Mechanical and histological investigation of hydrothermally treated and untreated anodic titanium oxide films containing Ca and P

Abstract

In a previous study a new method for forming thin hydroxyapatite (HA) layers on titanium was described. Titanium was anodized at 350 V in an electrolyte solution containing sodium beta-glycerophosphate and calcium acetate, and an anodic titanium oxide film containing Ca and P (AOFCP) was formed on the surface. Then numerous HA crystals were precipitated on the AOFCP during hydrothermal treatment in high-pressure steam at 300 degrees C. In this study three types of hydrothermally treated films differing in amounts of precipitated HA crystals and tensile adhesive strength, and untreated films were histologically and mechanically investigated in a transcortical rabbit femoral model for 8 weeks of implantation using light microscopy, scanning electron microscopy (SEM), and push-out tests. Machined titanium and HA ceramics served as control materials. The push-out shear strength and bone apposition of the AOFCP significantly increased after hydrothermal treatment, and were equivalent to those of HA ceramics, although the HA layer on the AOFCP was thin at 1-2 microns. From SEM observation of the pushed-out specimen, it was found that the thin HA layer had directly bonded to bone but the AOFCP had not. The push-out strength of the hydrothermally treated film resulted from the chemical bonding of the bone-HA layer interface, while that of the untreated film resulted from mechanical interlocking force between bone and the microprojections. There was a small difference in bone apposition but no significant difference in push-out strength with the amount of precipitated HA crystals on the treated films. Among the treated films, the film formed at the lowest electrolyte concentration showed the lowest bone apposition because of incomplete covering by the HA crystals, and showed the highest stability against mechanical failure because the adhesive strength was very high at about 38 mPa. Also, the hydrothermally untreated anodic oxide films, whose surfaces were rough as a result of the large microprojections, showed much higher push-out strength and bone apposition than titanium. The good hard-tissue compatibility may be attributed to the surface roughness and the possible inhibition of titanium ion release from the specimen.

The effect on immunocytes of anodic oxide titanium after hydrothermal treatment

“…However, the adhesive strength of the HA layer coating substrate interface of HA/Ti implant materials was much higher than that of the plasma-sprayed HA-coated implant materials. 8 Our research group also reported an in vitro study about the effects of HA/Ti implant materials on primary calcification of osteoblasts. During the culture period, the bone marrow cells adhered to HA/Ti and nontreated Ti surfaces, and an abundant amount of bone nodules was produced.…”

Histomorphometric and microhardness assessments of sheep cortical bone surrounding titanium implants with different surface treatments

“…The PVD process has been proposed by Ishizawa et al, who observed the formation of a thin (1-2 m) and porous HA layer directly on metal substrates, which they reported to be equivalent in terms of mechanical strength and bone apposition to those recorded on HA ceramics and much higher than those observed for Ti. [32][33] In a previous article the current authors showed that the anodized and hydrothermally treated Ti had the best performances regarding bone apposition to the cancellous bone of rat distal femoral epiphysis when compared to Ca-P amorphous coating and grade 2 Ti. 37 The same authors then conducted another in vivo study using sheep femurs and observed that adequate surface roughness, such as that obtained with HA vacuum plasma spray and anodization followed by hydrothermal treatment, may accelerate the osseointegration process and also appears to improve interlocking and mechanical bonding with the bone.…”

Effects of anodizing voltage on the anodized and hydrothermally treated titanium surface

“…When an anodized sample is treated hydrothermally at a high temperature in a high-pressure autoclave, crystals precipitate on top of the porous film [12,17,18]. In Fig.…”