Coaxial wet-spun fibers loaded with enzyme-inhibiting peptide for chronic wound care

Chronic wounds (CW) are a worldwide concern, causing serious strives on the health and quality of patients’ life. In CW, human neutrophil elastase (HNE) enzyme gets highly expressed during inflammation, reaching abnormally elevated concentrations. Additionally, prevalence of Staphylococcus aureus-induced infections remains very high and difficult to treat. Considering these phenomena, a drug delivery system made of coaxial wet-spun fibers, loaded with the tetrapeptide Ala-Ala-Pro-Val (AAPV, a known inhibitor of HNE activity) and N-carboxymethyl chitosan (NCMC, responsive to neutral-basic pH’s, characteristic of CW and endowed with antibacterial features), was proposed.

AAPV was synthesized by solid-phase peptide synthesis, whereas NCMC was synthesized from low molecular weight chitosan in a chloroacetic acid mixture. HNE inhibition tests were conducted to establish the AAPV IC₅₀ in 50 µg/mL and the NCMC minimum bactericidal concentration (MBC) against S. aureus in 3.072 mg/mL. These determinations were used to establish fiber loading amounts. Core-shell structures were produced with 10% w/v polycaprolactone (PCL) at the core and 2% w/v sodium alginate (SA) solutions at the shell. NCMC was mixed with SA at 2xMBC so neutral-basic pH-triggered solubility (characteristic of CW) would allow pores to be opened in the outer layer for accessing the core, where AAPV was combined with PCL.

Fourier-transform infrared spectroscopy and brightfield microscopy were used to confirm the presence of the four components on the fibers and the co-axial architecture, respectively. Fibers presented maximum elongations of over 100%. A chemically modified version of AAPV was synthesized by including a fluorescent group (Fmoc), attached to the last amino acid of AAPV, due to an overlapping of maximum absorbances between all fiber compounds, making it impossible to analyze AAPV release profile. Release kinetics studies were then conducted via spectrofluorimetry, which successfully mapped AAPV liberation overtime. Time-kill kinetics studies against S. aureus demonstrated the effectiveness of NCMC in eliminating this bacterium, particularly after 6 h of incubation. On its turn, AAPV guaranteed HNE inhibition. Data demonstrated the potential of SA-NCMC-PCL-AAPV coaxial systems to work as stepwise, pH-triggered delivery platforms.