Biomimetic Silk Scaffolds with an Amorphous Structure for Soft Tissue Engineering

Abstract

Fine tuning physical cues of silk fibroin (SF) biomaterials to match specific requirements for different soft tissues would be advantageous. Here, amorphous SF nanofibers were used to fabricate scaffolds with better hierarchical extracellular matrix (ECM) mimetic microstructures than previous silk scaffolds. Kinetic control was introduced into the scaffold forming process, resulting in the direct production of water-stable scaffolds with tunable secondary structures and thus mechanical properties. These biomaterials remained with amorphous structures, offering softer properties than prior scaffolds. The fine mechanical tunability of these systems provides a feasible way to optimize physical cues for improved cell proliferation and enhanced neovascularization in vivo. Multiple physical cues, such as partly ECM mimetic structures and optimized stiffness, provided suitable microenvironments for tissue ingrowth, suggesting the possibility of actively designing bioactive SF biomaterials. These systems suggest a promising strategy to develop novel SF biomaterials for soft tissue repair and regenerative medicine.

Water‐insoluble amorphous silk fibroin scaffolds from aqueous solutions

“…Different conformations of silk fibroin usually show various degradation peaks, where the random coil is degraded at the lowest temperature while silk II is impacted at the highest temperature. (Dong et al, ; Sang et al, ) The MS scaffolds showed a degradation peak at 274°C while two degradation peaks at lower temperatures (254°C and 267°C) appeared in the curves of the TS scaffolds, confirming the increased amorphous state of the TS scaffolds (vs. the MS). The crystallization peak at 200–220°C usually appears in the curves of amorphous RSF scaffolds, but disappeared in the curves of the TS scaffolds, which revealed their higher stability.…”

“…Silk fibroin conformations of the scaffolds were evaluated by FTIR. The amide I peaks of silk fibroin are usually used for the analysis of different secondary conformations where the peaks at 1610–1630 cm −1 are characteristic of beta‐sheet conformation while the peaks at 1635–1655 cm −1 are attributed to amorphous states (Bai et al, ; Sang et al, ; Wang et al, ). As shown in Figure a, typical peaks of amorphous structures and beta‐sheet conformations appeared on FTIR curves of the TS and MS scaffolds, respectively.…”

“…BMSCs were cultured in the MS and TS scaffolds to evaluate cytocompatibility in vitro. Both reduced beta‐sheet content and nanofibrous structures are considered important factors in improving cell compatibility of RSF scaffolds (Hu, Park, et al, ; Sang et al, ; Su et al, ). Therefore, the TS scaffolds were expected to achieve better cytocompatibility due to the nanofibrous morphology and amorphous structures.…”

“…For immunohistochemistry, the sections were stained by primary and secondary antibody against the endothelial cell marker, CD34 (1:100 dilution, Abcam, Cambridge, MA), and counterstained with hematoxylin using Histostain‐SP kit reagents (Invitrogen, Carlsbad, CA) to characterize the formation of newly formed blood vessels (Sang et al, ). The vessels formed in the scaffolds in vivo were quantified by counting above six random view fields (under 20× magnification) of the sections from three individual rats (two fields per rat) and the vessel density was calculated.…”

“…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, ).…”