Ti-15Mo for Trauma Applications

Transcription

1 Ti-15Mo for Trauma Applications John Disegi Synthes Technical Center West Chester, PA International Titanium Association 25th Annual Conference September 13-16, 2009 Waikoloa, Hawaii

2 Outline Alloy Design History Material Properties Implant Product Testing

3 Alloy Design History

4 Ti-15Mo Alloy Design Mo is an isomorphous beta stabilizer 1 -- min 10% beta stabilizer content (β c ) is needed in a Ti-Mo binary alloy to stabilize the beta structure at room temp -- will not decompose to form α + intermetallic compound XRD studies have verified that only β phase with a bcc structure is present when Mo content > 10% 2 1 Bania P, et. al., Beta Titanium Alloys and Their Role in the Titanium Industry, in Beta Titanium Alloys in the 1990 s, D.Eylon (Ed.), TMS, 1993, pp Ho W, Structure and properties of cast binary Ti-15Mo alloys, Biomaterials, Vol 20, 1999, pp

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6 Ti-15Mo Early History Originally developed by IMI Titanium Ltd for improved corrosion resistance in the chemical industry Aerospace applications were abandoned because of thermal handling problems and microstructure instability at moderate temperatures Ti-15Mo-5Zr was developed to minimize effect of solution treatment cooling rate without t suppressing α precipitation it ti during aging 1 Ti-15Mo-5Zr-3Al was developed by Kobe Steel to solution harden the α precipitate and retard ω phase formation during aging 1 1 Bania P, et. al., Beta Titanium Alloys and Their Role in the Titanium Industry, in Beta Titanium Alloys in the 1990 s, D.Eylon (Ed.), TMS, 1993, pp 3-14

7 Rationale for Implant Use Unique properties p of binary Ti-15Mo composition were not retained with the Zr and Al modifications Early material testing verified an excellent combination of biocompatibility, mechanical properties, and corrosion resistance Initial alloy screening suggested potential advantages for implant trauma applications Design opportunities related to tailored mechanical properties depending di whether the annealing temp was 725 C (α + β ) or 800 C (β)

8 Material Properties

9 Physical Properties Implant Density Modulus of Material (gm/cm 3 ) Elasticity (GPa) 316L ss Ti-6Al-4V ELI Ti-6Al-7Nb Ti Grade α + β Ti-15Mo β Ti-15Mo

10 Corrosion Resistance in Reducing Acids Accelerated Corrosion Rates (mm / year) 1 Material Boiling 5% HCl Boiling 10% HCl Boiling 5% H 2 SO 4 Boiling 20% H 2 SO 4 60 C 30% H 3 PO C 30% H 3PO 4 Ti Grade Ti-15Mo IMI Titanium 205, Alloy Data Sheet, IMI Titanium Ltd., Birmingham, England

11 Low Modulus of Elasticity E closer to bone (4-20 GPa) Prevents stress shielding -- bone must be stressed during the healing phase for normal consolidation -- high E can lower stress transfer to the bone ( stress shielding) -- low E is desirable for load sharing devices

12 Minimum Tensile Properties for Round Implant Bar Material Cond Standard UTS 0.2%YS Elong X ROA (MPa) (MPa) 4D (%) (%) Ti-15Mo β Anld ASTM F 2066 Ti Grade 4 CW ISO Ti-15Mo α + β Anld ASTM F Ti-6Al-7Nb α + β Anld ASTM F

13 Notch Tensile Comparison (Kt =3.2) ASTM E 602 Method for Sharp-Notch Tensile Testing NTS = Sharp Notch Tensile Strength NTS UTS >> 1.10 NSR (Notch Strength Ratio) = NTS Smooth 0.2% YS Material Condition NTS UTS NSR Ti-15Mo ß Anld L ss CW Ti Grade 4 CW Ti-6Al-7Nb Anld

14 Smooth Tension -Tension Corrosion Fatigue Testing Parameters --- Low stress ground rods --- ASTM F 1801 Corrosion Fatigue Testing of Metallic Implant Materials --- Load 1Hz frequency --- Aerated Ringer s 37 C Notch --- Kt factor 3.2

15 Ti-15Mo Smooth and Notched Endurance Limits 1 Alloy Condition Endurance 10 6 Cycles (MPa) Smooth Notched Ti-15Mo Aged α + β Ti-15Mo β Ti-6Al-4V ELI α + β Roach M, et al, Comparison of Corrosion Fatigue Characteristics of CP Ti Grade 4, Ti-6Al-4V ELI, Ti-6Al-7Nb, and Ti-15Mo, Journal of Testing and Evaluation, Vol 2, No 7, July-August 2005

16 Ti-15Mo Biocompatibility Testing Good Laboratory Practice Non GLP -- Rabbit Pyrogen -- Mo Sensitization Search -- Acute Systemic Injection -- Mo InVitro Organ Culture -- Agar Diffusion Cytotoxicity -- ASTM F 1408 Short -- Elution Cytotoxicity Term Muscle Implantation -- Mutagenicity (Reverse -- ASTM F 981 Long Term Mutation Assay) Bone Implantation

17 Implant Product Testing

18 Implant Plate Testing: Reverse Bend CMF plates tested according to ISO 7801 Metallic materials - Wire - Reverse bend test inserted between two vertical fixtures gripped constant distance above fixture bent 90 + returned to vertical (one cycle) bent 90 in opposite direction, returned to vertical, cycles repeated to fracture

19 Reverse Bend Testing

20 2.0 mm Intermediate Locking Plate 2.4 mm Universal Fracture Plate 2.4 mm Locking Reconstruction Plate

21 Reverse Bend Testing of Annealed dcmfpl Plates Lock Recon 20 Univ Frac 2.0 Locking 10 0 Ti Grade 4 Beta Ti- 15Mo

22 1.15 mm Thick CMF Adaption Plate

23 Reverse Bend Testing of CMF Adaption Plate 90 o Reverse Bends to Failure Bends to Failure α-β Ti-15Mo 316L Ti4 Ti2 TAN Ref: MT08-038

24 Four Point Bending Fatigue Test plate attached to two Delrin blocks with six screws torqued to 1.2Nm 35 mm span between blocks (fracture gap model) 6mm diameter rolls / 50mm top span width 120 mm bottom span width fixture attached to MTS 858 Mini Bionix 2 Hz frequency in ambient air

25 Bending Fatigue Test

26 Bending Fatigue Data (n = 4) 2.4 mm Locking Reconstruction Plates Material Cycles to Comments Failure Ti Grade Fractured Fractured Fractured Fractured β Ti-15Mo Fractured 1 X 10 6 Runout 1 X 10 6 Runout 1 X 10 6 Runout

27 Four Point Bending Fatigue Cycles to Failure 2.0 Intermediate t Locking Plates Ti Grade 4 (fractured Ti-15Mo (runout) Plate 1 Plate 2 Plate 3 Plate 4

28 Bending Fatigue Results 2.0 mm Intermediate Locking Plate -- Ti Grade 4 fatigue failure varied between cycles while all four β Ti-15Mo plates achieved runout 2.4 mm Locking Reconstruction Plate cycles to failure for Ti Grade 4 while three out of four β Ti-15Mo plates achieved runout

29 βti-15mo Locking Mandibular Plates

30 βti-15mo Locking Mandibular Plate Test Results for 2.5 mm thick -12 hole Ti Grade 4 β Ti-15Mo No. 90 Reverse Bends Bending Stiffness (N/mm) * Bending Strength (N m) Fatigue Cycles to Failure 62,000 >1X10 6 * 20% lower modulus of elasticity

31 Between fracture healing and device fatigue failure * * C li ti i O th di S Vl 1CE Ed J * Complications in Orthopaedic Surgery, Volume 1, C. Epps, Ed., J. B. Lippincott Co., 1978, p. 102

32 Torsion Testing of Cortex Screws Screw rigidly held in four jaw chuck at the threaded end Gage section included 5 exposed threads Cruciform screwdriver installed into the drive mechanism 1 kg. axial load applied to provide engagement between screwdriver and screw head recess Failure torque tests performed at 3 RPM N =5 for each group of screws Cold worked Ti Grade 4, cold worked 316L stainless, and β Ti-15Mo screws torque tested

33 Failure Torque and Failure Angle for 1.5 mm Cortex Screws Alloy Failure Torque Failure (N m) Angle ( ) CW 316L ± ± 18 CW Ti Grade ± ± 15 β Ti-15Mo ± ± 50

34 1.5 mm Cortex Bone Screw Mean Torsional Failure Angle ( ) mm 2.0 mm CW 316L CW Ti Grade 4 Beta Ti-15Mo

35 Summary

36 Ti-15Mo Implant Advantages No metal sensitivity reactions Superior corrosion resistance Improved reverse bending, fatigue, torsion, and notch sensitivity yproperties p Capability to match properties to specific applications (β or α + β ) Good MRI visualization - low artifact Anodized color coding

37 Reference Citations Technical references for this material presentation are documented at the Synthes Technical Center

38 Thanks for your attention