Promoted cell proliferation and mechanical relaxation of nanocomposite hydrogels prepared in cell culture medium

Nanocomposite hydrogels (NC gels) were synthesized through in situ polymerization of N-isopropylacryl-amide (NIPAm) in the hectorite clay suspension made from cell culture medium Dulbecco's modified Eagle medium (DMEM). Cell cultured on these NC gels (D-NC gels) surface proliferated faster compared with that on the NC gels synthesized in water due to the nutrients in the D-NC gels. Cells attached and proliferated faster on the D-NC gels with higher modulus. In addition, cell sheets with good viability spontaneously detached from the gel surface by lowering temperature. Their tensile elongation at break was higher than 7 and the true strength sigma(true) was up to 800 kPa. The stress-strain curves of the D-NC gels were described quantitatively with the Mooney-Rivlin equation. A stretched exponential stress equation was adopted to express the stress relaxation of the D-NC gels with an average relaxation timer tau(similar to 10(2) s) estimated from data fitting, showing a broad distribution (polydispersity k similar to 0.4). The tau value, which was used in simulation for the tensile creep compliance of the D-NC gels, became shorter with increasing clay concentration due to the decrease in the network chain length. The relaxation process was similar to the natural articular cartilage. This work provides a facile way to produce hydrogels with improved cell compatibility and satisfactory mechanical properties for biomedical applications. (C) 2013 Elsevier Ltd. All rights reserved.