Characterization of the pore structure of aqueous three-dimensional polyacrylamide gels with a novel cross-linker

Developing hydrogels for gene therapy and tissue engineering

Hydrogels are a class of highly absorbent and easily modified polymer materials suitable for use as slow-release carriers for drugs. Gene therapy is highly specific and can overcome the limitations of traditional tissue engineering techniques and has significant advantages in tissue repair. However, therapeutic genes are often affected by cellular barriers and enzyme sensitivity, and carrier loading of therapeutic genes is essential. Therapeutic gene hydrogels can well overcome these difficulties. Moreover, gene-therapeutic hydrogels have made considerable progress. This review summarizes the recent research on carrier gene hydrogels for the treatment of tissue damage through a summary of the most current research frontiers. We initially introduce the classification of hydrogels and their cross-linking methods, followed by a detailed overview of the types and modifications of therapeutic genes, a detailed discussion on the loading of therapeutic genes in hydrogels and their characterization features, a summary of the design of hydrogels for therapeutic gene release, and an overview of their applications in tissue engineering. Finally, we provide comments and look forward to the shortcomings and future directions of hydrogels for gene therapy. We hope that this article will provide researchers in related fields with more comprehensive and systematic strategies for tissue engineering repair and further promote the development of the field of hydrogels for gene therapy.

Development of a Disposable Polyacrylamide Hydrogel-Based Semipermeable Membrane for Micro Ag/AgCl Reference Electrode

Currently, Ag/AgCl-based reference electrodes are used in most electrochemical biosensors and other bioelectrochemical devices. However, standard reference electrodes are rather large and do not always fit within electrochemical cells designed for the determination of analytes in low-volume aliquots. Therefore, various designs and improvements in reference electrodes are critical for the future development of electrochemical biosensors and other bioelectrochemical devices. In this study, we explain a procedure to apply common laboratory polyacrylamide hydrogel in a semipermeable junction membrane between the Ag/AgCl reference electrode and the electrochemical cell. During this research, we have created disposable, easily scalable, and reproducible membranes suitable for the design of reference electrodes. Thus, we came up with castable semipermeable membranes for reference electrodes. Performed experiments highlighted the most suitable gel formation conditions to achieve optimal porosity. Here, Cl^- ion diffusion through the designed polymeric junctions was evaluated. The designed reference electrode was also tested in a three-electrode flow system. The results show that home-built electrodes can compete with commercial products due to low reference electrode potential deviation (~3 mV), long shelf-life (up to six months), good stability, low cost, and disposability. The results show a high response rate, which makes in-house formed polyacrylamide gel junctions good membrane alternatives in the design of reference electrodes, especially for these applications where high-intensity dyes or toxic compounds are used and therefore disposable electrodes are required.

Fe(III)-Complex-Imprinted Polymers for the Green Oxidative Degradation of the Methyl Orange Dye Pollutant

One of the biggest problems worldwide is the pollution of natural water bodies by dyes coming from effluents used in the textile industry. In the quest for novel effluent treatment alternatives, the aim of this work was to immobilize Fe(III) complexes in molecularly imprinted polymers (MIPs) to produce efficient Fenton-like heterogeneous catalysts for the green oxidative degradation of the methyl orange (MO) dye pollutant. Different metal complexes bearing commercial and low-cost ligands were assayed and their catalytic activity levels towards the discoloration of MO by H2O2 were assessed. The best candidates were Fe(III)-BMPA (BMPA = di-(2-picolyl)amine) and Fe(III)-NTP (NTP = 3,3',3″-nitrilotripropionic acid), displaying above 70% MO degradation in 3 h. Fe(III)-BMPA caused the oxidative degradation through two first-order stages, related to the formation of BMPA-Fe-OOH and the generation of reactive oxygen species. Only the first of these stages was detected for Fe(III)-NTP. Both complexes were then employed to imprint catalytic cavities into MIPs. The polymers showed catalytic profiles that were highly dependent on the crosslinking agent employed, with N,N-methylenebisacrylamide (MBAA) being the crosslinker that rendered polymers with optimal oxidative performance (>95% conversion). The obtained ion-imprinted polymers constitute cheap and robust solid matrices, with the potential to be coupled to dye-containing effluent treatment systems with synchronous H2O2 injection.

Protein imprinting in polyacrylamide-based gels

Protein imprinting in hydrogels is a method to produce materials capable of selective recognition and capture of a target protein. Here we report on the imprinting of fluorescently-labeled maltose binding protein (MBP) in acrylamide (AAm)/N-isopropylacrylamide (NIPAm) hydrogels. The targeting efficiency and selectivity of protein recognition is usually characterized by the imprinting factor, which in the simplest case is the ratio of protein uptake in an imprinted film divided by the uptake by the corresponding non-imprinted film. Our objective in this work is to study the dynamics of protein binding and elution in imprinted and non-imprinted films to elucidate the processes that control protein recognition. Protein elution from imprinted and non-imprinted films suggests that imprinting results in sites with a distribution of binding energies, and that only a relatively small fraction of these sites exhibit strong binding.

Use of Rigid Spherical Inclusions in Young’s Moduli Determination: Application to DNA-Crosslinked Gels

Current techniques for measuring the bulk shear or elastic (E) modulus of small samples of soft materials are usually limited by materials handling issues. This paper describes a nondestructive testing method based on embedded spherical inclusions. The technique simplifies materials preparation and handling requirements and is capable of continuously monitoring changes in stiffness. Exact closed form derivations of E as functions of the inclusion force-displacement relationship are presented. Analytical and numerical analyses showed that size effects are significant for medium dimensions up to several times those of the inclusion. Application of the method to DNA-crosslinked gels showed good agreement with direct compression tests.

Mechanical properties of a reversible, DNA-crosslinked polyacrylamide hydrogel

Mechanical properties of a polyacrylamide gel with reversible DNA crosslinks are presented. In this system, three DNA strands replace traditional chemical crosslinkers. In contrast to thermoset chemically crosslinked polyacrylamide, the new hydrogel is thermoreversible; crosslink dissociation without the addition of heat is also feasible by introducing a specific removal DNA strand. This hydrogel is characterized by a critical crosslink concentration at which gelation occurs. Below the critical point, a characteristic temperature exists at which a transition in viscosity is observed. Both temperature-dependent viscosity and elastic modulus of the material are functions of crosslink density.

Novel cross-linked polyacrylamide matrices: an investigation using gradient gel electrophoresis

Gradient gel electrophoresis was used to examine the separation properties of novel cross-linking compounds for polyacrylamide (PAAm). At low %T and at the same %C protein migration difference is accentuated for bismethacrylamide cross-linked networks relative to bisacrylamide cross-linked networks. Similar properties were observed for cyclic monomers at low %T. This trend is maintained throughout the gradient. However, at higher %T migration differential relative to N,N'-methylenebisacrylamide (Bis) was less pronounced. Evidence from gradient gels suggests that reactivity and functionality of vinyl groups impose an overriding control over network formation.

Novel cross-linked homogeneous polyacrylamide gels with improved separation properties: investigation of the cross-linker functionality

Polyacrylamide (PAAm) gels were synthesized using cross-linkers with their potential functionality (twice the number of double bonds of a cross-linker) varying from six to sixteen. Improved electrophoretic separation and highly desirable porosity and sieving properties were observed for most of the PAAm gels containing novel cross-linkers. An increase in the potential functionality of cross-linkers used in PAAm gels was an important factor, influencing the pore size and pore size distribution of the network.