Rheological properties of cross-linked hyaluronan-gelatin hydrogels for tissue engineering

Hydrogels that mimic the natural extracellular matrix (ECM) are used in three-dimensional cell culture, cell therapy, and tissue engineering. A semi-synthetic ECM based on cross-linked hyaluronana offers experimental control of both composition and gel stiffness. The mechanical properties of the ECM in part determine the ultimate cell phenotype. We now describe a rheological study of synthetic ECM hydrogels with storage shear moduli that span three orders of magnitude, from 11 to 3 500 Pa, a range important for engineering of soft tissues. The concentration of the chemically modified HA and the cross-linking density were the main determinants of gel stiffness. Increase in the ratio of thiol-modified gelatin reduced gel stiffness by diluting the effective concentration of the HA component.     

DNA-induced distamycin A fluorescence

The fluorescent properties of the antibiotic distamycin A were investigated in a range of materials including Trypanosoma cruzi epimastigotes, chicken erythrocytes, calf thymus DNA and synthetic polynucleotides using both microscopic and spectroscopic techniques. A bright blue-white fluorescence was observed from kinetoplast DNA and chromatin after treatment with distamycin A under ultraviolet (365 nm) excitation. Considerable enhancement of distamycin A fluorescence (emission peak at 455 nm under 320-340 nm excitation) was found in the presence of DNA and poly(dA-dT).poly(dA-dT). We discuss a possible explanation for this unexpected fluorescent emission, as well as its implications for microscopic and fluorimetric studies.