Biomedical Engineering Reference
In-Depth Information
bonded to the
flat
surface of a Ti disk using the HHP method at 150˚C and 40MPa. The
thickness of the HA ceramics bonded was about 10mm. It has been shown from three point
bending tests that the fracture strength of the HA/Ti interface was equal to or higher than
that of the HA ceramics. Additionally, X-ray diffraction analyses revealed that the HA
ceramics bonded had high crystallinity without any decomposition and impurity. However,
the HA bonding was achieved only on
flat
surfaces of Ti because of uniaxial pressing. In
order for the hydrothermal method to be applicable to orthopedic and dental implant
materials, we should develop a method for coating thin HA layer onto curved surface. This
section describes a new methods for coating HA ceramics layer on Ti rod at the low
temperature as low as 135˚C by using the newly developed double layered capsule
hydrothermal hot-pressing (DC-HHP) method, which utilizes isostatic pressing under
hydrothermal conditions.
The synthetic DCPD and calcium hydroxide (95.0%; Ca(OH)
2
; KANTO CHEMICAL CO.,
INC., Japan) were mixed in a mortar for 60min with a Ca/P ratio of 1.67 which was
stoichiometric ratio of HA. A commercially available pure Ti rod (99.5%; Nilaco, Japan),
1.5mm in diameter, was used in this study. The Ti rod was cut into a length of
approximately 20mm. Ti surfaces were finished using #1500 emery paper. The rods were
cleaned in deionized water and acetone by using an ultrasonic cleaner.
Recently, it has been reported that surface modifications for forming bonelike apatite can
induce the high bioactivity of bioinert materials in simulated body fluid (SBF) [Kokubo et
al., 2004]. In our previous research [Onoki et al., 2003], bonding HA ceramics and Ti alloys
(Ti-15Mo-5Zr-3Al and Ti-6Al-2Nb-1Ta) was achieved by the HHP method through the
surface modification of Ti alloys with alkali solution (5
M
NaOH). It is reported that the
surface treatment of the Ti alloys with the alkali solution was very effective to improve the
fracture strength of the interface between HA and Ti alloys produced by the HHP method.
Based on the above results, the Ti rods used in this study were treated with 5
M
NaOH
solution after the emery paper finish. The hydrothermal treatment with the NaOH solution
was conducted at 150˚C for 2 hours using a small vessel (volume: 7.5ml). After the surface
treatment, the Ti rods were washed by deionized water, and then dried in air.
4.2 Double layered capsule hydrothermal hot-pressing (DC-HHP) method
A new technique was developed in this study in order to prepare HA coating layers on a
cylindrical rod with the objective of applying the hydrothermal hot-pressing method to a
substrates with more complicated configurations, as shown in Fig.11. The newly developed
method uses a cylindrical capsule having the double layered structure, which is subjected to
isostatic pressing under hydrothermal conditions. A schematic illustration of the capsule in
a cross section view is shown in Fig.12.
Firstly, the Ti rod and the powder mixture of DCPD and Ca(OH)
2
were placed into a tube
made of polyfluoroethylene (FEP). The weight of the powder mixture put into was
approximate 0.1g. The initial diameter and thickness of the FEP tube was 1.8mm and 100m.
The FEP shrinks thermally by approximately 25% at around 130˚C. The powder mixture was
loaded into the FEP tube such that the Ti rod was concentrically positioned with respect to
the tube axis. Both the ends of the FEP tube were fastened with paper staples. The sample
assemblage encapsulated using the FEP tube is called “capsule I” in this study. Secondly,
the capsule I was further encapsulated using a poly-vinylidene-chloride (PVC; 11m
thickness, Asahi-KASEI, Japan) film. Between the capsule I and PVC film, alumina powder
