Biomedical Engineering Reference
In-Depth Information
lower steady state of 0.12 or lower has been achieved for optimized HDPE-
20 vol% Al
2
O
3
- 20 vol% HAp materials.
Under the investigated fretting conditions, HDPE/20 vol% HAp/20 vol%
Al
2
O
3
composite showed enhanced wear resistance against both zirconia
95
(wear
rate
1 0
− 6
m m
3
/Nm in SBF and atmospheric condition,
respectively) and steel counterface
96
(wear rate
∼
1.08
×
1 0
− 6
and 1.787
×
1 0
− 6
m m
3
/
Nm in SBF and air, respectively) in comparison to unreinforced HDPE (wear
rate
∼
2.3
×
1 0
− 6
and 3.87
×
order of 10
− 5
m m
3
/Nm). Overall, the lowest wear rate is recorded against
alumina counter - body
97
, irrespective of fretting environment and composite com-
position. Table 3.5, summarizes COF and wear rate of different composites against
different counterbodies and fretting mediums.
In general, a decrease in wear rate in SBF condition is observed for all the
tested materials. Importantly, the present investigation reveals that partial re-
placement of HAp by 20 vol% Al
2
O
3
in the HAPEX
TM
(40 vol% HAp - HDPE
composite) composition improves the wear properties of the developed compos-
ites. Figure 3.11 shows the fretted zone of this composite and emphasized the
hindrance in material removal by addition of hard ceramic particulates.
Cell culture experiments for 24 hours, involving L929 fi broblast cells, clearly
reveal the favorable cell adhesion property of the newly developed HDPE/20 vol%
HAp/20 vol% Al
2
O
3
biocomposite. To provide evidence, SEM images are ac-
quired and presented in Figure 3.12.
In addition to results obtained with HDPE-20HAp-20Al
2
O
3
and HDPE-
40HAp composite, cell attachment on the standard biocompatible disc (poly-L-
lysine-coated glass coverslips, negative control sample) is also shown. Figures
3.12e and 3.12f clearly show that fi broblast cells proliferated to a considerable
extent on the control sample surface. Importantly, cells are also proliferated to a
greater extent on the HDPE- 20HAp - 20Al
2
O
3
composite as well as on the HDPE-
40HAp sample. At many of the investigated regions, the general observation has
been that the cells are attached closely with neighboring cells, and thereby form a
cellular network (characteristic of fi broblast type cells) on the composite surface.
Closer observations of SEM images reveals that in the case of control disc,
the cells are more round-shaped; whereas in the case of developed composites,
cells are fl attened with cell fi lapodia extending sideways in order to increase con-
tact with the underlying substrate (composite).
In many investigated regions, such phenomenon resulted in enhanced cell-
cell interactions, leading to formation of cellular bridges (see Figures 3.12b, 3.12d,
and 3.12 f).
The above observations are clear indicators of good biocompatibility prop-
erty. It can be inferred that the HAp containing composite is as biocompatible
as the control disc. However, pure HDPE (unreinforced) is essentially bioinert
polymer and the addition of ceramic fi llers (HAp), in the present case, clearly
enhanced the cell adhesion property, even when a large amount of Al
2
O
3
fi ller
was added.
The above observations also confi rm favorable cell adhesion properties of
HDPE - 20HAp - 20Al
2
O
3
composite, which would encourage tissue formation/
∼
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