Developing the Potential Ophthalmic Applications of Pilocarpine Entrapped Into Polyvinylpyrrolidone–Poly(acrylic acid) Nanogel Dispersions Prepared By γ Radiation

Design and preparation of hydrogel microspheres for spinal cord injury repair

A severe disorder known as spinal cord damage causes both motor and sensory impairment in the limbs, significantly reducing the patients' quality of life. After a spinal cord injury, functional recovery and therapy have emerged as critical concerns. Hydrogel microspheres have garnered a lot of interest lately because of their enormous promise in the field of spinal cord injury rehabilitation. The material classification of hydrogel microspheres (natural and synthetic macromolecule polymers) and their synthesis methods are examined in this work. This work also covers the introduction of several kinds of hydrogel microspheres and their use as carriers in the realm of treating spinal cord injuries. Lastly, the study reviews the future prospects for hydrogel microspheres and highlights their limitations and problems. This paper can offer feasible ideas for researchers to advance the application of hydrogel microspheres in the field of spinal cord injury.

A Comprehensive Review of Nanogel-Based Drug Delivery Systems

Polymers can be crosslinked chemically or physically to create three-dimensional hydrogel particles with sub-micron dimensions, known as nanogels. Their customizable size, ease of manufacture, expansion potential, bio-integration, water affinity, and reactivity to various stimuli, including temperature, pH, light, and biological agents, provide them with considerable advantages over conventional drug delivery techniques. Nanogels possess properties of both hydrogels and nanoparticles and can be categorized into nanohydrogels and nano-organogels. These systems exhibit exceptional drug-loading capability, stability, biological consistency, and environmental responsiveness. Their hallmark lies in their swelling behavior, enabling substantial water absorption while maintaining structural integrity. Preparation methods involve polymer precursors or heterogeneous polymerization of monomers. Nanogels are promising for various drug administration techniques, including local anesthetics, vaccines, and transdermal drug delivery, due to their ability to encapsulate multiple bioactive ingredients, enhancing therapeutic efficacy and stability.

Injectable nanogels to improve triamcinolone acetonide delivery and toxicity on the treatment of eye diseases

Triamcinolone acetonide (TA) is a corticosteroid, and widely used in the treatment of eye diseases such as macular edema, proliferative vitreoretinopathy, and chronic uveitis. It's also used in diseases such as osteoarthritis and rheumatoid arthritis. Despite the width of its usage, it has toxicity in the eye. Nanogels are advantageous in applying toxic and low bioavailability drugs thanks to their swelling ability and stability. In the presented study, to minimize the disadvantages of TA, and to reach the drug into the back segment of the eye, TA-loaded chitosan (CS) nanogel (CS-TA Nanogel) has been prepared, and in vitro characterized. CS-TA nanogels were prepared by ionic gelation and characterized by SEM, FTIR, and TGA. Drug release profile, and in vitro cytotoxicity was determined to evaluate the efficacy of nanogels for intravitreal eye applications. DNA damage, and oxidative stress caused by nanogels in eye endothelial cells were investigated. CS and CS-TA nanogels were synthesized in the sizes range 200-300 nm with an overall positive charge surface. The loading efficiency of TA on nanogels was determined as 50%. Cells exposed to 250 µg/ml free TA showed 74% viability, while this rate was 90% in cells exposed to CS-TA nanogels. 8-OHdG levels were determined as 54.93 ± 1.118 ng/mL in control cells and 92.47 ± 0.852 ng/mL in cells exposed to 250 µg/ml TA. TA both induces oxidative stress and causes DNA damage in HRMEC cells. However, administration of TA with carrier increased cell viability, total antioxidant capacity, and reduced oxidative DNA damage.

Fostering the unleashing potential of nanocarriers-mediated delivery of ocular therapeutics

Ocular delivery is the most challenging aspect in the field of pharmaceutical research. The major hurdle for the controlled delivery of drugs to the eye includes the physiological static barriers such as the complex layers of the cornea, sclera and retina which restrict the drug from permeating into the anterior and posterior segments of the eye. Recent years have witnessed inventions in the field of conventional and nanocarrier drug delivery which have shown considerable enhancement in delivering small to large molecules across the eye. The dynamic challenges associated with conventional systems include limited drug contact time and inadequate ocular bioavailability resulting from solution drainage, tear turnover, and dilution or lacrimation. To this end, various bioactive-based nanosized carriers including liposomes, ethosomes, niosomes, dendrimer, nanogel, nanofibers, contact lenses, nanoprobes, selenium nanobells, nanosponge, polymeric micelles, silver nanoparticles, and gold nanoparticles among others have been developed to circumvent the limitations associated with the conventional dosage forms. These nanocarriers have been shown to achieve enhanced drug permeation or retention and prolong drug release in the ocular tissue due to their better tissue adherence. The surface charge and the size of nanocarriers (10-1000 nm) are the important key factors to overcome ocular barriers. Various nanocarriers have been shown to deliver active therapeutic molecules including timolol maleate, ampicillin, natamycin, voriconazole, cyclosporine A, dexamethasone, moxifloxacin, and fluconazole among others for the treatment of anterior and posterior eye diseases. Taken together, in a nutshell, this extensive review provides a comprehensive perspective on the numerous facets of ocular drug delivery with a special focus on bioactive nanocarrier-based approaches, including the difficulties and constraints involved in the fabrication of nanocarriers. This also provides the detailed invention, applications, biodistribution and safety-toxicity of nanocarriers-based therapeutcis for the ophthalmic delivery.

Advances in Hydrogels for Periodontitis Treatment

Periodontitis is a common condition characterized by a bacterial infection and the disruption of the body's immune-inflammatory response, which causes damage to the teeth and supporting tissues and eventually results in tooth loss. Current therapy involves the systemic and local administration of antibiotics. However, the existing treatments cannot exert effective, sustained release and maintain an effective therapeutic concentration of the drug at the lesion site. Hydrogels are used to treat periodontitis due to their low cytotoxicity, exceptional water retention capability, and controlled drug release profile. Hydrogels can imitate the extracellular matrix of periodontal cells while offering suitable sites to load antibiotics. This article reviews the utilization of hydrogels for periodontitis therapy based on the pathogenesis and clinical manifestations of the disease. Additionally, the latest therapeutic strategies for smart hydrogels and the main techniques for hydrogel preparation have been discussed. The information will aid in designing and preparing future hydrogels for periodontitis treatment.

Developments in Emerging Topical Drug Delivery Systems for Ocular Disorders

According to the current information, using nano gels in the eyes have therapeutic benefits. Industry growth in the pharmaceutical and healthcare sectors has been filled by nanotechnology. Traditional ocular preparations have a short retention duration and restricted drug bioavailability because of the eye's architectural and physiological barriers, a big issue for physicians, patients, and chemists. In contrast, nano gels can encapsulate drugs within threedimensional cross-linked polymeric networks. Because of their distinctive structural designs and preparation methods, they can deliver loaded medications in a controlled and sustained manner, enhancing patient compliance and therapeutic efficacy. Due to their excellent drugloading capacity and biocompatibility, nano-gels outperform other nano-carriers. This study focuses on using nano gels to treat eye diseases and provides a brief overview of their creation and response to stimuli. Our understanding of topical drug administration will be advanced using nano gel developments to treat common ocular diseases such as glaucoma, cataracts, dry eye syndrome, bacterial keratitis, and linked medication-loaded contact lenses and natural active ingredients.

Trans-corneal drug delivery strategies in the treatment of ocular diseases

The cornea is a remarkable tissue that possesses specialized structures designed to safeguard the eye against foreign objects. However, its unique properties also make it challenging to deliver drugs in a non-invasive manner. This review highlights recent advancements in achieving highly efficient drug transport across the cornea, focusing on nanomaterials. We have classified these strategies into three main categories based on their mechanisms and have analyzed their success and limitations in a systematic manner. The purpose of this review is to examine potential general principles that could improve drug penetration through the cornea and other natural barriers in the eye. We hope it will inspire the development of more effective drug delivery systems that can better treat ocular diseases.

Advances in Nanogels for Topical Drug Delivery in Ocular Diseases

Nanotechnology has accelerated the development of the pharmaceutical and medical technology fields, and nanogels for ocular applications have proven to be a promising therapeutic strategy. Traditional ocular preparations are restricted by the anatomical and physiological barriers of the eye, resulting in a short retention time and low drug bioavailability, which is a significant challenge for physicians, patients, and pharmacists. Nanogels, however, have the ability to encapsulate drugs within three-dimensional crosslinked polymeric networks and, through specific structural designs and distinct methods of preparation, achieve the controlled and sustained delivery of loaded drugs, increasing patient compliance and therapeutic efficiency. In addition, nanogels have higher drug-loading capacity and biocompatibility than other nanocarriers. In this review, the main focus is on the applications of nanogels for ocular diseases, whose preparations and stimuli-responsive behaviors are briefly described. The current comprehension of topical drug delivery will be improved by focusing on the advances of nanogels in typical ocular diseases, including glaucoma, cataracts, dry eye syndrome, and bacterial keratitis, as well as related drug-loaded contact lenses and natural active substances.

Polymer- and lipid-based nanocarriers for ocular drug delivery: Current status and future perspectives

Ocular diseases seriously affect patients' vision and life quality, with a global morbidity of over 43 million blindness. However, efficient drug delivery to treat ocular diseases, particularly intraocular disorders, remains a huge challenge due to multiple ocular barriers that significantly affect the ultimate therapeutic efficacy of drugs. Recent advances in nanocarrier technology offer a promising opportunity to overcome these barriers by providing enhanced penetration, increased retention, improved solubility, reduced toxicity, prolonged release, and targeted delivery of the loaded drug to the eyes. This review primarily provides an overview of the progress and contemporary applications of nanocarriers, mainly polymer- and lipid-based nanocarriers, in treating various eye diseases, highlighting their value in achieving efficient ocular drug delivery. Additionally, the review covers the ocular barriers and administration routes, as well as the prospective future developments and challenges in the field of nanocarriers for treating ocular diseases.

Dendrimer and dendrimer gel-derived drug delivery systems: Breaking bottlenecks of topical administration of glaucoma medications

Due to high structural flexibility, multidrug carrying capability, and tunable size, dendrimers have been used as suitable carriers for ophthalmic drug delivery. Drug molecules can be either encapsulated or chemically coupled to dendrimers. The nanoscopic size, spheroidal shape, and cationic surface of polyamidoamine (PAMAM) dendrimers promote their interaction with the cornea and result in prolonged precorneal retention. Dendrimers could be further cross-linked to produce three-dimensional hydrogel networks or dendrimer hydrogels (DH). The properties of the DH can be readily adjusted to maintain both fluidity and adhesiveness, making them suitable for developing topical ocular drug formulations. Micro-/nano-sized DHs, that is, dendrimer micro-/nano-gels, have unique properties such as ease of administration, large specific surface area for adhesion, and drug targeting functionalities, making them attractive for ophthalmic drug delivery. This perspective reports advances in PAMAM dendrimer based drug delivery systems including drug conjugates and micro- and nano-gels to enhance and sustain the delivery of multiple anti-glaucoma drugs, Dendrimer and dendrimer gel-derived drug delivery systems hold great potential as multifunctional topical drug delivery systems for the eye.

Recent Advances in Smart Hydrogels Prepared by Ionizing Radiation Technology for Biomedical Applications

Materials with excellent biocompatibility and targeting can be widely used in the biomedical field. Hydrogels are an excellent biomedical material, which are similar to living tissue and cannot affect the metabolic process of living organisms. Moreover, the three-dimensional network structure of hydrogel is conducive to the storage and slow release of drugs. Compared to the traditional hydrogel preparation technologies, ionizing radiation technology has high efficiency, is green, and has environmental protection. This technology can easily adjust mechanical properties, swelling, and so on. This review provides a classification of hydrogels and different preparation methods and highlights the advantages of ionizing radiation technology in smart hydrogels used for biomedical applications.

Recent Developments of Nanostructures for the Ocular Delivery of Natural Compounds

Ocular disorders comprising various diseases of the anterior and posterior segments are considered as the main reasons for blindness. Natural products have been identified as potential treatments for ocular diseases due to their anti-oxidative, antiangiogenic, and anti-inflammatory effects. Unfortunately, most of these beneficial compounds are characterised by low solubility which results in low bioavailability and rapid systemic clearance thus requiring frequent administration or requiring high doses, which hinders their therapeutic applications. Additionally, the therapeutic efficiency of ocular drug delivery as a popular route of drug administration for the treatment of ocular diseases is restricted by various anatomical and physiological barriers. Recently, nanotechnology-based strategies including polymeric nanoparticles, micelles, nanofibers, dendrimers, lipid nanoparticles, liposomes, and niosomes have emerged as promising approaches to overcome limitations and enhance ocular drug bioavailability by effective delivery to the target sites. This review provides an overview of nano-drug delivery systems of natural compounds such as thymoquinone, catechin, epigallocatechin gallate, curcumin, berberine, pilocarpine, genistein, resveratrol, quercetin, naringenin, lutein, kaempferol, baicalin, and tetrandrine for ocular applications. This approach involves increasing drug concentration in the carriers to enhance drug movement into and through the ocular barriers.

Purified mucins in drug delivery research

One of the main challenges in the field of drug delivery remains the development of strategies to efficiently transport pharmaceuticals across mucus barriers, which regulate the passage and retention of molecules and particles in all luminal spaces of the body. A thorough understanding of the molecular mechanisms, which govern such selective permeability, is key for achieving efficient translocation of drugs and drug carriers. For this purpose, model systems based on purified mucins can contribute valuable information. In this review, we summarize advances that were made in the field of drug delivery research with such mucin-based model systems: First, we give an overview of mucin purification procedures and discuss the suitability of model systems reconstituted from purified mucins to mimic native mucus. Then, we summarize techniques to study mucin binding. Finally, we highlight approaches that made use of mucins as building blocks for drug delivery platforms or employ mucins as active compounds.

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.

Polyethylene oxide-polyacrylic acid-folic acid (PEO-PAAc) nanogel as a 99m Tc targeting receptor for cancer diagnostic imaging

Nanoparticles are frequently used as targeting delivery systems for therapeutic and diagnostic radiopharmaceuticals. Polyethylene oxide-polyacrylic acid (PEO-PAAc) nanogel was prepared via γ-radiation-induced polymerization. Variable factors affecting nanoparticles size were investigated. The nanogel was radiolabeled with the imaging radioisotope ^99m Tc and finally conjugated with folic acid to target folate receptor actively. PEO-PAAc-folic acid gel was characterized by dynamic light scattering (DLS) and atomic force microscopy (AFM). Biodistribution was studied in normal mice and solid tumor-bearing mice via intravenous and intratumor injections of the radiolabeled PEO-PAAc-folic acid nanogel. Results of biodistribution showed high selective uptake of the prepared complex in tumor muscle compared with normal muscle for both intravenous and intratumor injections. The T/NT ratio was found to be 6.186 and 294.5 for intravenous and intratumor injections, respectively. Consequently, ^99m Tc-PEO-PAAc-folic acid complex could be a promising agent for cancer diagnostic imaging.

Nose-to-brain delivery of amisulpride-loaded lipid-based poloxamer-gellan gum nanoemulgel: In vitro and in vivo pharmacological studies

Unfavorable side effects of available antipsychotics limit the use of conventional delivery systems, where limited exposure of the drugs to the systemic circulation could reduce the associated risks. The potential of intranasal delivery is gaining interest to treat brain disorders by delivering the drugs directly to the brain circumventing the tight junctions of the blood-brain barrier with limited systemic exposure of the entrapped therapeutic. Therefore, the present research was aimed to fabricate, optimize and investigate the therapeutic efficacy of amisulpride (AMS)-loaded intranasal in situ nanoemulgel (AMS-NG) in the treatment of schizophrenia. In this context, AMS nanoemulsion (AMS-NE) was prepared by employing aqueous-titration method and optimized using Box-Behnken statistical design. The optimized nanoemulsion was subjected to evaluation of globule size, transmittance, zeta potential, and mucoadhesive strength, which were found to be 92.15 nm, 99.57%, -18.22 mV, and 8.90 g, respectively. The AMS-NE was converted to AMS-NG using poloxamer 407 and gellan gum. Following pharmacokinetic evaluation in Wistar rats, the brain C_max for intranasal AMS-NG was found to be 1.48-folds and 3.39-folds higher when compared to intranasal AMS-NE and intravenous AMS-NE, respectively. Moreover, behavioral investigations of developed formulations were devoid of any extrapyramidal side effects in the experimental model. Finally, outcomes of the in vivo hematological study confirmed that intranasal administration of formulation for 28 days did not alter leukocytes and agranulocytes count. In conclusion, the promising results of the developed and optimized intranasal AMS-NG could provide a novel platform for the effective and safe delivery of AMS in schizophrenic patients.

Ocular drug delivery to the anterior segment using nanocarriers: A mucoadhesive/mucopenetrative perspective

There is a growing demand for effective treatments for ocular conditions that improve patient compliance and reduce side-effects. While methods such as implants and injections have proven effective, topical administration remains the method of choice for the delivery of therapeutics to the anterior segment of the eye. However, topical administration suffers from multiple drawbacks including low bioavailability of the target therapeutic, systemic toxicity, and the requirement for high therapeutic doses due to the effective clearance mechanisms that exist in the eye. Nanoparticles that have tunable mucoadhesion and/or mucopenetration offer outstanding potential to overcome the anatomical and physiological barriers present to improve ocular bioavailability, reduce toxicity, and increase ocular retention, among other benefits. The current review highlights recent advances in the field of developing nanocarriers with tunable mucoadhesion and mucopenetration for drug delivery to the eye.

Micro- to Nanoscale Bio-Hybrid Hydrogels Engineered by Ionizing Radiation

Bio-hybrid hydrogels consist of a water-swollen hydrophilic polymer network encapsulating or conjugating single biomolecules, or larger and more complex biological constructs like whole cells. By modulating at least one dimension of the hydrogel system at the micro- or nanoscale, the activity of the biological component can be extremely upgraded with clear advantages for the development of therapeutic or diagnostic micro- and nano-devices. Gamma or e-beam irradiation of polymers allow a good control of the chemistry at the micro-/nanoscale with minimal recourse to toxic reactants and solvents. Another potential advantage is to obtain simultaneous sterilization when the absorbed doses are within the sterilization dose range. This short review will highlight opportunities and challenges of the radiation technologies to produce bio-hybrid nanogels as delivery devices of therapeutic biomolecules to the target cells, tissues, and organs, and to create hydrogel patterns at the nano-length and micro-length scales on surfaces.

Polymerization Reactions and Modifications of Polymers by Ionizing Radiation

Ionizing radiation has become the most effective way to modify natural and synthetic polymers through crosslinking, degradation, and graft polymerization. This review will include an in-depth analysis of radiation chemistry mechanisms and the kinetics of the radiation-induced C-centered free radical, anion, and cation polymerization, and grafting. It also presents sections on radiation modifications of synthetic and natural polymers. For decades, low linear energy transfer (LLET) ionizing radiation, such as gamma rays, X-rays, and up to 10 MeV electron beams, has been the primary tool to produce many products through polymerization reactions. Photons and electrons interaction with polymers display various mechanisms. While the interactions of gamma ray and X-ray photons are mainly through the photoelectric effect, Compton scattering, and pair-production, the interactions of the high-energy electrons take place through coulombic interactions. Despite the type of radiation used on materials, photons or high energy electrons, in both cases ions and electrons are produced. The interactions between electrons and monomers takes place within less than a nanosecond. Depending on the dose rate (dose is defined as the absorbed radiation energy per unit mass), the kinetic chain length of the propagation can be controlled, hence allowing for some control over the degree of polymerization. When polymers are submitted to high-energy radiation in the bulk, contrasting behaviors are observed with a dominant effect of cross-linking or chain scission, depending on the chemical nature and physical characteristics of the material. Polymers in solution are subject to indirect effects resulting from the radiolysis of the medium. Likewise, for radiation-induced polymerization, depending on the dose rate, the free radicals generated on polymer chains can undergo various reactions, such as inter/intramolecular combination or inter/intramolecular disproportionation, b-scission. These reactions lead to structural or functional polymer modifications. In the presence of oxygen, playing on irradiation dose-rates, one can favor crosslinking reactions or promotes degradations through oxidations. The competition between the crosslinking reactions of C-centered free radicals and their reactions with oxygen is described through fundamental mechanism formalisms. The fundamentals of polymerization reactions are herein presented to meet industrial needs for various polymer materials produced or degraded by irradiation. Notably, the medical and industrial applications of polymers are endless and thus it is vital to investigate the effects of sterilization dose and dose rate on various polymers and copolymers with different molecular structures and morphologies. The presence or absence of various functional groups, degree of crystallinity, irradiation temperature, etc. all greatly affect the radiation chemistry of the irradiated polymers. Over the past decade, grafting new chemical functionalities on solid polymers by radiation-induced polymerization (also called RIG for Radiation-Induced Grafting) has been widely exploited to develop innovative materials in coherence with actual societal expectations. These novel materials respond not only to health emergencies but also to carbon-free energy needs (e.g., hydrogen fuel cells, piezoelectricity, etc.) and environmental concerns with the development of numerous specific adsorbents of chemical hazards and pollutants. The modification of polymers through RIG is durable as it covalently bonds the functional monomers. As radiation penetration depths can be varied, this technique can be used to modify polymer surface or bulk. The many parameters influencing RIG that control the yield of the grafting process are discussed in this review. These include monomer reactivity, irradiation dose, solvent, presence of inhibitor of homopolymerization, grafting temperature, etc. Today, the general knowledge of RIG can be applied to any solid polymer and may predict, to some extent, the grafting location. A special focus is on how ionizing radiation sources (ion and electron beams, UVs) may be chosen or mixed to combine both solid polymer nanostructuration and RIG. LLET ionizing radiation has also been extensively used to synthesize hydrogel and nanogel for drug delivery systems and other advanced applications. In particular, nanogels can either be produced by radiation-induced polymerization and simultaneous crosslinking of hydrophilic monomers in "nanocompartments", i.e., within the aqueous phase of inverse micelles, or by intramolecular crosslinking of suitable water-soluble polymers. The radiolytically produced oxidizing species from water, •OH radicals, can easily abstract H-atoms from the backbone of the dissolved polymers (or can add to the unsaturated bonds) leading to the formation of C-centered radicals. These C-centered free radicals can undergo two main competitive reactions; intramolecular and intermolecular crosslinking. When produced by electron beam irradiation, higher temperatures, dose rates within the pulse, and pulse repetition rates favour intramolecular crosslinking over intermolecular crosslinking, thus enabling a better control of particle size and size distribution. For other water-soluble biopolymers such as polysaccharides, proteins, DNA and RNA, the abstraction of H atoms or the addition to the unsaturation by •OH can lead to the direct scission of the backbone, double, or single strand breaks of these polymers.

Mucoadhesive and responsive nanogels as carriers for sustainable delivery of timolol for glaucoma therapy

Topical administration to the eye for the treatment of glaucoma is a convenient route because it increases the patient comfort. Timolol can efficiently diminish the intraocular pressure (IOP) of the eye; however the topical application as a solution of timolol maleate (TM) has poor therapeutic index and presents severe side effects. The encapsulation of timolol in nanomaterials has appeared as a technology to increase its residence time in the eye thus achieving a sustained release and consequently diminishing the doses of this drug and their number. The preparation of nanogels (NGs) based on N-isopropylacrylamide (NIPA) and acrylic acid (AAc), easily synthesized by precipitation/dispersion free radical polymerization, is reported in this paper. Such NGs presented excellent dispersability in eye simulated fluid and ideal size for topical application. NGs can load efficiently timolol through ionic interaction, and the in vitro release showed that NGs deliver timolol in a sustained manner. In vivo sustained efficacy of the NGs-timolol nanoformulations was demonstrated in rabbit's glaucoma model, in which the IOP could be diminished and maintained constant for 48 h with only one application. Overall, the synthesized NGs in combination with timolol have potential as drug delivery system for glaucoma therapy.

Nanoscale poly(acrylic acid)-based hydrogels prepared via a green single-step approach for application as low-viscosity biomimetic fluid tears

The present work reports a nanotechnology strategy to prepare a low-viscosity poly(acrylic acid) (PAAc)-based tear substitute with enhanced efficacy and compliance. Specifically, nanogels composed of PAAc and polyvinylpyrrolidone (PVP) were prepared by adapting an ionizing radiation method. For this purpose, different aqueous systems: PVP/PAAc nanoparticulate complexes, PVP/acrylic acid (AAc), N-vinylpyrrolidone (N-VP)/PAAc, and N-VP/AAc were exposed to gamma rays. The dynamic light scattering technique showed that stable nanogels are only produced in a relatively high yield from the PVP/AAc system. Nanogel formation was driven by the hydrogen-bonding complexation between PVP and PAAc (formed in situ) as well as the radiation-induced cross-linking. Transparency, viscosity and mucoadhesiveness of emerged nanogels were optimized by controlling the feed composition and irradiation dose. Furthermore, neutralized nanogels were topically applied in a dry eye model and compared with a PAAc-based commercial tear substitute, namely Vidisic® Gel. The results of Schirmer's test and tear break-up time demonstrated that nanogels prepared from AAc-rich feed solutions at 20 kGy enhanced markedly the dry eye conditions. The histopathological analysis also ensured the competence of PAAc-rich nanogels to completely return the corneal epithelium to its normal state.

Preparation of Radiation Cross-Linked Poly(Acrylic Acid) Hydrogel Containing Metronidazole with Enhanced Antibacterial Activity

Metronidazole (MD) is known as a periodontitis medicine and has been widely used in antibiotics for resistance to anaerobic bacteria, periodontal disease, and other threats. To treat diseases, drug delivery carriers are needed with a high bioadhesive property and enhanced drug penetration. Poly (acrylic acid) (PAA) hydrogel films have a good bioadhesive property and are able to localize the absorption site and increase the drug residence time. In this study, we fabricated a MD loaded PAA hydrogel with different MD content (0.1, 0.25, 0.5, and 1 wt%) using varying doses (25, 50, and 75 kGy) and the radiation doses (25, 50, or 75 kGy) in a one-step gamma-ray irradiation process. The chemical and physical structure were determined through a Fourier transformed infrared spectroscopy, X-ray photoelectron spectroscopy, gel content, and compressive strength. In addition, MD loaded PAA hydrogels were performed to MD release behaviors and cytotoxicity. Finally, we conducted antibacterial activity to demonstrate the prevention of growth of bacteria as a therapeutic dressing. The basic chemical structure analysis of MD was changed greatly at radiation doses of 50 and 75 kGy due to degradation by gamma-ray irradiation. However, when the absorbed dose was 25 kGy, the chemical structure analysis of MD did not change significantly, and the gel content and compressive strength of MD/PAA hydrogel were approximately 80% and 130 kPa, respectively. The MD/PAA hydrogels exhibited no cytotoxicity and good antibacterial activity against Escherichia coli, Staphylococcus aureus, and Streptococcus mutans. These results provide good evidence that MD/PAA hydrogel prepared by gamma-ray irradiation has potential as a competitive candidate for the therapeutic dressing.

Micelle-nanogel platform for ferulic acid ocular delivery

Corneal wound healing after a trauma or a chemical injury has been shown to correlate with antioxidant levels at the ocular surface. However, ocular bioavailability of efficient antioxidants (e.g. ferulic acid) after topical administration is limited by their poor solubility, low stability and short residence time. The aim of this work was to formulate ferulic acid in a nanocomposite platform composed of nanogels and micelles for efficient delivery to cornea. Solubility enhancement factor of ferulic acid was found to be equal to 1.9 ± 0.3 and 3.4 ± 0.3 for 50 and 100 mg/ml Pluronic® F68 micellar solutions. Hyaluronan was added to blank and ferulic acid loaded micelles, and then cross-linked with ε-polylysine. Hyaluronan nanogels showed dimensions of ~300 nm with positive zeta potential values. The formulations were characterized in terms of rheological behavior, biocompatibility, wound healing properties, ferulic acid release pattern and penetration into excised bovine corneas. In comparison to Pluronic® micelles that released ferulic acid rapidly, micelle-nanogel composites sustained the release up to 2 days. Furthermore, the micelle-nanogel formulation favored in vitro wound closure promoting fibroblasts growth and ex vivo accumulation of ferulic acid into both healthy and damaged corneas (>100 µg/cm²).

Nanogels as drug-delivery systems: a comprehensive overview

Nanogels have attracted considerable attention as nanoscopic drug carriers, particularly for site-specific or time-controlled delivery of bioactive mediators. A high diversity of polymer systems and the simple modification of their physicochemical features have provided multipurpose forms of nanogel preparations. Nanogels have outstandingly high stability, drug loading ability, biologic consistence, good permeation capability and can be responsive to environmental stimuli. Great potential has been shown by nanogels in many fields including delivery of genes, chemotherapy drugs, diagnosis, targeting of specific organs and several others. This review focuses mainly on different types of nanogels, methods of preparation including methods of drug loading, different modes of biodegradation mechanisms as well as main mechanisms of drug release from nanogels. Recent applications of nanogels are also briefly discussed and exemplified.

A Novel Phytantriol-Based Lyotropic Liquid Crystalline Gel for Efficient Ophthalmic Delivery of Pilocarpine Nitrate

The purpose of this paper was to investigate the potential of liquid crystalline (LC) gels for ophthalmic delivery, so as to enhance the bioavailability of pilocarpine nitrate (PN). The gels were prepared by a vortex method using phytantriol and water (in the ratio of 73:27 w/w). Their inner structures were confirmed by crossed polarized light microscopy, small-angle X-ray scattering, attenuated total reflectance-Fourier transform infrared spectrum, and rheology. The in vitro release studies revealed that PN could keep sustained release from the gels over a period of 12 h. The ex vivo apparent permeability coefficient of the gels demonstrated a 3.83-folds (P < 0.05) increase compared with that of eye drops. The corneal hydration levels of the gel maintained in the normal range of 79.46 ± 2.82%, hinting that the gel could be considered non-damaging and safe to the eyes. Furthermore, in vivo residence time evaluation suggested that a better retention performance of LC gel was observed in rabbit's eyes compared to eye drops. In vivo ocular irritation study indicated that LC gel was nonirritant and might be suitable for various eye applications. In conclusion, LC gels might represent a potential ophthalmic delivery strategy to overcome the limitations of eye drops.

Effect of Methylcellulose Molecular Weight on the Properties of Self-Assembling MC-g-PNtBAm Nanogels

The efficiency of drug delivery to the eye using topical drop therapy is limited by the ocular clearance mechanisms. Nanocarriers, able to encapsulate bioactive compounds and slow down their release, may allow for prolonged on-eye residence times when combined with topical application for treatment of ocular conditions. Previously, self-assemblies of methylcellulose (MC) hydrophobized with N-tert-butylacrylamide side chains (MC-g-PNtBAm) were developed. The purpose of the current study was to investigate the impact of the methylcellulose backbone length on the properties of the nanogels. We synthesized MC-g-PNtBAm nanogels using four different molecular weights of MC with two degrees of hydrophobic modification and investigated the physical and chemical properties of the resulting polymeric nanogels. While no significant change could be observed at a high degree of hydrophobization, properties were affected at a lower one. Increasing the molecular weight of MC improved the swelling capacity of the nanogels, increasing their size in water. An effect on the drug release was also noted. Nanogels prepared using MC with a molecular weight of 30 kDa did not retain as much dexamethasone and released it faster compared to those prepared using 230 kDa MC. Thus, besides the degree of hydrophobization, the length of MC chains provides another means of tuning the properties of MC-g-PNtBAm nanogels.

Nanogels of methylcellulose hydrophobized with N-tert-butylacrylamide for ocular drug delivery

While eye drops account for the majority of ophthalmic formulation for drug delivery, their efficiency is limited by rapid pre-corneal loss. In this study, we investigate nanogel suspensions in order to improve the topical ocular therapy by reducing dosage and frequency of administration. We synthesized self-assembling nanogels of 140 nm by grafting side chains of poly(N-tert-butylacrylamide) (PNtBAm) on methylcellulose via cerium ammonium nitrate. Successful grafting of PNtBAm onto methylcellulose (MC) was confirmed by both NMR and ATR. Synthesized molecules (MC-g-PNtBAm) self-assembled in water driven by hydrophobic interaction of the grafted side chains creating colloid solutions. Materials were synthesized by changing feed ratios of acid, initiator and monomer in order to control the degree of hydrophobic modification. The nanogels were tested for different degrees of grafting. Viability studies performed with HCE cells testified to the biocompatibility of poly(N-tert-butylacrylamide) grafted methylcellulose nanogels. Dexamethasone was entrapped with an efficiency superior to 95 % and its release presented minimal burst phase. Diffusion of drug from the nanogels was found to be delayed by increasing the degree of grafting. The release profile of the entrapped compound from the MC-g-PNtBAm nanogels can thus be tuned by simply adjusting the degree of hydrophobic modification. MC-g-PNtBAm nanogels present promising properties for ocular drug delivery.

Design of Isoniazid Smart Nanogel by Gamma Radiation-Induced Template Polymerization for Biomedical Application

PURPOSE

Preparation of Isoniazid (INH) loaded nanogel particles using gamma radiation as safe, simple, cheap and reproducible technique for promoting mycobacterial killing in a lower-dose system aiming in developing of drug resistance.

METHODS

Polymeric pH-sensitive nanogels were prepared by gamma radiation-induced polymerization of Acrylic acid (AAc) or Itaconic acid (IA), in aqueous solution of polyvinylpyrrolidone (PVP), as template polymer. The prepared nanogels were utilized for encapsulation of INH. 3¹X2² factorial design was employed for optimization and exploring the effect of radiation dose (X₁) (30-50kGy), ratio of PVP: acid (X₂) (50:50-30:70) and type of acid (X₃) on the prepared nanogel characterization RESULTS: The optimized levels of X₁, X₂ and X₃ were (50 KGy, 30:70 and Itaconic acid, respectively), with a desirability of 0.959. In-vitro INH release rate from the prepared nanogels decreased with increasing gamma radiation doses, with the predominance of the diffusion mechanism for drug release pattern. In addition, it was perceived that the minimum inhibitory concentration (MIC) of INH loaded PVP/PIA nanogels on Mycobacteria Tuberculosis was 8 folds lower than that of INH solution.

CONCLUSION

The prospective of PVP-K90/PIA was recommended as a smart candidate for delivery of INH with promising achievements against tuberculosis than free drug. Graphical abstract Mechanism of formation and loading of Isoniazid PVP/PIA nanogel.

Synthesis of polyacid nanogels: pH-responsive sub-100 nm particles for functionalisation and fluorescent hydrogel assembly

Nanogels are crosslinked polymer particles with a swollen size between 1 and 100 nm. They are of major interest for advanced surface coatings, drug delivery, diagnostics and biomaterials. Synthesising polyacid nanogels that show triggered swelling using a scalable approach is a key objective of polymer colloid chemistry. Inspired by the ability of polar surfaces to enhance nanoparticle stabilisation, we report the first examples of pH-responsive polyacid nanogels containing high -COOH contents prepared by a simple, scalable, aqueous method. To demonstrate their functionalisation potential, glycidyl methacrylate was reacted with the -COOH chemical handles and the nanogels were converted to macro-crosslinkers. The concentrated (functionalised) nanogel dispersions retained their pH-responsiveness, were shear-thinning and formed physical gels at pH 7.4. The nanogels were covalently interlinked via free-radical coupling at 37 °C to form transparent, ductile, hydrogels. Mixing of the functionalised nanogels with polymer dots enabled covalent assembly of fluorescent hydrogels.

Radiation Engineering of Multifunctional Nanogels

Nanogels combine the favourable properties of hydrogels with those of colloids. They can be soft and conformable, stimuli-responsive and highly permeable, and can expose a large surface with functional groups for conjugation to small and large molecules, and even macromolecules. They are among the very few systems that can be generated and used as aqueous dispersions. Nanogels are emerging materials for targeted drug delivery and bio-imaging, but they have also shown potential for water purification and in catalysis. The possibility of manufacturing nanogels with a simple process and at relatively low cost is a key criterion for their continued development and successful application. This paper highlights the most important structural features of nanogels related to their distinctive properties, and briefly presents the most common manufacturing strategies. It then focuses on synthetic approaches that are based on the irradiation of dilute aqueous polymer solutions using high-energy photons or electron beams. The reactions constituting the basis for nanogel formation and the approaches for controlling particle size and functionality are discussed in the context of a qualitative analysis of the kinetics of the various reactions.

On the origin of functionalization in one-pot radiation synthesis of nanogels from aqueous polymer solutions

E-beam irradiation is a “green”, one-step route for the production of biocompatible nanogels from polymer aqueous solutions. Functional group density is tuned independently from size and molecular weight by a proper choice of irradiation conditions.

Dextrin and poly(lactide)-based biocompatible and biodegradable nanogel for cancer targeted delivery of doxorubicin hydrochloride

Herein, we report the development and application of a novel biocompatible, chemically crosslinked nanogel for use in anticancer drug delivery.

Preparation and characterization of a novel pH-sensitive Salecan-g-poly(acrylic acid) hydrogel for controlled release of doxorubicin

Salecan is a novel water-soluble extracellular β-glucan produced by a salt-tolerant strain Agrobacterium sp. ZX09. Salecan is suitable for the fabrication of hydrogels for biomedical applications due to its excellent physicochemical and biological properties. In this paper, a series of pH-sensitive hydrogels were prepared in aqueous solution by the graft copolymerization of Salecan and acrylic acid (AA) using N,N'-methylene diacrylamide as a crosslinker for controlled drug delivery. The structure and thermal stability of the resulting hydrogels were characterized by FT-IR, XRD and TGA. By SEM analysis, freeze-dried hydrogels displayed an interconnected porous structure with tunable pore size in the range of 23.2-90.3 μm. The swelling behavior of the hydrogels was shown to be highly dependent on the environmental pH, salt type and concentration, as well as the contents of Salecan and BAAm. They are almost unswellable at pH 1.2 and swollen extensively at pH 6.86. Meanwhile, the increase in the content of hydrophilic Salecan could enhance the swelling ratio, whereas the presence of more BAAm reduced the swelling capacity but promoted the water retention to some extent. Rheological tests revealed that storage modulus G' was strongly influenced by the crosslink density of the obtained hydrogel network. Especially, doxorubicin (DOX) as a model anti-cancer drug was very efficiently loaded into the negatively charged hydrogels (up to 69.4 wt%) through electrostatic interactions. More importantly, the release of DOX from this intelligent system exhibited pH-responsive behavior and a sustained release pattern. For SPA2, the cumulative release profile showed a low level of drug release (about 12.3 wt% in 24 h) at pH 7.4, and was significantly accelerated at pH 4.0 (over 40 wt% in 6 h). Cytotoxicity experiments confirmed that all blank hydrogels were non-toxic to A549 cells, while DOX released from the drug-loaded hydrogels remained biologically active and had the capability to kill cancer cells. The preliminary results clearly suggested that the Salecan-g-PAA hydrogels may be promising carriers for controlled drug delivery.