Antibacterial Porous Coaxial Drug-Carrying Nanofibers for Sustained Drug-Releasing Applications

Abstract

The phenomenon of drug burst release is the main problem in the field of drug delivery systems, as it means that a good therapeutic effect cannot be acheived. Nanofibers developed by electrospinning technology have large specific surface areas, high porosity, and easily controlled morphology. They are being considered as potential carriers for sustained drug release. In this paper, we obtained polycaprolactone (PCL)/polylactic acid (PLA) core-shell porous drug-carrying nanofibers by using coaxial electrospinning technology and the nonsolvent-induced phase separation method. Roxithromycin (ROX), a kind of antibacterial agent, was encapsulated in the core layer. The morphology, composition, and thermal properties of the resultant nanofibers were characterized by scanning electron microscopy (SEM), attenuated total reflection Fourier transform infrared (ATR-FTIR) spectroscopy, differential scanning calorimetry (DSC) and thermogravimetry analysis (TGA). Besides this, the in vitro drug release profile was investigated; it showed that the release rate of the prepared coaxial porous nanofibers with two different pore sizes was 30.10 ± 3.51% and 35.04 ± 1.98% in the first 30 min, and became 92.66 ± 3.13% and 88.94 ± 1.58% after 14 days. Compared with the coaxial nonporous nanofibers and nanofibers prepared by uniaxial electrospinning with or without pores, the prepared coaxial porous nanofibers revealed that the burst release was mitigated and the dissolution rate of the hydrophobic drugs was increased. The further antimicrobial activity demonstrated that the inhibition zone diameter of the coaxial nanofibers with two different pore sizes was 1.70 ± 0.10 cm and 1.73 ± 0.23 cm, exhibiting a good antibacterial effect against Staphylococcus aureus. Therefore, the prepared nanofibers with the coaxial porous structures could serve as promising drug delivery systems.

Keywords: PCL/PLA; antibacterial activity; coaxial electrospinning; drug release; phase separation; porous nanofibers.

Figure 1

Schematic illustrations of the fabrication of the nanofibers by (a) coaxial electrospinning and (b) uniaxial electrospinning. PPR1, PPR2, and PPR3 represent the Roxithromycin (ROX)-loaded PCL/PLA nanofibers with various solvent types, and PR1, PR2 represent the ROX-loaded PCL nanofibers created by uniaxial electrospinning with different solvents. Polycaprolactone (PCL) solution and polylactic acid (PLA) solution were used as the core layer and the shell layer of the coaxial electrospinning, respectively. The solvents volatile speeds were chloroform (CF) > Trifluoroethanol (TFE) > dimethylsulphoxide (DMSO). The presence of nonsolvent DMSO, which is difficult to volatilize, and the volatile solvent CF can induce nonsolvent-induced phase separation and generate the porous structure.

Figure 2

SEM images of the coaxial nanofibers: (a,d) PPR1, (b,e) PPR2, (c,f) PPR3. The red arrows highlight the coaxial structure.

Figure 3

SEM images of nanofibers (a,b) PR1, (c,d) PR2, as prepared by uniaxial electrospinning.

Figure 4

FTIR spectra of (a–c) drug-loaded nanofibers PPR1, PPR2, PPR3, as prepared by coaxial electrospinning; drug-loaded nanofibers PR1, PR2 and drug-free nanofibers P1, P2, as prepared by uniaxial electrospinning; and (d) ROX. Figure 4c is a partial enlargement of Figure 4d.

Figure 5

(a) DSC curve and (b) TGA curve of nanofibers PPR1, PR1, P1 and ROX.

Figure 6

Photographs of the antibacterial test of (a) PPR1, (b) PPR2, (c)PPR3, (d) PR1 and (e) PR2 after incubation for 24 h at 37 °C.

Figure 7

The standard curve of ROX.

Figure 8

ROX release profiles of coaxial nanofibers PPR1, PPR2 and PPR3, and nanofibers PR1 and PR2, as prepared by uniaxial electrospinning (a) for 14 days, and (b) for 10 h.