A Facile Strategy for Fabrication Lysozyme-Loaded Mesoporous Silica Nanotubes from Electrospun Silk Fibroin Nanofiber Templates

Abstract

This paper presents a facile and low-cost strategy for fabrication lysozyme-loaded mesoporous silica nanotubes (MSNTs) by using silk fibroin (SF) nanofiber templates. The "top-down method" was adopted to dissolve degummed silk in CaCl₂/ formic acid (FA) solvent, and the solution containing SF nanofibrils was used for electrospinning to prepare SF nanofiber templates. As SF contains a large number of -OH, -NH₂ and -COOH groups, the silica layer could be easily formed on its surface by the Söber sol-gel method without adding any surfactant or coupling agent. After calcination, the MSNTs were obtained with inner diameters about 200 nm, the wall thickness ranges from 37 ± 2 nm to 66 ± 3 nm and the Brunauer-Emmett-Teller (BET) specific surface area was up to 200.48 m²/g, the pore volume was 1.109 cm³/g. By loading lysozyme, the MSNTs exhibited relatively high drug encapsulation efficiency up to 31.82% and an excellent long-term sustained release in 360 h (15 days). These results suggest that the MSNTs with the hierarchical structure of mesoporous and macroporous will be a promising carrier for applications in biomacromolecular drug delivery systems.

Keywords: drug release; electrospinning; lysozyme; mesoporous silica nanotubes; silk fibroin.

Figure 1

The viscosity changes of different silk fibroin (SF)/CaCl₂/formic acid (FA) solutions (a) the content of CaCl₂ in CaCl₂/FA solvent was 3, 5, and 8 (w/v) %, respectively, when SF concentration was 15 (w/v) %. (b) The concentration of SF was 15, 20, and 25 (w/v) %, respectively, when the content of CaCl₂ was 5 (w/v) %.

Figure 2

SEM images of SF nanofibers from different SF/CaCl₂/FA spinning dopes. (a–c) the concentration of CaCl₂ was 3, 5, and 8 (w/v) %, respectively, when the concentration of SF is 15 (w/v)%, (d–f) the concentration of SF was 15, 20, and 25 (w/v) %, respectively, when the concentration of CaCl₂ was 5 (w/v) %. The insert graphs were the diameter distribution of SF nanofibers.

Figure 3

SEM images and EDS spectrum of SF@silica nanofibers (NFs) prepared from the SF fiber templates with the concentration of CaCl₂ at 3, 5, and 8 (w/v) % when SF concentration was 15 (w/v) %, respectively, (a–d) before the calcinations of the SF@silica NFs, (e–h) after the calcinations of the SF@silica NFs.

Figure 4

FTIR spectra of (a) SF fiber templates, (b) SF@silica NFs, (c) mesoporous silica nanotubes (MSNTs).F

Figure 5

TEM images of (a) MSNTs-1, (b) MSNTs-2, (c) MSNTs-3, corresponding tetraethoxysilane (TEOS) additions from 3, 5 to 7 mL, respectively.

Figure 6

TGA curves of (a) SF fiber templates, (b–d) the SF@silica NFs corresponding TEOS additions from 3, 5 to 7 mL, respectively.

Figure 7

N₂ adsorption–desorption isotherms of (a) MSNTs-1, (b) MSNTs-2, (c) MSNTs-3. The insert was the Barrett–Joyner–Halenda (BJH) pore size distribution plot of corresponding MSNTs.

Figure 8

Cumulative release profiles of lysozyme from (a) lysozyme-loaded MSNTs-1, (b) lysozyme-loaded MSNTs-2, (c) lysozyme-loaded MSNTs-3. The insets (a’–c’) correspond to the cumulative release profiles of (a–c) in the first 24 h, respectively.

Scheme 1

Schematic of fabrication MSNT (a) preparation of SF spinning dope, (b) electrospinning for SF nanofiber templates, (c) coating of SF nanofiber templates, and calcing of SF@silica NF.