Layer-by-layer self-assembly, controllable disintegration of polycarboxybetaine multilayers and preparation of free-standing films at physiological conditions

The self-assembly and disintegration behavior of polyzwitterion, poly(4-vinylpyridiniomethanecarboxylate) (PVPMC), and negatively charged polyelectrolyte, poly(acrylic acid) (PAA), layer-by-layer (LbL) multilayer films were investigated in detail by using UV-vis absorption spectroscopy, quartz crystal microbalance (QCM) and atomic force microscopy (AFM). The results indicated that the PVPMC/PAA multilayer films grew linearly with increasing bilayer number. The disintegration rate of PVPMC/PAA multilayers could be well controlled by varying the concentration of salt in aqueous solution. It was found that PVPMC/PAA multilayer films could be completely disintegrated in 0.9% normal saline solution within 15 min. Such controllable disintegration behavior rendered the PVPMC/PAA multilayer as an excellent sacrificial sublayer for fabricating freestanding LbL multilayer films. Free-standing multilayer films were then successfully fabricated by LbL self-assembly of positively charged polyelectrolyte complex (PEC), made from poly(diallyldimethylammonium) (PDDA) and poly(sodium 4-styrenesulfonate) (PSS), and negatively charged PSS with PVPMC/PAA as a sacrificial sublayer, which was disintegrated in 0.9% normal saline solution. The obtained free-standing films had good mechanical properties with 24.1 MPa tensile strength at break and 0.56 GPa Young's modulus.