Novel in situ gelling ophthalmic drug delivery system based on gellan gum and hydroxyethylcellulose: Innovative rheological characterization, in vitro and in vivo evidence of a sustained precorneal retention time

Gellan gum-based microbeads for Colon-targeted drug delivery: A promising polysaccharide for controlled and site-specific release

Targeting drug delivery to the colon presents significant challenges due to unfavorable pH conditions and enzymatic activity in the upper gastrointestinal tract. This obstacle can be overcome with colon-targeted microbeads, which have led to significant advancements in treating colonic diseases such as inflammatory bowel disease and colorectal cancer, as well as in achieving sustained delivery of macromolecules like peptides and proteins. Polysaccharide-based microbeads (MBs) formulated with gellan gum (GLG) offer a robust platform for controlled and site-specific drug release. GLG, a natural anionic polysaccharide, is renowned for its gelation properties in the presence of divalent cations, biocompatibility, and enzymatic degradability, making it ideal for colon-specific applications. In this review, we explored the potential of GLG-MBs for colon-targeted drug delivery and their physicochemical properties, drug release mechanisms, formulation strategies, therapeutic applications, methods for analytical characterizations, highlighting their advantages over conventional drug delivery, and target specificity towards the colonic disease. Furthermore, we discussed the significant limitations of GLG-MBs, such as burst release, processing, scaling up production, regulatory challenges, and clinical uniformity towards colonic environments. We explored the strategies to overcome key limitations in clinical translation, such as uniformity and regulatory hurdles. The review concludes by outlining the direction of advancing GLG-MBs, emphasizing their potential in achieving efficient and targeted drug delivery towards the colon.

Stability and Efficacy of Mucoadhesive Eye Drops Containing Olopatadine HCl: Physicochemical, Functional, and Preclinical In Vivo Assessment

Background: The incorporation of polymers into drug delivery vehicles has been shown to be an effective strategy to prolong the residence time of active ingredients in the precorneal tear film and to increase ocular bioavailability. Objectives: The aim of this study was to develop novel, viscous eye drops containing olopatadine (OCH) as the active ingredient, polysaccharides hydroxypropyl guar gum (HPG), and sodium hyaluronate (SH), individually, and in combination as functional polymers. Methods: Viscous eye drops containing 0.1% OCH in combination with HPG (0.25%) and SH (0.4%), were prepared and evaluated for their physicochemical properties, rheological behavior, mucoadhesion, and preliminary stability. A novel rheological method was used to evaluate the resistance of the eye drops under simulated blinking conditions. In vivo efficacy was evaluated using an ocular itch test in mice to compare the formulations with a commercial product. Results: The formulations remained stable and transparent, with physicochemical parameters within acceptable ranges. Rheological studies confirmed pseudoplastic flow, with the HPG-SH combination exhibiting enhanced viscosity and shear-thinning properties for prolonged retention in the eye. Mucoadhesion was highest in SH-HPG formulations. During simulated blinking cycles, eye drops containing a combination of SH and HPG polymers fully regained their initial viscosity during the resting periods. Preliminary stability studies indicate that the formulated eye drops exhibit satisfactory physicochemical stability under various storage conditions. In vivo, OCH-SH and OCH-HPG-SH drops provided prolonged antipruritic and analgesic effects compared to the reference product. Conclusions: Polysaccharide-based innovative formulations improve OCH retention, enhancing therapeutic efficacy and patient compliance in the treatment of allergic conjunctivitis.

Chitosan/carbomer nanoparticles- laden in situ gel for improved ocular delivery of timolol: in vitro, in vivo, and ex vivo study

Due to the small capacity of the eye cavity and the rapid drainage of liquid into the nasolacrimal duct, patients must frequently administer the drops. Nanoparticles (NPs) and in situ gel systems have each proven their ability to achieve eye retention independently. In this study, timolol-loaded chitosan-carbomer NPs were prepared using the polyelectrolyte complexation method, and incorporated into a pH-responsive in situ gel system made of carbomer. The rheological behavior of NPs-laden in situ gel was examined at room and physiological conditions. Characteristics such as zeta potential, surface tension, refractive index, mucoadhesive properties, drug release, transcorneal permeability, and intra-ocular pressure (IOP) lowering activity were investigated on NPS and NPs-laden in situ gel formulations. The optimum gained NPs system had an encapsulation efficiency of about 69% with a particle size of 196 nm. The zeta potential of the NP and NPs-laden in situ gel were - 16 and + 11 mV respectively. NPs-laden in situ gel presented enhanced viscosity at physiological pH. All physicochemical properties were acceptable for both formulations. NPs and NPs-laden in situ gel systems proved to sustain drug release. They showed mucoadhesive properties which were greater for NPs-laden in situ gel. IOP reduction by NPs-laden in situ gel was significantly higher and more long-lasting than the timolol solution and NPs. In conclusion, the developed NPs-laden in situ gel is a promising carrier for ocular drug delivery due to the slow release of drug from nanoparticles, its mucoadhesive properties, and high viscosity acquisition in contact with precorneal film, which lead to improved therapeutic efficacy.

Nanoemulsion-based pseudopolyrotaxane hydrogel for enhanced corneal bioavailability and treatment of corneal inflammation

Corneal inflammation, a condition that can potentially lead to blindness, is often treated with topical eye drops. However, the limited ocular drug bioavailability of the eye drops necessitates frequent dosing. Herein, a nanoemulsion-based pseudopolyrotaxane hydrogel was fabricated to improve corneal bioavailability and thereby suppress inflammation. In this approach, dexamethasone was encapsulated into a nanoemulsion emulsified by Tween 80. The nanoemulsion was then mixed with γ-Cyclodextrin (γ-CD) aqueous solution to produce dexamethasone-loaded nanoemulsion-based pseudopolyrotaxane hydrogel (DEX-NPH) via host-guest interaction between Tween 80 and γ-CD. The hydrogel exhibited a shear-thinning and thixotropy character. In vitro drug release and hydrogel dissolution studies showed that drugs released from hydrogel predominantly in the form of nanoemulsion. The ocular surface fluorescence imaging and tear pharmacokinetics indicated that the hydrogel could significantly prolong precorneal residence time. The corneal pharmacokinetics suggested that DEX-NPH with 35 % γ-CD improved corneal bioavailability by 1.29-fold compared with nanoemulsion and by 4.09-fold compared with free drug solution. In particular, the precorneal retention capacity and corneal bioavailability could be adjusted by changing the γ-CD content in the hydrogel. Moreover, ocular irritation evaluation confirmed the excellent safety of such hydrogel. In an alkali burn-induced corneal inflammation model, the hydrogel exhibited a superior anti-inflammatory effect compared to nanoemulsion or free drug solution alone. In summary, the nanoemulsion-based pseudopolyrotaxane hydrogel is promising for enhancing corneal bioavailability and treating corneal inflammation.

Preparation of dried nanoemulsion formulation by electrospinning

Dry eye disease is a multifactorial condition characterized by a loss of homeostasis of the tear film. Among the various treatment approaches, the application of ophthalmic oil-in-water nanoemulsions with incorporated anti-inflammatory drugs represents one of the most advanced approaches. However, the liquid nature of nanoemulsions limits their retention time at the ocular surface. Transforming the nanoemulsions into a dry form that would disperse rapidly in the tear fluid would improve the retention of the drug at the ocular surface. The aim of this study was to investigate electrospinning as a method for the preparation of a solid eye preparation based on nanoemulsion loaded with the anti-inflammatory drug loteprednol etabonate. Four nanoemulsions differing in oil-to-surfactant ratios were incorporated in hydrophilic nanofibers based on polyethylene oxide, poloxamer 188, and Soluplus®. The dried nanoemulsions in the form of nanofibers dispersed readily on contact with aqueous medium, resulting in a dispersion of nanometre-sized droplets with average size comparable to the average droplet size of the initial nanoemulsions. A rheological study revealed the predominant elastic behavior of the dispersed nanofibers, which indicates the formation of a weak gel after the dispersion of the dried nanoemulsion in tear fluid at the ocular surface. The biocompatibility of the dried nanoemulsions in the form of nanofibers after a single and multiple-dose application was confirmed using the 3D HCE-T model of the stratified epithelium of the human cornea, suggesting that this innovative solid eye preparation could represent a new approach to the treatment of dry eye disease.

An innovative rheology analysis method applies to the formulation optimization of Panax notoginseng total saponins ocular gel

Emphasizing the viscoelasticity of ophthalmic gels is crucial for understanding the residence time, structure, and stability of hydrogels. This study primarily aimed to propose an innovative rheology analysis method for ophthalmic gels, considering complex eye movements. This method was applied to select ophthalmic gels with favorable rheological characteristics. Additionally, the physical characteristics and in vitro release of the selected Panax notoginseng total saponins (PNS) gel were demonstrated. The selected PNS gel significantly increased the activities of SOD and decreased intracellular levels of MDA, TNF-α, and IL-1β in H2O2-treated ARPE-19 cells. Finally, the optimal formulation was selected as a suitable platform for ophthalmic delivery and was shown to significantly rescue ARPE-19 cells from oxidative cellular damage.

Gellan gum-based in-situ gel formulations for ocular drug delivery: A practical approach

Ophthalmic disorders significantly impact global health, affecting millions worldwide. Conventional treatments often face challenges related to poor bioavailability and short residence times on the ocular surface. In recent years, in-situ gels prepared using different natural gums including gellan gum has been investigated as a viable means of improving ocular medication delivery. Gellan gum undergoes ionotropic-gelation in the presence of multivalent cations, making it suitable for ocular formulations. The synthesis and purification of gellan gum involve microbial fermentation processes. Incorporating gellan gum into ophthalmic formulations offers several advantages, including prolonged residence time, enhanced drug retention, and improved bioavailability. Characterisation techniques such as gelling capacity determination, FTIR spectroscopy, TEM, viscosity and rheological studies and ex-vivo or in-vitro release studies are crucial for assessing the structural and functional properties of gellan gum-based in-situ gels. Numerous investigations have exhibited gellan gum's potential in different drug loaded in-situ gels for ophthalmic uses, resulting in extended drug residency on the ocular surface and enhanced therapeutic effects. The current review presents a comprehensive discussion on preparation, characterisation, recent applications and future prospects of gellan gum-based in-situ gels for ocular drug delivery. In addition, it covers molecular structure, synthesis and characterisation of gellan gum.

Simultaneous viscoelasticity and sprayability in antimicrobial acetic acid-alginate fluid gels

Acetic acid is a promising alternative to antibiotics for topical applications, particularly burn wounds, however its site specificity and retention are impaired by poor material properties. In this study, acetic acid was investigated as both the gelling agent and antimicrobial active in alginate fluid gels. The formed microstructure was found to be directly dependent on acetic acid concentration, leading to highly tuneable material properties. At clinically relevant concentrations of 2.5-5 % acetic acid, the fluid gels were elastically dominated at rest, with viscosities up to 7 orders of magnitude greater than acetic acid alone. These material properties imparted long term surface retention and microparticle barrier function, not seen with either acetic acid or alginate solutions. Most notably, sprayability was enhanced simultaneously with the increased viscosity and elasticity due to the introduction of a discretised microstructure, leading to a remarkable tenfold increase in spray coverage. Formulation was found not to inhibit antimicrobial activity, despite the less acidic pH, with common burn wound pathogens Staphylococcus aureus and Pseudomonas aeruginosa being equally susceptible to the fluid gels as to acetic acid solutions.

Development and Characterization of Dual-Loaded Niosomal Ion-Sensitive In Situ Gel for Ocular Delivery

The study investigates the development and characterization of dual-loaded niosomes incorporated into ion-sensitive in situ gel as a potential drug delivery platform for ophthalmic application. Cannabidiol (CBD) and epigallocatechin-3-gallate (EGCG) simultaneously loaded niosomes were prepared via the thin film hydration (TFH) method followed by pulsatile sonication and were subjected to comprehensive physicochemical evaluation. The optimal composition was included in a gellan gum-based in situ gel, and the antimicrobial activity, in vitro toxicity in a suitable corneal epithelial model (HaCaT cell line), and antioxidant potential of the hybrid system were further assessed. Dual-loaded niosomes based on Span 60, Tween 60, and cholesterol (3.5:3.5:3 mol/mol) were characterized by appropriate size (250 nm), high entrapment efficiency values for both compounds (85% for CBD and 50% for EGCG) and sustained release profiles. The developed hybrid in situ gel exhibited suitable rheological characteristics to enhance the residence time on the ocular surface. The conducted microbiological studies reveal superior inhibition of methicillin-resistant Staphylococcus aureus (MRSA) adhesion by means of the niosomal in situ gel compared to the blank gel and untreated control. Regarding the antioxidant potential, the dual loading of CBD and EGCG in niosomes enhances their protective properties, and the inclusion of niosomes in gel form preserves these effects. The obtained outcomes indicate the developed niosomal in situ gel as a promising drug delivery platform in ophthalmology.

Food-based biomaterials: pH-responsive alginate/gellan gum/carboxymethyl cellulose hydrogel beads for lactoferrin delivery

The present study utilizes a combination of sodium alginate (Alg), gellan gum (GG), and sodium carboxymethyl cellulose (CMC) to fabricate a ternary composite hydrogel system to encapsulate and release lactoferrin (LF). Rheological properties as well as extensive microscopy and spectroscopy characterization are performed on these materials demonstrating that the physical properties of the resultant hydrogels, such as particle size, water content, gray value, and shrinkage rate were related to the concentration of Alg. In addition, most of these hydrogels were found to have reticulated shells and inner laminar structures assembled based on hydrogen bonding and electrostatic forces. Furthermore, the encapsulation efficiency of LF in hydrogels ranged from 78.3 ± 0.3 to 83.5 ± 0.2 %. Notably, a small amount of encapsulated LF was released from the hydrogel beads in an acid environment (up to 2.2 ± 0.3 % in 2 h), while a controlled release manner was found to take place in an alkaline environment. This phenomenon indicated the potential of these hydrogels as promising matrices for bioactive compound loading and adsorption. The release mechanism varied from Alg concentration suggesting the tunable and versatile properties of this ternary composite hydrogel system. Our findings identify the potential of Alg-GG-CMC hydrogel as a delivery system suitable for various applications in the food industry.

Preparation of a thermosensitive and antibacterial in situ gel using poloxamer-quaternized chitosan for sustained ocular delivery of Levofloxacin hydrochloride

In this study, a thermosensitive in situ gel with porous structure was developed using poloxamer (Po) and N-(2-hydroxy-3-trimethyl ammonium) propyl chitosan chloride (HTCC). The poloxamer-quaternized chitosan (Po-HTCC) in situ gel exhibited superior rheological property, water absorption capacity and antibacterial activity against Escherichia coli, Staphylococcus aureus, Pseudomonas aeruginosa and Streptococcus pyogenes, making it well-suited for ocular applications. Scanning electron microscope revealed a macroporous architecture with pore sizes ranging from 1 to 2 μm, suggesting that the gel has desirable breathability, corneal adhesion capability, and overall conformability. In vitro drug release assay was conducted with levofloxacin hydrochloride, demonstrating that sustained release over 48 h could be achieved at 34 °C, with approximately 80 % of the drug released within this timeframe. Computational simulations revealed substantial binding affinity between the material and the Escherichia coli outer membrane lipopolysaccharide-associated protein and corneal mucin. The protein showing the strongest binding energy to N-(2-hydroxy-3-trimethyl ammonium) propyl chitosan chloride (HTCC), as calculated by the Molecular Mechanics Generalized Born Surface Area Method (MM-GBSA), was LptD-LptE, with a binding energy of -61.14 ± 4.72 kcal/mol. These results underscore the potential of this system for effective and convenient ocular delivery with sustained drug release.

Formulation of Thermo-Sensitive In Situ Gels Loaded with Dual Spectrum Antibiotics of Azithromycin and Ofloxacin

In situ gels have been developed as an innovative strategy to prolong corneal residence time and enhance drug absorption compared to traditional eye drops. Our study aimed to formulate an ophthalmic in situ gel with a combination of two thermosensitive poloxamers, P407 and P188, in an optimal ratio not only to increase the time of action but also to increase the solubility of selected antibiotics for the treatment of ophthalmic infections. Two BSC II class substances, Azithromycin and Ofloxacin, with different mechanisms of action, have been incorporated into the in situ gel system after determining their solubility. The antibiotics-loaded in situ gel formulation was evaluated for its clarity, pH, rheological properties, and gel characteristics of gelling time, temperature, and capacity. The formulation demonstrated satisfactory clarity, appropriate pH, effective gelation properties in simulated tear fluid, and suitable rheological characteristics. In addition, APIs release insight has been studied through a dissolution test, and the effectivity against sensitive and resistant bacterial strains has been proved through the antimicrobial study. Therefore, our in situ gel system based on thermosensitive poloxamers, with two hydrophobic antibiotics, AZM and OFX, can be considered a valuable approach for ophthalmic drug delivery with an enhancement of the antibiotics bioavailability through increasing the contact time with the ocular surface and enhancing patient compliance.

Dasatinib and erianin co-loaded ion-responsive in-situ hydrogel for effective treatment of corneal neovascularization

Corneal neovasularization (CNV) is one of the leading causes for visual impairment. Dasatinib is a multi-target tyrosine kinase inhibitor, which can inhibit both platelet derived growth factor receptor and Src family kinases. Erianin exhibits excellent anti-inflammatory and anti-angiogenic effects. In this study, dasatinib and erianin were found to synergically inhibit the proliferation, migration and tube formation of Ea.hy926 cells, the three most important cellular processes of CNV. Next, dasatinib and erianin were co-encapsulated in nanostructured lipid carriers (dasa-eri-NLC), which increased the solubility of dasatinib by about 1790 times, increased the solubility of erianin by about 3 times. To improve its retention time on the ocular surface, dasa-eri-NLC was mixed with gellan gum (dasa-eri-NLC-gel), which achieved a sol-gel transformation when got in contact with tears. The dasa-eri-NLC-gel exhibited good rheological properties with shear thinning properties, extended the ocular residence time by more than 6 times, sustained the drug release, improved the corneal permeability of drug and exhibited good biocompatibility. Finally, the in vivo anti-CNV effect was evaluated in an alkaline burned mouse model of CNV, in which, the dasa-eri-NLC-gel significantly impeded the development and pathological changes of CNV, inhibited the expression of TNF-α, VEGF-A, HIF-1α, Src, pSrc in the cornea. In summary, dasa-eri-NLC-gel safely and efficiently delivered dasatinib and erianin to the cornea and exhibited significantly anti-CNV effect via inhibiting various angiogenesis related cytokines or factors. Dasa-eri-NLC-gel showed a great promise for the treatment of CNV and our study laid a solid foundation for future clinical transformation.

Augmented ocular uptake and anti-inflammatory efficacy of decorated Genistein-loaded NLCs incorporated in in situ gel

Genistein (Gen); a naturally occurring isoflavone, acts as a tyrosine kinase inhibitor and efficiently downregulates inflammatory cytokines, which are pivotal in eye inflammation. Also, Gen suffers from sparse ocular bioavailability due to poor solubility. In this work, nanostructured lipid carriers (NLCs) were successfully fabricated by using solid (stearic acid and compritol) and liquid (oleic acid) lipids. The optimized Gen-loaded NLCs showed a nanosize range of 140-246 nm, ≥ 98 % entrapment efficiency, and controlled release over 48 h. The ζ-potential of NLCs was increased from -27.3 mV to 25-27.4 mV due to surface modification with chitosan (CS) or eudragit RS100 (ERS 100). All NLCs showed prominent biocompatibility with enhanced cellular uptake on corneal stromal fibroblasts. Moreover, the different NLCs were incorporated into a mucoadhesive in situ gel. The optimized in situ gel (G9), containing 20 % poloxamers and 0.5 % hydroxyethyl cellulose, exhibited excellent gelling ability within 10.5 s, gelling temperature at 33.1 ± 0.6 ℃, spreadability diameter of 4.73 ± 0.12 cm, shear-thinning behavior, and 20 min ex vivo mucoadhesion time with drug release for 120 h. The in vivo results showed distinguished permeation and distribution potential for ocular delivery. In vivo anti-inflammatory effects after 3 days of treatment with CS-Gen-NLCs/G9 and ERS-Gen-NLCs/G9 revealed a downregulation of interleukin-6 levels in the cornea and retina compared to the untreated group. Our research highlights the promising anti-inflammatory potential of ERS-Gen-NLCs/G9 as an efficient, non-irritant Gen nanodelivery system for managing anterior and posterior ocular inflammation.

Tamarind seed polysaccharide-metformin insert: Higher ocular retention, slow-release, and efficacy against corneal burn

Metformin (MET) can be an alternative therapeutic strategy for managing ocular burn primarily because of its pleiotropic mechanism. Longer retention on the ocular surface and sustained release are necessary to ensure the efficacy of MET for ocular application. Although the high aqueous solubility of MET is good for formulation and biocompatibility, it makes MET prone to high nasolacrimal drainage. This limits ocular residence and may be a challenge in its application. To address this, polymers approved for ophthalmic application with natural origin were analyzed through in silico methods to determine their ability to bind to mucin and interact with MET. An ocular insert of MET (3 mg/6 mm) was developed using a scalable solvent casting method without using preservatives. The relative composition of the insert was 58 ± 2.06 %w/w MET with approximately 14 %w/w tamarind seed polysaccharide (TSP), and 28 %w/w propylene glycol (PG). Its stability was demonstrated as per the ICH Q1A (R2) guidelines. Compatibility, ocular retention, drug release, and other functional parameters were evaluated. In rabbits, efficacy was demonstrated in the 'corneal alkali burn preclinical model'. TSP showed potential for mucoadhesion and interaction with MET. With adequate stability and sterility, the insert contributed to adequate retention of MET (10-12 h) in vivo and slow release (30 h) in vitro. This resulted in significant efficacy in vivo.

Carrageenan films as promising mucoadhesive ocular drug delivery systems

Polymer mucoadhesive films being developed for use in ophthalmology represent a new tool for drug delivery and are considered an alternative to traditional dosage forms. Due to their mucoadhesive properties, carrageenans (CRGs) are widely used in various forms for drug delivery. In this study, films based on CRGs of various structural types (κ/β, κ, x, and λ) for use in ophthalmology were studied. The films were loaded with the active substance echinochrome (ECH), a sea urchin pigment used in ophthalmology. Spectral data showed that ECH remained stable after its incorporation into the CRG films and did not oxidize for at least six months. Hydrophilic CRG films with a thickness of 10-12 µm were characterized in terms of their swelling and mucoadhesive properties. The rheological properties of solutions formed after film dissolution in artificial tears were also assessed. κ- and κ/β-CRG films with ECH exhibited pseudoplastic behavior after rehydrating films with an artificial tear solution. The CRG-loaded films had different swelling characteristics depending on the structure of the CRG used. The films based on highly sulfated CRGs dissolved in artificial tears, while the films of low-sulfated κ/β-CRG exhibited limited swelling. All studied ECH-loaded films exhibited mucoadhesive properties, which were evaluated by a texture analyzer using mucous tissue of the small intestine of the pig as a model. There was a slight prolongation of ECH release from CRG films in artificial tears. The effect of CRG/ECH on the epithelial cell lines of the outer shell of the human eye was investigated. At low concentrations, ECH in the composition of the CRG/ECH complex had no cytotoxic effect on corneal epithelial and conjunctival human cells. The use of ECH-containing films can prevent the drug from being immediately washed away by tears and help to retain it by increasing viscosity and having mucoadhesive properties.

Nickel-cobalt metal-organic frameworks based flexible hydrogel as a wearable contact lens for electrochemical sensing of urea in tear samples

A flexible, wearable, non-invasive contact lens sensor utilizing nickel-cobalt metal-organic framework (Ni-Co-MOF) based hydrogel is introduced for urea monitoring in tear samples. The synthesized Ni-Co-MOF hydrogel exhibits a porous structure with interconnected voids, as visualized by Scanning Electron Microscopy (SEM). Detailed structural and vibrational properties of the material were characterized using X-ray Diffraction (XRD), Fourier Transform Infrared (FTIR) spectroscopy, and Raman spectroscopy. The developed Ni-Co-MOF hydrogel sensor showcases a detection limit of 0.445 mM for urea within a linear range of 0.5-70 mM. Notably, it demonstrates exceptional selectivity, effectively distinguishing against interfering species like UA, AA, glucose, dopamine, Cl-, K+, Na+, Ca2+, and IgG. The enhanced electrocatalytic performance of the Ni-Co-MOF hydrogel electrode is attributed to the presence of Ni and Co, fostering Ni2+ oxidation on the surface and forming a Co2+ complex that acts as a catalyst for urea oxidation. The fabricated sensor exhibits successful detection and retrieval of urea in simulated tear samples, showcasing promising potential for bioanalytical applications. The binder-free, non-toxic nature of the Ni-Co-MOF hydrogel sensor presents exciting avenues for future utilization in non-enzymatic electrochemical sensing, including applications in wearable devices, point-of-care diagnostics, and personalized healthcare monitoring.

In-situ gel: A smart carrier for drug delivery

In-situ gel technology is a promising drug delivery strategy that undergoes a 'sol to gel' transition upon administration, providing controlled and prolonged drug release. These gels are composed of cross-linked 3D networks of polymers, with hydrogels being a specific type of absorbing water while retaining their shape. Gelation can be triggered by various stimuli, such as temperature, pH, ions, and light. They offer several advantages like improved patient compliance, extended drug residence time, localized drug delivery, etc, but also have some disadvantages like drug degradation and limited mechanical strength. In-situ gel falls into three categories: temperature-sensitive, ion-sensitive, and pH-sensitive, but multi-responsive gels that respond to multiple stimuli have better drug release characteristics. The mechanism of in-situ gel formation involves physical and chemical mechanisms. There are various applications of in-situ gel, like ocular drug delivery, nose-to-brain delivery, etc. In this review, we have discussed the types, and mechanisms of in-situ gel & use of in-situ gel in the treatment of different diseases through various routes like buccal, vaginal, ocular, nasal, etc., along with its use in targeted drug delivery.

Poloxamer sols endowed with in-situ gelability and mucoadhesion by adding hypromellose and hyaluronan for prolonging corneal retention and drug delivery

The purpose of this study was to develop poloxamer (P407)-based in-situ thermogellable hydrogels with reducing concentration of P407 by adding hypromellose (HPMC) and with enhancing mucoadhesion of resulting hydrogels by adding hyaluronic acid (HA) for prolonging ocular delivery of hydroxypropyl-β-cyclodextrin (HPβCD)-solubilized testosterone (TES). Results demonstrated that 0.5% TES solution was successfully solubilized with adding 10% HPβCD. Non-gellable 13% P407 sol became in-situ gellable with adding 2.0-2.5% HPMC and mucoadhesibility was further imporved with adding 0.3% HA-L (low MW) or HA-H (high MW). Optimized 0.5% HPβCD-solubilized TES P407-based thermogellable hydrogels with enhancement of mucoadhesion for prolonging ocular delivery comprised 13% P407, 2.5% HPMC, and 0.3% HA-L or HA-H. Furthermore, rheological measurements under simulated eye blinking confirmed that non-thixotropic properties of optimized hydrogels could be spreaded evenly and retain a greater amount of drug-loaded hydrogels on the ocular surface for a longer period to prolong drug delivery. Compared with conventional eye drops, the prolonged residence time of optimized hydrogels from ex vivo and in vivo studies were observed, indicating relationships between rheological properties and in vivo performances. It was concluded that P407-based thermosensitive hydrogels with reducing concentration of P407 and enhancing mucoadhesion was successfully formulated by adding 2.5% HPMC and 0.3% HA in 13% P407 for potentially accomplishing effective clinical treatment of DED.

Intranasal in situ gelling liquid crystal for delivery of resveratrol ameliorates memory and neuroinflammation in Alzheimer's disease

Alzheimer's disease (AD) is an illness that affects people aged 65 or older and affects around 6.5 million in the United States. Resveratrol is a chemical obtained from natural products and it exhibits biological activity based on inhibiting the formation, depolymerization of the amyloid, and decreasing neuroinflammation. Due to the insolubility of this compound; its incorporation in surfactant-based systems was proposed to design an intranasal formulation. A range of systems has been produced by mixing oleic acid, CETETH-20 and water. Polarised light microscopy (PLM), small angle x-ray scattering (SAXS) and transmission electron microscopy (TEM) confirm the initial liquid formulation (F) presented as microemulsion (ME). After dilution, the gelled systems were characterized as hexagonal mesophase and they showed feasibility proprieties. Pharmacological assays performed after intranasal administration showed the ability to improve learning and memory in animals, as well as remission of neuroinflammation via inhibition of interleukin.

Optimization and in vivo evaluation of triamcinolone acetonide loaded in situ gel prepared using reacted tamarind seed xyloglucan and kappa-carrageenan for ocular delivery

In the current work, triamcinolone acetonide (TAA) loaded dual responsive in situ gelling system was designed and optimized using reacted tamarind seed xyloglucan (RXG) (thermoresponsive) and kappa-Carrageenan (κ-CRG) (ion-sensitive) polymers. Tamarind seed xyloglucan (TSX) was subjected to purification followed by enzymatic treatment to produce RXG with ~40 % reduction in galactose content compared to TSX. RXG was characterized using size exclusion chromatography, Fourier transform infrared and proton nuclear magnetic resonance spectroscopy to confirm the ~40 % reduction in galactoside content compared to TSX. The proportions of RXG and κ-CRG in the in situ gels (TAA loaded RXG-κ-CRG) were optimized based on their rheological properties. The optimized in situ gel exhibited good flow properties at 25 °C, but transformed rapidly into a stronger gel in the presence of STF at 35 °C. The optimized formulation had strong mucoadhesion with good spreadability on the surface of excised goat cornea. The drug release followed zero-order kinetics from the optimized in situ gel. Ex vivo ocular toxicity studies indicate that the optimized formulation was well tolerated. The ocular pharmacokinetic studies in rabbits showed significantly higher and sustained vitreous humor exposure of TAA for optimized in situ gel compared to hydroxypropyl-β-cyclodextrin based aqueous suspension of TAA.

Improving ocular bioavailability of hydrophilic drugs through dynamic covalent complexation

The clinical benefits of diquafosol tetrasodium (DQS), a hydrophilic P2Y2 receptor agonist for dry eye, have been hindered by a demanding dosing regimen. Nevertheless, it is challenging to achieve sustained release of DQS with conventional drug delivery vehicles which are mainly designed for hydrophobic small molecule drugs. To address this, we developed an affinity hydrogel for DQS by taking advantage of borate-mediated dynamic covalent complexation between DQS and hydroxypropyl guar. The resultant formulation (3% DQS Gel) was characterized by sustained release, low corneal permeation, and extended ocular retention, which were desirable attributes for ocular surface drug delivery. Both in vitro and in vivo studies had been carried out to verify the biocompatibility of 3% DQS Gel. Using corneal fluorescein staining, the Schirmer's test, PAS staining, quantitative PCR and immunohistological analyses as outcome measures, the superior therapeutic effects of 3% DQS Gel over PBS, the hydrogel vehicle and free DQS were demonstrated in a mouse dry eye model. Our DQS delivery strategy reported herein is readily applicable to other hydrophilic small molecule drugs with cis-diol moieties, thus providing a general solution to improve clinical outcomes of numerous diseases.

In situ gelling drug delivery systems for topical drug delivery

In situ gelling formulations are drug delivery systems which typically exist in a liquid form at room temperature and change into gel state after application to the body in response to various stimuli such as changes in temperature, pH and ionic composition. Their biomedical application can further be improved by incorporating drug nanoparticles into in situ gelling systems in order to prolong drug release, reduce dosing frequency and improve therapeutic outcomes of patients, developing highly functional but challenging dosage forms. The composition of in situ gelling formulations influence factors relating to performance such as their syringeability, rheology, drug release profile and drug bioavailability at target sites, amongst other factors. The inclusion of mucoadhesive polymeric constituents into in situ gelling formulations has also been explored to ensure that the therapeutic agents are retained at target site for extended period of time. This review article will discuss traditional techniques (water bath-based vial inversion and viscometry) as well as advanced methodology (rheometry, differential scanning calorimetry, Small Angle Neutron Scattering, Small Angle X-ray Scattering, etc.) for evaluating in situ gel forming systems for topical drug delivery. The clinical properties of in situ gelling systems that have been studied for potential biomedical applications over the last ten years will be reviewed to highlight current knowledge in the performance of these systems. Formulation issues that have slowed the translation of some promising drug formulations from the research laboratory to the clinic will also be detailed.

Towards the development of a biorelevant in vitro method for the prediction of nanoemulsion stability on the ocular surface

Ophthalmic oil-in-water nanoemulsions (NEs) are a complex technological platform, representing an advancement in the treatment of dry eye disease. In addition to enabling the incorporation of poorly soluble active pharmaceutical ingredients (APIs), NEs provide prolonged residence time of APIs and other formulation components and consequent replenishment and stabilization of the compromised tear film. Ophthalmic NEs have been on the market for over 20 years, but considering their complexity, as well as the complex nature of the ocular surface, they are still a poorly understood advanced dosage form. The objective of this study was to develop a biorelevant in vitro method that would be able to predict the behavior of ophthalmic NEs after application. With that goal, NE formulations differing in critical material attributes and critical formulation variables were employed and subjected to simulated tear turnover and blinking. By gradually increasing the complexity of the in vitro method, we were able to detect key parameters influencing NE stability. The undertaken study presents a step forward in the development of in vitro tools that are fundamental to the reliable, cost and time-effective development of innovative and generic topical ophthalmic NEs.

Preparation and Characterization of Ion-Sensitive Brimonidine Tartrate In Situ Gel for Ocular Delivery

Brimonidine tartrate (BRT) is a highly selective α2 adrenergic receptor agonist as treatment for patients with open angle glaucoma and high intraocular pressure. The objective of this study was to formulate an ophthalmic ion-sensitive in situ gel (ISG) of BRT to increase the retention time of the drug and its bioavailability. The optimum formulation of 2 mg/mL BRT-ISG was obtained with 0.45% gellan gum as the gel matrix. In vitro release results showed that the water-soluble drug bromonidine tartrate in ocular in situ gels exhibited a high burst effect and fast release in solution. The results of dialysis membrane permeation showed that there was a significant difference between the commercially available and BRT-ISG groups after 45 min. The results of the pre-corneal retention study indicated that gellan gum can effectively prolong ocular surface retention. Preliminary stability results showed that it should be stored in a cool and dark place, and the formulation under long-term preservation can be basically stable. The pharmacokinetic study of the BRT-ISG in the anterior chamber of the rabbit eye was studied by microdialysis technique, and microdialysis samples were analyzed by LC-MS/MS. The pharmacokinetic study showed that the BRT-ISG reached Cmax (8.16 mg/L) at 93 min after administration, which was 2.7 times that of the BRT eye drops, and the AUC(0-t) (1397.08 mg·min/L) was 3.4 times that of the BRT eye drops. The optimal prescription can prolong the retention time of BRT in front of the cornea and significantly improve the bioavailability of BRT in the eye. Combined with the results of in vitro release, permeation and pre-corneal retention studies, the improvement of BRT-ISG bioavailability in rabbit eyes was found to be mainly due to the retention effect after the mixture of ISG and tears.

Development of Ciprofloxacin-Loaded Bilosomes In-Situ Gel for Ocular Delivery: Optimization, In-Vitro Characterization, Ex-Vivo Permeation, and Antimicrobial Study

Conventional eye drops are most commonly employed topically in the eye for the management of bacterial conjunctivitis. Eye drops have a low corneal residence time and 90−95% of the administered dose is eliminated from the eye by blinking and the nasolacrimal drainage system. This problem can be minimized by formulating a mucoadhesive ocular in-situ gel system that undergoes sol-gel transition upon stimulation by temperature, pH, and ions. The goal of this study was to develop ciprofloxacin (CIP) loaded bilosomes (BLO) in-situ gel for the improvement of therapeutic efficacy. The BLO was prepared by the thin-film hydration method and optimized by the Box−Behnken design. Cholesterol (CHO), surfactant (Span 60), and bile salt (sodium deoxycholate/SDC) were used as formulation factors. The vesicle size (nm) and entrapment efficiency (%) were selected as responses (dependent factors). The optimized CIP-BLO (CIP-BLO-opt) formulation displayed a vesicle size of 182.4 ± 9.2 nm, a polydispersity index of 0.274, a zeta potential of −34,461.51 mV, and an entrapment efficiency of 90.14 ± 1.24%. Both x-ray diffraction and differential scanning calorimetry spectra did not exhibit extensive peaks of CIP in CIP-BLO-opt, revealing that CIP is encapsulated in the BLO matrix. The CIP-BLO-opt formulation was successfully incorporated into an in-situ gel system using a gelling agent, i.e., Carbopol 934P and hydroxyl propyl methyl cellulose (HPMC K100 M). CIP-BLO-opt in-situ gel formulation (CIP-BLO-opt-IG3) was evaluated for gelling capacity, clarity, pH, viscosity, in-vitro CIP release, bio-adhesive, ex-vivo permeation, toxicity, and antimicrobial study. The CIP-BLO-opt-IG3 exhibited satisfactory gelling properties with a viscosity of 145.85 ± 9.48 cP in the gelling state. CIP-BLO-opt-IG3 displayed sustained CIP release (83.87 ± 5.24%) with Korsmeyer−Peppas kinetic as a best-fitted model (R2 = 0.9667). CIP-BLO-opt-IG3 exhibited a 1.16-fold than CIP-IG and a 2.08-fold higher permeability than pure CIP. CIP-BLO-opt-IG3 displayed a significantly greater bio-adhesion property (924.52 ± 12.37 dyne/cm2) than tear film. Further, CIP-BLO-opt-IG3 does not display any toxicity as confirmed by corneal hydration (76.15%), histology, and the HET-CAM test (zero scores). CIP-BLO-opt-IG3 shows significantly higher (p < 0.05) antimicrobial activity against P. aeruginosa and S. aureus than pure CIP. From all these findings, it could be concluded that CIP-BLO-opt-IG3 might be an effective strategy for the increment of corneal residence time and therapeutic activity of CIP.

Comparative Study of Polysaccharide-Based Hydrogels: Rheological and Texture Properties and Ibuprofen Release

Polysaccharides are attractive gelling agents in pharmacy due to their safety, biocompatibility, biodegradability, relatively easy way of preparation, and low price. Due to their variable physical-chemical properties, polysaccharides have potentialities to be used for designing new drug delivery systems for controlled drug release. In this comparative study, rheological and texture properties as well as the in vitro release of model drug ibuprofen (IBU) with 11 polysaccharide-based hydrogels were investigated. The in vitro release of IBU significantly differed between (i) neutral (hydroxy/alkylcelluloses), (ii) anionic (carboxyalkylcellulose and its sodium salt, tragacanth, carrageenan, xanthan gum), and (iii) cationic (chitosans) hydrogels due to different contribution of provided interactions and viscosity within the hydrogel groups. The drug release kinetics of each hydrogel system was evaluated for five kinetic models. Several combinations of cationic hydrogels with neutral or anionic ones were performed to illustrate possibilities of providing modified IBU release profiles. In this context, chitosan was presented as an effective modifier of diffusion profiles for negatively charged drugs formulated into combined polymeric systems, providing their prolonged release. The most appropriate hydrogel for the topical application (i.e., providing favorable rheological and texture properties along with the highest drug release) was selected from a studied series of polysaccharide-based hydrogels.

New Preservative-Free Formulation for the Enhanced Ocular Bioavailability of Prostaglandin Analogues in Glaucoma

Glaucoma is a wide-spread eye disease caused by elevated intraocular pressure. Uncontrolled, this pressure may lead to damages to the optic nerve. Prostaglandin analogues, such as latanoprost and travoprost (which are water-insoluble active substances), are the most used class of active pharmaceutical ingredient. To administer them as eye drops, preservatives, such as benzalkonium chloride, are used as solubilizers. The latter is known to cause a local inflammation when used chronically and is not recommended for patients with ocular surface disorders. In this work, we sought to use polysorbate 80 (PS80) as a solubilizing agent simultaneously with sodium hyaluronate (NaHA) as a thickener and cytoprotective agent for the corneal surface. The first part of this study assessed the compatibility of the excipients with the active substance, using physicochemical methods such as spectra fluorescence and differential scanning calorimetry (DSC), as well as the solubilization mechanism of PS80 regarding prostaglandin analogues using nuclear magnetic resonance (NMR). The second part evaluated the stability of a formula candidate, its viscosity upon instillation, and its pharmacokinetic profile in rabbits as compared to the commercially approved medicine Travatan®. The results show that sodium hyaluronate is inert with respect to travoprost, while PS80 successfully solubilizes it, meaning that benzalkonium chloride is no longer required. Moreover, the pharmacokinetic profiles of the rabbits showed that the original formula described in the present study enhanced the ocular bioavailability of the drug, making it a promising product to control intraocular pressure with a potential reduced dosage of travoprost, therefore minimizing its related side effects.

Imaging Methods for the Assessment of a Complex Hydrogel as an Ocular Drug Delivery System for Glaucoma Treatment: Opportunities and Challenges in Preclinical Evaluation

Glaucoma is one of the leading causes of loss of vision. The problems associated with the marketed formulations of anti-glaucoma drugs are low bioavailability, unwanted side effects, and low patient compliance. Hydrogels are an important class of soft materials that play a crucial role in developing an ocular drug delivery system. They assume a special significance in addressing the problems associated with the marketed formulations of eyedrops. An appropriate design of the hydrogel system capable of encapsulating single or multiple drugs for glaucoma has emerged in recent times to overcome such challenges. Although various modes of imaging play critical roles in assessing the efficacy of these formulations, evaluating hydrogels for drug permeation and retention remains challenging. Especially, the assessment of dual drugs in the hydrogel system is not straightforward due to the complexity in measuring drug penetration and retention for in vivo or ex vivo systems. There is a need to develop tools for the fabrication and validation of hydrogel-based systems that give insight into precorneal retention, biocompatibility, cellular uptake, and cell permeation. The current review highlights some of the complexities in formulating hydrogel and benchmarking technologies, including confocal laser scanning microscopy, fluorescent microscopy, slit-lamp biomicroscopy, and camera-based imaging. This review also summarizes recent evaluations of various hydrogel formulations using in vitro and in vivo models. Further the article will help researchers from various disciplines, including formulation scientists and biologists, set up preclinical protocols for evaluating polymeric hydrogels.

In-situ tear fluid dissolving nanofibers enable prolonged viscosity-enhanced dual drug delivery to the eye

Liquid and semi-solid formulations are the most commonly used drug delivery systems for ophthalmic diseases. Upon application into the conjunctival sac, these systems introduce a variable and unphysiologically high liquid volume to the eye, resulting in overflow and extensive nasolacrimal drainage, accounting for dosing inaccuracy and short ocular residence time. In this study, we present nanofibrous electrospun scaffolds composed of biocompatible polymers, overcoming these challenges by immediate drug release. The fibers incorporate gentamicin and dexamethasone, intended for the treatment of bacterial conjunctivitis. Upon contact with the ocular surface, the nanofibers immediately dissolve in the tear fluid, quantitatively releasing the two actives, yielding over92% drug recovery, determined with fluorimetric and chromatographic quantifications methods. Simultaneously, the viscosity of the tear fluid increases, shown by complex viscometry measurements. A newly developed ex vivo microfluidic porcine cornea model was used to evaluated ocular residence time. In contrast to fluid eye drops, the contact time was significantly prolonged and 20min after application, an increase in drug availability on the ocular surface of 342% was observed. Biocompatibility of the polymer system was demonstrated in an OECD approved in vitro cornea model. The antibacterial activity after processing was evaluated according to EUCAST guidelines, and storage stability of the system was confirmed over a 12-week period. This innovative drug delivery system poses a highly promising platform technology, overcoming challenges associated with conventional dosage forms for drug delivery to the anterior eye and thus significantly advancing therapeutic approaches.

Intranasal Hydrogel of Armodafinil Hydroxypropyl-β-Cyclodextrin Inclusion Complex for the Treatment of Post-Traumatic Stress Disorder

Armodafinil inclusion complex (AIC) hydrogel was prepared and evaluated for its therapeutic effect on Post-traumatic Stress Disorder (PTSD). After computer simulation and physicochemical property investigation, the AIC was formed by lyophilization of armodafinil with ethanol as solvent and hydroxypropyl-beta-cyclodextrin (HP-β-CD) aqueous solution, in which the molar ratio of armodafinil and HP-β-CD was 1–1. The AIC encapsulation efficiency (EE) was (90.98 ± 3.72)% and loading efficiency (LE) was (13.95 ± 0.47)% and it increased the solubility of armodafinil in aqueous solution to 21 times. AIC hydrogel was prepared by adding AIC to methylcellulose (MC) hydrogels (3.33% w/v), and its higher drug release amount and slower release rate were testified by the in-vitro release assay and the rheological test. The mucosa irritation of AIC hydrogel was also evaluated. Healthy group, Model group, Sertraline group with 30 mg/kg sertraline gavage, AIC Hydrogel group with 20 mg/kg AIC hydrogel intranasal administration and AIC Aqueous Solution group with 20 mg/kg AIC aqueous solution gavage were set up for the treatment of mice with PTSD generated from foot shock method. Based on freezing response test in fear-conditioning box and open field test, compared with other groups, PTSD mice in AIC Hydrogel group showed significant improvement in behavioral parameters after 11 days of continuous drug administration and 5 days of drug withdrawal. After sacrifice, the plasma CORT level of PTSD mice in AIC Hydrogel group was elevated compared to Model group. Besides, the western blot (WB) of hippocampal brain-derived neurotrophic factor (BDNF) and amygdala dopamine transporter (DAT) immunohistochemistry sections indicated that AIC hydrogel had a protective effect on the brain tissue of PTSD mice. The brain targeting of intranasal administration was evaluated by fluorescence imaging characteristics of Cy7 hydrogel in the nasal route of drug administration, pharmacokinetics and in-vivo distribution of armodafinil. In short, AIC hydrogel is a promising formulation for the treatment of PTSD based on its high brain delivery and anti-PTSD effect.

Mucoadhesive Polymers Enhance Ocular Drug Delivery: Proof of Concept Study with 0.5% Tropicamide in Dogs

Purpose: To assess the efficacy of 0.5% tropicamide applied after topical administration of 1.4% hydroxyethyl cellulose (HEC) or 1.2% hyaluronic acid (HA) at different time intervals. Methods: Eleven healthy Labrador retriever dogs were used. The study consisted of 7 trials in which pupil diameter (PD) was measured every 30 min for 7 h after drug administration. In trial 1, PD was measured after tropicamide application (control). In trials 2-7, PD was measured after treatment with tropicamide 10 s, 1 and 5 min after application of HEC or HA. Data were analyzed using analysis of variance and post hoc Holm-Sidak tests. Results: Maximal PD (mean ± standard deviation) was significantly greater (P < 0.001) in 5 of 6 experimental trials, with the greatest PD recorded when HEC was applied 1 min (12.2 ± 0.4 mm) and HA 10 s (12.3 ± 0.5 mm) before tropicamide, compared with 11.2 ± 0. 7 mm in control trial 1. PD >10 mm was maintained for 2.75-5 h in trials 2-7 and 2.25 h in trial 1 (P < 0.001). Area under the PD-time curve ranged from 61.9 to 71.3 ± 2.9 mm·hours in trials 2-7, significantly greater than 59.3 ± 1.8 mm·hours in control trial 1 (P ≤ 0.031). Conclusions: Tropicamide efficacy was enhanced by prior administration of a mucoadhesive polymer. Additional studies are needed to determine if HEC and HA of varying concentrations similarly extend and potentiate the effect of other topical ophthalmic drugs in canine eyes.

Cellulosic Polymers for Enhancing Drug Bioavailability in Ocular Drug Delivery Systems

One of the major impediments to drug development is low aqueous solubility and thus poor bioavailability, which leads to insufficient clinical utility. Around 70–80% of drugs in the discovery pipeline are suffering from poor aqueous solubility and poor bioavailability, which is a major challenge when one has to develop an ocular drug delivery system. The outer lipid layer, pre-corneal, dynamic, and static ocular barriers limit drug availability to the targeted ocular tissues. Biopharmaceutical Classification System (BCS) class II drugs with adequate permeability and limited or no aqueous solubility have been extensively studied for various polymer-based solubility enhancement approaches. The hydrophilic nature of cellulosic polymers and their tunable properties make them the polymers of choice in various solubility-enhancement techniques. This review focuses on various cellulose derivatives, specifically, their role, current status and novel modified cellulosic polymers for enhancing the bioavailability of BCS class II drugs in ocular drug delivery systems.

Polymeric long-acting drug delivery systems (LADDS) for treatment of chronic diseases: Inserts, patches, wafers, and implants

Non-oral long-acting drug delivery systems (LADDS) encompass a range of technologies for precisely delivering drug molecules into target tissues either through the systemic circulation or via localized injections for treating chronic diseases like diabetes, cancer, and brain disorders as well as for age-related eye diseases. LADDS have been shown to prolong drug release from 24 h up to 3 years depending on characteristics of the drug and delivery system. LADDS can offer potentially safer, more effective, and patient friendly treatment options compared to more invasive modes of drug administration such as repeated injections or minor surgical intervention. Whilst there is no single technology or definition that can comprehensively embrace LADDS; for the purposes of this review, these systems include solid implants, inserts, transdermal patches, wafers and in situ forming delivery systems. This review covers common chronic illnesses, where candidate drugs have been incorporated into LADDS, examples of marketed long-acting pharmaceuticals, as well as newly emerging technologies, used in the fabrication of LADDS.

Wettability and contact angle affect precorneal retention and pharmacodynamic behavior of microspheres

In the present study, we describe the development of betaxolol hydrochloride and montmorillonite with ion exchange in a single formulation to create a novel micro-interactive dual-functioning sustained-release delivery system (MIDFDS) for the treatment of glaucoma. Betaxolol hydrochloride molecule was loaded onto the montmorillonite by ion exchange and MIDFDS formation was confirmed by XPS data. MIDFDS showed similar physicochemical properties to those of Betoptic, such as particle size, pH, osmotic pressure, and rheological properties. Nevertheless, the microdialysis and intraocular pressure test revealed better in vivo performance of MIDFDS, such as pharmacokinetics and pharmacodynamics. With regards to wettability, MIDFDS had a larger contact angle (54.66 ± 5.35°) than Betoptic (36.68 ± 1.77°), enabling the MIDFDS (2.93 s) to spread slower on the cornea than Betoptic (2.50 s). Moderate spreading behavior and oppositely charged electrostatic micro-interactions had a comprehensive influence on micro-interactions with the tear film residue, resulting in a longer precorneal retention time. Furthermore, MIDFDS had a significant sustained-release effect, with complete release near the cornea. The dual-functioning sustained-release carrier together with prolonged pre-corneal retention time (80 min) provided sufficiently high drug concentrations in the aqueous humor to achieve a more stable and long-term IOP reduction for 10 h. In addition, cytotoxicity and hemolysis tests showed that MIDFDS had better biocompatibility than Betoptic. The dual-functioning microspheres presented in this study provide the possibility for improved compliance due to low cytotoxicity and hemolysis, which suggests promising clinical implications.

Promising Polymeric Drug Carriers for Local Delivery: The Case of in situ Gels

BACKGROUND

At present, the controlled local drug delivery is a very promising approach compared to systemic administration, since it mostly targets the affected tissue. In fact, various drug carriers for local delivery have been prepared with improved therapeutic efficacy.

OBJECTIVE

in situ polymer gels are drug delivery systems that not only present liquid characteristics before their administration in body, but once they are administered, form gels due to gelation. Their gelation mechanism is due to factors such as pH alteration, temperature change, ion activation or ultraviolet irradiation. in situ gels offer various advantages compared to conventional formulations due to their ability to release drugs in a sustainable and controllable manner. Most importantly, in situ gels can be used in local drug delivery applications for various diseases.

METHODS

This review includes the basic knowledge and theory of in situ gels as well as their various applications according to their administration route.

RESULTS

Various natural, semisynthetic, and synthetic polymers can produce in situ polymeric gels. For example, natural polysaccharides such as alginic acid, chitosan, gellan gum, carrageenan etc. have been utilized as in situ gels for topical delivery. Besides the polysaccharides, poloxamers, poly(Nisopropylacrylamide), poly(ethyleneoxide)/ (lactic-co-glycolic acid), and thermosensitive liposome systems can be applied as in situ gels. In most cases, in situ polymeric gels could be applied via various administration routes such as oral, vaginal, ocular, intranasal and injectable.

CONCLUSION

To conclude, it can be revealed that in situ gels could be a promising alternative carrier for both chronic and immediate diseases.

Betaxolol-loaded niosomes integrated within pH-sensitive in situ forming gel for management of glaucoma

Blindness and impaired vision are considered as the most troublesome health conditions leading to significant socioeconomic strains. The current study focuses on development of nanoparticulate systems (i.e., niosomes) as drug vehicles to enhance the ocular availability of betaxolol hydrochloride for management of glaucoma. Betaxolol-loaded niosomes were further laden into pH-responsive in situ forming gels to further extend precorneal retention of the drug. The niosomes were evaluated in terms of vesicle size, morphology, size distribution, surface charge and encapsulation efficiency. The optimized niosomes, comprised of Span® 40 and cholesterol at a molar ratio of 4:1, displayed particle size of 332 ± 7 nm, zeta potential of -46 ± 1 mV, and encapsulation efficiency of 69 ± 5%. The optimal nanodispersion was then incorporated into a pH-triggered in situ forming gel comprised of Carbopol® 934P and hydroxyethyl cellulose. The formed gels were translucent, pseudoplastic, mucoadhesive, and displayed a sustained in vitro drug release pattern. Upon instillation of the betaxolol-loaded niosomal gel into rabbits' eyes, a prolonged intraocular pressure reduction and significant enhancement in the relative bioavailability of betaxolol (280 and 254.7%) in normal and glaucomatous rabbits, were attained compared to the marketed eye drops, respectively. Hence, the developed pH-triggered nanoparticulate gelling system might provide a promising carrier for ophthalmic drug delivery and for improved augmentation of glaucoma.

Ocular films versus film-forming liquid systems for enhanced ocular drug delivery

The short residence time, corneal barrier functions, and other effective eye protective mechanisms limited the ocular availability after topical application. Ocular inserts are being developed as polymer films for insertion into the conjunctival sac with the goal of increasing ocular availability. Unfortunately, these devices are not convenient for patients and are associated with many problems. The use of in situ gel/film-forming systems may provide promising alternative with comparable efficacy but this requires verification. Therefore, the current study compared ocular inserts with in situ film-forming liquids containing the same polymer components for ocular delivery of pilocarpine nitrate. Solvent casting technique was employed to prepare the inserts using and polyvinyl alcohol (PVA) as film-forming polymer blended with sodium alginate, as bioadhesive polymer. The effect of addition of either carboxymethycellulose, carbopol, polyvinylpyrrolidone, or methylcellulose was investigated. Solid-state characterization of the inserts indicated compatibility of the drug with film component. All inserts were of acceptable bioadhesive parameters and folding endurance that depended on the film composition. In vitro release studies reflected matrix diffusion kinetics for the film and liquid formulations. This confirms the in situ gelation of liquids. The calculated in vivo miotic pharmacokinetics parameters, using albino rabbits, reflected a better rank for the film but the difference was not statistically different from the in situ gel/film-forming systems. Ocular safety, as reflected by tear volume test, indicated acceptable safety of both liquid and inserts to the eye. The study suggested comparable efficacy of film-forming liquids to that of ocular films. Graphical abstract.

In Situ Gelling Ophthalmic Drug Delivery System for the Optimization of Diagnostic and Preoperative Mydriasis: In Vitro Drug Release, Cytotoxicity and Mydriasis Pharmacodynamics

Mydriasis is required prior to many eye examinations and ophthalmic surgeries. Nowadays, phenylephrine hydrochloride (PHE) and tropicamide (TPC) are extensively used to induce mydriasis. Several pharmaceutic dosage forms of these two active ingredients have been described. However, no optimal therapeutic strategy has reached the market. The present work focuses on the formulation and evaluation of a mucoadhesive ion-activated in situ gelling delivery system based on gellan gum and hydroxyethylcellulose (HEC) for the delivery of phenylephrine and tropicamide. First, in vitro drug release was studied to assess appropriate sustained drug delivery on the ocular surface region. Drug release mechanisms were explored and explained using mathematical modeling. Then, in situ gelling delivery systems were visualized using scanning electron microscopy illustrating the drug release phenomena involved. Afterward, cytotoxicity of the developed formulations was studied and compared with those of commercially available eye drops. Human epithelial corneal cells were used. Finally, mydriasis intensity and kinetic was investigated in vivo. Mydriasis pharmacodynamics was studied by non-invasive optical imaging on vigilant rabbits, allowing eye blinking and nasolacrimal drainage to occur physiologically. In situ gelling delivery systems mydriasis profiles exhibited a significant increase of intensity and duration compared with those of conventional eye drops. Efficient mydriasis was achieved following the administration of a single drop of in situ gel reducing the required amount of administered active ingredients by four- to eight-fold compared with classic eye drop regimen.