Insignificant Difference in Biocompatibility of Regenerated Silk Fibroin Prepared with Ternary Reagent Compared with Regenerated Silk Fibroin Prepared with Lithium Bromide

In vitro chemical treatment of silk increases the expression of pro-inflammatory factors and facilitates degradation in rats

OBJECTIVES

Silk fiber is difficult to degrade in vivo, which limits its application in tissue engineering materials such as artificial nerves. Therefore, in this study aim to promote its degradation in vivo by chemical treating silk fibers in vitro.

MATERIALS AND METHODS

Sulfate-polyacrylamide gel electrophoresis (SDS-PAGE), scanning electron microscopy (SEM) observations, mechanical test, Fourier transform infrared spectroscopy (FT-IR) measurements were used to investigate the degradation effect of chemicals (hydrochloric acid, phosphoric acid, acetic acid, sodium hydroxide, calcium hydroxide, sodium bicarbonate, and calcium chloride) on silk fiber in vitro. Immunofluorescence staining and transcriptome analysis were used to investigate the effect of inflammatory factors on the degradation of chemically treated silk fiber in rats.

RESULTS

(1) Silks were separated into finer fibers in each group. (2) FT-IR absorption peaks of amides I, II, and III overlap in each group. (3) Silk degradation degree in each group was higher than that in an untreated group. The calcium chloride-treated group was completely degraded. (4) Fibronectin, collagen I, collagen III, integrin α and CD68 were immunofluorescence positive in all vegetation section. (5) There were no significant differences in the expressions of collagen I, collagen III, and fibronectin in the vegetations formed on the 14th day of subcutaneous implantation, while integrin α, CD68, TNF-α, IL-1b, and IL-23 express at higher levels with IL-10 at lower levels.

CONCLUSIONS

All chemicals could completely degrade silk; however, their degradation products were not the same. The chemicals change the mechanical properties of silk by separating it into finer fibers, which increase the contact surface area between the silk and tissue fluid, accelerating the degradation of monofilaments in vivo by promoting inflammation and macrophage activity through the increased and decreased expressions of pro- and anti-inflammatory factors, respectively.

Advances in Preparation and Properties of Regenerated Silk Fibroin

Over the years, silk fibroin (SF) has gained significant attention in various fields, such as biomedicine, tissue engineering, food processing, photochemistry, and biosensing, owing to its remarkable biocompatibility, machinability, and chemical modifiability. The process of obtaining regenerated silk fibroin (RSF) involves degumming, dissolving, dialysis, and centrifugation. RSF can be further fabricated into films, sponges, microspheres, gels, nanofibers, and other forms. It is now understood that the dissolution method selected greatly impacts the molecular weight distribution and structure of RSF, consequently influencing its subsequent processing and application. This study comprehensively explores and summarizes different dissolution methods of SF while examining their effects on the structure and performance of RSF. The findings presented herein aim to provide valuable insights and references for researchers and practitioners interested in utilizing RSF in diverse fields.

The Loss of Structural Integrity of 3D Chitin Scaffolds from Aplysina aerophoba Marine Demosponge after Treatment with LiOH

Aminopolysaccharide chitin is one of the main structural biopolymers in sponges that is responsible for the mechanical stability of their unique 3D-structured microfibrous and porous skeletons. Chitin in representatives of exclusively marine Verongiida demosponges exists in the form of biocomposite-based scaffolds chemically bounded with biominerals, lipids, proteins, and bromotyrosines. Treatment with alkalis remains one of the classical approaches to isolate pure chitin from the sponge skeleton. For the first time, we carried out extraction of multilayered, tube-like chitin from skeletons of cultivated Aplysina aerophoba demosponge using 1% LiOH solution at 65 °C following sonication. Surprisingly, this approach leads not only to the isolation of chitinous scaffolds but also to their dissolution and the formation of amorphous-like matter. Simultaneously, isofistularin-containing extracts have been obtained. Due to the absence of any changes between the chitin standard derived from arthropods and the sponge-derived chitin treated with LiOH under the same experimental conditions, we suggest that bromotyrosines in A. aerophoba sponge represent the target for lithium ion activity with respect to the formation of LiBr. This compound, however, is a well-recognized solubilizing reagent of diverse biopolymers including cellulose and chitosan. We propose a possible dissolution mechanism of this very special kind of sponge chitin.