Symposium on Materials ChallengesFor Safety and Reliability y y

4th World Materials Research Institute ForumIMR-CAS, Shenyang

Biomedical titanium alloys for improved implant reliability and compatibility

Rui Yang, Yulin Hao and Shujun Lig, j

Shenyang National Laboratory for Materials ScienceInstitute of Metal Research, Chinese Academy of Sciences

23 May 2011

Earliest application of biomedical materials

• Artificial toe made of wood and leather found on a mummyD t d t l t 4000• Dated at least 4000 years ago

• Used by its carrier for both aesthetic and functional values

2

Current problem of orthopaedic implants Stress shielding: Reduction in bone stress in vivo following the introduction of orthopaedic implants and it causes loss of bone and loosening of the implant.

Statistical significance of correlation between severe t hi ldi d i i fl i f t

3

stress shielding and various influencing factors.

Z. Wan, L.D. Dorr, T. Woodsome, A. Ranawat and M. Song, J. Arthroplasty 1999; 14: 149

The alternative design does not work

Overhauling implant design has greater effect on stress distribution than anything possible by altering material properties but newthan anything possible by altering material properties, but new

design is not considered safe(bars show changes in absolute values of the major principal strains,

% of the intact femur, after implantation)

4R. Decking, W. Puhl, U. Simon, L.E. Claes, Clin. Biomech. 2006; 21: 495

% of the intact femur, after implantation)

mented and cementless implant

Survival of cemented and cement-less hip prostheses in Finland (1985 1999)

portunities for low-modulus implant materials

alleviate short-m/long-term designm/long term design nflict

reduce sensitivity of plant performance to

dividual factors

allow incrementalallow incremental provement to current signs

Survival of hip prostheses in Finland 1985-1999, by age of patient

anium alloys as implant materials: story and current problemsstory and current problems

ee generations of development: Problems to be solved:g pTi-6Al-4V (Aerospace alloy)Ti-6Al-7Nb (Removes poisonous elements)

(by alloy design)1. Some alloys still contain

i l t ( Al)Ti-13Nb-13Zr (To reduce modulus) poisonous elements (e.g., Al)2. Elastic modulus still too

high compared to human ar 7 alloys are approved by M for surgical implant (only 3 roved in China *):

ghard tissue

(by surface engineering)1 Bi ti it t id lTi *

Al-4V *Al-2.5V

1. Bioactivity not ideal2. Relatively poor wear

resistanceAl-7Nb*F

3. Corrosion resistance can be further improved

st recent developments: m Metal (Toyota) vs Ti2448 (IMR)m Metal (Toyota) vs. Ti2448 (IMR)

Ti2448 Gum MetalTi2448 Gum Metal

P ti Ti2448 G M t l

H. Ikehata et al. MRS Bullitin 2006; 31: 688et al., Acta Biomater. 2007; 3: 277.

Properties Ti2448 Gum MetalElectron/atom ratio 4.15 4.24Dynamic modulus (GPa) 40 42 55 65

ta type biomedical titanium alloys: mmary of recent developmentmmary of recent development

Ti-29Nb-13Ta-4.6Zr Ti-15Mo

Ti-13Nb-13ZrTi-35Nb-5Ta-7Zr

GUM METALTi-12Mo-6Zr-2Fe

Ti-15Mo-3Nb-0.3O

"

Ti-V Ti-Nb Ti-Mo

Ti 24Nb 4Z 8S

Fedotov, Proc. of 2nd World erence on Titanium (1973)

ficulty in reducing elastic modulus

MetalsAlloys

GraphiteCeramicsSemicond

Composites/fibers

strength and elastic ulus of metals tend to ease or decrease

Al oxide Carbon fibers only

600800

10001200

400 TungstenSi carbide

Diamond

ySemicond

Ti

ultaneously

ngth must be maximised

Platinum

Silver Gold

Tantalum

Zinc, Ti

Steel, NiMolybdenum

Si crystal

Gl d

Si nitrideAl oxide Carbon fibers only

Aramid fibers only

80100

200

400

Cu alloys

Tungsten

<100>

<111>

AFRE(|| fibers)*

CFRE(|| fibers)*

Ti: ~110GPa

rder to ensure the ue life and thus the bility of the implant

Magnesium,AluminumSilver, Gold Glass-soda

Concrete

CFRE*

GFRE*

Glass fibers only

20

406080

Tin GFRE(|| fibers)*

AFRE(|| fibers)

Bone:

hanisms such as stress-ced martensitic sformation are

8Graphite

AFRE( fibers)*

CFRE*

46

10

Polyester

PSPET

CFRE( fibers)*

GFRE( fibers)*Bone: <30GPa

sformation are ficient in this task

problem must be

1

PC Epoxy only

0 8

2

HDPEPP

PS

E GP

problem must be led from a more amental level

k modulus of Ti-TM binary alloys: Predictions

method was proposed to estimate the bulk modulus of Ti-TM nary alloys based on first principles computationnary alloys based on first principles computation

followed by Nb, Ta, was predicted to lower the bulk modulus of c Ti

oice of primary binary system: Ti-Nb

does not change the e/a ratio of Ti (same group)is high melting thus difficult to process and also too expensiveNb is a suitable primary system: intrinsic minimum of E at e/a ~4.15

4 wt.% Nb)Ti-NbTi Nb

moving the modulus peak

Both Zr and Sn reduce Ms for "wt.% of Nb, Zr, Sn reduces Ms by 7 6K 41 2K 40 9K ti l7.6K, 41.2K, 40.9K, respectivelyr + Sn suppress the r and Sn are potent strengtheners for i alloy

Alloy T, C MS, C Phase E, GPa

Ti-24Nb ~700 380~400 ++ ~90

ect of alloying on phase stability: Computation

A+first principles mputation enable sonably accurate atment of solid

tiutionsth Nb and Sn are bilizing elements h respect to the ase and can vent formation of phases neutral

ect of Sn on elastic properties of 24Nb 4Z b d ll24Nb-4Zr based alloysminimum of bulk modulus (B) and Poisson’s ratio () at 9wt % Sn was identified9wt.% Sn was identifiedr the 7.9wt.%Sn alloy, the bulk modulus (B) approximately uals the shear modulus (G)

50

60

0 30

0.35E Depending on impurity

40

50

0.25

0.30

B

Poisso

Bulk modulus：17-24 GPaShear modulus：21-23 GPa

contents and heat treatment:

20

30

0.15

0.20

Gon's rat

Shear modulus：21-23 GPaYoung’s modulus：40-50 GPaPoisson’s ratio：0.09-0.14

7.5 7.6 7.7 7.8 7.9 8.0 8.1 8.210 0.10

G io

S t t %

B G E/2

astic modulus of Ti2448 single crystals

E011

E001

E111

E011E001

Ti V

E111

4 0 4 2 4 4 4 6 4 84 2 4 4 4 6 4 8

Ti-V Ti-Cr Ti-Nb

4 0 4 2 4 4 4 6 4 84.0 4.2 4.4 4.6 4.8

Electron/atom (e/a) ratio4.2 4.4 4.6 4.8

ectron/atom (e/a)ratio

G011

G111

G001

4.0 4.2 4.4 4.6 4.8

Electron/atom (e/a) ratio

011

111

Ti V

001

Ti-V Ti-Cr Ti-Nb

chanical properties of Ti2448

ery short linear elastic stage; mostly non-linear elatic deformation; bsence of “double yielding”y glastic strain recovery of 3.3% occurs at 4% applied strainensile strength ~850MPaignificant elastic softening was found (decrease of incipient Young’significant elastic softening was found (decrease of incipient Young s

modulus with prestraining)1000

65

600

80065

43

MP

a) 42GPa33GPa

850 MPa

400

6002

tress

(M

1

18GPa

0

200S 1

ay and TEM show large elastic deformation

>3% elasticity confirmed by x-ray measurementTEM observed significant recoverable lattice distortion

8000

1%

Unloading after 4% strain

4000

6000 1%2%3%4%

Before loading

2000

37.5 38.0 38.5 39.0 39.50

(110) diffraction peaks

2, Degree

.L. Hao et al., Phys. Rev. Lett. 2007; 98: 216405

situ neutron diffraction analyses

2.0

2.5

y

5MPa 159MPa350MPa

(110)• Below ~500 MPa (200) spacing

change contributes more to the

1.0

1.5

y 350MPa 396MPa 472MPa 537MPa 594MPa

change contributes more to the reversible strain

• Above 500 MPa (110) spacing change contributes more

2.10 2.15 2.20 2.25 2.30 2.35 2.40 2.45

0.5 650MPa

change contributes more• Switchover at ~1.5%

Lattice spacing, nm/10

600

700

300

400

500

600

s, M

Pa

100

200

300 (110) (200)SpecimenSt

ress

plications of B≈G in crystals

Lowest bulk modulus (23.9 GPa) of known structural metalsLowerest Poisson’s ratio (0.14) second only to Be

•The bulk modulus B measures resistance to bond breaking

•The shear modulus G measures•The shear modulus G measures resistance to bond angle change (bending)F t t l d ll B G•For most metals and alloys B > G

onsequence of low B: Large elastic lattice stretching

servation of amorphization and no crystal formation during compressionno crystal formation during compression

ghly localised plastic deformation

~[111] [ ]

ntation m

1m

1m~[113]

m

Intersection and extension of shear bands leading to refinement of coarse grains to tens nanometer

w mechanisms of elastic deformation d grain refinement

Alloy B (GPa) G (GPa)

d grain refinement

4Nb-4Zr-7.9Sn 23.9 22.7 0.144Nb-4Zr-7.6Sn 43 21 0.29

er Sn contentscreate a more favourable condition for slipenable martensitic transformation (”)

u stretching experiment under TEM found that, i i t i 3 h i f l ti

enable martensitic transformation ( )

increasing strain, 3 mechanisms of elastic rmation operate:

fy planar lattice

ti

Reversible motion of dislocation loops

nucleated

Stress-induced martensitic

t f ti

situ observation of homogeneous nucleation d reversible movement of dislocationsd reversible movement of dislocations

om dipoles to disclinations: A mechanism of pid nano grain formationpid nano-grain formation

ect of low modulus and high elasticity:ramedullary nails on fractured tibiaramedullary nails on fractured tibia

Ti2448Ti-6Al-4V

448 Ti-6Al-4V l out force:l out force:

7.9N 110.9N

ne volume fractions:8% 32 6%8% 32.6%

Micro-CT analysis

gh cycle fatigue properties of Ti2448

gue strength/yield strength ratio 0.50.6，similar to conventional beta titanium alloystitanium alloys

gue strength can be improved by heat treatment and TMPm rolling + triple heat treatment improves fatigue strength to >1000MPa

500

600

a

As-forged1000

1100

1200

a

R=0.1

400 re

ss, M

Pa

R=0.1800

900

1000

ess,

MPa

Warm rolling Warm rolling + aging

104 105 106 107200

300R=-1

Str

104 105 106 107500

600

700Stre

10 10 10 10 N

104 105 106 107

N

lationship of fatigue strength to Young’s dulus of titanium alloys

1200a

dulus of titanium alloys

1000

1200Ti2448-O(WR+HT)

, MP

a

R = 0.1

600

800 Ti2448-O(WR)

engt

h,

400

600

type alloysTi2448(WR)

ue s

tre

0 20 40 60 80 100 1200

200 type alloys CP-Ti

Fatig

u

0 20 40 60 80 100 120F

Young's modulus, GPa

ain-controlled low cycle fatigue of Ti2448

6

%

R=0.3 R=0.1 R=-1R=0.1(Ti-39Nb-13Ta-4Zr)

(a)

4

5

m st

rain

, %

( )

2

3

Max

imum

5.05.5

(b) R=0.3 R=0.1 R=-1R=0.1(Ti-39Nb-13Ta-4Zr)

4(c) R=0.3 R=0.1 R=-1

R=0 1(Ti-39Nb-13Ta-4Zr)

100 101 102 103 104 1052

Reversals to failure, 2Nf

3 03.54.04.5

stra

in, %

R 0.1(Ti 39Nb 13Ta 4Zr)

2

3

stra

in, %

R=0.1(Ti-39Nb-13Ta-4Zr)

2.02.53.0

Ela

stic

1

Plas

tic

w notch sensitivity of Ti2448

600

700

MPa

smooth Kt=3Kt=3 5

R = 0.1

300

400

500

ic st

ress

, M

Kt=3.5 Kt=4

105 106 107100

200Cyc

li

N b f l t f il

Material K =3 r=0 34 K =3 5 r=0 28 K =4 r=0 14Notch sensitivity factor q in the range 106 cycles

Number of cycles to failure

Material Kt=3, r=0.34 Kt=3.5, r=0.28 Kt=4, r=0.14

Ti2448 (R=-1) 0.37 0.27 0.27

Ti2448 (R=0 1) 0 33 0 35 0 26Ti2448 (R 0.1) 0.33 0.35 0.26

Ti2448 (R=0.3) 0.30 0.28 0.26

Ti 13Nb 13Z 0 78 0 70 0 79

gh threshold / low crack propagation rate

1E-3

ycle

)

1E-5

1E-4

N

(mm

/cy

TC4 Ti Ti2448(R=0.1)

10 20 30 40 50 601E-6da

/dN

K (MP / 1/2)

100µm100µm

Pure Titanium

500µm

K (MPa/m1/2)1E-4

cycl

e)

Ti2448 alloy

1E-5 N

(mm

/c

500µm500µm 100nm100nm

Ti2448 alloy 25 30 35 40 451E-6da

/dN

K (MP / 1/2)

200µm

ack growth experiments

000 cycles 1 000 000 l300 000 l,000 cycles 1,000,000 cycles300,000 cycles

plication

February 2008: Tests of biochemical compatibility authorised by the State Food and Drug Administration of China completed

June 2009: Clinical trials of bone plates and nails in human body completed

M h 2010 Cli i l t i l f i l fi ti l t dMarch 2010: Clinical trials of spinal fixation completed

nical trials: Ankle bone repair

nical trials: Shoulder bone repair

nical trials: Tibia repair

nical trials: Spinal fixation

mmary

A new titanium alloy Ti2448 for biomedical use was developed– High strength (850 MPa) /excellent fatigue properties– Lowest bulk modulus of structural metals (23.9 GPa), and incipient

Young’s modulus almost matching that of human bone (~40 GPa)– Superelastic deformation up to 3.3%– Good biocompatibility

New mechanisms of elastic deformation: lattice distortionNew mechanisms of elastic deformation: lattice distortion, reversible motion of dislocation loops nucleated homogeneously

The alloy has passed biochemical compatibility tests authorised by e a oy as passed b oc e ca co pat b ty tests aut o sed bythe State Food and Drug Administration of China, and has completed clinical trials of typical implants in hospitals

Low modulus ensures improved biomechanical compatibility and safety of implants; High recoverable strain enables high fatigue strength and thus improves life-time and reliability

knowledgements

G d t St d tGraduate StudentsDr Caiyun Zheng, Dr Yanwei Zhang, Dr Siqian Zhang, Dr Edward G. ObbardDr Edward G. Obbard

Collaboration withWego GroupProfessor Zheng Guo, The Fouth Military Medical University Professor Yue Zhu, China Medical UniversityProfessor Yue Zhu, China Medical UniversityProfessor Manling Sui, Beijing Polytechnical University

Funding fromMoST 973 grant 2006CB605104