Crosslinker Concentration Research Articles

Synthesis and evaluation of cross-linked gelatin nanoparticles for controlled release of an anti-diabetic drug: Gliclazide

The main problem with oral drug delivery using gelatin is rapid dissolution in aqueous mediums, which results in high-speed drug release. In the present study to overcome the challenge, we used glutaraldehyde to cross-link gelatin in order to control the burst release of drug. A drug delivery system based on gelatin nanoparticles (GNPs) for carrying Gliclazide was prepared by a two-step dissolution method. FTIR spectrum showed the presence of an aldimine functional group in GNPs, which confirms that gelatin structure is cross-linked by glutaraldehyde. XRD pattern showed that the crystallinity and crystal size of GNPs were 8% and 73 nm, respectively. SEM images showed the cross-linked structure of GNPs by glutaraldehyde, and DLS analysis exhibited an average particle size of about 88 nm. Ninhydrin assay showed the GNPs completely cross-linked for all ratios of gelatin to cross-linker (8%v/v, 16%v/v, and 25%v/v). After 8 h, the highest and lowest swelling percentages were related to cross-linked samples with 8%v/v and 25%v/v glutaraldehyde (in PBS buffer, pH=7.4, and 37 °C), respectively. The nanoparticle yield and drug loading were optimized via cross-linker concentration and GNPs: GLI ratio. The drug-release behavior from GNPs was controlled by the degree of swelling. The results showed that cross-linked GNPs via 8 %v/v and 25%v/v glutaraldehyde had the highest and lowest GLI release, (70% and 34% after 480 min, respectively, in PBS buffer, pH=7.4, and 37 °C). GLI release from GNPs showed controlled behavior compared with commercial anti-diabetic drugs, including Diabezide 80 mg and Diamicron MR 30 mg. MTT assay results showed that 94.5% of cells in contact with GLI-loaded GNPs survived.

Development and assessment of carboxymethyl tamarind kernel gum-based pH-responsive hydrogel for release of diclofenac sodium

The current research work focuses on the fabrication of carboxymethyl tamarind kernel gum/polyvinylpyrrolidone/polyacrylamide (CMTKG/PVP/PAM) based hydrogel and its loading was done with diclofenac sodium drug (DS) to obtain smart pH-responsive hydrogels. In addition, the effect of concentration of cross-linker- N, N′-methylene bis(acrylamide) (MBA), biopolymer (CMTKG), as well as initiator- potassium persulphate (KPS) on the swelling behavior of smart hydrogel was also analyzed. The synthesized hydrogels were characterized using Scanning Electron Microscopy (SEM), Powder X-ray Diffraction (PXRD), Thermogravimetry Analysis (TGA), and Attenuated Total Reflection-Fourier Transform Infrared spectroscopy (ATR-FTIR). ATR-FTIR confirms the successful formation of hydrogels, while PXRD and SEM indicate the amorphous and porous nature of the polymeric network. The TGA results indicate higher thermal stability for DS-loaded hydrogel than unloaded hydrogel. However, sol–gel analysis shows a rise in gel fraction, with increased concentrations of CMTKG, MBA, and KPS. The swelling ratio as well as the release of DS were found to be higher under slightly alkaline conditions. The result of drug loading and release indicates that PVP increases drug loading (%) and release (%). The drug release behavior of DS-loaded hydrogel follows the Fickian mechanism of diffusion with the Korsmeyer-Peppas model as the best-fitted one. The synthesized DS-loaded CMTKG/PVP/PAM hydrogels could be a promising substitute for prolonged delivery of sparingly soluble DS in pH 7.4.

Weakly Cross-Linked Anionic Copolymers: Kinetics of Swelling and Water-Retaining Properties of Hydrogels.

Six cross-linked copolymers consisting of sodium acrylate, N-acrylamide, starch fragments and a cross-linker were synthesized, potentially suitable for use in agriculture as superabsorbents. The copolymers had the same content of carboxyl groups equal to 6.2 mmoles per 1 g of copolymer and the content of cross-linker (Q) varied from 0.04 up to 1 wt.%. The copolymers swelled in a pH 6.5 aqueous buffer solution thus giving hydrogel particles, which were characterized by a set of methods including gravimetry, rheometry, swelling pressure analysis, equilibrium centrifugation and water retention analysis with the following main conclusions. An increase in Q decreases the equilibrium degree of swelling. When swelling in a solid substrate, sand or soil, the equilibrium degree of swelling shows the maximum at Q = 0.14 wt.%. The cross-linking degree controls the swelling pressure of hydrogels and water-retaining properties of solid substrates with embedded hydrogels; in both cases, the maximum effects are observed at Q = 0.14 wt.%. These extreme dependences set the algorithm for synthesis of polymeric superabsorbents and optimization of their operational characteristics.

Temperature-directed fluorescent switchable nanoparticles based on P3OT–PNIPAM nanogel composite

Poly(N-isopropylacrylamide) (PNIPAM) is a unique stimuli-responsive material that exhibits a lower critical solution temperature (LCST). Owing to this characteristic temperature-dependent behavior, PNIPAM has found extensive utilization as an active material in various applications, including sensors, drug delivery, and cellular imaging. Herein, we demonstrate temperature-directed fluorescent switchable nanoparticles based on poly(3-octylthiophene-2,5-diyl) (P3OT) nanoaggregate-embedded PNIPAM nanogel composites (POPNs) featuring different crosslinker contents. The amount of P3OT loading in the nanogel composites can be gradually controlled by varying the crosslinking density of the PNIPAM matrix; this may be attributable to the efficient entrapment of P3OT nanoaggregates in case of a dense polymeric network with the increase in crosslinking density. POPNs exhibit dramatic temperature-dependent fluorescence enhancement (by a factor of 2.11). This is based on the environmental changes affecting fluorescent P3OT chains at temperatures below and above the LCST of the PNIPAM matrix. Based on this temperature-directed fluorescent switching capability, POPN could find potential applications in various fields, including biomedical imaging and sensors.

Equimolar Polyampholyte Hydrogel Synthesis Strategies with Adaptable Properties.

Polyampholyte hydrogels exhibit great antibacterial and antifouling properties, which make them attractive for biomedical applications, such as drug delivery, wound healing, and tissue engineering. They also have potential applications in food safety, wastewater treatment, and desalination. Since they are based on ionic interactions, polyampholytes are known to require lower amounts of chemical cross-linkers as compared with traditional gels. However, the effects of both chemical and physical interactions on the material's performance are yet to be fully understood and were examined in the present work. Here, four series of equimolar polyampholyte hydrogels were synthesized with anionic (acrylamidomethylpropane sulfonic acid sodium salt) and cationic monomers (acrylamidopropyl-trimethylammonium chloride) along with a cross-linker (N,N'-methylenebisacrylamide). The mechanical and rheological properties of the gels were characterized following changes to the initial monomer concentration and crosslinker ratios, which led to gels with different toughness, stretchability, and compressibility. The direct correlation of the cross-linking degree with the initial monomer concentration showed that the chemical crosslinker could be further reduced at a high monomer concentration of 30% by weight, which creates an inter-chain network at a minimal crosslinker concentration of 0.25%. Lastly, N'N-dimethylacrylamide was added, which resulted in an increase in the number of H-bonds in the structure, noticeably raising material performance.

Self-Healing Redox-Active Coatings Based on Ferrocenyl-Containing Polysiloxanes

The known ferrocenyl-containing silicone materials have redox activity and electrical conductivity at the level of antistatic materials, but they are incapable of self-healing due to their irreversible cross-linking, which significantly reduces their application area. The development of novel self-healing ferrocenyl-containing silicone rubbers (FSRs) is a promising area of research that extends the possibilities of their application as protective coatings. In this work, a new method was developed to synthesize FSRs with different ferrocenyl unit content (25 and 50 mol.%) by anionic copolymerization of cyclic octamethylcyclotetrasiloxane (D4), cyclic tetraferrocenyl-substituted 1,3,5,7-tetramethyltetrasiloxane (Fc4D4), and bicyclic cross-linking agent (bis-D4). The optimal concentrations of the cross-linking agent and ferrocenyl-substituted unit content for FSRs are 5 wt.% and 25 mol.%, respectively. The FSRs exhibit tensile strength and elongation at break up to 0.1 MPa and 215%. The FSRs possess both self-healing at room and/or elevated temperatures (100 °C) and redox activity (Fc/Fc+ transformations at E0 = 0.43 V) and conductivity at the antistatic level (ca. 10−10–10−11 S·cm−1). The thermal properties of the FSRs were studied. The proposed approach is relevant for the creation of new functional silicone materials as flexible, self-healing, and antistatic protective coatings.

Preparation and characterization of red mud/liquid silicon rubber with good thermal‐stability and processability

AbstractAs reported herein, a novel addition‐type liquid silicone rubber (LSR)/red mud (RM) composite has been synthesized. Triethoxyvinylsilane (KH151) was used as a surface modification agent to treat RM and form hydrophobic surfaces. The optimal formulation of the composite was determined by the mechanical properties of the LSR that were prepared at different crosslinker and filler contents. The reinforcement mechanism of modified RM on LSR was revealed by combining Fourier transform infrared (FTIR) spectroscopy, x‐ray photoelectron spectroscopy and mechanical property tests. Thermal degradation behavior of RM/LSR at elevated temperature was investigated by the thermogravimetric analysis (TG), TG‐FTIR and alteration of mechanical properties after thermal aging. The results of the experiment indicate that modified RM increased the tensile strength and Young's modulus of LSR dramatically and provides superior thermal stability to the LSR. With 100 phr RM added, the tensile strength of RM/LSR composite was almost 12 times greater than that of pure LSR, and pure LSR degrades completely after aging at 300°C for 24 h while RM/LSR retains its mechanical properties.

Bioprinting of bioglass-alginate/carboxymethyl cellulose for bone tissue engineering

Bone regenerative medicine requires suitable substitutes that promote osteogenesis. Most of the bio-macromolecular hydrogels are promising because they are biocompatible and biodegradable, but their viscoelastic properties make them challenging to use, especially in 3D bioprinting applications. This study aimed to enhance the mechanical properties of a bone substitute made of bioprinted alginate, carboxymethyl cellulose, and 58S bioglass. We used dual cross-linking and optimized the concentration of cross-linking agents to improve hydrogel biological activity and mechanical stability. The compression test indicated that the combination of Ca2+ and Fe3+ significantly improved the mechanical properties of the alginate/carboxymethyl cellulose hydrogel. The hydrogel crosslinked with 4% Ca2+ and 1.5% Fe3+ showed the highest Young's modulus. The study also found that the hydrogel rigidity influenced cell proliferation capability during bioprinting, as observed in the cell viability results. At day 7, the cell viability of the bioprinted constructs cross-linked with 0.5% and 1% Fe3+ exhibited significant increases. Similarly, these groups also demonstrated the highest alkaline phosphatase (ALP) activity at the same time. Results suggested that cross-linking density and resultant rigidity achieved by optimal concentrations of Fe3+ have very significant effects on cell viability and osteogenesis.

Constriction of Actin Rings by Passive Crosslinkers.

In many organisms, cell division is driven by the constriction of a cytokinetic ring, which consists of actin filaments and crosslinking proteins. While it has long been believed that the constriction is driven by motor proteins, it has recently been discovered that passive crosslinkers that do not turn over fuel are able to generate enough force to constrict actin filament rings. To study the ring constriction dynamics, we develop a model that includes the driving force of crosslinker condensation and the opposing forces of friction and filament bending. We analyze the constriction force as a function of ring topology and crosslinker concentration, and predict forces that are sufficient to constrict an unadorned plasma membrane. Our model also predicts that actin-filament sliding arises from an interplay between filament rotation and crosslinker hopping, producing frictional forces that are low compared with those of crosslinker-mediated microtubule sliding.

Highly swollen ROMP-based gels

The leakage of organic solvent during the transportation and storage is one of the major threats to the environment. Networks/gels acting as the absorbing materials for organic solvents are the most promising solution for the organic solvent pollution. Here, we report the synthesis of highly swollen networks/gels in high yield (≥95%) via ring opening metathesis polymerization (ROMP) using Grubbs’ first generation catalyst/initiator (G1), a crosslinker (1,1′-(methylenedi-4,1-phenylene)bis-exo-7-oxanorbornenecarboximide) and monofunctional monomer/diluent (exo-N-phenyl-7-oxanorbornenecarboximide). The mesh size of the network was varied by keeping the concentration of monomer constant while changing the concentrations of crosslinker and G1 (initiator). The swelling capacity of the network in N,N-dimethylformamide (DMF) solvent increased from 41 to 53 and to 61 with the increase of theoretical mesh size (molar ratio of monomer to crosslinker) from 20 to 40 and to 60, respectively. By further increasing the mesh size from 60 to 80 there was no significant change in swelling capacities (63). Thus, the gel with the mesh size of 60 was selected for swelling capacity analysis in other polar organic solvents such as dimethyl sulfoxide (DMSO), dichloromethane (DCM), chloroform and lithium-ion battery electrolyte solution (1.0 M LiPF6 in ethylene carbonate (EC)/diethyl carbonate (DEC) = 50/50 (v/v)). They showed the decreased swelling capacity value from 61 to 57, 40, 31 and 5, respectively. For a controlled mesh size ROMP-based gel, we observed the highest swelling capacity values to date.

Flexible Topical Hydrogel Patch Loaded with Antimicrobial Drug for Accelerated Wound Healing.

A hydrogel topical patch of neomycin was developed by using sodium alginate (SA) and hydroxyethylcellulose (HEC) as polymers. Free radical polymerization in an aqueous medium was initiated by using acrylic acid (AA) and N,N'-methylenebisacrylamide (MBA). Prepared hydrogels were characterized for pH sensitivity and sol-gel analysis. In addition, the effect of reactant contents on the developed formulation was evaluated by swelling behavior. SEM assay showed the rough structure of the hydrogel-based polymeric matrix, which directly enhances the ability to uptake fluid. FTIR spectra revealed the formation of a new polymeric network between reactant contents. TGA and DSC verified that fabricated polymeric patches were more thermodynamically stable than pure components. Gel fractions increased with increases in polymer, monomer, and cross-linker contents. The swelling study showed the pH-dependent swelling behavior of patches at pH 5.5, 6.5, and 7.4. The release pattern of the drug followed zero-order kinetics, with diffusion-controlled drug release patterns according to the Korsmeyer-Peppas (KP) model. Ex vivo studies across excised rabbit skin verified the drug retention in the skin layers. The hydrogel patch effectively healed the wounds produced on the rabbit skin, whereas the formulation showed no sign of irritation on intact skin. Therefore, neomycin hydrogel patches can be a potential candidate for controlled delivery for efficient wound healing.

Some problem questions in studying the properties of dynamically vulcanized polymer systems based on ethylene/1-hexene copolymer and nitrile butadiene rubber

The article presents the results of a study of the influence of the type and concentration of nitrile butadiene rubber on the main physical and mechanical properties of polymer compositions based on compatibilized ethylene/1-hexene copolymer (EHC*). SKN-18, SKN-26, and SKN-40 were used as nitrile butadiene rubber. The compatibilizer – polyethylene-graft-methacrylic acid was used to improve the compatibility of the mixed components of the mixture. At the first stage, the task of the study was to investigate the effect of the concentration of the considered nitrile rubbers on such properties of the compositions as yield strength, tensile strength, elongation at break, flexural strength, melt flow rate and heat resistance. It was found that, regardless of the type of used nitrile butadiene rubber, with an increase in its content in the composition of the ethylene/1-hexene copolymer, a regular decrease in strength parameters, heat resistance, and melt fluidity is observed. It is shown that with the loading of 30 wt% SKN-18 or 40 wt% SKN-26 and SKN-40 into the composition of the ethylene/1-hexene copolymer phase inversion occurs in the composite materials, according to which the dispersed phase becomes a dispersed medium. The thermomechanical properties of the considered samples were studied. It was found that in those samples in which phase inversion occurred, a region of a highly elastic plateau is formed, which increases with an increase in the content of the rubber component. This area indicates the formation of elastomer with rubber properties. The regularities of crystallization of the compositions depending on the content of the amorphous component were studied by the method of stepwise dilatometry. The mechanism of crystal formation was studied depending on the content of the amorphous component. The influence of the crosslinking agent concentration – dicumyl peroxide on the main properties of dynamically vulcanized elastomers has been studied.

The Role of Crosslinker Content of Positively Charged NIPAM Nanogels on the In Vivo Toxicity in Zebrafish.

Polymeric nanogels as drug delivery systems offer great advantages, such as high encapsulation capacity and easily tailored formulations; however, data on biocompatibility are still limited. We synthesized N-isopropylacrylamide nanogels, with crosslinker content between 5 and 20 mol%, functionalized with different positively charged co-monomers, and investigated the in vivo toxicity in zebrafish. Our results show that the chemical structure of the basic unit impacts the toxicity profile depending on the degree of ionization and hydrogen bonding capability. When the degree of crosslinking of the polymer was altered, from 5 mol% to 20 mol%, the distribution of the positively charged monomer 2-tert-butylaminoethyl methacrylate was significantly altered, leading to higher surface charges for the more rigid nanogels (20 mol% crosslinker), which resulted in >80% survival rate (48 h, up to 0.5 mg/mL), while the more flexible polymers (5 mol% crosslinker) led to 0% survival rate (48 h, up to 0.5 mg/mL). These data show the importance of tailoring both chemical composition and rigidity of the formulation to minimize toxicity and demonstrate that using surface charge data to guide the design of nanogels for drug delivery may be insufficient.

Development of chitosan-graphene oxide blend nanoparticles for controlled flurbiprofen delivery

The use of natural polymeric nanoparticles (Nps) as drug carriers is a highly promising area of research in the field of drug delivery systems because of their high efficiency. In this study, flurbiprofen (FB) loaded chitosan-graphene oxide (CS-GO) blend Nps were synthesized as a controlled delivery system using the emulsion method. The crystalline, molecular, and morphological structures of the prepared CS-GO Nps were characterized using a variety of analytical methods, including Fourier transform infrared (FT-IR) spectroscopy, differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), X-Ray diffractometry (XRD), scanning electron microscopy (SEM), and atomic force microscopy (AFM). It was found that the introduction of GO into the CS nanoparticle formulation increased its thermal stability. The range of the average particle size was between 362 ± 5.06 and 718 ± 2.21 nm, with negative zeta potential values between −7.67 ± 4.16 and − 27.93 ± 2.26 mV. The effects of the CS/GO ratio, the FB/polymer ratio, the amount of span 80, and the cross-linker concentration were assessed on FB release profiles. In vitro release studies displayed a two-stage release behaviour with a fast initial release of the FB, followed by sustained and extended release, and the incorporation of GO into the CS Nps made the FB release more sustained and controlled manner. Besides, the cytotoxicity test of the FB-loaded CS-GO Nps was studied through MTT assay, and it was found that they were biocompatible. Based on these findings, it can be inferred that the prepared CS-GO Nps might be a promising candidate drug carrier system for FB.

Aqueous polyacrylate latex nanodispersions used as consolidation agents to improve mechanical properties of Prague sandstone

This investigation aims at assessing the potential of polyacrylate latex nanodispersions as consolidation agents for sandstones. Four different latex types, implementing polymer fluorination and chemical crosslinking, have been synthesized at the scope and fully characterized. The Prague sandstone employed in this study has been selected as an example of highly porous stones used as building materials for many historical monuments. Two different concentration levels of nanodispersions have been adopted. The consolidated stone samples have been tested using a combination of physical-mechanical tests and microscopic observations. Compared to the non-treated samples, significant increments of mechanical properties (e.g. up to 3.3 times higher bending strength) have been detected after the consolidation treatment with concentrated products. Moreover, when 10 times diluted latex nanodispersions have been applied, the improvement of mechanical properties has still been significant, while moisture transport properties, such as water absorption, have been found to be comparable with those of the untreated sample. Fluorinated polymers imparted better hydrophobic properties with a contact angle above 100°. Observations using a scanning electron microscope revealed the good filling and bridging capacity of the applied consolidation agents. As demonstrated, by acting on the polymer structure, that is, by tuning the degree of crosslinking, polymer fluorination and gel content, the properties of these novel polyacrylate latex nanodispersions can be tailored to the specific stone and type of decay in order to improve the effectiveness of the treatments and obtain the desired final properties. The flexibility of their chemistry offers new opportunities for preserving objects of cultural heritage that are also at risk due to the ongoing climate change.

Galactose-functionalized injectable thermosensitive microgels for target specific uptake in hepatoma cells.

Microgels acts as a potential candidate for responsive composite materials, which has been favored by scientists because of its excellent colloid stability, easy integration, and most of their surface area can be used as support after modification. Specififically, microgels are fascinating capable of maintaining good biocompatibility and controlled-release in vivo and making the possible for applications in biomaterials and biomedicines. Besides, in the process of microgel synthesis, some targeting factors can be combined to achieve the purpose of cell targeting and uptake. Therefore, how to fundamentally design microgels is an urgent problem to be solved. In this study, we design and synthesize an injectable microgel P(DEGMA-co-OVNGal) that is made of 2-methyl-2-acrylate-2-(2-methoxy ethoxy) ethyl ester (DEGMA) and glycopolymer (OVNGal) that is thermoresponsive and contains galactose. When the content of crosslinking agent is regulated, the microgel will realize the transformation from sol to gel at the temperature around human body, causing the controlled release of the loaded drugs. With the increase of crosslinker content from 1% to 7%, the appearance of microgel changed from loose and ordered to compact and hard morphology, the swelling ratio of microgel decreased from 187% to 142%, and the phase volume transition temperature decreased from 29.2°C to 28°C. The results indicated that when the monomer ratio (DEGMA: OVNGal) increased from 2:1 to 40:1 with the amount of crosslinking agent at 1%, the particle size of microgel increased from 460nm to 660nm. In vitro released studies confirmed that the cumulative released DOX (doxorubicin, as a selected model drug) from the microgel can reach 50% after 7days. Furthermore, in vitro experiments demonstrated that the injectable microgel P(DEGMA-co-OVNGal) can target HepG2 cells effectively and meantime dispalys excellent biocompatibility. Therefore, the injected microgels based on P(DEGMA-co-OVNGal) have the potential to serve as a robust and promising drug delivery carrier for targeted cancer therapy.

Designing bilayered composite films by direct agar/chitosan and citric acid-crosslinked PVA/agar layer-by-layer casting for packaging applications

Packaging is a crucial tool for reducing food waste and enhancing product competitiveness. Fossil fuel-based plastics, mostly used for food packaging, account for nearly 40% of global plastic waste. To address this issue, this study developed a layer-by-layer casting technique to create novel bilayered plastic composites with distinct agar/chitosan and PVA/agar layers. Film's properties, such as thickness, plasticity, and tensile strength, were affected by adjusting the volume of the layers. The elongation at break was positively related to the presence of citric acid (up to 30 wt%) as a crosslinker. The chitosan-rich first layer provided better UV-light blocking potential and opacity, which were beneficial in the prevention of lipid oxidation. Increasing the second layer by 40–60% substantially reduced the light absorption, while the colors were proportional to the citric acid content. The FT-IR band at 1713 cm−1 indicated an increase in C=O ester groups with crosslinker content. The hydrophobicity of the films was enhanced by the chitosan-rich layer. XRD supported intramolecular and intermolecular hydrogen bonding, whereas the micrographs revealed tightly bound structure between layers. The results corroborated that the inclusion of agar in the formulations increased the stability of the film, making it ideal for various packaging applications.

Impact of composition and salinity on swelling and gel strength of poly (acrylamide-co-acrylic acid) preformed particle gel

The effects of various material compositions and reservoir environments on the ultimate strength and swelling kinetics of a commercial preformed particle gel (PPG) have been investigated. This study used different ratios of acrylamide and acrylic acid copolymers with a specific crosslinker concentration. Results have indicated that increasing the acrylic acid proportion enhances the PPGs’ ability to swell but weakens their network structure. In contrast, increasing the crosslinker content decreases the swelling ratio and increases the gel strength. The highest equilibrium swelling capacity among the six preformed particle gel samples was obtained for PPG2, which has the highest acrylic acid amount and the lowest crosslinker content, with a swelling ratio of 2400 g/g in deionized water and 59.8 g/g in brine 1 (67535.8 mg/l). On the contrary, PPG5, with the lowest acrylic acid and highest crosslinker content, has a swelling capacity of 239 g/g and more than 17 g/g in distilled and brine 1, respectively. Yet, PPG5 has the highest swollen gel strength of 615.5 Pa in deionized water and 3344 Pa in brine 1. The PPGs’ swelling ratios showed stepwise improvements along with increasing temperature, notably after 50 °C, yet, the storage modulus (G′) was negatively affected. The PPGs revealed the highest swelling behavior in pH 6–8, decreasing dramatically in more acidic and basic conditions. The swelling ratios of the PPGs in brine 1 at 50 °C were between 12 and 32 g/g, having strengths in the range of 566–5508 Pa, depending on the crosslinker ratio. The PPGs also demonstrated the ability to compete with other commercial PPGs as they have shown physical and thermal stability when aging at 50 °C, specifically those with high crosslinker content (PPG5).

Rheological properties of cross-linked inulin solutions as a function of cross-linker concentration and temperature

The purpose of this study is to determine the rheological properties of cross-linked inulin solutions in two different polymerization degrees (native and degree of polymerization of >23%). Thus, the effect of cross-linking, a new approach applied to support a specific property (stabilization) of inulin, which has many benefits, has been demonstrated. Sodium hexametaphosphate was used as a cross-linking agent at three different ratios (0.375%, 0.500%, and 0.750%). The cross-linked inulin solutions were lyophilized, and the lyophilized mixture was then reconstituted at 25 °C and 45 °C to obtain cross-linked inulin solutions with 1% and 5% (w/v) concentrations. The control samples (native and with a high degree of polymerization) were treated similarly without a cross-linking agent. The samples were subjected to a dynamic frequency sweep test in the range of 0.01–10 Hz as well as shear viscosity measurements at 1–500/s shear rates for the determination of rheological properties. The thixotropic curves were analyzed as the shear rate increased from 0.1/s to 300/s in the first 120 s (up curve), and then decreased to the same point in the subsequent 120 s. Results indicated that cross-linking increased inulin solution viscosity, particularly at 5% concentration, and solubility. Solutions with 5% inulin containing 0.750% and 0.375% cross-linker yielded the highest viscosities at 45 °C and 25 °C, respectively. Samples with 5% inulin concentration exhibited solid-like behavior in the oscillation test. Thixotropic curves revealed antithixotropy at low shear rates and thixotropy at high shear rates. The study demonstrated the impact of cross-linking on inulin stabilization, providing insights for future applications. Results indicated that cross-linking increased inulin solution viscosity, particularly at 5% concentration, and solubility. Solutions with 5% inulin containing 0.750% and 0.375% cross-linker yielded the highest viscosities at 45 °C and 25 °C, respectively. Samples with 5% inulin concentration exhibited solid-like behavior in the oscillation test. Thixotropic curves revealed antithixotropy at low shear rates and thixotropy at high shear rates. The study demonstrated the impact of cross-linking on inulin stabilization, providing insights for future applications.

Modified Sulfanilamide Release from Intelligent Poly(N-isopropylacrylamide) Hydrogels.

The aim of this study was to examine homopolymeric poly(N-isopropylacrylamide), p(NIPAM), hydrogels cross-linked with ethylene glycol dimethacrylate as carriers for sulfanilamide. Using FTIR, XRD and SEM methods, structural characterization of synthesized hydrogels before and after sulfanilamide incorporation was performed. The residual reactants content was analyzed using the HPLC method. The swelling behavior of p(NIPAM) hydrogels of different crosslinking degrees was monitored in relation to the temperature and pH values of the surrounding medium. The effect of temperature, pH, and crosslinker content on the sulfanilamide release from hydrogels was also examined. The results of the FTIR, XRD, and SEM analysis showed that sulfanilamide is incorporated into the p(NIPAM) hydrogels. The swelling of p(NIPAM) hydrogels depended on the temperature and crosslinker content while pH had no significant effect. The sulfanilamide loading efficiency increased with increasing hydrogel crosslinking degree, ranging from 87.36% to 95.29%. The sulfanilamide release from hydrogels was consistent with the swelling results-the increase of crosslinker content reduced the amount of released sulfanilamide. After 24 h, 73.3-93.5% of incorporated sulfanilamide was released from the hydrogels. Considering the thermosensitivity of hydrogels, volume phase transition temperature close to the physiological temperature, and the satisfactory results achieved for sulfanilamide incorporation and release, it can be concluded that p(NIPAM) based hydrogels are promising carriers for sulfanilamide.