Biomedical Engineering Reference
In-Depth Information
TABLE 9.1. Analysis of the XPS Spectra: A Summary of the Different Oxides Detected in
the Passive Oxide Layer on the Surface
Sputtering time (min)
Ti based
Nb based
Ta based
Zr based
0
TiO
2
N b
2
O
5
, NbN(1 - y)O(y)
Ta
2
O
5
, Ta
ZrO
2
12
TiO
2
, T i
N b
2
O
5
, NbO
2
, NbO0.2/Nb
Ta
2
O
5
, Ta
ZrO
2
22
TiO
2
, T i
N b
2
O
5
, NbO, Nb
Ta
2
O
5
, Ta
ZrO
2
, Zr
Base
TiO
2
, T i
N b
2
O
5
, NbO, Nb
Ta
2
O
5
, Ta
ZrO
2
, Zr
9.3.3.6 Preliminary In Vitro Studies on LENS™ Deposited TNZT.
Bone
formation is a complex process involving the migration of bone cells to the bone
surfaces termed as bone proliferation of the osteoprogenitor cells and their sub-
sequent differentiation into osteoblasts. Hence assessing the extent of bone pro-
liferation and bone differentiation on the surface of a material of interest is a
method to evaluate its biocompatibility. In this study, primary rat bone marrow
cells isolated from the femurs of Sprague Dawley rats were seeded in T-75 fl asks
and subsequently incubated. Seeded cells were then detached and resuspended
in media to achieve a seeding density of 10,000 cells /cm
2
and added on to the
Ti-6Al-4V and TNZT disk samples. Following this the disks were incubated for
6 hours to allow for cell adhesion. The disks were then transferred to well plates
used as positive controls. After the fourth and the seventh day or (third and the
sixth day) the disks were treated with a lysing agent and cells grown on top of the
disks were scraped and the lysate was pippetted out. A Pico green assay kit was
used to quantitatively determine the amount of double stranded DNA present
in the cultured cells. Alkaline phosphate, an enzyme found in the early stages of
osteoblast formation, was used as an early marker of the differentiation of bone
marrow stromal cells into osteoblast cells. This experiment was repeated twice to
ensure the reproducibility in the test results.
In the fi rst set of data obtained, shown in Figure 9.17a, it was observed that
rate of bone proliferation measured as a function of the amount of DNA present
in the cultured cells was higher in the case of LENS™ deposited TNZT alloys
when compared to the control Ti-6Al-4V ELI after four days. However, after
seven days, both the Ti-6Al-4V and TNZT exhibited almost the same rate of bone
proliferation. The rate of bone differentiation studied using Alkaline Phosphate
enzyme as a marker showed a signifi cant amount of ALP enzyme in the TNZT
sample when compared to the Ti-6Al-4V, indicating enhanced bone differentia-
tion after a period of seven days. As seen from Figure 9.17b, the amount of ALP
enzyme that was present in case of the Ti-6Al-4V sample was relatively lower
than that present in the TNZT sample. These preliminary
in vitro
results are quite
encouraging and suggest that laser deposited TNZT alloys are biocompatible
since they aid both in bone cell proliferation and differentiation. The second sets
of experiments were also done under conditions similar to those used for the fi rst
set of tests and the results from these experiments are shown in Figures 9.18a and
9.18b. The PicoGreen DNA assays (Invitrogen) have been used to measure total
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