Osmotic pressure exerted by entangled polysaccharide chains.
The osmotic behavior of neutral and charged polysaccharide chains was studied utilizing membrane osmometry. Two neutral dextran fractions characterized by weight-average molecular weights of 5 X 10(5) and 2 X 10(6) daltons yielded identical osmotic pressure (pi)--mass concentration (C) relationships in the range of 0 to 8 g/dl. Furthermore, the relations were highly non-linear and departed markedly from the ideal Van't Hoff equation. For hyaluronate characterized by a weight-average molecular weight of 2 X 10(6) daltons, the pi vs C relations were dependent on the electrolyte (NaCl) concentration of the solution. In the polymer concentration range of 0.5 to 1 g/dl, increasing the ionic strength from 0.15 to 2 M NaCl caused a reduction in oncotic activity. At lower hyaluronate concentrations, oncotic activity was not altered by neutralizing the anionic sites with excess NaCl. The non-ideal behavior of the neutral and charged polysaccharide chains are compatible with recent statistical thermodynamic analyses of oncotic activity in concentrated polymer solutions. Finally, nonlinear pi vs C relationships of the matrix biopolymers provide a sensitive mechanism for volume buffering in the interstitium.