Growth of Novel Ceramic Layers on Metals via Chemical and Heat Treatments for Inducing Various Biological Functions

Abstract

The present authors' systematic studies on growth of novel ceramic layers on Ti metal and its alloys by chemical and heat treatments for inducing bone-bonding bioactivity and some other biological functions are reviewed. Ti metal formed an apatite on its surface in a simulated body fluid, when heat-treated after exposure to strong acid solutions to form rutile surface layer, or to strong alkali solutions to form sodium titanate surface layer. Both types of Ti metal tightly bonded to the living bone. The alkali and heat treatment was applied to the surface Ti metal of an artificial hip joint and successfully used in the clinic since 2007. The acid and heat treatments was applied to porous Ti metal to induce osteoconductivity as well as osteoinductivity. The resulting product was successfully used in clinical trials for spinal fusion devices. For the Ti-based alloys, the alkali and heat treatment was little modified to form calcium titanate surface layer. Bone-growth promoting Mg, Sr, and Zn ions as well as the antibacterial Ag ion were successfully incorporated into the calcium titanate layer.

Keywords: Ti metal; Ti-based alloys; acid and heat treatment; alkali and heat treatment; apatite; bioactivity; osteoconduction; osteoinduction.

Figure 1

SEM photographs of surfaces of Ti metal exposed to solutions with different pHs (top) and those of the same surfaces after soaking in SBF for 3 days (bottom). TH, titanium hydride; SHT, sodium hydrogen titanate. Reproduced from Pattanayak et al. (2012) with permission The Royal Society.

Figure 2

SEM photographs of surfaces of Ti metal heat-treated after exposure to solutions with different pHs (top) and those of the same surfaces after soaking in SBF (bottom). ST, sodium titanate. Reproduced from Pattanayak et al. (2012) with permission The Royal Society.

Figure 3

Zeta potentials of Ti metal heat-treated after exposure to solutions with different pH values. Reproduced from Pattanayak et al. (2012) with permission The Royal Society.

Figure 4

Process of apatite formation on Ti metals heat-treated after exposure to strong acid solutions (top), and to strong alkali solutions (bottom). Reproduced from Pattanayak et al. (2012) with permission The Royal Society.

Figure 5

Optical micrographs of non-decalcified sections of Ti metals subjected to no treatment (A), only H₂SO₄/HCl acid treatment (B), only heat treatment at 600°C (C) and H₂SO₄/HCl acid and heat treatment at 600°C (D), 4 weeks after implantation into the tibia of rabbit. Reproduced from Kawai et al. (2012) with permission Springer.

Figure 6

Contact radiomicrograph (left hand) and SEM photograph (right hand) of Ti metal heat-treated after exposure to NaOH solution at its interface with the bone, 8 weeks after implantation into the tibia of rabbits. Reproduced from Yan et al. (1997) with permission John Willey and Sons.

Figure 7

Titanium metal rod untreated (top) and heat-treated after exposure to NaOH solution (bottom), both of which were pulled out after implanted into medullary canal of a rabbit for 12 weeks, after Nishiguchi et al. (2003).

Figure 8

Artificial hip joint, porous Ti metal layer of which was heat-treated after exposure to NaOH solution, after Kawanae et al. (2009).

Figure 9

Structures of sodium hydrogen titanate, calcium hydrogen titanate, and calcium titanate projected on a plane perpendicular to the crystallographic b axis. Reproduced from Kokubo and Yamaguchi (2015) with permission Elsevier.

Figure 10

Depth profile of Auger electron spectroscopy of the surface of Ti–15Zr–4Nb–4Ta alloy subjected to NaOH, CaCl₂, heat, and water treatments. Reproduced from Yamaguchi et al. (2010) with permission Springer.

Figure 11

Failure load under tensile stress perpendicular to the interface of Ti–15Zr–4Nb–4Ta alloy subjected to NaOH, CaCl₂, heat, and water treatment with the bone, in comparison with that for untreated alloy, after Fukuda et al. (2011a).

Figure 12

Depth profile of XPS of Ti metal subjected to NaOH, CaCl₂/SrCl₂, heat, and SrCl₂ treatments. Reproduced from Yamaguchi et al. (2014) with permission Elsevier.

Figure 13

Bone formation in porous Ti metals subjected to no treatment and NaOH, HCl, and heat treatments, 26 weeks after implantation into rabbit femur, after Takemoto et al. (2005) and Tanaka et al. (2009).

Figure 14

Bone formation in porous Ti metals subjected to NaOH, HCl, and heat treatments, 3 and 12 months after implantation into muscle of beagle dog. Reproduced from Takemoto et al. (2006) with permission Elsevier.

Figure 15

Spinal fusion device of porous Ti metal subjected to NaOH, HCl and heat treatments (left hand side) and its clinical application (right hand side). Reproduced from Fujibayashi et al. (2011) with permission Springer.