Biomedical Engineering Reference
In-Depth Information
TABLE 4.3
In Vivo Mechanical Properties of Ha Coatings after Implantation Duration
Mechanical
StrengthMPa(SD)
Weeks
Implant
TypeofTest
Comment
Reference
2
HA-coated Ti6Al4V
Uncoated
1.35
0.53
Push-out
Goat tibia
Oonishi et al. (1989)
3
HA-coated Ti6Al4V
Uncoated
6.05 (1.94)
4.43 (1.32)
Push-out
Thomas et al. (1987)
4
HA-coated Ti6Al4V
3.484 (0.616)
Push-out
Rabbit femoral
Maxian et al. (1993b)
4
HA-coated Ti6Al4V
Uncoated
4.43
1.49
Push-out
Goat tibia
Cook et al. (1992)
5
HA-coated Ti6Al4V
Uncoated
9.56 (3.55)
4.88 (1.01)
Push-out
Dog femur
Cook et al. (1991)
6
HA-coated Ti6Al4V
Uncoated
14.15
7.5
Push-out
Goat tibia
Oonishi et al. (1989)
10
HA-coated Ti6Al4V
Uncoated
14.17 (4.87)
10.53 (3.29)
Push-out
Goat tibia
Thomas et al. (1987)
12
HA-coated Ti6Al4V
6.244 (0.282)
Push-out
Rabbit femoral
Maxian et al. (1993b)
12
HA-coated Ti6Al4V
14.71 (2.84)
Push-out
Dog femora
Yang et al. (1997)
12
HA-coated Ti6Al4V
Uncoated
HA-coated Ti6Al4V
25.41
22.5
11.7 (1.7)
Push-out
Push-out
Goat tibia
Dog femora
Oonishi et al. (1989)
Wang et al. (1996)
24
HA-coated Ti6Al4V
14.64 (2.14)
Push-out
Dog femora
Yang et al. (1997)
24
HA-coated Ti6Al4V
12.4 (2.0)
Push-out
Dog femora
(failure-c/sub)
Wang et al. (1996)
32
HA-coated Ti6Al4V
Uncoated
12.12 (2.43)
none
Push-out
Dog femur
Thomas et al. (1987)
with a continuous gradation of structure and composition across the tissue-implant inter-
face (Black 1999). In either case of integration or bonding, the implant becomes mechani-
cally coupled to the adjacent tissue. For the latter, biomaterials should be in recognition
of the necessity of chemical reaction with local host environment prior to bond forma-
tion. The satisfactory implantation, which is indicated by high bonding strength, implies
adaptive remodeling. It was pointed out that cell adhesion, proliferation, and detachment
strength were surface roughness sensitive and increased as the roughness of HA increased
(Deligianni et al. 2001). An ideal coating surface might incorporate mechanical interlocks
as well as chemical attachment. Generally, it was believed that bonding mechanism of
bone with HA seemed to involve dissolution/reprecipitation phenomena (Bagambisa et
al. 1993). However, Munting (1996) pointed out that implant fixation must depend on a
mechanical interlock with bone and was not related to the duration of implantation.
The strength of interfacial bond that is formed by bioactive materials and adjacent tissue
is time-dependent (Laurent et al. 1999). Formation of the bone/HA bond seems to involve
dissolution/reprecipitation phenomena. Furthermore, reabsorption of HA is mainly a cell-
mediated phenomenon (Kwong et al. 1989). The degree of HA degradation determines the
ultramorphological appearance and ultrastructure of the bone/HA bond (Bagambisa et
al. 1993). In vivo study of HA-coated cylinders by plasma spraying implanted in femoral
diaphyses of sheep showed that the failure during shear test was within the bone, indicat-
ing a strong link between bone and implant and between HA coating and titanium sub-
strate (Lopez-Sastre et al. 1998). As the final approach, clinical testing is the only technique
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