Abstract:

Objective Bio-based polyamide (PA) polymers have emerged as sustainable alternatives to petroleum-based counterparts, which have attracted significant attention in recent years. Among these, polyamide 56 (PA56) is polymerized from adipic acid and 1,5-pentanediamine, the latter of which can be commercially produced through biological fermentation. This particular PA holds significant potential in textiles, food packaging, engineering plastic and other fields, owing to its high-temperature and chemical resistance, excellent toughness and easy processability. Despite its promising prospects, limited studies have been given to the development of PA56 for functional biomaterials. In this study, we prepared S-nitrosoglutathione (GSNO), a nitric oxide (NO) donor, and encapsulated it within PA56 nanofibers using coaxial electrospinning. This work presents a novel strategy for engineering functionalized PA56 biomaterials with controlled NO release capabilities.

Method GSNO was synthesized using glutathione as the precursor and sodium nitrite as a nitrosylating reagent. GSNO was loaded into PA56 nanofibers via coaxial electrospinning with PA56 as the shell, and a blend of GSNO and polyvinyl pyrrolidone (PVP) as the core. The minimum inhibitory concentration (MIC) values of GSNO were determined using the broth microdilution method. The morphology of PA56/PVP coaxial nanofiber loaded with GSNO was characterized with transmission electron microscopy (TEM) and scanning electron microscopy (SEM). The NO release, mechanical and wettability properties of PA56/PVP coaxial nanofiber membranes were investigated. Furthermore, the antibacterial activity and skin stimulation were analyzed.

Results The MIC values of GSNO against Escherichia coli and Staphylococcus aureus were 10.51-21.02 μg/L, comparable to those of antibacterial agents such as oxytetracycline, florfenicol and canthin-6-one. The PA56/PVP coaxial nanofibers loaded with GSNO exhibited a core-shell structure, although no distinct interface was observed between the core and shell layers. This structural feature was attributed to the penetration of core PVP into the shell PA56. The fibers displayed uniform morphology and smooth surfaces, albeit with a minor occurrence of stripped PA56 nanofibers from the core, likely due to differences in the viscosity and volatilization rate between the core and shell solutions. The average diameter of PA56/PVP coaxial nanofibers increased with GSNO loading because of the increased viscosity and concentration of the core solution. When GSNO loading was 9%, the average diameter of PA56/PVP coaxial nanofibers became 942.70 nm, which is 198% of the average diameter of the blank PA56/PVP nanofibers (475.94 nm). The blank PA56/PVP coaxial nanofiber membranes presented an ultimate tensile strength of 5.57 MPa, which rose to 13.51 MPa with 9% GSNO loading. This enhancement is likely due to the formation of hydrogen bonds between the hydroxyl and amino groups of GSNO and the carbonyl groups of PVP. The surface water contact angle (WCA) of blank PA56/PVP coaxial nanofiber membranes was about 50.95°, with complete wetting occurring within 2.14 s. The WCA and complete wetting time of PA56/PVP coaxial nanofiber membranes increased with GSNO loading. The NO release from the PA56/PVP coaxial nanofiber membranes was evaluated using the Griess method. The sustained release times for membranes loaded with 3%, 6%, and 9% GSNO were 132 h, 140 h, and 168 h, respectively. Using a standard plate counting method, both Escherichia coli and Staphylococcus aureus in PA56/PVP coaxial nanofiber membranes loaded with GSNO showed lower viability than those in the PA56/PVP and blank groups, where bacterial colonies proliferate extensively. Increasing GSNO loading in the membranes significantly enhanced their antibacterial capability. The antibacterial rates were 60.20% for Escherichia coli and 79.38% for Staphylococcus aureus at 3% GSNO loading, 84.54% and 92.18% at 6% loading, and nearly 100% at 9% loading. For the potential skin inflammation, no evidence of erythema, edema or other changes was found on the skin surface after patch application for 24 h. Histological examination revealed no significant local inflammation or adverse events in the viable epidermis and dermis, indicating that the GSNO-loaded PA56/PVP coaxial nanofiber meshes are well-tolerated by the skin.

Conclusion GSNO was prepared as NO donor and loaded into PA56 nanofibers via coaxial electrospinning. The MIC values of GSNO are 31.25-62.5 μmol/L (10.51-21.02 μg/L). The PA56/PVP coaxial nanofibers loaded with GSNO have round cross-section and core-shell structure, albeit with a minor occurrence of stripped PA56 nanofibers from the core. With the increase of GSNO loading, the average diameter of PA56/PVP coaxial nanofibers and the tensile strength of the membranes increase, while the hydrophilicity of the membranes decreases. The PA56/PVP coaxial nanofiber membranes have sustained release profiles. The sustained release time for membranes loaded with 3%, 6% and 9% GSNO can reach 132 h, 140 h and 168 h, respectively. The antibacterial rates of PA56/PVP coaxial nanofiber membranes loaded with 6% GSNO against Staphylococcus aureus and Escherichia coli are 92.18% and 84.54% respectively. The PA56/PVP coaxial nanofiber membranes loaded with GSNO also have good skin tolerability, which offers a great potential in functional biomaterials, especially in medical dressings.

Key words: bio-based fiber, functional fiber, coaxial electrospinning, S-nitrosoglutathione, nitric oxide donor, antibacterial property