Synthesis of a novel clay-based nanocomposite hydrogel with attractive mechanical properties and its potential application in 3D-Printing

Abstract

Event Abstract Back to Event Synthesis of a novel clay-based nanocomposite hydrogel with attractive mechanical properties and its potential application in 3D-Printing Xinyun Zhai1, 2*, William Lu1* and Wenguang Liu2* 1 The University of Hong Kong, Department of Orthopaedics and Traumatology, Li Ka Shing Faculty of Medicine, Hong Kong, SAR China 2 Tianjin University, School of Materials Science and Engineering, China Introduction: In our study a novel nanocomposite hydrogel (NC gel) was successfully prepared by in situ free-radical photo-polymerization of the acrylic acid derivatives – 4-Acryloylmorpholine in the presence of exfoliated clay platelets in aqueous systems with different clay contents. Although N-isopropylacrylamide (NIPAM) and N, N-dimethylacrylamide (DAMAA) have already been used as monomers in the clay-based hydrogel, this was the first time to add this kind of acrylic acid derivative into clay system and hydrogel could form without using an organic cross-linker[1],[2]. The obtained hydrogel not only exhibits dramatic improvements in mechanical properties but also has drug loading and release behaviors. Materials and Methods: 4-Acryloylmorpholine (monomer) and 2-Hydroxy-2-methylpropiophenone (1173, initiator) were purchased from Sigma-Aldrich. Synthetic hectorite clay of sol-forming grade LAPONITE XLS (Rockwood Ltd., 92.32 wt % of Mg5.34Li0.66Si8O20(OH)4Na0.66 and 7.68 wt % of Na4P2O7) was used directly. The 4-Acryloylmorpholine/clay nanocomposite hydrogels were synthesized by in situ free-radical photo-polymerization of 4-Acryloylmorpholine in the presence of exfoliated clay. Firstly, clay was dispersed in water under ultrasonication for 1 h. Secondly, 4-Acryloylmorpholine and 1173 were added to the clay suspension. After the solution was mixed well, it was transferred into plastic tubes with about 2 mm inner diameter. Photo-polymerization was carried out for 50 min in a crosslink oven (XL-1000 UV Crosslinker, Spectronics Corporation, NY, USA). The clay content was varied from 1 to 10 wt % with respect to the 4-Acryloylmorpholine weight and the solid content of the nanocomposite hydrogel was varied from 20% to 30%. Tensile tests, compression tests, FTIR, XRD, SEM, TEM, XRD and Raman spectrum were used in our experiment. Results and Discussion: Mechanical tests show that the obtained 4-Acryloylmorpholine clay-based hydrogel has the best tensile strength (about 400 kPa) and excellent stretch ability (higher than 5000%) when clay content and solid content are 5% and 20% respectively. The compression strength of the hydrogel is higher than 8 MPa and can recover to its original shape when compression ratio is less than 80% which will be very attractive for tissue engineering. It is very different from the original physically cross-linked nanocomposite hydrogels that the resulting hydrogel can still stretch up to 2000% in the swollen state. Unlike conventional physically cross-linked hydrogels, this kind of clay-based hydrogel is insoluble in PBS or hot water even the temperature is 80~90 ℃ due to the high hydrogen bonds exist between 4-Acryloylmorpholine polymer and clay which has been confirmed by Raman spectroscopy. Both the XRD and TEM results demonstrate the uniform dispersion of clay in the nanocomposite hydrogel and the formation of the clay-based hydrogel. Furthermore, by using 4-Acryloylmorpholine as the monomer, the hydrogel has drug loading and release behaviors, as the weight ratio of 4-Acryloylmorpholine increases, higher drug release can be observed. Conclusion: Nanocomposite hydrogels composed of 4-Acryloylmorpholine and Laponite XLG clay showed attractive fracture strain up to 5000% and good compression strength (higher than 8 MPa). This kind of hydrogel was synthesized by in situ photo-polymerization of 4-Acryloylmorpholine with the presence of exfoliated Laponite XLG clay. The strong hydrogen bonds between 4-Acryloylmorpholine polymer and clay are suggested to account for the good mechanical properties of the hydrogel. More interestingly, the obtained hydrogel has good biocompatibility and high viscosity before photo-polymerization, which means this kind of hydrogel is a very suitable bioink candidate of the layer-by-layer bioprinting method for the fabrication of stratified tissues[3].