Melatonin-loaded PVDF–alginate emulsion-electrospun nanofibers modulate macrophage function and tissue-associated responses after experimental spinal cord compression

Spinal cord injury (SCI) is characterized by persistent neuroinflammation and limited tissue repair, creating a need for local drug-delivery systems that combine structural support with immunomodulatory activity. In this study, melatonin-loaded polyvinylidene fluoride–alginate (PVDF–ALG–MEL) nanofibers were fabricated by emulsion electrospinning and evaluated for physicochemical properties, drug release, biocompatibility, macrophage responses, and tissue-associated effects in a rat compression-SCI model, in comparison with free MEL. A formulation containing a nominal 2% (w/w) MEL feed produced stable, bead-free fibers and was selected for further testing. MEL incorporation increased tensile strength from 5.25 ± 0.11 to 6.14 ± 0.12 MPa, reduced the water contact angle from 72.5 ± 1.2° to 57.6 ± 1.1°, and increased swelling at 168 h from 225 ± 8% to 275 ± 9%, while porosity remained above 90%. Under the hydroalcoholic sink conditions used for in vitro characterization, cumulative MEL release reached approximately 95% of the experimentally determined MEL content of the 3.4-mg scaffold specimen within 72 h. Both scaffolds showed low hemolysis and maintained L929 cell metabolic activity. In macrophages, both free MEL and PVDF–ALG–MEL reduced yeast uptake and nitrite accumulation, enhanced apoptotic-cell engulfment, downregulated Il1b, Tnf, and Nos2, and upregulated Il10 and Arg1; however, the effects of the MEL-loaded scaffold were generally more pronounced. At 28 days after SCI, free MEL and the MEL-loaded scaffold were associated with lower Iba-1 and GFAP concentrations, reduced Bax and Gfap expression, and increased NSE, Bcl2, and Gap43. Whole-lesion gene-expression analysis additionally showed lower Il1b and Tnf and higher Il10 and Arg1 expression in the treated groups relative to untreated SCI, with the PVDF–ALG–MEL group showing the most pronounced directional changes in several markers. Functional assessment demonstrated progressive improvement in BBB locomotor scores, gait parameters, and motor-evoked potential responses, with the PVDF–ALG–MEL group showing the most pronounced improvements in several functional endpoints; however, quantitative histomorphometry, cell-specific mechanisms, and physiologically relevant in vivo drug-release kinetics require further investigation. Download: Download high-res image (275KB) Download: Download full-size image