Josué D. Mota-Morales

Synthesis of macroporous poly(acrylic acid)–carbon nanotube composites by frontal polymerization in deep-eutectic solvents

Deep Eutectic Solvents (DESs) formed between Acrylic Acid (AA) and Choline Chloride (CCl) exhibit certain properties of ionic liquids (e.g. high viscosity) that make them suitable for frontal polymerization (FP). The use of DESs not only as a monomer but also as the solvent prevents the use of additional solvents (i.e. typically of organic nature) and offers a green tool for the synthesis of functional composites. We have recently explored this approach for the preparation of poly(acrylic acid) (PAA) and poly(methacrylic acid). In this work, we have taken advantage of the outstanding capability of DESs to solubilize and/or disperse a number of substances to incorporate – in a homogeneous fashion – carbon nanotubes (in this particular case, N-doped MWCNT – CNxMWCNTs) in the polymerizable DES. Interestingly, CNxMWCNTs also played the role of an inert filler in FP. The resulting PAA–CNxMWCNT composites exhibited some distinct features as compared to previous PAA also obtained via DES-assisted FP. For instance, PAA–CNxMWCNT composites can undergo swelling depending on the pH, as bare PAA. However, the presence of CNxMWCNTs allows the formation of a macroporous structure after submission to a freeze-drying process, the achievement of which was not possible in bare PAA. The combination of structural (e.g. macroporosity) and functional (e.g. stimuli responsive) properties exhibited by these materials besides an eventually high biocompatibility – coming from the green character of the DES-assisted synthesis – should make the resulting macroporous PAA–CNxMWCNT composites excellent candidates for their future application as biomaterials.

New insights into the bactericidal activity of chitosan-Ag bionanocomposite: the role of the electrical conductivity.

The relationship between electrical conductivity, structure and antibacterial properties of chitosan-silver nanoparticles (CS/AgnP) biocomposites has been analyzed. To test the films antimicrobial activity, Gram-positive and Gram-negative bacteria were studied. The interactions between silver nanoparticles with chitosan suggest the formation of silver ions which plays a major role in nanocomposites bactericidal potency. In CS/AgnP biocomposites, the bactericide effectiveness increases by increasing AgnP concentrations up to 3 wt%, which is close to the electrical percolation threshold of ca. 3 wt%. As the AgnP concentration increases above this threshold, the bactericidal potency is greatly diminished. The elucidated correlation between electrical conductivity and antibacterial activity could be useful in the design of other nanocomposites that involve polymeric-based matrices.

Processing of lignin in urea–zinc chloride deep-eutectic solvent and its use as a filler in a phenol-formaldehyde resin

The main goal of our research deals with a new greener and more efficient lignin modification method to optimize its structural performance as a phenol-formaldehyde resin filler. Through the appropriate increase in the phenolic hydroxyl content, added value as a raw material was intended. For that, a series of mixtures of zinc chloride–urea with different molar ratios was prepared to obtain deep-eutectic solvents (DESs). Two heating methods (oil bath and microwave heating) were compared and optimized. Microwave helps in reducing the preparation time but to the detriment of temperature control. On the other hand, heating with an oil bath provided better temperature control and homogeneity of the mixture. The preferable molar ratio of ZnCl2–urea was 3 : 10 (Tg = −26.3 °C). The structural changes of the pretreated lignin samples were investigated by Fourier transformed infrared and X-ray photoelectron spectroscopies, scanning electron microscopy, induced coupled plasma and X-ray diffraction. Thermogravimetric analysis demonstrated significant differences in the thermal behavior of the recovered lignin as a result of DES treatment. The weight of lignin recovered was 4 times that of original lignin, indicating that the structure of lignin was transformed through the integration of Zn. The integration of Zn enhanced the thermal stability and enhanced lignins reactivity towards phenol-formaldehyde resin formation. Phenol-formaldehyde resin containing the recovered lignin exhibited lower thermocuring temperatures and better thermostability than those without filler. To the best of our knowledge, this is the first report on the investigation of the structural transformations of lignin through its dissolution in urea–ZnCl2 DES and subsequent use as filler for phenol formaldehyde resin synthesis.

Controlled release of lidocaine hydrochloride from polymerized drug-based deep-eutectic solvents

This work takes advantage of the transformation of lidocaine hydrochloride into deep-eutectic solvents (DESs) - ionic liquid analogues - to incorporate polymerizable counterparts into DESs, such that polymer-drug complexes are synthesized by free-radical frontal polymerization without the use of a solvent. DESs are formed through hydrogen bonding of an ammonium salt with a hydrogen-bond donor (HBD). It is demonstrated that lidocaine hydrochloride - as the ammonium salt - is able to form DESs with acrylic acid and methacrylic acid. The properties of DESs allow frontal polymerization in the bulk with full conversion achieved in a one-pot synthesis, yielding monoliths of polymers loaded with a high concentration of drug. In in vitro experiments, the sustained release of the drug takes place in a controlled manner triggered by the pH, ionic strength and solubility of the drug in the medium. Such control is owed to the swelling of polymers as well as to the specific interactions between the drug and the polymers already established in the DES precursor. Finally, it is noteworthy that different monomers (such as HBD) and crosslinkers can be used, thus expanding the possibilities of drug delivery systems for transdermal technologies by exploiting the DES chemistry.

Porous monoliths synthesized via polymerization of styrene and divinyl benzene in nonaqueous deep-eutectic solvent-based HIPEs

Stable nonaqueous high internal phase emulsions (HIPEs) were prepared and thermally polymerized to yield poly(HIPEs). The internal phase accounting for 80 vol% of the HIPE consisted of a deep-eutectic solvent (DES) while the continuous one comprised styrene and divinyl benzene in a 10 : 1 molar ratio. DESs with different viscosities were used as an internal phase: choline chloride combined with urea, glycerol or ethylene glycol in a 1 : 2, salt : hydrogen bond donor molar ratio, respectively. HIPEs were stabilized with different amounts of the surfactant Span 60 (10, 20 and 50 wt% with respect to the total amount of monomers). DESs viscosity and the amount of surfactant employed impact the morphology and mechanical properties of poly(HIPEs). Resulting poly(HIPEs) showed interconnected porosity and high thermal stability above 310 °C. Its worth noting that DES was recovered from 89 to nearly 95 wt% and the monomer conversion was as high as 0.96. In addition, water-in-oil HIPEs were stabilized and then polymerized under the same conditions, but the porous structure of the resulting poly(HIPEs) collapsed. This research demonstrates that DESs are a suitable internal phase for HIPEs thus expanding on the range of monomers forming polymerizable DES-based HIPEs.

Deep-eutectic solvents as a support in the nonaqueous synthesis of macroporous poly(HIPEs)

This study demonstrates the formation and polymerization of high internal phase emulsions (HIPEs) with (meth)acrylic monomers as a continuous phase and urea–choline chloride deep-eutectic solvent as a favorable nonaqueous internal phase. After recovery of DES, the resultant poly(HIPEs) showed interconnected macroporosity which can be tuned by varying the experimental conditions.

Potential application of silver nanoparticles to control the infectivity of Rift Valley fever virus in vitro and in vivo.

In this work we have tested the potential antiviral activity of silver nanoparticles formulated as Argovit™ against Rift Valley fever virus (RVFV). The antiviral activity of Argovit was tested on Vero cell cultures and in type-I interferon receptor deficient mice (IFNAR (-/-) mice) by two different approaches: (i) different dilutions of Argovit were added to previously infected cells or administrated to animals infected with a lethal dose of virus; (ii) virus was pre-incubated with different dilutions of Argovit before inoculation in mice or cells. Though the ability of silver nanoparticles to control an ongoing RVFV infection in the conditions tested was limited, the incubation of virus with Argovit before the infection led to a reduction of the infectivity titers both in vitro and in vivo. These results reveal the potential application of silver nanoparticles to control the infectivity of RVFV, which is an important zoonotic pathogen.

Temperature-induced Au nanostructure synthesis in a nonaqueous deep-eutectic solvent for high performance electrocatalysis

Structure-controlled synthesis of gold nanostructures (AuNSs) induced by temperature in a nonaqueous urea–choline chloride deep eutectic solvent (DES) is reported. Modulation of nanostructures with well-defined structures and shapes is obtained by simply varying the reaction temperature. The supramolecular soft template provided by the DES structure and its viscosity at different temperatures drives directed growth of crystalline gold and self-assembly producing star-shaped AuNSs. Additionally, the effect of AuNS shape and surface area on their catalytic activity towards the reduction of hydrogen peroxide (H2O2) has been tested. With the advantage of their high surface area and presence of high-index facets in the edge of the star arms, the star-shaped nanostructures showed superior electrocatalytic activity than other morphologies. The use of DES as a green chemistry platform for the synthesis of shape-controlled Au nanostructures with high catalytic properties may offer new avenues for fuel cell and biosensor applications.

Synthesis of Biodegradable Macroporous Poly(l-lactide)/Poly(ε-caprolactone) Blend Using Oil-in-Eutectic-Mixture High-Internal-Phase Emulsions as Template

We have demonstrated that l-lactide (LLA) forms a eutectic mixture with ε-caprolactone (CL) in a 30:70 mol ratio with a melting point of -19 °C. Taking advantage of the liquid nature and polarity at the LLA-CL eutectic mixture, we have formulated oil-in-eutectic-mixture high-internal-phase emulsions (HIPEs) by stepwise addition of the oil phase (tetradecane) into the continuous phase (mixture of surfactant and LLA-CL eutectic mixture) at room temperature and under stirring. The oil-in-LLA-CL-eutectic-mixture HIPEs were polymerized in the presence of both the organocatalysts 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU) and methanesulfonic acid (MSA) and the initiator benzyl alcohol (BnOH) at 37 °C and without the addition of any extra reagent or solvent in one single pot. The catalytic selectivities of DBU and MSA for the ring-opening polymerizations of LLA and CL, respectively, allowed the synthesis of macroporous poly(l-lactide)/poly(ε-caprolactone) blend materials. The resulting materials exhibited a macroporous morphology that resembled that of the HIPE internal-phase droplets used as templates. These materials proved effective as oil absorbents for oil/water separation with not only a noticeable performance, similar to that of conventional sorbents in terms of both selectivity and recyclability, but also unprecedented safe disposability, certainly of interest for applications in the cleanup of industrial oily wastewaters and oil spills, thanks to the biodegradable features of both poly(ε-caprolactone) and poly(l-lactide).

Effect of doping in carbon nanotubes on the viability of biomimetic chitosan‐carbon nanotubes‐hydroxyapatite scaffolds

This work describes the preparation and characterization of biomimetic chitosan/multiwall carbon nanotubes/nano-hydroxyapatite (CTS/MWCNT/nHAp) scaffolds and their viability for bone tissue engineering applications. The cryogenic process ice segregation-induced self-assembly (ISISA) was used to fabricate 3D biomimetic CTS scaffolds. Proper combination of cryogenics, freeze-drying, nature and molecular ratio of solutes give rise to 3D porous interconnected scaffolds with clusters of nHAp distributed along the scaffold surface. The effect of doping in CNT (e.g. with oxygen and nitrogen atoms) on cell viability was tested. Under the same processing conditions, pore size was in the range of 20-150 μm and irrespective on the type of CNT. Studies on cell viability with scaffolds were carried out using human cells from periosteum biopsy. Prior to cell seeding, the immunophenotype of mesenchymal periosteum or periosteum-derived stem cells (MSCs-PCs) was characterized by flow cytometric analysis using fluorescence-activated and characteristic cell surface markers for MSCs-PCs. The characterized MSCs-PCs maintained their periosteal potential in cell cultures until the 2nd passage from primary cell culture. Thus, the biomimetic CTS/MWCNT/nHAp scaffolds demonstrated good biocompatibility and cell viability in all cases such that it can be considered as promising biomaterials for bone tissue engineering.