Factors Controlling the Deposition of Silk Fibroin Nanofibrils during Layer-by-Layer Assembly

Abstract

The layer-by-layer technique has been used as a powerful method to produce multilayer thin films with tunable properties. When natural polymers are employed, complicated phenomena such as self-aggregation and fibrilogenesis can occur, making it more difficult to obtain and characterize high-quality films. The weak acid and base character of such materials provides multilayer systems that may differ from those found with synthetic polymers due to strong self-organization effects. Specifically, LbL films prepared with chitosan and silk fibroin (SF) often involve the deposition of fibroin fibrils, which can influence the assembly process, surface properties, and overall film functionality. In this case, one has the intriguing possibility of realizing multilayer thin films with aligned nanofibers. In this article, we propose a strategy to control fibroin fibril formation by adjusting the assembly partner. Aligned fibroin fibrils were formed when chitosan was used as the counterpart, whereas no fibrils were observed when poly(allylamine hydrochloride) (PAH) was used. Charge density, which is higher in PAH, apparently stabilizes SF aggregates on the nanometer scale, thereby preventing their organization into fibrils. The drying step between the deposition of each layer was also crucial for film formation, as it stabilizes the SF molecules. Preliminary cell studies with optimized multilayers indicated that cell viability of NIH-3T3 fibroblasts remained between 90 and 100% after surface seeding, showing the potential application of the films in the biomedical field, as coatings and functional surfaces.

Surface Modification and Characterisation of Silk Fibroin Fabric Produced by the Layer-by-Layer Self-Assembly of Multilayer Alginate/Regenerated Silk Fibroin

“…The fabrication process is shown in Fig 2 . The 1.5 to 9.5 polyelectrolyte bilayers on the surface of the SF fabrics were assembled by alternately dipping the substrate into solutions of ALG and RSF [ 35 ]. First, the SF fabrics were immersed in HCl (pH = 2) for 20 min.…”

New garment proposal for prevention of spreading Gram-negative bacteria resistant to carbapenem antibiotic class under hospital settings

“…When K. pneumoniae was exposed to SF- l -Cys (ΔG Adhesion TOT = −7.37) and SF- l -Cys after five washing cycles (ΔG Adhesion TOT = −3.96), the ΔG Adhesion TOT decreased when compared to control SF (ΔG Adhesion TOT = 8.91), meaning that the adhesion trend of SF- l -Cys to K. pneumoniae increased with the introduced modification. SF with an isoelectric point (pI) of 4.2 is negatively charged at neutral physiologic pH’s [21]. SF fibers took for granted their affinity with water molecules in an environment which exposes the –OH and –SH groups to environment.…”

Biopolymer nanofibrils: Structure, modeling, preparation, and applications

“…The random distribution of SNFs in scaffolds makes it more difficult to tailor cell alignment, which is the essential for many tissue and organ functions. Accordingly, various approaches have been explored for the regulation of SNF alignment in scaffolds, including layer-bylayer assembly [469], dry-spinning [115], electric fields [470] and tensile induced alignment [296]. Through the successive deposition of chitosan and silk fibroin on substrates, highlyaligned SNF layers were obtained due to electrostatically induced self-assembly [469], and this layer-by-layer assembly technique is suitable for producing thin films.…”

“…Accordingly, various approaches have been explored for the regulation of SNF alignment in scaffolds, including layer-bylayer assembly [469], dry-spinning [115], electric fields [470] and tensile induced alignment [296]. Through the successive deposition of chitosan and silk fibroin on substrates, highlyaligned SNF layers were obtained due to electrostatically induced self-assembly [469], and this layer-by-layer assembly technique is suitable for producing thin films. Fiber-spinning techniques, including electronic spinning [275], wet-spinning [471,472], dry-spinning [115,473,474], and microfluidic-assisted spinning [475,476] are other useful approaches to regulate nanofibril orientation.…”