Enhancing Mucoadhesive Properties of Gelatin through Chemical Modification with Unsaturated Anhydrides.

Gelatin is a water-soluble natural polyampholyte with poor mucoadhesive properties. It has traditionally been used as a major ingredient in many pharmaceuticals, including soft and hard capsules, suppositories, tissue engineering, and regenerative medicine. The mucoadhesive properties of gelatin can be improved by modifying it through conjugation with specific adhesive unsaturated groups. In this study, gelatin was modified by reacting with crotonic, itaconic, and methacrylic anhydrides in varying molar ratios to yield crotonoylated-, itaconoylated-, and methacryloylated gelatins (abbreviated as Gel-CA, Gel-IA, and Gel-MA, respectively). The successful synthesis was confirmed using 1H NMR, FTIR spectroscopies, and colorimetric TNBSA assay. The effect of chemical modification on the isoelectric point was studied through viscosity and electrophoretic mobility measurements. The evolution of the storage (G') and loss (G'') moduli was employed to determine thermoreversible gelation points of modified and unmodified gelatins. The safety of modified gelatin derivatives was assessed with an in vivo slug mucosal irritation test (SMIT) and an in vitro MTT assay utilizing human pulmonary fibroblasts cell line. Two different model dosage forms, such as physical gels and spray-dried microparticles, were prepared and their mucoadhesive properties were evaluated using a flow-through technique with fluorescent detection and a tensile test with ex vivo porcine vaginal tissues and sheep nasal mucosa. Gelatins modified with unsaturated groups exhibited superior mucoadhesive properties compared to native gelatin. The enhanced ability of gelatin modified with these unsaturated functional groups is due to the formation of covalent bonds with cysteine-rich subdomains present in the mucin via thiol-ene click Michael-type addition reactions occurring under physiologically relevant conditions.

Exploring Potential of Gellan Gum for Enhanced Oil Recovery.

Extensive laboratory and field tests have shown that the gelation response of gellan gum to saline water makes it a promising candidate for enhanced oil recovery (EOR). The objective of this mini-review is to evaluate the applicability of gellan gum in EOR and compare its efficiency to other precursors, in particular, hydrolyzed polyacrylamide (HPAM). At first, the "sol-gel" phase transitions of gellan gum in aqueous-salt solutions containing mono- and divalent cations are considered. Then the rheological and mechanical properties of gellan in diluted aqueous solutions and gel state are outlined. The main attention is paid to laboratory core flooding and field pilot tests. The plugging behavior of gellan in laboratory conditions due to "sol-gel" phase transition is discussed in the context of conformance control and water shut-off. Due to its higher strength, gellan gum gel provided ~6 times greater resistance to the flow of brine in a 1 mm-width fracture compared to HPAM gel. The field trials carried out in the injection and production wells of the Kumkol oilfield, situated in Kazakhstan, demonstrated that over 6 and 11 months, there was an incremental oil recovery of 3790 and 5890 tons, respectively. To put it into perspective, using 1 kg of dry gellan resulted in the incremental production of 3.52 m3 (or 22 bbls) of oil. The treatment of the production well with 1 wt.% gellan solution resulted in a considerable decrease in the water cut up to 10-20% without affecting the oil flow rate. The advantages and disadvantages of gellan compared to HPAM are analyzed together with the economic feasibility of gellan over HPAM. The potential for establishing gellan production in Kazakhstan is emphasized. It is anticipated that gellan gum, manufactured through fermentation using glucose-fructose syrup from Zharkent and Burunday corn starch plants, could be expanded in the future for applications in both the food industry and oil recovery.

Comparative Study of Oil Recovery Using Amphoteric Terpolymer and Hydrolyzed Polyacrylamide.

This paper presents the viscosifying and oil recovery efficiencies of a novel high-molecular-weight ternary polyampholyte (TPA), composed of 80 mol.% acrylamide (AAm) (a nonionic monomer), 10 mol.% 2-acrylamido-2-methyl-1-propanesulfonic acid sodium salt (AMPS) (an anionic monomer), and 10 mol.% (3-acrylamidopropyl) trimethylammonium chloride (APTAC) (a cationic monomer), in various high-salinity brines as compared to the efficiency of hydrolyzed poly(acrylamide) (HPAM), which is the most commonly used polymer in oil production. The results show that, in a range of salinity from 200 to 300 g∙L-1, the viscosity of the TPA solution is rather high and relatively stable, whereas that of HPAM severely decreases. The ability of TPA to increase its viscosity in extremely high salinity brines is explained by the antipolyelectrolyte effect, resulting in the unfolding of macromolecular chains of charge-balanced polyampholytes at a quasi-neutral state, which occurs due to the screening of the electrostatic attraction between oppositely charged moieties. The novelty of this research is that, in high-salinity reservoirs, the amphoteric terpolymer Aam-AMPS-APTAC may surpass HPAM in oil displacement capability.

Temperature and Salt Responsive Amphoteric Nanogels Based on N-Isopropylacrylamide, 2-Acrylamido-2-methyl-1-propanesulfonic Acid Sodium Salt and (3-Acrylamidopropyl) Trimethylammonium Chloride.

Polyampholyte nanogels based on N-isopropylacrylamide (NIPAM), (3-acrylamidopropyl) trimethylammonium chloride (APTAC) and 2-acrylamido-2-methyl-1-propanesulfonic acid sodium salt (AMPS) were synthesized via conventional redox-initiated free radical copolymerization. The resultant nanogels of various compositions, specifically [NIPAM]:[APTAC]:[AMPS] = 90:5:5; 90:7.5:2.5; 90:2.5:7.5 mol.%, herein abbreviated as NIPAM90-APTAC5-AMPS5, NIPAM90-APTAC7.5-AMPS2.5 and NIPAM90-APTAC2.5-AMPS7.5, were characterized by a combination of 1H NMR and FTIR spectroscopy, TGA, UV-Vis, DLS and zeta potential measurements. The temperature and salt-responsive properties of amphoteric nanogels were studied in aqueous and saline solutions in a temperature range from 25 to 60 °C and at ionic strengths (µ) of 10-3 to 1M NaCl. Volume phase transition temperatures (VPTT) of the charge-balanced nanogel were found to reach a maximum upon the addition of salt, whereas the same parameter for the charge-imbalanced nanogels exhibited a sharp decrease at higher saline concentrations. A wide bimodal distribution of average hydrodynamic sizes of nanogel particles had a tendency to transform to a narrow monomodal peak at elevated temperatures and higher ionic strengths. According to the DLS results, increasing ionic strength results in the clumping of nanogel particles.

Basic Approaches to the Design of Intrinsic Self-Healing Polymers for Triboelectric Nanogenerators.

Triboelectric nanogenerators (TENGs) as a revolutionary system for harvesting mechanical energy have demonstrated high vitality and great advantage, which open up great prospects for their application in various areas of the society of the future. The past few years have seen exponential growth in many new classes of self-healing polymers (SHPs) for TENGs. This review presents and evaluates the SHP range for TENGs, and also attempts to assess the impact of modern polymer chemistry on the development of advanced materials for TENGs. Among the most widely used SHPs for TENGs, the analysis of non-covalent (hydrogen bond, metal-ligand bond), covalent (imine bond, disulfide bond, borate bond) and multiple bond-based SHPs in TENGs has been performed. Particular attention is paid to the use of SHPs with shape memory as components of TENGs. Finally, the problems and prospects for the development of SHPs for TENGs are outlined.

Synthesis of Copper(II) Trimesinate Coordination Polymer and Its Use as a Sorbent for Organic Dyes and a Precursor for Nanostructured Material.

Several important synthesis pathways for metal-organic frameworks (MOFs) were applied to determine how the synthesis methods and conditions affect the structure and adsorption capacity of the resulting samples. In the present work, three different synthesis routes were used to obtain copper trimesinate coordination polymer: Slow evaporation (A), solvothermal synthesis using a polyethylene glycol (PEG-1500) modulator (B), and green synthesis in water (C). This MOF was characterized by elemental analysis, infrared spectrometry, X-ray diffraction, scanning electron microscopy, thermogravimetry and volumetric nitrogen adsorption/desorption. The samples have permanent porosity and a microporous structure with a large surface area corresponding to the adsorption type I. The obtained MOF was tested as a sorbent to remove organic dyes methylene blue (МВ), Congo red (CR) and methyl violet (MV) as examples. Dye adsorption followed pseudo-first-order kinetics. The equilibrium data were fitted to the Langmuir and Freundlich isotherm models, and the isotherm constants were determined. Thermodynamic parameters, such as changes in the free energy of adsorption (ΔG0), enthalpy (ΔH0), and entropy (ΔS0), were calculated. Thermolysis of copper trimesinate leads to the formation of carbon materials Cu@C with a high purity.

Chitosan/Poly(2-ethyl-2-oxazoline) Films with Ciprofloxacin for Application in Vaginal Drug Delivery.

Chitosan (CHI) and chitosan/poly(2-ethyl-2-oxazoline) (CHI/POZ)-based films were prepared by casting from aqueous solutions of polymer blends with different compositions. Ciprofloxacin was used as a model drug in these formulations. The weight, thickness, folding endurance and transparency of blend films were measured and characterised. All films had a uniform thickness (0.06 ± 0.01 mm) and exhibited sufficient flexibility. The surface pHs of films ranged from 3.76 ± 0.49 to 4.14 ± 0.32, which is within the pH range suitable for vaginal applications. The cumulative release of the drug from the films in experiments in vitro was found to be 42 ± 2% and 56 ± 1% for pure CHI and CHI/POZ (40:60) films, respectively. Drug-free chitosan/poly(2-ethyl-2-oxazoline) films showed weak antimicrobial activity against Escherichia coli. Drug-loaded CHI and CHI/POZ films showed good antimicrobial properties against both Gram-positive Staphylococcus aureus and Gram-negative bacteria Escherichia coli. Mucoadhesive properties of these films with respect to freshly excised sheep vaginal mucosa were evaluated using a tensile method. It was established that all films were mucoadhesive, but an increase in POZ content in the blend resulted in a gradual reduction of their ability to stick to vaginal mucosa. These films could potentially find applications in vaginal drug delivery.

Flow-Through Catalytic Reactors Based on Metal Nanoparticles Immobilized within Porous Polymeric Gels and Surfaces/Hollows of Polymeric Membranes.

State-of-the-art of flow-through catalytic reactors based on metal nanoparticles immobilized within the pores of nano-, micro- and macrosized polymeric gels and in the surface or hollow of polymeric membranes is discussed in this mini-review. The unique advantages of continuous flow-through nanocatalysis over the traditional batch-type analog are high activity, selectivity, productivity, recyclability, continuous operation, and purity of reaction products etc. The methods of fabrication of polymeric carriers and immobilization technique for metal nanoparticles on the surface of porous or hollow structures are considered. Several catalytic model reactions comprising of hydrolysis, decomposition, hydrogenation, oxidation, Suzuki coupling and enzymatic reactions in the flow system are exemplified. Realization of "on-off" switching mechanism for regulation of the rate of catalytic process through controlling the mass transfers of reactants in liquid media with the help of stimuli-responsive polymers is demonstrated. Comparative analysis of the efficiency of different flow-through catalytic reactors for various reactions is also surveyed.

Gellan gum and its methacrylated derivatives as in situ gelling mucoadhesive formulations of pilocarpine: In vitro and in vivo studies.

Gellan gum was chemically modified by the reaction with methacrylic anhydride to produce derivatives with 6, 14 and 49% methacrylation. The structure and substitution degrees of these derivatives were confirmed by 1H NMR- and FTIR-spectroscopy. These derivatives are more hydrophobic compared to pristine gellan and form turbid solutions in water. In vitro study performed with formulations of sodium fluorescein containing gellan gum and its methacrylated derivatives indicated that methacrylation enhances their retention on bovine conjunctival mucosa. In vivo experiments with the formulations of pilocarpine hydrochloride containing gellan gum and methacrylated derivatives have demonstrated that all polymers enhance the drug effect significantly, but best performance is observed for the polysaccharide with 6% methacrylation.

Physicochemical, Complexation and Catalytic Properties of Polyampholyte Cryogels.

Polyampholyte cryogels are a less considered subject in comparison with cryogels based on nonionic, anionic and cationic precursors. This review is devoted to physicochemical behavior, complexation ability and catalytic properties of cryogels based on amphoteric macromolecules. Polyampholyte cryogels are able to exhibit the stimuli-responsive behavior and change the structure and morphology in response to temperature, pH of the medium, ionic strength and water⁻organic solvents. Moreover, they can uptake transition metal ions, anionic and cationic dyes, ionic surfactants, polyelectrolytes, proteins, and enzymes through formation of coordination bonds, hydrogen bonds, and electrostatic forces. The catalytic properties of polyampholyte cryogels themselves and with immobilized metal nanoparticles suspended are outlined following hydrolysis, transesterification, hydrogenation and oxidation reactions of various substrates. Application of polyampholyte cryogels as a protein-imprinted matrix for separation and purification of biomacromolecules and for sustained release of proteins is demonstrated. Comparative analysis of the behavior of polyampholyte cryogels with nonionic, anionic and cationic precursors is given together with concluding remarks.

Intra- and Interpolyelectrolyte Complexes of Polyampholytes.

At present, a large amount of research from experimental and theoretical points of view has been done on interpolyelectrolyte complexes formed by electrostatic attractive forces and/or interpolymer complexes stabilized by hydrogen bonds. By contrast, relatively less attention has been given to polymer⁻polymer complex formation with synthetic polyampholytes (PA). In this review the complexation of polyampholytes with polyelectrolytes (PE) is considered from theoretical and application points of view. Formation of intra- and interpolyelectrolyte complexes of random, regular, block, dendritic polyampholytes are outlined. A separate subsection is devoted to amphoteric behavior of interpolyelectrolyte complexes. The realization of the so-called "isoelectric effect" for interpolyelectrolyte complexes of water-soluble polyampholytes, amphoteric hydrogels and cryogels with respect to surfactants, dye molecules, polyelectrolytes and proteins is demonstrated.