Figure 4.25: SEM Photo of Hyaluronic Acid Specimen, High Load, 22X

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1 Figure 4.25 shows the specimen from test CS18 at a magnification of 22X. Hyaluronic acid, dissolved at a concentration of wt.% in buffered saline solution, was the lubricant in this test, with high load. The wear scar is clearly visible over nearly the entire surface of the plug, running from the upper-left to lower-right of the photograph. The small, pebble-like objects on the surface are most probably artifacts that arose as a result of the gold-coating process. In Figure 4.26, the same specimen is shown at a magnification of 540X. Two types of primary ridges are visible in this photograph. The larger ridges, running in the direction of sliding, are more than 100 µm wide, while the smaller Figure 4.25: SEM Photo of Hyaluronic Acid Specimen, High Load, 22X 45

2 ridges, which run in the same direction, are on the order of 10 µm in width. The perpendicular secondary ridges also appear on this surface, though very small. The wear appears fairly severe on this specimen, as indicated by the depth of the large primary wear scar. Figure 4.26: SEM Photo of Hyaluronic Acid Specimen, High Load, 540X The specimen from test CS18 is shown at a magnification of 2000X in Figure The secondary ridges are shaped differently than before, and do not appear on all surfaces of the primary ridges. Instead of surrounding the primary ridges like rings, these features are smaller and more bulbous. While the primary ridges on this specimen are more pronounced than on the previous two specimens, the surface appears smoother in the direction of sliding; the perpendicular secondary features are not as prominent as before. 46

3 Figure 4.27: SEM Photo of Hyaluronic Acid Specimen, High Load, 2000X 47

4 4.5.2 SEM COMPARISON OF WEAR SURFACES AMONG LOADS The following section compares tests for each lubricant, under high and low load, to illustrate the differences that occur as a result of changes in applied load. Figures 4.28 and 4.29 show the specimen from test CS01, a high-load test using saline solution as the lubricant. These two photographs show deep grooves in the direction of sliding, which is from left to right in the image. Some perpendicular ridges are also visible on the top of one of the primary ridges, but these are not as prominent as on other specimens. Figure 4.28: SEM Photo of Saline Specimen, High Load, 540X 48

5 Figure 4.29: SEM Photo of Saline Specimen, High Load, 2000X Figures 4.30 and 4.31 show a similar specimen; this cartilage plug, CS03, was tested under low load with saline solution as the lubricant. The most prominent features on this surface are the deep wear tracks that run from left to right in the photograph. The perpendicular secondary features are almost nonexistent on this specimen, though some small perpendicular markings are visible on the large ridges. In both the high and low load saline tests, the primary wear tracks are the most notable characteristics of the surfaces. The perpendicular secondary features are visible on both, but only barely so on the low-load specimens. 49

6 Figure 4.30: SEM Photo of Saline Specimen, Low Load, 540X Figure 4.31: SEM Photo of Saline Specimen, Low Load, 2000X 50

7 The specimen from test CS02, a high-load synovial fluid test, is shown in Figures 4.32 and These two photographs exhibit deep ridges and grooves that run parallel to the sliding direction (from the left to the right of each photograph), as well as secondary markings perpendicular to this direction. Figure 4.32: SEM Photo of Synovial Fluid Specimen, High Load, 540X 51

8 Figure 4.33: SEM Photo of Synovial Fluid Specimen, High Load, 2000X Another synovial fluid test specimen, from test CS04, is shown in Figures 4.34 and This cartilage specimen was tested with synovial fluid under low load. In these photographs, the sliding direction is from the top to the bottom of the image. The primary wear track is visible in these images, parallel to the direction of sliding. These features do not penetrate particularly deeply into the cartilage surface, however, as those on the high-load specimen did. Secondary wear markings are not present at all on this specimen s surface; such features were a prominent characteristic of the high-load cartilage specimens. In the case of the saline and synovial fluid tests, the perpendicular wear markings tended to appear most prominently on the high-load test specimens. On low-load cartilage specimens, the primary wear track was much more pronounced than the secondary, if the perpendicular markings appeared at all. 52

9 Figure 4.34: SEM Photo of Synovial Fluid Specimen, Low Load, 540X Figure 4.35: SEM Photo of Synovial Fluid Specimen, Low Load, 2000X 53

10 The specimen from test CS18, a high-load hyaluronic acid test, is shown in Figures 4.36 and The sliding direction runs from the upper left to the lower right of the photograph, as indicated by the deep ridges in this direction. Perpendicular features are also visible, though small and more rounded than those observed on other specimens. Figure 4.36: SEM Photo of Hyaluronic Acid Specimen, High Load, 540X 54

11 Figure 4.37: SEM Photo of Hyaluronic Acid Specimen, High Load, 2000X Figure 4.38 shows the specimen from test CS23, a low-load hyaluronic acid test. The direction of sliding is approximately horizontal in this photograph. An uneven wear scar is visible, but most of the plug surface appeared relatively smooth and undamaged under low magnification. The primary wear track is barely visible in this photograph, running from the lower left to upper right of the image. The secondary wear marks are much more prominent than the primary, and can be seen as pronounced ridges perpendicular to the direction of sliding. The primary ridges are about 20 µm in width, while the secondary ridges are much smaller. Figure 4.39 shows the specimen from test CS23 at a magnification of 2000X. The primary ridges are no longer visible at all, and the secondary ridges are now the prominent feature. In addition to these markings, which are roughly 4 µm in width, fibers are visible between the ridges. These fibers are not visible on any of the high-load test specimens that were photographed at this magnification, but can be seen on several of the high magnification images of low-load test specimens. In locations in which the secondary ridges appear to have been pulled together by the opposing stainless steel surface, the fibers run primarily in the sliding direction. 55

12 Figure 4.38: SEM Photo of Hyaluronic Acid Specimen, Low Load, 540X Figure 4.39: SEM Photo of Hyaluronic Acid Specimen, Low Load, 2000X 56

13 The prominence of the secondary, perpendicular ridges is a feature that was observed on more than one of the low-load hyaluronic acid specimens. While high loads tended to produce more pronounced primary tracks in the direction of sliding, the perpendicular features tend to be the most pronounced features on the surfaces that were tested under low load. This difference, which only occurred with hyaluronic acid test specimens, suggests that the wear that occurs under low load may be caused by a different phenomenon than that which is found with high loads. The large primary ridges on the high load specimens are most likely the result of plowing from asperities on the harder surface of the stainless steel. The secondary features may result from adhesion between the surfaces, or some other factor that exaggerates the natural lubricant-rich hollows in the surface of the cartilage. 57