A bioinspired and sustainable route for the preparation of Ag-crosslinked alginate fibers decorated with silver nanoparticles.

Functional materials obtained through green and sustainable routes are attracting particular attention due to the need to reduce the environmental impact of the chemical industry. In this work we propose a bioinspired approach for the preparation of alginate fibers containing silver nanoparticles (AgNPs), to be used for antimicrobial purposes. We demonstrate that filiform polymeric structures with length of a few meters can be easily obtained by extruding an alginate solution in an aqueous Ag+-containing bath (i.e. wet spinning) and that treating the fibers with freshly-squeezed lemon juice leads to the formation of AgNPs homogeneously distributed within the polymeric network. Using mixtures of ascorbic and citric acid to mimic lemon juice composition we highlight the influence of the aforementioned molecules on the nanoparticles formation process as well as on the properties of the fibers. Varying the amount of citric and ascorbic acid used for the treatment allows to finely tune the thermal, morphological and water absorption properties of the fibers. This evidence, along with the possibility to easily monitor the preparation through FT-IR spectroscopy, endows the fibers with a high application potential in several fields such as wound healing, water/air purification and agriculture.

Effect of Atmospheric Pressure Plasma Jet Treatments on Magnesium Phosphate Cements: Performance, Characterization, and Applications.

Atmospheric pressure plasma treatments are nowadays gaining importance to improve the performance of biomaterials in the orthopedic field. Among those, magnesium phosphate-based cements (MPCs) have recently shown attractive features as bone repair materials. The effect of plasma treatments on such cements, which has not been investigated so far, could represent an innovative strategy to modify MPCs' physicochemical properties and to tune their interaction with cells. MPCs were prepared and treated for 5, 7.5, and 10 min with a cold atmospheric pressure plasma jet. The reactive nitrogen and oxygen species formed during the treatment were characterized. The surfaces of MPCs were studied in terms of the phase composition, morphology, and topography. After a preliminary test in simulated body fluid, the proliferation, adhesion, and osteogenic differentiation of human mesenchymal cells on MPCs were assessed. Plasma treatments induce modifications in the relative amounts of struvite, newberyite, and farringtonite on the surfaces on MPCs in a time-dependent fashion. Nonetheless, all investigated scaffolds show a good biocompatibility and cell adhesion, also supporting osteogenic differentiation of mesenchymal cells.

N-Doped Carbon Dot Hydrogels from Brewing Waste for Photocatalytic Wastewater Treatment.

The brewery industry annually produces huge amounts of byproducts that represent an underutilized, yet valuable, source of biobased compounds. In this contribution, the two major beer wastes, that is, spent grains and spent yeasts, have been transformed into carbon dots (CDs) by a simple, scalable, and ecofriendly hydrothermal approach. The prepared CDs have been characterized from the chemical, morphological, and optical points of view, highlighting a high level of N-doping, because of the chemical composition of the starting material rich in proteins, photoluminescence emission centered at 420 nm, and lifetime in the range of 5.5-7.5 ns. With the aim of producing a reusable catalytic system for wastewater treatment, CDs have been entrapped into a polyvinyl alcohol matrix and tested for their dye removal ability. The results demonstrate that methylene blue can be efficiently adsorbed from water solutions into the composite hydrogel and subsequently fully degraded by UV irradiation.

Analysis of oxidative degradation and calcification behavior of a silicone polycarbonate polyurethane-polydimethylsiloxane material.

The biocompatibility and chemical stability of implantable devices are crucial for their long-term success. CarboSil® is a silicon polycarbonate polyurethane copolymer with good biocompatibility and biostability properties. Here, we explored the possibility to improve these characteristics by introducing 30% of extra-chain cross-linkable poly(dimethyl siloxane) (PDMS). Patches made of CarboSil and CarboSil-30% PDMS were manufactured by spray, phase-inversion technique and subjected to a heating-pressure treatment. Both materials showed good biocompatibility, either in viability and proliferation of cell-based experiments both with mouse fibroblasts and subcutaneous implant in rats. Fourier-transform infrared spectroscopy showed a significant decrease in soft segment loss in CarboSil-30% PDMS samples with respect to CarboSil in in vitro accelerated oxidative treatments with CoCl2 and 20% H2 O2 at 37°C up to 36 days. Same results were observed in subcutaneous implants up to 90 days. Field-emission scanning electron microscopy on samples exposed to calcification solutions during 80 days highlighted the presence of a homogeneous distribution of calcium deposition over the entire surface of CarboSil samples, while no calcium deposits were observed in CarboSil-30% PDMS samples. Patches subjected to subcutaneous experiments showed no sign of calcification after 90 days, irrespectively of their composition. Thanks to the improved characteristics in terms of degradation and calcification the modified materials described in this work hold great promise for their use in the manufacture of cardiovascular devices.

Cross-linked Porous Gelatin Microparticles with Tunable Shape, Size, and Porosity.

Gelatin particles are relevant to many applications in the biomedical field due to their excellent biocompatibility and versatility. When prepared by double emulsion methods, porous microparticles with different architectures can be obtained. Controlling the shape, size, porosity, swelling, and stability against dissolution is fundamental toward their application under physiological conditions. We prepared porous gelatin microparticles from oil-in-water-in-oil emulsions, modifying the gelatin/surfactant ratio and the stirring speed. The effect on structural properties, including surface and inner porosities, was thoroughly assessed by multiple microscopy techniques (optical, electron, and confocal Raman). Selected samples were cross-linked with glutaraldehyde or glyceraldehyde, and their swelling properties and stability against dissolution were evaluated, while the influence of the cross-linking at the nanoscale was studied by scattering of X-rays. Depending on the preparation protocol, we obtained particles with different shapes (irregular or spherical), radii within ∼40 to 90 µm, and porosities up to 10 µm. The cross-linking extends the stability in water from a few minutes up to several days while the swelling ability and the mesh size at the nanoscale of the gelatin network are preserved. The analysis of the experimental results as a function of the preparation parameters demonstrates that microparticles with tunable features can be designed.

3D printable magnesium-based cements towards the preparation of bioceramics.

HYPOTHESIS: Among all the materials used so far to replace and repair damaged bone tissues, magnesium silicate bioceramics are one of the most promising, thanks to their biocompatibility, osteoinductive properties and good mechanical stability. EXPERIMENTS: Magnesium silicate cement pastes were prepared by hydration of MgO mixed with different SiO2 batches at different Mg/Si molar ratios. Pastes were either moulded or 3D printed to obtain set cements that were then calcined at 1000 °C to produce biologically relevant ceramic materials. Both cements and ceramics were characterized by means of X-ray diffraction, while two selected formulations were thoroughly characterized by means of injectability tests, Raman confocal microscopy, scanning electron microscopy, atomic force microscopy, gas porosimetry, X-ray microtomography and compressive tests. FINDINGS: The results show that bioceramic scaffolds, namely forsterite and clinoenstatite, can be effectively obtained by 3D printing MgO/SiO2 cement pastes, paving the way towards important advances in the field of bone tissue engineering.

Photopolymerizable pullulan: Synthesis, self-assembly and inkjet printing.

HYPOTHESIS: Pullulan, an exopolysaccharide consisting of maltotriose repeating units, has recently found many applications in different fields, such as food, packaging, cosmetics and pharmaceuticals. The introduction of photo-crosslinkable methacrylic units potentially allows to use pullulan derivative in inkjet 3D printing. EXPERIMENTS: Pullulan was functionalized with methacrylic groups and the derivative was characterized by NMR, FT-IR and Raman spectroscopy. Water dispersions were thoroughly investigated by optical microscopy, SAXS and rheology to evaluate the self-assembly properties and they were used as photo-crosslinkable inks in a 3D printer, also in comparison with pristine pullulan. The structural and mechanical properties of the obtained films were studied by Atomic Force Microscopy and tensile strength tests. FINDINGS: The introduction of methacrylic groups moderately affects the self-assembly of the polymer in water, resulting in a slight increase of the gyration radius of the polymer coils and in a small decrease of the viscosity, retaining the typical shear-thinning behavior of concentrated polysaccharides in water. The structural and mechanical properties of the 3D printed films are much more affected, showing the presence of sub-micrometric phase segregated domains which are further separated by the cross-linking. As a result, the deformability of the materials is improved, with a lower tensile strength.

Physico-Chemical Challenges in 3D Printing of Polymeric Nanocomposites and Hydrogels for Biomedical Applications.

Additive manufacturing techniques (i.e., 3D printing) are rapidly becoming one of the most popular methods for the preparation of materials to be employed in many different fields, including biomedical applications. The main reason is the unique flexibility resulting from both the method itself and the variety of starting materials, requiring the combination of multidisciplinary competencies for the optimization of the process. In particular, this is the case of additive manufacturing processes based on the extrusion or jetting of nanocomposite materials, where the unique properties of nanomaterials are combined with those of a flowing matrix. This contribution focuses on the physico-chemical challenges typically faced in the 3D printing of polymeric nanocomposites and polymeric hydrogels intended for biomedical applications. The strategies to overcome those challenges are outlined, together with the characterization approaches that could help the advance of the field.

Modifying the crystallization of amorphous magnesium-calcium phosphate nanoparticles with proteins from Moringa oleifera seeds.

HYPOTHESIS: Endogenous Amorphous Magnesium-Calcium Phosphates (AMCPs) form in the human body and, besides their biomedical implications, the development of effective stabilization strategies is an open challenge. An interesting approach consists of stabilizing amorphous phosphates with macromolecules that have beneficial effects from a nutritional/medical point of view, for a potential application of the hybrid particles in nutraceutics or drug delivery. EXPERIMENTAL: We investigated the effect of proteins extracted from Moringa oleifera seeds (MO) on the features of synthetic analogs of AMCPs and on their crystallization pathway. The stability of the amorphous phase was studied using infrared spectroscopy and X-ray diffraction. To unravel the effect of the protein on the nano-scale structure of the inorganic particles, we also studied how MO affects the features of the amorphous phase using thermal analysis, small angle X-ray scattering and confocal Raman microscopy. FINDINGS: We observed that MO markedly delays the transition from amorphous to crystalline phosphate in a concentration-dependent fashion. Interestingly, MO not only enhances the lifetime of the amorphous phase, but also influences the type and amount of crystalline material formed. The results are relevant from both a fundamental and an applied perspective, paving the way for the use of these hybrids in the field of nutraceutics and drug delivery.

Dynamics of Water and Other Molecular Liquids Confined Within Voids and on Surface of Lignin Aggregates in Aging Bio Crude Oils.

Neutron scattering methods were employed to study the microscopic structure and dynamics of Bio Crude Oils (BCOs) and their lignin fractions. The structure of the carbonaceous aggregates was investigated using Small Angle Neutron Scattering to reveal a fractal hierarchy as well as a growth of the aggregates as the aging of the BCO proceeds. Elastic Neutron Scattering measurements indicate that BCO liquid phase, comprised of water and other hydrogenated molecular liquids, is in a state of extreme confinement. Quasi-Elastic Neutron Scattering yields information on the molecular motions, indicating that long range translational diffusion is suppressed and only localized dynamics take place on the tens of picosecond time range. The obtained results provide quantitative information on the molecular activity, as aging proceed, in these reactive materials of relevance as potential renewable energy sources.

Sustainable Strategies in the Synthesis of Lignin Nanoparticles for the Release of Active Compounds: A Comparison.

The preparation of nanoparticles represents a powerful tool for lignin valorization, as it combines easy methodologies with high application potential. Different synthetic strategies and various lignin sources have been employed in the process. However, the great variability in the lignin structure prevents a direct comparison of the so far reported lignin nanoparticles (LNPs), especially as regards their physicochemical and functional properties. To this purpose, two green protocols, that is, solvent-antisolvent and hydrotropic, were optimized and used to generate LNPs from the same softwood kraft lignin. The nanomaterials were fully characterized to extrapolate structure/property relationships and reveal any differences in the mechanism of self-assembly. Furthermore, tests on methylene blue entrapment capacity and release behavior at two different pH values (2.0 and 7.4) evidenced a clear dependence on the LNPs characteristics and thus on the strategy adopted for their production.

Liquid Crystal-Induced Myoblast Alignment.

The ability to control cell alignment represents a fundamental requirement toward the production of tissue in vitro but also to create biohybrid materials presenting the functional properties of human organs. However, cell cultures on standard commercial supports do not provide a selective control on the cell organization morphology, and different techniques, such as the use of patterned or stimulated substrates, are developed to induce cellular alignment. In this work, a new approach toward in vitro muscular tissue morphogenesis is presented exploiting liquid crystalline networks. By using smooth polymeric films with planar homogeneous alignment, a certain degree of cellular order is observed in myoblast cultures with direction of higher cell alignment corresponding to the nematic director. The molecular organization inside the polymer determines such effects since no cell organization is observed using homeotropic or isotropic samples. These findings represent the first example of cellular alignment induced by the interaction with a nematic polymeric scaffold, setting the stage for new applications of liquid crystal polymers as active matter to control tissue growth.

Molecule-Graphene Hybrid Materials with Tunable Mechanoresponse: Highly Sensitive Pressure Sensors for Health Monitoring.

The development of pressure sensors is crucial for the implementation of electronic skins and for health monitoring integrated into novel wearable devices. Tremendous effort is devoted toward improving their sensitivity, e.g., by employing microstructured electrodes or active materials through cumbersome processes. Here, a radically new type of piezoresistive pressure sensor based on a millefeuille-like architecture of reduced graphene oxide (rGO) intercalated by covalently tethered molecular pillars holding on-demand mechanical properties are fabricated. By applying a tiny pressure to the multilayer structure, the electron tunnelling ruling the charge transport between successive rGO sheets yields a colossal decrease in the material's electrical resistance. Significantly, the intrinsic rigidity of the molecular pillars employed enables the fine-tuning of the sensor's sensitivity, reaching sensitivities as high as 0.82 kPa-1 in the low pressure region (0-0.6 kPa), with short response times (≈24 ms) and detection limit (7 Pa). The pressure sensors enable efficient heartbeat monitoring and can be easily transformed into a matrix capable of providing a 3D map of the pressure exerted by different objects.

Effect of pH and Mg2+ on Amorphous Magnesium-Calcium Phosphate (AMCP) stability.

HYPOTHESIS: Amorphous Magnesium-Calcium Phosphate (AMCP) particles in the distal small intestine have been shown to have a fundamental role in mammals' immune-surveillance mechanisms. Their formation in the gut lumen and their stability against crystallization are expected to depend upon physiological conditions such as pH and [Mg2+]. Knowing the influence of these parameters on AMCP stability would allow to predict the presence and the activity of the particles in physiological or pathological conditions. EXPERIMENTS: We performed the synthesis of AMCP particles at physiological temperature, in phosphate buffer at variable pH from ∼7.0 to 7.4. The stability of the particles was then tested by dispersing them in different conditions of [Mg2+], pH and concentration, so to mimic different biological conditions. The particles were characterized in terms of morphology, crystallinity, chemical composition and porosity. FINDINGS: The characterization showed that we managed to prepare AMCPs with features matching those of the endogenous particles. Both the lifetime of the amorphous phase and the nature of the formed crystalline material were found to depend upon [Mg2+], pH and concentration. This article paves the way for the comprehension of possible dysfunctions of the gut immune-surveillance mechanisms due to imbalances of these physico-chemical parameters.

Poly(N-isopropylacrylamide)-hydroxyapatite nanocomposites as thermoresponsive filling materials on dentinal surface and tubules.

HYPOTHESIS: Dental decay, asa consequence of exposure to acidic foods and drinks, represents one of the most important tooth pathologies. Recently, enamel and dentinal surface remineralization using hydroxyapatite nano- and microparticles has been proposed; however, commercial remineralizing toothpastes are quite expensive, mostly due to the high costs of hydroxyapatite. Hence, we propose a thermoresponsive hybrid nanocomposite material as filler for tooth defects. The use of thermoresponsive composite particles aims at filling exposed dentinal tubules in response to a change of temperature in the oral cavity. In addition, the presence of the organic matrix contributes to the occlusion of the dentinal tubules, therefore reducing the needed amount of hydroxyapatite. EXPERIMENTS: Poly-N-isopropylacrylamide microgels containing different amounts of hydroxyapatite nanoparticles were prepared via radical polymerization in the presence of N-N'-methylenebisacrylamide as cross-linker followed by mechanical grinding. The nano- and microstructure of the hydrogels and their thermal behavior were studied via small-angle X-ray scattering (SAXS), scanning electron microscopy (SEM) and differential scanning calorimetry (DSC). Defected teeth were treated with a dispersion of nanocomposite microparticles to simulate toothpaste action. FINDINGS: The hydrogels maintain their structure and thermal responsiveness when loaded with an amount of hydroxyapatite nanoparticles up to 2.3%w/w. In addition, the lower critical solution temperature is not affected by the presence of the mineral particles. Exposed dentinal tubules on the surface of test tooth samples were successfully occluded after 15 cycles of treatment with a dispersion of nanocomposite microparticles alternated with washing steps.

Enhanced formation of hydroxyapatites in gelatin/imogolite macroporous hydrogels.

HYPOTHESIS: Gelatin is widely investigated for the fabrication of synthetic scaffolds in bone tissue engineering. Practical limitations to its use are mainly due to the fast dissolution rate in physiological conditions and to the lack of pores with suitable dimensions for cell permeation. The aim of this work is to exploit imogolite clays as nucleation sites for the growth of calcium phosphates in gelatin-based hydrogels and to take advantage of a cryogenic treatment to obtain pores of ∼100µm. EXPERIMENTS: We evaluated the effect of imogolites and a biocompatible cross-linker on the gelatin network in terms of morphology, thermal and rheological behavior. The hydrogels were cryogenically-treated and characterized to investigate the modification of the polymer network, both at the micro- and nano-scale. The samples were mineralized to investigate the effect of imogolites on the formation of calcium phosphates. FINDINGS: The interaction between gelatin, imogolite and cross-linker leads to the modification of the hydrogel structure at the micro-scale, while minor effects are detected at the nano-scale. The cryogenic procedure is successful in generating pores with the desired size, while the presence of imogolites in the hydrogel promotes hydroxyapatites formation. These results demonstrate that imogolites can be effectively employed as functional fillers in polymer-based scaffolds.

Adsorption of Amino Acids and Glutamic Acid-Based Surfactants on Imogolite Clays.

Aluminum oxide surfaces are of utmost interest in different biotech applications, in particular for their use as adjuvants (i.e., booster of the immune response against infectious agents in vaccines production). In this framework, imogolite clays combine the chemical flexibility of an exposed alumina surface with 1D nanostructure. This work reports on the interaction between amino acids and imogolite, using turbidimetry, ζ-potential measurements, and Fourier transform infrared spectroscopy as main characterization tools. Amino acids with different side chain functional groups were investigated, showing that glutamic acid (Glu) has the strongest affinity for the imogolite surface. This was exploited to prepare a composite material made of a synthetic surfactant bearing a Glu polar head and a hydrophobic C12 alkyl tail, adsorbed onto the surface of imogolite. The adsorption of a model drug (rhodamine B isothiocyanate) by the hybrid was evaluated both in water and in physiological saline conditions. The findings of this paper suggest that the combination between the glutamate headgroup and imogolite represents a promising platform for the fabrication of hybrid nanostructures with tailored functionalities.

Functional calcium phosphate composites in nanomedicine.

Calcium phosphate (CaP) materials have many peculiar and intriguing properties. In nature, CaP is found in nanostructured form embedded in a soft proteic matrix as the main mineral component of bones and teeth. The extraordinary stoichiometric flexibility, the different stabilities exhibited by its different forms as a function of pH and the highly dynamic nature of its surface ions, render CaP one of the most versatile materials for nanomedicine. This review summarizes some of the guidelines so far emerged for the synthesis of CaP composites in aqueous media that endow the material with tailored crystallinity, morphology, size, and functional properties. First, we introduce very briefly the areas of application of CaP within the nanomedicine field. Then through some selected examples, we review some synthetic routes where the presence of functional units (small templating molecules like surfactants, or oligomers and polymers) assists the synthesis and at the same time impart the functionality or the responsiveness desired for the end-application of the material. Finally, we illustrate two examples from our laboratory, where CaP is decorated by biologically active polymers or prepared within a thermo- and magneto-responsive hydrogel, respectively.

Injectable composites via functionalization of 1D nanoclays and biodegradable coupling with a polysaccharide hydrogel.

The use of injectable materials in minimally invasive surgical procedures could help in facing the bone diseases connected to the ageing of world population. To this aim, materials integrating the rheological properties of biocompatible polymers with the mechanical properties of 1D inorganic nanostructures represent promising scaffolds. Here we describe the preparation of hydrogel composites made of carboxymethyl cellulose (CMC) and halloysite nanotubes (HNT) as injectable materials for the local treatment of bone defects. The rheology and injectability of the materials reflects their structural properties, showing the possibility of successfully injecting the prepared composites over a large range of operative conditions.

Magnetic field responsive drug release from magnetoliposomes in biological fluids.

The final fate of nano-scaled drug delivery systems into the body is highly affected by their interaction with proteins in biological fluids (serum, plasma, etc.). Nanocarriers dispersed in biological fluids bear a protein "corona" that covers their surface. Thus, it is extremely important to evaluate the drug release efficiency also in the biological environment where protein-nanocarrier complexes are formed. The purpose of this work is to determine how drug release from lipid vesicle carriers is influenced by the interaction with serum proteins, highlighting the importance to test the effectiveness of such systems in the biological milieu. In particular, this paper describes the magnetically triggered release behaviour of magnetoliposomes (MLs) dispersed both in aqueous physiological buffer and in bovine serum at two different concentrations (10% and 55% v/v) upon exposure to a low-frequency alternating magnetic field (LF-AMF). We studied the release from MLs loaded with two types of magnetic nanoparticles (MNPs): citrate coated Fe3O4 and oleic acid coated γ-Fe2O3. The permeability in the above-mentioned fluids was evaluated in terms of the fluorescence self-quenching of carboxyfluorescein (CF) entrapped inside the liposome aqueous pool. The results showed a strong reduction of the release in biological fluids, in particular at high serum concentration. We related this decrease to the formation of protein-liposome complexes that, under LF-AMF exposure, are subjected to destabilization and tend to form aggregates. Our results clearly highlight the importance of testing the release efficiency of self-assembled drug delivery systems in biological fluids, in order to understand their behaviour in the presence of proteins and biomolecules.