Silk Hydrogels as Soft Substrates for Neural Tissue Engineering

Abstract

There is great need for soft biomaterials that match the stiffness of human tissues for tissue engineering and regeneration. Hydrogels are frequently employed for extracellular matrix functionalization and to provide appropriate mechanical cues. It is challenging, however, to achieve structural integrity and retain bioactive molecules in hydrogels for complex tissue formation that may take months to develop. This work aims to investigate mechanical and biochemical characteristics of silk hydrogels for soft tissue engineering, specifi cally for the nervous system. The stiffness of 1 to 8% silk hydrogels, measured by atomic force microscopy, is 4 to 33 kPa. The structural integrity of silk gels is maintained throughout embryonic chick dorsal root ganglion (cDRG) explant culture over 4 days whereas fi brin and collagen gels decrease in mass over time. Neurite extension of cDRGs cultured on 2 and 4% silk hydrogels exhibit greater growth than softer or stiffer gels. Silk hydrogels release < 5% of neurotrophin-3 (NT-3) over 2 weeks and 11-day old gels show maintenance of growth factor bioactivity. Finally, fi bronectin-and NT-3-functionalized silk gels elicit increased axonal bundling suggesting their use in bridging nerve injuries. These results support silk hydrogels as soft and sustainable biomaterials for neural tissue engineering.

Bioengineered functional brain-like cortical tissue

“…However, ECM gel-based in vitro 3D systems have not yielded tissue-level functional assessments, possibly because of their inadequate mechanical properties and fast degradation compared with brain tissue. Here, we developed 3D compartmentalized neuronal cultures with silk fibroin-based biomaterials offering tunable mechanical properties, versatile structural forms, and brain and neural culture compatibility (18)(19)(20)(21). This brain-like tissue provides rudimentary but relevant features of brain neural networks.…”

Bio-inspired mineralization of hydroxyapatite in 3D silk fibroin hydrogel for bone tissue engineering

“…The choice of silk fibroin protein as hydrogel matrix is due to its natural origin, abundance in nature, low cost and notable biocompatibility [28]. Mineralization process of gels containing different Ca 2+ concentration was characterized using FE-SEM (Fig.1a-d).…”

Engineered 3D Silk-collagen-based Model of Polarized Neural Tissue

“…Due to the inert nature of the silk scaffold, functionalization with poly-D-lysine is required for neuronal attachment. However, other cell adhesion promoting factors can be applied such as RGD 25 or fibronectin 26 . To achieve the 3D network formation the silk scaffold needs to be filled with hydrogel in a timely manner as soon as neurons are attached to the scaffold.…”