Silkworms and spiders generate fibres that exhibit high strength and extensibility. The underlying mechanisms involved in processing silk proteins into fiber form remain incompletely understood, resulting in the failure to fully recapitulate the remarkable properties of native fibers in vitro from regenerated silk solutions. In the present study, the extensibility and high strength of regenerated silks were achieved by mimicking the natural spinning process. Conformational transitions inside micelles, followed by aggregation of micelles and their stabilization as they relate to the metastable structure of silk are described. Subsequently, the mechanisms to control the formation of nanofibrous structures were elucidated. The results clarify that the self-assembly of silk in aqueous solution is a thermodynamically driven process where kinetics also play a key role. Four key factors, molecular mobility, charge, hydrophilic interactions and concentration underlie the process. Adjusting these factors can balance nanostructure and conformational composition, and be used to achieve silk-based materials with properties comparable to native fibers. These mechanisms suggest new directions to design silk-based multifunctional materials.

Controlling the degradation process of silk is an important and interesting subject in biomaterials field. In the present study, silk fibroin films with different secondary conformations and nanostructures were used to study the degradation behavior. Silk fibroin films with highest β-sheet content achieved highest degradation rate, different from the previous studies. A new degradation mechanism revealed that degradation behavior of silk fibroin was related to not only crystal content, but also hydrophilic interaction and crystal-noncrystal alternant nanostructures. The hydrophilic blocks of silk were firstly degraded. Then, the hydrophobic crystal blocks which were formerly surrounded and immobilized by hudrophilic blocks, became free particles and moved into solution. Based on the mechanism, which enables the process more controllable and flexible, controlling the degradation behavior of silk fibroin without sacrificing other performances such as mechanical or hydrophilic properties become feasible, and this would greatly expand the applications of silk as a biomedical material.

Silkworm silk has been widely used as a textile fiber, as biomaterials and in optically functional materials due to its extraordinary properties. The β-sheet-rich natural nanofiber units of about 10–50 nm in diameter are often considered the origin of these properties, yet it remains unclear how silk self-assembles into these hierarchical structures. A new system composed of β-sheet-rich silk nanofibers about 10–20 nm in diameter is reported here, where these nanofibers formed into “flowing hydrogels” at 0.5–2% solutions and could be transformed back into the solution state at lower concentrations, even with a high β-sheet content. This is in contrast with other silk processed materials, where significant β-sheet content negates reversibility between solution and solid states. These fibers are formed by regulating the self-assembly process of silk in aqueous solution, which changes the distribution of negative charges while still supporting β-sheet formation in the structures. Mechanistically, there appears to be a shift toward negative charges along the outside of the silk nanofibers in our present study, resulting in a higher zeta potential (above −50 mV) than previous silk materials which tend to be below −30 mV. The higher negative charge on silk nanofibers resulted in electrostatic repulsion strong enough to negate further assembly of the nanofibers. Changing silk concentration changed the balance between hydrophobic interactions and electrostatic repulsion of β-sheet-rich silk nanofibers, resulting in reversible hydrogel–solution transitions. Furthermore, the silk nanofibers could be disassembled into shorter fibers and even nanoparticles upon ultrasonic treatment following the transition from hydrogel to solution due to the increased dispersion of hydrophobic smaller particles, without the loss of β-sheet content, and with retention of the ability to transition between hydrogel and solution states through reversion to longer nanofibers during self-assembly. These reversible solution-hydrogel transitions were tunable with ultrasonic intensity, time, or temperature.

Au@Cu2- x S core-shell nanocrystals (NCs) have been synthesized under large lattice mismatch with high crystallinity, controllable shape, and nonstoichiometric composition. Both experimental observations and simulations are used to verify the flexible dual-mode plasmon coupling. The enhanced photothermal effect is harnessed for diverse HeLa cancer cell ablation applications in the NIR-I window (750-900 nm) and the NIR-II window (1000-1400 nm).

The existence of lattice strain between two different materials can be used to control the fine structural configuration in a hybrid colloidal nanostructure. Enabled by such, the relative position change of Au and CdX in Au-CdX from a symmetric to an asymmetric configuration is demonstrated, which can further lead to fine tuning of plasmon-exciton coupling and different hydrogen photocatalytic performance. These results provide new insight into plasmon enhanced photocatalytic mechanisms and provide potential catalysts for photoreduction reactions.