Although natural silk fibers have excellent strength and flexibility, the regenerated silk materials generally become brittle in the dry state. How to reconstruct the flexibility for silk fibroin has bewildered scientists for many years. In the present study, the flexible regenerated silk fibroin films were achieved by simulating the natural forming and spinning process. Silk fibroin films composed of silk I structure were firstly prepared by slow drying process. Then the silk fibroin films were stretched in the wet state, following the structural transition from silk I to silk II. The difference between the flexible film and different brittle regenerated films was investigated to reveal the critical factors in regulating the flexibility of regenerated silk materials. Compared to the methanol-treated silk films, although having similar silk II structure and water content, the flexible silk films contained more bound water rather than free water, implying the great influence of bound water on the flexibility. Then, further studies revealed that the distribution of bound water was also a critical factor in improving silk flexibility in the dry state, which could be regulated by the nano-assembly of silk fibroin. Importantly, the results further elucidate the relation between mechanical properties and silk fibroin structures, pointing to a new mode of generating new types of silk materials with enhanced mechanical properties in the dry state, which would facilitate the fabrication and application of regenerated silk fibroin materials in different fields.
Cell behavior is dependent in part
on chemical and physical cues
from the extracellular matrix. Although the influence of various cues
on cell behavior has been studied, challenges remain to incorporate
multiple cues to matrix systems to optimize and control cell outcomes.
Here, aligned silk fibroin (SF)-graphene hydrogels with preferable
stiffness were developed through arranging SF nanofibers and SF-modified
graphene sheets under an electric field. Different signals, such as
bioactive graphene, nanofibrous structure, aligned topography, and
mechanical stiffness, were tailored into the hydrogel system, providing
niches for nerve cell responses. The desired adhesion, proliferation,
differentiation, extensio,n and growth factor secretion of multiple
nerve-related cells was achieved on these hydrogels, suggesting strong
synergistic action through the combination of different cues. Based
on the fabrication strategy, our present study provides a useful materials
engineering platform for revealing cooperative influences of different
signals on nerve cell behavior, to help in the understanding of cell–biomaterial
interactions, with potential toward studies related to nerve regeneration.
Deoxyribonucleic
acid (DNA) evolved as a tool for storing and transmitting
genetic information within cells, but outside the cell, DNA can also
serve as “construction material” present in microbial
biofilms or various body fluids, such as cystic fibrosis, sputum,
and pus. In the present work, we investigate the mechanics of biofilms
formed from Pseudomonas aeruginosa Xen
5, Staphylococcus aureus Xen 30, and Candida albicans 1408 using oscillatory shear rheometry
at different levels of compression and recreate these mechanics in
systems of entangled DNA and cells. The results show that the compression-stiffening
and shear-softening effects observed in biofilms can be reproduced
in DNA networks with the addition of an appropriate number of microbial
cells. Additionally, we observe that these effects are cell-type dependent.
We also identify other mechanisms that may significantly impact the
viscoelastic behavior of biofilms, such as the compression-stiffening
effect of DNA cross-linking by bivalent cations (Mg2+,
Ca2+, and Cu2+) and the stiffness-increasing
interactions of P. aeruginosa Xen 5
biofilm with Pf1 bacteriophage produced by P. aeruginosa. This work extends the knowledge of biofilm mechanobiology and demonstrates
the possibility of modifying biopolymers toward obtaining the desired
biophysical properties.
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