Ultrasonic depolymerization of hyaluronic acid

Hyaluronic acid (HA) was depolymerized by ultrasonication. Changes in molecular weight and molecular weight distribution were observed by size exclusion chromatography with a low-angle laser light scattering photometer. We investigated the influence of sonication intensity, temperature, HA concentration, coexisting cations and ionic strength. Results demonstrated that, with an increase of intensity, initial depolymerization rate (k) increased and ultimatedepolymerized molecular weight (M-lim) converged to smaller size. The factors that change high-order structure of HA molecules had great influence upon the k, but not so much upon the Mlim. For example, continuous sonication with 55 W depolymerized the HA to almost the same M-lim (approximately 0.1 x 10(6)), with a few exceptions. Where exceptions occurred, they were in concentrated monovalent cation solutions; the M-lim increased up to about 0.3 x 10(6). Consequently, by regulating the sonication conditions, HA with the desired lower molecular weight and a narrow distribution could be prepared from high molecular weight samples. (C) 2001 Elsevier Science Ltd. All rights reserved.