Streamlining Skin Regeneration: A Ready-To-Use Silk Bilayer Wound Dressing

Abstract

Silk proteins have been highlighted in the past decade for tissue engineering (TE) and skin regeneration due to their biocompatibility, biodegradability, and exceptional mechanical properties. While silk fibroin (SF) has high structural and mechanical stability with high potential as an external protective layer, traditionally discarded sericin (SS) has shown great potential as a natural-based hydrogel, promoting cell-cell interactions, making it an ideal material for direct wound contact. In this context, the present study proposes a new wound dressing approach by developing an SS/SF bilayer construct for full-thickness exudative wounds. The processing methodology implemented included an innovation element and the cryopreservation of the SS intrinsic secondary structure, followed by rehydration to produce a hydrogel layer, which was integrated with a salt-leached SF scaffold to produce a bilayer structure. In addition, a sterilization protocol was developed using supercritical technology (sCO₂) to allow an industrial scale-up. The resulting bilayer material presented high porosity (>85%) and interconnectivity while promoting cell adhesion, proliferation, and infiltration of human dermal fibroblasts (HDFs). SS and SF exhibit distinct secondary structures, pore sizes, and swelling properties, opening new possibilities for dual-phased systems that accommodate the different needs of a wound during the healing process. The innovative SS hydrogel layer highlights the transformative potential of the proposed bilayer system for biomedical therapeutics and TE, offering insights into novel wound dressing fabrication.

Keywords: bilayer; silk fibroin; silk sericin; wound dressing.

Figure 1

Morphology and typical pore size of the bilayer structures after preparation by SEM (A), macroscopic bilayer and SS and SF pore size (B), and FTIR spectra (C).

Figure 2

Micro-CT of the bilayer, and individual SS and SF structures.

Figure 3

Morphology and porosity of the bilayer structures after rehydration for 12 h and 3 days (cryo−SEM) (A) SS, SF, SS/SF interface and SDS elemental analysis of SF and SS layer after rehydration for 12 h, and (B) swelling properties of the bilayer structure and individual SS and SF (C).

Figure 4

Mechanical properties of the sterile bilayer structures in the dry state and after rehydration for 12 h and 3 days. (A) Representative images of the bilayer compression tests performed using the rheometer. (B) Stress–strain curves with the enlarged area of the top graph show in detail the curves of the rehydrated bilayer scaffolds. (C) Young’s modulus of the bilayer scaffolds.

Figure 5

Drug release profile of the bilayer structure and individual SS and SF scaffolds.

Figure 6

SCO₂ sterilization of the silk-based wound dressings, (A) turbidity tests conducted after 14 days of incubation, (B) reactor used, (C) reactor vessel with samples stored in sterilization pouches, and (C) bilayers after sterilization.

Figure 7

(A) Rehydration of the sterilized dry scaffold and reversion of SS layer to a hydrogel-like structure before cell seeding; (B) seeding efficiency on the bilayer and SS structures; (C) cell metabolic activity of HDFs seeded on the bilayer and SS structures; (D) DNA content on the bilayer constructs. Asterisks correspond to statistically significant differences (*** p < 0.001, ** p < 0.01).

Figure 8

Illustration of silk cocoon composition, SS/SF bilayer assembly, and sCO₂ sterilization to obtain a ready-to-use wound dressing. Reprinted (adapted) with permission from [39]. Copyright {2019} American Chemical Society.