Electrospun natural melanin nanoparticles on polyvinyl alcohol nanofiber hybrid meshes: Processing and crosslinking optimization

Hybrid systems consisting the combination of nanofibers and nanoparticles provide great benefits for nanotechnology and its theranostic applications. Herein, a hybrid system incorporates natural melanin nanoparticles (MNPs) and polyvinyl alcohol (PVA) based nanofibers was introduced using electrospinning method by taking account the effects of viscosity and conductivity of MNP and PVA solutions along with the potential physicochemical effects of crosslinking on the process. Monolithic and core-shell hybrid substances were designed using single and coaxial nozzles at different voltage and flow rates. Scanning electron microscopy (SEM) images were employed for the evaluation of the nanofiber morphology to acquire optimized parameters of the electrospinning process. SEM analysis indicated that the diameters of monolithic and core-shell nanoparticle-nanofiber hybrids were 304 +/- 88 nm and 465 +/- 56 nm, respectively, depending on the nozzle type. Additionally, nanofibers were assessed in terms of mechanical strength and compatibility between MNPs and PVA. The stability of nanofibers was enhanced with solution crosslinking by considering swelling, degradation rates and in vitro release kinetics of MNPs. The most promising monolithic nanofibers were obtained at a ratio of 7:3 (PVA:MNP) and 10-30 min of crosslinking yielded stable nanofibers after interaction with water. ATR-FTIR spectrum analysis showed that compatibility in monolithic and core-shell nanofibers was rendered by hydrogen bonds between OH in PVA and -NH2/- OH in MNPs. As a result of the crosslinking process, the nanofibers gained better swelling and less degradable properties, thus no MNP release occurred from the matrix. As another notable point, compared to monolithic and non-crosslinked nanofibers, core-shell and crosslinked nanofibers presented stronger mechanical properties. Consequently, an optimization study incorporating both crosslinking and electrospinning methods was conducted to obtain MNPs and PVA based nanofibers for applications with green, sustainable, multifunctional and photoactive substances in biomedical engineering.