Biomedical Engineering Reference
In-Depth Information
anodized oxides were in the range of 60-90 degrees, suggesting relatively high
hydrophobicity. It was also mentioned that cell culture experiments demon-
strated absence of cytotoxicity and an increase of osteoblast adhesion and pro-
liferation by the anodic oxides [Zhu et al., 2004].
Characteristics of the porous surfaces may be important in improving the
bone in-growth into the porous coatings. Quicker and more mature interstitial
bone formation was obtained using a porous rather than a solid structure, due to
differences of penetration by some growth factors and bone marrow cells [Jasty
et al., 1993; Simske et al., 1995; Chang et al., 1996]. Li et al. [1997] examined the
effect of the surface macrostructure of a dimpled CpTi implant on bone in-growth
in vivo
by means of histological examination and a push-out test. Dimples had
diameters of 100, 140, and 160
μ
m, and distance between dimple centers of about
400
m. Cylindrical implants were inserted in one of each rabbit for one-and-a-
half, three, and 13 months. The femur with the implant of each animal was then
examined in a push-out test. It was found that the dimpled CpTi surface results
in an increased retention of the implant in bone due to interlocking between vital
bone and the dimples.
Nishiguchi et al. [Nishiguchi et al., 1999] evaluated the bone-bonding ability
of three differently treated samples of CpTi: as a smooth surface control; treated
in 5 M NaOH solution for 24 hr at 60 ° C, and; plus - heated at 600 ° C for one hour.
The plates were inserted transcortically into the proximal metaphyses of bilateral
rabbit tibiae. The tensile failure loads between implants and bones were mea-
sured at two intervals using a detaching test. It was reported that the tensile
failure loads of the alkali- and alkali-heat treated group were 27 and 40 MPa, at
8 and 16 weeks, and signifi cantly higher than those of the other Ti groups, and
that histological examination revealed that alkali- and heat-treated Ti was in
direct contact with bone, but the other Ti groups had a thin intervening fi brous
tissue. It was concluded that the alkali-treated Ti without heat treatment had no
bone-bonding ability due to the unstable reactive surface layer of alkali-treated
Ti, and that both alkali and heat treatment are essential for preparing bioactive
Ti. This bioactive Ti is thought to be useful for orthopedic implants with cement-
less fi xation.
There is increasing attention given to the infl uence of surface condition, in
particular, on methods to control. Strain hardening [Montero-Ocampo et al.,
1996], laser-surface treatment [Villermaux et al., 1997], and chemical passivation
methods [Trépanier et al., 1998] are all well known. From histological examina-
tions, it has been found that implant loosening is generally associated with
the formation of fi brous tissue at the bone-implant interface. To improve
implant biocompatibility and osseointegrtaion, Ti-6Al-4V alloy was treated by
passivation by immersion in 30% HNO
3
for 1 hr, or passivation in boiling distilled
water for 10 hr [Ku et al., 2002], allowing an increase in the oxide layer thickness
of Ti-6Al-4V alloy used in orthopedic implants. The kinetics of gene expression
over 120 hours was followed for 58 genes to quantify the effect of the developed
surface treatment. Twenty-eight genes were further selected to compare the
effects of surface treatments on osteoblasts. Based on the genes studied, a general
μ
Search WWH ::
Custom Search