Improved biological performance of microarc-oxidized low-modulus Ti-24Nb-4Zr-7.9Sn alloy

Improved Biological Performance of Microarc-OxidizedLow-Modulus Ti-24Nb-4Zr-7.9Sn Alloy

Jiang Wu,1 Zheng-Ming Liu,2 Xiang-Hui Zhao,3 Yang Gao,1 Jiang Hu,1 Bo Gao1

1 School of Stomatology, Fourth Military Medical University, Xi’an 710032, China

2 Nanjing Stomatological Hospital, Nanjing University, 210008 China

3 School of Basic Medicine, Fourth Military Medical University, Xi’an 710032, China

Received 7 April 2009; revised 3 July 2009; accepted 27 July 2009Published online 10 November 2009 in Wiley InterScience (www.interscience.wiley.com). DOI: 10.1002/jbm.b.31515

Abstract: Ti-24Nb-4Zr-7.9Sn (TNZS) is a newly developed b-titanium alloy with low

modulus and it has been considered as good material for dental or orthopedic implant. The

purpose of the current study is to evaluate the effect of micro-arc oxidation (MAO) treatment

on the biological performance of TNZS surface. The phases, morphology and chemical

composition of the MAO-treated surface were characterized by X-ray diffraction, energy

dispersive spectroscope and scanning electron microscopy analysis respectively. Then we

tested the biocompatibility by examining the cell morphology and viability of osteoblast cells

growing on MAO-TNZS surface. The bone binding strength of the specimens was evaluated by

removal torque test after implantation in rabbit tibiae for 6 weeks. Compared with the none-

treated titanium and TNZS specimens, MAO treated TNZS specimens showed a significant

increase (p<0.05) in hydrophilicity, roughness, cell viability and removal torque forces. In

summary, MAO treatment helps to form a porous surface with a biologically active bone-like

apatite layer on TNZS specimens, which may improve the biological response of MAO-TNZS

implants. ' 2009 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater 92B: 298–306, 2010

Keywords: biocompatibility; �-titanium alloys; Ti-24Nb-4Zr-7.9Sn; osteoblast

INTRODUCTION

Titanium and its alloys have been widely used for dental

and orthopedic implants. They show excellent mechanical

properties, good biocompatibility, and inert oxide’s superior

chemical stability.1–4 Among all types of titanium alloys,

b-titanium alloys have nontoxicity character in a variety of

medical implants5 and they have the unique lowest elastic

modulus, which is important for implant in avoiding the

stress shielding-bone resorption caused by unbalanced

stress distribution between bone and implant.6

Ti-24Nb-4Zr-7.9Sn (wt %) (TNZS) is a novel b-titaniumalloy developed by Institute of Metal Research Chinese

Academy of Science (PCT/CN2004/001352) and it possesses

low elastic modulus (42GPa) closing to that of human bone.

TNZS also has better balance of high strength and low mod-

ulus than other titanium alloys reported so far.7

However, being bioinert, the integration of titanium

alloy implants in bone was not in good condition.8 Studies

suggest that the osseointegration of titanium alloys is

mainly determined by the properties of the surface oxide

layer in terms of its structure, morphology, and composi-

tion.9 To achieve improved osseointegration, various physi-

cal and chemical treatments of the titanium surface have

been proposed to obtain the bioactive implant surface and

to improve the integration of titanium alloys with bone tis-

sue. Sandblasting, acid-etching, and plasma spraying of hy-

droxyapatite are the most widely used commercial

techniques.10,11 The first two coating methods have disad-

vantages in brittleness and low adhesion to the metal sub-

strate. The plasma spraying technique also has some

defects: the ceramics coating is easy to decompose at high

temperature. And it is hard and expensive to treat implant

surface with complicated geometric shapes.8

To get both high stability and low mechanical fracture

coating for TNZS in living tissue, new methods for surface

modification are highly essential. Recently, an electrochem-

ical technique, microarc oxidation (MAO), has been used

successfully in producing inorganic glass-ceramic-like coat-

ing onto titanium surface.12 The resulting ceramic coating

has high adhesive strength to the substrate, and the wear re-

sistance, corrosion resistance, heat resistance, and micro-

hardness of the coating are greatly improved. Recent

Jiang Wu and Zheng-Ming Liu contributed equally as the first author to thearticle.

' 2009 Wiley Periodicals, Inc.

Correspondence to: B. Gao (e-mail: [email protected])

298

studies indicate that MAO treatment would be one of the

best methods for modifying titanium implant surface and

improving their bioactive capability.13–18

This study has been performed to evaluate the validity

of MAO oxidation on Ti-24Nb-4Zr-7.9Sn and to investi-

gate the bioactivity of the coating. Cell response to the

MAO layer was examined by studying the viability and

morphology of rat calvarial osteoblasts grown on the coat-

ing surface; bone response was evaluated by removal tor-

que test and morphological analysis of the interface

between bone and implant after implantation in rabbit

tibiae.

MATERIALS AND METHODS

Preparation of TNZS Specimens and MicroarcOxidation (MAO)

Ti-24Nb-4Zr-7.9Sn (TNZS) alloy was provided by Institute

of Metal Research Chinese Academy of Sciences (She-

nyang, China) and the chemical composition is shown in

Table I.7 TNZS disks, with 14 mm diameter and 1.5 mm

thickness, were used to analyze the surface characterization

and biocompatibility in cell cultures. TNZS cylindrical

implants with 2 mm external diameter and 6 mm length19

were used in animal studies. Cp-titanium (Ti) was used for

making the control specimens, and non-MAO-treated

TNZS specimens were also included as control. All sam-

ples were ground by 400-grit SiC sandpaper, and cleaned

ultrasonically in acetone, ethanol, and deionized water suc-

cessively. TNZS specimens were subjected to MAO pro-

cess by applying a pulsed DC field to the specimens and in

an aqueous electrolyte containing calcium (0.2M) and phos-

phate (0.09M). The voltage, frequency, and oxidizing time

were set as 350 V, 200 Hz, and 5 min according to our

previous study.20 The electrolyte was kept at 408C by a

cooling system. The MAO processing was carried out in a

water-cooled stainless steel bath, and a stainless steel plate

(120 3 70 3 2 mm3) was used as the counter electrode

(MAO equipment was designed and manufactured by Xi’an

University of Technology, Xi’an, China). All specimens

were sterilized by radiation before experiment.

Characterization of Oxide Layer

The surface and cross-sectional morphology were analyzed

by scanning electron microscopy (SEM; HITACHI S3400,

Japan), operating at 20 kV and 15 kV, respectively. The

phase and element composition were characterized by X-

ray diffraction (XRD, XRD-7000, Shimadzu, Japan) and

associated energy dispersive spectroscope (EDS, INCA

Energy, Oxford Instruments, Oxford, Britain). The surface

roughness parameters were measured by surface profilome-

ter (TR240, Time Group, Beijing, China).

Surface wettablility of MAO-TNZS, TNZS, and Ti

specimens were evaluated by measuring water contact

angle using a sessile drop method on a Drop Shape Analy-

sis System DSA 10 (Kruss, Hamburg, Germany) at room

temperature. Deionized water was used for the measure-

ments and the test was repeated at nine different sites on

each of three samples.

InVitro Test the Biocompatibility ofMAO-TNZS Specimen

Osteoblast Cell Culture. Mouse calvaria osteoblast cells

were isolated via sequential collagenase digestions of neo-

natal rat calvarial according to established protocol.21

Briefly, cells were maintained in Dulbecco’s Modified

Eagle Medium (DMEM; Gibco) with 10% fetal bovine se-

rum (FBS; Gibco) and split every 2 days by trypsin-EDTA

solution (0.25% trypsin, 1 mM EDTA; Gibco). For each

handling, the number of cells was determined with an elec-

tronic cell counter (Beckman Coulter Z1, Fullerton, Eng-

land) and plated at a density of 20,000 cells/cm2 onto each

disk placed in standard 24-well tissue culture plate.

MTT Assay and ALP Activity Assay. The cell viability

was evaluated by a quantitative colorimetric test-methyl-

thiozol tetrazolium (MTT) test, which characterizes cellular

metabolism and cell viability.22 Cell cultures from day 1,

4, 7, 10 after plating were incubated with MTT solution (5

mg/mL, Sigma-Aldrich) for 4 h at 378C. Five disks from

each group were measured at each time point. Then the

medium was aspirated and DMSO (Hongsheng, Jiangsu,

China) was used to dissolve the darkblue crystals. The opti-

cal density (OD) was measured at 570 nm using a 96-well

microplate reader in the ELX800 enzyme immunoassay an-

alyzer. The blank reference was taken from an ethanol-

DMSO solution alone.

To analyze the differences of cell number on different

substrates, the catalytic activity of alkaline phosphatase

(ALP) was tested. Osteoblast cultures were lysed in 1.5MTris-HCl (pH 10.2) containing 1 mM ZnCl2, 1 mM MgCl2,

and 1% Triton X-100 at 48C for 10 min at different plating

time points. After clarifying the cell lysates by centrifuga-

tion, ALP activity was assessed by measuring the release

of p-nitrophenol spectrophotometrically at 405 nm by

ELX800 enzyme immunoassay analyzer. Measurements

were compared with p-nitrophenol standard and normalized

using the total protein amounts at individual time points.

Scanning Electron Microscopy (SEM) Examination of

Cell Morphology. At each culture period, TNZS and

MAO-TNZS specimens were processed for SEM examina-

tion. Samples were fixed in 2% paraformaldehyde in 0.2Mmonosodic dipotassic buffer, rinsed, dehydrated in graded

alcohol, critical-point dried with CO2 (JEOL, JEE-4X),

TABLE I. Chemical Composition of Ti-Nb-Zr-Sn (wt %)

Ti Nb Zr Sn O N H

Balance 24.1 3.92 7.85 0.11 0.008 0.006

299MICROARC-OXIDIZED LOW-MODULUS TI-24NB-4ZR-7.9SN ALLOY

Journal of Biomedical Materials Research Part B: Applied Biomaterials

sputter-coated with a gold-palladium layer (JEOL, JFC-

1100, Tokyo, Japan), and examined with SEM (HITACHI,

S3400, Japan) at an accelerating voltage of 5.0 kV.

InVivo Test the Bone Response of MAO-TNZS Specimen

Animals and Implantation Procedure. Six adult male

New Zealand White rabbits were used for implantation

study. The animal experiment was approved by the Institu-

tional Animal Care and Use Committee of the Fourth Mili-

tary Medical University (NIH guidelines [NIH Publication

#85-23 Rev. 1985] for laboratory animals care and use

have also been observed). The medial surfaces of the proxi-

mal tibiae were used as implantation sites. After general

anesthesia, each site was shaved and isolated for implant

placement using an incision. The implant sites were pre-

pared at 3–4 cm distal to the tibial diaphysis with dental

drills under sterile saline irrigation with 2 mm diameter

and 4 mm depth. Two implants, randomly selected from

the three implant types, were inserted into each tibia. The

top surfaces of implants were 1.5 mm above the cortical

bone surface. After surgery, the sites were closed using

resorbable sutures. All procedures were performed under

meticulous aseptic technique. After a healing period of 6

weeks, the animals were killed by intravenous injections of

air under general anesthesia. Tissues included implants

were taken for removal torque tests and SEM observation.

Removal Torque Measurements. Bone response was

evaluated by removal torque (RTQ) measurements, which

is used for testing the implant stability and thus can be

regarded as a three dimensional test roughly reflecting the

Figure 1. SEM of surface morphology of Ti (A), TNZS (B), and MAO-TNZS(C–D): (A and B) only the

machining grooves and some pits and surface-defects were observed on the surface of the Ti and

TNZS; (C and D) considerable porous morphology was observed on surface of the MAO-TNZSspecimen and the details of small craters with holes were at the center on porous layer.

Figure 2. Cross-section of MAO layer (‘‘�’’ is the symbol of theMAO layer).

300 WU ET AL.


interfacial shear strength between bone tissue and the

implant. In the RTQ test, the tibia was stabilized and the

implant was pulled out along the axial at 1.0 mm/min dis-

placement. A torque measurement device (AGS-10kNG,

Shimadzu, Japan) was used to test the bond strength

between bone and implant. After RTQ test, the bone to the

implant surface interface of the sixth week was analyzed

by SEM. The specimens were fixed in 10% neutral buf-

fered formaldehyde and 4% paraformaldehyde, dehydrated

in an ethanol series, and embedded in methylmethacrylate.

Then the three kinds of specimens were produced at a final

thickness of 30 lm using a Macro cutting and grinding sys-

tem (LEICA2500, LEICA, Germany), and examined with

SEM (HITACHI, S3400, Japan).

Statistical Analysis

Where applicable, all data are expressed as mean 6 stand-

ard deviation. Statistical analyses were performed using the

Student’s t-test for the purpose of multiple comparisons.

Differences were considered significant at p\ 0.05.

RESULTS

Morphology of Microarc Oxidation Layer on MAO-TNZS

The specimens’ surface morphologies from three different

groups were shown in Figure 1. The machining grooves,

pits, and surface-defects were observed on the surfaces of

Ti and TNZS specimens [Figure 1(A,B)]. After MAO-oxi-

dation, considerable porous morphology with 1–3 lm di-

ameter appeared on the TNZS specimen surface and small

craters with holes in the center were shown in magnified

images [Figure 1(C–D)]. The cross-section of the oxide

layer was shown in Figure 2 and the thickness of MAO

layer was about 6–8 lm.

Surface Characterization of Three Different Specimens

The phase of oxide layer formed by MAO process was

characterized by XRD analysis, as shown in Figure 3. The

peaks of titanium, anatase, and rutile were detected and the

surface titanium oxide on MAO-TNZS was predominantly

rutile TiO2.

The chemical composition of the surface layer formed

by the MAO process was determined by EDS analysis,

shown in Figure 4. Ca and P were detected in the oxidation

layer, which indicated that Ca and P from the electrolyte

were involved in the physicochemical reaction of the MAO

process.

The rugosity of three different specimens was listed in

Table II. The roughness values of Ti and TNZS surfaces

were very similar (Ra values of Ti and TNZS were 0.221

and 0.251 lm, respectively); MAO-TNZS surface showed a

significant increase in roughness (Ra values was 0.575 lm)

when compared with the other two (p\ 0.05).

As surface treatments modified the wettability, the water

contact angles on each of the test materials were summar-

ized in Table III. Significant decrease of the water contact

angle was found on TNZS specimen compared to Ti (p \0.05); moreover, MAO treatment significantly decreased

the water contact angle of the TNZS specimens from 56.49

to 41.71 (p \ 0.05). These results indicated that MAO

treatment effectively improved the surface hydrophilicity.

InVitro Biocompatibility Test

Viability and ALP Activity of Osteoblast Cells Grown

on Different Specimens. From day 1 to day 10, the viabil-

ity of osteoblast indicated by MTT assay continuously

increased in all three kinds of specimens (Figure 5). There

Figure 3. XRD spectra of MAO-TNZS, TNZS, and Ti. The peaks of

titanium, anatase, and rutile were detected and the surface titanium

oxide on MAO-TNZS was predominantly rutile TiO2. [Color figure

can be viewed in the online issue, which is available at www.interscience.wiley.com.]

Figure 4. EDS anaylsis of MAO-TNZS. The EDS results indicatedthat there were Ca and P in the microarc oxidation layer.

TABLE II. Surface Roughness Parameters for Ti, TTNZS, andMAO-TNZS Specimens’ Surfaces

Group Ra (lm) Rz (lm)

Ti 0.221 6 0.104 2.26 6 0.15

TNZS 0.251 6 0.017 2.63 6 0.28

MAO-TNZS 0.575 6 0.196 8.47 6 0.46



was no statistical difference from day 1 to day 4 (p [0.05); after day 7, significant differences were detected

between Ti and TNZS specimens (p \ 0.05) and the ab-

sorbance from MAO-TNZS group was significantly higher

than both Ti and TNZS group.

ALP-specific activity relates to the production of a min-

eralized matrix and it is an early marker for osteoblast dif-

ferentiation.23 Similar to the viability of osteoblast cells,

the ALP activity of Ti, TNZS, and MAO-TNZS groups

increased from day 1 to 10 (Figure 6). There was no statis-

tical difference on ALP activity among three kinds of

specimens at day 1 and 4 (p [ 0.05); but from day 7, the

ALP activity of cells grown on MAO-TNZS surface was

significantly higher than that of Ti and TNZS.

Above results indicated that MAO treatment promoted

the proliferation and increased the ALP activity of osteo-

blast cells grown on TNZS specimen.

The Morphology of Osteoblast Cells Grown on Differ-

ent Specimens. The SEM images of osteoblast cells grown

on TNZS and MAO-TNZS specimens for different culture

periods were shown in Figures 7 and 8. Cells attached,

spread, and proliferated on both substrates, with filopodia

extending from cell bodies. One day after plating, isolated

cells covered both of the substrates; from day 4, the cell

number became numerous and cells were connected to

each other with characteristic dendritic digitations; at day

7, well-flattened cells were observed on surfaces of TNZS

and MAO-TNZS; at day 10, cells adhered and spread on

top of each other for both samples.

Cells grown on TNZS surface arranged according to the

direction of grooves, but on MAO-TNZS substrate, a more

dense growth of osteoblasts with numerous cell–cell con-

tacts was observed. With magnification, it can be detected

that cells appeared long, flat, and the fine and long filopo-

dia formed a cellular group and located into the holes of

the porous layer of MAO-TNZS.

RTQ Tests of the MAO-TNZS and TNZS Implant

The removal torque of the specimens implanted in the tibia

of rabbits for 6 weeks was measured. The average RTQ

force value (51.8N) of MAO-TNZS implants was signifi-

cantly higher than both that of TNZS (32.3N) and Ti

implant (30.2N) (Figure 9).

Moreover, SEM images showed that the fracture line of

MAO-TNZS implant appeared inside the bone tissue,

between immature and mature bone; whereas the fracture

line of Ti and TNZS implant propagated between implant

surface and surrounding bone tissues (Figure 10).

DISCUSSIONS

TNZS is a novel b-titanium alloy with elastic modulus

closing to that of human bone and it has good balance

between high strength and low modulus. This unique

advantage can minimizes the undesirable phenomenon of

stress shielding-bone resorption and makes TNZS alloy an

excellent candidate for dental or orthopedic implant appli-

cation.24 However, it is known that the direct chemical

bond between Ti (Ti alloy) and bone tissue never happens.

So we tried to modify the chemical composition and mor-

phology of TNZS surface by MAO method, and then tested

its biocompatibility. For titanium implant, the surface tex-

ture and/or surface composition determine its interaction

with bone.23 When compared with smooth surface, the

roughened surface layer will encourage bony ingrowth and

provide the implant a morphological fixation, essentially a

TABLE III. Water Contact Angle in Degrees of Ti, TNZS, andMAO-TNZS specimens

Materials Water Contact Angle (8)

Ti 67.11 6 4.65

TNZS 56.49 6 4.50

MAO-TNZS 41.71 6 4.21

Figure 5. Osteoblast cell viability on the surface of Ti, TNZS, and

MAO-TNZS for D1, D4, D7, and D10. Since D7, increased high val-

ues of OD on MAO-TNZS were statistically noted for those of Tiand TNZS specimens (p\ 0.05).

Figure 6. ALP activity on the surface of Ti, TNZS, and MAO-TNZS

for D1, D4, D7, and D10. The statistic analysis of ALP data of MAO-

TNZS showed significantly higher absorbance compared with thatof the cells on the Ti and TNZS at D7 and D10 (p\ 0.05).

302 WU ET AL.


mechanical fixation to the bone.25 In our study, the SEM

images showed that after MAO treatment the TNZS surface

was firmly coated with a molten porous layer, which would

greatly improve its roughness. The cross-section image also

showed that the MAO layer was integrated with the TNZS

substrate without a distinct interface, which provided a

Figure 7. SEM micrographs showing osteoblastic cell morphology after D1, D4, D7, and D10 cul-

ture on TNZS surface. Cells on TNZS surface arranged with the direction of the grooves and‘‘contact guidance’’ phenomenon was observed.

Figure 8. SEM micrographs showing osteoblastic cell morphology after D1, D4, D7, and D10 cul-

ture on MAO-TNZS surface: The osteoblast cells on the MAO-TNZS substrate showed a more

dense growth and protruded multiple filopodia and located areas of pores to form anchoring struc-tures strongly adhered to the porous surfaces.



high bonding strength between the substrate and layer. In

Figures 1(C–D) and 2, the uniformity of the pore size and

homogeneity of the cross-section layer can also be

observed from different point of view. These characters

will make the surrounding bone ingrow uniformly into pore

space to the bottom of the porous layer and be tightly

bonded to the implants. In addition, MAO provides an ideal

method of producing uniform, even layers on implants with

complex surface geometries, such as screws and metal po-

rous coatings.

On MAO-TNZS specimens, rat osteoblasts cells

extended multiple filopodia and formed anchoring struc-

tures, which strongly adhered to the porous surfaces. But

on the untreated TNZS surface, the cells grew along the

direction of the grooves and attached to the bottom of the

grooves. On the other hand, the number of adhered cells

and the ALP-specific activity were increased after MAO

modification, which was also considered to be attributed to

the surface roughness.26–28 Therefore, the porous layer may

provide positive guidance cues for enhancing the osteo-

blasts cell attachment. Zhu also reported that the cells on

micron- and submicron-scale structures were observed to

enter the pores and attach to the substrate by filopodia, and

he attributed this phenomenon to pores acting as positive

attachment sites for the filopodia.29

Hydrophilicity is also an important factor for cells adhe-

sion to the substrates30 and in our study, the water contact

angle on the MAO treated TNZS surface was significantly

decreased compared with control specimens, which sug-

gested that the surface hydrophilicity was effectively

improved.

Furthermore, to improve and accelerate the integration

of titanium implant surfaces with bony tissue, researchers

have developed various biomimetic methods to produce

calcium phosphate coatings onto the surface, which imitate

the natural biomineralization process for the formation of

bones and teeth. In MAO process, Ca and P ions in electro-

lytes will enter the ceramic layer, exist in amorphous form,

and then increase the bioactive potential of titanium

alloys.31 Therefore, initial cell adhesion will change from

physical interactions to chemical ones. In our studies, Ca

and P ions were found in the coating layer after MAO

treatment and the osteoblasts grown on Ca and P-enriched

MAO-TNZS surfaces exhibited significantly higher viabil-

ity than on Ti and TNZS. Because the bone-like apatite

formed makes the surface bioactive, the bony ingrowth into

the porous layer of the TNZS will be appreciably acceler-

ated.

With MAO method, it can offer not only a mechanical

interlocking force between the bone and the porous surface,

which is necessary for a long-term clinical use, but also a

chemical bonding attained by the apatite-layer, which acts

on short-term fixation. So, hopefully, through the layer

both chemical bonding and mechanical interlocking can be

utilized to improve the implant surface and the ideal inter-

locking attachment will be achieved.32,33

Along with in vitro cell tests, the strong osteo-conduc-

tive effect of MAO-TNZS alloy is further investigated by

fractures through bone at RTQ testing. It is believed that

the fracture line propagation in the present study depends

Figure 9. Removal torque force values of Ti, TNZS, and MAO-TNZS implants. Mean RTQ force value of MAO-TNZS implants

showed significantly higher than that of the TNZS and Ti implants

after 6 weeks (p\ 0.05).

Figure 10. SEM analysis of bond failure shows that fracture line for the Ti, TNZS, and MAO-TNZS

implants. A and B: Fracture lines for the Ti and TNZS were more often observed between the sur-

face of the implant and immature bone. C: Fracture line for the MAO-TNZS implant more often

occurred between immature and mature bone while actual interface remained. (‘‘�’’ is the symbol ofthe MAO layer, ‘‘#’’ is the symbol of the fractured space during mechanical loads).

304 WU ET AL.


on how strong the bonding of the bone and the implant sur-

face/oxide film is and also the fracture yield strength of the

oxide film and bone perse.34 Theoretically, seven kinds of

interfacial bond failure exist between bone and implant

when mechanical loads applied including (1) at the tita-

nium substrate/coated materials (oxide films), (2) inside the

coating materials (oxide films), (3) at the interface implant

surface (oxide)/immature bone, (4) inside the immature

bone perse, (5) between the immature bone and the sur-

rounding mature bone, (6) in the surrounding bone, (7) any

combined fracture types-heterogeneous fracture mode.35

Where the actual bond failure occurs may be determined

by the biochemical bonding strength in this study. In this

RTQ tests, the fracture line analysis showed that interfacial

bond failure generally, occurred at the bone to implant

interface for Ti and TNZS implants and mainly occurred in

the bone for the MAO-TNZS implant. This indicates that

the biochemical bonding strength of the MAO-TNZS

implant was stronger than bonding strength between the

bone tissues, that is, the amorphous immature bone and the

surrounding mature bone. Furthermore, SEM observation of

the MAO-TNZS implant confirmed that fracture line did

not occur at the implant-surface oxide interface or in the

oxide layer, proving that the MAO process may not suffer

from the same possible problem as plasma-sprayed CaP

coatings, that is, delamination. The similar results by Li9

also showed that the RTQ test of the MAO-treated Ti

implants was much higher than that of the untreated Ti

implants. And he also attributed this enhancement to the

increase of surface roughness and to the presence of the Ca

and P ions, which were incorporated into oxide layer dur-

ing the MAO process.

In summary, MAO is a simple, controllable and cost-

effective method of producing porous TiO2 layer on the

TNZS implant surface. Our results revealed that the

micro-arc oxidation may be an effective tool for

improving the biocompatibility of Ti-24Nb-4Zr-7.9Sn

implants.

CONCLUSION

The Ca-incorporated MAO-TNZS, by bringing about posi-

tive physical and chemical changes to the TNZS surface,

demonstrated significantly stronger integration in bone

when compared with Ti and TNZS.

With MAO treatment, the thickness and roughness of

the oxide layer was greatly enhanced, as well as the con-

centrations of Ca and P ions in the oxide layer. As a result

of these changes, both the cell viability and ALP activity

increased. The in vivo tests showed a considerable increase

in removal torque after the MAO treatment when compared

with the machined Ti and TNZS samples. These results

demonstrated that the microarc oxidation may be an effec-

tive tool for the improvement of the biocompatibility of Ti-

24Nb-4Zr-7.9Sn implants.

We would like to thank Dr. Yu-lin Hao for providing us withTNZS material.

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Improved biological performance of microarc-oxidized low-modulus Ti-24Nb-4Zr-7.9Sn alloy