Novel self-assembled hydrogels by stereocomplex formation in aqueous solution of enantiomeric lactic acid oligomers grafted to dextran

This paper describes a novel hydrogel concept, which is based on self-assem bling of enantiomeric lactic acid oligomers (stereocomplex formation) graft ed to dextran. The hydrogels are prepared in an all-aqueous environment. Fo r this purpose, L- and D-lactic acid oligomers were coupled to dextran, yie lding dex-(L)lactate and dex-(D)lactate, respectively. Upon dissolving each product in water separately and mixing the solutions, we observed that a h ydrogel is formed at room temperature as demonstrated by rheological measur ements. The storage modulus of the obtained hydrogel strongly decreased upo n heating to 80 degrees C, while it was restored upon cooling to 20 degrees C, demonstrating the thermoreversibility and the physical nature of the cr oss-links. Rheological experiments with monodisperse lactic acid oligomers grafted to dextran showed that the dey ee of polymerization (DP) of the lac tic acid oligomers must be at least 11 to obtain. a hydrogel. The hydrogel characteristics can be modulated by varying the degree of polymerization (D P, number of lactate units per oligomer) and the degree of substitution (DS , number of lactic acid side chains per 100 glucopyranose units) of the dex -lactate products, as well as the water content of the dex-lactate solution s. Stronger gels were obtained by increasing the DP and DS and by decreasin g the water content. FTIR-photoacoustic (PA) analysis demonstrated that in the hydrogels stereocomplexes were formed between the lactic acid oligomers of opposite chirality.