POSS-Induced Dynamic Cross-Links Produced Self-Healing and Shape Memory Physical Hydrogels When Copolymerized with N-Isopropyl acrylamide.

The hydrogel morphology and viscoelasticity and the two-way shape memory behavior of copolymers of N-isopropyl acrylamide-polyhedral oligomeric silsesquioxane (PNIPAm-POSS) were investigated. NIPAm-POSS copolymers are unentangled and exhibit a thermoplastic and thermoresponsive hydrogel behavior ( Romo-Uribe ; ; Albanil , Eur. Polym. J. 2018 , 99 , 350 - 360 ). Here, we demonstrated by high-resolution transmission electron microscopy that POSS segregated into crystals to form physical cross-links. The hydrogels exhibited significant swelling, higher than chemical hydrogels at the same POSS content. The morphology of the hydrogels consisted of a honeycomb structure, and the pore size and swelling were a decreasing function of POSS. Moreover, the hydrogels were self-healing, exhibiting a liquid-like behavior under large amplitude shear and rubber-like behavior immediately after cessation of shear, that is, the POSS aggregates break and re-form, acting as dynamic cross-linkers. Strikingly, the physical networks behaved as perfect networks, thus matching chemically cross-linked networks and holding the scaling |η*| ∼ ω-1. Furthermore, the physical hydrogels exhibited a thermally activated shape memory (SM) behavior, without external stress and the lower critical solution temperature (LCST) being the only stimulus. The SM process involved swelling-deswelling, effectively opening opportunities for drug delivery. Furthermore, the SM was reversible, and no external stress was involved, therefore behaving as the two-way SM. Finally, POSS modulated the shear elastic modulus G' and LCST; therefore, the PNIPAm-POSS copolymers open opportunities for reusable, thermoformable SM hydrogels with tuned mechanical modulus and activation temperature.

Viability of HEK 293 cells on poly-ß-hydroxybutyrate (PHB) biosynthesized from a mutant Azotobacter vinelandii strain. Cast film and electrospun scaffolds.

Sterilization, cytotoxicity and cell viability are essential properties defining a material for medical applications and these characteristics were investigated for poly(ß-hydroxybutyrate) (PHB) of 230kDa obtained by bacterial synthesis from a mutant strain of Azotobacter vinelandii. Cell viability was investigated for two types of PHB scaffolds, solution cast films and non-woven electrospun fibrous membranes, and the efficiency was compared against a culture dish. The biosynthesized PHB was sterilized by ultraviolet radiation and autoclave, it was found that the thermal properties and intrinsic viscosity remained unchanged indicating that the sterilization methods did not degrade the polymer. Sterilized scaffolds were then seeded with human embryonic kidney 293 (HEK 293) cells to evaluate the cytotoxic response. The cell viability of these cells was evaluated for up to six days, and the results showed that the cell morphology was normal, with no cytotoxic effects. The films and electrospun membranes exhibited over 95% cell viability whereas the viability in culture dishes reached only ca. 90%. The electrospun membrane, however, exhibited significantly higher cell density than the cast film suggesting that the fibrous morphology enables better nutrients transfer. The results indicate that the biosynthesized PHB stands UV and autoclave sterilization methods, it is biocompatible and non-toxic for cell growth of human cell lines. Furthermore, cell culture for up to 18 days showed that 62% and 90% of mass was lost for the film and fibrous electrospun scaffold, respectively. This is a favorable outcome for use in tissue engineering where material degradation, as tissue regenerates, is desirable.

3D-Hydrogel Based Polymeric Nanoreactors for Silver Nano-Antimicrobial Composites Generation.

This study underscores the development of Ag hydrogel nanocomposites, as smart substrates for antibacterial uses, via innovative in situ reactive and reduction pathways. To this end, two different synthetic strategies were used. Firstly thiol-acrylate (PSA) based hydrogels were attained via thiol-ene and radical polymerization of polyethylene glycol (PEG) and polycaprolactone (PCL). As a second approach, polyurethane (PU) based hydrogels were achieved by condensation polymerization from diisocyanates and PCL and PEG diols. In fact, these syntheses rendered active three-dimensional (3D) hydrogel matrices which were used as nanoreactors for in situ reduction of AgNO3 to silver nanoparticles. A redox chemistry of stannous catalyst in PU hydrogel yielded spherical AgNPs formation, even at 4 °C in the absence of external reductant; and an appropriate thiol-functionalized polymeric network promoted spherical AgNPs well dispersed through PSA hydrogel network, after heating up the swollen hydrogel at 103 °C in the presence of citrate-reductant. Optical and swelling behaviors of both series of hydrogel nanocomposites were investigated as key factors involved in their antimicrobial efficacy over time. Lastly, in vitro antibacterial activity of Ag loaded hydrogels exposed to Pseudomona aeruginosa and Escherichia coli strains indicated a noticeable sustained inhibitory effect, especially for Ag-PU hydrogel nanocomposites with bacterial inhibition growth capabilities up to 120 h cultivation.

Electrospun nylon nanofibers as effective reinforcement to polyaniline membranes.

This research demonstrates that a nylon nanofiber (NNF) mat can be an effective mechanical reinforcement to polyaniline (PANI) thin films. Nanofibers of ca. 250 nm diameter were produced by electrospinning of a nylon 6 solution in formic acid. Scanning electron microscopy showed that the solution impregnation method utilized was effective to embed the nanofibers into the PANI matrix. The effectiveness of NNFs as a mechanical reinforcement of a PANI thin film was assessed via dynamic mechanical analysis in tension mode. The as-cast PANI films displayed a tensile dynamic modulus, E', of ca. 0.65 GPa at room temperature. Scanning in the temperature showed that the PANI film has a usage temperature of up to about 80 degrees C, with this being limited by its glass transition temperature, and over this temperature range, the elastic modulus was nearly independent of the temperature. On the other hand, the PANI-NNF composite displayed a significantly higher tensile modulus at room temperature (1.1 GPa) and its usage temperature was extended up to just over 200 degrees C, with this being limited by the melting transition of nylon 6 (at 220 degrees C). The results therefore showed that the NNF mat increased the usage temperature of PANI films over 100 degrees C, opening up applications for PANI membranes.