Biomedical Engineering Reference
In-Depth Information
Hasegawa et al.
92
studied
in vivo
, spanning over a period of 5-7 years, high-
strength HAp/poly(L-lactide) composite rods for the internal fi xation of bone
fractures. In this work, uncalcined HAp (u-HAp) and calcined HAp (c-HAp)
were used as reinforcing phases in PLLA matrix. The u-HAp and c-HAP rods
were implanted in the femurs of 25 rabbits. The samples were collected after the
natural death of the rabbits. It was found that the implanted materials were re-
sorbed after six years of implantation. The presence of remodeled bone and tra-
becular bone bonding were the signifi cant outcome. Osteolytic and osteoarthritis
problem was not observed.
Another possible application of polymer matrix composite could be cranial
implants. Itokawa et al.
93
reported the results of an
in vivo
study (spanning over a
year) on the response of bone to a hydroxyapatite-polymethylmethacrylate cra-
nioplasty composite. New bone formation was observed after 12 and 24 weeks of
implantation. After one year, the presence of new bone formation was seen at the
interface region.
3.5.2.1 HDPE-HAp-Al
2
O
3
Hybrid Composites.
In a recent approach by
Basu and his coworkers
94
, HDPE - HAp - Al
2
O
3
composites were developed and
the mechanical, tribological and cell adhesion properties evaluated. This work
demonstrated how the stiffness and hardness as well as the biocompatibility prop-
erty of bioinert High density Polyethylene (HDPE) can be signifi cantly improved
by the combined addition of both bioinert and bioactive ceramic fi llers. In the
work of Basu et al., HDPE/HAp/Al
2
O
3
biocomposites with various compositions
were processed at the optimized compression molding condition (130 °C, 0.5 h,
92 MPa pressure). The microstructural analysis confi rms homogeneous distribu-
tion of fi ner ceramic fi llers (2 - 5
m) in HDPE matrix.
Importantly, higher elastic modulus (6.2 GPa) and improved hardness
(226.5 MPa) were obtained with the HDPE/20 vol% HAp/20 vol% Al
2
O
3
com-
posite. The simultaneous addition of Al
2
O
3
and HAp leads to an improvement
in mechanical properties, when compared to that of HDPE-20 vol% Al
2
O
3
(H
v
- 131.1 MPa,
μ
E - modulus - 2.7 GPa)
or
HDPE/20 vol%
HAp
(H
v
- 129.5 MPa,
E - modulus - 2.4 GPa).
Another important result was that the maximum hardness (252 MPa) and
elastic modulus (7.1 GPa) have been attained in case of 40 vol% Al
2
O
3
reinforced
HDPE composite (without any HAp).
The above experimental results also required an assessment as to whether or
not good tribological properties of HDPE are compromised due to HAp/Al
2
O
3
addition. Therefore, a series of wear experiments were conducted. The fretting
testing parameters included a normal load of 10 N, relative displacement of 80
m,
frequency of 10 Hz and testing duration of 100,000 cycles. The accuracy of the
temperature and humidity maintained in this investigation was 35
μ
±
2 ° C and
45
5%, respectively.
The results of a number of a fretting tests on developed biocomposites against
steel/Al
2
O
3
/ZrO
2
reveal that the addition of HAp and/or Al
2
O
3
(up to a maxi-
mum of 40 vol%) to HDPE still allow to retain favorable friction properties, as a
±
Search WWH ::
Custom Search