Technical note
Breakdown corrosion potential of ceramic coated metal implants K. Hayashi* Department of Orthopaedic Surgery, Faculty of Medicine, Kyushu University, Fukuoka 872, Japan I. Noda Research F Development Dqartment, Bioceram Division, Kyocera Corporation, Kyoto 607, Japan K. Uenoyama and Y. Sugioka Department of Orthopaedic Surgery, Faculty of Medicine, Kyushu University, Fukuoka 812, Japan
The long-term success of joint replacement largely depends on the stable fixation of the implant to bone. Current methods rely on mechanical fixation either with or without the use of acrylic bone cement. The drawbacks of cement are well known’ and the newer porous metal coatings are still under review.2r3 Studies on composites in which metals are coated with ceramics have been reported recently as an alternative method of long-term fixati~n.~” We have devised hydroxyapatite (A) . alumina (B) titanium-nitride (C) (HAP . a-AlZO3. TiN)-coated SUS-316L stainless steel and HAP (D) . titanium-oxide (E) (TiOJ-coated Ti-6A1-4V.
-
TABLE I Ceramic Coatings
Coatings Alloy
HAP
316L (Film thickness) Ti-6A1-4V (Film thickness)
Plasma spray (20 pm) (A) Plasma spray (20 pm) (D)
CY-A~~O~
Plasma spray (20 p.m) (B)
TiN
Ion plating (1.5w-4 (C)
TiOz
Anodic oxidation (3000-5000 %.) (E)
The corrosion reaction of metals is an electrochemical reaction.’ Therefore we measured the breakdown corrosion potential of each material by the potentiodynamic an‘To whom correspondence should be addressed. Journal of Biomedical Materials Research, Vol. 24, 1111-1113 (1990) CCC 0021-9304/90/081111-03$04.00 0 1990 John Wiley & Sons, Inc.
1112
HAYASHI ET AL.
odic polarization method.8 The Automatic Polarization system (Hokuto Denko Co.) included a polarization cell with salt bridge and Calomel electrode and appropriate potentiostatic recording equipment. Test pieces were cylinders (6 mm diameter, 20 mm length) and the ceramic coatings were applied to one half of the cylinder (ceramic coatings were not applied to the one half of each cylinder where attached to the Automatic Polarization system). The test was performed in a saline bath at 37°C; specimen immersion time was for 10 min, and the sweep rate was 5 mV/S.
TABLE I1 Breakdown Corrosion Potential for Each Material Mean HAP on 316L (A)
0.47
k
S.D. [V(SCE)I
* 0.09"
(N = 10)
a-ALZO3on 316L (B) TiN on 316L (C)
0.32 2 0.07 (N = 10) 0.47 t 0.06** (N = 10)
316L (control) (F) HAP on Ti-6A1-4V (D) TiO, on Ti-6A1-4V (E) TidAI-4V (control) (G)
0.32 2 0.01 (N = 10) 1.93 t 0.04 (N = 10) 3.74 2 0.50"' (N = 10) 1.99 k 0.04 (N = 10)
The values for the ceramic-coated composites and the control were compared by Student's t-test (Table 11). Noncoated Ti-6Al-4V ( G )had a sixfold higher breakdown corrosion potential compared to noncoated SUS-316L steel (F). The breakdown corrosion potential of HAP-coated Ti-6A1-4V (D) was about four times higher than that of HAP-coated SUS316L stainless steel (A). However, the breakdown corrosion potential of HAP-coated Ti-6A1-4V (D) was lower than that of Ti02-coated Ti-6A1-4V (E). We previously compared the biocompatibility of each material in dog femurs using the Affinity Index (the length of bone directly opposed to the implant without the presence of an intervening fibrous membraneithe total length of the bone-implant interface x 100%). The materials were inserted into the mid-diaphyseal region of the femurs of adult dogs, and follow-up quantitative histological comparisons were performed for a period of up to 96 weeks. The HAP-coated SUS-316L stainless steel showed the highest Affinity Index and this value was maintained up to 96 weeks. HAP-coated implants were superior to the stainless-steel controls, the bioinert ceramic (a-AIp03,TiN-coated implants) (P < 0.01). In this study we also studied the affinity of the Ti-6A1-4V based material. HAP-coated material also showed the best biocompatibility in Ti-6A1-4V composites (noncoated Ti-6AL4V, HAP . TiOz coated Ti-6Al-4V)6. Thus HAP-coated composite had the best biocompatibility in both SUS-316L stainless steel and TidA1-4V based material. However, in regard to the breakdown corrosion potential, HAP-coated Ti-6A1-4V had a lower breakdown corrosion potential than Ti0,-coated Ti-6A1-4V and almost the same value compared to noncoated Ti-6A1-4V. However HAPcoated Ti-6A1-4V had a much higher breakdown corrosion potential than HAP-coated SUS-316L stainless steel. Therefore since the HAP-coated Ti-6A14V had the best biocompatibility in vivo, it would appear that the most promising composite for use as a biomaterial.
CERAMIC COATED IMPLANTS
1113
References 1. S. R. Goldring, A. L. Schiller, M. Roelke, C. M. Roourke, D. A. O’Neill, and W. H. Harris, “The synovial-like membrane at the bone-cement interface in loose total hip replacements and its proposed role in bone lysis,” J. Bone Joint Surg., 65-A, 575-584 (1983). 2. H. Ronningen, L. F. Solheim, and N. Langeland, ”Invasion of bone into porous fiber metal implants in cats,” Acta. Orthop. Scand., 55, 352-358 (1984). 3. H. Ronningen, L. F. Solheim, and N. Langeland, “Bone formation enhanced by induction: bone growth in titanium implants in rats,” Acta. Orthop. Scand., 56, 67-71 (1985). 4. S. F. Hulbert, H. L. Richbourg, J. J. Klawitter, and B. W. Sauer, “Evaluation of a metal ceramic composite hip prosthesis,” J. Biomed. Muter. Res., 6, 189-198 (1975). 5. R. G. T. Geesink, K. de Groot, and C. P. A. T. Klein, “Chemical implant fixation using hydroxyl-apatite coatings,” Clin. Orthop., 225, 147-170 (1987). 6. K. Hayashi, N. Matsuguchi, K. Uenoyama, T. Kanemaru, and Y. Sugioka, “Evaluation of metal implants coated with several types of ceramics as biomaterials,” J. Biomed. Muter. Xes., 23, 1247-1259 (1989). 7. M. Pourbaix, “Electrochemical corrosion of metallic biomaterials,” Biomaterials, 5, 12-12 (1984). 8. ASTM G5-82, Standard reference method for making potentiostatic and potentiodynamic anodic polarization measurements.
Breakdown corrosion potential of ceramic coated metal implants K. Hayashi* Department of Orthopaedic Surgery, Faculty of Medicine, Kyushu University, Fukuoka 872, Japan I. Noda Research F Development Dqartment, Bioceram Division, Kyocera Corporation, Kyoto 607, Japan K. Uenoyama and Y. Sugioka Department of Orthopaedic Surgery, Faculty of Medicine, Kyushu University, Fukuoka 812, Japan
The long-term success of joint replacement largely depends on the stable fixation of the implant to bone. Current methods rely on mechanical fixation either with or without the use of acrylic bone cement. The drawbacks of cement are well known’ and the newer porous metal coatings are still under review.2r3 Studies on composites in which metals are coated with ceramics have been reported recently as an alternative method of long-term fixati~n.~” We have devised hydroxyapatite (A) . alumina (B) titanium-nitride (C) (HAP . a-AlZO3. TiN)-coated SUS-316L stainless steel and HAP (D) . titanium-oxide (E) (TiOJ-coated Ti-6A1-4V.
-
TABLE I Ceramic Coatings
Coatings Alloy
HAP
316L (Film thickness) Ti-6A1-4V (Film thickness)
Plasma spray (20 pm) (A) Plasma spray (20 pm) (D)
CY-A~~O~
Plasma spray (20 p.m) (B)
TiN
Ion plating (1.5w-4 (C)
TiOz
Anodic oxidation (3000-5000 %.) (E)
The corrosion reaction of metals is an electrochemical reaction.’ Therefore we measured the breakdown corrosion potential of each material by the potentiodynamic an‘To whom correspondence should be addressed. Journal of Biomedical Materials Research, Vol. 24, 1111-1113 (1990) CCC 0021-9304/90/081111-03$04.00 0 1990 John Wiley & Sons, Inc.
1112
HAYASHI ET AL.
odic polarization method.8 The Automatic Polarization system (Hokuto Denko Co.) included a polarization cell with salt bridge and Calomel electrode and appropriate potentiostatic recording equipment. Test pieces were cylinders (6 mm diameter, 20 mm length) and the ceramic coatings were applied to one half of the cylinder (ceramic coatings were not applied to the one half of each cylinder where attached to the Automatic Polarization system). The test was performed in a saline bath at 37°C; specimen immersion time was for 10 min, and the sweep rate was 5 mV/S.
TABLE I1 Breakdown Corrosion Potential for Each Material Mean HAP on 316L (A)
0.47
k
S.D. [V(SCE)I
* 0.09"
(N = 10)
a-ALZO3on 316L (B) TiN on 316L (C)
0.32 2 0.07 (N = 10) 0.47 t 0.06** (N = 10)
316L (control) (F) HAP on Ti-6A1-4V (D) TiO, on Ti-6A1-4V (E) TidAI-4V (control) (G)
0.32 2 0.01 (N = 10) 1.93 t 0.04 (N = 10) 3.74 2 0.50"' (N = 10) 1.99 k 0.04 (N = 10)
The values for the ceramic-coated composites and the control were compared by Student's t-test (Table 11). Noncoated Ti-6Al-4V ( G )had a sixfold higher breakdown corrosion potential compared to noncoated SUS-316L steel (F). The breakdown corrosion potential of HAP-coated Ti-6A1-4V (D) was about four times higher than that of HAP-coated SUS316L stainless steel (A). However, the breakdown corrosion potential of HAP-coated Ti-6A1-4V (D) was lower than that of Ti02-coated Ti-6A1-4V (E). We previously compared the biocompatibility of each material in dog femurs using the Affinity Index (the length of bone directly opposed to the implant without the presence of an intervening fibrous membraneithe total length of the bone-implant interface x 100%). The materials were inserted into the mid-diaphyseal region of the femurs of adult dogs, and follow-up quantitative histological comparisons were performed for a period of up to 96 weeks. The HAP-coated SUS-316L stainless steel showed the highest Affinity Index and this value was maintained up to 96 weeks. HAP-coated implants were superior to the stainless-steel controls, the bioinert ceramic (a-AIp03,TiN-coated implants) (P < 0.01). In this study we also studied the affinity of the Ti-6A1-4V based material. HAP-coated material also showed the best biocompatibility in Ti-6A1-4V composites (noncoated Ti-6AL4V, HAP . TiOz coated Ti-6Al-4V)6. Thus HAP-coated composite had the best biocompatibility in both SUS-316L stainless steel and TidA1-4V based material. However, in regard to the breakdown corrosion potential, HAP-coated Ti-6A1-4V had a lower breakdown corrosion potential than Ti0,-coated Ti-6A1-4V and almost the same value compared to noncoated Ti-6A1-4V. However HAPcoated Ti-6A1-4V had a much higher breakdown corrosion potential than HAP-coated SUS-316L stainless steel. Therefore since the HAP-coated Ti-6A14V had the best biocompatibility in vivo, it would appear that the most promising composite for use as a biomaterial.
CERAMIC COATED IMPLANTS
1113
References 1. S. R. Goldring, A. L. Schiller, M. Roelke, C. M. Roourke, D. A. O’Neill, and W. H. Harris, “The synovial-like membrane at the bone-cement interface in loose total hip replacements and its proposed role in bone lysis,” J. Bone Joint Surg., 65-A, 575-584 (1983). 2. H. Ronningen, L. F. Solheim, and N. Langeland, ”Invasion of bone into porous fiber metal implants in cats,” Acta. Orthop. Scand., 55, 352-358 (1984). 3. H. Ronningen, L. F. Solheim, and N. Langeland, “Bone formation enhanced by induction: bone growth in titanium implants in rats,” Acta. Orthop. Scand., 56, 67-71 (1985). 4. S. F. Hulbert, H. L. Richbourg, J. J. Klawitter, and B. W. Sauer, “Evaluation of a metal ceramic composite hip prosthesis,” J. Biomed. Muter. Res., 6, 189-198 (1975). 5. R. G. T. Geesink, K. de Groot, and C. P. A. T. Klein, “Chemical implant fixation using hydroxyl-apatite coatings,” Clin. Orthop., 225, 147-170 (1987). 6. K. Hayashi, N. Matsuguchi, K. Uenoyama, T. Kanemaru, and Y. Sugioka, “Evaluation of metal implants coated with several types of ceramics as biomaterials,” J. Biomed. Muter. Xes., 23, 1247-1259 (1989). 7. M. Pourbaix, “Electrochemical corrosion of metallic biomaterials,” Biomaterials, 5, 12-12 (1984). 8. ASTM G5-82, Standard reference method for making potentiostatic and potentiodynamic anodic polarization measurements.
