sol-gel biomaterials. The novel low temperature
sol-gel TiO2-SiO2 90/10 coating was found to perform
equally well with traditional high temperature TiO2 coat-
ing in rat subcutaneous environment after a four weeks
implantation period.
7. Acknowledgements
This work was supported in part by the National Techn-
ology Agency of Finland (40222/05, 40171/06). V. Ä.
was supported by the Biomaterial and Tissue Engineer-
ing Graduate School in Finland.
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