Manipulating the degradation rate of PVA nanoparticles by a novel chemical-free method

The high water solubility of poly (vinyl alcohol) (PVA) is one of the challenging problems in its application. In order to rectify this problem, PVA needs to be crosslinked. Freeze-thawing in solid state as a novel physical crosslinking method was employed for enhancement the stability of PVA nanoparticles in aqueous solutions during this study. PVA nanoparticles were successfully prepared by electrospraying and electrospray conditions were optimized in the view points of polymer concentration and solvent system. The morphology of nanoparticles was tailored from collapsed particles and mixture of particles/fibers to spherical particle by manipulating of polymer solution concentration and solvent system. After preparation of PVA nanoparticles in optimum condition, they were frozen at -20 degrees C and subsequently thawed at 25 degrees C for different cycles of 1, 2, and 3. Field-emission scanning electron microscope (FE-SEM), Fourier-transform infrared (FTIR), X-ray diffraction (XRD), differential scanning calorimeter (DSC), and biodegradation were used to evaluate the effect of freeze-thawing on properties of PVA nanoparticles. FE-SEM showed the spherical morphology of the PVA nanoparticles with sizes ranging from 200 to 300 nm. The FTIR spectroscopy indicated that the crystallinity of PVA nanoparticles increases after freeze-thawing process. Moreover, by increasing the number of cycles, degree of crystallinity of nanoparticles increases. The XRD and DSC analysis of PVA nanoparticles again demonstrated the increasing of crystallinity of nanoparticles after freeze-thawing process. The biodegradation behavior of PVA nanoparticles after freeze-thawing exhibited the decreasing of degradation rate by increasing the number of cycles. Our overall results present a solvent-less and safe method for crosslinking of PVA nanoparticles in solid state, which make it suitable for biomedical applications.