Polydopamine Antioxidant Hydrogels for Wound Healing Applications.

Antioxidants are known to improve the wound healing process and are researched as a therapeutic strategy to treat chronic wounds. Dopamine is a known neurotransmitter with antioxidant properties that can be polymerized to form polydopamine (PDA). Herein, polydopamine is demonstrated as an antioxidant biomaterial. In prior work, we developed methodology to prepare hydrogels by crosslinking polysaccharides with polyamines via epichlorohydrin and NaOH. Using this previously developed methodology, dextran hydrogels crosslinked with polydopamine were prepared. Darkening of the gels indicated the increasing incorporation of polydopamine within the hydrogels. In addition to basic pH, polydopamine can be formed by reaction with polyethylene imine (PEI), which results in PEI-PDA copolymer. Dextran was similarly crosslinked with the PEI-PDA copolymer and resulted in sturdier, darker gels, which had more polydopamine incorporated. Hydrogel morphology and strength were dependent on the feed ratios of dopamine. Antioxidant activity of polydopamine containing hydrogel was confirmed and shown to be dependent on the amount of dopamine used in hydrogel synthesis. Hydrogels with 0.5 dopamine to dextran feed ratio scavenged 78.8% of radicals in a 2,2'-azinobis-(3-ethylbenzothiazoline-6-sulfonic acid) antioxidant assay while gels with no dopamine scavenged only 1.4% of radicals. An ex vivo wound healing assay showed considerable cell migration with the PEI-PDA containing hydrogel.

Consolidated Melting Gel Coatings on AZ31 Magnesium Alloy with Excellent Corrosion Resistance in NaCl Solutions: An Interface Study.

Magnesium alloys, with a density two-thirds that of aluminum, are very attractive for the industry. However, these alloys are extremely susceptible to corrosion in the presence of aggressive electrolytes such as NaCl solutions. Here, we designed hybrid coatings obtained by the consolidation of organically modified polysilsesquioxanes called "melting gels" for the corrosion protection of AZ31 magnesium alloy in NaCl solutions. The main focus was to study the interaction between coatings and substrate and the influence of the coating thickness on the final properties. Micro-scratch tests, adhesion by tape tests, confocal Raman microscopy, SEM-EDS, and ToF-SIMS indicate good adhesion of coatings based on the interaction of melting gels and substrate. These measurements indicate the presence of the Si-O-Mg bonds between the substrate and coatings. Electrochemical results show very low current densities (10-13 A cm-2) without any breakdown potential and impedance values of 1010 Ω cm2.

A Self-degradable Curcumin Polymer with Anti-cancer Activity.

Curcumin is a widely researched and utilized natural product used for a variety of ailments including as a gastrointestinal aide and an anticancer agent. Curcumin however suffers from poor bioavailability. A strategy to circumvent poor bioavailability is to administer with an adjuvant or by synthetic modification. Herein we demonstrate the incorporation of curcumin into a self-degradable polymer by condensation with N,N'-di-Boc-L-cystine. The polymer is made self-degradable upon deprotection of the cystine amines. Degradation is confirmed by thermogravimetric analysis and differential scanning calorimetry. Curcumin retains its anti-cancer activity within the polymer showing activity against HT29 human colon cancer cells and DU-145 prostate cancer cells. The self-degrading polymer showed enhanced activity against HT29 cells compared to that of curcumin.

Obtaining Thickness-Limited Electrospray Deposition for 3D Coating.

Electrospray processing utilizes the balance of electrostatic forces and surface tension within a charged spray to produce charged microdroplets with a narrow dispersion in size. In electrospray deposition, each droplet carries a small quantity of suspended material to a target substrate. Past electrospray deposition results fall into two major categories: (1) continuous spray of films onto conducting substrates and (2) spray of isolated droplets onto insulating substrates. A crossover regime, or a self-limited spray, has only been limitedly observed in the spray of insulating materials onto conductive substrates. In such sprays, a limiting thickness emerges, where the accumulation of charge repels further spray. In this study, we examined the parametric spray of several glassy polymers to both categorize past electrospray deposition results and uncover the critical parameters for thickness-limited sprays. The key parameters for determining the limiting thickness were (1) field strength and (2) spray temperature, related to (i) the necessary repulsive field and (ii) the ability for the deposited materials to swell in the carrier solvent vapor and redistribute charge. These control mechanisms can be applied to the uniform or controllably-varied microscale coating of complex three-dimensional objects.

Dextran hydrogels by crosslinking with amino acid diamines and their viscoelastic properties.

Amine functionalized polysaccharide hydrogels such as those based on chitosan are widely examined as biomaterials. Here we set out to develop a facile procedure for developing such hydrogels by crosslinking dextran with amino acid diamines. The dextran-amino acid gels were formed by the addition of the amino acid diamines to a dextran and epichlorohydrin solution once it became homogeneous. This was demonstrated with three amino acid diamines, lysine, lysine methyl ester, and cystine dimethyl ester. Hydrogel networks with albumin entrapped were also demonstrated. These hydrogels were characterized by FTIR, SEM, rotational rheometry, swelling studies and cell biocompatibility analysis. These hydrogels showed the unexpected pH-responsive behavior of greater swelling at more basic pH, similar to that of an anionic hydrogel. This is uncharacteristic for amine functionalized gels as they typically exhibit cationic hydrogel behavior. All hydrogels showed similar biocompatibility to that of dextran crosslinked without amino acids.

29Si NMR and SAXS investigation of the hybrid organic-inorganic glasses obtained by consolidation of the melting gels.

This study is focused on structural characterization of hybrid glasses obtained by consolidation of melting gels. The melting gels were prepared in molar ratios of methyltriethoxysilane (MTES) and dimethyldiethoxysilane (DMDES) of 75%MTES-25%DMDES and 65%MTES-35%DMDES. Following consolidation, the hybrid glasses were characterized using Raman, 29Si and 13C Nuclear Magnetic Resonance (NMR) spectroscopies, synchrotron Small Angle X-Ray Scattering (SAXS) and scanning electron microscopy (SEM). Raman spectroscopy revealed the presence of Si-C bonds in the hybrid glasses and 8-membered ring structures in the Si-O-Si network. Qualitative NMR spectroscopy identified the main molecular species, while quantitative NMR data showed that the ratio of trimers (T) to dimers (D) varied between 4.6 and 3.8. Two-dimensional 29Si NMR data were used to identify two distinct types of T3 environments. SAXS data showed that the glasses are homogeneous across the nm to micrometer length scales. The scattering cross section was one thousand times lower than what is expected when phase separation occurs. The SEM images show a uniform surface without defects, in agreement with the SAXS results, which further supports that the hybrid glasses are nonporous.

A simple preparative route to highly stable dispersions of uniform silver nanoparticles.

Stable dispersions of uniform silver nanoparticles were prepared by heating silver salts in polyols in the presence of a naphthalene sulfonate/formaldehyde copolymer as dispersant. In the temperature range explored (150-190 degrees C) the modal size and the size distribution of the particles depended on the nature and concentration of the silver salt and the polyol used. Highly dispersed uniform nanoparticles with a diameter of approximately 12 nm were obtained by reducing silver salicylate in diethylene glycol at a metal concentration of 2.5 x 10(-2) mol x cm(-3). Larger silver nanoparticles (approximately 30 nm) and more concentrated dispersions (1.0 mol x cm(-3)) were prepared in ethylene glycol. In all cases the selected dispersant yielded remarkably stable silver sols and facilitated the transfer of the nanoparticles into water, while preserving the stability of the dispersions.

Amplified light scattering and emission of silver and silver core-silica shell particles.

Side versus forward light scattergrams, and fluorescence (488 nm excitation) intensity versus particle count histograms were gathered for bare, R6G-coated, and silica-R6G-coated silver particles of 150-200 nm diameter, one-by-one by flow cytometry. Fluorescence emission intensity of the composite particles monotonically increased and then reached a plateau with greater R6G concentrations, as measured by flow cytometry. Fluorescence amplification factors of up to 3.5x10(3) were estimated by reference to measurements on core-shell particles with silica instead of silver cores. Huge surface enhanced Raman scattering (SERS) intensities, at least 10(14)-fold greater than normal Raman scattering intensities, were observed with 633 nm excitation for molecules such as rhodamine 6G (R6G) on the same single particles of silver. Although routine transmission (TEM) and scanning (SEM) electron microscopies showed gross structures of the bare and coated particles, high-resolution field emission scanning electron microscopy (FE-SEM), revealed Brownian roughness describing quantum size and larger structures on the surface of primary colloidal silver particles. These silver particles were further characterized by extinction spectra and zeta potentials. Structural and light scattering observations that are reported herein were used to tentatively propose a new hierarchical model for the mechanism of SERS.