Lyophilization of protein solutions, such as silk fibroin (silk), produces porous scaffolds useful for tissue engineering (TE). The impact of modifying lyophilization primary drying parameters on scaffold properties has not yet been explored previously.In this work, changes to primary drying duration and temperature were investigated using 3%, 6%, 9%, and 12% (w/v) silk solutions, via protocols labeled as Long Hold, Slow Ramp, and Standard. The 9% and 12% scaffolds were not successfully fabricated using the Standard protocol, while the Long Hold and Slow Ramp protocols resulted in scaffolds from all silk solution concentrations. Scaffolds fabricated using the Long Hold protocol had higher Young's moduli, smaller pore Feret diameters, and faster degradation. To investigate the utility of the different lyophilized scaffolds for in vitro cell culturing, the HepaRG liver cell line was cultured in the 3% to 12% scaffolds fabricated using the Long Hold protocol. The HepaRG cells grown in 3% scaffolds initially had greater lipid accumulation and metabolic activity than the other groups, although these differences were no longer apparent by Day 28. The deoxyribonucleic acid content of the HepaRG cells grown in 3% scaffold group was also initially significantly higher than the other groups. Significant differences in gene expression by 9% scaffolded HepaRG cells (CK19, HNFα) were seen on Day 14 while significant differences by 12% scaffolded HepaRG cells (ALB, APOA4) were seen on Day 28. Overall, modifying the primary drying parameters and silk concentration resulted in lyophilized scaffolds with tunable properties useful for TE applications.
Biomaterials are an important source of inspiration for
the development
of strong and tough materials. Many improved and optimized synthetic
materials have been recently developed utilizing this bioinspiration
concept. Using side-chain-to-side-chain polymerization of cyclic β-peptide
rings, a novel class of nanomaterials was recently introduced with
outstanding mechanical properties such as toughness values greater
than natural silks. In this work, molecular dynamics is used to understand
the mechanics of side-chain-to-side-chain polymerization of cyclic
β-peptide rings. Unbiased steered molecular dynamics simulations
are used to show the difference in the strength of polymerized and
unpolymerized processing of similar cyclic rings. The simulations
are performed both in aqueous and vacuum environments to capture the
role of water on the mechanical properties of the cyclic peptides.
Our results show that unpolymerized peptides behave like brittle material,
whereas polymerized ones can withstand some stress after initial failure
with large values of strain-to-failure. Finally, we have shown that
the strength of cyclic peptides in water is higher than in a vacuum.
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