Silk-derived peptide nanospirals assembled by self-propelled wormlike filaments

Swirl-like nanospiral is a common structure found in free-swimming biological systems,such as microtubules and actin filaments or slender bacteria.It is desired for artificially designed dynamic nanomaterials.However,the spiral formation has rarely been reported in both engineered peptides and regenerated proteins.Herein,we report that such a unique assembly behavior can be achieved by using a fusion peptide consisting of a silk-derived peptide(i.e.,GAGAGAGY)and a hydrophobic,photoresponsive azobenzene(Azo)segment.In this fusion structure,GAGAGAGY acts as a domain that spontaneously forms an elongated filament in an aqueous solution,while Azo acts as a"light-operated switch"that can undergo photoinduced isomerization to modulate the self-propulsion forces and assembly behavior.With this design,the critical factors that affect the assembly of Azo-GAGAGAGY filament,including(i)length and flexibility of filaments;(ii)propulsion,and(iii)excluded volume interactions force the tip of the filament to wind up,can be regulated to realize the spiral formation.In addition,the configurations of Azo-GAGAGAGY filaments,such as straight nanoribbons,wavy nanoribbons,single-circle spiral,and multiple-circle spiral,can be facilely mediated by changing the preparation procedure,concentration,and pH value of Azo-GAGAGAGY solution,as these changes have significant influences on self-propulsion forces.Our findings can help in the better understanding of nonequilibrium thermodynamics and collective behavior of biological systems.The findings can be used as a guideline for the designs of nanoactuators,microswimmers,transformable microrobots,and intelligent drug carriers.

Silk microfibrous mats with long-lasting antimicrobial function

The controlled release of antibiotic drugs to injured sites has great advantages over the conventional intravenous administration of antibiotics,which is associated with systemic toxicity,for wound care.Electrospun nanofibrous/microfibrous mats,with a similar structure to the native extracellular matrix,is a promising wound dressing.Herein,drug-loaded halloysite nanotubes(HNTs)incorporated into regenerated silk fibroin(RSF)microfibrous mats were prepared by electrospinning to achieve sustained drug release and long-lasting antimicrobial protection.A broad-spectrum antibiotic,tetracycline hydrochloride(TCH),was selected as the model drug.Transmission electron microscopic images revealed that the TCH-loaded HNTs were homogeneously embedded in the RSF electrospun microfibers without significant changes in morphology.The drug release profiles showed that the RSF microfibrous mats with TCH-loaded HNTs exhibited a significantly reduced burst phase and a long release time over two weeks compared to the pure TCH-loaded HNTs and the TCH-loaded RSF microfibrous mats without HNTs.These results were attributed to the two-step release of TCH first from the HNTs and then RSF matrix in the electrospun mats.Finally,the antimicrobial properties of the RSF microfibrous mats with TCH-loaded HNTs were evaluated using both Gram-positive Staphylococcus aureus and Gram-negative Escherichia coli bacteria.The results demonstrated long-lasting antimicrobial activity for at least one week,showing the great potential of TCH-loaded RSF microfibrous mat as a wound dressing material.Therefore,these TCHloaded RSF microfibrous mats with excellent biocompatibility and sustained antimicrobial protection are extremely attractive systems for clinical applications.