Biomedical Engineering Reference
In-Depth Information
cartilage, on the analysis of the effects of shear stresses on changes in SF viscosity and on the
analysis of the residual strains arising in AC at cyclic loading.
2.1 Rheological properties of synovial fluid
With respect to the project objectives, the focus of interest was on the confirmation of the
rheological properties of hyaluronic acid with sodium anions (sodium hyaluronan, NaHA)
in an amount of 3.5 mg ml
-1
in distilled water without any other additives. The use of only
NaHA was based on the verification of the association of HA macromolecules and on the
manifestation of highly specific rheological properties of SF, which regulate its lubrication
function. The rheological properties were verified using the rotation viscometer Rheolab QC
(Anton Paar, Austria). Viscosity values were measured continuously within 8 minutes.
Fig. 5. SF apparent viscosity as related to time (velocity gradient 100s
-1
)
Samples were subjected to the effect of constant velocity gradient (100s
-1
- 500s
-1
- 1000s
-1
-
2000s
-1
) in time 0 - 120s and 240 - 360s. Samples were subjected in the tranquility state in
time 120 - 240s and 360 - 480s. The measurements were performed at the temperature of
human body (37°C).
Fig. 5. clearly shows that at the constant SF flow velocity gradient 100s
-1
there is a distinct
time-related constant values in viscosity. The verified synthetic synovial fluid possesses
pseudoplastic properties
. It is evident that the
macromolecules of hyaluronic acid (NaHA/HA) in a
water dispersion environment principally contribute to the pseudoplastic behaviour of the fluid. This
property is of key importance for controlling the quality of the AC surface protection.
Fig. 6. also shows that at the constant SF flow velocity gradient 2000s
-1
there is a distinct
time-related constant values in viscosity. The viscosity of SFafter unloading always returns
to the same values (ca 0.8 Pa s).
Fig. 7. shows that viscosity values of SF with increasing rate of flow velocity gradient 0 -
2000 s
-1
(in time 0 - 60s) decrease. Viscosity values of SF are constant with constant rate of
velocity gradient 2000 s
-1
(in time 60 - 180s).
