U.v. irradiation-induced crosslinking of solid poly(ethylene oxide) modified with tetraalkyl ammonium salt

Emerging Fabrication Strategies of Hydrogels and Its Applications

Recently, hydrogels have been investigated for the controlled release of bioactive molecules, such as for living cell encapsulation and matrices. Due to their remote controllability and quick response, hydrogels are widely used for various applications, including drug delivery. The rate and extent to which the drugs reach their targets are highly dependent on the carriers used in drug delivery systems; therefore the demand for biodegradable and intelligent carriers is progressively increasing. The biodegradable nature of hydrogel has created much interest for its use in drug delivery systems. The first part of this review focuses on emerging fabrication strategies of hydrogel, including physical and chemical cross-linking, as well as radiation cross-linking. The second part describes the applications of hydrogels in various fields, including drug delivery systems. In the end, an overview of the application of hydrogels prepared from several natural polymers in drug delivery is presented.

Shape and Mechanical Control of Poly(ethylene oxide) Based Polymersome with Polyoxometalates via Hydrogen Bond

Polymersomes are self-assembled vesicles of amphiphilic block copolymers and have been explored for wide applications from drug delivery to micro/nanoreactors. As polymersomes are soft and highly deformable, their shape instability due to osmolarity difference across polymer membranes and low elasticity could conversely limit their practical use. Instead of selecting particular polymer chemical reactions to enhance the mechanical properties, we have employed inorganic polyoxometalate (POM) clusters as simple physical cross-linkers to control the shape and mechanical stability of polymersomes in aqueous suspensions. Robust spherical shape with enhanced elastic and bending moduli of POM-dressed poly(ethylene oxide) (PEO) based polymersomes is achieved. We have accounted for the hydrogen bonding between POM and PEO blocks for the adsorption and stabilization of POMS on polymersomes, whose interaction strength could also be tuned by mixing solvents of hydrogen bond donors or receptors with water. The stimuli-responsive properties of POMs are introduced in POM-dressed polymersomes upon the interaction of POMs with PEO blocks in aqueous media. As POM can be used as nanomedicines, catalysts, and other functional nanomaterials, POM-dressed polymersomes with significant shape and mechanical reinforcement could broaden the applications of PEO-based polymersomes and other PEO-tethered nanocolloids.

Water Sorption of Interpenetrating Polymer Network Hydrogels Composed of Poly(Ethylene Oxide) and Poly(Methyl Methacrylate)

Anomalous water sorption behavior has been observed in interpenetrating polymer network (IPN) hydrogels composed of poly (ethylene oxide) and poly (methyl methacrylate). The water sorption of IPN hydrogels was investigated gravimetrically by dynamic vapor sorption at a relative humidity of 95%, and the collective diffusion coefficients determined at 25, 35 and 45° C. With increasing temperature the vapor sorption behavior, was affected more by the density of the water vapor than by the hydrophilic properties of the IPN hydrogels. The apparent activation energy was independent on the composition of the IPN hydrogels, with a value of 1.31∼1.90 kJ mol -1. However; the equilibrium water content was dependent on the temperature, decreasing as the temperature increased. The IPN hydrogels exhibited a relatively high equilibrium water contents, in the range 13∼68%.

Thermal Characteristics of Poly(Ethylene Oxide)/Poly(Methyl Methacrylate) Interpenetrating Polymer Networks

Poly(ethylene oxide) (PEO)/poly(methyl methacrylate) (PMMA) interpenetrating polymer networks (IPNs) were synthesized by radical polymerization of methyl methacrylate in the presence of PEO. Thermal properties were investigated using differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), dielectric analysis (DEA) and Fourier transform infrared (FT-IR) spectroscopy. The DEA was employed to ascertain the glass transition temperature (Tg) and melting temperature (Tm) of IPN. Tm for the IPNs was observed at 206 'C. The IPNs exhibited two Tgs, indicating the presence of phase separation in the IPN at -46.8 and 78.2 'C. The thermal decomposition of the IPNs occurred near 250 'C. The IPNs exhibited a higher weight retention at elevated temperature than the cross-linked homopolymer.

A novel amphoteric ion-exchange membrane prepared by the pore-filling technique for vanadium redox flow batteries

A novel amphoteric ion-exchange membrane (AIEM) was prepared through the pore-filling technique, for vanadium redox flow battery (VRBs) applications.

Characterization of Biomaterials by Soft X-Ray Spectromicroscopy

Synchrotron-based soft X-ray spectromicroscopy techniques are emerging as useful tools to characterize potentially biocompatible materials and to probe protein interactions with model biomaterial surfaces. Simultaneous quantitative chemical analysis of the near surface region of the candidate biomaterial, and adsorbed proteins, peptides or other biological species can be obtained at high spatial resolution via scanning transmission X-ray microscopy (STXM) and X-ray photoemission electron microscopy (X-PEEM). Both techniques use near-edge X-ray absorption fine structure (NEXAFS) spectral contrast for chemical identification and quantitation. The capabilities of STXM and X-PEEM for the analysis of biomaterials are reviewed and illustrated by three recent studies: (1) characterization of hydrophobic surfaces, including adsorption of fibrinogen (Fg) or human serum albumin (HSA) to hydrophobic polymeric thin films, (2) studies of HSA adsorption to biodegradable or potentially biocompatible polymers, and (3) studies of biomaterials under fully hydrated conditions. Other recent applications of STXM and X-PEEM to biomaterials are also reviewed.

Integral geometry analysis of fluorescence micrographs for quantitative relative comparison of protein adsorption onto polymer surfaces

Most methods developed to study protein binding to distinct surfaces can only determine the average amount of adsorbed protein or merely provide (qualitative) information on its spatial distribution. Both these features can be characterized rigorously by integral geometry analysis of fluorescence micrographs. This approach is introduced here to compare the relative protein adsorption onto various polymer surfaces: polystyrene (PS), poly(methyl methacrylate) (PMMA), poly( n-butyl methacrylate) (PnBMA), poly( tert-butyl methacrylate) (PtBMA), and PS(PETA) and cross-linked poly(ethylene oxide) (PEO*(PETA)), admixed with pentaerythritol triacrylate (PETA). The polymeric surfaces were incubated for 15 min in phosphate-buffered saline (pH 7.4) containing 125 mug/mL fluorescently labeled lectins, either lentil lectin (LcH) or concanavalin A (ConA). Fluorescence images were recorded at identical conditions (physiological buffer, same exposure time, magnification, gain). For each image, taken a few times for each polymer, the distribution and average value of the normalized intensity were determined. The results show that the binding of LcH to PS(PETA), PtBMA, PS, PnBMA, PMMA, and PEO*(PETA) can be expressed by the ratio of the following values (mean +/- 95% confidence interval): 0.356 +/- 0.022, 0.298 +/- 0.030, 0.241 +/- 0.014, 0.083 +/- 0.008, 0.039 +/- 0.008, and 0.010 +/- 0.006, respectively. In turn, the relative adsorption of ConA is described by the values 0.252 +/- 0.016, 0.217 +/- 0.014, 0.222 +/- 0.016, 0.046 +/- 0.006, 0.116 +/- 0.008, and 0.006 +/- 0.002, respectively. Low dispersions of fluorescence intensity around average values indicate homogeneous distribution of adsorbed proteins. The introduced approach enables a fast and easy way not only to quantify the relative amount of bound proteins but also to characterize quantitatively the organization of their surface distribution, as demonstrated for patchlike protein adsorption onto the polymer blend surface.