Development of in situ thermosensitive drug vehicles for glaucoma therapy

Recent Updates on Nanocarriers for Drug Delivery in Posterior Segment Diseases with Emphasis on Diabetic Retinopathy

In recent years, various conventional formulations have been used for the treatment and/or management of ocular medical conditions. Diabetic retinopathy, a microvascular disease of the retina, remains the leading cause of visual disability in patients with diabetes. Currently, for treating diabetic retinopathy, only intraocular, intravitreal, periocular injections, and laser photocoagulation are widely used. Frequent administration of these drugs by injections may lead to serious complications, including retinal detachment and endophthalmitis. Although conventional ophthalmic formulations like eye drops, ointments, and suspensions are available globally, these formulations fail to achieve optimum drug therapeutic profile due to immediate nasolacrimal drainage, rapid tearing, and systemic tearing toxicity of the drugs. To achieve better therapeutic outcomes with prolonged release of the therapeutic agents, nano-drug delivery materials have been investigated. These nanocarriers include nanoparticles, solid lipid nanoparticles (SLN), nanostructured lipid carriers (NLC), dendrimers, nanofibers, in-situ gel, vesicular carriers, niosomes, and mucoadhesive systems, among others. The nanocarriers carry the potential benefits of site-specific delivery and controlled and sustained drug release profile. In the present article, various nanomaterials explored for treating diabetic retinopathy are reviewed.

Single Hydrogel Particle Mechanics and Dynamics Studied by Combining Capillary Micromechanics with Osmotic Compression

Hydrogels can exhibit a remarkably complex response to external stimuli and show rich mechanical behavior. Previous studies of the mechanics of hydrogel particles have generally focused on their static, rather than dynamic, response, as traditional methods for measuring single particle response at the microscopic scale cannot readily measure time-dependent mechanics. Here, we study both the static and the time-dependent response of a single batch of polyacrylamide (PAAm) particles by combining direct contact forces, applied by using Capillary Micromechanics, a method where particles are deformed in a tapered capillary, and osmotic forces are applied by a high molecular weight dextran solution. We found higher values of the static compressive and shear elastic moduli for particles exposed to dextran, as compared to water (KDex≈63 kPa vs. Kwater≈36 kPa, and GDex≈16 kPa vs. Gwater≈7 kPa), which we accounted for, theoretically, as being the result of the increased internal polymer concentration. For the dynamic response, we observed surprising behavior, not readily explained by poroelastic theories. The particles exposed to dextran solutions deformed more slowly under applied external forces than did those suspended in water (τDex≈90 s vs. τwater≈15 s). The theoretical expectation was the opposite. However, we could account for this behaviour by considering the diffusion of dextran molecules in the surrounding solution, which we found to dominate the compression dynamics of our hydrogel particles suspended in dextran solutions.

The gamut of perspectives, challenges, and recent trends for in situ hydrogels: a smart ophthalmic drug delivery vehicle

Polymers have a major role in the controlled delivery of pharmaceutical compounds to a targeted portion of the body. In this quest, a high priority research area is the targeted delivery of ophthalmic drugs to the interior regions of the eyes. Due to their complex anatomical/biochemical nature. This necessitates an advanced drug delivery cargo that could administer a therapeutic agent to the targeted location by evading various obstacles. The ongoing focus is to design an ophthalmic formulation by coupling it with a smart in situ forming polymeric hydrogel. These smart macromolecules have an array of unique theranostic properties and can utilize the in vivo biological parameters as a stimulus to change their macromolecular state from liquid to gel. The fast gelling hydrogel improves the corneal contact time, facilitates sustained drug release, resists the burst-out effect, and assists drug permeability to anterior regions. This review summarizes the rationale, scientific objectives, properties, and classification of the biologically important in situ hydrogels in the niche of ophthalmic drug delivery. The current trends and prospectives of the array of stimulus-responsive polymers, copolymers, and nanomaterials are discussed broadly. The crucial biointerfacial attributes with pros and cons are reviewed by investigating the effect of the nature of polymers as well as the ratio/percentage of additives and copolymers that influence the overall performance.

Effect of tamarind seed polysaccharide on thermogelation property and drug release profile of poloxamer 407-based ophthalmic formulation

Herein, the potential impact of tamarind seed polysaccharide (TSP) on the gelation nature and in vitro release of a particular drug, pilocarpine hydrochloride, from different poloxamer 407-based ophthalmic formulations were evaluated.

Novel hydrogel-based ocular drug delivery system for the treatment of conjunctivitis

PURPOSE

Conventional dosage form like eye drops showed poor therapeutic response and also require frequent dosing. Therefore, developing the dosage form to deliver the drug to the target site without much loss of drug or without causing any systemic side effects is the challenging job for the researchers in pharmaceutical industries.

OBJECTIVE

The main aim of the present work was to formulate and evaluate hydrogel-based drug delivery containing combination of neomycin sulphate and betamethasone sodium phosphate in order to provide prolonged release and also better bioavailability of drugs for the treatment of eye infections.

METHODS

In this study, poloxamer 407 and chitosan at different concentrations were used as the gelling agents. The prepared formulations were evaluated for clarity, pH, drug content, gelling capacity, gelling temperature and in vitro drug release study.

RESULTS

From the preliminary studies, F5 formulation was selected as an optimized formulation. The optimized formulation was further evaluated for ex vivo permeation study, sterility test, HET-CAM and ocular irritation testing using rabbits. Ocular irritation by HET-CAM assay showed that the formulated gel does not cause any irritation to the blood vessels. Draize irritation test was performed using rabbits and results showed that formulation was non-irritant to the eye.

CONCLUSION

The formulated hydrogel formulation can be used as an alternative to conventional ophthalmic eye drop formulation of drugs neomycin and betamethasone for the purpose of providing prolonged therapy for the treatment of conjunctivitis.

Effect of substrate storage conditions on the stability of "Smart" films used for mammalian cell applications

When poly(N-isopropyl acrylamide) (pNIPAM) is tethered to a surface, it can induce the spontaneous release of a sheet of mammalian cells. The release of cells is a result of the reversible phase transition the polymer undergoes at its lower critical solution temperature (LCST). Many techniques are used for the deposition of pNIPAM onto cell culture substrates. Previously, we compared two methods of deposition (plasma polymerization, and co-deposition with a sol-gel). We proved that although both were technically appropriate for obtaining thermoresponsive pNIPAM films, the surfaces that were co-deposited with a sol-gel caused some disruption in cell activity. The variation of cell behavior could be due to the delamination of pNIPAM films leaching toxic chemicals into solution. In this work, we assessed the stability of these pNIPAM films by manipulating the storage conditions and analyzing the surface chemistry using X-ray photoelectron spectroscopy (XPS) and contact angle measurements over the amount of time required to obtain confluent cell sheets. From XPS, we demonstrated that ppNIPAM (plasma polymerized NIPAM) films remains stable across all storage conditions while sol-gel deposition show large deviations after 48 h of storage. Cell response of the deposited films was assessed by investigating the cytotoxicity and biocompatibility. The 37°C and high humidity storage affects sol-gel deposited films, inhibiting normal cell growth and proper thermoresponse of the film. Surface chemistry, thermoresponse and cell growth remained similar for all ppNIPAM surfaces, indicating these substrates are more appropriate for mammalian cell culture applications.

A Review of Injectable Polymeric Hydrogel Systems for Application in Bone Tissue Engineering

Biodegradable, stimuli-responsive polymers are essential platforms in the field of drug delivery and injectable biomaterials for application of bone tissue engineering. Various thermo-responsive hydrogels display water-based homogenous properties to encapsulate, manipulate and transfer its contents to the surrounding tissue, in the least invasive manner. The success of bioengineered injectable tissue modified delivery systems depends significantly on their chemical, physical and biological properties. Irrespective of shape and defect geometry, injectable therapy has an unparalleled advantage in which intricate therapy sites can be effortlessly targeted with minimally invasive procedures. Using material testing, it was found that properties of stimuli-responsive hydrogel systems enhance cellular responses and cell distribution at any site prior to the transitional phase leading to gelation. The substantially hydrated nature allows significant simulation of the extracellular matrix (ECM), due to its similar structural properties. Significant current research strategies have been identified and reported to date by various institutions, with particular attention to thermo-responsive hydrogel delivery systems, and their pertinent focus for bone tissue engineering. Research on future perspective studies which have been proposed for evaluation, have also been reported in this review, directing considerable attention to the modification of delivering natural and synthetic polymers, to improve their biocompatibility and mechanical properties.

Ocular Biocompatibility of Poly-N-Isopropylacrylamide (pNIPAM)

Purpose. To study the safety of intravitreal injections of poly-N-isopropylacrylamide (pNIPAM) tissue adhesive in rabbit eyes. Methods. Twelve study rabbits received an intravitreal injection of 0.1 mL 50% pNIPAM in the right eye. Follow-up examinations included color fundus photography, fundus fluorescein angiography (FA), optical coherence tomography (OCT), and electroretinography (ERG). Subsequent to the last follow-up assessment, the rabbits were sacrificed and histopathological study on the scleral incision sites was performed. Results. All study animals developed mild to moderate levels of inflammatory reaction in the conjunctiva, anterior chamber, and the anterior vitreous during the first month of follow-up. After this period, the level of the inflammatory reaction progressively decreased and completely disappeared after the third month of follow-up. The lens and cornea remained clear during the entire follow-up period. OCT and FA did not show areas of retinal damage or neovascularization. Histological and ERG studies of eyes injected with pNIPAM demonstrated absence of retinal toxicity. Conclusion. Intravitreal injections of pNIPAM were nontoxic in this animal study, and pNIPAM may be safe to be used as a bioadhesive in certain retinal diseases.

Poly-N-isopropylacrylamide (pNIPAM): a reversible bioadhesive for sclerotomy closure

PURPOSE

To determine the safety and efficacy of poly-N-isopropylacrylamide, a thermoresponsive adhesive, for sutureless sclerotomy closure in rabbits.

METHODS

Eight rabbits were randomized into three groups: short-term acute, mid-term chronic, and long-term chronic studies. A corresponding control group in which the scleral wounds were sutured by 6-0 vicryl sutures was assigned for each study group. A 20-gauge sclerotomy was performed following a core vitrectomy and 0.1 mL of 50 % liquid poly-N-isopropylacrylamide was applied to the scleral wounds. Before the polymer application, the scleral surface was raised above 32 °C using a halogen bulb lamp. Follow-up exams included color external and fundus photography, fundus fluorescein angiography, optical coherence tomography, and electroretinography. After the last follow-up assessment, the rabbits were sacrificed and histopathological studies on the scleral incision sites were performed.

RESULTS

Scleral wound healing was observed in the long-term chronic study rabbits. Histological studies were able to identify poly-N-isopropylacrylamide polymer at the sclerotomy site in the mid-term chronic study rabbits. Besides iatrogenic cataracts due to mechanical instrument touch in 2 rabbits, no other ocular abnormalities were identified in any of the eyes in the perioperative setting or during the follow-up period. Cornea, retina, and vitreous remained unaffected, and no abnormal inflammatory reaction or endophthalmitis was noticed in the 3 study groups. Filtering blebs indicative of leakage through the sclerotomies were not observed during the follow-up period.

CONCLUSION

Poly-N-isopropylacrylamide may provide effective in vitro scleral adhesion above 32 °C. Clinical studies are required to evaluate its utility in patients undergoing pars plana vitrectomy.

Functionalized graphene oxide-based thermosensitive hydrogel for near-infrared chemo-photothermal therapy on tumor

PURPOSE

A functionalized graphene oxide-based thermosensitive hydrogel loaded with docetaxel for intratumoral delivery was designed to enhance therapeutic efficacy and alleviate system toxicity.

METHODS

First, graphene oxide was functionalized with chitosan to acquire high stability in physiological solutions. And then docetaxel-graphene oxide/chitosan gel was formed by mixed docetaxel-graphene oxide/chitosan suspension with hydrogel which was made from Poloxamer 407 and Poloxamer 188. Cellular uptake, antitumor effect in vitro and in vivo, cell apoptosis, and biodistribution of docetaxel-graphene oxide/chitosan gel were investigated, compared with the docetaxel solution.

RESULTS

Graphene oxide/chitosan was stable in physiological solution, and docetaxel released much slower from docetaxel-graphene oxide/chitosan gel with a pH-responsive feature. Compared with free docetaxel, docetaxel-graphene oxide/chitosan could afford higher antitumor efficacy in Michigan Cancer Foundation-7 (MCF-7) cells in vitro. Furthermore, docetaxel-grapheme oxide/chitosan gel which was injected within tumor could afford higher concentration and longer resident time in tumor tissues of mice in vivo, without obvious toxic effects to normal organs. Meanwhile, the combination of near-infrared laser irradiation at 808 nm significantly enhanced tumor inhibition in vitro and in vivo.

CONCLUSIONS

Docetaxel-graphene oxide/chitosan gel in combination with 808 nm near-infrared laser irradiation had great potential for cancer chemo-photothermal therapy.

Functionalized graphene oxide-based thermosensitive hydrogel for magnetic hyperthermia therapy on tumors

A novel locally injectable, biodegradable, and thermo-sensitive hydrogel made from chitosan and β-glycerophosphate salt was prepared. It incorporated polyethylenimine (PEI)-modified super-paramagnetic graphene oxide (GO/IONP/PEI) as a form of minimally invasive treatment of cancer lesions by magnetically induced local hyperthermia. Doxorubicin (DOX) was mixed into the hydrogel which was pre-loaded on GO/IONP/PEI to create a drug delivery system DOX-GO/IONP/PEI-gel. In addition to the evaluation of in vitro and in vivo antitumor activities, the physicochemical properties, magnetic properties and DOX release profile of the DOX-GO/IONP/PEI-gel were determined. The aqueous solution of the hydrogel showed a sol-gel transition behavior depending on temperature changes. Magnetization loops indicated the super-paramagnetic properties of GO/IONP/PEI. Compared with free DOX, DOX-GO/IONP/PEI could efficiently pass through cell membranes, leading to more apoptosis and demonstrating higher antitumor efficacy on MCF-7 cells in vitro. Furthermore, DOX-GO/IONP/PEI-gel intratumorally injected (i.t.) showed high antitumor efficacy on tumor-bearing mice in vivo, with no obvious toxicity. The antitumor efficacy was higher when combined with an alternating magnetic field (AMF), showing that DOX-GO/IONP/PEI-gel under AMF has great potential for cancer magnetic hyperthermia therapy.

Optimization and evaluation of a thermoresponsive ophthalmic in situ gel containing curcumin-loaded albumin nanoparticles

This study aimed to optimize and evaluate a thermoresponsive ophthalmic in situ gel containing curcumin-loaded albumin nanoparticles (Cur-BSA-NPs-Gel). Albumin nanoparticles were prepared via a desolvation method, and the gels were prepared via a cold method. The central composite design and response surface method was used to evaluate the effects of varying Pluronic^® F127 and Pluronic^® F68 concentrations on the sol–gel transition temperature, which is an indicator of optimum formulations. The optimized formulation was a free-flowing liquid below 30.9°C that transformed into a semi-solid gel above 34.2°C after dilution with simulated tear fluid. Results of the in vitro release and erosion behavior study indicated that Cur-BSA-NPs-Gel achieved superior sustained-release effects and that incorporation of albumin nanoparticles exerted minimal effects on the gel structure. In addition, in vivo ophthalmic experiments employing Cur-BSA-NPs-Gel were subsequently performed in rabbits. In vivo eye irritation results showed that Cur-BSA-NPs-Gel might be considered safe for ophthalmic drug delivery. The in vivo study also revealed that the formulation could significantly increase curcumin bioavailability in the aqueous humor. In conclusion, the optimized in situ gel formulation developed in this work has significant potential for ocular application.

Biodegradable in situ gelling delivery systems containing pilocarpine as new antiglaucoma formulations: effect of a mercaptoacetic acid/N-isopropylacrylamide molar ratio

Ocular drug delivery is one of the most commonly used treatment modalities in the management of glaucoma. We have recently proposed the use of gelatin and poly(N-isopropylacrylamide) (PNIPAAm) graft copolymers as biodegradable in situ forming delivery systems for the intracameral administration of antiglaucoma medications. In this study, we further investigated the influence of carrier characteristics on drug delivery performance. The carboxyl-terminated PNIPAAm samples with different molecular weights were synthesized by varying the molar ratio of mercaptoacetic acid (MAA)/N-isopropylacrylamide (NIPAAm) from 0.05 to 1.25, and were determined by end-group titration. The preparation of gelatin-g-PNIPAAm (GN) copolymers from these thermoresponsive polymers was achieved using carbodiimide chemistry. Our results showed that the carboxylic end-capped PNIPAAm of high molecular weight may lead to the lower thermal phase transition temperature and slower degradation rate of GN vehicles than its low molecular weight counterparts. With a decreasing MAA/NIPAAm molar ratio, the drug encapsulation efficiency of copolymers was increased due to fast temperature-triggered capture of pilocarpine nitrate. The degradation of the gelatin network could greatly affect the drug release profiles. All of the GN copolymeric carriers demonstrated good corneal endothelial cell and tissue compatibility. It is concluded that different types of GN-based delivery systems exhibit noticeably distinct intraocular pressure-lowering effect and miosis action, thereby reflecting the potential value of a MAA/NIPAAm molar ratio in the development of new antiglaucoma formulations.

In situ gel systems as 'smart' carriers for sustained ocular drug delivery

INTRODUCTION

In situ gel systems refer to a class of novel delivery vehicles, composed of natural, semisynthetic or synthetic polymers, which present the unique property of sol-gel conversion on receipt of biological stimulus.

AREAS COVERED

The present review summarizes the latest developments in in situ gel technology, with regard to ophthalmic drug delivery. Starting with the mechanism of ocular absorption, the review expands on the fabrication of various polymeric in situ gel systems, made up of two or more polymers presenting multi-stimuli sensitivity, coupled with other interesting features, such as bio-adhesion, enhanced penetration or sustained release. Various key issues and challenges in this area have been addressed and critically analyzed.

EXPERT OPINION

The advent of in situ gel systems has inaugurated a new transom for 'smart' ocular delivery. By virtue of possessing stimuli-responsive phase transition properties, these systems can easily be administered into the eye, similar to normal eye drops. Their unique gelling properties endow them with special features, such as prolonged retention at the site of administration, followed by sustained drug release. Despite the superiority of these systems as compared with conventional ophthalmic formulations, further investigations are necessary to address the toxicity issues, so as to minimize regulatory hurdles during commercialization.

Preparation of PNIPAM-g-P (NIPAM-co-St) microspheres and their blood compatibility

The poly(N-isopropylacrylamide)-g-poly(N-isopropylacrylamide-co-styrene) microspheres (PNNS-MSs) were prepared by an emulsifier-free emulsion polymerization method. The blood compatibility of PNNS-MSs was characterized by in vitro for coagulation tests, hemolysis assay, plasma recalcification time, complement activation, platelet activation, and cytotoxicity experiments. The results showed that the PNNS-MSs have good blood compatibility and lack cytotoxicity, which may be attributed to the formation of a strong interfacial hydration layer that result from amphiphilic molecular structure of the PNIPAM shell and minimal interaction between PNNS-MSs interfaces and blood components. The PNNS-MSs provide a promising platform of blood circulation system for early illness diagnosis and therapy.

Patterning methods for polymers in cell and tissue engineering

Polymers provide a versatile platform for mimicking various aspects of physiological extracellular matrix properties such as chemical composition, rigidity, and topography for use in cell and tissue engineering applications. In this review, we provide a brief overview of patterning methods of various polymers with a particular focus on biocompatibility and processability. The materials highlighted here are widely used polymers including thermally curable polydimethyl siloxane, ultraviolet-curable polyurethane acrylate and polyethylene glycol, thermo-sensitive poly(N-isopropylacrylamide) and thermoplastic and conductive polymers. We also discuss how micro- and nanofabricated polymeric substrates of tunable elastic modulus can be used to engineer cell and tissue structure and function. Such synergistic effect of topography and rigidity of polymers may be able to contribute to constructing more physiologically relevant microenvironment.

Study of thermo-sensitive in-situ gels for ocular delivery

The aim of the present study was the development of thermo-sensitive in-situ gels for in-vitro evaluation of ophthalmic delivery systems of ketorolac tromethamine (KT), based on methylcellulose (MC) in combination with hydroxypropylmethyl cellulose (HPMC). The gel temperature of 1% MC solution was observed at 60°C. It was found that 6% oral rehydration salt without dextrose (ORS) was capable to reduce the gel temperature below physiological temperature. HPMC was added to increase viscosity and drug release time. The results indicated a large increase in viscosity at 37°C with addition of HPMC whch provided sustained release of the drug over a 4h period. From in-vitro release studies, it could be concluded that the developed systems were thus a better alternative to conventional eye drops.

Effective and sustained delivery of hydrophobic retinoids to photoreceptors

PURPOSE

Delivery of hydrophobic compounds to the retina/RPE has been challenging. The purpose of this study was to develop an effective method for the sustained delivery of retinoids to rod and cone photoreceptors of young mice lacking a normal supply of 11-cis retinal.

METHODS

Solubilized basement membrane matrix (Matrigel; BD Biosciences, San Jose, CA) loaded with 9-cis retinal was administered subcutaneously into Rpe65(-/-) mouse pups for assessment of delivery to rods and cones and to Rpe65(-/-)Rho(-/-) mouse pups for assessment of delivery to cones. Intraperitoneal injections of 9-cis retinal were used for comparison. Cone density and opsin localization were evaluated with immunohistochemistry. Cone opsin protein levels were assayed with immunoblots, and cone function was analyzed by electroretinography (ERG) recordings. Retinoid content was determined by high-performance liquid chromatography analysis of retinal extracts. Pigment levels were quantified in homogenized retinas by absorption spectroscopy before and after light exposure.

RESULTS

Single administration of Matrigel loaded with 9-cis retinal to Rpe65(-/-) mice increased cone densities in all analyzed regions of the retina compared with mice treated using intraperitoneal delivery. Cone opsin levels increased to near wild-type levels. Similar treatment in Rpe65(-/-)Rho(-/-) mice increased b-wave ERG amplitudes significantly, indicating the maintenance of cone function. Matrigel was shown to continuously release 9-cis retinal for periods up to 1 week.

CONCLUSIONS

As a method for sustained drug delivery, subcutaneous administration using Matrigel proved more efficacious than intraperitoneal injection for in vivo delivery of retinoids to cone photoreceptors. These experiments are the first to show a sustained delivery of retinoids in mice and suggest a strategy for potential clinical therapeutic development.

Intracellular localisation, geno- and cytotoxic response of polyN-isopropylacrylamide (PNIPAM) nanoparticles to human keratinocyte (HaCaT) and colon cells (SW 480)

PNIPAM nanoparticles, with and without a covalently linked fluorescent label, were prepared by a free radical polymerisation technique. The cyto- and genotoxicity of PNIPAM nanoparticles were analysed in two representative mammalian cell lines, SW480, a colon, and HaCaT, a dermal cell line. Physical characterisation in terms of particle size and zeta potential of the PNIPAM nanoparticles was carried out both in aqueous solution and in the appropriate cell culture media. Uptake and co-localisation of fluorescently labelled PNIPAM nanoparticles was monitored in both cell lines using confocal laser scanning microscope. Genotoxicity analysis using the Comet assay was performed in both cell lines to evaluate any DNA damage. It was observed that the PNIPAM nanoparticles were internalized and localised in lysosomes within 24h. No significant cytotoxic response (p<or.05) was observed in either cell line over concentration ranges from 25 to 1000mg/l for all exposure time periods. Furthermore, no significant genotoxic response (p<or.05) was observed in either cell line over concentration ranges from 12.5 to 800mg/l for all exposure time periods. The results suggest that the PNIPAM nanoparticles show excellent biocompatibility in vitro.

Effect of salts on gelation and drug release profiles of methylcellulose-based ophthalmic thermo-reversible in situ gels

The poor bioavailability and therapeutic response exhibited by conventional ophthalmic solutions may be overcome by the use of thermo-reversible in situ gel. The purpose of this study was to examine the influence of different salts on the gelation, rheology and drug release of in situ gel based on methylcellulose. The gel temperature of 1% w/v methylcellulose (MC) was 60?C. It was found that 5?7% w/v sodium chloride (NaCl), 8?9% w/v potassium chloride (KCl), or 5% w/v sodium bicarbonate (NaHCO(3)) was capable of decreasing the gel temperature below physiological temperature, i.e. 37?C. Rheological studies indicated a large increase in viscosity at 37?C with the addition of salts in MC solutions. The duration of drug release from MC solution was 1.5?h. The significant observation was that the duration of drug release increased from 1.5?h to 3?5?h from salted MC solutions depending on the concentration and the type of salt. So, it can be concluded that the salted MC solutions were a better alternative than the MC solution to enhance the ocular bioavailability of the drug.

Preparation and evaluation of thermosensitive liposomal hydrogel for enhanced transcorneal permeation of ofloxacin

Ofloxacin, available as ophthalmic solution, has two major problems: first, it needs frequent administration every 4 hours or even every 1 hour to treat severe eye infection; second, there is formation of white crystalline deposit on cornea due to its pH-dependent solubility, which is very low at pH of corneal fluid. In order to provide a solution to previous problems, ofloxacin in this study is prepared as topically effective in situ thermosensitive prolonged release liposomal hydrogel. Two preparation procedures were carried out, leading to the formation of multilamellar vesicles (MLVs) and reverse-phase evaporation vesicles (REVs) at pH 7.4. Effects of method of preparation, lipid content, and charge inducers on encapsulation efficiency were studied. For the preparation of in situ thermosensitive hydrogel, chitosan/beta-glycerophosphate system was synthesized and used as carrier for ofloxacin liposomes. The effect of addition of liposomes on gelation temperature, gelation time, and rheological behaviors of the hydrogel were evaluated. In vitro transcorneal permeation was also determined. MLVs entrapped greater amount of ofloxacin than REVs liposomes at pH 7.4; drug loading was increased by including charge-inducing agent and by increasing cholesterol content until a certain limit. The gelation time was decreased by the addition of liposomes into the hydrogel. The prepared liposomal hydrogel enhances the transcorneal permeation sevenfold more than the aqueous solution. These results suggested that the in situ thermosensitive ofloxacin liposomal hydrogel ensures steady and prolonged transcorneal permeation, which improves the ocular bioavailability, minimizes the need for frequent administration, and decreases the ocular side effect of ofloxacin.

Hybrid polymeric hydrogels for ocular drug delivery: nanoparticulate systems from copolymers of acrylic acid-functionalized chitosan and N-isopropylacrylamide or 2-hydroxyethyl methacrylate

Nanoparticulate hybrid polymeric hydrogels (10-70 nm) have been obtained via the radical-induced co-polymerization of acrylic acid-functionalized chitosan with either N-isopropylacrylamide or 2-hydroxyethyl methacrylate, and the materials have been investigated for their ability to act as controlled release vehicles in ophthalmic drug delivery. Studies on the effects of network structure upon swelling properties, adhesiveness to substrates that mimic mucosal surfaces and biodegradability, coupled with in vitro drug release investigations employing ophthalmic drugs with differing aqueous solubilities, have identified nanoparticle compositions for each of the candidate drug molecules. The hybrid nanoparticles combine the temperature sensitivity of N-isopropylacrylamide or the good swelling characteristics of 2-hydroxyethyl methacrylate with the susceptibility of chitosan to lysozyme-induced biodegradation.

Preparation and characterization of thermo-responsive PDMS surfaces grafted with poly(N-isopropylacrylamide) by benzophenone-initiated photopolymerization

In the preparation of a thermo-responsive, poly(N-isopropylacrylamide) (PNIPAAm)-grafted polydimethylsiloxane (PDMS) surface by means of benzophenone-initiated photopolymerization, we observed that thick (>1 mm) PDMS substrates were much more difficult to be grafted with PNIPAAm than thin ones. Investigations revealed that the shortage of diffused benzophenone molecules in the surface region of the thick substrate might be the reason. By prolonging the time spent for treating the substrate with a benzophenone solution, PNIPAAm could be successfully grafted onto thick PDMS substrates. The PNIPAAm-grafted PDMS surface was highly thermo-responsive. The contact angle on a grafted surface increased from 38 to 91 degrees in response to the temperature increase from 20 to 38 degrees C. An electroosmotic flow (EOF) mobility of 5x10(-4) cm(2)/Vs was supported by a PNIPAAm-grafted PDMS channel at 50 degrees C, whereas negligible EOF was observed at 20 degrees C. Doxorubicin (DX), an anticancer drug, was adsorbed by the grafted surface at 40 degrees C, and the majority of the adsorbed DX was quickly released from the surface to a stripping solution at 5 degrees C. Osteoblast cells adhered onto the PNIPAAm-grafted PDMS surface and proliferated therein at 37 degrees C, while the cell sheet detached from the surface by lowering the temperature to 25 degrees C without using any enzymatic agent.

Light Scattering as Spectroscopic Tool for the Study of Disperse Systems Useful in Pharmaceutical Sciences

The use of colloidal systems in pharmaceutical formulations, for addressing the issue of selective and controlled drug delivery or for improving drug availability, requires an accurate previous characterization of their chemical and physical properties. Light scattering is a useful and non-invasive method to study the structure and conformation of colloids in a wide space-scale, encompassing nanometric- to micrometric-sized particles, as well as their size distribution, surface electrostatic potential and aggregation phenomena occurring under proper conditions. In this review the physical bases of the light scattering approach are described and many examples are reported to discuss the examination of various multiphase systems useful in pharmaceutical fields.

Poly(N-isopropylacrylamide)–chitosan as thermosensitive in situ gel-forming system for ocular drug delivery

A novel copolymer, poly(N-isopropylacrylamide)-chitosan (PNIPAAm-CS), was investigated for its thermosensitive in situ gel-forming properties and potential utilization for ocular drug delivery. The thermal sensitivity and low critical solution temperature (LCST) were determined by the cloud point method. PNIPAAm-CS had a LCST of 32 degrees C, which is close to the surface temperature of the eye. The in vivo ocular pharmacokinetics of timolol maleate in PNIPAAm-CS solution were evaluated and compared to that in conventional eye drop solution by using rabbits according to the microdialysis method. The C(max) of timolol maleate in aqueous fluid for the PNIPAAm-CS solution was 11.2 microg/ml, which is two-fold higher than that of the conventional eye drop, along with greater AUC. Furthermore, the PNIPAAm-CS gel-forming solution of timolol maleate had a stronger capacity to reduce the intra-ocular pressure (IOP) than that of the conventional eye drop of same concentration over a period of 12 h. In addition, the MTT assay showed that there is little cytotoxicity of PNIPAAm-CS at concentration range of 0.5-400 microg/ml. These results suggest that PNIPAAm-CS is a potential thermosensitive in situ gel-forming material for ocular drug delivery, and it may improve the bio-availability, efficacy, and compliance of some eye drugs.

Development of a poloxamer analogs/carbopol-based in situ gelling and mucoadhesive ophthalmic delivery system for puerarin

Conventional ophthalmic solutions often eliminate rapidly after administration and cannot provide and maintain an adequate concentration of the drug in the precorneal area. To solve these problems, we developed a thermosensitive in situ gelling and mucoadhesive ophthalmic drug delivery system containing puerarin based on poloxamer analogs (21% (w/v) poloxamer 407/5% (w/v) poloxamer 188) and carbopol (0.1% (w/v) or 0.2% (w/v) carbopol 1342P NF). The combined solutions would convert to firm gels under physiological condition and attach to the ocular mucosal surface for a relative long time. The incorporation of carbopol 1342P NF not only did not affect the pseudoplastic behavior with hysteresis of the poloxamer analogs solution and led to a higher shear stress at each shear rate, but also enhanced the mucoadhesive force significantly. In vitro release studies demonstrated diffusion-controlled release of puerarin from the combined solutions over a period of 8h. In vivo evaluation (the elimination of puerarin in tear and intraocular pressure-lowering effect) indicated the combined solutions had better ability to retain drug than poloxamer analogs or carbopol alone. It appears that ocular bioavailability can be increased more readily by using the in situ gelling and mucoadhesive vehicle.

Effects of the length of crosslink chain on poly(2-hydroxyethyl methacrylate) (pHEMA) swelling and biomechanical properties

Polymers are widely used in medicine for vascular prostheses, bone substitutes, and devices for controlled release. Among these polymers, poly(2-hydroxyethyl methacrylate) (pHEMA) is the most employed. To confer particular properties, pHEMA can be copolymerized with other monomers or in the presence of plasticizers or crosslinking agents. The influence of the length of crosslink chains on swelling, surface rugosity, hardness, and stiffness of crosslinked pHEMA were studied by several techniques, including fractal analysis and AFM. Four crosslinking agents (divinyl benzene, DVB; ethylene glycol dimethacrylate, EGDMA; tetraethylene glycol diacrylate, TEGDA; and polyethylene glycol diacrylate, PEGDA) were added to the bulk polymerization mixture. Only linear and PEGDA-pHEMA presented a significant decrease in surface roughness confirmed by fractal analysis. Differences in hardness and biomechanical properties were evidenced on dried polymers but the highest differences were exhibited for hydrated pHEMA. Correlations between the length of the crosslink chain and hardness or stiffness of hydrated crosslinked pHEMA were evidenced. TEGDA and PEGDA appeared to be the two most suitable crosslinking agents for controlled release of bioactive molecules in bone.