Silk Fibroin Materials: Biomedical Applications and Perspectives

Abstract

The golden rule in tissue engineering is the creation of a synthetic device that simulates the native tissue, thus leading to the proper restoration of its anatomical and functional integrity, avoiding the limitations related to approaches based on autografts and allografts. The emergence of synthetic biocompatible materials has led to the production of innovative scaffolds that, if combined with cells and/or bioactive molecules, can improve tissue regeneration. In the last decade, silk fibroin (SF) has gained attention as a promising biomaterial in regenerative medicine due to its enhanced bio/cytocompatibility, chemical stability, and mechanical properties. Moreover, the possibility to produce advanced medical tools such as films, fibers, hydrogels, 3D porous scaffolds, non-woven scaffolds, particles or composite materials from a raw aqueous solution emphasizes the versatility of SF. Such devices are capable of meeting the most diverse tissue needs; hence, they represent an innovative clinical solution for the treatment of bone/cartilage, the cardiovascular system, neural, skin, and pancreatic tissue regeneration, as well as for many other biomedical applications. The present narrative review encompasses topics such as (i) the most interesting features of SF-based biomaterials, bare SF's biological nature and structural features, and comprehending the related chemo-physical properties and techniques used to produce the desired formulations of SF; (ii) the different applications of SF-based biomaterials and their related composite structures, discussing their biocompatibility and effectiveness in the medical field. Particularly, applications in regenerative medicine are also analyzed herein to highlight the different therapeutic strategies applied to various body sectors.

Keywords: 3D scaffolds; biomaterials; biomedicine; bone regeneration; fibroin; films; hydrogels; regenerative medicine; silk; tissue engineering.

Figure 1

Representation of the patterns of Hc’s repetitive or non-repetitive regions and an illustration of Hc’s crystallization degrees relationship with spatial organization, conformational state, and hydrophobicity. (a) Amorphous and unstructured SF conformational states typical of SF aqueous solutions. (b) Silk I form, characterized by the predominance of α-helix structures naturally present in silk glands and reproducible in the laboratory by slow drying, freezing-induced crystallization, and other methods. (c) Silk II form, with a high density of β-sheet crystallites, is produced by silkworms during the spinning process; this SF form can be obtained by several techniques due to the spontaneous tendency of SF to assume this conformation. Created using Biorender.com.

Figure 2

Schematic representation of the canonical degumming and purification of SF. Created using Biorender.com.

Figure 3

Several SF regeneration techniques that lead to the production of materials with different chemo-physical properties and applications. Created using Biorender.com.

Figure 4

SF-based materials prepared from amorphous aqueous solution and related device applications: (a) electrospun silk fibroin tubes [151], (b) fibers [152], (c) films [153,154], (d,e) 3D scaffolds [155], (f,g) patches [156], and (h) hydrogels [157] are some concrete applications of these devices for the regeneration of cardiovascular, neural, skin, cartilage, bone, abdominal, pancreas, and breast tissues, respectively (figure adapted from the mentioned papers). Created using Biorender.com.