Development of photo-crosslinked poly(aspartic acid) fiber networks via electrospinning

Poly(aspartic acid) (pAsp)-based fiber networks were developed via electrospinning and photo-crosslinking. Fiber networks hold the advantage that they exhibit a high surface-to-volume ratio, giving rise to a high water uptake and retention capacity, along with the ability to release moisture under desired circumstances (e.g. reduced relative humidity, mechanical pressure, etc.). Herein, polysuccinimide (PSI), the precursor of pAsp, was modified with 5-norbornene-2-methylamine to obtain crosslinkable norbornene-modified PSI (PSI-NB) with two different degrees of substitution, i.e. 19% and 46%. These derivatives were electrospun into thin uniform fibers after optimization of the processing parameters. The fiber sheets were crosslinked via a thiol-ene step-growth mechanism with three different thiol crosslinkers exploiting UV-A irradiation in the presence of TPO-L as photo-initiator. Using this strategy, fiber networks with diameters ranging between 1.27 ± 0.29 and 2.20 ± 1.05 µm were obtained, as visualized with scanning electron microscopy (SEM). Successful crosslinking was evidenced by a dissolution test in dimethylformamide and through X-ray photoelectron spectroscopy. Finally, the PSI-NB fiber networks were hydrolyzed to obtain pAsp-NB fiber networks by alkaline hydrolysis in a carbonate buffer solution, as confirmed by Fourier-transform infrared spectroscopy. The morphology of the fibers following hydrolysis was visualized by SEM and the average fiber diameters were calculated and compared to the diameters before hydrolysis, generally showing a diameter increase due to swelling of the fibers in aqueous solution. In conclusion, pAsp-based fiber networks were successfully developed and stabilized via photo-crosslinking.