Nacre-like Nanocomposite Films From Fluorescent Hyperbranched Polymer And Clay Nanosheets

The mechanical properties of nacre are very excellent. Its strength is as high as135MPa, and its modulus is as high as70GPa. Such excellent properties come from theunqiue brick-and-mortar structure of Nacre. Inspired by the hierarchical structure ofnacre, lots of high strength nacre-like composites have been fabricated. Through finelyadjusting the components and the structure, some other multi-functional nacre-likecomposites were also prepared. However, there are only few reports on the fluorescentnacre-like composites. During the preparation of such fluorescent materials, the layereddouble hydroxide or quantum dots containing heavy metals, or the conjugated polymerwith aromatic groups on their backbone were use. Consequently, these fluorescentnacre-like composites are of poor biocompatibility. To make the fluorescent nacre-likematerials useful in biological or biomedical applications, it is urgent to explore somenew approaches to fabricate nacre-like nanocomposites with both good biocompatibilityand good fluorescent properties.Because of its good fluorescent property and good biocompatibility, aliphatichyperbranched poly(amido amine)(HPAMAM) becomes an ideal raw material infabricating such multifunctional nacre-like composites. Here in this work, we assemblythe HPAMAM and clay nanosheets to form the multi-functional composites withlayered structure. The results showed that the composite films fabricated were ofexcellent mechanical properties and good fluorescent property. Analysis on the structureof the composite films showed that the HPAMAM and clay nanosheets were assembledorderly. The alignment of the clay nanosheets was in the direction of the surface of thefilms. Such fluorescent and biocompatible composite films are very promising inbio-sensors, biomedical research and high performance display devices.Considering that the HPAMAM can bond many metal ions strongly, we used somekinds of metal ions, including Cu2+and Al3+to modify the HPAMAM/nanoclaycomposite films. The HPAMAM was successfully crosslinked by the metal ions, andthus the mechanical strength of the HPAMAM/nanoclay composite films could begreatly improved further. The metal ions modified composites films were also oflayered structure similar to the brick-and-mortar structure of nacre and fluorescentemission ability. The mechanical strength of the modified composite films was2timesthat of the original films, which was almost8-10times that of the pristine HPAMAM. In the former reports, it was revealed that the Cu2+could enhance the cell adhesive ability,so that it was expected that this kind of high strength, fluorescent and biocompatiblecomposite films would open the door to the wide applications of cell culture and tissueengineering.