Thermosensitive chitosan-based hydrogel as a topical ocular drug delivery system of latanoprost for glaucoma treatment

Emerging trends in long-acting sustained drug delivery for glaucoma management

Glaucoma is an optic neuropathy in which progressive degeneration of retinal ganglion cells and the optic nerve leads to irreversible visual loss. Glaucoma is one of the leading causes of blindness. The pathogenesis of glaucoma is determined by different pathogenetic mechanisms, including increased intraocular pressure, mechanical stress, excitotoxicity, resistance to aqueous drainage and oxidative stress. Topical formulations are often used in glaucoma treatment, whereas surgical measures are used in acute glaucoma cases. For most patients, long-term glaucoma treatments are given. Poor patient compliance and low bioavailability are often associated with topical therapy, which suggests that sustained-release, long-acting drug delivery systems could be beneficial in managing glaucoma. This review summarizes the eye's physiology, the pathogenesis of glaucoma, current treatments, including both pharmacological and nonpharmacological interventions, and recent advances in long-acting drug delivery systems for the treatment of glaucoma.

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.

Absorption enhancement strategies in chitosan-based nanosystems and hydrogels intended for ocular delivery: Latest advances for optimization of drug permeation

Ophthalmic diseases can be presented as acute diseases like allergies, ocular infections, etc., or chronic ones that can be manifested as a result of systemic disorders, like diabetes mellitus, thyroid, rheumatic disorders, and others. Chitosan (CS) and its derivatives have been widely investigated as nanocarriers in the delivery of drugs, genes, and many biological products. The biocompatibility and biodegradability of CS made it a good candidate for ocular delivery of many ingredients, including immunomodulating agents, antibiotics, ocular hypertension medications, etc. CS-based nanosystems have been successfully reported to modulate ocular diseases by penetrating biological ocular barriers and targeting and controlling drug release. This review provides guidance to drug delivery formulators on the most recently published strategies that can enhance drug permeation to the ocular tissues in CS-based nanosystems, thus improving therapeutic effects through enhancing drug bioavailability. This review will highlight the main ocular barriers to drug delivery observed in the nano-delivery system. In addition, the CS physicochemical properties that contribute to formulation aspects are discussed. It also categorized the permeation enhancement strategies that can be optimized in CS-based nanosystems into four aspects: CS-related physicochemical properties, formulation components, fabrication conditions, and adopting a novel delivery system like implants, inserts, etc. as described in the published literature within the last ten years. Finally, challenges encountered in CS-based nanosystems and future perspectives are mentioned.

In situ forming hydrogels based on modified gellan gum/chitosan for ocular drug delivery of timolol maleate

In situ forming hydrogels are suitable candidates for increasing drug residence time in ocular drug delivery. In this study, gellan gum (GG) was oxidized to form aldehyde groups and in situ gelling hydrogels were synthesized based on a Schiff-base reaction between oxidized GG (OGG) and chitosan (CS) in the presence of β-glycerophosphate. The effect of OGG and CS concentration on the physical and chemical properties of the resulting hydrogels was investigated. The FT-IR spectroscopy confirmed the chemical modification of OGG as well as the functional groups of the prepared hydrogels. The scanning electron microscope (SEM) revealed the highly porous structure of hydrogels. The obtained hydrogels indicated a high swelling degree and degradability. Also, the rheological studies demonstrated self-healing behavior, shear thinning, thixotropy, and mucoadhesion properties for the developed hydrogels. The results of in vitro and ex vivo studies showed that the timolol-loaded hydrogel with a higher amount of OGG has a higher release rate. Moreover, the MTT cytotoxicity test on bone marrow mesenchymal stem cells (BMSCs) confirmed that developed hydrogels are not toxic. The obtained results revealed that the developed hydrogels can be a desirable choice for the ocular drug delivery of timolol in the treatment of glaucoma.

Recent advances in modified chitosan-based drug delivery systems for transmucosal applications: A comprehensive review

Recently, transmucosal drug delivery systems (TDDSs) have been extensively studied because they protect therapeutic agents from degradation; improve drug residence time at the mucosal membranes; and facilitate sustained drug release for a prolonged period. Chitosan is a well-researched polymeric excipient due to its biocompatibility, non-toxicity, biodegradability, mucoadhesive, antimicrobial, and low immunogenicity. Its limited mucoadhesiveness in the physiological environment necessitated its chemical modification. This review highlights the recent advances in the chemical modification of chitosan with various chemical groups to generate various functionalized chitosan derivatives, such as thiolated, acrylated, methacrylated, boronated, catechol, and maleimide-functionalized chitosans with superior mucoadhesive capabilities compared to the parent chitosan. Moreover, it presents the different prepared dosage forms, such as tablets, hydrogels, films, micro/nanoparticles, and liposomes/niosomes for drug administration within various mucosal routes including oral, buccal, nasal, ocular, colonic, intravesical, and vaginal routes. The reported data from preclinical studies of these pharmaceutical formulations have revealed the controlled and target-specific delivery of therapeutics because of their formation of covalent bonds with thiol groups on the mucosal surface. All functionalized chitosan derivatives exhibited long drug residence time on mucosal surfaces and sustainable drug release with excellent cellular permeability, drug efficacy, and biocompatibility. These promising data could be translated from the research laboratories to the clinics with consistent and intensive research effort.

Exploring Hydrogel Nanoparticle Systems for Enhanced Ocular Drug Delivery

Drug delivery to the ocular system is affected by anatomical factors like the corneal epithelium, blinking reflex, aqueous blood barrier, and retinal blood barrier, which lead to quick removal from the site and inefficient drug delivery. Developing a drug delivery mechanism that targets specific eye tissue is a major hurdle for researchers. Our study examines the challenges of drug absorption in these pathways. Hydrogels have been researched as a suitable delivery method to overcome some obstacles. These are developed alone or in conjunction with other technologies, such as nanoparticles. Many polymer hydrogel nanoparticle systems utilizing both natural and synthetic polymers have been created and investigated; each has pros and cons. The complex release mechanism of encapsulated agents from hydrogel nanoparticles depends on three key factors: hydrogel matrix swelling, drug-matrix chemical interactions, and drug diffusion. This mechanism exists regardless of the type of polymer. This study provides an overview of the classification of hydrogels, release mechanisms, and the role of controlled release systems in pharmaceutical applications. Additionally, it highlights the integration of nanotechnology in ocular disease therapy, focusing on different types of nanoparticles, including nanosuspensions, nanoemulsions, and pharmaceutical nanoparticles. Finally, the review discusses current commercial formulations for ocular drug delivery and recent advancements in non-invasive techniques. The objective is to present a comprehensive overview of the possibilities for enhancing ocular medication delivery through hydrogel nanoparticle systems.

Interaction-Based Perspective for Designing Polymer Biomaterial: A Strategic Approach to the Chitosan-Glycerophosphate System

The conventional approach for developing any polymeric biomaterial is to follow protocols available in the literature and/or perform trial-and-error runs without a scientific basis. Here, we propose an analysis of a complex overlay of molecular interactions between drugs and polymers that provides a strategic pathway for biomaterial development. First, this work provides an innovative interaction-based method for developing an ocular formulation involving in situ gelling chitosan, gelatin, and glycerophosphate systems. A systematic interaction study is conducted based on the measurement of hydrodynamic radius, zeta potential, and viscosity with the sequential addition of formulation components. The increase in the hydrodynamic radius of the polymer with the addition of drugs can be interpreted as better diffusion of the drug inside the charged polymer chains and vice versa. Based on the knowledge of these interactions, a formulation has been designed that shows better drug release results with extended and sustained release compared to literature protocols, hence accentuating the importance of this study. An in-depth analysis of interactions can lead to a better understanding of the system. Second, we demonstrate the development of two dual-drug biomaterial systems, i.e., an in situ gelling and a liquid formulation at ocular surface temperature from the same polymers, which can be used as an ocular antiglaucoma formulation. Prior knowledge of the interactions between the drug polymers can be used to design a better formulation. The demonstrated application of this interaction-based protocol development can be extended universally to any biomaterial. This would provide a comprehensive idea about the properties and interactions of polymers and drugs, which can also serve as a base/starting point for a new formulation/biomaterial development.

Synergistic effect of chitosan and β-carotene in inhibiting MNU-induced retinitis pigmentosa

In this study, N-Methyl-N-nitrosourea (MNU) was intraperitoneally injected to construct a mouse retinitis pigmentosa (RP) model to evaluate the protective effect of chitosan and β-carotene on RP. The results demonstrated that chitosan synergized with β-carotene significantly reduced retinal histopathological structural damage in RP mice. The co-treatment group of β-carotene and chitosan restored the retinal thickness and outer nuclear layer thickness better than the group treated with the two alone, and the thickness reached the normal level. The content of β-carotene and retinoids in the liver of chitosan and β-carotene co-treated group increased by 46.75 % and 20.69 %, respectively, compared to the β-carotene group. Chitosan and β-carotene supplement suppressed the expressions of Bax, Calpain2, Caspase3, NF-κB, TNF-α, IL-6, and IL-1β, and promoted the up-regulation of Bcl2. Chitosan and β-carotene interventions remarkably contributed to the content of SCFAs and enhanced the abundance of Ruminococcaceae, Rikenellaceae, Odoribacteraceae and Helicobacteraceae. Correlation analysis demonstrated a strong association between gut microbiota and improvement in retinitis pigmentosa. This study will provide a reference for the study of the gut-eye axis.

Biomedical Trends in Stimuli-Responsive Hydrogels with Emphasis on Chitosan-Based Formulations

Biomedicine is constantly evolving to ensure a significant and positive impact on healthcare, which has resulted in innovative and distinct requisites such as hydrogels. Chitosan-based formulations stand out for their versatile utilization in drug encapsulation, transport, and controlled release, which is complemented by their biocompatibility, biodegradability, and non-immunogenic nature. Stimuli-responsive hydrogels, also known as smart hydrogels, have strictly regulated release patterns since they respond and adapt based on various external stimuli. Moreover, they can imitate the intrinsic tissues' mechanical, biological, and physicochemical properties. These characteristics allow stimuli-responsive hydrogels to provide cutting-edge, effective, and safe treatment. Constant progress in the field necessitates an up-to-date summary of current trends and breakthroughs in the biomedical application of stimuli-responsive chitosan-based hydrogels, which was the aim of this review. General data about hydrogels sensitive to ions, pH, redox potential, light, electric field, temperature, and magnetic field are recapitulated. Additionally, formulations responsive to multiple stimuli are mentioned. Focusing on chitosan-based smart hydrogels, their multifaceted utilization was thoroughly described. The vast application spectrum encompasses neurological disorders, tumors, wound healing, and dermal infections. Available data on smart chitosan hydrogels strongly support the idea that current approaches and developing novel solutions are worth improving. The present paper constitutes a valuable resource for researchers and practitioners in the currently evolving field.

Chitosan oligosaccharide/pluronic F127 micelles exhibiting anti-biofilm effect to treat bacterial keratitis

Mono or dual chitosan oligosaccharide lactate (COL)-conjugated pluronic F127 polymers, FCOL1 and FCOL2 were prepared, self-assembled to form micelles, and loaded with gatifloxacin. The Gati@FCOL1/Gati@FCOL2 micelles preparation process was optimized by QbD analysis. Micelles were characterized thoroughly for size, CMC, drug compatibility, and viscosity by GPC, DLS, SEM, IR, DSC, and XRD. The micelles exhibited good cellular uptake in both monolayers and spheroids of HCEC. The antibacterial and anti-biofilm activities of the micelles were evaluated on P. aeruginosa and S. aureus. The anti-quorum sensing activity was explored in P. aeruginosa by analyzing micelles' ability to produce virulence factors, including AHLs, pyocyanin, and the motility behavior of the organism. Gati@FCOL2 Ms was mucoadhesive, cornea-penetrant, antibacterial, and inhibited the biofilm formation by P. aeruginosa and S. aureus significantly more than Gati@FCOL1. A significant reduction in bacterial load in mice cornea was observed after Gati@FCOL2 Ms-treatment to the P. aeruginosa-induced bacterial keratitis-infected mice.

Next generation therapeutics for retinal neurodegenerative diseases

Neurodegenerative diseases affecting the visual system encompass glaucoma, macular degeneration, retinopathies, and inherited genetic disorders such as retinitis pigmentosa. These ocular pathologies pose a serious burden of visual impairment and blindness worldwide. Current treatment modalities include small molecule drugs, biologics, or gene therapies, most of which are administered topically as eye drops or as injectables. However, the topical route of administration faces challenges in effectively reaching the posterior segment and achieving desired concentrations at the target site, while injections and implants risk severe complications, such as retinal detachment and endophthalmitis. This necessitates the development of innovative therapeutic strategies that can prolong drug release, deliver effective concentrations to the back of the eye with minimal systemic exposure, and improve patient compliance and safety. In this review, we introduce retinal degenerative diseases, followed by a discussion of the existing clinical standard of care. We then delve into detail about drug and gene delivery systems currently in preclinical and clinical development, including formulation and delivery advantages/drawbacks, with a special emphasis on potential for clinical translation.

Topical ocular administration using thermosensitive chitosan-glycerophosphate-PRP hydrogels for improved ocular bioavailability

PURPOSE

One of the difficulties in the pharmacy field is the delivery of drugs for the eyes. Topical therapy is one of the most common methods for treating eye diseases. Due to their unique properties, including biocompatibility and suitable degradation, hydrogels are appropriate for biological purposes. Platelet-rich plasma (PRP), as a designated concentration of platelets, is in a smaller volume than the plasma and is considered a rich source of growth factor that has been used in recent years, including applications in eye diseases including corneal wound healing, improvement of dry eye and post-LASIK syndrome.

METHODS

The present study was performed to fabricate Chitosan (CS) and glycerophosphate (GP) based hydrogels that are temperature-sensitive for PRP and investigate their effect on ocular stem cells.

RESULTS

CS-GP-based temperature-sensitive hydrogels containing PRP were successfully fabricated using CS and GP. This hydrogel is liquid at ambient temperature and a gel at ocular temperature. Rheology, FTIR, and SEM tests assessed the properties of the hydrogels. The results of the MTT test showed that the hydrogel made with the optimal formulation was not toxic to LSC cell lines.

CONCLUSIONS

Given this, CS-GP-based hydrogels can be applied as a biocompatible formulation in ocular medication administration with increased bioavailability at the ocular surface and topical delivery of PRP.

Recent developments in natural biopolymer based drug delivery systems

Targeted delivery of drug molecules to diseased sites is a great challenge in pharmaceutical and biomedical sciences. Fabrication of drug delivery systems (DDS) to target and/or diagnose sick cells is an effective means to achieve good therapeutic results along with a minimal toxicological impact on healthy cells. Biopolymers are becoming an important class of materials owing to their biodegradability, good compatibility, non-toxicity, non-immunogenicity, and long blood circulation time and high drug loading ratio for both macros as well as micro-sized drug molecules. This review summarizes the recent trends in biopolymer-based DDS, forecasting their broad future clinical applications. Cellulose chitosan, starch, silk fibroins, collagen, albumin, gelatin, alginate, agar, proteins and peptides have shown potential applications in DDS. A range of synthetic techniques have been reported to design the DDS and are discussed in the current study which is being successfully employed in ocular, dental, transdermal and intranasal delivery systems. Different formulations of DDS are also overviewed in this review article along with synthesis techniques employed for designing the DDS. The possibility of these biopolymer applications points to a new route for creating unique DDS with enhanced therapeutic qualities for scaling up creative formulations up to the clinical level.

Chitosan-poly(lactide-co-glycolide)/poloxamer mixed micelles as a mucoadhesive thermo-responsive moxifloxacin eye drop to improve treatment efficacy in bacterial keratitis

A mucoadhesive self-assembling polymeric system was developed to carry moxifloxacin (M) for treating bacterial keratitis (BK). Chitosan-PLGA (C) conjugate was synthesized, and poloxamers (F68/127) were mixed in different proportions (1: 5/10) to prepare moxifloxacin (M)-encapsulated mixed micelles (M@CF68/127(5/10)Ms), including M@CF68(5)Ms, M@CF68(10)Ms, M@CF127(5)Ms, and M@CF127(10)Ms. The corneal penetration and mucoadhesiveness were determined biochemically, in vitro using human corneal epithelial (HCE) cells in monolayers and spheroids, ex vivo using goat cornea, and in vivo via live-animal imaging. The antibacterial efficacy was studied on planktonic biofilms of P. aeruginosa and S. aureus (in vitro) and Bk-induced mice (in vivo). Both M@CF68(10)Ms and M@CF127(10)Ms demonstrated high cellular uptake, corneal retention, muco-adhesiveness, and antibacterial effect, with M@CF127(10)Ms exhibiting superior therapeutic effects in P. aeruginosa and S. aureus-infected BK mouse model by reducing the corneal bacterial load and preventing corneal damage. Therefore, the newly developed nanomedicine is promising for clinical translation in treating BK.

Preparation and performance of latanoprost-loaded hydrogels as a lacrimal suppository for the treatment of glaucoma

Glaucoma is the leading cause of irreversible blindness, and its treatment is attracting widespread attention. Drug-loaded lacrimal suppositories can effectively treat xerophthalmia, but there is little research on the treatment of glaucoma with drug-loaded lacrimal suppositories. This article explored and expanded the non-pharmacological model of lacrimal suppository therapy for glaucoma by using a combination of lacrimal suppository and medication. The drug-loaded lacrimal suppository was rationally designed through the conjugation of gelatin with polyamide (PAM) via the formation of amide linkages, followed by Schiff base reaction grafting with latanoprost. In vitro drug release studies showed that latanoprost released from drug-loaded lacrimal embolus had sustained-release properties with a release time of 33 days and a drug release volume of 82.6%. The biological evaluation of drug-loaded lacrimal thrombus was carried out by IOP test, retinal potential test, and retinal H&E staining. The results showed that the IOP decreased to 27.125 ± 1.1254 mmHg, and the a and b waves of retinal potential increased to 4.39 ± 0.16 μV and 67.9 ± 2.17 μV, respectively. It indicated that latanoprost lacrimal suppository has a good therapeutic effect on glaucoma.

Trends in development and quality assessment of pharmaceutical formulations - F2α analogues in the glaucoma treatment

The ocular delivery route presents a number of challenges in terms of drug administration and bioavailability. The low bioavailability following topical ophthalmic administration shows that there is a clear need for in-depth research aimed at finding both more efficacious molecules and formulations precisely targeted at the site of action. Continuous technological development will eventually result in improved bioavailability, lower dosages, reduced toxicity, fewer adverse effects, and thus better patient compliance and treatment efficacy. Technological development, as well as increasingly stringent quality requirements, help stimulate analytical progress. This is also clearly evident in the case of medicinal products used in the treatment of glaucoma, which are the subject of this review. Impurity profiling of PGF2α analogues, either in the pure substance or in the finished formulation, is a crucial step in assessing their quality. The development of specific, accurate and precise stability-indicating analytical methods for determining the content and related substances seems to be an important issue in relation to this tasks. A total of 27 official and in-house analytical methods are presented that are used for the analysis of latanoprost, travoprost and bimatoprost. The conditions for chromatographic separation with UV or MS/MS detection and the available results obtained during method validation are described. In addition, several aspects are discussed, with particular emphasis on the instability of the analogues in aqueous solution and the phenomenon of isomerism, which affects a potentially large number of degradation products.

Poloxamer and Chitosan-Based In Situ Gels Loaded with Orthosiphon stamineus Benth. Extracts Containing Rosmarinic Acid for the Treatment of Ocular Infections

Objectives

Orthosiphon stamineus Benth. (OS) is a commonly used medicinal plant for curbing bacterial infections globally. This work aimed to fabricate poloxamer and chitosan-based in situ gels loaded with standardized aqueous-ethanolic OS leaf extracts and investigate their antimicrobial efficacy as a potential remedy against ocular infections.

Materials and Methods

In situ gels containing 0.5% w/v OS extract prepared using cold dispersion method were subjected to physicochemical characterization, including in vitro-release studies. Antimicrobial efficacy was tested against Staphylococcus aureus, Micrococcus luteus, Escherichia coli, and Pseudomonas aeruginosa using agar diffusion method.

Results

Thin layer chromatography and high performance liquid chromatography chromatograms confirmed the presence of rosmarinic acid (RA) and sinensitin in OS extracts with same retention factor (0.26 and 0.49) and retention times (12.2 and 20.7 min) against reference standards. A homogenous brown coloured in situ gel exhibited low viscosity as a solution and increased viscosity in gel form at ocular temperature. The optimized formulations, P7 (21% P407/4% P188), P8 (21% P407/5% P188) and F5 (1.5% chitosan and 45% β-glycerophosphate) exhibited ideal ocular pH (7.27-7.46), phase transition at ocular temperature (33-37°C) and prolonged RA release up to 12 h. Formulation F5 showed an inhibition zone of 4.3 mm against M. luteus.

Conclusion

Among all, formulation F5 alone exhibited modest antimicrobial activity against M. luteus. OS extracts at 5% and 10% were most active against tested bacteria however, loading them into in situ gels resulted in sedimentation. Hence, isolation of RA from OS extract is suggested before loading into formulations for a better antimicrobial activity.

Polysaccharide-based hydrogels for drug delivery and wound management: a review

INTRODUCTION

Polysaccharide-based hydrogels (PBHs) offer several advantages over their synthetic counterparts. Their natural origin contributes to their nontoxicity, high biocompatibility, and in vivo biodegradability. Their properties can be tuned finely to obtain hydrogels with desired mechanical, structural, and chemical properties.

AREAS COVERED

Such versatile characteristics have potentiated the use of PBHs for the delivery of drugs, vaccines, protein and peptide therapeutics, genes, cells, probiotics, bacteriophages, and other therapeutic agents. Recent advances in hydrogel-based formulations such as nanogels, microgels, microneedles, hydrogel beads, nanocarrier-loaded hydrogels, and complexation hydrogels have enabled the precise delivery of a wide range of therapeutics. This review aims to give a holistic overview of hydrogels in the delivery of a variety of therapeutics through different routes.

EXPERT OPINION

PBHs have been used to enable the oral delivery of vaccines and other biologicals, thereby allowing self-administration of life-saving vaccines during public health emergencies. There is a lack of commercialized wound dressings for the treatment of chronic wounds. PBH-based wound dressings, especially those based on chitosan and loaded with actives and growth factors, have the potential to help in the long-term treatment of such wounds. Recent developments in the 3D printing of hydrogels can enable the quick and large-scale production of drug-loaded hydrogels.

Aqueous Prostaglandin Eye Drop Formulations

Glaucoma is one of the leading causes of irreversible blindness worldwide. It is characterized by progressive optic neuropathy in association with damage to the optic nerve head and, subsequently, visual loss if it is left untreated. Among the drug classes used for the long-term treatment of open-angle glaucoma, prostaglandin analogues (PGAs) are the first-line treatment and are available as marketed eye drop formulations for intraocular pressure (IOP) reduction by increasing the trabecular and uveoscleral outflow. PGAs have low aqueous solubility and are very unstable (i.e., hydrolysis) in aqueous solutions, which may hamper their ocular bioavailability and decrease their chemical stability. Additionally, treatment with PGA in conventional eye drops is associated with adverse effects, such as conjunctival hyperemia and trichiasis. It has been a very challenging for formulation scientists to develop stable aqueous eye drop formulations that increase the PGAs' solubility and enhance their therapeutic efficacy while simultaneously lowering their ocular side effects. Here the physiochemical properties and chemical stabilities of the commercially available PGAs are reviewed, and the compositions of their eye drop formulations are discussed. Furthermore, the novel PGA formulations for glaucoma treatment are reviewed.

Long-acting formulation strategies for protein and peptide delivery in the treatment of PSED

The invigoration of protein and peptides in serious eye disease includes age-related macular degeneration, choroidal neovascularization, retinal neovascularization, and diabetic retinopathy. The transportation of macromolecules like aptamers, recombinant proteins, and monoclonal antibodies to the posterior segment of the eye is challenging due to their high molecular weight, rapid degradation, and low solubility. Moreover, it requires frequent administration for prolonged therapy. The long-acting novel formulation strategies are helpful to overcome these issues and provide superior therapy. It avoids frequent administration, improves stability, high retention time, and avoids burst release. This review briefly enlightens posterior segments of eye diseases with their diagnosis techniques and treatments. This article mainly focuses on recent advanced approaches like intravitreal implants and injectables, electrospun injectables, 3D printed drug-loaded implants, nanostructure thin-film polymer devices encapsulated cell technology-based intravitreal implants, injectable and depots, microneedles, PDS with ranibizumab, polymer nanoparticles, inorganic nanoparticles, hydrogels and microparticles for delivering macromolecules in the eye for intended therapy. Furthermore, novel techniques like aptamer, small Interference RNA, and stem cell therapy were also discussed. It is predicted that these systems will make revolutionary changes in treating posterior segment eye diseases in future.

Glaucoma Treatment and Hydrogel: Current Insights and State of the Art

Aqueous gels formulated using hydrophilic polymers (hydrogels) and those based on stimuli-responsive polymers (in situ gelling or gel-forming systems) attract increasing interest in the treatment of several eye diseases. Their chemical structure enables them to incorporate various ophthalmic medications, achieving their optimal therapeutic doses and providing more clinically relevant time courses (weeks or months as opposed to hours and days), which will inevitably reduce dose frequency, thereby improving patient compliance and clinical outcomes. Due to its chronic course, the treatment of glaucoma may benefit from applying gel technologies as drug-delivering systems and as antifibrotic treatment during and after surgery. Therefore, our purpose is to review current applications of ophthalmic gelling systems with particular emphasis on glaucoma.

More than Antibiotics: Latest Therapeutics in the Treatment and Prevention of Ocular Surface Infections

Ocular surface infections have been common issues for ophthalmologists for decades. Traditional strategies for infection include antibiotics, antiviral agents, and steroids. However, multiple drug-resistant bacteria have become more common with the prevalence of antibiotic use. Furthermore, an ideal treatment for an infectious disease should not only emphasize eliminating the microorganism but also maintaining clear and satisfying visual acuity. Immunogenetic inflammation, tissue fibrosis, and corneal scarring pose serious threats to vision, and they are not attenuated or prevented by traditional antimicrobial therapeutics. Herein, we collected information about current management techniques including stem-cell therapy, probiotics, and gene therapy as well as preventive strategies related to Toll-like receptors. Finally, we will introduce the latest research findings in ocular drug-delivery systems, which may enhance the bioavailability and efficiency of ocular therapeutics. The clinical application of improved delivery systems and novel therapeutics may support people suffering from ocular surface infections.

Emerging Fabrication Strategies of Hydrogels and Its Applications

Recently, hydrogels have been investigated for the controlled release of bioactive molecules, such as for living cell encapsulation and matrices. Due to their remote controllability and quick response, hydrogels are widely used for various applications, including drug delivery. The rate and extent to which the drugs reach their targets are highly dependent on the carriers used in drug delivery systems; therefore the demand for biodegradable and intelligent carriers is progressively increasing. The biodegradable nature of hydrogel has created much interest for its use in drug delivery systems. The first part of this review focuses on emerging fabrication strategies of hydrogel, including physical and chemical cross-linking, as well as radiation cross-linking. The second part describes the applications of hydrogels in various fields, including drug delivery systems. In the end, an overview of the application of hydrogels prepared from several natural polymers in drug delivery is presented.

Thermo-sensitivity and erosion of chitosan crosslinked poly[N-isopropylacrylamide-co-(acrylic acid)-co-(methyl methacrylate)] hydrogels for application to the inferior fornix

Thermo-gels based on chitosan crosslinked poly(N-isopropylacrylamide) were developed as alternatives to conventional eye drops for the sustained release of ketotifen fumarate in the treatment of allergic conjunctivitis. The thermo-gelling properties of the base polymer were altered prior to crosslinking with chitosan by incorporation of the hydrophilic and hydrophobic comonomers acrylic acid and methyl methacrylate respectively. Varying amounts of chitosan were incorporated by ionic interaction to produce polyelectrolyte complexes or by carbodiimide chemistry to produce covalently crosslinked networks. The lower critical solution temperature of all the chitosan crosslinked thermo-gels produced was below the surface temperature of the eye. All the chitosan crosslinked thermo-gels were found to have greater than 80% equilibrium water contents following gelation. The method and amount of chitosan incorporation allowed for tailor-ability of material rheologic properties, with full degradation occurring over a one-to-four-day period, and tailorable rates of release of 40-60% of the loaded allergy medication ketotifen fumarate. The chitosan crosslinked thermo-gels were demonstrated to be nontoxic both in vitro and in vivo. It was demonstrated that the synthesized materials could be applied to the inferior fornix of eye, sustaining a multiple day release of ketotifen fumarate, as an alternative to conventional eyedrops. STATEMENT OF SIGNIFICANCE: Topical eyedrops are the main treatment modality for anterior ocular conditions. However, due to the natural clearance mechanisms of the eye, topical eyedrops are well established to be largely ineffective as a method of drug delivery. Herein, we investigate a method of altering thermo-gel properties of an n-isopropylacrylamide based polymer to enable the incorporation of greater amounts of chitosan by different methods of crosslinking. By controlling the synthesis parameters, final material properties can be tailored to impart ideal spreading, retention on the eye, and the rate of degradation and drug release over several days. This work also focuses on studying the rheological properties of the chitosan crosslinked thermo-gels which has not been investigated previously.

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.

Considerations for Polymers Used in Ocular Drug Delivery

PURPOSE

Age-related eye diseases are becoming more prevalent. A notable increase has been seen in the most common causes including glaucoma, age-related macular degeneration (AMD), and cataract. Current clinical treatments vary from tissue replacement with polymers to topical eye drops and intravitreal injections. Research and development efforts have increased using polymers for sustained release to the eye to overcome treatment challenges, showing promise in improving drug release and delivery, patient experience, and treatment compliance. Polymers provide unique properties that allow for specific engineered devices to provide improved treatment options. Recent work has shown the utilization of synthetic and biopolymer derived biomaterials in various forms, with this review containing a focus on polymers Food and Drug Administration (FDA) approved for ocular use.

METHODS

This provides an overview of some prevalent synthetic polymers and biopolymers used in ocular delivery and their benefits, brief discussion of the various types and synthesis methods used, and administration techniques. Polymers approved by the FDA for different applications in the eye are listed and compared to new polymers being explored in the literature. This article summarizes research findings using polymers for ocular drug delivery from various stages: laboratory, preclinical studies, clinical trials, and currently approved. This review also focuses on some of the challenges to bringing these new innovations to the clinic, including limited selection of approved polymers.

RESULTS

Polymers help improve drug delivery by increasing solubility, controlling pharmacokinetics, and extending release. Several polymer classes including synthetic, biopolymer, and combinations were discussed along with the benefits and challenges of each class. The ways both polymer synthesis and processing techniques can influence drug release in the eye were discussed.

CONCLUSION

The use of biomaterials, specifically polymers, is a well-studied field for drug delivery, and polymers have been used as implants in the eye for over 75 years. Promising new ocular drug delivery systems are emerging using polymers an innovative option for treating ocular diseases because of their tunable properties. This review touches on important considerations and challenges of using polymers for sustained ocular drug delivery with the goal translating research to the clinic.

Dexamethasone-Loaded Injectable In-situ Thermal Crosslinking Magnetic Responsive Hydrogel for the Physiochemical Stimulation of Acupoint to Suppress Pain in Sciatica Rats

The physicochemical stimulation of acupoints is a widespread treatment strategy for different diseases, such as sciatica. Its efficacy is mainly based on the temporal and spatial modulation of the physicochemical properties of the acupoints. The existing therapies based on the stimulation of acupoints have certain disadvantages. Therefore, in this study, injectable dexamethasone (DXM)- and magnetic Fe₃O₄ nanoparticles-loaded chitosan/β-glycerophosphate (CS/GP) thermal crosslinking hydrogels were prepared, thereby improving the performance of embedding materials. The sciatica rat models were established to compare the therapeutic effects of hydrogels and catgut. The DXM or Fe₃O₄-loaded CS/GP hydrogels were compared in terms of their gelation kinetics, release kinetics, magnetic responsiveness in-vitro, and biocompatibility as well as their analgesic effects on the chronic constriction injury of the sciatic nerve (CCI) rats in-vivo. The CS/GP/Fe₃O₄/DXM hydrogel showed comparable gelation kinetics and good magnetic responsiveness in-vitro. This hydrogel could relieve sciatica by reducing the expression levels of inflammatory factors in serum, inhibiting the p38MAPK (p38, mitogen-activated protein kinase) phosphorylation, and decreasing the expression level of the P2X4 receptor (P2X4R) in the spinal dorsal horn. In conclusion, the DXM or Fe₃O₄-loaded CS/GP hydrogels can be considered as a treatment option for the physiochemical stimulation therapy of acupoints to improve sciatica.

Hydrogels as Emerging Materials for Cornea Wound Healing

Hydrogel biomaterials have many favorable characteristics including tuneable mechanical behavior, cytocompatibility, optical properties suitable for regeneration and restoration of the damaged cornea tissue. The cornea is a tissue susceptible to various injuries and traumas with a complicated healing cascade, in which conserving its transparency and integrity is critical. Accordingly, the hydrogels' known properties along with the stimulation of nerve and cell regeneration make them ideal scaffold for corneal tissue engineering. Hydrogels have been used extensively in clinical applications for the repair and replacement of diseased organs. The development and optimizing of novel hydrogels to repair/replace corneal injuries have been the main focus of researches within the last decade. This research aims to critically review in vitro, preclinical, as well as clinical trial studies related to corneal wound healing using hydrogels in the past 10 years, as this is considered as an emerging technology for corneal treatment. Several unique modifications of hydrogels with smart behaviors have undergone early phase clinical trials and showed promising outcomes. Financially, this considers a multibillion dollars industry and with huge interest from medical devices as well as pharmaceutical industries with several products may emerge within the next five years.

Thermosensitive Chitosan-β-Glycerophosphate Hydrogels as Targeted Drug Delivery Systems: An Overview on Preparation and Their Applications

Today, with the advances in technology and science, more advanced drug delivery formulations are required. One of these new systems is an intelligent hydrogel. These systems are affected by the environment or conditions that become a gel, stay in the circumstance for a certain period, and slowly release the drug. As an advantage, only a lower dose of the drug is required, and it provides less toxicity and minor damage to other tissues. Hydrogels are of different types, including temperature-sensitive, pH-sensitive, ion change-sensitive, and magnetic field-sensitive. In this study, we investigated a kind of temperature-sensitive smart hydrogel, which has a liquid form at room temperature and becomes gel with increasing temperature. Chitosan-β-glycerophosphate hydrogels have been researched and used in many studies. This study investigates the various factors that influence the gelation mechanism, such as gel formation rates, temperature, pH, time, and gel specificity. Hydrogels are used in many drug delivery systems and diseases, including nasal drug delivery, vaginal drug delivery, wound healing, peritoneal adhesion, ophthalmic drug delivery, tissue engineering, and peptide and protein delivery. Overall, the chitosan-β-glycerophosphate hydrogel is a suitable drug carrier for a wide range of drugs. It shows little toxicity to the body, is biodegradable, and is compatible with other organs. This system can be used in different conditions and different medication ways, such as oral, nasal, and injection.

Recent Biomedical Approaches for Chitosan Based Materials as Drug Delivery Nanocarriers

In recent decades, drug delivery systems (DDSs) based on nanotechnology have been attracting substantial interest in the pharmaceutical field, especially those developed based on natural polymers such as chitosan, cellulose, starch, collagen, gelatin, alginate and elastin. Nanomaterials based on chitosan (CS) or chitosan derivatives are broadly investigated as promising nanocarriers due to their biodegradability, good biocompatibility, non-toxicity, low immunogenicity, great versatility and beneficial biological effects. CS, either alone or as composites, are suitable substrates in the fabrication of different types of products like hydrogels, membranes, beads, porous foams, nanoparticles, in-situ gel, microparticles, sponges and nanofibers/scaffolds. Currently, the CS based nanocarriers are intensely studied as controlled and targeted drug release systems for different drugs (anti-inflammatory, antibiotic, anticancer etc.) as well as for proteins/peptides, growth factors, vaccines, small DNA (DNAs) and short interfering RNA (siRNA). This review targets the latest biomedical approaches for CS based nanocarriers such as nanoparticles (NPs) nanofibers (NFs), nanogels (NGs) and chitosan coated liposomes (LPs) and their potential applications for medical and pharmaceutical fields. The advantages and challenges of reviewed CS based nanocarriers for different routes of administration (oral, transmucosal, pulmonary and transdermal) with reference to classical formulations are also emphasized.

Elastin-inspired supramolecular hydrogels: a multifaceted extracellular matrix protein in biomedical engineering

The phenomenal advancement in regenerative medicines has led to the development of bioinspired materials to fabricate a biomimetic artificial extracellular matrix (ECM) to support cellular survival, proliferation, and differentiation. Researchers have diligently developed protein polymers consisting of functional sequences of amino acids evolved in nature. Nowadays, certain repetitive bioinspired polymers are treated as an alternative to synthetic polymers due to their unique properties like biodegradability, easy scale-up, biocompatibility, and non-covalent molecular associations which imparts tunable supramolecular architecture to these materials. In this direction, elastin has been identified as a potential scaffold that renders extensibility and elasticity to the tissues. Elastin-like polypeptides (ELPs) are artificial repetitive polymers that exhibit lower critical solution temperature (LCST) behavior in a particular environment than synthetic polymers and hence have gained extensive interest in the fabrication of stimuli-responsive biomaterials. This review discusses in detail the unique structural aspects of the elastin and its soluble precursor, tropoelastin. Furthermore, the versatility of elastin-like peptides is discussed through numerous examples that bolster the significance of elastin in the field of regenerative medicines such as wound care, cardiac tissue engineering, ocular disorders, bone tissue regeneration, etc. Finally, the review highlights the importance of exploring short elastin-mimetic peptides to recapitulate the structural and functional aspects of elastin for advanced healthcare applications.

Development of a dual delivery of levofloxacin and prednisolone acetate via PLGA nanoparticles/ thermosensitive chitosan-based hydrogel for postoperative management: An in-vitro and ex-vivo study

Post-operative endophthalmitis (POE) is one of the most dreadful complications after intraocular surgery. For cataract surgery patients, both commercially available topical 0.5% levofloxacin and 1% prednisolone acetate (PA) ophthalmic solution require at least 3 to 4 times application daily. In this study, we develop a dual drug delivery system composed of the thermosensitive chitosan/gelatin-based hydrogel containing PA and levofloxacin-loaded nanoparticles (LNPs). LNPs with negative surface charge show the monodisperse (polydispersity index ~0.045), nanosize (~154.7 nm) and sphere-like structure. The optimal concentration of LNPs and PA to corneal epithelial cells was 5 μg/mL and 50 μg/mL, respectively. The developed dual drug delivery system (PAgel-LNPs) could gel at 34 °C within 63 s. The osmolarity of PAgel-LNPs was 301.2 ± 1.5 mOsm/L. PAgel-LNPs showed a sustained-release profile for 7 days. Post-treatment of PAgel-LNPs in TNF-α-damaged corneal epithelial cells could decrease the inflammation (inflammatory genes (TNF-α, IL-6, MMP-3 andMMP-9) and IL-6 production) and cell death. In ex-vivo rabbit model of S. aureus keratitis, the anti-inflammation and anti-bacterial property have been demonstrated. These results suggest that thermosensitive PAgel-LNPs may have the potential to use for the prevention of POE.

Gelatine-based drug-eluting bandage contact lenses: Effect of PEGDA concentration and manufacturing technique

Drug-eluting bandage contact lenses (BCLs) have been widely studied as an alternative to eye drops due to their ability to increase the drug residence time and bioavailability as well as improve patient compliance. While silicone hydrogel polymers are commonly used in drug-eluting BCLs due to their transparency, mechanical properties and high oxygen permeability, gelatine hydrogels are also clear, flexible and have high oxygen permeability and may therefore be suitable contact lens materials. Moreover, the rheological properties of gelatine hydrogels allow their use as inks in extrusion-based 3D printers, therefore opening the door to a wide range of applications. Drug-loaded gelatine methacryloyl (GelMA) BCLs with different concentrations of poly (ethylene glycol) diacrylate (PEGDA) were prepared using solvent casting and 3D printing. The prepared lenses were characterised for their swelling ratio, in vitro degradation, and drug release properties. The results showed that the incorporation of 10% PEGDA improved the lenses' resistance to handling and protected them during degradation testing, reduced the swelling ratio and prolonged the release of dexamethasone (DEX). Both techniques were deemed suitable to use in the manufacturing of drug-eluting BCLs noting that the optimal formulation may vary according to the preparation technique utilised.

Why chitosan could be apt candidate for glaucoma drug delivery - An overview

Most of the people in the world are affected by glaucoma, which leads to irreversible blindness. Several patient friendly treatments are available, nevertheless medications lack an easy and efficient way of sustained delivery. To make the delivery with enhanced bioavailability, biodegradable and non-biodegradable polymers-based drug carriers are explored. However, ocular drug delivery issues have not been resolved yet due to less adhesiveness, poor penetration ability, pH, and temperature dependent burst releases. Chitosan is found to be effective for ocular drug delivery due to excellent physio-chemical properties in terms of overcoming the existing issues. In this review, we aim to highlight why it has been chosen and the holy grail for ocular drug delivery. Besides, we have comprehensively reviewed recent patents on chitosan as a platform for ocular drug delivery and future perspectives on factors, lacunae and challenges that need to be addressed for better ocular delivery methods for glaucoma management.

Strategies to prolong the residence time of drug delivery systems on ocular surface

Ocular diseases may be treated via different routes of administration, such as topical, intracameral, intravitreal, oral and parenteral. Among them the topical route is most accepted by patients, although it provides in many cases the lowest bioavailability. Indeed, when a topical formulation reaches the precorneal area, i.e., the drug absorption and/or action site, it is rapidly eliminated due to eye protection mechanisms such as blinking, basal and reflex tearing, and naso-lacrimal draining. To avoid this and to reduce the frequency of dosing, various strategies have been developed to prolong drug residence time after topical administration. These strategies include the use of viscosity increasing and mucoadhesive excipients as well as combinations thereof. From the drug delivery system point of view, liquid and semisolid formulations are preferred over solid formulations such as ocular inserts and contact lenses. Furthermore, liquid and semisolid formulations can contain nano- and microcarrier systems that contribute to a prolonged residence time. Within this review an overview about the different types of excipients and formulations as well as their performance in valid animal models and clinical trials is provided.

Application of a novel thermo-sensitive injectable hydrogel in therapy in situ for drug accurate controlled release

Local drug injection therapy for tumor site, as a neoadjuvant chemotherapy method, shows important significance in clinical application; however, it obtains unsatisfying therapeutic effect due to the serious toxic and side effect in normal tissues caused by drug diffusion or complexity of the preparation. In this article, the influence factors of the gelling time of traditional Chitosan (CTS) thermo-sensitive hydrogels were analyzed, and the gelling properties were improved significantly, and a thermo-sensitive hydrogel with precisely regulated gelling time was obtained through a green and simple preparation method, and the shortest gelling time (gelling time = 27 ± 2 s) of this hydrogel was 5% of that of the common CTS thermo-sensitive hydrogels. After loaded with different chemotherapy drugs with different pH values (gemctiabin hydrochloride, levofloxacin, and 5-foluorouracil), the hydrogels' gelling performance was not affected, while the gelling time could be shortened by 5-foluorouracil, effectively hindering the drug loss at the early stage of sustained release. in vitro and in vivo experiments proved that precise encapsulation toward tumors with different volumes was achieved by the hydrogels, with minimal damage to surrounding normal tissues and higher utilization of drugs in tumor sites, ultimately achieving better tumor therapeutic effect. In conclusion, the new thermo-sensitive hydrogels with precisely regulated gelling time showed great significance and potential for drug delivery and neoadjuvant chemotherapy.

Chitosan based-nanoparticles and nanocapsules: Overview, physicochemical features, applications of a nanofibrous scaffold, and bioprinting

Recent advancements in the synthesis, properties, and applications of chitosan as the second after cellulose available biopolymer in nature were discussed in this review. A general overview of processing and production procedures from A to Z was highlighted. Chitosan exists in three polymorphic forms which differ in degree of crystallinity (α, β, and γ). Thus, the degree of deacetylation, crystallinity, surface area, and molecular mass significantly affect most applications. Otherwise, the synthesis of chitosan nanofibers is suffering from many drawbacks that were recently treated by co-electrospun with other polymers such as polyvinyl alcohol (PVA), polyethylene oxide (PEO), and polycaprolactone (PCL). Ultimately, this review focuses on the area of new trend utilization of chitosan nanoparticles as nanospheres and nanocapsules, in cartilage and bone regenerative medicine. Owing to its biocompatibility, bioavailability, biodegradability, and costless synthesis, chitosan is a promising biopolymeric structure for water remediation, drug delivery, antimicrobials, and tissue engineering.

In vitro study of SDF-1α-loaded injectable and thermally responsive hydrogels for adipose stem cell therapy by SDF-1/CXCR4 axis

Stem cell-based approaches have become a promising therapeutic strategy for treating ischemic diseases. The aim of this study was to develop injectable hydrogel systems for the local release of stromal cell-derived factor-1α (SDF-1α) to recruit adipose stem cells (ASCs) that express CXCR4 to achieve stem cell therapy and therapeutic angiogenesis. Thermoresponsive and injectable chitosan (CS)/β-glycerophosphate disodium salt pentahydrate (βGP) hydrogels with different concentrations of hyaluronic acid (HA) were designed and fabricated to achieve local and sustained release of SDF-1α for ASC recruitment. Herein, the material structures, physical properties, gelation temperature, and gelation time of hydrogels with different compositions were determined. The incorporation of 0.9% HA in CS-based hydrogels not only enhanced the gelation time but also increased the strength of the hydrogels. In addition, the results revealed that the thermoresponsive and injectable CS/βGP/HA hydrogels showed good biocompatibility. In addition, the in vitro release profiles showed that the hydrogels achieved sustained release of SDF-1α over 7 days and enhanced ASC migration. The results revealed that the hydrogels with HA enhanced the sustained release effect compared with the hydrogel without HA, indicating that the HA content regulated the physical and release properties of the injectable hydrogels. Therefore, thermoresponsive and injectable CS/βGP/HA hydrogels may provide an alternative for treating ischemic diseases via SDF-1/CXCR4 axis for ASC recruitment and retention.

Intravitreal hydrogels for sustained release of therapeutic proteins

This review highlights how hydrogel formulations can improve intravitreal protein delivery to the posterior segment of the eye in order to increase therapeutic outcome and patient compliance. Several therapeutic proteins have shown excellent clinical successes for the treatment of various intraocular diseases. However, drug delivery to the posterior segment of the eye faces significant challenges due to multiple physiological barriers preventing drugs from reaching the retina, among which intravitreal protein instability and rapid clearance from the site of injection. Hence, frequent injections are required to maintain therapeutic levels. Moreover, because the world population ages, the number of patients suffering from ocular diseases, such as age-related macular degeneration (AMD) and diabetic retinopathy (DR) is increasing and causing increased health care costs. Therefore, there is a growing need for suitable delivery systems able to tackle the current limitations in retinal protein delivery, which also may reduce costs. Hydrogels have shown to be promising delivery systems capable of sustaining release of therapeutic proteins and thus extending their local presence. Here, an extensive overview of preclinically developed intravitreal hydrogels is provided with attention to the rational design of clinically useful intravitreal systems. The currently used polymers, crosslinking mechanisms, in vitro/in vivo models and advancements are discussed together with the limitations and future perspective of these biomaterials.

Chitin and its derivatives: Structural properties and biomedical applications

Chitin, a polysaccharide that occurs abundantly in nature after cellulose, has attracted the interest of the scientific community due to its plenty of availability and low cost. Mostly, it is derived from the exoskeleton of insects and marine crustaceans. Often, it is insoluble in common solvents that limit its applications but its deacetylated product, named chitosan is found to be soluble in protonated aqueous medium and used widely in various biomedical fields. Indeed, the existence of the primary amino group on the backbone of chitosan provides it an important feature to modify it chemically into other derivatives easily. In the present review, we present the structural properties of chitin, and its derivatives and highlighted their biomedical implications including, tissue engineering, drug delivery, diagnosis, molecular imaging, antimicrobial activity, and wound healing. We further discussed the limitations and prospects of this versatile natural polysaccharide.

Chitosan and its Derivatives for Ocular Delivery Formulations: Recent Advances and Developments

Chitosan (CS) is a hemi-synthetic cationic linear polysaccharide produced by the deacetylation of chitin. CS is non-toxic, highly biocompatible, and biodegradable, and it has a low immunogenicity. Additionally, CS has inherent antibacterial properties and a mucoadhesive character and can disrupt epithelial tight junctions, thus acting as a permeability enhancer. As such, CS and its derivatives are well-suited for the challenging field of ocular drug delivery. In the present review article, we will discuss the properties of CS that contribute to its successful application in ocular delivery before reviewing the latest advances in the use of CS for the development of novel ophthalmic delivery systems. Colloidal nanocarriers (nanoparticles, micelles, liposomes) will be presented, followed by CS gels and lenses and ocular inserts. Finally, instances of CS coatings, aiming at conferring mucoadhesiveness to other matrixes, will be presented.

Chitosan hydrogels for sustained drug delivery

Sustainable and controlled delivery of drugs is at the centre of a huge amount of undertaken researches. The ability of hydrogels, high water content materials, to achieve a local and delayed-delivery has already been demonstrated for a wide variety of therapeutic agents and various polymer natures. In particular, chitosan, a natural polymer, stands out as a first choice material for hydrogels elaboration in biomedical, cosmetic, and health related applications, owing to its interesting properties (as biocompatibility, biodegradability, antimicrobial capacity, and mucoadhesivity). Moreover, chitosan also allows drugs to go easier through biological barriers. The main objective of this review is to report the various uses of chitosan hydrogels as drug delivery devices to control and/or delay the release of drugs loaded into their three dimensional matrix. A wide spectrum of corresponding biomedical applications of these systems can be encountered in the literature, whatever the physicochemical nature of drugs (hydrophilic, hydrophobic, macromolecular), as detailed in this review.