Tunable Enzymatically Cross‐Linked Silk Fibroin Tubular Conduits for Guided Tissue Regeneration

Abstract

Hollow tubular conduits (TCs) with tunable architecture and biological properties are in great need for modulating cell functions and drug delivery in guided tissue regeneration. Here, a new methodology to produce enzymatically cross-linked silk fibroin TCs is described, which takes advantage of the tyrosine groups present in silk structure that are known to allow the formation of a covalently cross-linked hydrogel. Three different processing methods are used as a final step to modulate the properties of the silk-based TCs. This approach allows to virtually adjust any characteristic of the final TCs. The final microstructure ranges from a nonporous to a highly porous network, allowing the TCs to be selectively porous to 4 kDa molecules, but not to human skin fibroblasts. Mechanical properties are dependent both on the processing method and thickness of the TCs. Bioactivity is observed after 30 days of immersion in simulated body fluid only for the TCs submitted to a drying processing method (50 °C). The in vivo study performed in mice demonstrates the good biocompatibility of the TCs. The enzymatically cross-linked silk fibroin TCs are versatile and have adjustable characteristics that can be exploited in a variety of biomedical applications, particularly in guidance of peripheral nerve regeneration.

Fundamentals and Current Strategies for Peripheral Nerve Repair and Regeneration

“…Such characteristic must be previously tested and avoided at all costs, since calcification of a conduit would hinder regeneration in a great extent. In fact, Carvalho et al [71] recently reported on a silk fibroin NGC that would or not calcify, according to the method of solvent removal and final surface properties.…”

“…Carvalho et al [71] produced tunable enzymatically cross-linked SF NGCs, resourcing to tyrosine groups present in silk structure that are known for allowing the formation of a covalently cross-linked hydrogel. The fact that the process involves an enzymatic crosslinking allows tuning several parameters in the final conduit, i.e.…”

“…from its mechanical properties to porosity or biological properties. [71] for application in PNR. The developed NGC presents outstanding mechanical properties, with kinking-resistant capacity and suturability, as can be seen by the images (in that row); (B) Images of a 5% of degree of acetylation chitosan membrane, which can be further used as a NGC by rolling-up or in a different strategy, as a luminal filler; C) 5% degree of acetylation chitosan membrane incorporating human hair keratin, developed at our research institute; and D) Confocal laser microscopy showing macroporous alginate fibers incorporating gelatin particle porogens.…”

Enhanced performance of chitosan/keratin membranes with potential application in peripheral nerve repair

“…16,52 An ideal NGC or PNW intended for PNR needs to feature a combination of optimal material, size, architecture and surface properties to be fully effective. 53 These features must allow the formation of a new ECM, consisting of endothelial cells, and subsequently blood vessels, Schwann cells and the correct type and amount of fibroblasts, which will collectively create favourable circumstances for nerve regeneration to occur. 54 In this study, we propose the use of solvent cast CHT/ keratin membranes as possible tools to aid in the repair of damaged nerves.…”

3D Bioprinting Strategies for the Regeneration of Functional Tubular Tissues and Organs

“…Various microfabrication techniques for tissue engineering, such as electrospinning [ 14 , 15 , 16 , 17 , 18 , 19 ], cell-sheet engineering [ 20 , 21 , 22 ], and mold-casting [ 23 , 24 , 25 , 26 ], have been widely studied to make complex multi-layered architecture for artificial functional tubular tissues. These approaches would use additional substrates (e.g., rotating rod, sacrificial mold) to create the tubular architecture, as well as requiring complex and multiple manufacturing processes.…”