Characterization of Hydrogels Made of a Novel Spider Silk Protein eMaSp1s and Evaluation for 3D Printing

Spidroin N-terminal domain forms amyloid-like fibril based hydrogels and provides a protein immobilization platform

Recombinant spider silk proteins (spidroins) have multiple potential applications in development of novel biomaterials, but their multimodal and aggregation-prone nature have complicated production and straightforward applications. Here, we report that recombinant miniature spidroins, and importantly also the N-terminal domain (NT) on its own, rapidly form self-supporting and transparent hydrogels at 37 °C. The gelation is caused by NT α-helix to β-sheet conversion and formation of amyloid-like fibrils, and fusion proteins composed of NT and green fluorescent protein or purine nucleoside phosphorylase form hydrogels with intact functions of the fusion moieties. Our findings demonstrate that recombinant NT and fusion proteins give high expression yields and bestow attractive properties to hydrogels, e.g., transparency, cross-linker free gelation and straightforward immobilization of active proteins at high density.

Recombinant spider silks are of interest but the multimodal and aggregation-prone nature of them is a limitation. Here, the authors report on a miniature spidroin based on the N-terminal domain which forms a hydrogel at 37 °C which allows for ease of production and fusion protein modification to generate functional biomaterials.

The novel aciniform silk protein (AcSp2-v2) reveals the unique repetitive domain with high acid and thermal stability and self-assembly capability

Orb-weaving spiders spin a mechanically and functionally diverse range of silk fibers, each composed of one or more specific silk proteins. Of all silk types, wrapping silk combines high strength and extensibility and is made of multiple aciniform silk proteins (AcSp) that can be grouped into two AcSp types (AcSp1 and AcSp2) according to their distinct repetitive regions. Here, we present a novel and complete AcSp gene from orb weaving spider Araneus ventricosus. Phylogenetic analysis of the terminal regions of spidroins reveals that the new silk protein and the published A. ventricosus AcSp2 together form a subclade, indicating that this protein is a member of AcSp2 subclass and therefore named AcSp2 variant 2 (AcSp2-v2). The repetitive region of A. ventricosus AcSp2-v2 contains 24 cysteine residues, which is the first time that cysteine has been found in repetitive regions of spidroins. Moreover, the discovery of the ability of AcSp2-v2 repetitive domain to self-assemble into silk fibers expands the repertoire of known self-assembling sequences.

Silk-Based Materials for Hard Tissue Engineering

Hard tissues, e.g., bone, are mechanically stiff and, most typically, mineralized. To design scaffolds for hard tissue regeneration, mechanical, physico-chemical and biological cues must align with those found in the natural tissue. Combining these aspects poses challenges for material and construct design. Silk-based materials are promising for bone tissue regeneration as they fulfill several of such necessary requirements, and they are non-toxic and biodegradable. They can be processed into a variety of morphologies such as hydrogels, particles and fibers and can be mineralized. Therefore, silk-based materials are versatile candidates for biomedical applications in the field of hard tissue engineering. This review summarizes silk-based approaches for mineralized tissue replacements, and how to find the balance between sufficient material stiffness upon mineralization and cell survival upon attachment as well as nutrient supply.

Nanostructured, Self-Assembled Spider Silk Materials for Biomedical Applications

The extraordinary mechanical properties of spider silk fibers result from the interplay of composition, structure and self-assembly of spider silk proteins (spidroins). Genetic approaches enabled the biotechnological production of recombinant spidroins which have been employed to unravel the self-assembly and spinning process. Various processing conditions allowed to explore non-natural morphologies including nanofibrils, particles, capsules, hydrogels, films or foams. Recombinant spider silk proteins and materials made thereof can be utilized for biomedical applications, such as drug delivery, tissue engineering or 3D-biomanufacturing.