Silk scaffolds with tunable mechanical capability for cell differentiation

Abstract

Bombyx mori silk fibroin is a promising biomaterial for tissue regeneration and is usually considered an “inert” material with respect to actively regulating cell differentiation due to few specific cell signaling peptide domains in the primary sequence and the generally stiffer mechanical properties due to crystalline content formed in processing. In the present study, silk fibroin porous 3D scaffolds with nanostructures and tunable stiffness were generated via a silk fibroin nanofiber-assisted lyophilization process. The silk fibroin nanofibers with high β-sheet content were added into the silk fibroin solutions to modulate the self-assembly, and to directly induce water-insoluble scaffold formation after lyophilization. Unlike previously reported silk fibroin scaffold formation processes, these new scaffolds had lower overall β-sheet content and softer mechanical properties for improved cell compatibility. The scaffold stiffness could be further tuned to match soft tissue mechanical properties, which resulted in different differentiation outcomes with rat bone marrow-derived mesenchymal stem cells towards myogenic and endothelial cells, respectively. Therefore, these silk fibroin scaffolds regulate cell differentiation outcomes due to their mechanical features.

Water‐insoluble amorphous silk fibroin scaffolds from aqueous solutions

“…Endothelial differentiation based on gene expression of BMSCs cultured in the scaffolds was analyzed by qRT‐PCR (Bai et al, ). On 7, 14, and 28 days, the total cellular RNA from each sample was extracted with Trizol reagent (Invitrogen, Carlsbad, CA) and reverse transcribed into complementary DNA (cDNA) using a High‐Capacity cDNA Reverse Transcription kit (Applied Biosystems, Carlsbad, CA) in a 2720 thermal cycler (Applied Biosystems, Foster City, CA).…”

“…Various studies have addressed this issue, such as by adjusting RSF fabrication processes (Bai et al, ; Brown et al, ; Dong, Zhao, Xiao, Lu, & Kaplan, ; Rnjak‐Kovacina et al, ; Sang et al, ; Wang et al, ). Limited reduction of beta sheet content has been achieved for water insoluble RSF scaffolds through water annealing post‐treatment, and glycerol as additive in lyophilization (Chlapanidas et al, ; Chlapanidas et al, ; Lin et al, ; Q. Lu et al, ; Oliveira et al, ; Pei et al, ; Perteghella et al, ).…”

“…Beta‐sheet rich RSF nanofibers were assembled in aqueous solution and then used to induce assembly, resulting in insoluble RSF scaffold formation after lyophilization. A high ratio of RSF nanofibers was required in the process, which resulted in heterogeneous structures and beta‐sheet rich conformations (Bai et al, , ). Acid was then added to aqueous RSF solution containing lower contents of RSF nanofibers to form stronger hydrophilic interactions and reduce beta sheet formation (Han et al, ).…”

Silk-based stabilization of biomacromolecules

“…This transition is accelerated at ambient temperatures as well as at higher concentrations or lower pH [17]. Additionally, the age (time since extraction/purification) of the silk solution [18] and concentration at which it is stored [19] have a significant impact on the structure and stability of the material, which has downstream effects on the generation of materials [20]. Therefore, new approaches are needed to circumvent silk fibroin liquid storage requirements in order to provide a more stable feedstock for liquid stability applications.…”

Simulation of ECM with silk and chitosan nanocomposite materials

“…46,47 Fresh SF solution was treated by a concentration-dilution process. The solution (6 wt%) was slowly concentrated to about 20 wt% over 24 h at 60 °C to form metastable nanoparticles, and then diluted to 0.5 wt% with distilled water.…”