Porous Poly(vinyl alcohol)-Based Hydrogel for Knee Meniscus Functional Repair.

The meniscus has a key role within the knee joint, conferring stability, absorbing and redistributing loads, and influencing the overall movement proprioception. Recent developments in the treatment of meniscal injury have progressively shifted the focus from general resection to functional repair, with the recognition that restoring the biomechanical meniscal function helps to prevent degenerative changes in the knee joint and the insurgence of osteoarthritis. To address this clinical need, we have developed a biomimetic implant based on a porous poly(vinyl alcohol) (PVA) hydrogel. Such hydrogels are stable, biocompatible, and suitable to surgical translation, and their mechanical properties can be tuned to reduce the mismatch in the case of partial meniscectomy. The PVA implant structure is porous and permeable, allowing fluid flows and facilitating anatomical integration in situ. Here, we present a chemo-physical characterization of PVA porous hydrogels, focusing on their tunable morphology and associated viscoelastic properties. Biocompatibility was evaluated using primary bovine meniscal fibrochondrocytes, and integration with native tissues was assessed in an ex vivo model. Overall, our results suggest that a synthetic meniscal implant based on a porous PVA hydrogel could restore the physiological function of the meniscus and represent a promising clinical alternative to current resection treatments.

Mechanically flexible and optically transparent three-dimensional nanofibrous amorphous aerocellulose.

Aerocelluloses are considered as "third generation" aerogels after the silica and synthetic polymer-based ones. However, their brittleness and low optical translucency keep quite narrow their fields of applications. Here, both issues are addressed successfully through the fabrication of flexible and mechanically robust amorphous aerocellulose with high optical transparency, using trifluoroacetic acid as a solvent and ethanol as a non-solvent. The developed aerocellulose displays a meso-macroporous interconnected nanofibrous cellulose skeleton with low density and high specific surface area. We demonstrate its high efficiency as supporting matrix for nanoscale systems by incorporating a variety of colloidal quatum dots, that provide bright and stable photoluminescence to the flexible aerocellulose host.

Synthesis of water dispersed nanoparticles from different polysaccharides and their application in drug release.

This work describes an original method to synthesize nanoparticles of starch (NPS), cellulose (NPC), and cellulose/hemicellulose (NPCH) from corn starch (S), microcrystalline cellulose (MCC) and hemp fibers (H), respectively. The synthesis is simply based on the treatment of the latter with trifluoroacetic acid. The resultant nanoparticles are easily dispersed in aqueous solutions. The size of these quasi-spherical particles, as measured by TEM and AFM, is less than 10nm. Fourier transform infrared spectroscopy (FTIR) and X-ray diffraction analysis (XRD) of NPC revealed the loss of original cellulose crystallinity and formation of cellulose II structure after dispersion in water, while the structures of NPCH and NPS were found to be amorphous. Thermogravimetric analysis (TGA) results indicated that the resultant NPC and NPS undergo a two-step pyrolysis, whereas the unprocessed MCC and S undergo one-step pyrolysis. Curcumin was chosen as a model drug. As a model drug release system, NPS were found to release curcumin in a controlled way through a pH-dependent mechanism, with release capacity of about 43% and 65% of the original loaded curcumin under pH 7.4 and 1.2, respectively.

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.

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.

Surprising high hydrophobicity of polymer networks from hydrophilic components.

We report a simple and inexpensive method of fabricating highly hydrophobic novel materials based on interpenetrating networks of polyamide and poly(ethyl cyanoacrylate) hydrophilic components. The process is a single-step solution casting from a common solvent, formic acid, of polyamide and ethyl cyanoacrylate monomers. After casting and subsequent solvent evaporation, the in situ polymerization of ethyl cyanoacrylate monomer forms polyamide-poly(ethyl cyanoacrylate) interpenetrating network films. The interpenetrating networks demonstrate remarkable waterproof properties allowing wettability control by modulating the concentration of the components. In contrast, pure polyamide and poly(ethyl cyanoacrylate) films obtained from formic acid solutions are highly hygroscopic and hydrophilic, respectively. The polymerization of ethyl cyanoacrylate in the presence of polyamide promotes molecular interactions between the components, which reduce the available hydrophilic moieties and render the final material hydrophobic. The wettability, morphology, and thermo-physical properties of the polymeric coatings were characterized. The materials developed in this work take advantage of the properties of both polymers in a single blend and above all, due to their hydrophobic nature and minimal water uptake, can extend the application range of the individual polymers where water repellency is required.

Tailoring the morphology of poly(ethylene oxide)/silver triflate blends: from crystalline to self-assembled nanofibrillar structures.

Interaction of polyethylene oxide (PEO) with transition metal triflates is a newly emerging research area due to its numerous application fields, such as thin-film power conversion devices and sensors. In the present study, we demonstrate, for the first time, that PEO can solvate silver triflate organic salts in large quantities when formic acid is used as a common solvent for both. Nanocomposites with unique structural and electrical properties are fabricated by simply drop casting formic acid solutions of PEO and silver triflate salts. We present a detailed experimental study on the characterization of morphological and electrical properties of PEO-silver triflate nanocomposite films as a function of silver triflate concentration and discuss their potential applications as humidity sensors. In particular, by increasing the concentration of the salt in the initial solution the morphological features of the formed nanocomposites can be varied from well defined microcrystals to amorphous nanofibers. Of special interest are the nanocomposite films fabricated from a 1:1 (PEO-unit:Ag(+)) molar ratio, since they consist of self-assembled nanofibrillar structures, which exhibit good electrical conductivity as well as highly repeatable sensitivity towards humidity.

Probing stereoselectivity and pro-chirality of hydride transfer during short-chain alcohol dehydrogenase activity: a combined quantitative 2H NMR and computational approach.

Different members of the alcohol oxidoreductase family can transfer the hydride of NAD(P)H to either the re- or the si-face of the substrate. The enantioselectivity of transfer is very variable, even for a range of substrates reduced by the same enzyme. Exploiting quantitative isotopic (2)H NMR to measure the transfer of (2)H from NAD(P)(2)H to ethanol, a range of enantiomeric excess between 0.38 and 0.98, depending on the origin of the enzyme and the nature of the cofactor, has been determined. Critically, in no case was only (R)-[1-(2)H]ethanol or (S)-[1-(2)H]ethanol obtained. By calculating the relative energies of the active site models for hydride transfer to the re- or si-face of short-chain aldehydes by alcohol dehydrogenase from Saccharomyces cerevisiae and Lactobacillus brevis, it is shown that the differences in the energy of the systems when the substrate is positioned with the alkyl group in one or the other pocket of the active site could play a role in determining stereoselectivity. These experiments help to provide insight into structural features that influence the potential catalytic flexibility of different alcohol dehydrogenase activities.

Non-equivalence of hydrogen transfer from glucose to the pro-R and pro-S methylene positions of ethanol during fermentation by Leuconostoc mesenteroides quantified by 2H NMR at natural abundance.

The anaerobic fermentation of glucose by Leuconostoc mesenteroides via the reductive pentose phosphate pathway leads to the accumulation of lactic acid and ethanol. The isotope redistribution coefficients (a(ij)) that characterize the specific derivation of each hydrogen atom in ethanol in relation to the non-exchangeable hydrogen atoms in glucose and the medium water have been determined using quantitative (2)H NMR. First, it is confirmed that the hydrogens of the methylene group are related only to the 1 and 3 positions of glucose via the NAD(P)H pool and not to the 4 position, in contrast to ethanol produced by Saccharomyces cerevisiae. Second, it is found that the conversion factors (C(f)) for the transfer of hydrogen to the pro-S and pro-R positions of the methylene group are not equivalent: the C(f)-1-R:C(f)-1-S ratio is 2.1, whereas the C(f)-3-R:C(f)-3-S ratio is 0.8. It is shown that this non-equivalence is not determined by the stereochemistry of the terminal NADH- and NADPH-dependent alcohol dehydrogenases, but is dependent on the cofactor selectivities of the reductive and oxidative steps of the reduced nucleotide cycle.

Fluorescence study of lipid-based DNA carriers properties: influence of cationic lipid chemical structure.

We report here a study on the physicochemical properties of cationic phospholipids liposomes used for lipoplex formulation and DNA transfer. The original cationic phospholipids synthesized in our laboratory are first presented with the liposome formulation process. The second part deals with the liposomes fusogenic properties studied by fluorescence resonant energy transfer (FRET). The nature of the cationic polar head and the formulation with or without a neutral colipid have a great influence on the FRET signal. The third part reports the study of the viscosity of the liposome by fluorescence anisotropy measurements. It has been observed that the vectors having a saturated lipid chain exhibit a more pronounced anisotropy than those having unsaturated lipid chains. Finally, liposomes formed by a mixture of phospholipids and DC-Chol (a rigid lipid) leads to increase the anisotropy denoting a more rigid liposome.