Linear amphoteric polyamidoamines (PAAs) are usually water-soluble, biodegradable and biocompatible. Crosslinked PAAs form in water hydrogels, retaining most of the favorable properties of their ...linear counterparts. The hydrogels prepared by the radical post-polymerization of the oligo-α,ω-bisacrylamido-terminated PAA called AGMA1, obtained by the polyaddition of 4-aminobutylguanidine (agmatine) with 2,2-bis(acrylamido)acetic acid, exhibit excellent cell-adhesion properties both in vitro and in vivo. However, due to their low mechanical strength, AGMA1 hydrogels cannot be sewn to biological tissues and need to be reinforced with fibrous materials. In this work, short silk fibers gave excellent results in this sense, proving capable of establishing covalent bonds with the PAA matrix, thanks to their lysine content, which provided amino groups capable of reacting with the terminal acrylamide groups of the AGMA1 precursor in the final crosslinking phase. Morphological analyses demonstrated that the AGMA1 matrix was intimately interconnected and adherent to the silk fibers, with neither visible holes nor empty volumes. The silk/H-AGMA1 composites were still reversibly swellable in water. In the swollen state, they could be sewn and showed no detachment between fibers and matrix and exhibited significantly improved mechanical properties compared with the plain hydrogels, particularly as regards their Young's modulus and elongation at break.
The exploitation of self-assembled coatings comprising graphite oxide (GO) nanoplates has been recently demonstrated as a promising route to improve the fire safety of flexible polyurethane (PU) ...foams. However, limited knowledge has been gathered on the correlations between the physical and chemical properties of different GO grades and the performance obtained in this application. This work addresses the effects of the nanoparticle dimensions on the layer-by-layer (LbL) assembly and flame-retardant properties of GO-based coatings deposited on PU foams. To this aim, three GO bearing different lateral sizes and thicknesses were selected and LbL-assembled with chitosan (CHIT). Coating growth and morphology were evaluated by FTIR and FESEM, respectively. The resulting CHIT/GO assemblies were demonstrated to be capable of slowing down the combustion of the PU both in flammability and forced combustion tests. In addition, compressive stress/strain tests pointed out that the LbL-coated foams (22-24 kg/m
) could easily replace denser commercial PU foam (40-50 kg/m
) with weight reduction potentials in the transport field. These results are correlated with the properties of the employed GO. The production of assemblies characterized by a high density of CHIT/GO interfaces is identified as the main parameter controlling the FR efficiency and the mechanical properties of the coatings.
The polyelectrolyte (PE)-based water dispersion of graphene-related materials (GRMs) represents an interesting intermediate for the development of advanced materials by sustainable processes. ...Although the proof of concept has been demonstrated, there is a lack of knowledge for what concerns the effects of parameters typical of PEs such as functionalization, molecular weight, and charge density. In this work, we evaluate the effects of such parameters on the quality and long-term stability of reduced graphite oxide (rGO) dispersion in aqueous media prepared by ultrasound sonication in the presence of different PEs. Four PEs were evaluated: polyacrylic acid (PAA), branched poly(ethylenimine) (BPEI), sodium carboxymethyl cellulose (CMC), and poly(sodium 4-styrenesulfonic acid) (PSS). The prepared dispersions were thoroughly characterized by means of UV-visible spectroscopy, thermogravimetric analysis, dynamic light scattering, and Raman spectroscopy. The highest concentrations of rGO were achieved by BPEI with a molecular weight of 25,000 and 270,000 Da (33 and 26 µg/mL, respectively). For other PEs, the rGO concentration was found to be independent of the molecular weight. The PAA-based dispersions displayed the best through-time stability while yielding homogeneous dispersion with a smaller average size and narrower size distribution.
In the field of bone regeneration, considerable attention has been addressed towards the use of mesoporous bioactive glasses (MBGs), as multifunctional therapeutic platforms for advanced medical ...devices. In fact, their extremely high exposed surface area and pore volume allow to load and the release of several drugs, while their framework can be enriched with specific therapeutic ions allowing to boost the tissue regeneration. However, due to the open and easily accessible mesopore structure of MBG, the release of the incorporated therapeutic molecules shows an initial burst effect leading to unsuitable release kinetics. Hence, a still open challenge in the design of drug delivery systems based on MBGs is the control of their release behavior. In this work, Layer-by-layer (LbL) deposition of polyelectrolyte multi-layers was exploited as a powerful and versatile technique for coating the surface of Cu-substituted MBG nanoparticles with innovative multifunctional drug delivery systems for co-releasing of therapeutic copper ions (exerting pro-angiogenic and anti-bacterial effects) and an anti-inflammatory drug (ibuprofen). Two different routes were investigated: in the first strategy, chitosan and alginate were assembled by forming the multi-layered surface, and, successively, ibuprofen was loaded by incipient wetness impregnation, while in the second approach, alginate was replaced by ibuprofen, introduced as polyelectrolyte layer. Zeta-potential, TGA and FT-IR spectroscopy were measured after the addition of each polyelectrolyte layer, confirming the occurrence of the stepwise deposition. In addition, the in vitro bioactivity and the ability to modulate the release of the cargo were evaluated. The polyelectrolyte coated-MBGs were proved to retain the peculiar ability to induce hydroxyapatite formation after 7 days of soaking in Simulated Body Fluid. Both copper ions and ibuprofen were co-released over time, showing a sustained release profile up to 14 days and 24 h, respectively, with a significantly lower burst release compared to the bare MBG particles.
The layer-by-layer (LbL) technique is adopted for the construction of multilayers encompassing chitosan and graphene oxide (GO) platelets capable of improving the flame retardant properties open cell ...PU foams. The LbL assembly follows a linear growth regime as evaluated by infrared spectroscopy and yields a multilayer structure where GO platelets are embedded within a chitosan continuous matrix. 3 and 6 bi-layers (BL) can efficiently coat the complex 3D structure of the foam and substantially improve its flame retardant properties. 3BL only add 10% to the original mass and can suppress the melt dripping during flammability and reduce both the peak of heat release rate by 54% and the total smoke released by 59% in forced combustion tests. Unprecedented among other LbL assemblies employed for FR purposes, the deposition 6BL is capable of slowing down the release of combustible volatile to the limits of non-ignitability thus preventing ignition in half of the specimens during cone calorimetry tests. This has been ascribed to the formation of a protective coating where the thermally stable char produced by chitosan serves as a continuous matrix embedding GO platelets, which control volatile release while mechanically sustaining the PU foam structure.
•The LbL assembly is used to impart flame retardant properties to PU foams.•Chitosan and graphene oxide are employed as coating constituents.•The melt dripping was suppressed during flammability tests.•3 bi-layers allow for a 54% reduction in the peak of heat release rate.•6 bi-layers can slow down volatile release to lower flammability limit.
The layer‐by‐layer surface modification of open cell foams is a recently developed route to reduce the fire threat of this class of materials. This approach generally requires a high number of ...deposition steps to achieve the desired properties. This paper reports the water‐based single‐step deposition of efficient flame retardant coatings encompassing graphene oxide (GO) and DNA. During the deposition, a temperature‐induced in situ assembly of the GO+DNA produces a continuous and thermally robust protective layer on the structure of the polyurethane (PU) foam where GO nanoplates are held together by DNA acting as a ligand. This GO+DNA coating can effectively prevent flame spread during flammability tests performed in horizontal or vertical configuration while considerably reducing the rate of combustion and production of smoke by cone calorimetry (−75% and 30% in peak of heat release rate and total smoke release, respectively). The DNA promotes the formation of a protective structure that efficiently limits heat and volatiles transfer from and to the flame thus resulting in flame retardant (FR) performances capable of outperforming many of the FR coatings developed so far for PU foams. The proposed approach potentially opens up to the development of high performing FR solutions based on graphene‐related materials and bio‐based components.
The single‐step deposition of a DNA/graphene oxide nanocoating provides exceptional flame retardant properties to open cell flexible polyurethane foams. The coated foams cannot be ignited by the application of a small flame and burn with extremely low combustion rates and smoke release when exposed to an impinging heat flux, thus achieving unprecedented fire safety performances.
The potential safety hazard associated to commonly used flame retardant chemicals generates a strong demand for new, sustainable, and high performing solutions to reduce the fire threats of ...widespread polymer foams. In this work, the production of self‐extinguishing, nonignitable, and flame resistant flexible polyurethane foams by means of simple layer‐by‐layer assembly of graphene oxide nanoplatelets is reported. The process builds a protective exoskeleton that completely wraps the complex 3D structure of the foam and is capable of stopping flame spread in flammability tests and preventing ignition when exposed to heat fluxes typical of developing fires. In addition, treated foams are found able to withstand the penetration of a flame torch, successfully protecting the unexposed side from thermal decomposition for more than 6 min. The outstanding temperature gradient greater than 500 °C cm−1 achieved through the foam thickness makes the performances of these foams comparable to those of a silica aerogel, while maintaining excellent flexibility and toughness. The results reported in this paper represent a tremendous opportunity for the production of a novel class of organic and flexible foams, capable of ensuring unprecedented fire safety properties while relying on an easy, green, and straightforward approach to material design.
Graphene oxide nanoplatelets are employed for the self‐assembly of a nanostructured exoskeleton on flexible polymer foams. These graphene oxide‐based foams will neither start nor propagate the fire, thus providing unprecedented fire safety performances. The combination of mechanical flexibility and flame resistance makes these foams a groundbreaking solution for heat shielding applications, capable of outclassing inorganic silica aerogels.
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Transparent wood (TW) biocomposites combine high optical transmittance and good mechanical properties and can contribute to sustainable development. The safety against fire is ...important for building applications. Here, a “green” bleached wood reinforcement is impregnated by water soluble and flame-retardant melamine formaldehyde (MF) in a scalable process, for a wood content of 25 vol%. FE-SEM is used for characterization of optical defects and EDX to examine MF distribution at nanoscale cell wall pore space. Curing (FTIR-ATR), mechanical properties, optical transmittance (74% at 1.2 mm thickness) and flame-retardant properties are also characterized (self-extinguishing behavior and cone calorimetry), and scattering mechanisms are discussed. The fire growth rate of transparent wood was less than half the values for neat wood. Transparent wood/MF biocomposites show interesting wood-MF synergies and are of practical interest in building applications. Critical aspects of processing are analyzed for minimization of optical defects.
•The Layer-by-Layer is used to coat keratin fibers from the tannery wastes.•Chitosan and cellulose nanofibrils are employed as coating constituents.•The coated fibers are used to produce lightweight ...fiber networks.•The produced lightweight materials show excellent flame retardant properties.
The increasing consciousness about the depletion of natural resources and the sustainability agenda are the major driving forces to try to reuse and recycle organic materials such as agri-food and industrial wastes. In this context, keratin fibers, as a waste from the tannery industry, represent a great opportunity for the development of green functional materials. In this paper, keratin fibers were surface functionalized using the Layer-by-Layer (LbL) deposition technique and then freeze-dried in order to obtain a lightweight, fire-resistant, and sustainable material. The LbL coating, made with chitosan and carboxymethylated cellulose nanofibers, is fundamental in enabling the formation of a self-sustained structure after freeze-drying. The prepared porous fiber networks (density 100 kg m–3) display a keratin fiber content greater than 95 wt% and can easily self-extinguish the flame during a flammability test in a vertical configuration. In addition, during forced combustion tests (50 kW m–2) the samples exhibited a reduction of 37 % in heat release rate and a reduction of 75 % in smoke production if compared with a commercial polyurethane foam. The results obtained represent an excellent opportunity for the development of fire-safe sustainable materials based on fiber wastes.
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In this work, novel composite microparticles based on chitosan (CHI) and graphite nanoplatelets (GNP) were developed as 3D scaffolds for neuronal cells. The aim is to improve the scaffold strength ...while maintaining its ability to sustain cell adhesion and differentiation. An air-assisted jetting technique followed by physical crosslinking is employed to obtain CHI/GNP microparticles. Optical and Field Emission Scanning Electron Microscopy micrographs showed a uniform distribution of GNP within the CHI porous matrix. The presence of GNP turned out to improve the strength of the microparticles while conferring good electrical conductivity and ameliorating their stability in aqueous environment. The morphological and immunocytochemical characterization, combined with a preliminary electrophysiological analysis, evidenced the effectiveness of the developed composite microparticles as a scaffold for neuron growth. These scaffolds could be employed for the development of advanced 3D neuronal in vitro models for networks dynamics analysis and drug screening.
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•A 3D neuronal network scaffold is developed.•The scaffold is made of microparticles based on chitosan and GNP.•GNP is homogeneously dispersed within the polymer matrix.•GNP increases the strength and improves the stability in water of the scaffold.•GNP confers electrical conductivity to the scaffold.•The scaffold supports the development of complex neuronal networks.
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