Athanassia Athanassiou

Elastomeric Nanocomposite Foams for the Removal of Heavy Metal Ions from Water

We report the fabrication and utilization of elastomeric polymer nanocomposite foams for the efficient removal of Pb2+ and Hg2+ heavy metal ions from polluted water. The polydimethylsiloxane (PDMS) foams are properly modified in order to become hydrophilic and allow the polluted water to penetrate in their volume. The ZnSe colloidal nanocrystals (NCs) that decorate the surface of the foams, act as active components able to entrap the metal ions. In this way, after the dipping of the nanocomposite foams in water polluted with Pb2+ or Hg2+, a cation exchange reaction takes place, and the heavy metal ions are successfully removed. The removal capacity for the Pb2+ ions exceeds 98% and the removal of Hg2+ ions approaches almost 100% in the studied concentrations region of 20-40 ppm. The reaction is concluded after 24 h, but it should be noticed that after the first hour, more than 95% of both the metal ions is removed. The color of the foams changes upon heavy metal ions entrapment, providing thus the opportunity of an easy detection of the presence of the ions in water. Taking into account that the fabricated foams provide good elastic properties and resistance to heat, they can be used in different conditions of water remediation.

Robust and Biodegradable Elastomers Based on Corn Starch and Polydimethylsiloxane (PDMS)

Designing starch-based biopolymers and biodegradable composites with durable mechanical properties and good resistance to water is still a challenging task. Although thermoplastic (destructured) starch has emerged as an alternative to petroleum-based polymers, its poor dimensional stability under humid and dry conditions extensively hinders its use as the biopolymer of choice in many applications. Unmodified starch granules, on the other hand, suffer from incompatibility, poor dispersion, and phase separation issues when compounded into other thermoplastics above a concentration level of 5%. Herein, we present a facile biodegradable elastomer preparation method by incorporating large amounts of unmodified corn starch, exceeding 80% by volume, in acetoxy-polyorganosiloxane thermosets to produce mechanically robust, hydrophobic bioelastomers. The naturally adsorbed moisture on the surface of starch enables autocatalytic rapid hydrolysis of polyorganosiloxane to form Si-O-Si networks. Depending on the amount of starch granules, the mechanical properties of the bioelastomers can be easily tuned with high elastic recovery rates. Moreover, starch granules considerably lowered the surface friction coefficient of the polyorganosiloxane network. Stress relaxation measurements indicated that the bioelastomers have strain energy dissipation factors that are lower than those of conventional rubbers, rendering them as promising green substitutes for plastic mechanical energy dampeners. Corn starch granules also have excellent compatibility with addition-cured polysiloxane chemistry that is used extensively in microfabrication. Regardless of the starch concentration, all of the developed bioelastomers have hydrophobic surfaces with lower friction coefficients and much less water uptake capacity than those of thermoplastic starch. The bioelastomers are biocompatible and are estimated to biodegrade in Mediterranean seawater within three to six years.

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.

Controlled antiseptic/eosin release from chitosan-based hydrogel modified fibrous substrates

Fibers of cellulose networks were stably coated with N-methacrylate glycol chitosan (MGC) shells using subsequent steps of dip coating and photo-curing. The photo-crosslinked MGC-coated cellulose networks preserved their fibrous structure. A model hydrophilic antiseptic solution containing eosin, chloroxylenol and propylene glycol was incorporated into the shells to study the drug release dynamics. Detailed drug release mechanism into phosphate buffered saline (PBS) solutions from coated and pristine fibers loaded with the antiseptic was investigated. The results show that the MGC-coated cellulose fibers enable the controlled gradual release of the drug for four days, as opposed to fast, instantaneous release from eosin coated pristine fibers. This release behavior was found to affect the antibacterial efficiency of the fibrous cellulose sheets significantly against Staphylococcus aureus and Candida albicans. In the case of the MGC-eosin functionalized system the antibacterial efficiency was as high as 85% and 90%, respectively, while for the eosin coated pristine cellulose system the efficiency was negative, indicating bacterial proliferation. Furthermore, the MGC-eosin system was shown to be efficacious in a model of wound healing in mice, reducing the levels of various pro-inflammatory cytokines that modulate early inflammatory phase responses. The results demonstrate good potential of these coated fibers for wound dressing and healing applications. Due to its easy application on common passive commercial fibrous dressings such as gauzes and cotton fibers, the method can render them active dressings in a cost effective way.

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.

Laser-induced localized formation of silver nanoparticles on chitosan films: study on particles size and density variation

We present the in situ localized formation of silver nanoparticles in chitosan films by pulsed UV laser irradiation, as a result of the photoreduction of the silver nitrate precursor loaded throughout the volume of the polymer. The UV pulsed irradiation is also found to be responsible for the photofragmentation of the previously formed nanoparticles, leading to their average size reduction as the number of pulses increases. In fact, their diameter changes from ~150 to ~30 nm for irradiation with 5 to 200 pulses, respectively. After irradiation the formation of nanoparticles continues for several days, since the already formed nanoparticles act as seeds for the reduction of the unreacted precursor. Indeed, few weeks after irradiation, the chitosan films present a metallic mirror-like appearance on the previously irradiated areas, as they are fully covered by silver. Taking advantage of all these simultaneous mechanisms, and controlling the number of pulses and elapsed time after irradiation, Ag nanoparticles of specific size can be formed in situ on desired areas of the film. Through this process is envisioned the fabrication of nanocomposites with functional properties.

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.