Spatiotemporal Temperature Distribution of NIR Irradiated Polypyrrole Nanoparticles and Effects of pH.

The spatiotemporal temperature distributions of NIR irradiated polypyrrole nanoparticles (PPN) were evaluated by varying PPN concentrations and the pH of suspensions. The PPN were synthesized by oxidative chemical polymerization, resulting in a hydrodynamic diameter of 98 ± 2 nm, which is maintained in the pH range of 4.2-10; while the zeta potential is significantly affected, decreasing from 20 ± 2 mV to -5 ± 1 mV at the same pH range. The temperature profiles of PPN suspensions were obtained using a NIR laser beam (1.5 W centered at 808 nm). These results were analyzed with a three-dimensional predictive unsteady-state heat transfer model that considers heat conduction, photothermal heating from laser irradiation, and heat generation due to the water absorption. The temperature profiles of PPN under laser irradiation are concentration-dependent, while the pH increase only induces a slight reduction in the temperature profiles. The model predicts a value of photothermal transduction efficiency (η) of 0.68 for the PPN. Furthermore, a linear dependency was found for the overall heat transfer coefficient (U) and η with the suspension temperature and pH, respectively. Finally, the model developed in this work could help identify the exposure time and concentration doses for different tissues and cells (pH-dependent) in photothermal applications.

Synthesis and Characterization of a Bioconjugate Based on Oleic Acid and L-Cysteine.

One of the main challenges facing materials science today is the synthesis of new biodegradable and biocompatible materials capable of improving existing ones. This work focused on the synthesis of new biomaterials from the bioconjugation of oleic acid with L-cysteine using carbodiimide. The resulting reaction leads to amide bonds between the carboxylic acid of oleic acid and the primary amine of L-cysteine. The formation of the bioconjugate was corroborated by Fourier transform infrared spectroscopy (FTIR), Raman spectroscopy, and nuclear magnetic resonance (NMR). In these techniques, the development of new materials with marked differences with the precursors was confirmed. Furthermore, NMR has elucidated a surfactant structure, with a hydrophilic part and a hydrophobic section. Ultraviolet-visible spectroscopy (UV-Vis) was used to determine the critical micellar concentration (CMC) of the bioconjugate. Subsequently, light diffraction (DLS) was used to analyze the size of the resulting self-assembled structures. Finally, transmission electron microscopy (TEM) was obtained, where the shape and size of the self-assembled structures were appreciated.

PLGA nanoparticle preparations by emulsification and nanoprecipitation techniques: effects of formulation parameters.

This study presents the influence of the primary formulation parameters on the formation of poly-dl-lactic-co-glycolic nanoparticles by the emulsification-solvent evaporation, and the nanoprecipitation techniques. In the emulsification-solvent evaporation technique, the polymer and tensoactive concentrations, the organic solvent fraction, and the sonication amplitude effects were analyzed. Similarly, in the nanoprecipitation technique the polymer and tensoactive concentrations, the organic solvent fraction and the injection speed were varied. Additionally, the agitation speed during solvent evaporation, the centrifugation speeds and the use of cryoprotectants in the freeze-drying process were analyzed. Nanoparticles were characterized by dynamic light scattering, laser Doppler electrophoresis, and scanning electron microscopy, and the results were evaluated by statistical analysis. Nanoparticle physicochemical characteristics can be adjusted by varying the formulation parameters to obtain specific sizes and stable nanoparticles. Also, by adjusting these parameters, the nanoparticle preparation processes have the potential to be tuned to yield nanoparticles with specific characteristics while maintaining reproducible results.

Drug Release Properties of Diflunisal from Layer-By-Layer Self-Assembled κ-Carrageenan/Chitosan Nanocapsules: Effect of Deposited Layers.

Engineering of multifunctional drug nanocarriers combining stability and good release properties remains a great challenge. In this work, natural polymers κ-carrageenan (κ-CAR) and chitosan (CS) were deposited onto olive oil nanoemulsion droplets (NE) via layer-by-layer (LbL) self-assembly to study the release mechanisms of the anti-inflammatory diflunisal (DF) as a lipophilic drug model. The nano-systems were characterized by dynamic light scattering (DLS), zeta potential (ζ-potential) measurements, transmission electron microscopy (TEM), scanning electron microscopy (SEM), X-ray energy dispersive spectroscopy (XEDS) and Fourier transform infrared spectroscopy (FTIR) to confirm the NE-coating with polymer layers. In addition, kinetic release studies of DF were developed by the dialysis diffusion bag technique. Mathematical models were applied to investigate the release mechanisms. The results showed that stable and suitably sized nanocapsules (~300 nm) were formed. Also, the consecutive adsorption of polyelectrolytes by charge reversal was evidenced. More interestingly, the drug release mechanism varied depending on the number of layers deposited. The nanosized systems containing up to two layers showed anomalous transport and first order kinetics. Formulations with three and four layers exhibited Case II transport releasing diflunisal with zero order kinetics. Hence, our results suggest that these polyelectrolyte nanocapsules have great potential as a multifunctional nanocarrier for drug delivery applications.

Photo-oxidative enhancement of polymeric molecular sieve membranes.

High-performance membranes are attractive for molecular-level separations in industrial-scale chemical, energy and environmental processes. The next-generation membranes for these processes are based on molecular sieving materials to simultaneously achieve high throughput and selectivity. Membranes made from polymeric molecular sieves such as polymers of intrinsic microporosity (pore size<2 nm) are especially interesting in being solution processable and highly permeable but currently have modest selectivity. Here we report photo-oxidative surface modification of membranes made of a polymer of intrinsic microporosity. The ultraviolet light field, localized to a near-surface domain, induces reactive ozone that collapses the microporous polymer framework. The rapid, near-surface densification results in asymmetric membranes with a superior selectivity in gas separation while maintaining an apparent permeability that is two orders of magnitude greater than commercially available polymeric membranes. The oxidative chain scission induced by ultraviolet irradiation also indicates the potential application of the polymer in photolithography technology.

Collective osmotic shock in ordered materials.

Osmotic shock in a vesicle or cell is the stress build-up and subsequent rupture of the phospholipid membrane that occurs when a relatively high concentration of salt is unable to cross the membrane and instead an inflow of water alleviates the salt concentration gradient. This is a well-known failure mechanism for cells and vesicles (for example, hypotonic shock) and metal alloys (for example, hydrogen embrittlement). We propose the concept of collective osmotic shock, whereby a coordinated explosive fracture resulting from multiplexing the singular effects of osmotic shock at discrete sites within an ordered material results in regular bicontinuous structures. The concept is demonstrated here using self-assembled block copolymer micelles, yet it is applicable to organized heterogeneous materials where a minority component can be selectively degraded and solvated whilst ensconced in a matrix capable of plastic deformation. We discuss the application of these self-supported, perforated multilayer materials in photonics, nanofiltration and optoelectronics.