The viscosity values of the PVP solutions with different concentrations
are shown in Fig. 3(a). Regardless of the solvent, the
viscosity became higher with the PVP concentration increasing. The
viscosity of the PVP bovine serum solution was similar to that of the
PVP deionized water solution under the concentration of 0 and 5 wt%,
but became significantly higher when the concentration was beyond
5 wt%. Compared with the deionized water (i.e., 0 wt% PVP), the 5 wt%
PVP aqueous solution had a viscosity with about two-fold value. Each
5% increase of the PVP concentration led to about one time increase of
the solution viscosity. Similar trend was found in the variation of the
bovine serum solution viscosity with the PVP concentration varying.