Cationic brush-like terpolymer with pH responsive thickening behavior in a surfactant system

Smart Hydrogel Formed by Alginate-g-Poly(N-isopropylacrylamide) and Chitosan through Polyelectrolyte Complexation and Its Controlled Release Properties

Smart hydrogels that can respond to external stimuli such as temperature and pH have attracted tremendous interest for biological and biomedical applications. In this work, we synthesized two alginate-graft-poly(N-isopropylacrylamide) (Alg-g-PNIPAAm) copolymers and aimed to prepare smart hydrogels through formation of polyelectrolyte complex (PEC) between the negatively charged Alg-g-PNIPAAm copolymers and the positively charged chitosan (Cts) in aqueous solutions. The hydrogels were expected to be able to respond to both temperature and pH changes due to the nature of Alg-g-PNIPAAm and chitosan. The hydrogel formation was determined by a test tube inverting method and confirmed by the rheological measurements. The rheological measurements showed that the PEC hydrogels formed at room temperature could be further enhanced by increasing temperature over the lower critical solution temperature (LCST) of PNIPAAm, because PNIPAAm would change from hydrophilic to hydrophobic upon increasing temperature over its LCST, and the hydrophobic interaction between the PNIPAAm segments may act as additional physical crosslinking. The controlled release properties of the hydrogels were studied by using the organic dye rhodamine B (RB) as a model drug at different pH. The PEC hydrogels could sustain the RB release more efficiently at neutral pH. Both low pH and high pH weakened the PEC hydrogels, and resulted in less sustained release profiles. The release kinetics data were found to fit well to the Krosmyer-Peppas power law model. The analysis of the release kinetic parameters obtained by the modelling indicates that the release of RB from the PEC hydrogels followed mechanisms combining diffusion and dissolution of the hydrogels, but the release was mainly governed by diffusion with less dissolution at pH 7.4 when the PEC hydrogels were stronger and stabler than those at pH 5.0 and 10.0. Therefore, the PEC hydrogels are a kind of smart hydrogels holding great potential for drug delivery applications.

Synthesis and characterization of a novel antibacterial material containing poly(sulfobetaine) using reverse atom transfer radical polymerization

A novel antibacterial agent was synthesized using 2-(dimethylamino)ethyl methacrylate (DM) and sodium 3-chloro-2-hydroxypropane sulfonate (CHPS). It was characterized by Fourier transform infrared spectroscopy (FTIR), NMR Spectroscopy (¹H NMR), and X-ray photoelectron spectroscopy (XPS). This new agent DMCHPS was then grafted onto a polyurethane (PU) substrate via surface-initiated reverse atom transfer radical polymerization (SI-RATRP). The modified PU was characterized by FTIR and XPS. The hydrophilic properties of the PU surface before and after the incorporation of DMCHPS were determined by static contact angle (SCA) measurements. The results showed that the hydrophilicity of the PU surface after the modification was remarkably improved. MIC tests and bacterial adhesion confirmed that modified PU has good antibacterial properties. Protein adsorption experiments show that the material has a certain ability to resist pollution. Furthermore, the high survival rate of HEK293 human embryonic kidney cells shows that the modified PU has a potential use as a medicinal material.

A novel antibacterial agent was synthesized using 2-(dimethylamino)ethyl methacrylate (DM) and sodium 3-chloro-2-hydroxypropane sulfonate (CHPS).

Studying mixing in Non-Newtonian blue maize flour suspensions using color analysis

Background

Non-Newtonian fluids occur in many relevant flow and mixing scenarios at the lab and industrial scale. The addition of acid or basic solutions to a non-Newtonian fluid is not an infrequent operation, particularly in Biotechnology applications where the pH of Non-Newtonian culture broths is usually regulated using this strategy.

Methodology and Findings

We conducted mixing experiments in agitated vessels using Non-Newtonian blue maize flour suspensions. Acid or basic pulses were injected to reveal mixing patterns and flow structures and to follow their time evolution. No foreign pH indicator was used as blue maize flours naturally contain anthocyanins that act as a native, wide spectrum, pH indicator. We describe a novel method to quantitate mixedness and mixing evolution through Dynamic Color Analysis (DCA) in this system. Color readings corresponding to different times and locations within the mixing vessel were taken with a digital camera (or a colorimeter) and translated to the CIELab scale of colors. We use distances in the Lab space, a 3D color space, between a particular mixing state and the final mixing point to characterize segregation/mixing in the system.

Conclusion and Relevance

Blue maize suspensions represent an adequate and flexible model to study mixing (and fluid mechanics in general) in Non-Newtonian suspensions using acid/base tracer injections. Simple strategies based on the evaluation of color distances in the CIELab space (or other scales such as HSB) can be adapted to characterize mixedness and mixing evolution in experiments using blue maize suspensions.