Gabriele Nanni

Biomimetic Approach for Liquid Encapsulation with Nanofibrillar Cloaks

Technologies that are able to handle microvolumes of liquids, such as microfluidics and liquid marbles, are attractive for applications that include miniaturized biological and chemical reactors, sensors, microactuators, and drug delivery systems. Inspired from natural fibrous envelopes, here, we present an innovative approach for liquid encapsulation and manipulation using electrospun nanofibers. We demonstrated the realization of non-wetting soft solids consisting of a liquid core wrapped in a hydrophobic fibrillar cloak of a fluoroacrylic copolymer and cellulose acetate. By properly controlling the wetting and mechanical properties of the fibers, we created final architectures with tunable mechanical robustness that were stable on a wide range of substrates (from paper to glass) and floated on liquid surfaces. Remarkably, the realized fiber-coated drops endured vortex mixing in a continuous oil phase at high stirring speed without bursting or water losses, favoring mixing processes inside the entrapped liquid volume. Moreover, the produced cloak can be easily functionalized by incorporating functional particles, active molecules, or drugs inside the nanofibers.

Nanocomposite Pattern-Mediated Magnetic Interactions for Localized Deposition of Nanomaterials

We present a method to create, align, and locate magnetic wires throughout and on the surface of patterned polymer matrices, following the magnetophoretic transport and self-assembly of ferromagnetic nanoparticles under a static magnetic field during laser photopolymerization of monomer/nanoparticle casted solutions. The resulting films have the ability to attract and immobilize small quantities of magnetic nanomaterials locally on the ferromagnetic wires, as proved by a detailed topography study. Magnetic studies on the films before and after the spontaneous deposition, demonstrate that the deposited nanomaterials alter significantly the magnetic character of the system, making thus possible their macroscopic identification. This offers the possibility to realize sensing devices based on hybrid materials with magnetic properties.

Oil removal from water–oil emulsions using magnetic nanocomposite fibrous mats

Herein we present the fabrication of hydrophobic and oleophilic poly(methyl methacrylate)-based nanocomposite fibrous mats with magnetic properties, and their utilization for oil removal from stable water–oil emulsions. The incorporation of ferromagnetic iron nanoparticles into the polymeric fibers increases the selectivity and oil removal performance of the fibers, as well as introduces magnetic actuation properties to the material. In all the water–oil emulsions used in this work ranging from 5 to 30 v%, the functional mats can obtain oil absorption efficiencies up to 90%. The oil removal efficiency can reach nearly 100% with just two successive absorption cycles. The high performance achieved makes the presented material a promising candidate for efficient water–oil emulsions separation.

Tunable Friction Behavior of Photochromic Fibrillar Surfaces

Grasslike compliant micro/nano crystals made of diarylethene (DAE) photochromic molecules are spontaneously formed on elastomer films after dipping them in a solution containing the photochromic molecules. The frictional forces of such micro- and nanofibrillar surfaces are reversibly tuned upon ultraviolet (UV) irradiation and dark storage cycles. This behavior is attributed to the Youngs modulus variation of the single fibrils due to the photoisomerization process of the DAE molecules, as measured by advanced atomic force microscopy (AFM) techniques. In fact, a significant yet reversible decrease of the stiffness of the outer part of the fibrils in response to the UV light irradiation is demonstrated. The modification of the molecular structure of the fibrils influences their mechanical properties and affects the frictional behavior of the overall fibrillar surfaces. These findings provide the possibility to develop a system that controllably and accurately generates both low and high friction forces.

Light Responsive Silk Nanofibers: An Optochemical Platform for Environmental Applications

Photochromic spiropyran-doped silk fibroin poly(ethylene oxide) nanofibers which combine the attractive properties and biocompatibility of silk with the photocontrollable and reversible optical, mechanical, and chemical response of the spiropyran dopants are herein presented. As proved, the reversible variation of the absorption and emission signals of the mats and of their Youngs modulus upon alternate UV and visible light irradiation is ascribed to the reversible photoconversion of the spiropyran form to its polar merocyanine counterpart. Most importantly, the interactions of the merocyanine molecules with acidic vapors as well as with heavy metal ions dispersed in solution produce analyte-specific spectral changes in the emission profile of the composite, accompanied by a characteristic chromic variation. Because of the high surface-to-volume ratio of the nanofibrous network, such interactions are fast, thus enabling both an optical and a visual detection in a 30-60 s time scale. The sensing platform can be easily regenerated for more than 20 and 3 cycles upon acid or ion depletion, respectively. Overall, the photocontrolled properties of the silk composites combined with a straightforward preparation method render them suitable as porous materials and scaffolds with tunable compliance and reusable nanoprobes for real time optical detection in biomedical, environmental, and industrial applications.

Enhanced oil removal from water in oil stable emulsions using electrospun nanocomposite fiber mats

Fibrous mats with hydrophobic and oleophilic properties have been fabricated and used as absorbents of oil from stable water in oil emulsions. The mats were prepared by initially mixing two polymers, poly(methyl methacrylate) (PMMA) and polycaprolactone (PCL), in a common solvent. The subsequent electrospinning of the prepared solutions resulted in the production of mechanically stable fiber mats, with enhanced oil absorption capacity and oil absorption selectivity from the emulsions, compared to the pure PMMA or PCL mats. Furthermore, the formed fibrous substrates have been successful in the absorption of oil from different emulsions with a wide range of oil content, from 10 to 80 v%. The performance of the fibrous mats was optimized by the incorporation of hydrophobic silica nanoparticles, reaching oil absorption capacities of 28 g g−1 and negligible water uptake, in the emulsions with 80 v% oil content.

Photochromic Paper Indicators for Acidic Food Spoilage Detection

A photoresponsive microstructured composite is fabricated through the impregnation of cellulosic filter paper (FP) with a spiropyran-modified acrylic polymer. The polymer enwraps uniformly each individual cellulose fiber, increases the thermal stability of cellulose, and ensures the preservation of the composite functionalities even upon removal of the surface layers through mechanical scratching. The photochromic spiropyran moieties of the polymer, even while embedded in the cellulosic sheet, can reversibly interconvert between the colorless spiropyran and the pink merocyanine isomeric states upon irradiation with UV and visible light, respectively. Moreover, the photochromic polymer presents a faster photochromic response and a higher resistance to photodegradation, with an outstanding reusability for more than 100 switching cycles when it is incorporated in the cellulose network. Most importantly, the acidochromism of the modified FP, attributed to the spiropyran molecules after UV activation, allows the real-time optical and visual detection of acidity changes and spoilage in food products, such as wine and milk. Spoilage due to bacterial degradation and oxidation processes generates acidic vapors that induce the protonation of the merocyanine. This results in a visually detectable chromic transition from pink to white of the treated cellulose fibers, corresponding to a blue shift in the absorption spectrum. The developed photoresponsive cellulose composite can serve as cost-effective robust optical component in integrated functional platforms and consumer-friendly indicators for smart food packaging, as well as portable on demand acidoresponsive interfaces for gas monitoring in industrial and environmental applications.