Thermal degradation of high molar mass hyaluronan in solution and in powder; comparison with BSA Jakub Mondek, Michal Kalina, Vasile Simulescu * , Miloslav Peka  r Materials Research Centre, Faculty of Chemistry, Brno University of Technology, Purky nova 118, 612 00 Brno, Czech Republic article info Article history: Received 15 May 2015 Received in revised form 11 June 2015 Accepted 13 June 2015 Available online 18 June 2015 Keywords: Bovine serum albumin Hyaluronic acid Thermal degradation SEC-MALLS Electrophoretic light scattering abstract The aim of the present work was to compare the thermal degradation of bovine serum albumin and hyaluronic acid of different molar masses by determining the loss in molecular weight by means of SEC- MALLS (size exclusion chromatography e multi angle laser light scattering). For all measured samples, the results obtained by this method were compared with the results for stability determined by elec- trophoretic light scattering. The degradation study was performed in solution and in powder. Bovine serum albumin (also known as BSA) is a protein derived from cows, which has many biochemical applications. Hyaluronic acid (hyaluronan or HA) is an anionic nonsulfated glycosamino- glycan distributed widely throughout connective, epithelial, and neural tissues. The powder and solutions of BSA and HA were heated at different temperatures ranging from 37  C to 120  C for certain periods (the highest temperature was used only for the powder). The observed degradation increased with the duration of heating and with temperature for all hyaluronic acid samples analyzed in this work, in accord with Arrhenius law. At 37  C and 60  C, only moderate degradation was observed for hyaluronic acid solutions. For BSA at 37  C no degradation was observed and at 60  C significant aggregation occurred. © 2015 Published by Elsevier Ltd. 1. Introduction Hyaluronic acid, in the form of a sodium salt (hyaluronan or HA) is one of the most important polysaccharides originating in the mammalian body. During the last few decades, many studies have focused on its role in tissues, body fluids, and cell proliferation, and developed ways to use this polysaccharide in wound healing, drug delivery systems, and anti-aging applications. Hyaluronan is a linear natural polysaccharide of the glycosaminoglycans family. Its chemical structure comprises disaccharide units composed of D- glucuronic acid and N-acetyl-D-glucosamine, which are alterna- tively linked through 1,3 and 1,4 glycosidic bonds [1]. Hyaluronic acid can be synthesized via polymerization reactions [2], as in the case of other polymers obtained by different synthetic processes (co-polymerization, polymerization in solution, enzymatic poly- merization etc) [3e6]. Hyaluronan of different molar masses has different roles in the body. For example, high molar mass hyaluronan organizes the extracellular matrix and low molar mass hyaluronan can be found in injured tissue or in certain tumors [7,8]. The stability of hyalur- onan and its molar mass are important not only from the point of view of its physiological functions but also in the development of its applications (e.g. tailoring its molar mass to a specific application) and in how it is handled, both in its solid and dissolved form. Many methods of how to cleave hyaluronan were summarized in the review by Stern et al. [9]. Low or high pH conditions have obvious effects on hyaluronan. In acid solution, hydrolysis occurs on the glucuronic acid residue and the hemiacetal ring remains. In basic solution, hydrolysis oc- curs on the N-acetylglucosamine residue. Such hydrolysis obeys first order kinetics [10]. Other observations suggest that random chain scission occurs during hydrolytic degradation [1,10,11], and this same mechanism has also been proposed for the thermal degradation of hyaluronan [12e14]. The degradation of hyaluronic acid powder using different methods (electron beam irradiation, gamma ray irradiation, microwave irradiation, and thermal treat- ment) was reported in a study by Choi et al. [15]. The thermal degradation of hyaluronan has not been investigated from the point of view of the decrease in its molar mass. This, therefore, was the main focus of this work, in which the thermal behavior of * Corresponding author. E-mail address: simulescu@fch.vutbr.cz (V. Simulescu). Contents lists available at ScienceDirect Polymer Degradation and Stability journal homepage: www.elsevier.com/locate/polydegstab http://dx.doi.org/10.1016/j.polymdegradstab.2015.06.012 0141-3910/© 2015 Published by Elsevier Ltd. Polymer Degradation and Stability 120 (2015) 107e113