Study On Degradable Alginate Hydrogels

Alginate has been widely used in a variety of biomedical applications includingtissue engineering. However, alginate itself has a very slow degradation rate, and itsgels degraded in an uncontrollable manner, releasing high molecular weight strandsthat may have difficulty being cleared from the body. On purpose of improving thebiodegradability of alginate, commercially available guluronic acid-rich highmolecular weight alginate was oxidized using sodium periodate. CD analysis revealedthat the content of mannuronic acid (M) in sodium alginate hardly decreased whenmore oxidizers were used. IR analysis confirmed the characteristic peak of aldehydegroup in the oxidized alginate. Additionally, the oxidation degree (OD) or thealdehyde contents were measured by using photometry and titration methods. The ODof alginate increased as the amount of added sodium periodate was increased, whilethe molecular weights were reduced obviously. The molecular weights of alginatewere also markedly affected by reaction temperature. Oxidized sodium alginate withproper doses sodium periodate (NaIO4/mono=0.05) reacted for 24h at roomtemperature fully degraded at physiological condition (37℃, pH 7.4 SBF) after 5days incubation and the molecular weight reduced from 13.2×104 to 3.9×104.Initial and oxidized sodium alginates were ionically cross-linked withCaCO3-GDL (D-glucono-δ-lactone). The rheological behavior of alginate i.e. sol-geltransition was measured by a rheometer. The gelation time of hydrogels could becontrolled within 5-8 min with proper cross-linking density and sodium alginatesolution concentration. The result is excited for injectable hydrogels used in tissueengineering. The water content of oxidized alginate hydrogels was similar to theinitial ones and kept at relatively high levels (10-60 g water/g polymer). Compressivemodulus (E) and dynamic modulus (G*) measurements confirmed that the oxidizedalginate hydrogels showed poorer mechanical properties than initial hydrogels.However, E and G* could keep in 0.5-1MPa and 3-12kPa, respectively throughadjusting the oxidation and cross-linking condition. Being immersed in SBF under37℃ for several days, E of oxidized alginate hydrogels decreased obviously withincubation time and reached a constant value. Partially oxidized alginate hydrogelscross-linked with CaCO3-GDL, could be endued with good degradability, mechanicalproperty and gelation rate. The results will be helpful for the further research anddevelop on alginate hydrogels for tissue engineering.