Silk fibroin scaffolds with stable silk I crystal and tunable properties.

It is crucial to develop a three-dimensional scaffold with tunable physical properties for the biomedical application of silk fibroin (SF). The crystallization of polymers dictates their bulk properties. The presence of two unique crystal types, silk I and silk II, provides a mechanism for controlling the properties of SF biomaterials. However, it remains challenging to manipulate silk I crystallization. In this study, we demonstrate the stability and tunability of SF scaffolds with silk I structure prepared by a freezing-annealing processing. The porous structure and mechanical properties of the scaffolds can be readily regulated by SF concentration. XRD results show that the typical peaks representing silk I do not shift when subjected to various post-treatments, such as ethanol soaking, heating, water vapor annealing, UV irradiation, and high-temperature/high-pressure, indicating the stability of silk I crystal type. Moreover, the crystallization kinetics can be regulated by changing annealing time. This physical process can regulate the transition from non-crystalline to silk I, in turn controlling the mechanical properties and degradation rate of the SF scaffolds. Our result show that this green, all-aqueous strategy provides new directions for the design of SF-based biomaterials with controllable properties.

Silk as templates for hydroxyapatite biomineralization: A comparative study of Bombyx mori and Antheraea pernyi silkworm silks.

Silk is extensively investigated in bone tissue engineering due to its extraordinary mechanical properties and ability to regulate biomineralization. Protein templates regulate biomineralization process through chemical interaction with ions. However, the effect of structural differences in silk fibroin on biomineralization has not been studied in detail. In this study, Antheraea pernyi silk fibroin (ASF) and Bombyx mori silk fibroin (BSF) fibers were used as templates to study the effect of silk species on biomineralization. The results showed that silk fibroin could induce the formation of calcium-deficient hydroxyapatite in simulated body fluid (SBF), and the SBF treatment resulted in the formation of silk I crystals. Compared with BSF, ASF exhibited a higher ability to induce mineralization, which may depend on the differences in hydrophilic amorphous fractions between ASF and BSF. The amorphous fractions of ASF contain more acidic amino acids, which can provide more nucleation sites in the initial stage of mineralization, resulting in faster mineralization process and more mineral deposits. This study decodes the key role of silk fibroin fractions on biomineralization, and provides deeper insights for the study of silk fibroin as biomineralization template and bone repair materials.