Solvent Effect on Antimicrobial Hydrophilic Xerogel Coating of Medicinal Leathers in Simulated Industrial Finishing Process

Ioannidis I., Aristotelous E., Pashalidis I., Dosche C., Giannakopoulos K., Karastergiou E., Arkas M.

Ioannidis I., Pashalidis I., Arkas M.

The binding of actinide ions (Am(III) and U(VI)) in aqueous solutions by hybrid silica–hyperbranched poly(ethylene imine) nanoparticles (NPs) and xerogels (XGs) has been studied by means of batch experiments at different pH values (4, 7, and 9) under ambient atmospheric conditions. Both materials present relatively high removal efficiency at pH 4 and pH 7 (>70%) for Am(III) and U(VI). The lower removal efficiency for the nanoparticles is basically associated with the compact structure of the nanoparticles and the lower permeability and access to active amine groups compared to xerogels, and the negative charge of the radionuclide species is formed under alkaline conditions (e.g., UO2(CO3)34− and Am(CO3)2−). Generally, the adsorption process is relatively slow due to the very low radionuclide concentrations used in the study and is basically governed by the actinide diffusion from the aqueous phase to the solid surface. On the other hand, adsorption is favored with increasing temperature, assuming that the reaction is endothermic and entropy-driven, which is associated with increasing randomness at the solid–liquid interphase upon actinide adsorption. To the best of our knowledge, this is the first study on hybrid silica–hyperbranched poly(ethylene imine) nanoparticle and xerogel materials used as adsorbents for americium and uranium at ultra-trace levels. Compared to other adsorbent materials used for binding americium and uranium ions, both materials show far higher binding efficiency. Xerogels could remove both actinides even from seawater by almost 90%, whereas nanoparticles could remove uranium by 80% and americium by 70%. The above, along with their simple derivatization to increase the selectivity towards a specific radionuclide and their easy processing to be included in separation technologies, could make these materials attractive candidates for the treatment of radionuclide/actinide-contaminated water.

Arkas M., Bompotis T., Giannakopoulos K., Favvas E.P., Arvanitopoulou M., Arvanitopoulos K., Arvanitopoulos L., Kythreoti G., Vardavoulias M., Giannakoudakis D.A., Castellsagués L., Soto González S.M.

Four leather substrates from different animals were treated by dispersions containing hydrophilic composite silica-hyperbranched poly(ethylene imine) xerogels. Antimicrobial activity was introduced by incorporating silver nanoparticles and/or benzalkonium chloride. The gel precursor solutions were also infused before gelation to titanium oxide powders typically employed for induction of self-cleaning properties. The dispersions from these biomimetically premade xerogels integrate environmentally friendly materials with short coating times. Scanning electron microscopy (SEM) provided information on the powder distribution onto the leathers. Substrate and coating composition were estimated by infrared spectroscopy (IR) and energy-dispersive X-ray spectroscopy (EDS). Surface hydrophilicity and water permeability were assessed by water-contact angle experiments. The diffusion of the leather’s initial components and xerogel additives into the water were measured by Ultraviolet-Visible (UV-Vis) spectroscopy. Protection against GRAM- bacteria was tested for Escherichia coli, Pseudomonas aeruginosa, and Klebsiella Pneumoniae against GRAM+ bacteria for Staphylococcus aureus and Enterococcus faecalis and against fungi for Candida albicans. Antibiofilm capacity experiments were performed against Staphylococcus aureus, Klebsiella Pneumoniae, Enterococcus faecalis, and Candida albicans. The application of xerogel dispersions proved an adequate and economically feasible alternative to the direct gel formation into the substrate’s pores for the preparation of leathers intended for medical uses.

Arkas M., Giannakopoulos K., Favvas E.P., Papageorgiou S., Theodorakopoulos G.V., Giannoulatou A., Vardavoulias M., Giannakoudakis D.A., Triantafyllidis K.S., Georgiou E., Pashalidis I.

Two different silica conformations (xerogels and nanoparticles), both formed by the mediation of dendritic poly (ethylene imine), were tested at low pHs for problematic uranyl cation sorption. The effect of crucial factors, i.e., temperature, electrostatic forces, adsorbent composition, accessibility of the pollutant to the dendritic cavities, and MW of the organic matrix, was investigated to determine the optimum formulation for water purification under these conditions. This was attained with the aid of UV-visible and FTIR spectroscopy, dynamic light scattering (DLS), ζ-potential, liquid nitrogen (LN2) porosimetry, thermogravimetric analysis (TGA), and scanning electron microscopy (SEM). Results highlighted that both adsorbents have extraordinary sorption capacities. Xerogels are cost-effective since they approximate the performance of nanoparticles with much less organic content. Both adsorbents could be used in the form of dispersions. The xerogels, though, are more practicable materials since they may penetrate the pores of a metal or ceramic solid substrate in the form of a precursor gel-forming solution, producing composite purification devices.

Arkas M., Vardavoulias M., Kythreoti G., Giannakoudakis D.A.

The capability of radially polymerized bio-dendrimers and hyperbranched polymers for medical applications is well established. Perhaps the most important implementations are those that involve interactions with the regenerative mechanisms of cells. In general, they are non-toxic or exhibit very low toxicity. Thus, they allow unhindered and, in many cases, faster cell proliferation, a property that renders them ideal materials for tissue engineering scaffolds. Their resemblance to proteins permits the synthesis of derivatives that mimic collagen and elastin or are capable of biomimetic hydroxy apatite production. Due to their distinctive architecture (core, internal branches, terminal groups), dendritic polymers may play many roles. The internal cavities may host cell differentiation genes and antimicrobial protection drugs. Suitable terminal groups may modify the surface chemistry of cells and modulate the external membrane charge promoting cell adhesion and tissue assembly. They may also induce polymer cross-linking for healing implementation in the eyes, skin, and internal organ wounds. The review highlights all the different categories of hard and soft tissues that may be remediated with their contribution. The reader will also be exposed to the incorporation of methods for establishment of biomaterials, functionalization strategies, and the synthetic paths for organizing assemblies from biocompatible building blocks and natural metabolites.

Arkas M., Kythreoti G., Favvas E.P., Giannakopoulos K., Mouti N., Arvanitopoulou M., Athanasiou A., Douloudi M., Nikoli E., Vardavoulias M., Dimitriou M., Karakasiliotis I., Ballén V., González S.M.

Hybrid organic-inorganic (dendritic polymer-silica) xerogels containing silver nanoparticles (Ag Nps) were developed as antibacterial leather coatings. The preparation method is environmentally friendly and is based on two biomimetic reactions. Silica gelation and spontaneous Ag Nps formation were both mediated by hyperbranched poly (ethylene imine) (PEI) scaffolds of variable Mw (2000–750,000). The formation of precursor hydrogels was monitored by dynamic light scattering (DLS). The chemical composition of the xerogels was assessed by infrared spectroscopy (IR) and energy-dispersive X-ray spectroscopy (EDS), while the uniformity of the coatings was established by scanning electron microscopy (SEM). The release properties of coated leather samples and their overall behavior in water in comparison to untreated analogs were investigated by Ultraviolet-Visible (UV-Vis) spectroscopy. Antibacterial activity was tested against Escherichia coli, Pseudomonas aeruginosa, and Staphylococcus aureus, and antibiofilm properties against Staphylococcus aureus, Staphylococcus epidermidis, Escherichia coli, Acinetobacter baumannii, and Enterococcus faecalis, while the SARS-CoV-2 clinical isolate was employed for the first estimation of their antiviral potential. Toxicity was evaluated using the Jurkat E6.1 cell line. Finally, water-contact angle measurements were implemented to determine the enhancement of the leather surface hydrophilicity caused by these composite layers. The final advanced products are intended for use in medical applications.

Jensen L.K., Jensen H.E., Blirup-Plum S.A., Bue M., Hanberg P., Kvich L., Aalbæk B., López Y., Soto S.M., Douloudi M., Papageorgiou M., Nikoli E., Arkas M., Gutiérrez-del-Río I., López-Ibáñez S., et. al.

The use of bone implants and prostheses has contributed to a revolution in modern medicine; however, in the beginning, not much was asked from the implant and prosthetic materials per se . Therefore, the next game-changer in orthopedic research will come from new material designs which for instance can aid in prevention of implant-associated bone infections. Here, we describe the development of a new sol-gel coating technique that can deliver an efficient antimicrobial surface coating on orthopedic implants. Gentamicin was stocked in a novel nanocomposite xerogel made from silica and hyperbranched polyethyleneimine. The xerogel was anchored inside a porous surface made by coating of bone implants with titanium microspheres. Thereby, only the small water-soluble gentamicin molecules diffused in an aqueous environment, i.e., just after surgical insertion and leaving behind a titanium scaffold for osseointegration. The novel xerogel coating prevented development of severe Staphylococcus aureus induced osteomyelitis in a porcine model, which untreated, replicated the pathology seen in stage 3A on the Cierny–Mader classification system for osteomyelitis in adults.

Arkas M., Douloudi M., Nikoli E., Karountzou G., Kitsou I., Kavetsou E., Korres D., Vouyiouka S., Tsetsekou A., Giannakopoulos K., Papageorgiou M.

Silica-organic matrix-silver, nano-catalysts, were synthesized employing four different hyperbranched poly(ethylene imines) (MW 2000 to 750,000) to reduce Ag+ to metal nanoparticles and the formation of formation SiO2 shells. The latter is performed at pH 7,5 employing three different pH regulating agents Hepes, Trizma, and Phosphate Salts. Characterization of the resulting materials with spectroscopy (FTIR), thermogravimetry (TG), scanning electron microscopy (SEM), and ζ-potential is reported. Kinetic studies of standard reactions, 4-nitrophenol and 4-nitroaniline reduction to 4-aminophenol and p-phenylenediamine, respectively by UV-Visible spectroscopy are also included. This data in brief article is related to the "Investigation of two Bioinspired Reaction Mechanisms for the Optimization of Eco Composites-Nano Catalysts Generated from Hyperbranched Polymer Matrices" manuscript submitted to reactive & functional polymers.

Arkas M., Douloudi M., Nikoli E., Karountzou G., Kitsou I., Kavetsou E., Korres D., Vouyiouka S., Tsetsekou A., Giannakopoulos K., Papageorgiou M.

Silver nanoparticles were templated employing hyperbranched poly (ethylene imines) (PEI). Then they were immobilized to silica substrates also formed by the mediation of the same dendritic polymer matrices to produce hybrid nanocatalysts. The effect of four different PEIs (MW 2000 to 750,000) was investigated. In the first stage, the mechanisms of the already known spontaneous transformation of Ag ions to metal nanoparticles were monitored by UV Visible Spectroscopy and dynamic light scattering (DLS). Then the effect of three different pH regulating agents on the formation of SiO 2 at pH 7,5 was investigated. An additional optional step, the organic scaffold pyrolysis and the repercussions to the catalytic activity was researched as well. This treatment accelerated reactants' diffusion into silica, eliminated induction periods, and improved reaction rates. Furthermore, compatibility with reactions at high temperatures was established. The characterization of the resulting materials also involved, thermogravimetry (TG), FTIR spectroscopy, ζ-potential, and scanning electron microscopy (SEM)/energy-dispersive X-ray spectroscopy (EDS). Kinetic studies were conducted to investigate catalytic performance and the effect of the different composite formation methods on the accessibility to the silver nanoparticles. The majority of the samples tested, exhibited excellent results. Taking into account the ecological synthesis procedure that is carried out at ambient temperature without toxic compounds or solvents the overall procedure emerges as a prosperous alternative for the production of a wide range of multifunctional nanomaterials. • 2 biomimetic approaches for the production of multifunctional materials. • Two different (polymer MW dependent) silver ion reduction mechanisms. • Substantial influence of buffering agents on the composite's properties. • Catalyst performance analogous to accessibility (and not quantity) of silver. • High-temperature treatment causes disparate catalytic efficiency increase.

Arkas M., Anastopoulos I., Giannakoudakis D.A., Pashalidis I., Katsika T., Nikoli E., Panagiotopoulos R., Fotopoulou A., Vardavoulias M., Douloudi M.

Radially polymerized dendritic compounds are nowadays an established polymer category next to their linear, branched, and cross-linked counterparts. Their uncommon tree-like architecture is characterized by adjustable internal cavities and external groups. They are therefore exceptional absorbents and this attainment of high concentrations in their interior renders them ideal reaction media. In this framework, they are applied in many environmentally benign implementations. One of the most important among them is water purification through pollutant decomposition. Simple and composite catalysts and photo-catalysts containing dendritic polymers and applied in water remediation will be discussed jointly with some unconventional solutions and prospects.

Renganath Rao R., Sathish M., Raghava Rao J.

With the recent events following the pandemic COVID-19, global awareness about the use of biosafety materials has been in raise. Leather industry being a major commodity-driven sector, its role in addressing the issues concerning the safe use of leather products has become inevitable for the sustainability of the industry. A significant number of researches have been conducted to fabricate bio-safe leather by incorporating different types of antimicrobial agents during leather manufacturing. Besides, the increasing diversity in the development of synthetic materials and the impact of COVID-19 outbreak on automotive industry may create more demand from customers for incorporating different functionalities in leather without losing its inherent properties. Some of the key functionalities discussed include resistance to microbial growth, self-cleaning through superhydrophobicity and photocatalysis, thermal regulation, flame retardance and scented leather. This review focusses on the fabrication of such advanced functional leather materials over the past decade with special emphasis on antimicrobial leather. Some of the key factors elaborated in the review include the state of art approaches for the preparation of functional materials, mode of incorporation of the same into the leather matrix, the mechanism behind with a perspective on the challenges involved in fabrication for real-world applications. A major outcome of this review is that even though several kinds of cutting edge researches are happening in the field of leather manufacturing, most of them were not validated for its practical applicability and sustainability of the proposed solution. This could be majorly attributed to the cost involved in fabrication of such materials, which forms a crucial factor when it comes to a mass production industry such as leather. Also, the researchers should concentrate on the toxicity of the fabricated materials which can impede the process of adopting such emerging and need of the hour technologies in the near future. Knowledge obtained from this review on fabrication of bio-safety leather against bacteria, mold and fungi would help further to integrate the antiviral property into the same which is a global need. Also, fabrication of functionalized leather would open new avenues for leather manufactures to venture into the development of advanced leather products such as flexible electronics, radiation shielding and fire fighting garments etc.

Douloudi M., Nikoli E., Katsika T., Vardavoulias M., Arkas M.

As the field of nanoscience is rapidly evolving, interest in novel, upgraded nanomaterials with combinatory features is also inevitably increasing. Hybrid composites, offer simple, budget-conscious and environmental-friendly solutions that can cater multiple needs at the same time and be applicable in many nanotechnology-related and interdisciplinary studies. The physicochemical idiocrasies of dendritic polymers have inspired their implementation as sorbents, active ingredient carriers and templates for complex composites. Ceramics are distinguished for their mechanical superiority and absorption potential that render them ideal substrates for separation and catalysis technologies. The integration of dendritic compounds to these inorganic hosts can be achieved through chemical attachment of the organic moiety onto functionalized surfaces, impregnation and absorption inside the pores, conventional sol-gel reactions or via biomimetic mediation of dendritic matrices, inducing the formation of usually spherical hybrid nanoparticles. Alternatively, dendritic polymers can propagate from ceramic scaffolds. All these variants are covered in detail. Optimization techniques as well as established and prospected applications are also presented.

Petrucci O.D., Hilton R.J., Farrer J.K., Watt R.K.

We previously reported that ferritin acts as a photocatalyst to form monodispersed gold nanoparticles. Because silver possesses a favorable reduction potential (+0.80 V), we postulated that the ferritin photochemical method could be used to reduce Ag(I) to Ag(0). Additionally, we postulated that similar to gold, the reduced silver should nucleate and form silver nanoparticles (AgNPs) on the external surface of ferritin. This study reports that Ag(I) can function as an electron acceptor to form monodispersed AgNPs using the ferritin photocatalytic method. The formation and growth of the AgNPs were monitored by following the surface plasmon resonance (SPR) peak at 420 nm by spectrophotometry. The resulting monodispersed AgNPs were analyzed by transmission electron microscopy (TEM), scanning transmission electron microscopy (STEM), and energy-dispersive X-ray spectroscopy (EDX). Gel filtration chromatography demonstrated that the AgNPs comigrated with ferritin through the column suggesting a strong association with ferritin. AgNPs are known to possess antimicrobial properties. The antimicrobial properties of Ferritin-AgNPs were compared to commercially available AgNPs by testing the minimal growth inhibition ofStaphylococcus aureus. Commercially available AgNPs inhibited bacterial growth at 5 ppm AgNPs, and Ferritin-AgNPs inhibited growth at 20 ppm Ferritin-AgNPs.

Kitsou I., Panagopoulos P., Maggos T., Arkas M., Tsetsekou A.

Silica-titania core-shell nanospheres, CSNp, were prepared via a simple and environmentally friendly two step route. First, silica cores were prepared through the hydrolysis-condensation reaction of silicic acid in the presence of hyperbranched poly(ethylene)imine (HBPEI) followed by repeating washing, centrifugation and, finally, calcination steps. To create the core-shell structure, various amounts of titanium isopropoxide were added to the cores and after that a HBPEI-water solution was added to hydrolyze the titanium precursor. Washing with ethanol and heat treatment followed. The optimization of processing parameters led to well-developed core-shell structures bearing a homogeneous nanocrystalline anatase coating over each silica core. The photocatalytic activity for NO was examined in a continuous flux photocatalytic reactor under real environmental conditions. The results revealed a very potent photocatalyst as the degradation percentage reached 84.27% for the core-shell material compared to the 82% of pure titania with the photodecomposition rates measured at 0.62 and 0.55 μg·m−2·s−1, respectively. In addition, catalytic activities of the CSNp and pure titania were investigated by monitoring the reduction of 4-nitrophenol to 4-aminophenol by an excess of NaBH4. Both materials exhibited excellent catalytic activity (100%), making the core-shell material a promising alternative catalyst to pure titania for various applications.

Arkas M., Kithreoti G., Boukos N., Kitsou I., Petrakli F., Panagiotaki K.

An environment friendly procedure for the preparation of inorganic/organic/inorganic i.e. silica/hyperbranched poly(ethyleneimine) (PEI)/silver nanoparticles employing two biomimetic reactions is described. Silver ions can be absorbed into the hyperbranched PEI cavities and undergo reduction without employing a reducing agent. This is a process mimicking biomineralization, realized by specific proteins in some microorganisms. Dendritic poly(ethyleneimine) possesses size and functions that are similar to proteins and thus presents an ideal alternative to their role by mimicking their catalytic activity. At the periphery of PEI another procedure mimicking biosilicification can also be performed due to the presence of amino groups mimicking another category of proteins. To our knowledge this is the first example of a combination of two different biomimetic reactions performed by a single molecule in one pot synthesis procedure. The resulting hybrid nanoparticles are characterized by spectroscopy (FTIR, visible), thermogravimetry (TG), scanning electron microscopy (SEM), dynamic light scattering (DLS) X-ray diffraction, Energy-dispersive X-ray spectroscopy. Their antibacterial activity was assessed towards Escherichia coli, Pseudomonas aeruginosa and Staphylococcus aureus.