Ocular drug delivery system: a reference to natural polymers

A sterilizable platform based on crosslinked xanthan gum for controlled-release of polymeric micelles: Ocular application for the delivery of neuroprotective compounds to the posterior eye segment

TPGS (D-α-tocopheryl polyethylene glycol 1000 succinate) polymeric micelles show interesting properties for ocular administration thanks to their solubilization capability, nanometric size and tissue penetration ability. However, micelles formulations are generally characterized by low viscosity, poor adhesion and very short retention time at the administration site. Therefore, the idea behind this work is the preparation and characterization of a crosslinked film based on xanthan gum that contains TPGS micelles and is capable of controlling their release. The system was loaded with melatonin and cyclosporin A, neuroprotective compounds to be delivered to the posterior eye segment. Citric acid and heating at different times and temperatures were exploited as crosslinking approach, giving the possibility to tune swelling, micelles release and drug release. The biocompatibility of the platform was confirmed by HET-CAM assay. Ex vivo studies on isolated porcine ocular tissues, conducted using Franz cells and two-photon microscopy, demonstrated the potential of the xanthan gum-based platform and enlightened micelles penetration mechanism. Finally, the sterilization step was approached, and a process to simultaneously crosslink and sterilize the platform was developed.

Trans-eyelid distribution of epinastine to the conjunctiva following eyelid application in rabbits

PURPOSE

To reveal the penetration of epinastine, an anti-allergic ophthalmic agent, into the eyelid and its distribution to the conjunctiva after administration of a cream formulation on rabbit eyelid skin.

STUDY DESIGN

Experimental study.

METHODS

Rabbits were treated with 0.5% epinastine cream on hair-shaved eyelids, followed by preparation of eyelid tissue slices to determine spatial tissue distribution of epinastine by liquid chromatography-tandem mass spectrometry (LC-MS/MS) quantification using laser-microdissected tissues and desorption electrospray ionization mass spectrometry imaging (DESI-MSI). In addition, following either eyelid application of 0.5% epinastine cream or ocular instillation of 0.1% epinastine eye drops, concentration-time profiles of epinastine in the palpebral conjunctiva and bulbar conjunctiva were determined using LC-MS/MS.

RESULTS

Laser microdissection coupled with LC-MS/MS analysis detected high concentrations of epinastine around the outermost layer of the eyelid at 0.5 h post-administration that gradually diffused deeper into the eyelid and was distributed in the conjunctival layer at 8 and 24 h post-administration. Similar time-dependent drug distribution was observed in high-spatial-resolution images obtained using DESI-MSI. Epinastine concentrations in the conjunctival tissues peaked at 4-8 h after administration of 0.5% epinastine cream and then decreased slowly over 72 h post-administration. In contrast, epinastine concentrations peaked quickly and decreased sharply after epinastine eye drop administration.

CONCLUSION

After the application of epinastine cream to the eyelid skin, epinastine gradually permeated the eyelid. The compound was retained in the conjunctiva for 8-24 h post-administration, indicating that epinastine cream is a promising long-acting formulation for treating allergic conjunctivitis.

Synergism of polysaccharide polymers in antihistamine eye drops: Influence on physicochemical properties and in vivo efficacy

The incorporation of polymers into drug delivery vehicles has been shown to be a useful approach to prolong the residence time of drugs in the precorneal tear film and to improve penetration into biological membranes. The main objective of this research was to formulate novel viscous eye drops with ketotifen as the active ingredient, containing the polysaccharides: chitosan (MCH), hydroxypropyl guar gum (HPG) and hyaluronic acid (SH) alone and in combination as functional polymers. DSC and FT-IR techniques showed the compatibility between ketotifen and polymers. Physicochemical and rheological analysis at ambient and simulated physiological conditions, as well as the evaluation of mucoadhesive properties showed that vehicles containing combinations of polymers have suitable physicochemical and functional properties with demonstrated synergism between combined polymers (MCH and HPG i.e. SH and HPG). The drug permeability was successfully estimated in vitro using HCE-T cell-based models. MTT cytotoxicity assay demonstrates that the tested formulations were non-toxic and well tolerated. In vivo preclinical study on mice revealed that both vehicles containing mixed polymers enhanced and prolonged the antipruritic/analgesic-like effect of ophthalmic ketotifen. Based on these results, both combinations of polysaccharide polymers, especially SH-HPG, could be considered as potential new carriers for ketotifen for ophthalmic use.

Polymers and their engineered analogues for ocular drug delivery: Enhancing therapeutic precision

Ocular drug delivery is constrained by anatomical and physiological barriers, necessitating innovative solutions for effective therapy. Natural polymers like hyaluronic acid, chitosan, and gelatin, alongside synthetic counterparts such as PLGA and PEG, have gained prominence for their biocompatibility and controlled release profiles. Recent strides in polymer conjugation strategies have enabled targeted delivery through ligand integration, facilitating tissue specificity and cellular uptake. This versatility accommodates combined drug delivery, addressing diverse anterior (e.g., glaucoma, dry eye) and posterior segment (e.g., macular degeneration, diabetic retinopathy) afflictions. The review encompasses an in-depth exploration of each natural and synthetic polymer, detailing their individual advantages and disadvantages for ocular drug delivery. By transcending ocular barriers and refining therapeutic precision, these innovations promise to reshape the management of anterior and posterior segment eye diseases.

Dual properties of pharmacological activities and preparation excipient: Bletilla striata polysaccharides

Bletilla striata has been used for thousands of years and shows the functions of stopping bleeding, reducing swelling, and promoting healing in traditional applications. For Bletilla striata, Bletilla striata polysaccharides (BSP) is the main active ingredient, exhibiting biological functions of anti-inflammatory, anti-oxidant, anti-fibrotic, immune modulation, anti-glycation, and so on. In addition, BSP has exhibited the characteristics of excipient such as bio-adhesion, bio-degradability, and bio-safety and has been prepared into a series of preparations such as nanoparticles, microspheres, microneedles, hydrogels, etc. BSP, as both a drug and an excipient, has already aroused more and more attention. In this review, publications in recent years related to the extraction and identification, biological activities, and excipient application of BSP are reviewed. Specifically, we focused on the advances in the application of BSP as a formulation excipient. We hold opinion that BSP not only needed more researches in the mechanisms, but also the development into hydrogels, nano-formulations, tissue engineering, and so on. And we believe that this paper provides a beneficial reference for further BSP innovation and in-depth research and promotes the use of these natural products in pharmaceutical applications.

Progress in Ocular Drug Delivery: Challenges and Constraints

The eye has several dynamic and static barriers in place to limit the entry of foreign substances including therapeutics. As such, efficient drug delivery, especially to posterior segment tissues, has been challenging. This chapter describes the anatomical and physiological challenges associated with ocular drug delivery before discussing constraints with regard to formulation parameters. Finally, it gives an overview of advanced drug delivery technologies with a specific focus on recently marketed and late-stage clinical trial products.

Biopolymers in Mucoadhesive Eye Drops for Treatment of Dry Eye and Allergic Conditions: Application and Perspectives

Dry eye syndrome and allergic conjunctivitis are the most common inflammatory disorders of the eye surface. Although eye drops are the most usual prescribed dosage form, they are characterized by low ocular availability due to numerous barrier mechanisms of the eye. The use of biopolymers in liquid ophthalmic preparations has numerous advantages, such as increasing the viscosity of the tear film, exhibiting bioadhesive properties, and resisting the drainage system, leading to prolonged retention of the preparation at the site of application, and improvement of the therapeutic effect. Some mucoadhesive polymers are multifunctional excipients, so they act by different mechanisms on increasing the permeability of the cornea. Additionally, many hydrophilic biopolymers can also represent the active substances in artificial tear preparations, due to their lubrication and moisturizing effect. With the modification of conventional ophthalmic preparations, there is a need for development of new methods for their characterization. Numerous methods for the assessment of mucoadhesiveness have been suggested by the literature. This review gives an overview related to the development of mucoadhesive liquid ophthalmic formulations for the treatment of dry eye and allergic conditions.

Nanosuspension: A Formulation Technology for Tackling the Poor Aqueous Solubility and Bioavailability of Poorly Soluble Drugs

The poor water solubility of numerous novel drug candidates presents significant challenges, particularly in terms of oral administration. This limitation can result in various undesirable clinical implications, such as inter-patient variability, poor bioavailability, difficulties in achieving a safe therapeutic index, increased costs, and potential risks of toxicity or inefficacy. Biopharmaceutics Classification System (BCS) class II drugs face particular hurdles due to their limited solubility in the aqueous media of the gastrointestinal tract. In such cases, parenteral administration is often employed as an alternative strategy. To address these challenges, nanosuspension techniques offer a promising solution for enhancing drug solubility and overcoming oral delivery obstacles. This technique has the potential to bridge the gap between drug discovery and preclinical use by resolving problematic solubility. This literature review has delved into contemporary nanosuspension preparation technologies and the incorporation of stabilizing ingredients within the formulation. Furthermore, the manuscript explores nanosuspension strategies for both oral and parenteral/other delivery routes, and separate discussions have been presented to establish a suitable flow that addresses the challenges and strategies relevant to each administration method.

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.

Comparative Study of Ocular Pharmacokinetics of Topical 0.3% Gatifloxacin Eye Gel and Solution in Rabbits

Few articles have reported drug concentrations of different ophthalmic dosage forms in the ocular tissues. This study aimed to determine the ocular pharmacokinetics of gatifloxacin 0.3% eye gel (GTX-Gel) and gatifloxacin 0.3% eye solution (GTX-Sol) at different time intervals after topical instillation in rabbits. A total of 126 healthy New Zealand rabbits were included, of which six rabbits did not receive antibiotics (control group). The remaining rabbits were randomly divided into four groups. GTX-Gel and GTX-Sol (50 μL) were topically instilled every hour in groups A1 and B1, respectively, and every two hours in groups A2 and B2, respectively, for 12 h. Ocular tissues were collected 2, 4, 8, 12, and 24 h after administration. Gatifloxacin concentration was measured using high-performance liquid chromatography coupled with tandem mass spectrometry. The drug reached peak concentrations (Cmax) in all tissues at 8−12 h. With the same administration frequency, the Cmax was higher with GTX-Gel than with GTX-Sol (p < 0.05). Except for the iris-ciliary body, other ocular tissues did not show significant difference (p > 0.05) in gatifloxacin concentration between either pair of groups. Gatifloxacin ophthalmic gel was found to attain significantly higher concentrations than the ophthalmic solution in ocular tissues.

Chitosan-coated bovine serum albumin nanoparticles for topical tetrandrine delivery in glaucoma: in vitro and in vivo assessment

Glaucoma is one of the leading causes of blindness. Therapies available suffer from several drawbacks including low bioavailability, repeated administration and poor patient compliance with adverse effects thereafter. In this study, bovine serum albumin nanoparticles (BSA-NPs) coated with chitosan(CS) were developed for the topical delivery of tetrandrine (TET) for glaucoma management. Optimized nanoparticles were prepared by desolvation. pH, BSA, CS and cross-linking agent concentrations effects on BSA-NPs colloidal properties were investigated. CS-BSA-NPs with particle size 237.9 nm and zeta potential 24 mV was selected for further evaluation. EE% exceeded 95% with sustained release profile. In vitro mucoadhesion was evaluated based on changes in viscosity and zeta potential upon incubation with mucin. Ex vivo transcorneal permeation was significantly enhanced for CS coated formulation. In vitro cell culture studies on corneal stromal fibroblasts revealed NPs biocompatibility with enhanced cellular uptake and improved antioxidant and anti-proliferative properties for the CS-coated formulation. Moreover, BSA-NPs were nonirritant as shown by HET-CAM test. Also, bioavailability in rabbit aqueous humor showed 2-fold increase for CS-TET-BSA-NPs compared to TET with a sustained reduction in intraocular pressure in a rabbit glaucoma model. Overall, results suggest CS-BSA-NPs as a promising platform for topical ocular TET delivery in the management of glaucoma.

Nanoparticles Loaded Thermoresponsive In Situ Gel for Ocular Antibiotic Delivery against Bacterial Keratitis

Antibiotics delivered through conventional dosage against ophthalmic infections show lower therapeutic efficacy due to their low residence time. Therefore, there is a great need to design and develop novel dosage forms that would increase the ocular residence time of antibiotics at the site of infection. This study describes the development of nanoparticles laden in situ gelling solution, intended to sustain antibiotic release for improved therapeutic efficiency. Oxytetracycline-loaded gelatin-polyacrylic acid nanoparticles were prepared and incorporated in poloxamer-N407 solution. The rheological properties of the system were studied concerning time and temperature. Moreover, in vivo biocompatibility of the system was ascertained using the Draize test and histological studies. Finally, the optimized formulation was evaluated for in vitro antibacterial activity against one of the most common keratitis causing bacteria, Pseudomonas aeruginosa. Additionally, the in vivo efficacy was evaluated on the rabbit’s eye conjunctivitis model. The formulation showed a sustained effect against keratitis; furthermore, the antibacterial activity was comparable with the commercial product.

The Use of Natural Collagen Obtained from Fish Waste in Hair Styling and Care

Chemically speaking, polymers are multi-molecular compounds that have specific physicochemical properties. Hair cosmetics utilize their ability to create a protective film and make the cosmetic formulation more viscous, which facilitates its application. Natural polymers are encountered in nature, but, in hair cosmetics, artificially modified ones are more often used. Unfortunately, artificially modified polymers are characterized by high resistance to biological factors, which creates an ecological problem. Another reason for a search for natural polymers is their milder action when compared to synthetic ones. One of the new sources of obtaining collagen is the waste connective tissue materials of aquatic animals—skins, spines, dorsal chords and scales, and swim bladders. These raw materials are most often disposed of in landfills, processed into fish meal, or destined for food for animals. The conducted research was aimed at proving the action of natural collagen in hair cosmetics as a substitute for synthetic polymers. In the patients using collagen laminate, it is possible to notice the complete elimination of excessive sebum production, restoration of the correct pH value, and reduction in skin inflammations.

Assessment of the Efficiency of HP-Guar and hyaluronic Acid Tear Supplements to Control Tear Film Evaporation Rate in Dry Eye Subjects

Background:

The most common factor that could lead to dryness is the accelerated tear evaporation rate. Controlling the tear evaporation rate is increasingly used as a method to control dry eye complications. The present study explores the effects of different tear supplements formulations on tear film evaporation rate.

Objective:

This study aimed to evaluate the short-term effects of Systane ULTRA and Artelac Advanced eye drops on the tear film evaporation rate.

Methods:

Fifteen male dry eye subjects were enrolled in the current study. Tear film parameters were observed at several time points post installation (10, 20, 30, and 60 min). The tear film parameters observed in the current study were tear evaporation rate, noninvasive breakup time (NITBUT) and tear meniscus height (TMH). Two visits were required to conduct this study. One visit was conducted to assess the physiological tear film parameters with the use of Systane® ULTRA eye drop. The other visit was conducted to assess tear film parameters with the use of Artelac Advanced eye drop.

Results:

The mean tear evaporation rate at baseline was 52.58 ± 23.24 g/m2 h. A box plot of tear evaporation showed a reduction in tear film evaporation rate after instillation of Systane eye drop. A drop in tear film evaporation rate of 14% was observed at 20 and 60 min time point after instillation of Systane ULTRA eye drop. A significant increase in NITBUT was found after instillation of Systane ULTRA (P = 0.01) and Artelac Advanced (P = 0.02).

Conclusion:

The current study indicates a significant improvement in the tear film parameters using both HP-Guar and hyaluronic acid formulations. However, it was apparent that the use of HP-Guar was superior to hyaluronic acid in controlling the tear evaporation rate in dry eye subjects.

Load phycocyanin to achieve in vivo imaging of casein-porous starch microgels induced by ultra-high-pressure homogenization

Traditional bioactive substances are often limited in practical application due to their poor stability and low solubility. Therefore, it is imperative to develop biocompatible high loading microgel carriers. In this study, a novel type of casein-porous starch microgel was prepared under ultra-high-pressure homogenization, by using porous starch with the honeycomb three-dimensional network porous structure. Molecular interaction force analysis and thermodynamic analysis showed that electrostatic interaction played a major role in the formation of microgels. Circular dichroism and Fourier transform infrared spectroscopy showed that homogenization and pH were the main factors, which affected the formation and structural stability of microgels. Compared with casein-glutinous rice starch microgels, the encapsulation efficiency and loading capacity of phycocyanin in casein-porous starch microgels were increased by 77.27% and 135.10%, respectively. Thus, casein-porous starch microgels could not only achieve a sustained release effect, but also effectively transport phycocyanin to the gastrointestinal tract of zebrafish, while achieving good fluorescence imaging in vivo. Ultimately, the prepared casein-porous starch microgels could enrich the nanocarriers material, and contribute to the research of safe and effective fluorescent imaging materials.

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.

Soft Contact Lenses as Drug Delivery Systems: A Review

This review describes the role of contact lenses as an innovative drug delivery system in treating eye diseases. Current ophthalmic drug delivery systems are inadequate, particularly eye drops, which allow about 95% of the active substance to be lost through tear drainage. According to the literature, many interdisciplinary studies have been carried out on the ability of contact lenses to increase the penetration of topical therapeutic agents. Contact lenses limit drug loss by releasing the medicine into two layers of tears on either side of the contact lens, eventually extending the time of contact with the ocular surface. Thanks to weighted soft contact lenses, a continuous release of the drug over an extended period is possible. This article reviewed the various techniques to deliver medications through contact lenses, examining their advantages and disadvantages. In addition, the potential of drug delivery systems based on contact lenses has been extensively studied.

Current Insights into Collagen Type I

Collagen type I (Col-I) is unique due to its high biocompatibility in human tissue. Despite its availability from various sources, Col-I naturally mimics the extracellular matrix (ECM) and generally makes up the larger protein component (90%) in vasculature, skin, tendon bone, and other tissue. The acceptable physicochemical properties of native Col-I further enhance the incorporation of Col-I in various fields, including pharmaceutical, cosmeceutical, regenerative medicine, and clinical. This review aims to discuss Col-I, covering the structure, various sources of availability, native collagen synthesis, current extraction methods, physicochemical characteristics, applications in various fields, and biomarkers. The review is intended to provide specific information on Col-I currently available, going back five years. This is expected to provide a helping hand for researchers who are concerned about any development on collagen-based products particularly for therapeutic fields.

Natural-Based Biomaterial for Skin Wound Healing (Gelatin vs. Collagen): Expert Review

Collagen (Col) and gelatin are most extensively used in various fields, particularly in pharmaceuticals and therapeutics. Numerous researchers have proven that they are highly biocompatible to human tissues, exhibit low antigenicity and are easy to degrade. Despite their different sources both Col and gelatin have almost the same effects when it comes to wound healing mechanisms. Considering this, the bioactivity and biological effects of both Col and gelatin have been, and are being, constantly investigated through in vitro and in vivo assays to obtain maximum outcomes in the future. With regard to their proven nutritional values as sources of protein, Col and gelatin products exert various possible biological activities on cells in the extracellular matrix (ECM). In addition, a vast number of novel Col and gelatin applications have been discovered. This review compared Col and gelatin in terms of their structures, sources of derivatives, physicochemical properties, results of in vitro and in vivo studies, their roles in wound healing and the current challenges in wound healing. Thus, this review provides the current insights and the latest discoveries on both Col and gelatin in their wound healing mechanisms.

Bubble Forming Films for Spatial Selective Cell Killing

Photodynamic and photothermal cell killing at the surface of tissues finds applications in medicine. However, a lack of control over heat dissipation following a treatment with light might damage surrounding tissues. A new strategy to kill cells at the surface of tissues is reported. Polymeric films are designed in which iron oxide nanoparticles are embedded as photosensitizers. Irradiation of the films with pulsed laser light generates water vapor bubbles at the surface of the films. It is found that "bubble-films" can kill cells in close proximity to the films due to mechanical forces which arise when the bubbles collapse. Local irradiation of bubble-films allows for spatial selective single cell killing. As nanosurgery becomes attractive in ophthalmology to remove superficial tumors, bubble-films are applied on the cornea and it is found that irradiation of the bubble-films allows spatial and selective killing of corneal cells. As i) the photosensitizer is embedded in the films, which reduces its uptake by cells and spreading into tissues and ii) the bubble-films can be removed from the tissue after laser treatment, while iii) a low laser fluence is sufficient to generate vapor bubbles, it is foreseen that bubble-films might become promising for safe resection of superficial tumors.

Intellective and stimuli-responsive drug delivery systems in eyes

Stimuli-responsive drug delivery systems have attracted widespread attention in recent years since they can control drug release in a spatiotemporal manner and can achieve tunable drug release according to patient's physiological or pathological condition. In this review, we briefly introduce the drug delivery barriers and drug delivery systems in the anterior and posterior segment of eyes, and collect the recent advances in stimuli-responsive drug delivery systems in eyes for controlled drug release in response to exogenous stimuli (ultrasound, magnetic stimulus, electrical stimulus, and light) or endogenous stimuli (enzyme, active oxygen species, temperature, ions, and pH). In addition, the design and mechanisms of the stimuli-responsive drug delivery systems have been summarized in this review, and the advantages and limitations are also briefly discussed.

In vitro amoebicidal effects of arabinogalactan-based ophthalmic solution

The main corneal infections reported worldwide are caused by bacteria and viruses but, recently, the number of Acanthamoeba keratitis (AK) cases has increased. Acanthamoeba genus is an opportunistic free living protozoa widely distributed in environmental and clinical sources, with two life-cycle stages: the trophozoite and the cyst. AK presents as primary symptoms eye redness, epithelial defects, photophobia and intense pain. An early diagnosis and an effective treatment are crucial to avoid blindness or eye removal but, so far, there is no established treatment to this corneal infection. Diverse research studies have reported the efficacy of commercialized eye drops and ophthalmic solutions against the two life cycle stages of Acanthamoeba strains, that usually present preservatives such as Propylene Glycol of Benzalkonium chloride (BAK). These compounds present toxic effects in corneal cells, favouring the inflammatory response in the so sensitive eye tissue. In the present work we have evaluated the efficacy of nine proprietary ophthalmic solutions with and without preservatives (ASDA Dry Eyes Eyedrops, Miren®, ODM5®, Ectodol®, Systane® Complete, Ocudox®, Matrix Ocular®, Alins® and Coqun®) against the two life cycle stages of three Acanthamoeba strains. Our work has demonstrated the high anti-Acanthamoeba activity of Matrix Ocular®, which induces the programmed cell death mechanisms in Acanthamoeba spp. trophozoites. The high efficacy and the absence of ocular toxic effects of Matrix Ocular®, evidences the use of the Arabinogalactan derivatives as a new source of anti-AK compounds.

Hydroxypropyl methylcellulose: Physicochemical properties and ocular drug delivery formulations

Hydroxypropyl methylcellulose (HPMC) is a cellulose ether widely used in drug formulations due to its biocompatibility, uncharged nature, solubility in water and thermoplastic behavior. Particularly for ocular and ophthalmic formulations, HPMC is applied as viscosity enhancer agent in eye drops, gelling agent in injections, and polymeric matrix in films, filaments and inserts. The different therapeutic approaches are necessary due to the complex anatomic structure of the eye. The natural ocular barriers and the low drug permeation into the circulatory system make the drug administration challenging. This review presents the eye anatomy and the usual local routes of drugs administration, which are facilitated by the physicochemical properties of HPMC. The relationship between chemical structure and physicochemical properties of HPMC is displayed. The different types of formulations (local application) including HPMC for ocular drug delivery are discussed with basis on recent literature reports and patents.

Recent advances in guar gum based drug delivery systems and their administrative routes

Guar gum-based drug carrier systems have gained attention for the delivery of various therapeutic agents via different administration routes for attaining controlled and sustained release. Guar gum offers a safe and effective system for drug delivery due to its natural occurrence, easy availability, biocompatibility, and biodegradability, besides simple and mild preparation techniques. Furthermore, the possibility of using various routes such as oral, buccal, transdermal, intravenous, and gene delivery further diversify guar gum applications in the biomedical field. This review delineates the recent investigation on guar gum-based drug carrier systems like hydrogels, nanoparticles, nanocomposites, and scaffolds along with their related delivery routes. Also, the inclusion of data of the loading and subsequent release of the drugs enables to explore the noble and improved drug targeting therapies.

Experimental design, formulation and in vivo evaluation of a novel topical in situ gel system to treat ocular infections

In situ gels have been extensively explored as ocular drug delivery system to enhance bioavailability and efficacy. The objective of present study was to design, formulate and evaluate ion-activated in situ gel to enhance the ocular penetration and therapeutic performance of moxifloxacin in ophthalmic delivery. A simplex lattice design was utilized to examine the effect of various factors on experimental outcomes of the in situ gel system. The influence of polymers (independent variables) such as gellan gum (X₁), sodium alginate (X₂), and HPMC (X₃) on gel strength, adhesive force, viscosity and drug release after 10 h (Q₁₀) were assessed. Selected formulation (MH7) was studied for ex vivo permeation, in vivo irritation and pharmacokinetics in rabbits. Data revealed that increase in concentration of polymers led to higher gel strength, adhesive force and viscosity, however, decreases the drug release. MH7 exhibited all physicochemical properties within acceptable limits and was stable for 6 months. Release profile of moxifloxacin from MH7 was comparable to the check point batches and followed Korsmeyer-Peppas matrix diffusion-controlled mechanism. Ocular irritation study signifies that selected formulation is safe and non-irritant for ophthalmic administration. In vivo pharmacokinetics data indicates significant improvement of moxifloxacin bioavailability (p < 0.0001) from MH7, as evidenced by higher C_max (727 ± 56 ng/ml) and greater AUC (2881 ± 108 ng h/ml), when compared with commercial eye drops (C_max; 503 ± 85 ng/ml and AUC; 978 ± 86 ng h/ml). In conclusion, developed in situ gel system (MH7) could offers a more effective and extended ophthalmic therapy of moxifloxacin in ocular infections when compared to conventional eye drops.

Liposomes as vehicles for topical ophthalmic drug delivery and ocular surface protection

Introduction: The development of ophthalmic formulations able to deliver hydrophilic and hydrophobic drugs to the inner structures of the eye and restore the preocular tear film has been a leading topic of discussion over the last few years. In this sense, liposomes represent a suitable strategy to achieve these objectives in ocular drug delivery.Areas covered: Knowledge of the different physiological and anatomical eye structures, and specially the ocular surface are critical to better understanding and comprehending the characteristics required for the development of topical ophthalmic liposomal formulations. In this review, several features of liposomes are discussed such as the main materials used for their fabrication, basic structure and preparation methods, from already established to novel techniques, allowing the control and design of special characteristics. Besides, physicochemical properties, purification processes and strategies to overcome delivery or encapsulation challenges are also presented. Expert opinion: Regarding ocular drug delivery of liposomes, there are some features that can be redesigned. Specific biocompatible and biodegradable materials presenting therapeutic properties, such as lipidic compounds or polymers significantly change the way of tackling ophthalmic diseases. Besides, liposomes entail an effective, safe and versatile strategy for the treatment of diseases in the clinical practice.

Preparation and Evaluation of a Xanthan Gum-Containing Linezolid Ophthalmic Solution for Topical Treatment of Experimental Bacterial Keratitis

PURPOSE

To formulate a xanthan gum-containing linezolid ophthalmic solution (LZD-XG) as a new antibiotic treatment against ocular bacterial infection.

METHODS

LZD-XG was prepared and evaluated for its in vitro/in vivo ocular tolerance, in vitro/in vivo antibacterial activity, and in vivo ocular penetration.

RESULTS

The optimized LZD-XG exhibited good in vitro/in vivo eye tolerance. A prolonged ocular surface residence time of LZD-XG was observed after topical instillation, and the ocular permeation was significantly better for LZD-XG than fora linezolid (LZD) ophthalmic solution. The in vitro antimicrobial activity was significantly better with LZD-XG than with LZD. In vivo evaluation also confirmed a strong therapeutic treatment effect of LZD-XG, as it significantly improved the clinical symptoms, ameliorated the damage of Staphylococcus aureus to ocular tissues, lowered the colony forming unit counts in the cornea, and decreased the myeloperoxidase activity in the cornea.

CONCLUSION

LZD-XG was deemed a viable ophthalmic solution against ocular bacterial infection due to its excellent in vitro and in vivo characterizations.

Gelatin Microsphere for Cartilage Tissue Engineering: Current and Future Strategies

The gelatin microsphere (GM) provides an attractive option for tissue engineering due to its versatility, as reported by various studies. This review presents the history, characteristics of, and the multiple approaches to, the production of GM, and in particular, the water in oil emulsification technique. Thereafter, the application of GM as a drug delivery system for cartilage diseases is introduced. The review then focusses on the emerging application of GM as a carrier for cells and biologics, and biologics delivery within a cartilage construct. The influence of GM on chondrocytes in terms of promoting chondrocyte proliferation and chondrogenic differentiation is highlighted. Furthermore, GM seeded with cells has been shown to have a high tendency to form aggregates; hence the concept of using GM seeded with cells as the building block for the formation of a complex tissue construct. Despite the advancement in GM research, some issues must still be addressed, particularly the improvement of GM’s ability to home to defect sites. As such, the strategy of intraarticular injection of GM seeded with antibody-coated cells is proposed. By addressing this in future studies, a better-targeted delivery system, that would result in more effective intervention, can be achieved.

Contact Lenses as Drug Delivery System for Glaucoma: A Review

Glaucoma is an optical neuropathy associated to a progressive degeneration of retinal ganglion cells with visual field loss and is the main cause of irreversible blindness in the world. The treatment has the aim to reduce intraocular pressure. The first therapy option is to instill drugs on the ocular surface. The main limitation of this is the reduced time of the drug staying on the cornea. This means that high doses are required to ensure its therapeutic effect. A drug-loaded contact lens can diffuse into the post lens tear film in a constant and prolonged flow, resulting in an increased retention of the drug on the surface of the cornea for up to 30 min and thus providing a higher drug bioavailability, increasing the therapeutic efficacy, reducing the amount of administered drug, and thereby provoking fewer adverse events. Several different systems of drug delivery have been studied in recent decades; ranging from more simple methods of impregnating the lenses, such as soaking, to more complex ones, such as molecular imprinting have been proposed. Moreover, different drugs, from those already commercially available to new substances such as melatonin have been studied to improve the glaucoma treatment efficacy. This review describes the role of contact lenses as an innovative drug delivery system to treat glaucoma.

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.

Development and Optimization of Freeze-Dried Eye Drops Derived From Plasma Rich in Growth Factors Technology

Purpose

To investigate whether plasma rich in growth factors (PRGF) eye drops maintain their biological potential after a freeze drying process. The addition of a lyoprotectant like trehalose was also evaluated.

Methods

Blood from three healthy donors was collected to obtain eye drops by PRGF technology. The resultant eye drops were divided in four groups: PRGF, freeze-dried PRGF (PRGF lyo), and PRGF lyophilized mixed with 2,5% trehalose (PRGF lyo+2.5T) or 5% trehalose (PRGF lyof+5T). Chemical and biological characteristics were evaluated. Photorefractive keratectomy was performed on C57BL/6 mice which were divided in three treatment groups: control, PRGF, and PRGF lyo. Corneal wound healing and haze formation were evaluated macroscopically. Eyes were collected at 1, 2, 3, and 7 days after surgery, and were processed for histologic studies.

Results

The pH values of PRGF samples increased significantly after the lyophilization process. Osmolarity levels increased significantly in PRGF samples mixed with trehalose in comparison with PRGF samples without protectants. The freeze drying process maintained growth factors levels as well as the biological properties of PRGF eye drops even without the use of lyoprotectants. PRGF lyo treatment significantly decreased the re-epithelialization time and haze formation in photorefractive keratectomy-treated corneas regarding PRGF and control groups. Furthermore, the PRGF lyo group significantly decreased the number of smooth muscle actin-positive cells in comparison with the control group at each time of the study and at days 2 and 3 in the PRGF group.

Conclusions

The freeze drying process preserves the protein and growth factor content as well as the biological properties of PRGF eye drops, even without the use of protectants. Freeze-dried PRGF eye drops accelerate corneal tissue regeneration after photorefractive keratectomy in comparison with the control group.

Translational Relevance

Our study shows the feasibility to preserve the biological capability of PRGF eye drops as freeze-dried formulation, avoiding the addition of protectants.

Biomimetic hydrogels with spatial- and temporal-controlled chemical cues for tissue engineering

Biomimetic hydrogels have emerged as the most useful tissue engineering scaffold materials. Their versatile chemistry can recapitulate multiple physical and chemical features to integrate cells, scaffolds, and signaling molecules for tissue regeneration. Due to their highly hydrophilic nature hydrogels can recreate nutrient-rich aqueous environments for cells. Soluble regulatory molecules can be incorporated to guide cell proliferation and differentiation. Importantly, the controlled dynamic parameters and spatial distribution of chemical cues in hydrogel scaffolds are critical for cell-cell communication, cell-scaffold interaction, and morphogenesis. Herein, we review biomimetic hydrogels that provide cells with spatiotemporally controlled chemical cues as tissue engineering scaffolds. Specifically, hydrogels with temporally controlled growth factor-release abilities, spatially controlled conjugated bioactive molecules/motifs, and targeting delivery and reload properties for tissue engineering applications are discussed in detail. Examples of hydrogels that possess clinically favorable properties, such as injectability, self-healing ability, stimulus-responsiveness, and pro-remodeling features, are also covered.

Sustained delivery of alendronate by engineered collagen scaffold for the repair of osteoporotic bone defects and resistance to bone loss

Researches of biomaterials for osteoporotic bone defects focus on the improvement of its anti-osteoporosis ability, due to osteoporosis is a kind of systemic and long-range bone metabolism disorder. Nevertheless, how to steadily deliver anti-osteoporosis drugs in osteoporotic bone defects is rarely studied. Reported evidences have shown that alendronate (Aln) is known to not only restrain osteoclasts from mediating bone resorption but also stimulate osteoblasts to regenerate bone tissue. Here, we developed an engineered implantable scaffold that could sustainably release Aln for osteoporotic bone defects. Briefly, Aln was added into 2% collagen (Col) solution to form a 5 mg/ml mixture. Then the mixture was filled into pre-designed round models (diameter: 5 mm, height: 2 mm) and crosslinked to obtain engineered Col-Aln scaffolds. The release kinetics showed that Aln was released at an average rate of 2.99 μg/d in the initial 8 days and could sustainably release for 1 month. To detect the repair effects of the Col-Aln scaffolds for osteoporotic defects, the Col and Col-Aln scaffolds were implanted into 5 mm cranial defects in ovariectomized rats. After 3 months, the cranial defects implanted with Col-Aln scaffolds achieved more bone regeneration in defect area (11.74 ± 3.82%) than Col scaffold (5.12 ± 1.15%) (p < .05). Moreover, ovariectomized rats in Col-Aln scaffold group possessed more trabecular bone in femur metaphysis than Col scaffold group as analyzed by Micro-CT. This study demonstrated the engineered Col-Aln scaffold has the potential to repair osteoporotic bone defects and resist bone loss in osteoporosis.

Arabinogalactan and hyaluronic acid in ophthalmic solution: Experimental effect on xanthine oxidoreductase complex as key player in ocular inflammation (in vitro study)

Dry eye syndrome is a common disease associated to eyes inflammation, irritation and tear film instability. The enzymatic complex of xanthine oxidoreductase (XOR) is involved in the generation of reactive oxygen species (ROS) and uric acid that, in the end, can cause reperfusion injuries, irritation and pathological conditions. Furthermore, in the eye, it has been proposed that oxygen free radicals might play a significant role in retinal ischemic damage. A new artificial drop formulation based on arabinogalactan and hyaluronic acid has been proposed in this article. The uric acid and the ROS formation have been monitored. The effect of the arabinogalactan, the hyaluronic acid and their mixture has been studied. The arabinogalactan entails a uric acid and ROS reduction of 27% and 38% respectively; no significant reduction of uric acid or ROS has been observed after the addition of hyaluronic acid alone. Notably the combination of arabinogalactan and hyaluronic acid involves the reduction of uric acid and ROS equal to 38% and 62%, namely. This study demonstrates that this artificial drop formulation can markedly reduce the uric acid and ROS formation in vitro; thus, the use of this formulation may contribute in the resolution of the dry eye syndrome.

Formulation and In-Vitro Characterization of Chitosan-Nanoparticles Loaded with the Iron Chelator Deferoxamine Mesylate (DFO)

The objective of this study was to develop chitosan (CS) nanoparticles (NPs) loaded with deferoxamine mesylate (DFO) for slow release of this iron-chelating drug. Drug nanoencapsulation was performed via ionic gelation of chitosan using sodium tripolyphosphate (TPP) as cross-linker. Nanoparticles with a size ranging between 150 and 400 nm were prepared for neat CS/TPP with a 2/1 molar ratio while their yield was directly dependent on the applied stirring rate during the preparation process. DFO at different content (20, 45 and 75 wt %) was encapsulated into these nanoparticles. We found that drug loading correlates with increasing DFO content while the entrapment efficiency has an opposite behavior due to the high solubility of DFO. Hydrogen-bonding between amino and hydroxyl groups of DFO with reactive groups of CS were detected using FT-IR spectroscopy while X-ray diffraction revealed that DFO was entrapped in amorphous form in the CS nanoparticles. DFO release is directly dependent on the content of loaded drug, while model analysis revealed that the release mechanism of DFO for the CS/TPP nanoparticles is by diffusion. Treatment of murine RAW 264.7 macrophages with nanoencapsulated DFO promoted an increased expression of transferrin receptor 1 (TfR1) mRNA, a typical homeostatic response to iron deficiency. These data provide preliminary evidence for release of pharmacologically active DFO from the chitosan nanoparticles.

Terminalia arjuna gum/alginate in situ gel system with prolonged retention time for ophthalmic drug delivery

Poor availability is the major barrier to accept the new smart gel system as a preferred ophthalmic solution for various eye problems. Smart gel system especially derived from natural source allows the rapid transition of ocular solution into gel form upon contact to tear solution. The present experimental scheme was intended to prepare and characterize a pH triggered in situ gelling system using moxifloxacin HCl (MOX-HCl). Gum was extracted from Terminalia arjuna bark resin and used as gelling agent in blend with sodium alginate. Sterilized formulations were developed and characterized for their physicochemical attributes. These were further investigated for microbiological testing and eye irritation studies. Drug loaded in situ gel was appeared as clear sol that converted into gel phase in presence of tear solution. Optimized formulation was stable, therapeutically efficacious, non-irritant and has a sustained release of the drug for twelve hours period. Instillation of MOX-HCl loaded in situ gel did not cause any type of irritation symptoms like redness, inflammation and excessive tear production in rabbits as compared to control. MOX-HCl loaded in situ gel can be appraised as a substitute for conventional eye drops for extended precorneal retention, improved corneal permeability along with better ocular bioavailability.

Novel drug delivery methods for the treatment of keratitis: moving away from surgical intervention

Introduction: Corneal ulceration is one of the leading causes of blindness especially in low- and mid-income countries (LMICs). Surgical treatment of microbial keratitis is associated with multiple challenges that include non-availability of donor corneal tissues, lack of trained corneal surgeons, and poor compliance to follow up care. As a result, the surgery fails in 70-90% cases. Therefore, improving outcome of medical treatment and thereby avoiding the need for the surgery is an unmet need in the care of corneal ulcer cases.Areas covered: In this review article, the authors have tried to compile information on the novel drug-delivery systems that have potential to enhance success of medical management. We have discussed the following systems: cyclodextrins, gel formulations, colloidal system, nanoformulations, drug-eluting contact lens, microneedle patch, and ocular inserts.Expert opinion: The goals of corneal ulcer treatment are as follows: rapid eradication of causative microorganisms, control of damage from induced inflammation and microbial toxins, and facilitation of repair. The ocular surface anatomy poses several challenges for drug delivery using standard topical therapy. The novel drug-delivery systems mentioned above aim to enhanced tear solubility; superior stability; improved bio-availability; reduced toxicity; besides facilitating targeted drug delivery and convenience of administration.

Changes in conjunctival epithelial cells after treatment with 0.2% xanthan gum eye drops in mild-moderate dry eye

PURPOSE

To study the effects of xanthan gum eye drops on the ocular surface and conjunctival cytology of patients with mild-moderate dry eye.

METHODS

This prospective, double-masked, controlled trial included 30 patients (age > 60 and Ocular Surface Disease Index score >12 and <33), divided into two groups of 15 subjects and treated with 0.2% xanthan gum eye drops (group 1) or 0.5% carboxymethylcellulose (group 2) qid. After a run-in period with saline qid, patients were evaluated by Ocular Surface Disease Index questionnaire, clinical assessment, and impression cytology at baseline (T0) and after 1 month (T1). For impression cytology, cellularity, cell-to-cell contacts, nucleus/cytoplasm ratio, chromatin aspect, goblet cells distribution, keratinization, and the presence of inflammatory cells were considered. Parameters were scored from 0 (no alterations) to 3 (evident alterations). For statistical analysis, Student's t-test, Wilcoxon rank-sum test, and Mann-Whitney U-test were used.

RESULTS

Clinically, after 1 month of treatment, group 1 showed an improvement of corneal stain (T0 = 1.1 ± 1.4; T1 = 0.5 ± 0.7; p = 0.03) and a reduction of Schirmer I test (T0 = 9.8 ± 6.1; T1 = 5.9 ± 4.1; p = 0.001). In group 2, no differences were found between T0 and T1 for all the clinical tests. For impression cytology, in group 1 cellularity (T0 = 0.6 ± 0.5; T1 = 0.3 ± 0.5; p = 0.05), chromatin aspect (T0 = 1.2 ± 0.4; T1 = 0.8 ± 0.5; p = 0.01), keratinization (T0 = 1 ± 0.7; T1 = 0.5 ± 0.5; p = 0.03), and total score (T0 = 5.8 ± 1.3; T1 = 3.6 ± 1.7; p = 0.003) were significantly ameliorated, while in group 2 only total score improved significantly (T0 = 5 ± 1.4; T1 = 4.3 ± 1.5; p = 0.01). The comparison between groups showed significant amelioration for keratinization in group 1 at T1 (p = 0.02).

CONCLUSION

The treatment with xanthan gum, a molecule with anti-oxidant and mucoadhesive properties, ameliorated conjunctival epithelium of mild-moderate dry eye patients better than carboxymethylcellulose.

Applications of graphene oxide in case of nanomedicines and nanocarriers for biomolecules: review study

In this Review article, recent progress in matter of graphene oxide (GO) synthesis and its functionalization via a vast range of materials, including small molecules, polymers, and biomolecules, were reported and systematically summarized in order to overcome the inherent drawbacks of GO nanocarriers and thereby make these nanocarriers suitable for delivering chemotherapeutic agents, genes, and short interfering RNAs. Briefly, this work describes current strategies for the large scale production of GO and modification of graphene-based nanocarriers surfaces through practical chemical approaches, improving their biocompatibility and declining their toxicity. It also describes the most relevant cases of study suitable to demonstrate the role of graphene and graphene derivatives (GD) as nanocarrier for anti-cancer drugs and genes (e.g. miRNAs). Moreover, the controlled release mechanisms within the cell compartments and blood pH for targeted therapeutics release in the acidic environment of tumor cells or in intracellular compartments are mentioned and explored.

A novel ocular delivery of brinzolamide based on gellan gum: in vitro and in vivo evaluation

Background

The aim of the study was to develop a sustained ocular delivery of brinzolamide (BLZ) based on gellan gum.

Methods

The formulations were characterized for clarity, gelling capacity, rheological studies, pH, drug content, and in vitro drug-release behavior. In vivo rabbit eye irritation test was conducted to evaluate irritation of the BLZ gel drug-delivery system. The prepared BLZ formulations were then investigated in vivo and compared with commercially available BLZ eyedrops with regard to pharmacodynamics.

Results

The results showed that the optimum concentration of gellan gum was 0.25% w/v; the prepared liquid was converted into a flowing gel after the addition of simulated tear fluid. In vitro release profiles showed that the release of BLZ from the in situ gel exhibited sustained characteristics. Draize test results showed that BLZ in situ gels did not stimulate signs of eye tissue activity and were less irritating than BLZ solutions and commercial Azopt.

Conclusion

The results of pharmacodynamics implied that the novel preparation of BLZ in situ gel effectively prolonged the intraocular pressure-lowering effect after administration.

Supramolecular nanofibers of dexamethasone derivatives to form hydrogel for topical ocular drug delivery

The low bioavailability exhibits by conventional ocular formulation owing to rapid precorneal clearance and lower corneal permeability can be overcame by the application of the gelling system. In the present study, a prodrug supramolecular hydrogel derived from succinated dexamethasone (Dex-SA) was fabricated using a pH hydrolytic strategy and explored as a "self-delivery" system for ophthalmic drugs. The self-assembled Dex-SA supramolecular hydrogel exhibited a typical nano-fibrous microstructure and was thixotropic. Both dexamethasone (Dex) and Dex-SA prodrug sustainably released from Dex-SA supramolecular hydrogel in a period of 120 h in vitro release study, and the initial pH value of hydrogel significantly influence on the release ratio of Dex/Dex-SA. Furthermore, the lyophilized Dex-SA supramolecular hydrogel displayed long-term stability without causing any apparent hydrolysis of Dex-SA at -20 °C over 30 day and quickly re-formed a hydrogel after dissolving into aqueous solution. The formed Dex-SA supramolecular hydrogel had lower cytotoxicity than Dex at drug concentration up to 2.5 mM, and exhibited a comparable anti-inflammatory efficacy to a Dex sodium phosphate (Dexp) aqueous solution in lipopolysaccharide-activated RAW264.7 macrophages. Topical instillation of the Dex-SA supramolecular hydrogel showed excellent intraocular biocompatibility and it was not an irritant in rabbit eyes. More importantly, the Dex-SA supramolecular hydrogel provided a prolonged precorneal retention and significantly enhanced the ocular bioavailability over Dexp aqueous solution after topical instillation. Overall, this work illustrates an effective approach for the development of prodrug supramolecular hydrogels to extend the precorneal retention and enhance ocular bioavailability of drugs after topical instillation.

Principles of pharmacology in the eye

The eye is a highly specialized organ that is subject to a huge range of pathology. Both local and systemic disease may affect different anatomical regions of the eye. The least invasive routes for ocular drug administration are topical (e.g. eye drops) and systemic (e.g. tablets) formulations. Barriers that subserve as protection against pathogen entry also restrict drug permeation. Topically administered drugs often display limited bioavailability due to many physical and biochemical barriers including the pre-corneal tear film, the structure and biophysiological properties of the cornea, the limited volume that can be accommodated by the cul-de-sac, the lacrimal drainage system and reflex tearing. The tissue layers of the cornea and conjunctiva are further key factors that act to restrict drug delivery. Using carriers that enhance viscosity or bind to the ocular surface increases bioavailability. Matching the pH and polarity of drug molecules to the tissue layers allows greater penetration. Drug delivery to the posterior segment is a greater challenge and, currently, the standard route is via intravitreal injection, notwithstanding the risks of endophthalmitis and retinal detachment with frequent injections. Intraocular implants that allow sustained drug release are at different stages of development. Novel exciting therapeutic approaches include methods for promoting transscleral delivery, sustained release devices, nanotechnology and gene therapy.

Functional nanocarrier for drug and gene delivery via local administration in mucosal tissues

Local administration has many advantages for treating diseases. However, the surface mucus layer becomes a major obstacle that easily traps and fast removes local administrated drugs and genes in mucosal tissues. Fortunately, the rapidly developing nanocarriers with special physical and chemical properties may help to refine the treatment of mucosal tissues via delivering drugs and genes to the target tissue, and prolong the drug action time. Therefore, this review focuses on the strategies to apply different nanocarriers for drug-delivery in mucosal tissues, including mucoadhesive and mucus-penetrating types. Delivering drugs and genes to anatomical sites with high mucus turnover becomes more feasible and effective, and maintains sufficient local drug concentration to improve treatment efficacy.