Identifying small molecule impurities in electrospun poly(vinyl alcohol) nanofibres using ultra-selective NMR

Electrospinning is a widely employed manufacturing platform for preparing polymers for tissue engineering applications, producing structures that closely mimic the extracellular matrix. However, electrospinning is not benign, with high temperatures, pressures and voltages applied to the polymers throughout the process. Small molecule impurities have been detected using nuclear magnetic resonance (NMR) spectroscopy of electrospun poly(vinyl alcohol) materials. Different electrospinning techniques produce different impurities: DC needle electrospinning produces no observable impurities in the final sample, while both DC needleless and AC electrospinning produce a range of impurities. However, sample spectra feature both broad polymeric peaks and mixtures of the small molecule impurities. With most conventional NMR techniques, interpreting such spectra remains a major challenge. The use of ultra-selective magnetic resonance techniques, based on the GEMSTONE pulse sequence, allows for impurity peaks to be isolated, correlated to other signals in the spectrum, and for the structures of the chemicals responsible to be determined. Linear alkyl chains, differing in chain length, were identified in samples produced by DC needleless electrospinning. AC electrospinning produced small molecules with isopropyl groups, differing in molecular weight but not in structure, suggesting dimers, oligomers, or condensation products. For the set of samples measured, there was no apparent cytotoxic effect from the impurities. With a growing range of polymers processed by electrospinning, identification of small molecule impurities, and their effects on biomedical applications, will be increasingly important.