Breaking Nano-Spaghetti: Bending and Fracture Tests of Nanofibers

Micropatterned Nanofiber Scaffolds of Salmon Gelatin, Chitosan, and Poly(vinyl alcohol) for Muscle Tissue Engineering

The development of scaffolds that mimic the aligned fibrous texture of the extracellular matrix has become an important requirement in muscle tissue engineering. Electrospinning is a widely used technique to fabricate biomimetic scaffolds. Therefore, a biopolymer blend composed of salmon gelatin (SG), chitosan (Ch), and poly(vinyl alcohol) (PVA) was developed by electrospinning onto a micropatterned (MP) collector, resulting in a biomimetic scaffold for seeding muscle cells. Rheology and surface tension studies were performed to determine the optimum solution concentration and viscosity for electrospinning. The scaffold microstructure was analyzed using SEM to determine the nanofiber's diameter and orientation. Blends of SG/Ch/PVA exhibited better electrospinnability and handling properties than pure PVA. The resulting scaffolds consist of a porous surface (∼46%), composed of a random fiber distribution, for a flat collector and scaffolds with regions of aligned nanofibers for the MP collector. The nanofiber diameters are 141 ± 2 and 151 ± 2 nm for the flat and MP collector, respectively. In vitro studies showed that myoblasts cultured on scaffold SG/Ch/PVA presented a high rate of cell growth. Furthermore, the aligned nanofibers on the SG/Ch/PVA scaffold provide a suitable platform for myoblast alignment.

Towards Further Understanding the Secondary Fracture during Spaghetti Bent Break

When a brittle thin rod, such as a dry spaghetti stick, is bent beyond its flexural limit, it often breaks into more than two pieces, typically three or more. This phenomenon and puzzle has aroused widespread interest and discussion since its first proposal by Feynman. Previous work has partly explained the inevitability of the secondary fracture, but without any adjustable time parameter. In order to further understand this problem, especially the secondary fracture, in this paper we propose and study the dynamics of a half-infinite model to mimic the physics that a spaghetti stick is half-infinite under uniform bending. When the breaking process starts, a gradual release of initial moment of a linearly declining time at the free end, instead of a sudden release, is adopted, resulting in the introduction of a characteristic time parameter to the model and agrees better with the real situation. A specific analytical solution in terms of the excited bending moment using Euler–Bernoulli beam theory is derived, and that the gradual release of initial moment induces a burst of flexural waves, and these flexural waves locally increase the moment in the stick and progressively get to the maximum value, and then lead to the secondary fracture are concluded. The excited moment increases with time and distance, and has an asymptotic extremum value of 1.43 times initial moment. The gradual release in our model requires and gives certain distance and time when the excited bending moment reaches its extremum value, which provides a possibility to predict the detailed fracture parameters such as fragmentation length and time and thus to further understand the secondary fracture during spaghetti bent break.

Photocatalytic degradation of pesticides by nanofibrous membranes fabricated by colloid-electrospinning

Photocatalytic degradation of organic pollutants is a promising way to clean wastewater. Herein, we develop and compare two processes for fabricating nanofibrous membranes with photocatalytic properties. Hybrid nanofibers are produced by colloid-electrospinning and composed of metal oxide nanoparticles on sintered SiO₂ nanoparticles. The latter serves as support for the photocatalyst and preserves the structural integrity of nanofibers. Adsorption of metal salts on crosslinked polymer/SiO₂ fibers followed by calcination allows for the obtention of fibers with large amounts of metal oxide. Nanofibrous membranes with supported ZnO, In₂O₃, or mixture of both, display photocatalytic activity upon UV irradiation. The membranes can degrade a dye and an organophosphate pesticide more effectively than membranes directly fabricated from the calcination of metal oxides.

Nanozymes in Nanofibrous Mats with Haloperoxidase-like Activity To Combat Biofouling

Electrospun polymer mats are widely used in tissue engineering, wearable electronics, and water purification. However, in many environments, the polymer nanofibers prepared by electrospinning suffer from biofouling during long-term usage, resulting in persistent infections and device damage. Herein, we describe the fabrication of polymer mats with CeO_{2- x} nanorods that can prevent biofouling in an aqueous environment. The embedded CeO_{2- x} nanorods are functional mimics of natural haloperoxidases that catalyze the oxidative bromination of Br^- and H₂O₂ to HOBr. The generated HOBr, a natural signaling molecule, disrupted the bacterial quorum sensing, a critical step in biofilm formation. The polymer fibers provide porous structures with high water wettability, and the embedded cerium oxide nanozymes act as a catalyst that can efficiently trigger oxidative bromination, as shown by a haloperoxidase assay. Additionally, the embedded nanozymes enhance the mechanical property of polymer mats, as shown by a single-fiber bending test using atomic force microscopy. We envision that the fabricated polymer mats with CeO_{2- x} nanorods may be used to provide mechanically robust coatings with antibiofouling properties.