Preparation of a robust silk fibroin scaffold with a reinforced concrete structure constructed with silk nanofibers as the skeleton based on a CaCl2-formic acid solution and freeze-drying method

Abstract

Regenerated silk fibroin has been widely used in tissue engineering due to its tunable mechanical properties, biocompatibility and degradability, especially in biological scaffolds. In this paper, for the first time, a robust silk fibroin (SF) scaffold with a reinforced concrete structure constructed with silk nanofibers as the skeleton was prepared by combining a CaCl2-formic acid (FA-CaCl2) dissolving system with a freeze-drying method. This method consumes less time and greatly reduces the rate of silk loss, while formic acid can be collected and reused as a solvent during the lyophilization process. Moreover, the SF scaffolds prepared by this method retained the nanofibers of silk, thus preserving the mechanical toughness of the silk nanofibers. On this basis, a reinforced concrete structure with silk nanofibers as the skeleton and amorphous silk as the filler was constructed, which exhibited increased strength and toughness. Effects of preparation conditions (dissolution system, degumming time, silk content) on the mechanical properties and the relationship between structure and mechanical properties of the scaffolds were also studied. Among them, the strength of SF scaffold with degumming time of 10 min, silk content of 20 wt% and directional pores was the best, and its Young's modulus could reach 3.56 MPa. In addition, the scaffolds prepared by this method had good biocompatibility and biodegradability. This study provides a new strategy for manufacturing SF scaffolds and an alternative for the preparation of related silk fibroin materials, which have excellent potential in the field of tissue engineering.