On the swelling behavior of poly(N-Isopropylacrylamide) hydrogels exposed to perfluoroalkyl acids

Per- and polyfluoroalkyl substances (PFAS) have rapidly accumulated in the environment due to their widespread use prior to commercial discussion in the early 21st century, and their slow degradation has magnified concerns of their potential toxicity. Monitoring their distribution is, therefore, necessary to evaluate and control their impact on the health of exposed populations. This investigation evaluates the capability of a simple polymeric detection scheme for PFAS based on crosslinked, thermoresponsive poly(N-isopropylacrylamide) (PNIPAM) hydrogels. Surveying swelling perturbations induced by several hydrotropes and comparable hydrocarbon analogs, tetraethylammonium perfluorooctane sulfonate (TPFOS) showed a significantly higher swelling ratio on a mass basis (65.5 ± 8.8 at 15°C) than any of the other analytes tested. Combining swelling with the fluorimetric response of a solvachromatic dye, nile red, revealed the fluorosurfactant to initiate observable aggregation (i.e., its critical aggregation concentration) at 0.05 mM and reach saturation (i.e., its charge neutralization concentration) at 0.5 mM. The fluorosurfactant was found to homogeneously distribute throughout the polymer matrix with energy dispersive X-ray spectroscopy, marking the swelling response as a peculiar nexus of fluorinated interfacial positioning and delocalized electrostatic repulsion. Results from the current study hold promise for exploiting the physiochemical response of PNIPAM to assess TPFOS's concentration.     

Physicochemical characterization of nanotemplate engineered solid lipid nanoparticles

As the physicochemical characteristics of solid lipid nanoparticles (SLNs) play a critical role in their success, it is important to understand how the materials and process used in their preparation affect these properties. In this study, two stearyl alcohol-based formulations were prepared using nanotemplate engineering technology and characterized. Both formulations were of a small particle size (<100 nm), ellipsoidal shape, and low polydispersity. (1)H NMR spectroscopy confirmed that the SLNs have the expected solid core structure and PEGylated surface. Analysis of the bulk materials indicated that a number of complex interactions are present among the SLN components, including a eutectic between stearyl alcohol and Brij 78. The decreased crystallinity resulting from these interactions may allow for enhanced drug loading. Physiological stability was identified and confirmed as a potential problem due to the low melting point of the eutectic. However, it is expected that with appropriate formulation modifications nanotemplate engineered SLNs will possess the properties necessary for a successful drug delivery system.     

Carboxylesterase-Triggered Hydrolysis of Nanoparticle PEGylating Agents

Despite the importance of PEGylation in achieving long nanoparticle circulation times, many nanoparticles are coated with PEGylating agents susceptible to enzymatic degradation. In this study, solid lipid nanoparticles (SLNs) prepared with ester-containing compounds were evaluated for their stability in the presence of carboxylesterase. SLN suspensions became turbid within 30 min of enzymatic exposure, indicating possible disassociation of a portion of the nanoparticles. The particle size of SLNs incubated with the enzyme was smaller than the size of controls, although their morphologies appeared similar in transmission electron microscopy images. Although SLNs offered some protection over micelles, PEG6000 monostearate was rapidly degraded within 15 min. Hydrolysis of polysorbate 60 was much slower, reaching only 36% in 2 h. These studies reveal the importance of confirming the stability of PEG surface coatings prior to undertaking in vivo experiments in small animal models, which can have considerably higher plasma esterase activity than humans.     

Degradation of poly(β‐amino ester) gels in alcohols through transesterification: Method to conjugate drugs to polymer matrices

Poly(β amino ester) (PβAE) polymers have received growing attention in the literature, owing to their ease of synthesis, versatile co‐monomer selection, and highly tunable degradation kinetics. As such, they have shown extensive potential in many biomedical applications as well. In this work, it is demonstrated for the first time that PβAE polymers containing primary and secondary amine groups can undergo degradation by primary alcohols via transesterification mechanism. While this work emphasizes an important aspect of solvent compatibility of these networks, it also represents an interesting, simple mechanism for post synthesis drug incorporation, with riboflavin conjugation being demonstrated as a model compound. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2017 , 55, 2019–2026     

The photocurrent response of human cones is fast and monophasic

Background  

The precise form of the light response of human cone photoreceptors in vivo has not been established with certainty. To investigate the response shape we compare the predictions of a recent model of transduction in primate cone photoreceptors with measurements extracted from human cones using the paired-flash electroretinogram method. As a check, we also compare the predictions with previous single-cell measurements of ground squirrel cone responses.