Electrophoretic Deposition of Chitosan/45S5 Bioactive Glass Composite Coatings Doped with Zn and Sr

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T10321 Electrophoretic Deposition in Materials Science

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In this research work the original 45S5 bioactive glass (BG) was modified by introducing zinc and/or strontium oxide (6% mol) in place of calcium oxide. Sr was added for its ability to stimulate bone formation, Zn for its role in bone metabolism, antibacterial properties and anti-inflammatory effect. The glasses were produced by means of melting and quenching process. SEM and XRD analyses evidenced that Zr and Sr introduction did not modify the glass structure and morphology, while compositional analysis (EDS) demonstrated the effective addition of these elements inside the glass network. Bioactivity test in simulated body fluid (SBF) up to one month evidenced a reduced bioactivity kinetics for Zn-doped glasses. Doped glasses were combined with chitosan to produce organic/inorganic composite coatings on stainless steel AISI 316L by electrophoretic deposition (EPD). Two EPD processes were considered for coating development, namely direct current EPD (DC-EPD) and alternating current EPD (AC-EPD). The stability of the suspension was analysed and the deposition parameters were optimized. Tape and bending tests demonstrated a good coating-substrate adhesion for coatings containing 45S5-Sr and 45S5-ZnSr glasses, while the adhesion to the substrate decreased by using 45S5-Zn glass. FTIR analyses demonstrated the composite nature of coatings and SEM observations indicated that glass particles were well integrated in the polymeric matrix, the coatings were fairly homogeneous and free of cracks; moreover the AC-EPD technique provided better results than DC-EPD in terms of coating quality. SEM, XRD analyses and Raman spectroscopy, performed after bioactivity test in SBF solution, confirmed the bioactive behaviour of 45S5-Sr containing coating, while coatings containing Zn exhibited no hydroxyapatite formation.

본문

_Edited by:_
_Hae-Won Kim,_
_Institute of Tissue Regeneration_

_Engineering, South Korea_

_Reviewed by:_
_Ashutosh Goel,_
_Rutgers, The State University of_

_New Jersey, USA_

_Kapil Dev Patel,_
_Dankook University, South Korea_

_*Correspondence:_
_Enrica Verné_
_[enrica.verne@polito.it](mailto:enrica.verne@polito.it)_

_†Present address:_

_Marta Miola,_
_Department of Health Sciences,_
_Università degli Studi del Piemonte_

_Orientale “Amedeo Avogadro”,_

_Novara, Italy_

_Specialty section:_
_This article was submitted to_
_Biomaterials, a section of the journal_

_Frontiers in Bioengineering and_

_Biotechnology_

_Received:_ _11 August 2015_
_Accepted:_ _28 September 2015_

_Published:_ _19 October 2015_

_Citation:_
_Miola M, Verné E, Ciraldo FE,_
_Cordero-Arias L and Boccaccini AR_
_(2015) Electrophoretic deposition of_

_chitosan/45S5 bioactive glass_

_composite coatings_
_doped with Zn and Sr._
_Front. Bioeng. Biotechnol. 3:159._

_[doi: 10.3389/fbioe.2015.00159](http://dx.doi.org/10.3389/fbioe.2015.00159)_

[Original Research](http://www.frontiersin.org/Bioengineering_and_Biotechnology/editorialboard)
[published: 19 October 2015](http://www.frontiersin.org/Bioengineering_and_Biotechnology/editorialboard)
[doi: 10.3389/fbioe.2015.00159](http://dx.doi.org/10.3389/fbioe.2015.00159)

# E

_[Marta Miola](http://loop.frontiersin.org/people/251148/overview)_ _1†_ _[, Enrica Verné](http://loop.frontiersin.org/people/194504/overview)_ _1_ _[*, Francesca Elisa Ciraldo](http://loop.frontiersin.org/people/281342/overview)_ _1_ _[, Luis Cordero-Arias](http://loop.frontiersin.org/people/281389/overview)_ _2_ _[and](http://loop.frontiersin.org/people/161719/overview)_
_[Aldo R. Boccaccini](http://loop.frontiersin.org/people/161719/overview)_ _2_

_1 Department of Applied Science and Technology, Politecnico di Torino, Turin, Italy, 2 Department of Materials Science and_
_Engineering, Institute of Biomaterials, University of Erlangen-Nuremberg, Erlangen, Germany_

In this research work, the original 45S5 bioactive glass was modified by introducing zinc
and/or strontium oxide (6 mol%) in place of calcium oxide. Sr was added for its ability to
stimulate bone formation and Zn for its role in bone metabolism, antibacterial properties,
and anti-inflammatory effect. The glasses were produced by means of melting and
quenching process. SEM and XRD analyses evidenced that Zr and Sr introduction did not
modify the glass structure and morphology while compositional analysis (EDS) demonstrated the effective incorporation of these elements in the glass network. Bioactivity test
in simulated body fluid (SBF) up to 1 month evidenced a reduced bioactivity kinetics for
Zn-doped glasses. Doped glasses were combined with chitosan to produce organic/
inorganic composite coatings on stainless steel AISI 316L by electrophoretic deposition
(EPD). Two EPD processes were considered for coating development, namely direct current EPD (DC-EPD) and alternating current EPD (AC-EPD). The stability of the suspension
was analyzed and the deposition parameters were optimized. Tape and bending tests
demonstrated a good coating-substrate adhesion for coatings containing 45S5-Sr and
45S5-ZnSr glasses, whereas the adhesion to the substrate decreased by using 45S5-Zn
glass. FTIR analyses demonstrated the composite nature of coatings and SEM observations indicated that glass particles were well integrated in the polymeric matrix, the
coatings were fairly homogeneous and free of cracks; moreover, the AC-EPD technique
provided better results than DC-EPD in terms of coating quality. SEM, XRD analyses,
and Raman spectroscopy, performed after bioactivity test in SBF solution, confirmed the
bioactive behavior of 45S5-Sr-containing coating while coatings containing Zn exhibited
no hydroxyapatite formation.

Keywords: electrophoretic deposition, bioactive glasses, composite coatings, therapeutic ions, chitosan

INTRODUCTION

Metallic alloys (such as Ti alloys, stainless steel, or Co–Cr alloys)
are the materials of choice for bone implants where good mechanical properties and load-carrying ability are required (Niinomi,
2002; Chen and Thouas, 2015). These materials generally are
osteointegrated by morphological fixation, i.e., by bone ingrowth
on their surface irregularities by press fitting into a bone defect
or by cementing the implant with acrylic bone cement. Metallic
alloys generally lack osteoinductive properties and, if the bone
ingrowth is not effective, they could develop a fast formation of a
non-adherent fibrous capsule at the interface which, in turn, can
cause bone interfacial loosening and the failure of the implant. A
better behavior can be achieved if a bioactive fixation is induced,
i.e., a direct chemical bonding with the bone (Drnovšek et al.,
2012). For this purpose, the modification of the implant surface
with a bioactive coating (i.e., a coating with the ability of forming
a biologically active hydroxyapatite layer on its surface) can lead
to a significant improvement of its osteointegration. Bioactive
glasses (BGs) and glass-ceramics can be successfully used with
this purpose (Rahaman et al., 2012; Jones, 2013; Hench, 2015)
due to their peculiar ability of inducing bone ingrowth. BGs have
been studied and developed during the last 40 years for a vast
number of medical applications, including powders, granules,
3D scaffolds, additive for injectable or putty-like bone substitutes, second phases in bone cements, as well as dense coatings
on metallic and ceramic substrates (Gerhardt and Boccaccini,
2010; Jones, 2013). Moreover, BG compositions can be easily
modified by introducing several elements with therapeutic effect
(Mouriño et al., 2012); for example, Ag, Cu, and Ga have been
added for their antimicrobial effect, Cu was used for its ability to
stimulate angiogenesis and bone (Miola et al., 2014), and Mn for
its role in the metabolism of muscle and bone (Rath et al., 2014).
Among the investigated elements, also Zn and Sr have drawn the
attention of the researchers for their role in bone metabolism and
the Zn antibacterial effect (Balamurugan et al., 2007; Gentleman
et al., 2010; Jaiswala et al., 2012; Balasubramanian et al., 2015).

Bioactive ceramic coatings can be applied on the bioinert
implant surface by means of several methods, such as glazing, enameling, plasma praying, electrophoretic deposition
(EPD), RF-magnetron sputtering, and pulsed laser deposition
(Verné, 2012).

Electrophoretic deposition (Besra and Liu, 2007) has been
gaining interest in different sectors for its versatility and its
cost-effectiveness and EPD of biomaterials is being increasingly
investigated (Boccaccini et al., 2010). In particular, the advantages
of EPD are its applicability to a wide range of materials (ceramics,
polymers, metals, and composites), the use of simple equipment,
and the possibility to deposit homogenous thin or thick coatings
on substrates with different shapes and dimensions in a matter of
minutes. Moreover, EPD can be carried out using aqueous and
non-aqueous solvents (Besra and Liu, 2007). Even if water-based
EPD implies some problems due to the electrolysis phenomenon,
it has been shown that using relatively high voltages and alternating current EPD (AC-EPD), it is possible to obtain high-quality
coatings and films (Neirinck et al., 2009; Chávez-Valdez and
Boccaccini, 2012).

Since the deposition of pure ceramics can lead to the formation of a brittle coating, they often are codeposited with polymers,
especially natural polymers (Cordero-Arias et al., 2014). Among
biopolymers, chitosan, a linear, semicrystalline polysaccharide,
shows outstanding properties: biocompatibility, the ability to
complexes various species such as metal ions, pH-dependant
solubility, low cost, and antibacterial activity. Moreover, chitosan
is a suitable film-forming polymer that does not require further
heat treatment (Croisier and Jérôme, 2013). For these reasons,
chitosan is often used in EPD process to realize coatings suitable
for orthopedic applications and bone tissue engineering (Pishbin
et al., 2011; Cordero-Arias et al., 2013).

In this article, 45S5-base BGs doped with Zn and Sr were
combined with chitosan to produce organic/inorganic composite
coatings on stainless steel AISI 316L by direct current (DC)-EPD
and AC-EPD. The effects of the added ions on the glass and
coatings bioactivity combined with the influence of the two EPD
methods on coating properties were investigated.

MATERIALS AND METHODS

Glasses Synthesis and Characterization
Zinc oxide (6 mol%), strontium oxide (6 mol%), and both Zn and
Sr oxide (ZnO, 3 mol%; SrO, 3 mol%) were added to the original
45S5 BG composition (Hench, 2006) by replacing calcium oxide;
the doped glasses were named 45S5-Zn, 45S5-Sr, and 45S5-ZnSr
and their compositions are presented in Table 1 .

All the glasses were produced by means of melting and
quenching process: the reactants were accurately mixed and subsequently put in a Pt crucible maintained at 1500°C for 30 min.
The melt was then poured in water obtaining a frit, which was
dried at room temperature overnight and then milled and sieved
to reach a grain size <20 μm.

The influence of Zn and Sr on the glass structure was evaluated by X-ray diffraction (XRD – X’Pert Philips diffractometer),
using the Bragg Brentano camera geometry and the Cu-Ka
incident radiation; the obtained pattern was analyzed with
X’Pert High Score software and the PCPDF data bank. All glasses
were also analyzed from the morphological and compositional
points of view by Field Emission Scanning Electron Microscopy
(FESEM – SUPRATM 40, Zeiss) equipped with energy-dispersive
spectroscopy (EDS).

In order to assess the effect of the introduced oxides on the
mechanism of bioactivity, glass powders were immersed in SBF
(Kokubo and Takadama, 2006) for different time periods (1, 3, 7,
14, 21, and 28 days). The test was performed in an orbital shaker
(KS 4000i control, IKA ® ) at 37°C using a glass powder (mg)/SBF
(ml) ratio of 1 and an agitation rate of 120 rpm (MagallanesPerdomo et al., 2012). At the end of the incubation time, the
powders were washed with water and acetone, filtered, dried
during 3 h at 60°C, and analyzed by means of XRD and FESEMEDS. For comparison, the bioactivity of the original 45S5 BG was
evaluated for up to 3 days.

Suspension Preparation and Stability Evaluation
Doped glass powders and chitosan were used to produce organic/
inorganic composite coatings on AISI 316L stainless steel

substrate (15 mm × 20 mm) by EPD, using both direct current
(DC) and alternating current (AC). Suspensions containing
0.5 g/L chitosan (80 kDa, 85% deacetylation, Sigma) and 1.5 g/L
glass powders were prepared in a solvent mixture of 1 vol%
acetic acid (Sigma-Aldrich), 20 vol% pure water (Purelab Option
R7BP, ELGA), and 79 vol% ethanol (VWR). These experimental
parameters were chosen according to previously reported results
(Grandfield and Zhitomirsky, 2008; Cordero-Arias et al., 2013).
Before the EPD process, the suspensions were sonicated with a
VWR USC 300 sonicator for 1 h and stirred during 5 min to avoid
particle sedimentation. Suspension stability was evaluated by
measuring the ζ-potential, using a Zetasizer nano ZS equipment
(Malverb Instrument, UK).

Coatings Deposition and Characterization
Different deposition parameters were investigated. For the
DC-EPD process, the deposition time varied between 30 s and
2 min and the electric potential in a range of 20–80 V. Regarding
the AC-EPD, the voltage varied in the range of 8–20 V and the
deposition time between 1 and 2 min; moreover, a frequency
range of 4–10 KHz and a duty cycle of 70–80% were considered.
For both, DC- and AC-EPD procedures, the distance between the
deposition and counter electrodes was kept constant at 10 mm.
The choice of the optimal parameters was carried out on the basis
of morphological analysis of the samples by means of the coating
homogeneity in preliminary experiments. Coating microstructure was evaluated by SEM (Hitachi S4800) while FTIR (Nicolet
6700) analysis was carried out to determine the presence of
chitosan and the different glass particles in the coating.

The mechanical characterization of the coatings was performed through the tape test (four samples for each composition),
in accordance with ASTM D3359-09 standard, and a qualitative
flexural bend test by manually flexing the sample up to an angle
of 180° according to previous studies (two samples for each composition) (Chen et al., 2013; Cordero-Arias et al., 2013, 2014). The
deposited mass was calculated by weighing the samples before
and after the deposition process, both using AC- and DC-EPD
methods. Chitosan/45S5-Sr coatings were selected as an example,
and 10 measures were performed for each deposition by means of
a precision balance (0.0001 g).

The surface roughness (Ra) of all coatings, synthesized both
using AC-EPD and DC-EPD, was measured by means of a laser
profilometer (UBM, ISC-2); the analysis was performed in triplicate. The coating wettability was estimated through static contact
angle measurements using a DSA30 instrument (Kruess GmbH,

TABLE 1 | Compositions of the 45S5-based bioactive glasses
investigated.

%wt 45S5 45S5-Sr 45S5-Zn 45S5-Sr-Zn

SiO2 45.00 43.01 43.92 43.46

Na2O 24.50 23.42 23.91 23.66

P2O5 6.00 5.73 5.86 5.79

CaO 24.50 18.19 18.58 18.38

SrO 0.00 9.65 0.00 4.87

ZnO 0.00 0.00 7.74 3.83

Germany). Five measurements for each sample were carried out
using distilled water.

Bioactivity test in SBF was performed according to Kokubo’s
protocol (Kokubo and Takadama, 2006) to evaluate the influence of the doping elements on the final bioactivity of the coating. Coated samples were immersed in 40 ml of SBF solution
maintained at 37°C for 1, 3, 7, 14, 21, and 28 days. Every 7 days,
the SBF solution was refreshed. After the immersion period,
samples were analyzed by means of SEM, XRD, and Raman
spectroscopy (LabRAM HR800, Horiba Jobin Yvon) to evaluate
the formation of hydroxyapatite (HAp) or its precursor on the
samples surfaces.

RESULTS

Glasses Synthesis and Characterization
The structural analyses of Zn- and/or Sr-doped glasses ( Figure 1 )
demonstrated that all glass powders were amorphous; therefore,
the introduction of Zn and Sr oxides did not induce nucleation of
crystalline phases. Also from the morphological point of view, no
significant differences were evidenced by FESEM analyses while
the presence of doping elements was verified by means of EDS
analysis (data not shown here).

Immersion tests in SBF solution revealed the influence of Sr
and Zn on bioactivity of the glasses. In particular, Zn-containing
glasses showed a delay in the nucleation of HAp, even if the silica
gel formation and its enrichment in Ca and P were observed after
few days of SBF immersion.

Figure 1 reports the XRD patterns of all glasses before and
after SBF treatment up to 1 month; as it can be noticed, no crystallization peaks were observed for 45S5-Zn glasses ( Figure 1A ), but
only the typical silica-gel halo at about 2 theta = 20°–25° after
3 days of immersion in SBF was noticed. XRD analyses of 45S5-Sr
glasses ( Figure 1B ) showed always the presence of the silica-gel
halo after 1 day of treatment and the appearance of HAp peaks
after 7 days of immersion in SBF; then in this case only a slight
delay, in comparison to the pristine glass (45S5 BG, Figure 2 ), in
the HAp crystallization was observed. Glasses containing both
Zn and Sr showed an intermediate behavior: silica gel was present
after 3 days of SBF immersion, but the HAp peaks appeared only
after 1 month of treatment.

The results obtained by means of XRD analyses were confirmed by FESEM observation and EDS analyses, reported in
Figures 3 and 4 respectively. Regarding 45S5-Zn glass powders,
no formation of crystals with the typical globular shape of HAp
was evidenced up to 1 month, even if a reaction layer can be
noticed on SEM images ( Figure 3A ) and an increase of Ca
and most of all P was evidenced by EDS analysis ( Figure 4A ).
A noticeable increase of Ca and P concentration together
with the decrease of Na were also evidenced for 45S5-Sr glass
( Figure 4B ). SEM analyses revealed the presence of globular
agglomerates with the typical morphology of _in vitro_ self-grown
HAp (Kaur et al., 2014) after 7 days of SBF treatment. Also in
this case, 45S5-ZnSr presents an intermediate performance:
EDS analysis showed a significant increase of Ca and P and a
reduction of Na concentrations, which are intermediate between
those of 45S5-Sr and 45S5-Zn. Moreover, globular precipitates

FIGURE 1 | XRD patterns of 45S5-Zn (A), 45S5-Sr (B), and 45S5-ZnSr (C) before and after SBF treatment up to 1 month . (•) Hydroxyapatite, (–) silica gel.

FIGURE 2 | XRD patterns of 45S5 (BG) before and after SBF treatment up to 3 days . (•) Hydroxyapatite, (–) silica gel.

FIGURE 3 | SEM micrographs of 45S5-Zn (A), 45S5-Sr (B), and 45S5-ZnSr (C) after different times of immersion in SBF .

FIGURE 4 | Atomic percentages variation (EDS analyses of 500× area) of 45S5-Zn (A), 45S5-Sr (B), and 45S5-ZnSr (C) after immersion in SBF .

were confirmed to form after 28 days of immersion by means of
SEM observation.

Suspension Stability
The ζ-potential results for BG suspension stability are presented
in Table 2 . For the Sr- and Zn-doped BGs/chitosan suspensions,
the ζ-potential results show a similar value. All systems exhibit a
relative high standard deviation (14 mV), and this result can be
related to the large size of the glass particles decreasing the suspension stability. Nevertheless, a cathodic deposition is predicted for
all the systems. It can be assumed that deposition is controlled by
the chitosan molecules, which move the potential from a negative

value for the BG to a positive value when chitosan is incorporated,
this occurs by the esterification that the polymer chain has on
the surface of the BG particles, as discussed in previous studies
(Zhitomirsky et al., 2009; Pishbin et al., 2011; Chen et al., 2013;
Cordero-Arias et al., 2013).

The fresh prepared suspensions exhibited a pH value in the
range of 3–4.5 for all suspensions. Under those conditions, the
suspensions were used for EPD.

Coating Synthesis and Characterization
Using the DC-EPD technique, homogeneous and well-attached
coatings were obtained for the 45S5-Sr- and 45S5-ZnSr-based

coatings using 75 V and 1 min of deposition potential and time,
respectively ( Figures 5B,C ). In the case of the 45S5-Zn/Ch system, the coatings presented a higher porosity and microcracks,
which are likely due to a stronger hydrolysis during the deposition
( Figure 5A ). When AC-EPD was used, homogeneous and wellattached coatings were obtained for the different glasses using
20 V of deposition potential, 2 min of deposition time, 10 kHz of
frequency, and a duty charge of 80% ( Figures 5D–F ). Comparing
the 45S5-Zn/Ch produced by DC-EPD and AC-EPD, better coatings were produced using the AC-EPD method since the voltage
is periodically inverted, the supplied energy is not sufficient to
cause water hydrolysis, and the coatings appeared more homogeneous. These results are in accordance with previously reported
data (Neirinck et al., 2009; Chávez-Valdez and Boccaccini, 2012;
Chen et al., 2013). The used voltage did not have influence on the
deposition of 45S5-Sr powders, allowing a uniform deposition
both in AC and DC processes. Finally, in 45S5-ZnSr-containing
coating, a low amount of bubbles was detected, but there were no
differences between AC and DC deposition.

The qualitative bending test demonstrated an optimal adhesion of all coatings on the substrates, without the formation of
cracks or detachments ( Figure 6 ).

Concerning the measurement of deposited mass, AC-EPD led
to a deposited mass of 1.3 ± 0.2 mg/cm 2 while 0.8 ± 0.2 mg/cm 2
was calculated for DC-EPD coatings.

The tape test ( Figure 7 ), performed in accordance with ASTM
D3359-09, evidenced some differences among the various coatings; the 45S5-Zn coatings showed a damage classified as 2B

TABLE 2 | ζ-potential results for suspensions containing the different
doped bioactive glasses in a mixture with chitosan.

Suspension ζ-Potential (mV)

45S5-Sr/Ch +29 ± 14

45S5-Zn/Ch +31 ± 15

45S5-ZnSr/Ch +36 ± 14

for AC-EPD (65% of the coating removed) and 3B for DC-EPD
(25% of the coating removed). 45S5-Sr coatings revealed a damage <5% for both deposition modes and were classified as 4B.
Finally, 45S5-ZnSr coatings showed a significant damage both for
AC-EPD (classified as 1B, more than 65% of the coating removed)
and for DC-EPD (classified as 2B, 65% of the coating removed).

The morphological analysis of the coatings is reported in
Figure 8 . As it can be observed, the 45S5-Zn coatings exhibit poor
homogeneity, and the glass particles formed clusters which are
well embedded in the polymeric matrix. Regarding the deposition
process, AC-EPD allowed depositing glass particles/clusters with
greater dimensions than the DC-EPD process, covering more of
the substrate surface. 45S5-Sr coatings appear relatively more
homogenous and uniform with glass particles well integrated in
the chitosan matrix. No substantial difference between DC- and
AC-EPD is observed in terms of microstructure. Concerning
the 45S5-ZnSr coatings, a more pronounced difference was
noticed between DC and AC deposition; the coatings obtained
with DC-EPD are clearly less consistent and homogenous in
comparison to those synthesized with AC-EPD, similar results
for DC- and AC-EPD for organic/inorganic coatings have been
previously reported (Chen et al., 2013).

Figure 9 shows as example the FTIR spectrum of an
Sr-containing coating. In order to verify the presence of chitosan,
the FTIR spectrum of pure chitosan powder was obtained
together with that of pure glass powder (45S5-Sr). Moreover, also
the spectrum of a chitosan coating was obtained.

FTIR analysis evidenced the composite nature of all coatings.
The chitosan characteristic peaks were present in all spectra,
in particular the peaks around 891 cm −1 and 1150 cm −1, which
correspond to the saccharide structure and are due to the vibrations of the glycosidic bonding (–C–O–C–). The stretching of the
C=O group in the glucosamine unit appears at about 1650 cm −1
and corresponds to the amide ι band. The band at 1570 cm −1
corresponds to the amide II band, indicating the NH-bending
vibrations in the amide group (Gebhardt et al., 2012). Finally, the
peak at 1350 cm −1 is ascribable to the vibration of the C–H/N–H

FIGURE 5 | Images of the electrophoretic coatings using both DC (A–C) and AC-EPD (D–F) for the different chitosan/BG systems investigated .

FIGURE 6 | Digital camera images of the surface of coatings after bending tests . Coatings produced by means of DC-EPD (A–C) and AC-EPD (D–F) . Scale
bar: 1 mm.

FIGURE 7 | Tape test results for the different chitosan/45S5-doped BG coatings on stainless steel AISI 316L substrate confirming different adhesion
behavior of coatings depending on deposition mode (AC- or DC-EPD) .

group. Instead, the characteristic bands of BG are located at
about 916 cm −1 and 496 cm −1 and correspond to the vibration of
Si–O–Si and P–O groups, respectively.

The roughness of the coatings was evaluated and the obtained
values are reported in Table 3 . As it can be observed, the roughness values are generally higher for coatings obtained by AC-EPD

FIGURE 8 | SEM images of AC- and DC-EPD-obtained coatings showing glass particles in chitosan matrix .

FIGURE 9 | FTIR spectra of chitosan/45S5-Sr . The relevant peaks are
explained in the text.

process. This behavior is probably due to the grater amount of
material deposited.

Table 3 reports also the results of wettability test; the values of
the contact angle measurements varied between 35° and 80°. As

reported in the literature (Chen et al., 2013), the presence of BG
should lead to hydrophilic properties, and hydrophilic surfaces
are promising for the _in vitro/in vivo_ cells interaction.

Figure 10 shows the results obtained for 45S5-Zn-containing
coating upon immersion in SBF. SEM images confirmed the
results obtained on glass powders: the Zn presence causes a pronounced inhibition of the precipitation of HAp. No differences
were evidenced between AC- and DC-EPD modes at any time of
immersion in SBF.

On the contrary, Sr-containing coatings were able to induce
the precipitation of HAp after 1 day for AC-EPD and 3 days for
DC-EPD coatings. Figure 11 shows SEM micrographs, XRD,
and Raman analyses of the samples: globular agglomerates similar to _in vitro_ grown HAp are visible after few days of treatment;
the HAp presence is confirmed by XRD up to 7 days and Raman
analyses from 7 to 28 days (Koutsopoulos, 2002; Li et al., 2004).

Finally, a reduced bioactivity was also evidenced for
45S5-ZnSr-containing coatings, since up to 14 days no HAp
precipitation was detected both with SEM and XRD analyses
( Figure 12 ).

DISCUSSION

This research has considered the synthesis of Zn- and Sr-doped
glasses and their use to develop chitosan/glass composite coatings

TABLE 3 | Roughness (Ra) and contact angle values of the different produced coatings.

45S5-Zn AC 45S5-Zn DC 45S5-Sr AC 45S5-Sr DC 45S5-ZnSr AC 45S5-ZnSr DC

Ra (μm) 1.8 ± 0.2 1.6 ± 0.08 2.2 ± 0.4 1.2 ± 0.1 1.6 ± 0.04 1.7 ± 0.2

Contact angle 47° ± 5° 54° ± 9° 41° ± 6° 62° ± 12° 73° ± 7° 59° ± 8°

FIGURE 10 | SEM micrographs of 45S5-Zn-containing coatings after different times of immersion in SBF .

FIGURE 11 | SEM, XRD, and Raman analyses of 45S5-Sr up to 1 month of SBF immersion .

FIGURE 12 | SEM micrographs and XRD analyses of 45S5-ZnSr after immersion in SBF solution .

by means of EPD. In particular, the influence of Zn, Sr, and their
combination on the bioactivity process was investigated from
both glass powders and coatings. Moreover, the effect of these
ions in the EPD process was also evaluated.

Regarding the glass powders, both Zn and Sr introduction
did not change the structure of the pristine glass (45S5), since
no crystallization peaks were detected in XRD spectra. However,
the incorporation of these elements, especially Zn, generated
differences on the kinetics of bioactivity. In fact, Zn-doped glass
(45S5-Zn) did not show the precipitation of crystalline HAp up to
1 month of immersion in SBF solution ( Figure 1A ). The influence
of Zn on the bioactivity process and its role in glass structure
have been extensively debated in literature, as reviewed recently
(Balasubramanian et al., 2015). It has been reported that ZnO
can act as a modifier (Anand et al., 2014; Balasubramanian et al.,
2015), leading to the decrease in surface area and pore size of glass.
Moreover, when present in higher amount, ZnO can also act as an
intermediate oxide, thus creating a more stable glass structure by
forming covalent links between adjacent SiO4 tetrahedra (El-Kady
and Ali, 2012; Balasubramanian et al., 2015). Regarding ZnO role
in glass bioactivity and degradation, Kamitakahara et al. (2006)
reported that the introduction of ZnO (replacing CaO) in a bioactive apatite–wollastonite containing glass-ceramic decreases the
glass-ceramic bioactivity. They reported that the glass-ceramic
chemical durability was improved by adding ZnO because ZnO is
an amphoteric oxide and shows very low solubility in SBF. Similar
results were obtained by Goel et al. (2013). The silicon release of
the glass-ceramic decreased with increasing ZnO content, and as
a consequence, the formation of silanol groups was suppressed.
It has been observed that the presence of zinc causes a general
reduction in ion leaching in the 45S5 BG composition (Lusvardi
et al., 2009). This behavior was also confirmed by Aina et al.
(2009); in this study, it is proven that high level of ZnO (20 mol%)
caused a drastic reduction of 45S5 glass leaching activity and so
HAp formation. A 5 mol% of ZnO addition causes only a delay
in the HAp precipitation; however, in this case, Zn substituted all
glass elements. Oudadesse et al. (2011) reported that only 0.1 wt%

of Zn (replacing Ca and Na) inhibited the glass dissolution, limiting the formation of silica gel layer and generating a delay in the
HAp formation.

The present study confirms that Zn introduction retards the
glass degradation and the crystal nucleation of HAp, even if for
glass powders the silica gel formation and its enrichment in Ca
and P were observed after few days of SBF immersion.

Data regarding Sr introduction in glasses has shown that its
addition does not result in any structural alteration of the glass
network (Fredholm et al., 2010), since its role is similar to the
calcium one. Moreover, in general, this element does not modify
or even enhances the bioactivity of the pristine glass (Lao et al.,
2008, 2009). Only few studies reported a negative influence of Sr in
HAp nucleation. Hoppe et al. (2014) reported that Sr-containing
BG (type 1393) nanoparticles showed a delay in the bioactivity
mechanism by increasing the Sr content, and Goel et al. (2011)
showed that increasing the Sr2 + /Ca 2+ ratio in the glasses does
not affect their structure significantly, but the apatite-forming
ability is decreased considerably. In the present study, Sr introduction entails a slight delay in the bioactivity kinetics, but XRD
( Figure 1B ) and FESEM-EDS analyses ( Figures 3B and 4B ) demonstrated that after 3 days of SBF immersion, HAp crystals were
present on the surface of the glass powders. It must be underlined
that in the literature there are some controversies about the effect
of Sr/Ca substitution on the dissolution mechanism of the glasses.
These controversies seem to be due to the mixed use of weight
instead of mole percent in glasses composition design (O’Donnell
and Hill, 2010; Du and Xiang, 2012). In fact, if weight percentage
is used, the higher molecular weight of SrO than CaO can lead to
an actual increase of SiO2 content in mole percent, which involves
an increase of network connectivity and a decrease of dissolution
rate. Instead, if Sr is substituted in mole percent, the network
structure of the glass does not significantly change and a higher
dissolution rate is usually observed (Neel et al., 2009; O’Donnell
and Hill, 2010)

Finally, the substitution of both Zn and Sr leads to an intermediate behavior; the bioactivity process of 45S5-ZnSr glass is

obviously delayed; however, after 1 month in SBF solution, the
performed XRD and FESEM-EDS analyses ( Figures 1C and 4C )
demonstrated the formation of a crystalline HAp layer on glass
powders surface. Differently, Kapoor et al. evidenced HAp formation in few hours on Sr- and Zn-doped alkali-free glass, however
with very different composition respect to the ones of the glasses
investigated here (Kapoor et al., 2014).

The bioactivity test of composite coatings produced by EPD
leads to the same observations: Zn introduction significantly
modified the glass reactivity toward SBF solution while Sr
introduction allows maintaining the bioactivity of the coatings.

By tuning the EPD parameters, it was possible to obtain
composite coatings using all doped glasses with glass particles or
clusters well embedded in the chitosan matrix; however, the glass
composition seems to have an effect not only on the coating bioactivity but also on their deposition and adhesion to the metallic
substrate; in fact, Zn-containing coatings showed qualitative low
adhesion with respect to Sr-containing ones ( Figure 7 ).

Moreover, some differences were observed between AC and
DC deposition; usually, the AC-EPD technique allowed deposition of composite coating without the formation of cracks and
bubbles while some bubbles were observed using DC-EPD, specially for Zn-containing coatings. When water is used as solvent,
the use of DC can originate water electrolysis, which leads to the
formation of oxygen or hydrogen bubbles formation and their
entrapment in the coating; in the AC-EPD technique, the voltage
is periodically inverted, so the supplied energy is not sufficient
to cause water hydrolysis, and consequent bubble formation,
and the coatings appeared more homogeneous (Neirinck et al.,
2009; Chávez-Valdez and Boccaccini, 2012; Chen et al., 2013).
Moreover, AC-EPD allowed the deposition of a slightly greater
amount of material than DC-EPD. As confirmed by Kollatha
et al. (2013), AC-EPD is advantageous in depositing denser and
less cracked coatings in comparison to DC-EPD. The bubble
formation can also have some influence on the roughness of the
coatings; nevertheless, the observed difference among roughness
values can be due to the grater amount of material deposited on
the substrates using AC-EPD.

REFERENCES

CONCLUSION

The introduction of Zn and Sr in the 45S5 BG composition leads
to a different behavior in terms of bioactivity, both for glass
powders and composite coatings. The presence of ZnO allowed
silica gel formation and its enrichment in Ca and P after few
days of SBF immersion but inhibited the formation and precipitation of HAp while SrO introduction allowed the formation of a
crystalline HAp after 1–3 days of SBF treatment. All glasses were
successfully used to synthesize composite coatings by means of
EPD with chitosan as the biopolymer component by adjusting the
process parameters; however, Zn-containing coatings showed
low adhesion to the substrate in comparison with 45S5-Sr/chitosan coatings. The deposition using AC revealed better coating
quality than DC-EPD technique, since it allowed the realization
of compact coatings, reducing bubbles and cracks formation. In
conclusion, Zn concentration in 45S5 BG should be tailored to
not completely inhibit the bioactivity process but at the same
time to allow its antibacterial and anti-inflammatory effect and
its role in bone metabolism while Sr-containing coatings, due to
the bioactivity and biological effect of Sr, are promising materials for orthopedic coatings. A deeper investigation should be
carried out in future work to evaluate the Sr ability to stimulate
bone formation through _in vitro_ biological tests.

ACKNOWLEDGMENTS

The authors thank Prof. S. Virtanen and Prof. W. Peukert
(University of Erlangen-Nuremberg) for their support to
facilitate SEM and ζ-potential measurements at their institutes,
respectively. Dr. Sandra Cabanas-Polo is acknowledged for
carrying out the ζ-potential measurements. LC-A acknowledges support from the German Academic Exchange Service
(DAAD). Politecnico di Torino is acknowledged for funding
a six months period of study at Institute for Biomaterials,
Department of Materials Science and Engineering, University
of Erlangen-Nuremberg with a Mobility Grant (2013-2104)
for MS degree thesis.

Aina, V., Malavasi, G., Fiorio Pla, A., Munaron, L., and Morterra, C. (2009).

Zinc-containing bioactive glasses: surface reactivity and behaviour towards
endothelial cells. _Acta Biomater._ [5, 1211–1222. doi:10.1016/j.actbio.2008.10.020](http://dx.doi.org/10.1016/j.actbio.2008.10.020)
Anand, V., Singh, K. J., and Kaur, K. (2014). Evaluation of zinc and magnesium

doped 45S5 mesoporous bioactive glass system for the growth of hydroxyl apatite layer. _J. Non Cryst. Solids_ [406, 88–94. doi:10.1016/j.jnoncrysol.2014.09.050](http://dx.doi.org/10.1016/j.jnoncrysol.2014.09.050)
Balamurugan, A., Balossier, G., Kannan, S., Michel, J., Rebelo, A. H. S., and Ferreira,

J. M. F. (2007). Development and in vitro characterization of sol-gel derived
CaO-P2O5-SiO2-ZnO bioglass. _Acta Biomater._ [3, 255–262. doi:10.1016/j.](http://dx.doi.org/10.1016/j.actbio.2006.09.005)
[actbio.2006.09.005](http://dx.doi.org/10.1016/j.actbio.2006.09.005)
Balasubramanian, P., Strobel, L. A., Kneser, U., and Boccaccini, A. R. (2015).

Zinc-containing bioactive glasses for bone regeneration, dental and orthopedic
applications. _Biomed. Glasses_ [1, 51–69. doi:10.1515/bglass-2015-0006](http://dx.doi.org/10.1515/bglass-2015-0006)
Besra, L., and Liu, M. (2007). A review on fundamentals and applications of

electrophoretic deposition (EPD). _Prog. Mater. Sci._ [52, 1–61. doi:10.1016/j.](http://dx.doi.org/10.1016/j.pmatsci.2006.07.001)
[pmatsci.2006.07.001](http://dx.doi.org/10.1016/j.pmatsci.2006.07.001)
Boccaccini, A. R., Keim, S., Ma, R., Li, Y., and Zhitomirsky, I. (2010). Electrophoretic

deposition of biomaterials. _J. R. Soc. Interface_ [7, 581–613. doi:10.1098/](http://dx.doi.org/10.1098/rsif.2010.0156.focus)
[rsif.2010.0156.focus](http://dx.doi.org/10.1098/rsif.2010.0156.focus)

Chávez-Valdez, A., and Boccaccini, A. R. (2012). Innovations in electrophoretic

deposition: alternating current and pulsed direct current methods. _Electrochim._
_Acta_ [65, 70–89. doi:10.1016/j.electacta.2012.01.015](http://dx.doi.org/10.1016/j.electacta.2012.01.015)
Chen, Q., Cordero-Arias, L., Roether, J. A., Cabanas-Polo, S., Virtanen, S., and

Boccaccini, A. R. (2013). Alginate/bioglass ® composite coatings on stainless
steel deposited by direct current and alternating current electrophoretic
deposition. _Surf. Coat. Technol._ [233, 49–56. doi:10.1016/j.surfcoat.2013.01.042](http://dx.doi.org/10.1016/j.surfcoat.2013.01.042)
Chen, Q., and Thouas, G. A. (2015). Metallic implant biomaterials. _Mater. Sci. Eng._

_R Rep._ [87, 1–57. doi:10.1016/j.msea.2015.07.046](http://dx.doi.org/10.1016/j.msea.2015.07.046)
Cordero-Arias, L., Cabanas-Polo, S., Gao, H. X., Gilabert, J., Sanchez, E., Roether,

J. A., et al. (2013). Electrophoretic deposition of nanostructured-TiO2/chitosan composite coatings on stainless steel. _RSC Adv._ [3, 39–41. doi:10.1039/](http://dx.doi.org/10.1039/c3ra40535d)
[c3ra40535d](http://dx.doi.org/10.1039/c3ra40535d)
Cordero-Arias, L., Cabanas-Polo, S., Gilabert, J., Goudouri, O. M., Sanchez, E.,

Virtanen, S., et al. (2014). Electrophoretic deposition of nanostructured TiO2/
alginate and TiO2-bioactive glass/alginate composite coatings on stainless steel.
_Adv. Appl. Ceram._ [113, 42–49. doi:10.1179/1743676113Y.0000000096](http://dx.doi.org/10.1179/1743676113Y.0000000096)
Croisier, F., and Jérôme, C. (2013). Chitosan-based biomaterials for tissue engi
neering. _Eur. Polym. J._ [49, 780–792. doi:10.1016/j.eurpolymj.2012.12.009](http://dx.doi.org/10.1016/j.eurpolymj.2012.12.009)
Drnovšek, N., Novak, S., Dragin, U., Čeh, M., Gorenšek, M., and Gradišar, M.

(2012). Bioactive glass enhances bone ingrowth into the porous titanium

coating on orthopaedic implants. _Int. Orthop._ [36, 1739–1745. doi:10.1007/](http://dx.doi.org/10.1007/s00264-012-1520-y)
[s00264-012-1520-y](http://dx.doi.org/10.1007/s00264-012-1520-y)
Du, J., and Xiang, Y. (2012). Effect of strontium substitution on the structure, ionic

diffusion and dynamic properties of 45S5 bioactive glasses. _J. Non Cryst. Solids_
[358, 1059–1071. doi:10.1016/j.jnoncrysol.2011.12.114](http://dx.doi.org/10.1016/j.jnoncrysol.2011.12.114)
El-Kady, A. M., and Ali, A. F. (2012). Fabrication and characterization of ZnO mod
ified bioactive glass nanoparticles. _Ceram. Int._ [38, 1195–1204. doi:10.1016/j.](http://dx.doi.org/10.1016/j.ceramint.2011.07.069)
[ceramint.2011.07.069](http://dx.doi.org/10.1016/j.ceramint.2011.07.069)
Fredholm, Y. C., Karpukhina, N., Law, R. V., and Hill, R. G. (2010). Strontium

containing bioactive glasses: glass structure and physical properties. _J. Non_
_Cryst. Solids_ [356, 2546–2551. doi:10.1016/j.jnoncrysol.2010.06.078](http://dx.doi.org/10.1016/j.jnoncrysol.2010.06.078)
Gebhardt, F., Seuss, S., Turhan, M. C., Hornberger, H., Virtanen, S., and Boccaccini,

R. (2012). Characterization of electrophoretic chitosan coatings on stainless
steel. _Mater. Lett._ [66, 302–304. doi:10.3390/ijms150712231](http://dx.doi.org/10.3390/ijms150712231)
Gentleman, E., Fredholma, Y. C., Jell, G., Lotfibakhshaiesh, N., O’Donnell, M. D.,

Hill, R. G., et al. (2010). The effects of strontium-substituted bioactive glasses on
osteoblasts and osteoclasts in vitro. _Biomaterials_ [31, 3949–3956. doi:10.1016/j.](http://dx.doi.org/10.1016/j.biomaterials.2010.01.121)
[biomaterials.2010.01.121](http://dx.doi.org/10.1016/j.biomaterials.2010.01.121)
Gerhardt, L. C., and Boccaccini, A. R. (2010). Bioactive glass and glass-ceramic

scaffolds for bone tissue engineering. _Materials_ [3, 3867–3910. doi:10.3390/](http://dx.doi.org/10.3390/ma3073867)
[ma3073867](http://dx.doi.org/10.3390/ma3073867)
Goel, A., Kapoor, S., Tilocca, A., Rajagopal, R. R., and Ferreira, J. M. F. (2013).

Structural role of zinc in biodegradation of alkali-free bioactive glasses. _J. Mater._
_Chem. B_ [1, 3073–3082. doi:10.1039/c3tb20163e](http://dx.doi.org/10.1039/c3tb20163e)
Goel, A., Rajagopal, R. R., and Ferreira, J. M. F. (2011). Influence of strontium

on structure, sintering and biodegradation behaviour of CaO-MgOSrO-SiO2-P2O5-CaF2 glasses. _Acta Biomater._ [7, 4071–4080. doi:10.1016/j.](http://dx.doi.org/10.1016/j.actbio.2011.06.047)
[actbio.2011.06.047](http://dx.doi.org/10.1016/j.actbio.2011.06.047)
Grandfield, K., and Zhitomirsky, I. (2008). Electrophoretic deposition of com
posite hydroxyapatite-silica-chitosan coatings. _Mater. Charact._ 59, 61–67.
[doi:10.1016/j.matchar.2006.10.016](http://dx.doi.org/10.1016/j.matchar.2006.10.016)
Hench, L. L. (2006). The story of bioglass ® . _J. Mater. Sci. Mater. Med._ 17, 967–978.

[doi:10.1007/s10856-006-0432-z](http://dx.doi.org/10.1007/s10856-006-0432-z)
Hench, L. L. (2015). Opening paper 2015 – some comments on bioglass: four

eras of discovery and development. _Biomed. Glasses_ [1, 1–11. doi:10.1515/](http://dx.doi.org/10.1515/bglass-2015-0001)
[bglass-2015-0001](http://dx.doi.org/10.1515/bglass-2015-0001)
Hoppe, A., Sarker, B., Detsch, R., Hild, N., Mohn, D., Stark, W. J., et al. (2014).

In vitro reactivity of Sr-containing bioactive glass (type 1393) nanoparticles.
_J. Non Cryst. Solids_ [387, 41–46. doi:10.1016/j.jnoncrysol.2013.12.010](http://dx.doi.org/10.1016/j.jnoncrysol.2013.12.010)
Jaiswala, S., McHale, P., and Duffy, B. (2012). Preparation and rapid analysis of

antibacterial silver, copper and zinc doped sol-gel surfaces. _Colloids Surf. B_
_Biointerfaces_ [94, 170–176. doi:10.1016/j.colsurfb.2012.01.035](http://dx.doi.org/10.1016/j.colsurfb.2012.01.035)
Jones, J. R. (2013). Review of bioactive glass: from hench to hybrids. _Acta Biomater._

[9, 4457–4486. doi:10.1016/j.actbio.2012.08.023](http://dx.doi.org/10.1016/j.actbio.2012.08.023)
Kamitakahara, M., Ohtsuki, C., Inada, H., Tanihara, M., and Miyazaki, T. (2006).

Effect of ZnO addition on bioactive CaO-SiO2-P2O5-CaF2 glass-ceramics
containing apatite and wollastonite. _Acta Biomater._ [2, 467–471. doi:10.1016/j.](http://dx.doi.org/10.1016/j.actbio.2006.03.001)
[actbio.2006.03.001](http://dx.doi.org/10.1016/j.actbio.2006.03.001)
Kapoor, S., Goelb, A., Tiloccac, A., Dhunad, V., Bhatiae, G., Dhunae, K., et al.

(2014). Role of glass structure in defining the chemical dissolution behavior,
bioactivity and antioxidant properties of zinc and strontium co-doped alkali-free phosphosilicate glasses. _Acta Biomater._ [10, 3264–3327. doi:10.1016/j.](http://dx.doi.org/10.1016/j.actbio.2014.03.033)
[actbio.2014.03.033](http://dx.doi.org/10.1016/j.actbio.2014.03.033)
Kaur, G., Pandey, O. P., Singh, K., Homa, D., Scott, B., and Pickrell, G. (2014). A

review of bioactive glasses: their structure, properties, fabrication and apatite
formation. _J. Biomed. Mater. Res. A_ [102, 254–274. doi:10.1002/jbm.a.34690](http://dx.doi.org/10.1002/jbm.a.34690)
Kokubo, T., and Takadama, H. (2006). How useful is SBF in predicting

in vivo bone bioactivity? _Biomaterials_ [27, 2907–2915. doi:10.1016/j.](http://dx.doi.org/10.1016/j.biomaterials.2006.01.017)
[biomaterials.2006.01.017](http://dx.doi.org/10.1016/j.biomaterials.2006.01.017)
Kollatha, V. O., Chen, Q., Closset, R., Luyten, J., Traina, K., Mullens, S., et al. (2013).

AC vs. DC electrophoretic deposition of hydroxyapatite on titanium. _J. Eur._
_Ceram. Soc._ [33, 2715–2721. doi:10.1016/j.jeurceramsoc.2013.04.030](http://dx.doi.org/10.1016/j.jeurceramsoc.2013.04.030)
Koutsopoulos, S. (2002). Synthesis and characterization of hydroxyapatite crystals:

a review study on the analytical methods. _J. Biomed. Mater. Res._ 62, 600–612.
[doi:10.1002/jbm.10280](http://dx.doi.org/10.1002/jbm.10280)

Lao, J., Jallot, E., and Nedelec, J. M. (2008). Strontium-delivering glasses with

enhanced bioactivity: a new biomaterial for antiosteoporotic applications?
_Chem. Mater._ [20, 4969–4973. doi:10.1021/cm800993s](http://dx.doi.org/10.1021/cm800993s)
Lao, J., Nedelec, J. M., and Jallot, J. (2009). New strontium-based bioactive glasses:

physicochemical reactivity and delivering capability of biologically active
dissolution products. _J. Mater. Chem._ [19, 2940–2949. doi:10.1039/b822214b](http://dx.doi.org/10.1039/b822214b)
Li, H., Ng, B., Khor, K., Cheang, P., and Clyne, T. (2004). Raman spectroscopy

determination of phases within thermal sprayed hydroxyapatite splats and
subsequent in vitro dissolution examination. _Acta Mater._ 52, 445–453.
[doi:10.1016/j.actamat.2003.09.046](http://dx.doi.org/10.1016/j.actamat.2003.09.046)
Lusvardi, G., Zaffe, D., Menabue, L., Bertoldi, C., Malavasi, G., and Consolo, U.

(2009). In vitro and in vivo behaviour of zinc-doped phosphosilicate glasses.
_Acta Biomater._ [5, 419–428. doi:10.1016/j.actbio.2008.07.007](http://dx.doi.org/10.1016/j.actbio.2008.07.007)
Magallanes-Perdomo, M., Meille, S., Chenal, J. M., Pacard, E., and Chevalier, J.

(2012). Bioactivity modulation of bioglass ® powder by thermal treatment.
_J. Eur. Ceram. Soc._ [32, 2765–2775. doi:10.1016/j.jeurceramsoc.2012.03.018](http://dx.doi.org/10.1016/j.jeurceramsoc.2012.03.018)
Miola, M., Vitale Brovarone, C., Maina, G., Rossi, F., Bergandi, L., Ghigo, D., et al.

(2014). In vitro study of manganese-doped bioactive glasses for bone regeneration. _Mater. Sci. Eng. C_ [38, 107–118. doi:10.1016/j.msec.2014.01.045](http://dx.doi.org/10.1016/j.msec.2014.01.045)
Mouriño, V., Cattalini, J. P., and Boccaccini, A. R. (2012). Metallic ions as ther
apeutic agents in tissue engineering scaffolds: an overview of their biological
applications and strategies for new developments. _J. R. Soc. Interface_ 9, 401–419.
[doi:10.1098/rsif.2011.0611](http://dx.doi.org/10.1098/rsif.2011.0611)
Neel, E. A. A., Chrzanowski, W., Pickup, D. M., O’Dell, L. A., Mordan, N. J.,

Newport, R. J., et al. (2009). Structure and properties of strontium-doped phosphate-based glasses. _J. R. Soc. Interface_ [6, 435–446. doi:10.1098/rsif.2008.0348](http://dx.doi.org/10.1098/rsif.2008.0348)
Neirinck, B., Fransaer, J., Van der Biest, O., and Vleugels, J. (2009). Aqueous electro
phoretic deposition in asymmetric AC electric fields (AC-EPD). _Electrochem._
_Commun._ [11, 57–60. doi:10.1016/j.elecom.2008.10.028](http://dx.doi.org/10.1016/j.elecom.2008.10.028)
Niinomi, M. (2002). Recent metallic materials for biomedical applications. _Metall._

_Mater. Trans. A_ [33, 477–486. doi:10.1007/s11661-002-0109-2](http://dx.doi.org/10.1007/s11661-002-0109-2)
O’Donnell, M. D., and Hill, R. G. (2010). Influence of strontium and the importance

of glass chemistry and structure when designing bioactive glasses for bone
regeneration. _Acta Biomater._ [6, 2382–2385. doi:10.1016/j.actbio.2010.01.006](http://dx.doi.org/10.1016/j.actbio.2010.01.006)
Oudadesse, H., Dietrich, E., Gal, Y. L., Pellen, P., Bureau, B., Mostafa, A. A., et al.

(2011). Apatite forming ability and cytocompatibility of pure and Zn-doped
bioactive glasses. _Biomed. Mater._ [6, 1–9. doi:10.1088/1748-6041/6/3/035006](http://dx.doi.org/10.1088/1748-6041/6/3/035006)
Pishbin, F., Simchi, A., Ryan, M. P., and Boccaccini, A. R. (2011). Electrophoretic

deposition of chitosan/45S5 bioglass ® composite coatings for orthopaedic applications. _Surf. Coat. Technol._ [205, 5260–5268. doi:10.1016/j.surfcoat.2011.05.026](http://dx.doi.org/10.1016/j.surfcoat.2011.05.026)
Rahaman, M. N., Day, D. E., Bal, B. S., Fu, Q., Jung, S. B., Bonewald, L. F., et al.

(2012). Bioactive glass in tissue engineering. _Acta Biomater._ 7, 2355–2373.
[doi:10.1016/j.actbio.2011.03.016](http://dx.doi.org/10.1016/j.actbio.2011.03.016)
Rath, S. N., Brandl, A., Hiller, D., Hoppe, A., Gbureck, U., Horch, R. E., et al.

(2014). Bioactive copper-doped glass scaffolds can stimulate endothelial cells in
co-culture in combination with mesenchymal stem cells. _PLoS ONE_ 9:e113319.
[doi:10.1371/journal.pone.0113319](http://dx.doi.org/10.1371/journal.pone.0113319)
Verné, E. (2012). “Bioactive glass and glass-ceramic coatings,” in _Bio-Glasses – An_

_Introduction_, eds Jones R. J. and Clare A. G. (Chichester, UK: John Wiley &
[Sons, Ltd), 107–119. doi:10.1002/9781118346457.ch8](http://dx.doi.org/10.1002/9781118346457.ch8)
Zhitomirsky, D., Roether, J. A., Boccaccini, A. R., and Zhitomirsky, I. (2009).

Electrophoretic deposition of bioactive glass/polymer composite coatings with
and without HA nanoparticle inclusions for biomedical applications. _J. Mater._
_Process. Technol._ [209, 1853–1860. doi:10.1016/j.jmatprotec.2008.04.034](http://dx.doi.org/10.1016/j.jmatprotec.2008.04.034)

Conflict of Interest Statement: The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be
construed as a potential conflict of interest.

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