Development of Titanium Alloys
for Load Bearing Implant Devices
through Focusing on Young’s Modulus Control

Mitsuo Niinomi
Institute for Materials Research, Tohoku UniversityProperties required for medical metallic materials

aArtific
Artificial人工歯根
dental implants
ial

人工肩関節
Artificial
shoulder joints

Spinalfixation
腰椎固定用品devices

Artificial
elbow
人工肘関節
jointsArtificial
hip joints
人工股関節

Artificial finger joints
人工指関節Bone fixation devices
骨接合用品
Artificial
ankle
joints人工足関節

High mechanical reliability

Artifici
Artificial
knee joints
人工膝関節
alProperties required for medical metallic materialsReducing stress shielding

Bone absorption or shrinking occurs due to the remodeling according to thedecrease in mechanical stimulation when, for example, the artificial joints orbone plates made of the conventional high modulus metallic materials are
implanted or fixed to the fractured bone. They become to be the causes
loosening of the artificial hip joints or re-fracture of bone after extraction.
Development of metallic materials
with low moduli, which are similar tothat of the cortical bone is required.

Stres shielding
Brittlement of bone・Bone absorption

SUS316L stainless steel: 180 GPa
Co-Cr alloys : 210 GPa
Ti-6Al-4V ELI: 110 GPa
Cortical bone: 10-30 GPa

Properties required for medical metallic materials
Allergy problems appeared on fingersand hands due to metals in the mousev

Oxide
filmv

Metal

Disslusion ofelements

Allergic and toxic problems happen
when
the amountof dissolved metallic
Requiredproperties:
elements
exceeds
acceptableamount1. Highcorrosion
resistance toprevent. dissolution ofmetallic elements.
2. Using elements showing low toxicity and allergic
problems
T. Jarmar et al., J. Biomed. Mater. Res. A 87 (2008) 1003-1009.

Properties required for medical metallic materials

High mechanical reliability
High corrosion resistance to prevent
dissolution of metallic elements
Using elements showing low toxicity andallergic problems
Low Young’s modulus close to that of bone

Table Biocompatibility of various biomaterials judged by patterns of osteogenisis

Pattern of osteogenisis

Biomaterials

Intervend osteoginisis

Stainless steel, Vitallium,
PMMA(Polymethyl methacrylate)

Biotolerant materials

Contact osteogenisis

Titanium, Tianium alloys,Carbon, Alumina, Zirconia,
Titania, TiN, Si3N4

Bioinert materials

Bonding osteogenisis

Bioglass, Ceravital,
Tricalcium phosphate,
Hydroxyapatite,A-W glass ceramic

Bioactive materials

Crystal structures of titanium alloys+(a)Hexagonal close packedstructure(HCP)
α-type titanium alloy(c) Body centeredstructure(BCC)
β -type titanium alloy(b) HCP＋BCC(α+ β) -type titanium alloy

Fig. Schematic explanation of α-, (α + β)-, and β-type titanium alloys
based on crystal structure.
7

β-type titanium alloys are advantageous fordeveloping low Young’s modulus medical
metallic biomaterials.

Many kinds of low modulus β-type titanium alloys
with non-toxic and allergy-free elements
have been developted,.
Representative ones , for example, are as follows:
Ti-13Nb-13Zr (ASTM F1713-96) : near β type，Low modulus
Ti-12Mo-6Zr-2Fe (ASTM F1813-97): β type, Low modulus
Ti-15Mo : β type (ASTM F2066) (U.S.A.), Low modulus
Ti-16Nb-10Hf : β type, Low modulus
Ti-15Mo-2.8Nb-0.2Si-0.26O : β type, Low, modulus
Ti-35Nb-7Zr-5Ta (TNZT) : β type, Low modulus
Ti-29Nb-13Ta-4.6Zr (TNTZ): β type, Low modulus
Ti-Mo-Sn：β type, Low modulus
Ti-40Ta, Ti-50Ta : β type, High corrosion resistanceNickel sensitization in the population, [%]Polarization resistance (R/Ωm)

Toxic

Coefficient of fibroblastic outgrowth

Selection of non-toxic
and allergy-freeelements

1.8
Ti
1.6
InSn
Ni
Pd
1.4Ta Zr
1.2 Control : GlassAu Cr Si
1.0AlAg
0.8
Bi0.6
Fe Co0.4 Sr
Mg V,Cu,Zn0.2
Toxic Mo ?
Cd,Hg
00 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6
Relative growth rate of L-929 cells

Low

Biocompatibility

highZn Au Cd
1.8%1.5%
Pt 1.8%
Sb0.4%
Cu 3.6%
11.3%

2520Females under 30

Hg
23.0%

Cr

109.5%

5

Pd
11.3%

0Ti
Co-Cr Ta
316L
Toxic
Zr
304L
Cu
NbVPtAg
Al Au
Vital
NiMoFeCo

Fig. Corrosion resistance andbiocompatibility of representative
pure metals and metallic biomaterials

Fig. Cyto-toxicity of pure metals

15Capsule

Males under 30

Ni
13.5%

CoSn
12.8% 13.5%

84 86 88 90 92 94 96

year

Fig. Frequency of nickel sensitizationin the population.

Fig. Rate of metallic allergyof each pure metal.

2.90

Average bond order / Bo

2.86

Nb, Ta, and Zr are the most suitable
for alloying elements.

Target region
for designed alloy

2.88

β-type region

2.84

Low Young’s modulus β-type
Ti-Nb--Ta-Zr alloys

2.82
Slip deformation

2.80

Twin deformation

2.78

Ti

2.76
2.74 (α + β)- type region
2.72
2.25

2.30

2.35

α-type region

2.40

2.45

Average d-orbital energy level / Md

Bo-Md map.

2.50

Ti-29Nb-13Ta-4.6Zr(TNTZ)Table Young’s moduli of (α + β)− type Ti-6Al-4V ELI ,β -type Ti-29Nb-13Ta-4.6Zr (TNTZ), and cortical bone.
Material
Ti-6Al-4V ELI (WQ)

Young’s modulus (GPa)110

Ti-29Nb-13Ta-4.6Zr
・WQ
・WQ + aged at
673 K for 3.6 k
・WQ + CW

9755 - 60

Cortical bone

10 - 30

63

WQ: Water quenching after solution treatment
AC: Air cooling after solution treatment
CW: Cold working

EXPERIMENT 1: BIOCOMPATIBILITY TEST
φ 5x10 mm

Implantation of columnar
specimen into lateral femoral condyle
under intravenous
anesthesia.

C. M. R of boundary of bone and columnar specimen implanted into lateral femoral
condyle of rabbit at 8 weeks after implantation.

C.M.R.

DirectTNTZ

DirectTi6Al4V

Lucent line

SUS316L

Regarding biocompatibility, TNTZ is equal to or
possibly greater than Ti6Al4V both showing
direct contact, and much better than SUS316L
with a radio lucent line.

Evaluation of bone formation versus low modulus
Experiment 1 : Intramedullary fixation
Intramedullary rods made of
Ti-29Nb-13Ta-4.6Zr (TNTZ),
Ti-6Al-4V ELI and SUS 316 L
stainless steel
1.

Keeping
Fibula intact

Experimental fracture of thetibia

Longitudinal drilling

3.

2.

Sawing Tibia

Driving metal rod

Remodeling at 24 weeks after implantation

Bone absorption

Boneformation

TNTZ

Ti-6Al-4V ELISUS316LRESULT 2: C.M.R. CROSS SECTION AT 24W
Newly formed
cortical bone

TNTZ
(around 60 GPa)

Ti6Al4V(around 110 GPa)(around 160 GPa)

SUS316L

Based on the design ofAO mini dynamic compression plate(AO mini DCP)
AO mini DCP for humanfinger, the bone plate weremade of TNTZ.
The plate and screws ofTi-6Al-4V and SUS316L
were also provided ascontrol.

0.5

42

2.0

4.5
4.0

5.0

0.5

t=1.5

As experimental animal,mature New Zealand whiterabbits (all male, weightabout 3kg) were used.

Increase of tibia diameter in TNTZTheAIA

structureAH M

M HPIPAwithis

wall
observeddifferentX-P

densities and a clear
boundary line at themiddle and distal levels

BBis observed×50Middle

The shape of the innerwall is close to theoriginal cortical bone,
The outer wall seems
to benewly formed
cortical bone.

AA

The inner wall seems
to be the remains of oldcortical bone.

BB

double×50

DistalBone remodeling according
to the stress condition occurs

Principle for developing new medical devices

Material development for specific devices

Plug

Rod
Screw

Spinal fixation device is composed of tree parts of rod, screw andplug. Spine is corrected to be normal shape using two rods.

Principle for developing new medical devices
plug

Scoliosis
Operationrodscrew

Bending

Back view

Side viewPrinciple for developing new medical devices
Operation with spinal fixture

Bend during operation→ Portion needed bending is unknown before operation(treatment before operation is difficult)Space for bending is narrow → High bending formativeness is required.
Scratch is formed by contacting with bending device. → Fatigue strength is degradedby notch effect.

Required property: bending formativeness(easy operation)

Principle for developing new medical devices

Factor, which determines bending formativenessDifficultEasinessof bending
formativenessEasy&High

Springback

Small

Bending formativeness is higher with decreasing springback.

Principle for developing new medical devices

Concept of supressing springback

StressHighLow

Young’s modulus

Springback

StrainSmallLarge
Elastic recoveredstrain

Springback is smaller with increasing Young’s modulus
Fig. The relationship between Young’s modulus and springback

Principle for developing new medical devices

Young’s modulus required for spinal
fixation devices
SuregeonsHigh Young’smodulus

High formativeness is required.
Conflicting requirement

Patients
Suppressing stress shielding isrequired.

Low Young’smodulus

Achieving Young’s modulus satisfying both
requirements of surgeons and patients.

Principle for developing new medical devices
Titanium alloy of which Young’s modulus is changed
during operation
Low Young’salloys
modulusLow Young’s modulus(Biomedical titanium
phase: β phase
Low Young’swith changeable Young’s modulus)

modulus：good for patients

Bending

RodHigh Young’smodulus:
good for surgeon

High Young’s modulus: deformationinduced-transformation

β-typeα-type(α + β)-type(Meta stable)(Stable)1155 KMs（β→α’ or α”）

Temp.
Roomtemp.

αβα+ββ+ω

PureTiLowhcp-αphase

β transus（β→α+β）

β stabilizing element

β stability
hcp-α′
phase

orthorhombic- hexagonal(trigonal-)ω
α″ phasephase

Highbcc-β
phase

Relationship between schematic phase diagram of tittanium alloys and β stability.

Determining deformation induced phase
Realization of increase inYoung’s modulus bydeformation

ST: Solution treatment
CR: Cold rolling

β-typealloy Aβ-type
alloy Bβ-type
alloy Cωωωβ

CR

CRα’ST

CRα”

STCRNo phasetransformation

STα’

Young’s modulus , E / GPaα”

STChange in Young’s modulus due to deformation

Ti-12Cr

Utilizing ω phase is effective to increase Young’s modulus by deformation.

Optimizing alloy composition (example of Ti-12Cr)
Ti-10Cr ST

Ti-11Cr ST

Ti-12Cr ST

ωβ

Ti-13Cr ST

Ti-14Cr ST

Circular streaks related to athermal ω phase are recognized.
Amount of athermal ω phase is decreased due to increase in β stability.

Optimizing alloy composition (example of Ti-12Cr)
Ti-10Cr CR

Ti-11Cr CR

Ti-12Cr CR

ωβ

Ti-13Cr CR

Ti-14Cr CRDeflection from ω phase becomes to be strong → Formation ofdeformation induced ω phaseDetermining deformation induced phase

ヤング率，E/ GPa
Young'smodulus,E/GPa
Young’smodulus，E/ GPa

Change in Young’s modulus and microstructure due todeformation

110

After deformatioCR
Before deformation
ST

9070

Maximum increaseat 12Cr

5030
10Young’smodulus
increases by formationof deformation inducedω phase.

11121314
Chromium
content/%
Crcontent / (%)

Characteristics of Ti-12Cr
Ratio of springback per unit load, R/(% N-1)

Springback
0.07

TNTZ
Ti-30Zr-3Cr-3Mo△ Young’s modulus changeable
alloy ATi-17Mo□ Young’s modulus changeable alloy B
Ti-12Cr■ Young’s modulus changeable alloy C
Ti-11Cr-0.2O○ β-type alloy A

0.06
0.05

Young’s modulus changeable alloy (Ti-12Cr)

0.04
0.03

Deformation induced ω phasetransformation

0.02
0.01
0246Applied strain (%)

810

Biomedical titanium
alloy withchangeable Young’s
12modulus

Springback is supressed by increasing Young’s modulus due todeformation induced w phase transformation.

Future of titanium alloys with changeable Young’s modulus forbiomedical applications
New usage of deformation induced ω phase
Spinal fixation devices
Utilize deformation
Induced ω phasetransformationtosupress springback

Utilize deformationinduced ω phase tocontrolling shapeSelf-tunable Young’smodulus

Expanding scope of applications

Metallic medical devices,which exhibit optimized
mechanical functionality
according to theindivisual usage
Cerebral aneurysm
Bone fracture conditions such as treated
Artificial hip
Intramedullary
jointsfixation devices
rods
area, sex, year, living
Strengthening of loading portion by deformation induced ω phasecircumstances like living
Stress responding self-strengthening
functiontissues can be developed.

Thank you very much for your kind attention!