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Students
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Jennifer
Gordon
Biosystems Engineering
Applied Biotechnology Concentration
Summer Research
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A
Comparison of Wear on UHMWPE in Bovine Serum and Bovine Serum
with Added Phospholipase A2
Gordon, M. Gaevart, J. DesJardins, C. Bahler, M. LaBerge Department
of Bioengineering, Clemson University, Clemson, SC
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Introduction
Previous research has shown that Phospholipase A2 (PLA2), an enzyme
that hydrolyzes glycerophopholipids and can be found in synovial
fluid, has degradative effects on certain materials. This research
shows the effects of using bovine calf serum with Phospholipase
A2 as a lubricant during wear tests on UHMWPE. An analysis will
be made to compare the volume lost in UHMWPE samples in bovine
calf serum and UHMWPE samples in bovine calf serum with added
Phospholipase A2.
Methods and Materials
The samples being tested were UHMWPE. The surfaces of each sample
were analyzed under the Wyko NT-2000 surface profilometer, and
a roughness value was taken for each. After the samples were ready
for testing, the machine performing the test, the CU Tribo I,
was set up. For the upper bearing surface, six stainless steel
bolts were machined to have a radius of 15 mm. A weight of 254.84
g was applied to each of the six stations. The loading was determined
by inputing the modulus of elasticity, radius of curvature and
Poison’s ratio for each material into the Hertizian contact
equation.
UHMWPE
Modulus of Elasticity = 680 MPa
Radius of Curvature ~ 10000
Poison’s ratio = 0.45
The output determined the force (N) to be exerted on each sample.
The peak contact was then determined to be 12 MPa. A solution
of 50% bovine calf serum and 50% water was then prepared for use
as lubrication between the upper bearing surfaces and the UHMWPE
samples. A total of 600 mL was extracted from this portion of
bovine serum solution in order to add the needed amount of phospholipase
for testing. For the 600 mL extracted, 0.00065g of phospholipase
was added. For stations 1, 3 and 5, the phospholipase solution
was added. For stations 2, 4 and 6, the original bovine solution
was added. Once the test began, it ran for a total of 200,000
cycles. This was calculated to be 20 kilometers for the total
path length of the given star shape. (Figure 1) (This shape was
determined before testing began.)
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Figure
1: Star Pattern
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Figure
2: Cross-shear under the Wyko profilometer
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Results and Discussion
Comparing
PLA2 and non-PLA2 solution:
The CU Tribo I ran for approximately 9 days to reach a
total of 200,000 cycles. When analyzed under the profilometer,
the samples in phospholipase solution and the samples in non-phopholipase
solution showed no significant difference in wear (Figures 3
and 4). After performing a two-tailed distribution t-test for
a two-sample unequal variance calculation on both wear track
and cross-shear analysis, the numbers proved to be statistically
equal. P-values for PLA2 solution and non-PLA2 solution were
0.318 and 0.114, respectively.
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Figure
3: PLA2 vs. No PLA2 Wear Track
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Figure
4: PLA2 vs. No PLA2 Cross-shear
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References
Tanaka and H. Yu (2002) Langmuir. 18, 797-804, Y. Oda, A. Yonetsu,
T. Urakami, and K. Tonumura (2000) Journal of Polymers and Environment.
8, 29-32, S. Kobayashi, H. Uyama, and T. Takamoto (2000)
Biomacromolecules. 1, 3-5, C. Sumner, A. Sabot, K. Turner, and
S. Krause (2000) Anal. Chem. 72, 5225-5232, J. DesJardins
(2002) Trans. SFB. 28, 711,, R. Gahlin and S. Jacobson (1998)
Wear. 222, 93-102, Johnson (1985) Contact Mechanics. Cambridge
Univ. Press, 91-105. http://grove.ufl .edu/~wgsawyer/Laboratory/Software/Circular/CircularContacts.html<br>
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