Characteristics of complexes composed of sodium hyaluronate and bovine serum albumin

Complexes composed of sodium hyaluronate (NaHA) and bovine serum albumin (B SA) were studied to elucidate the exact composition of the complex, the pha se separation, the electrophoretic mobility and the size using dynamic ligh t scattering (DLS) and electrophoretic light scattering (ELS), etc. The pha se diagram of the mixed solutions was determined, The complexes were solubl e in neutral or weakly acidic pH regions and showed phase separation in the more acidic pH region. From the concentration of Na+ released from NaHA wh en it binds to BSA, the ratios of BSA to NaHA of the complexes were determi ned. In the region of soluble complexes, one BSA molecule was determined to bind with 15 carboxylic groups of NaHA and in the region of insoluble comp lexes to bind with 6 carboxylic groups. At the phase separation point, 117 BSA molecules bound with one NaHA molecule and 17% of the carboxylic groups of NaHA did not contribute to the binding of BSA, The sizes of the complex es decreased from several mu m to several hundred nm as the binding ratio o f BSA increases. Decreases in the viscosities of the mixed solutions were c onsistent with the decreases of the sizes. From these results, a model of c omplex formation is proposed.