Modulation of the internal structure and surface properties of natural and synthetic polymer matrices by graphene oxide doping

A facile strategy for constructing lightweight, fire safety and compression resistance poly(vinylalcohol) aerogels with highly-efficient expansible graphene oxide/layered double hydroxides hybrid synergistic flame retardant

Poly(vinyl alcohol) (PVA) aerogels with excellent environmentally friendly properties have been considered to replace undegradable polymer foams. However, due to highly flammable, hydrophilic, and worse compression resistance performance, PVA aerogels have always been excluded from practical. Herein, a fire safety and compression resistance PVA/expansible graphene oxide (EGO)/Layered double hydroxides (LDHs) (PGL) aerogel was prepared via the freeze-drying method and electrostatic adsorption of flame retardant. The ice crystals from aerogels were sublimated and left a mass of tree-like pore tunnel structures. Meantime, the compound of EGO and LDHs rendered PGL aerogels high compressive strength of 6.0917 MPa (at 80% of strains), a high specific modulus of 19.16 m2/s2, and an ultra-low density of 0.059 g/cm3. Especially, the as-prepared PGL aerogels showed heat release reduced by 55.4%, smoke release reduced by 54.3%, and the limiting oxygen index reaching up to 31%. Moreover, LDHs also enhanced the interface with PVA/EGO resulting in hydrophobic performance improvement. The proposed enhancements mechanism suggested that (i) chemical reactions between EGO and PVA matrix; (ii) a mass of negative potential sites from the interface of PVA/EGO composites made LDHs sheets easily adsorbing; (iii) oxygen-containing groups from EGO and LDHs absorbed mass of heat during combustion; (iv) the compact char residues on the surface of aerogels acting as barriers suppressed smoke and prevented PVA matrix from further combustion. Therefore, electrostatic adsorption as a facile production process was paved for meeting the compression resistance, flame-retardant, heat-insulating, and smoke-suppressed requirements of PVA aerogels in this work.

Polysaccharide-based nano-engineered multilayers for controlled cellular adhesion in label-free biosensors

Controlling cellular adhesion is a critical step in the development of biomaterials, and in cell- based biosensing assays. Usually, the adhesivity of cells is tuned by an appropriate biocompatible layer. Here, synthetic poly(diallyldimethylammonium chloride) (PDADMAC), natural chitosan, and heparin (existing in an extracellular matrix) were selected to assembly PDADMAC/heparin and chitosan/heparin films. The physicochemical properties of macroion multilayers were determined by streaming potential measurements (SPM), quartz crystal microbalance (QCM-D), and optical waveguide lightmode spectroscopy (OWLS). The topography of the wet films was imaged using atomic force microscopy (AFM). The adhesion of preosteoblastic cell line MC3T3-E1 on those well-characterized polysaccharide-based multilayers was evaluated using a resonant waveguide grating (RWG) based optical biosensor and digital holographic microscopy. The latter method was engaged to investigate long-term cellular behavior on the fabricated multilayers. (PDADMAC/heparin) films were proved to be the most effective in inducing cellular adhesion. The cell attachment to chitosan/heparin-based multilayers was negligible. It was found that efficient adhesion of the cells occurs onto homogeneous and rigid multilayers (PDADMAC/heparin), whereas the macroion films forming "sponge-like" structures (chitosan/heparin) are less effective, and could be employed when reduced adhesion is needed. Polysaccharide-based multilayers can be considered versatile systems for medical applications. One can postulate that the presented results are relevant not only for modeling studies but also for applied research.