Performance optimization in electric field gradient focusing

Electric field gradient focusing (EFGF) is a technique used to simultaneously separate and concentrate biomacromolecules, such as proteins, based on the opposing forces of an electric field gradient and a hydrodynamic flow. Recently, we reported EFGF devices fabricated completely from copolymers functionalized with poly(ethylene glycol), which display excellent resistance to protein adsorption. However, the previous devices did not provide the predicted linear electric field gradient and stable current. To improve performance, Tris–HCl buffer that was previously doped in the hydrogel was replaced with a phosphate buffer containing a salt (i.e., potassium chloride, KCl) with high mobility ions. The new devices exhibited stable current, good reproducibility, and a linear electric field distribution in agreement with the shaped gradient region design due to improved ion transport in the hydrogel. The field gradient was calculated based on theory to be approximately 5.76 V/cm² for R-phycoerythrin when the applied voltage was 500 V. The effect of EFGF separation channel dimensions was also investigated; a narrower focused band was achieved in a smaller diameter channel. The relationship between the bandwidth and channel diameter is consistent with theory. Three model proteins were resolved in an EFGF channel of this design. The improved device demonstrated 14,000-fold concentration of a protein sample (from 2 ng/mL to 27 μg/mL).     

Innovative Eco-Friendly Hydrogel Film for Berberine Delivery in Skin Applications

Hydrogel formulations (masks or patches, without tissue support) represent the new frontier for customizable skin beauty and health. The employment of these materials is becoming popular in wound dressing, to speed up the healing process while protecting the affected area, as well as to provide a moisturizing reservoir, control the inflammatory process and the onset of bacterial development. Most of these hydrogels are acrylic-based at present, not biodegradable and potentially toxic, due to acrylic monomers residues. In this work, we selected a new class of cellulose-derived and biodegradable hydrogel films to incorporate and convey an active compound for dermatological issues. Films were obtained from a combination of different polysaccharides and clays, and berberine hydrochloride, a polyphenolic molecule showing anti-inflammatory, immunomodulatory, antibacterial and antioxidant properties, was chosen and then embedded in the hydrogel films. These innovative hydrogel-based systems were characterized in terms of water uptake profile, in vitro cytocompatibility and skin permeation kinetics by Franz diffusion cell. Berberine permeation fitted well to Korsmeyer–Peppas kinetic model and achieved a release higher than 100 µg/cm² within 24 h. The latter study, exploiting a reliable skin model membrane, together with the biological assessment, gained insights into the most promising formulation for future investigations.     

Development of hydrogel microstructures on single-walled carbon nanotube films

In this study, the development of polyethylene glycol (PEG) hydrogel microstructures led to the micropatterning of single-walled carbon nanotube (SWCNT) films. Polyethylene glycol was patterned in a process analogous to photolithography in order to manufacture high-density arrays of micrometer-scale hydrogel wells on SWCNT film surfaces. These microwells were composed of hydrophobic SWCNT films surrounded by hydrophilic PEG hydrogel walls. Effects of PEG hydrogel microstructures on the micropatterning of SWCNT films were systematically investigated under different substrates prepared with 3-(trichlorosilyl)propyl methacrylate or octadecyltrichlorosilane solution. A characterization of protein adsorption and an electrochemiluminescence (ECL) reaction were performed to evaluate the biocompatible and electrical efficiency of the patterned SWCNT films in various applications. The proteins selectively adhered to the SWCNT surface inside the microwells, while adherent proteins were absent from the hydrogel walls. In the ECL reaction, the SWCNT films patterned with PEG hydrogel exhibited good, stable ECL behavior, a sign that patterned SWCNT films can be used as flexible and transparent electrodes.     

Functionalization of Hydrogels Based on N-Isopropyl-acrylamide and Cationic Surfactant Monomers upon Electrostatic Self-Assembly

Summary: Positively charged copolymer hydrogels based on N-isopropyl-acrylamide (NiPAAm) and a cationic surfactant monomer (surfmer) were functionalized upon electrostatic self-assembly of functional organic or inorganic complex counterions in the gel. As cationic surfmers 11-acryloylundecyltrimethylammonium bromide (AUTMAB) or 11-methacryloyl-undecyltrimethylammonium bromide (MUTMAB) were used. The hydrogels were prepared from a micellar aqueous solution of the surfmer and NiPAAm either upon ⁶⁰Co-gamma irradiation, or upon chemical cross-linking using methylenebisacrylamide as cross-linker and 1,4-diaminobutane as accelerator. Electrostatic self-assembly was facilitated utilizing the thermoresponsive swelling and shrinking of the hydrogel. Several examples of gel functionalization are described such as in-situ preparation of Prussian Blue and Pd⁰ nanoparticles, and induction of fluorescent properties. The catalytic activity of the palladium-containing gel was studied by investigating the reduction of 4-nitrophenol (4-NP) with sodium borohydride as a model reaction. Fluorescent gels can be prepared upon exchange of bromide against 1-pyrenesulfonate ions in the gel.     

β-Cyclodextrin-Polyacrylamide Hydrogel for Removal of Organic Micropollutants from Water

Water pollution by various toxic substances remains a serious environmental problem, especially the occurrence of organic micropollutants including endocrine disruptors, pharmaceutical pollutants and naphthol pollutants. Adsorption process has been an effective method for pollutant removal in wastewater treatment. However, the thermal regeneration process for the most widely used activated carbon is costly and energy-consuming. Therefore, there has been an increasing need to develop alternative low-cost and effective adsorption materials for pollutant removal. Herein, β-cyclodextrin (β-CD), a cheap and versatile material, was modified with methacrylate groups by reacting with methacryloyl chloride, giving an average degree of substitution of 3 per β-CD molecule. β-CD-methacrylate, which could function as a crosslinker, was then copolymerized with acrylamide monomer via free-radical copolymerization to form β-CD-polyacrylamide (β-CD-PAAm) hydrogel. Interestingly, in the structure of the β-CD-PAAm hydrogel, β-CD is not only a functional unit binding pollutant molecules through inclusion complexation, but also a structural unit crosslinking PAAm leading to the formation of the hydrogel 3D networks. Morphological studies showed that β-CD-PAAm gel had larger pore size than the control PAAm gel, which was synthesized using conventional crosslinker instead of β-CD-methacrylate. This was consistent with the higher swelling ratio of β-CD-PAAm gel than that of PAAm gel (29.4 vs. 12.7). In the kinetic adsorption studies, phenolphthalein, a model dye, and bisphenol A, propranolol hydrochloride, and 2-naphthol were used as model pollutants from different classes. The adsorption data for β-CD-PAAm gel fitted well into the pseudo-second-order model. In addition, the thermodynamic studies revealed that β-CD-PAAm gel was able to effectively adsorb the different dye and pollutants at various concentrations, while the control PAAm gel had very low adsorption, confirming that the pollutant removal was due to the inclusion complexation between β-CD units and pollutant molecules. The adsorption isotherms of the different dye and pollutants by the β-CD-PAAm gel fitted well into the Langmuir model. Furthermore, the β-CD-PAAm gel could be easily recycled by soaking in methanol and reused without compromising its performance for five consecutive adsorption/desorption cycles. Therefore, the β-CD-PAAm gel, which combines the advantage of an easy-to-handle hydrogel platform and the effectiveness of adsorption by β-CD units, could be a promising pollutant removal system for wastewater treatment applications.     

Super-tough and rapidly self-recoverable multi-bond network hydrogels facilitated by 2-ureido-4[1H]-pyrimidone dimers

Multi-bond network(MBN) hydrogels contain hierarchical dynamic bonds with different bond association energy as energy dissipation units,enabling super-tough mechanical properties.In this work,we copolymerize a protonated 2-ureido-4[1 H]-pyrimidone(UPy)-contained monomer with acrylic acid in HCl solution.After removing excess HCl,UPy motifs are deprotonated and from dimers,thus generating an UPy-contained MBN hydrogel.The obtained MBN hydrogels(75 wt% watercontent) exhibit super-tough mechanical properties(0.39 MPa to 2.51 MPa tensile strength),with tremendous amount of energy(1.68 MJ/m³ to 11.1 MJ/m³) dissipated by the dissociation of UPy dimers.The introduction of ionic bonds can further improve the mechanical properties.Moreover,owing to their dynamic nature,both UPy dimers and ionic bonds can re-associate after being dissociated,resulting in excellent self-recovery ability(around 90% recovery efficiency within only 1 h).The excellent self-recovery ability mainly originates from the re-association of UPy dimers based on the high dimerization constant of UPy motifs.     

磁性能可控的聚(N-异丙基丙烯酰胺)基纳米复合水凝胶的制备与表征

以N-异丙基丙烯酰胺(NIPAM)为单体、焦磷酸钠改性的无机锂皂石(Clay-S)为物理交联剂,制备了温敏性的纳米复合水凝胶(NC gels),通过原位化学沉淀法引入Fe3O4纳米粒子,制备了聚(N-异丙基丙烯酰胺)基磁性纳米复合水凝胶(MNC gels)。使用傅里叶变换红外光谱(FTIR)、X射线衍射(XRD)、扫描电子显微镜(SEM)、能量色散X射线光谱(EDX)、差示扫描量热分析(DSC)、综合物性测量系统(PPMS)等测试方法表征了凝胶网络的结构形态、磁性粒子的晶型及其分布、凝胶的温敏性和磁性能。重点研究了制备过程中的浸泡液铁盐浓度、预聚液的单体浓度及黏土含量对凝胶磁性能的影响,并对上述影响因素进行了分析和模拟。结果表明:MNC gels同时具有温敏性和磁敏性,且其磁性能受浸泡液铁盐浓度、预聚液的单体浓度及黏土含量影响;根据影响因素显著性水平建立了可预测MNC gels磁性能的模型,使磁性能的可控制备成为可能。     

Kinetic analyses of disulfide formation between thiol groups attached to linear poly(acrylamide)

Kinetic analyses were carried out for formation of disulfide crosslinkages between thiol groups on linear polymers, poly(acrylamide‐co‐N‐acrylcysteamine) (P‐SH). Disulfide crosslinkages were formed by auto‐oxidation of pendant thiol groups or through the thiol‐disulfide exchange reaction induced by addition of disulfide compounds gluthathione. In the auto‐oxidation reaction, the rate constant for disulfide formation highly depended on pH values of the reaction mixtures and the P‐SH concentrations. Gelation rate is too slow to enclose living cells into hydrogel under physiological pH 7.4. The hydrogel formation rate can be accelerated by addition of disulfides, such as oxidized glutathione. In the later case, oxygen in the reaction mixture is not consumed. The thiol‐disulfide exchange reaction is much more suitable for the cell encapsulation than the thiol auto‐oxidation reaction. These findings give a basis for enclosure of living cells in a hydrogel. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011     

Flexible Three‐Dimensional Graphene Hydrogels with Superior Conductivity and Excellent Electrochemical Performance for Supercapacitor Electrodes

Three‐dimensional porous graphene hydrogels have been prepared by a green and facile but very efficient approach using glucose as an assistant. Based on a one‐step hydrothermal reaction with optimal experimental conditions such as the reaction time and temperature, the graphene hydrogels exhibit a superior electrical conductivity (95.3 S/m) and can be used as supercapacitor electrode without any binder or conducting additives but showing a high specific capacitance of 384.6 F/g at a current density of 1 A/g. The results show that addition of glucose can not only greatly decrease the reaction temperature but also shorten the reaction time. The superior performance of the three‐dimensional porous graphene hydrogels as electrode for supercapacitor suggests its promising potentials in the field of energy storage devices.     

Investigation on the mechanical behavior of poly(2‐hydroxyethyl methacrylate) hydrogel membrane under compression in the assembly process of microfluidic system

A microfluidic system with an inserted membrane assembled using mechanical fastening process is described. The membrane is made of a biocompatible water swollen poly(2‐hydroxyethyl methacrylate) (PHEMA) hydrogel thin film as a sealing component. The hyperelastic characteristics of PHEMA membrane under the compression during fastening are investigated through numerical simulations, including strain and Von Mises stress distribution, and potential fracture in correlation with the microchannel's geometry and dimensions. To validate the modeling, the experiments have also been conducted to visualize the deformation induced in membrane and internal stress distribution using 3D optical measuring system. The results from this study have revealed the implications in connection with the mechanical behavior of the PHEMA membranes in the assembly of microfluidic system through mechanical fastening technique. This will ultimately assist to produce a guideline for the optimum design of microchannels in the uses of PHEMA membranes and associated assembly process. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2014 , 52, 485–495