Radiation-induced Crosslinking Research Articles

Mechanically Excellent, Notch-Insensitive, and Highly Conductive Double-Network Hydrogel for Flexible Strain Sensor.

A novel double-network conductive hydrogel based on lithium acetate/gelatin/polyacrylamide (PAAM) was synthesized by heating-cooling and subsequent γ-ray radiation-induced polymerization and cross-linking. Owing to the hydrogen bonding interaction between lithium acetate, physical cross-linked gelatin, and chemical cross-linked PAAM, the resultant hydrogel exhibited high tensile strength (1260 kPa), high ionic conductivity (35.2 mS cm-1), notch-insensitivity (tensile strength 415 kPa, elongation at break 872% with transverse notch), and extensive strain monitoring range (0.15-800%) under optimum conditions. The lithium acetate/gelatin/polyacrylamide hydrogel strain sensor attached to the skin can sensitively monitor the subtle movements of the human body. The strain sensor based on the resultant hydrogel with transverse notch can still work for 1200 cycles, due to that the covalent-cross-linked PAAm chain bridges the cracks and stabilizes the deformation, while the physical-cross-linked gelatin was unzipped to make the blunting of notch. The conductive hydrogel with high-sensitivity and high stability is expected to be used as materials for the preparation of flexible strain sensors in the future.

Gamma-ray irradiation to achieve high tensile performance of unidirectional CNT yarn laminates

Continuous carbon nanotube (CNT) yarn fabricated from a floating catalyst chemical vapor deposition (FCCVD) method is treated under gamma-ray irradiation to enhance the mechanical properties of the CNT yarn and its unidirectional composite laminates. Gammy-ray doses varying from 50 kGy to 1200 kGy are used to irradiate CNT yarns and their microstructures, tensile properties and surface characterizations are studied. The graphitic structure change is not clear from the transmission electron microscopy, however, the specific tensile strength and modulus of yarn vary slightly within 10 % as the dose increased. This modulus trend coincides with mesoscopic distinct element modeling (mDEM) simulation results. Surface characterization shows additional oxygen functional groups and smaller contact angles after irradiation. Interestingly, the specific tensile properties of composite laminates also increase relative to the yarns, and the unidirectional laminate from CNT yarn treated with the optimal dose of 700 kGy achieves specific strength and modulus as high as 1.89 GPa/gcm−3 and 258 GPa/gcm−3, respectively, which are 30.9 % and 37 % increases compared to the control laminate. The results indicate that radiation-induced crosslinking among the CNTs and the formation of surface-active sites leads to enhanced load transfer in the yarns and promote CNT/resin interfacial bonding.

Removal of Astrazon Red Dye from Wastewater using Eggshell/Graphene Oxide Embed in (Gum Acacia/Acrylamide) Hydrogel Nanocomposites Synthesized by Gamma Irradiation

This research aimed to use a low-cost, environmentally friendly adsorbent to eliminate the cationic dye Astrazon red 6B (AR) from an aqueous system. For this rationale, a nanocomposite hydrogel made of (Gum Acacia/Acrylamide)-calcinated Eggshell/Graphene oxide (GA/AAm)-ES/GO was created using Gamma radiation-induced copolymerization and cross-linking. FT-IR, XRD, EDX mapping, SEM, TGA and TEM were used to investigate the structures and properties. The nanocomposites exhibited superior adsorption behavior towards AR. Because of the dual effect of ES and GO, mixing ES with GO in (GA/AAm)-ES/GO nanocomposite hydrogel improved its adsorption capability. It was obtained that the optimum initial pH was 9 and the equilibrium contact time was 480 min. The removal percentage was enhanced by increasing the initial dye concentration. A little removal effectiveness was observed by increasing the adsorbent weight from 5.0 to 10.0 g for each liter of the dye solution. The Langmuir isotherm was found to be more suitable for analyzing the adsorption isotherm the maximal monolayer dye adsorption capacity (qmax) was 313.3 mg/g. The pseudo-second-order adsorption kinetics fitted the data well, and the rate constant was predicted to be (0.108 10–3) g mg−1 min−1. ∆H° values are negative at all investigated initial concentrations for (GA/AAm)-ES and (GA/AAm)-ES/GO. The values of ∆S° are negative for (GA/AAm)-ES/GO, while values for (GA/AAm) and (GA/AAm)-ES are positive. ∆G° are negative values for all systems that refer to the spontaneity of the adsorption process. High efficiency was observed for (GA/AAm)-ES/GO up to three rounds of reuse, while a drop in efficiency of the fourth round to 58.78%.Graphical

Dextran Methacrylate Reactions with Hydroxyl Radicals and Hydrated Electrons in Water: A Kinetic Study Using Pulse Radiolysis.

Dextran methacrylate (Dex-MA) is a biodegradable polysaccharide derivative that can be cross-linked by ionizing radiation. It is therefore considered a potential replacement for synthetic hydrophilic polymers in current radiation technologies used for synthesizing hydrophilic cross-linked polymer structures such as hydrogels, mainly for medical applications. This work is focused on the initial steps of radiation-induced cross-linking polymerization of Dex-MA in water. Rate constants of two major transient water radiolysis products-hydroxyl radicals (•OH) and hydrated electrons (eaq-)-with various samples of Dex-MA (based on 6-500 kDa dextrans of molar degree of substitution or DS with methacrylate groups up to 0.66) as well as non-substituted dextran were determined by pulse radiolysis with spectrophotometric detection. It has been demonstrated that these rate constants depend on both the molecular weight and DS; reasons for these effects are discussed and reaction mechanisms are proposed. Selected spectral data of the transient species formed by •OH- and eaq--induced reactions are used to support the discussion. The kinetic data obtained in this work and their interpretation are expected to be useful for controlled synthesis of polysaccharide-based hydrogels and nanogels of predefined structure and properties.

Optimization of thermoresponsive hydrogels based on oligomers with lower critical solution temperature (LCST) far below/above physiological temperatures for biomedical applications

Hydrogels with oligo(ethylene glycol) (OEG), oligo(propylene glycol) (OPG), and for the first time with combined OEG/OPG pendant chains within the methacrylate (MA) network, were synthesized and the swelling behavior, thermal properties, microstructure, and genotoxicity were investigated. Prior to hydrogel fabrication, an optimized method was developed for oligo(propylene glycol) methacrylate (OPGMA), i.e., oligomer with an LCST below a temperature at which synthesis occurs, indicating that proper preparation and tuning of reaction conditions were required. PEG6MA and PPG5MA homopolymers, as well as P(EG6/PG5)MA copolymer hydrogel, were produced by gamma radiation-induced polymerization and crosslinking of OEG and OPG monomers from the monomer-solvent mixture by using different water/ethanol composition as a solvent and by exposing the reaction mixture to various radiation doses. The combination of OEG and OPG pendant chains within the same network was advantageous in that it allowed an easy tuning of the phase transition temperature. Thus, the volume phase transition (VPT) at temperatures above 70 °C observed in the case of PEG6MA, and in the case of PPG5MA at temperatures below 15 °C, could easily be tuned close to physiological temperatures for P(EG6/PG5)MA hydrogel. Finally, all obtained thermoresponsive hydrogels showed non-genotoxic and non-cytotoxic properties, which indicate promising potential for biomedical applications.

Characterization of Biodegradable Food Contact Materials under Gamma-Radiation Treatment.

Radiation is an example of one of the techniques used for pasteurization and sterilization in various packaging systems. There is a high demand for the evaluation of the possible degradation of new composites, especially based on natural raw materials. The results of experimental research that evaluated the impact of radiation technology on biodegradable and compostable packaging materials up to 40 kGy have been presented. Two commercially available flexible composite films based on aliphatic-aromatic copolyesters (AA) were selected for the study, including one film with chitosan and starch (AA-CH-S) and the other with thermoplastic starch (AA-S). The materials were subjected to the influence of ionizing radiation from 10 to 40 kGy and then tests were carried out to check their usability as packaging material for the food industry. The results showed that the mechanical properties of AA-S films improved due to the radiation-induced cross-linking processes, while in the case of AA-CH-S films, a considerable decrease in the elongation at break was observed. The results also showed a decrease in the WVTR in the case of AA-S and no changes in barrier properties in the case of AA-CH-S. Both materials revealed no changes in the odor analyzed by sensory analysis. In the case of the AA-S films, the higher the radiation dose, the faster the biodegradation rate. In the case of the AA-CH-S film, the radiation did not affect biodegradation. The performed research enables the evaluation of the materials intended for direct contact with food. AA-CH-S was associated with unsatisfactory parameters (exceeding the overall migration limit and revealing color change during storage) while AA-S showed compliance at the level of tests carried out. The study showed that the AA-CH-S composite did not show a synergistic effect due to the presence of chitosan.

Short nylon tire cord and gamma irradiation impact on SBR/ultrasonic and mechanochemical devulcanized rubber blends

Abstract Devulcanization of discarded tire rubber (WR) has remained of prior attention to numerous researchers, aiming for unlimited commercial profits upon modification, especially to serve as a substituent for virgin rubber. In this concern, composites of styrene butadiene rubber (SBR) and devulcanized waste rubber, developed via two techniques: mechanochemical (DRm) and ultrasonic (DRus), and reinforced with short nylon tire cord (SNF), namely at a filling ratio of 3 and 5 phr were fabricated. All prepared specimens were exposed to various gamma radiation doses, namely 50, 100, and 150 kGy. The post-radiation characterization was investigated by FTIR and SEM techniques. Radiation-induced crosslinking density of the polymer composites was calculated and correlated with the different mechanical features. Furthermore, the TGA technique and activation energy measurement were implemented in studying the thermal behavior of the products. Incorporation of 5 phr SNF set out the thermal stability order: SBR/DRm/5 SNF > SBR/DRus/5 SNF > SBR/5 SNF. Ionizing irradiation of all composite–SNF formulations derived to a marked improvement in TS data as a result of creating further crosslinking within the polymeric matrix, reaching a maximum by the integral dose 150 kGy. The results were appreciably compared to a recently published study that applied reinforced tire fiber with polyester, as another cord utilized in the manufacture of tires. It is found that TS data observed by irradiation with 150 kGy of SBR/3 SNF, SBR/DRm/3 SNF, and SBR/DRus/3 SNF are respectively as follows: 3.7, 2.5, and 2.4 MPa, whereas the corresponding reported values for PTC reinforced counterpart blends were: 2, 1.7 and 1.8 MPa. Similarly, the TS respective values of SBR/5 SNF, SBR/DRm/5 SNF and SBR/DRus are 2.5, 1.9, and 2.2 MPa, whereas their counterparts reinforced with 5 phr PTC recorded 1.6, 1.8, and 1.2 MPa. SNF-reinforced SBR, SBR/DRm, and SBR/DRus were superior in their properties to PTC-reinforced counterpart specimens.

Ionizing radiation induces cross-linking of two noncovalently bound collagen mimetic peptide triple helices in the absence of a molecular environment.

Cross-linking is a fundamental molecular process that is highly important for many applications, in particular, to tune the properties of collagen-based biomaterials. Chemical reagents, the action of enzymes or physical factors such as heat or radiation can facilitate collagen cross-linking. Ionizing radiation has the advantages of being fast, efficient and free from potentially toxic reagents. Collagen cross-linking by ionizing radiation is thought to occur via a water-mediated pathway. In the past, synthesized collagen mimetic peptides have proven to be of great value for understanding the influence of the amino acid sequence on the stability of tertiary (fibrous) as well as secondary (triple helical) structures of collagen. Cross-linking of synthetic collagen mimetic peptides is often used for modifying the properties of biomaterials. In this work, for the first time, we apply radiation-induced cross-linking to synthetic collagen mimetic peptides and present an experimental and theoretical study of peptide hexamers consisting of two noncovalently bound triple helices in the absence of a molecular environment, i.e. in the gas phase. Our results show that X-ray photoabsorption of the hydroxylated hexamer leads to ionization and cross-linking of the two triple helices: thus, we found evidence that cross-linking can be achieved by ionizing radiation, without the presence of any reagent or water. We propose a cross-linking mechanism involving the creation of two radicals on hydroxyproline side-chains and their recombination, ultimately leading to covalent bond formation between the triple helices.

Dual Stimuli-Responsive Polysaccharide Hydrogels Manufactured by Radiation Technique

This paper describes the results of the radiation-induced crosslinking of polysaccharides modified with hydroxypropyl and carboxymethyl functional groups, hydroxypropylcellulose (HPC) and carboxymethylcellulose (CMC), respectively, without and with poly(ethylene glycol) diacrylate (PEGDA) as a crosslinking agent, to obtain dual stimuli-responsive hydrogels. The gels were characterized in terms of water uptake and gel fraction, parameters that mainly depend on the HPC–CMC compositions, but also on the macromer crosslinker content and the absorbed dose. The swelling of hydrogels is controlled by both the temperature, due to the amphiphilic character of HPC and pH, due to the anionic functional groups of CMC. In spite of a similar degree of substitution in both cellulose derivatives, 1.4 for HPC and 1.2 for CMC, the pH response of hydrogels with an equal content of both polysaccharides is considerably higher—a reduction in swelling of up to 95% with a decrease in the pH to 2 was recorded—than the response to thermal-stimulus—wherein a reduction in swelling of less than 70% with an increasing in temperature to 55 °C was found. These biopolymers-based hydrogels of specific, stimuli-responsive swelling properties are anticipated in applications where a combination of two stimuli is essential and biodegradation may be required.

P(HMA-co-ATU) hydrogel synthesis via gamma radiation and its use for in situ metal nanoparticle preparation and as catalyst in 4-nitrophenol reduction

Hydrogels with reactive thiourea functional groups were prepared by radiation-induced crosslinking of N-(Hydroxymethyl) acrylamide (HMA) and N-allyl thiourea (ATU) at different ATU content and irradiation doses. P(HMA-co-ATU) hydrogels were then utilized as template for in situ metal nanoparticle (MNP) preparation by the reduction of Ni2+, Co2+, and Cu2+ ions within the hydrogel matrix using sodium borohydride (NaBH4) as reducing agent. These MNP@p(HMA-co-ATU) hydrogel composites (MNP = Co, Ni, and Cu) were further used as catalysts in the reduction reaction of 4-nitrophenol (4-NP) to 4-aminophenol (AP). Various parameters such as the effect of ATU content, the total dose used in the hydrogel preparation, MNPs type, and temperature on the catalytic activity of hydrogel composites were investigated. The activation energy, enthalpy, and entropy of Ni@p(HMA-co-ATU) hydrogels for the reduction reaction of 4-NP to 4-AP were calculated as 42.5 kJ mol−1, 38.9 kJ mol−1, and −187.3 J mol−1 K−1, respectively.

Effect of irradiation on poly(acrylic acid)-polyethyleneimine interpolyelectrolyte complexes: An electron paramagnetic resonance study

The interpolyelectrolyte complexes (IPECs) are widely used for various applications, ranging from agriculture and medicine to advanced technological processes. In many cases, they are subjected to the action of ionizing radiation or hard UV light, either intentionally (e.g., for fabrication of nanocomposites) or in the course of routine treatment (sterilization or weathering), or unexpected accidents. In this communication, we report the first preliminary results on the effect of ionizing radiation on the poly(acrylic acid) (PAA) – polyethyleneimine (PEI) complexes and their components as revealed by EPR spectroscopic studies. The obtained results clearly reveal that the yield of primary radicals trapped after irradiation is comparable in all the studied systems and the main processes are decarboxylation in the PAA moiety and proton loss in the PEI moiety. There are no evidences for main-chain scission, which might lead to the degradation of material properties (at least, at moderate doses), instead of this, the radiation-induced crosslinking looks plausible. Generally, it provides a positive forecast for the radiation resistance of such complexes.

Gamma Radiation Processed Polymeric Materials for High Performance Applications: A Review.

The polymeric properties are tailored and enhanced by high energy radiation processing, which is an effective technique to tune the physical, chemical, thermal, surface, and structural properties of the various thermoplastic and elastomeric polymeric components. The gamma and electron beam radiation are the most frequent radiation techniques used for crosslinking, compatibilizing, and grafting of various polymer blends and composites systems. The gamma radiation-induced grafting and crosslinking are the effective, rapid, clean, user-friendly, and well-controlled techniques for the polymeric materials for their properties improvement for high performance applications such as nuclear, automobile, electrical insulation, ink curing, surface modification, food packaging, medical, sterilization, and health-care in a different environment. Similarly, electron beam radiations crosslinking has been a well-known technique for properties development and has economic benefits over chemical crosslinking techniques. This review focuses on the development of polymeric multi component systems (functionalized polymer, blends, and nanohybrids), where partially nanoscale clay incorporation can achieve the desired properties, and partially by controlled high energy radiations crosslinking of blends and nanocomposites. In this review, various investigations have been studied on the development and modifications of polymeric systems, and controlled dose gamma radiation processed the polymer blends and clay-induced composites. Radiation induced grafting of the various monomers on the polymer backbone has been focused. Similarly, comparative studies of gamma and electron beam radiation and their effect on property devlopment have been focused. The high energy radiation modified polymers have been used in several high performance sectors, including automotive, wire and cable insulation, heat shrinkable tube, sterilization, biomedical, nuclear and space applications.

Effect of oxygen on the radiation of silicone rubber determined by gaseous chromatograph and DFT calculation

The radiation effects of silicone rubber under different atmospheres are of great significance to evaluate the aging behavior of materials, and to assess their practical application life. The radiation-induced cross-linking and degradation of polydimethylsiloxane rubber were confirmed firstly by 1H NMR and high-temperature GPC, respectively. By using the established gas collecting system and gaseous chromatography method, we systematically investigated the gaseous products of irradiated silicone rubber at different oxygen concentrations. With the increase of oxygen concentration, the yield of CH4 decreases sharply, while the yield of hydrogen changes slightly. It can be further demonstrated that the reduction of CH4 concentration in the irradiated silicone rubber system is mainly due to the inhibition of CH4 formation, instead of the CH4 degradation, indicating that oxygen directly influences the conversion process of methyl radicals. Similarly, by monitoring the oxygen consumption, it is proved that oxygen is directly involved in the degradation process of silicone rubber, and oxygen scavenged the methyl radicals, which supressed the conversion process of methyl radicals to CH4. Finally, the radiation-induced crosslinking and degradation mechanism of raw silicone rubber was deduced by combining the gaseous products analysis and DFT calculation. It is demonstrated that the release of CH4 can be used to assess the radiation effect of silicone rubber. This work provides a novel method to understand deeply the radiation-induced crosslinking and degradation mechanism of silicone rubber under different atmospheres.

Mechanical properties, thermal stability and microstructure evolution of carbon fiber-reinforced epoxy composites exposed to high-dose γ-rays

Carbon fiber-reinforced composites with superior strength-to-weight and stiffness-to-weight ratio were highly resistant to ionizing radiation, which make them popular in nuclear reactor. There were large doses of γ-radiation in nuclear reactor, which caused damage in composites. In order to investigate effect of high γ-ray absorbed dose on carbon fiber (CF)/epoxy (EP) composite, the doses of 2 MGy, 7 MGy, and 20 MGy were applied in irradiating the samples, and the mechanical properties, thermal stability and microstructural changes of composites were analyzed. The results showed that under the absorbed dose of 2 MGy, the storage modulus, flexural strength and thermal stability of CF/EP composites increased. However, those properties decreased while the dose increased to 7 MGy and further decreased while the dose rise to 20 MGy. The evolution mechanism was understood by analyzing free radical and composition change of CF/EP after irradiation via electron spin resonance and X-ray photoelectron spectroscopy. Irradiation results in bond-breaking such as C–C bond and C–H bond, and also new bond-forming like C–O and CO, which forms competition effects among radiation-induced degradation and cross-linking reaction.

Development of carboxymethyl cellulose/gelatin hybrid hydrogels via radiation-induced cross-linking as novel anti-adhesion barriers

Adhesion after abdominal and pelvic surgery results in severe clinical outcomes and a negative impact on the quality of life of a patient. Implanting barrier materials is a common strategy for preventing postoperative adhesion, and non-adhesive carboxymethylcellulose (CMC) is a widely used material for such purpose. Herein, we present CMC/gelatin (CMC/G) hybrid hydrogels as novel barrier materials that aim to reduce the foreign body response (FBR) by combining the biocompatibility and biodegradability of gelatin and the non-adhesiveness of CMC and by realizing mechanical matching with the host tissue. The hydrogels were prepared by the simple reagent-free γ-ray irradiation-induced cross-linking of CMC and gelatin. The hydrogel composition was controlled by varying the initial mixing ratio. The gelatin fraction provided enzyme-mediated degradability at a content ≥ 40%, and the degradation rate was controlled by the radiation dose. The compressive moduli of the hydrogels were tuned to be identical to that of target abdominal organs (several tens of kPa) via 10–30 kGy radiation. The hydrogels sufficiently prevented adhesion of 3T3-Swiss fibroblast cells owing to the non-adhesive capability of CMC which surpassed the high cell adhesiveness of gelatin in the hydrogels. On the other hand, the added gelatin significantly improved the viability of the few cells that adhered to the hydrogels. We found that hydrogels composed of 60% CMC and 40% gelatin exhibited significantly higher cell viabilities while maintaining the non-adhesiveness which is desirable as barrier materials. The in vitro assessments demonstrated the potential of the hydrogel as a novel barrier material with excellent biocompatibility, wound healing promoting effect, and FBR reducing effect by realizing mechanical matching with the host abdominal organs, especially when it was composed of 60% CMC and 40% gelatin and cross-linked at 10–30 kGy to impart compressive modulus of 20–100 kPa.

Characterization and optimization of magnetic Gum-PVP/SiO2 nanocomposite hydrogel for removal of contaminated dyes

Gum-polyvinylpyrrolidone/silica (Gum-PVP/SiO2) nanocomposite hydrogel was prepared using gamma radiation-induced copolymerization and crosslinking. The magnetic nanocomposite hydrogel was carried out by in situ method. The structure of the magnetic and non-magnetic nanocomposite hydrogel was investigated and analyzed by FTIR, XRD, and TEM analysis. The swelling percentage decreases with increasing radiation dose due to the cross-linking is increasing by the irradiation dose. The factors that affect the adsorption behavior of the nanocomposite hydrogel toward basic and acidic dyes were studied. The magnetic nanocomposite hydrogel response a bit higher adsorption properties than the non-magnetic one. On the other hand, the nanocomposites showed better adsorption behavior towards Fuchsine basic dye (FC) than the methyl orange acidic dye (MO). The prepared nanocomposite has high adsorption efficiency that is recommended in treatment of dye effluents.

Curcumin delivery using novel chitosan-polyethylene glycol diacrylate microencapsulation prepared via radiation-induced crosslinking

Curcumin delivery using novel chitosan-polyethylene glycol diacrylate microencapsulation prepared via radiation-induced crosslinking

Polyacrylamide/Copper‐Alginate Double Network Hydrogel Electrolyte with Excellent Mechanical Properties and Strain‐Sensitivity

The double network (DN) hydrogel has attracted great attention due to its wide applications in daily life. However, synthesis DN hydrogel with excellent mechanical properties is still a big challenge. Here, polyacrylamide/copper-alginate double network (PAM/Cu-alg DN) hydrogel electrolyte is successfully synthesized by radiation-induced polymerization and cross-linking process of acrylamide with N, N'-methylene-bis-acrylamide and subsequent cupric ion (Cu2+ ) crosslinking of alginate. The content of sodium alginate, absorbed dose, and the concentration of Cu2+ are investigated in detail for improving the overall properties of PAM/Cu-alg DN hydrogel electrolyte. The PAM/Cu-alg DN hydrogel electrolyte synthesizes by radiation technique and Cu2+ crosslinking shows superior mechanical properties with a tensile strength of 2.25± 0.02MPa, excellent energy dissipation mechanism, and the high ionic conductivity of 4.08± 0.17 mS cm-1 . PAM/Cu-alg DN hydrogel is characterized with attenuated total reflection Fourier transform infrared spectroscopy, thermogravimetric analysis, scanning electron microscopy, and X-ray photoelectron spectroscopy analyses and the reason for the improvement of mechanical properties is illustrated. Furthermore, PAM/Cu-alg DN hydrogel electrolyte exhibits excellent strain-sensitivity, cyclic stability, and durability. This work paves for the new way for the preparation of DN hydrogel electrolytes with excellent properties.

Gamma radiation-induced crosslinking of Ca2+ loaded poly(acrylic acid) and poly(ethylene glycol) diacrylate networks for polymer gel electrolytes

Gel electrolytes based on poly(acrylic acid) and poly(ethylene glycol)diacrylate (PAA-PEGDA-Ca2+) loaded with Ca2+ ions were successfully prepared using gamma irradiation. The use of radiation provides benefits, such as solventless preparation without byproducts. The obtained gel fraction, porosity, and swelling ratio were in the range of 60–90%, 11–60%, and 4–12 g/g, respectively. Fourier transform infrared spectroscopy confirmed the successful crosslinking between PAA and PEGDA. Crystallinity remained unaffected by the incorporation of Ca2+ ions. The thermal decomposition of the gels started at 200°C. The morphology was reported to have a spherical shape. 0.36–0.74 wt.% of Ca2+ was uniformly distributed on the gel electrolyte surface. In the presence of Ca2+ ions, the ionic conductivity of the gels improved by ∼2 times, whereas compressive strength slightly dropped to the range of 6–12 MPa.Graphical abstract [Display omitted]

On the Mechanism and Kinetics of Synthesizing Polymer Nanogels by Ionizing Radiation-Induced Intramolecular Crosslinking of Macromolecules.

Nanogels—internally crosslinked macromolecules—have a growing palette of potential applications, including as drug, gene or radioisotope nanocarriers and as in vivo signaling molecules in modern diagnostics and therapy. This has triggered considerable interest in developing new methods for their synthesis. The procedure based on intramolecular crosslinking of polymer radicals generated by pulses of ionizing radiation has many advantages. The substrates needed are usually simple biocompatible polymers and water. This eliminates the use of monomers, chemical crosslinking agents, initiators, surfactants, etc., thus limiting potential problems with the biocompatibility of products. This review summarizes the basics of this method, providing background information on relevant aspects of polymer solution thermodynamics, radiolysis of aqueous solutions, generation and reactions of polymer radicals, and the non-trivial kinetics and mechanism of crosslinking, focusing on the main factors influencing the outcomes of the radiation synthesis of nanogels: molecular weight of the starting polymer, its concentration, irradiation mode, absorbed dose of ionizing radiation and temperature. The most important techniques used to perform the synthesis, to study the kinetics and mechanism of the involved reactions, and to assess the physicochemical properties of the formed nanogels are presented. Two select important cases, the synthesis of nanogels based on polyvinylpyrrolidone (PVP) and/or poly(acrylic acid) (PAA), are discussed in more detail. Examples of recent application studies on radiation-synthesized PVP and PAA nanogels in transporting drugs across the blood–brain barrier and as targeted radioisotope carriers in nanoradiotherapy are briefly described.