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
Outline Alloy Design History Material Properties Implant Product Testing
Alloy Design History
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 3-14 2 Ho W, Structure and properties of cast binary Ti-15Mo alloys, Biomaterials, Vol 20, 1999, pp 2115-2122
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
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)
Material Properties
Physical Properties Implant Density Modulus of Material (gm/cm 3 ) Elasticity (GPa) 316L ss 795 7.95 186 Ti-6Al-4V ELI 4.43 114 Ti-6Al-7Nb 4.52 105 Ti Grade 4 4.51 104 α + β Ti-15Mo 4.96 105 β Ti-15Mo 4.96 78
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 4 2 4 2 4 3 4 80 C 30% H 3PO 4 Ti Grade 2 27.9 76.5 43.2 144.8 3.76 12.42 Ti-15Mo 0.18 1.52 0.18 0.76 0.02 2.41 1 IMI Titanium 205, Alloy Data Sheet, IMI Titanium Ltd., Birmingham, England
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
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 690 483 20 60 F 2066 Ti Grade 4 CW ISO 680 520 10 5832-2 Ti-15Mo α + β Anld ASTM F 2066 900 800 10 25 Ti-6Al-7Nb α + β Anld ASTM F 1295 900 800 10 25
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 1.53 2.46 316L ss CW 144 1.44 183 1.83 Ti Grade 4 CW 1.47 1.81 Ti-6Al-7Nb Anld 1.46 1.57
Smooth Tension -Tension Corrosion Fatigue Testing Parameters --- Low stress ground rods --- ASTM F 1801 Corrosion Fatigue Testing of Metallic Implant Materials --- Load control @ 1Hz frequency --- Aerated Ringer s solution @ 37 C Notch --- Kt factor 3.2
Ti-15Mo Smooth and Notched Endurance Limits 1 Alloy Condition Endurance Limit @ 10 6 Cycles (MPa) Smooth Notched Ti-15Mo Aged α + β 800 250-300 Ti-15Mo β 500 200 Ti-6Al-4V ELI α + β 700 150 1 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
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
Implant Product Testing
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
Reverse Bend Testing
2.0 mm Intermediate Locking Plate 2.4 mm Universal Fracture Plate 2.4 mm Locking Reconstruction Plate
Reverse Bend Testing of Annealed dcmfpl Plates 60 50 40 30 Lock Recon 20 Univ Frac 2.0 Locking 10 0 Ti Grade 4 Beta Ti- 15Mo
1.15 mm Thick CMF Adaption Plate
Reverse Bend Testing of CMF Adaption Plate 90 o Reverse Bends to Failure 120 100 Bends to Failure 80 60 40 20 0 α-β Ti-15Mo 316L Ti4 Ti2 TAN Ref: MT08-038
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
Bending Fatigue Test
Bending Fatigue Data (n = 4) 2.4 mm Locking Reconstruction Plates Material Cycles to Comments Failure Ti Grade 4 49 194 Fractured 31 188 Fractured 31 236 Fractured 27 477 Fractured β Ti-15Mo 129 039 Fractured 1 X 10 6 Runout 1 X 10 6 Runout 1 X 10 6 Runout
Four Point Bending Fatigue Cycles to Failure 2.0 Intermediate t Locking Plates 1000000 900000 800000 700000 600000 500000 Ti Grade 4 (fractured 400000 Ti-15Mo (runout) 300000 200000 100000 0 Plate 1 Plate 2 Plate 3 Plate 4
Bending Fatigue Results 2.0 mm Intermediate Locking Plate -- Ti Grade 4 fatigue failure varied between 52 000-92 000 cycles while all four β Ti-15Mo plates achieved runout 2.4 mm Locking Reconstruction Plate -- 27 477-49 194 cycles to failure for Ti Grade 4 while three out of four β Ti-15Mo plates achieved runout
βti-15mo Locking Mandibular Plates
βti-15mo Locking Mandibular Plate Test Results for 2.5 mm thick -12 hole Ti Grade 4 β Ti-15Mo No. 90 Reverse Bends 10.7 32 Bending Stiffness (N/mm) 2783 2709* Bending Strength (N m) 10.77 12.55 Fatigue Cycles to Failure 62,000 >1X10 6 * 20% lower modulus of elasticity
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
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
Failure Torque and Failure Angle for 1.5 mm Cortex Screws Alloy Failure Torque Failure (N m) Angle ( ) CW 316L 0.236 ± 0.004 318 ± 18 CW Ti Grade 4 0.236 ± 0.009009 224 ± 15 β Ti-15Mo 0.246 ± 0.001 466 ± 50
1.5 mm Cortex Bone Screw Mean Torsional Failure Angle ( ) 500 450 400 350 300 250 200 150 100 50 0 1.5 mm 2.0 mm CW 316L CW Ti Grade 4 Beta Ti-15Mo
Summary
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
Reference Citations Technical references for this material presentation are documented at the Synthes Technical Center
Thanks for your attention