Biocompatibility and biodegradation studies of subconjunctival implants in rabbit eyes

Microfluidic Rheology: An Innovative Method for Viscosity Measurement of Gels and Various Pharmaceuticals

Measuring the viscosity of pharmaceutical dosage forms is a crucial process. Viscosity provides information about the stability of the composition, the release rate of the drug, bioavailability, and, in the case of injectable drug formulations, even the force required for injection. However, measuring viscosity is a complex task with numerous challenges, especially for non-Newtonian materials, which include most pharmaceutical formulations, such as gels. Selecting the appropriate shear rate is critical. Since viscosity in many systems is highly temperature-dependent, stable temperature control is necessary during the measurement. Using microfluidics technology, it is now possible to perform rheological characterization and conduct fast and accurate measurements. Small sample volumes (even below 500 µL) are required, and viscosity determination can be carried out over a wide range of shear rates. Nevertheless, the pharmaceutical application of viscometers operating on the principle of microfluidics is not yet widespread. In our work, we compare the results of measurements taken with a microfluidic chip-based viscometer on different pharmaceutical forms (gels, solution) with those obtained using a traditional rotational viscometer, evaluating the relative advantages and disadvantages of the different methods. The microfluidics-based method enables time- and sample-efficient viscosity analysis of the examined pharmaceutical forms.

Surface coating of orthopedic implant to enhance the osseointegration and reduction of bacterial colonization: a review

The use of orthopedic implants in surgical technology has fostered restoration of physiological functions. Along with successful treatment, orthopedic implants suffer from various complications and fail to offer functions correspondent to native physiology. The major problems include aseptic and septic loosening due to bone nonunion and implant site infection due to bacterial colonization. Crucial advances in material selection in the design and development of coating matrixes an opportunity for the prevention of implant failure. However, many coating materials are limited in in-vitro testing and few of them thrive in clinical tests. The rate of implant failure has surged with the increasing rates of revision surgery creating physical and sensitive discomfort as well as economic burdens. To overcome critical pathogenic activities several systematic coating techniques have been developed offering excellent results that combat infection and enhance bone integration. This review article includes some more common implant coating matrixes with excellent in vitro and in vivo results focusing on infection rates, causes, complications, coating materials, host immune responses and significant research gaps. This study provides a comprehensive overview of potential coating technology, with functional combination coatings which are focused on ultimate clinical practice with substantial improvement on in-vivo tests. This includes the development of rapidly growing hydrogel coating techniques with the potential to generate several accurate and precise coating procedures.

Considerations for Polymers Used in Ocular Drug Delivery

PURPOSE

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

METHODS

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

RESULTS

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

CONCLUSION

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

Electronic Drugs: Spatial and Temporal Medical Treatment of Human Diseases

Recent advances in diagnostics and medicines emphasize the spatial and temporal aspects of monitoring and treating diseases. However, conventional therapeutics, including oral administration and injection, have difficulties meeting these aspects due to physiological and technological limitations, such as long-term implantation and a narrow therapeutic window. As an innovative approach to overcome these limitations, electronic devices known as electronic drugs (e-drugs) have been developed to monitor real-time body signals and deliver specific treatments to targeted tissues or organs. For example, ingestible and patch-type e-drugs could detect changes in biomarkers at the target sites, including the gastrointestinal (GI) tract and the skin, and deliver therapeutics to enhance healing in a spatiotemporal manner. However, medical treatments often require invasive surgical procedures and implantation of medical equipment for either short or long-term use. Therefore, approaches that could minimize implantation-associated side effects, such as inflammation and scar tissue formation, while maintaining high functionality of e-drugs, are highly needed. Herein, the importance of the spatial and temporal aspects of medical treatment is thoroughly reviewed along with how e-drugs use cutting-edge technological innovations to deal with unresolved medical challenges. Furthermore, diverse uses of e-drugs in clinical applications and the future perspectives of e-drugs are discussed.

Polymeric Implants for the Treatment of Intraocular Eye Diseases: Trends in Biodegradable and Non-Biodegradable Materials

Intraocular/Intravitreal implants constitute a relatively new method to treat eye diseases successfully due to the possibility of releasing drugs in a controlled and prolonged way. This particularity has made this kind of method preferred over other methods such as intravitreal injections or eye drops. However, there are some risks and complications associated with the use of eye implants, the body response being the most important. Therefore, material selection is a crucial factor to be considered for patient care since implant acceptance is closely related to the physical and chemical properties of the material from which the device is made. In this regard, there are two major categories of materials used in the development of eye implants: non-biodegradables and biodegradables. Although non-biodegradable implants are able to work as drug reservoirs, their surgical requirements make them uncomfortable and invasive for the patient and may put the eyeball at risk. Therefore, it would be expected that the human body responds better when treated with biodegradable implants due to their inherent nature and fewer surgical concerns. Thus, this review provides a summary and discussion of the most common non-biodegradable and biodegradable materials employed for the development of experimental and commercially available ocular delivery implants.

Development of poly(D,L-lactic-co-glycolic acid) films coated with biomembrane-mimicking polymers for anti-adhesion activity

A physical barrier is one of the most effective strategies to alleviate excessive postoperative adhesion (POA) between tissues at an injury site. To overcome the limitations of current polymeric film-type physical barriers, we suggest a film of poly(lactic-co-glycolic acid) (PLGA) that is non-covalently coated with poly(2-methacryloyloxyethyl phosphorylcholine (MPC)-co-n-butyl methacrylate (BMA)) (PMB). While maintaining the degradability and mechanical properties of PLGA, the PMB coating introduces strong anti-adhesive properties to the film by forming a zwitterionic MPC-based surface through the hydrophobic interactions between BMA moieties and PLGA. Compared to SurgiWrap®, the commercially available poly(lactic acid)-based anti-adhesive film against POA, the PMB-coated PLGA film is much more inhibitory against protein adsorption and fibroblast adhesion, processes that are crucial to the POA process. PMB coating also inhibits the expression of fibronectin containing extra domain A (FN-EDA), α-smooth muscle actin (α-SMA), and collagen type IV alpha 2 (COL4A2), which are marker genes and proteins involved in fibroblast activation and excessive fibrosis during POA. Such inhibitory activities are clearly observed in a 3-dimensional culture of fibroblasts within a collagen matrix, which mimics the in vivo environment of an injury site, as well as in a 2-dimensional culture. The kinetics and the stability of the PMB coating suggest potential future clinical use to coat PLGA films to create a film-type anti-adhesion barrier that overcomes the limitations of current products.

Ocular Drug Delivery to the Retina: Current Innovations and Future Perspectives

Treatment options for retinal diseases, such as neovascular age-related macular degeneration, diabetic retinopathy, and retinal vascular disorders, have markedly expanded following the development of anti-vascular endothelial growth factor intravitreal injection methods. However, because intravitreal treatment requires monthly or bimonthly repeat injections to achieve optimal efficacy, recent investigations have focused on extended drug delivery systems to lengthen the treatment intervals in the long term. Dose escalation and increasing molecular weight of drugs, intravitreal implants and nanoparticles, hydrogels, combined systems, and port delivery systems are presently under preclinical and clinical investigations. In addition, less invasive techniques rather than intravitreal administration routes, such as topical, subconjunctival, suprachoroidal, subretinal, and trans-scleral, have been evaluated to reduce the treatment burden. Despite the latest advancements in the field of ophthalmic pharmacology, enhancing drug efficacy with high ocular bioavailability while avoiding systemic and local adverse effects is quite challenging. Consequently, despite the performance of numerous in vitro studies, only a few techniques have translated to clinical trials. This review discusses the recent developments in ocular drug delivery to the retina, the pharmacokinetics of intravitreal drugs, efforts to extend drug efficacy in the intraocular space, minimally invasive techniques for drug delivery to the retina, and future perspectives in this field.

Histological Study of The Healing of Traumatic Tympanic Membrane Perforation After Vivosorb and Epifilm Application

BACKGROUND

Untreated traumatic tympanic membrane perforations (TMPs) may lead to permanent perforations and hearing loss. There are many materials that have been previously used for repairing the TMPs.

AIMS AND OBJECTIVES

The purpose of this study is to evaluate the clinical and histological effects of Vivosorb (Vv) and Epifilm on healing of TMPs in a rat model.

MATERIAL AND METHODS

The posterior-inferior quadrant of the tympanic membranes (TMs) in right ears of 14 rats was perforated using a 20-g needle and then the animals were randomly divided into 2 equal groups (n = 7). The perforated right TMs were treated with either Vv (Vv group) or Epifilm (Ep group). The left TMs of 7 rats were perforated in same way and allowed to close spontaneously without any topical material applications (spontaneous closure group as sham control, SC). The left tympanic membranes of the other 7 rats were not perforated and used as normal controls (NC group). On postoperative 15th day, tympanic bullas were extracted from killed rats and examined morphometrically and histopathologically.

RESULTS

Perforation closure rate was 85.7% (6/7) in both Vv and SC groups. Perforations of Ep group closed in 7/7 (100%) ears. The thicknesses of the perforated membranes were increased in SC and especially Vv groups. Also, connective tissue fibrosis, blood clots, and epithelial degenerations were detected in SC and Vv groups. The mean fibroblastic reaction scores of Vv, Ep, and SC groups were 2.14(+), 0.57(+), and 1.71(+) respectively, on comparison with NC group. The mean neovascularization score was 1.42(+) in Vv group, 0.14(+) in Ep group, and 0.57(+) in SC group.

CONCLUSION AND SIGNIFICANCE

Vivosorb and especially Epifilm can improve the healing process in traumatic TMPs and additionally, Epifilm might be more preferred for the treatment of TMPs because of causing lesser fibrosis.

Bioresorbable Electronic Implants: History, Materials, Fabrication, Devices, and Clinical Applications

Medical implants, either passive implants for structural support or implantable devices with active electronics, have been widely used for the diagnosis and treatment of various diseases and clinical issues. These implants offer various functions, including mechanical support of biological structures in orthopedic and dental applications, continuous electrophysiological monitoring and feedback of electrical stimulation in neuronal and cardiac applications, and controlled drug delivery while maintaining arterial structure in drug-eluting stents. Although these implants exhibit long-term biocompatibility, surgery for their retrieval is often required, which imposes physical, biological, and economical burdens on the patients. Therefore, as an alternative to such secondary surgeries, bioresorbable implants that disappear after a certain period of time inside the body, including bioresorbable active electronics, have been highlighted recently. This review first discusses the historical background of medical implants and briefly define related terminology. Representative examples of non-degradable medical implants for passive structural support and/or for diagnosis and therapy with active electronics are also provided. Then, recent progress in bioresorbable active implants composed of biosignal sensors, actuators for therapeutics, wireless power supply components, and their integrated systems are reviewed. Finally, clinical applications of these bioresorbable electronic implants are exemplified with brief conclusion and future outlook.

Comparison of two prototypes of a magnetically adjustable glaucoma implant in rabbits

Glaucoma drainage devices are used in surgical glaucoma therapy. Success of controlling the intraocular pressure is limited due to fibrous implant encapsulation and fibrin coating on the implant which lead to drainage obstructions. An innovative implant with a magnetically adjustable valve was developed. The valve opening of the implant should eliminate inflammatory products from the outflow area and affect fibrous tissue formation to achieve a sufficient long-term aqueous humour outflow. Lifting of this valve should disturb cell adhesion by exerting mechanical forces. Before testing this hypothesis, the flow characteristics of glaucoma drainage devices, especially the outflow resistance by regular IOP, should be considered in a pilot study, as they are important in preventing too low postoperative intraocular pressure known as ocular hypotony. Therefore, two prototypes of the innovative implant differing in their valve area design were examined regarding their flow characteristics in a limited animal experiment lasting two weeks. Ten healthy New Zealand White rabbits were divided into two groups (A & B) with different implanted prototypes. Daily, tonometry and direct ophthalmoscopy were performed to assess the intraocular pressure and the inflammatory reaction of the eye. After two weeks, the rabbits were euthanised to evaluate the initially histological inflammatory reaction to the implant. In group A, one case of hypotony emerged. When considering the entire observation period, a highly statistically significant difference between the intraocular pressure in the operated eye and that in the control eye was detected in group A (p < 0.0001) in contrast to group B (p = 0.0063). The postoperative inflammatory signs decreased within two weeks. Histologically, a typical but low level foreign body reaction with macrophages and lymphocytes as well as mild to moderate fibrosis was seen after the short experimental period. Based on our tonometric results, prototype B seems to be the system of choice for further research assessing its long-term function and biocompatibility.

Synthetic biodegradable alternatives to the use of the amniotic membrane for corneal regeneration: assessment of local and systemic toxicity in rabbits

AIM

The aim of this study was to assess the local and systemic response to poly-lactic co-glycolic acid (PLGA) 50:50 membranes, developed as synthetic biodegradable alternatives to the use of human donor amniotic membrane in the treatment of limbal stem cell deficiency.

METHODS

PLGA membranes of 2  cm diameter and 50  µm thickness were placed on one eye of rabbits and secured in place using fibrin glue and a bandage contact lens, suturing the eye close with a single stitch. Control animals were treated identically, with the absence of the membranes. Plain and microfabricated electrospun membranes (containing micropockets which roughly emulate the native limbal niche) were examined over 29 days. All animals were subjected to a detailed gross and histopathological observation as well as a detailed examination of the eye.

RESULTS

Application of the membranes both with and without microfabricated pockets did not adversely affect animal welfare. There was complete degradation of the membranes by day 29. The membranes did not induce any significant local or systemic toxicity. Conjunctival congestion and corneal vascularisation were noted in a few control and PLGA-treated animals. Intraocular pressure was normal and the retinal status was unaltered. The ocular surface was clear and intact in all animals by the end of 29  days.

CONCLUSION

Membranes of 50:50 PLGA can be safely applied to rabbit corneas without inducing any local or systemic toxicity and these break down completely within 29 days.

Targeted Ocular Drug Delivery with Pharmacokinetic/Pharmacodynamic Considerations

The development of ophthalmic drug delivery systems is a long and comprehensive process including research, nonclinical, and clinical development stages. It is critical to understand the similarity and differences between animal models and patients. There are many anatomically and physiologically important parameters for targeted drug delivery into eyes. This paper reviews the constraints to various routes of ocular drug delivery and discusses the respective pharmacokinetic considerations, to lay the foundation for formulation approaches pharmaceutical scientists can use to maximize successful drug delivery for each route. The overall goal is to give both researchers and drug developers a better understanding of ocular drug delivery and offer tools to successfully develop new medicines that will fulfil unmet medical needs and improve patients' quality of life.

A bilayer swellable drug-eluting ureteric stent: Localized drug delivery to treat urothelial diseases

A bilayer swellable drug-eluting ureteric stent (BSDEUS) is engineered and implemented, as a sustained drug delivery platform technology that enhances localized drug delivery to the highly impermeable urothelium, for the treatment of urothelial diseases such as strictures and carcinomas. On deployment, the device swells to co-apt with the ureteric wall and ensure drug availability to these tissues. BSDEUS consists of a stent spray-coated with a polymeric drug containing polylactic acid-co-caprolactone (PLC) layer which is overlaid by a swellable polyethylene glycol diacrylate (PEGDA) based hydrogel. In-vitro quantification of released drug demonstrated a tunable time-profile, indicating sustained delivery over 1-month. The PEGDA hydrogel overlayer enhanced drug release and transport into explanted porcine ureteric tissues ex-vivo, under a simulated dynamic fluid flow. A preliminary pilot in-vivo feasibility study, in a porcine model, demonstrated that the swollen hydrogel co-apts with the urothelium and thus enables localized drug delivery to the target tissue section. Kidney functions remained unaffected and device did not result in either hydronephrosis or systemic toxicity. This successful engineering of a bilayer coated stent prototype, demonstrates its feasibility, thus offering a unique solution for drug-based urological therapy.

Evaluation of a Sustained-Release Prednisolone Acetate Biodegradable Subconjunctival Implant in a Non-Human Primate Model

PURPOSE

We evaluate the toxicity and plasma toxicokinetic (TK) profile of a biodegradable subconjunctival microrod for sustained prednisolone acetate (PA) release over 12 weeks in a non-human primate model.

METHODS

The biodegradable copolymer poly(l-lactide-co-ε-caprolactone) (PLC) and 40-wt% PA microrods were used and fashioned into 8 and 16 mm lengths. Twelve monkeys were divided into two treatment groups of PA-loaded and blank microrods, with six monkeys each receiving either 8- or 16-mm microrods subconjunctively implanted into both eyes. TK and hematology parameters were analyzed. Ophthalmic clinical evaluation, including slit-lamp and ophthalmoscopy examinations, was performed.

RESULTS

Over the study period of 12 weeks, the mean area under the plasma concentration-time curve was 45.7% higher, and the maximum plasma concentration was 17.2% lower for the animals treated with 40-wt% PA 16-mm microrods compared to 8-mm microrods (251.44 versus 172.54 hours × nanograms per milliliter and 8.53 versus 10.30 ng/mL, respectively). The PA release was significantly below the levels of assumed toxicity. There was no significant difference in the time to reach maximum concentration between the 8- and 16-mm microrod groups (7.33 and 8 hours; P = 0.421). Findings from clinical evaluation, hematology, and histopathology showed no ocular side effects and no significant adverse systemic effects.

CONCLUSION

The PA biodegradable microrods demonstrated safe toxicokinetics even with the larger size implant containing a higher amount of drug. The PA implant may be considered as a safe alternative to the application of topical PA eyedrops.

TRANSLATIONAL RELEVANCE

The results provide the evidence of the safety of implanting a steroid delivery system subconjunctively, offering an alternative to topical PA eyedrops.

Drug delivery to the eye: what benefits do nanocarriers offer?

Ocular drug delivery has seen several advances in the past few decades, with respect to new drugs, improved formulations, targeted delivery, as well as exploration of new routes of drug administration. New materials have been explored for encasing existing drugs, which can enhance treatment by increasing bioavailability, decreasing toxicity, providing better tissue adherence, targeted delivery as well as increased duration of action. The challenges and requirements are different for the anterior and posterior ocular segments. This review summarizes the recent advances in sustained ocular therapy, both to the anterior and posterior segments, which have been made possible, thanks to nanotechnology. We also discuss the distribution and fate of these nanocarriers themselves, postadministration, as well as clearance from ocular tissues.

Long-Term Subconjunctival Delivery of Brimonidine Tartrate for Glaucoma Treatment Using a Microspheres/Carrier System

Core-shell polymer microspheres with poly(d,l-lactic-co-glycolic acid) core and poly(l-lactic acid) (PLLA) shell are developed for the long-term subconjunctival release of brimonidine tartrate (BT) in order to reduce intraocular pressure (IOP) in the treatment of glaucoma. The PLLA-rich shell acts as a diffusion barrier, enabling linear release of BT over an extended period of 40 d. The microspheres are encased in a porous non-degradable methacrylate-based carrier for ease of subconjunctival implantation in a glaucoma-induced rabbit model. In vivo release of BT from the microspheres/carrier system has enabled a significant, immediate IOP reduction of 20 mmHg, which is sustained for 55 d. Long-term IOP reduction may be maintained by periodic replacement of the microspheres/carrier system.

Sustained Antibiotic-Eluting Intra-Ocular Lenses: A New Approach

Currently, infections following cataract surgery are not as effectively managed with antibiotic eye drops, which suffer from poor bioavailability of drug and low patient compliance. The ideal solution, which can help to overcome the issue of drug wastage and poor bioavailabilty, as well as the need for frequent applications (patient inconvenience), is a drug-eluting intraocular lens (IOL). We describe a novel approach to such a drug-eluting lens by using a peripheral IOL attachment as a drug depot to deliver antibiotics, Levofloxacin (LFX) or Moxifloxacin (MFX). In this work, drug was entrapped within a fully-degradable polymer, poly(L-lactide-co-ɛ-caprolactone) (PLC). The effects of drug loading and solvent type on drug release and film morphology were investigated using cast films. The study clearly demonstrated that a slower-evaporating solvent tetrahydrofuran (THF) resulted in a better surface morphology, as well as lower initial burst compared to dichloromethane (DCM), and hence, was better suited to developing a drug-eluting attachment with sustained release of drug. When attachments were fabricated with drugs at high loading percentages (20% and 25% in polymer), significant burst was observed compared to films: this is attributed to the higher surface-to-volume ratio of the attachments. When the levofloxacin (LFX) loading percentage was decreased to 3% and 5%, the attachments presented lower burst and sustained release with therapeutic efficacy. This work has demonstrated the potential of using an IOL attachment as a more efficacious anti-infective option compared to daily eye drops.

A biodegradable ocular implant for long-term suppression of intraocular pressure

Timolol maleate (TM) has been used for many years for the reduction of intraocular pressure (IOP) in glaucoma patients. However, the topical mode of administration (eyedrops) is far from optimal because of the issues of low bioavailability, high drug wastage, and lack of patient compliance. Suboptimal control of the IOP leads to disease progression and eventually to blindness. Ideally, TM is delivered to the patient so that its action is both localized and sustained for 3 months or more. In this work, we developed a subconjunctival TM microfilm for sustained, long-term delivery of TM to the eyes, using the biodegradable elastomer poly(lactide-co-caprolactone) (PLC). The copolymer is biocompatible and has flexibility and mechanical characteristics suitable for a patient-acceptable implant. Controlling the release of TM for 3 months is challenging, and this work describes how, by using a combination of multilayering and blending with poly(ethylene glycol) (PEG) copolymers, we were able to develop a TM-incorporated biodegradable film that can deliver TM at a therapeutic dose for 90 days in vitro. The data was further confirmed in a diseased primate model, with sustained IOP-lowering effects for 5 months with a single implant, with acceptable biocompatibility and partial degradation.

Advanced drug delivery and targeting technologies for the ocular diseases

INTRODUCTION

Ocular targeted therapy has enormously been advanced by implementation of new methods of drug delivery and targeting using implantable drug delivery systems (DDSs) or devices (DDDs), stimuli-responsive advanced biomaterials, multimodal nanomedicines, cell therapy modalities and medical bioMEMs. These technologies tackle several ocular diseases such as inflammation-based diseases (e.g., scleritis, keratitis, uveitis, iritis, conjunctivitis, chorioretinitis, choroiditis, retinitis, retinochoroiditis), ocular hypertension and neuropathy, age-related macular degeneration and mucopolysaccharidosis (MPS) due to accumulation of glycosaminoglycans (GAGs). Such therapies appear to provide ultimate treatments, even though much more effective, yet biocompatible, noninvasive therapies are needed to control some disabling ocular diseases/disorders.

METHODS

In the current study, we have reviewed and discussed recent advancements on ocular targeted therapies.

RESULTS

On the ground that the pharmacokinetic and pharmacodynamic analyses of ophthalmic drugs need special techniques, most of ocular DDSs/devices developments have been designed to localized therapy within the eye. Application of advanced DDSs such as Subconjunctival insert/implants (e.g., latanoprost implant, Gamunex-C), episcleral implant (e.g., LX201), cationic emulsions (e.g., Cationorm™, Vekacia™, Cyclokat™), intac/punctal plug DDSs (latanoprost punctal plug delivery system, L-PPDS), and intravitreal implants (I-vitaion™, NT-501, NT- 503, MicroPump, Thethadur, IB-20089 Verisome™, Cortiject, DE-102, Retisert™, Iluvein™ and Ozurdex™) have significantly improved the treatment of ocular diseases. However, most of these DDSs/devices are applied invasively and even need surgical procedures. Of these, use of de novo technologies such as advanced stimuli-responsive nanomaterials, multimodal nanosystems (NSs)/nanoconjugates (NCs), biomacromolecualr scaffolds, and bioengineered cell therapies need to be further advanced to get better compliance and higher clinical impacts.

CONCLUSION

Despite mankind successful battle on ocular diseases, our challenge will continue to battle the ocular disease that happen with aging. Yet, we need to understand the molecular aspects of eye diseases in a holistic way and develop ultimate treatment protocols preferably as non-invasive systems.

Effect of Two Novel Sustained-Release Drug Delivery Systems on Bleb Fibrosis: An In Vivo Glaucoma Drainage Device Study in a Rabbit Model

PURPOSE

To evaluate two drug delivery systems, a nonbiodegradable poly(2-hydroxyethyl methacrylate) (P[HEMA]) system with mitomycin C (MMC) and a biodegradable poly(lactic-co-glycolic acid) (PLGA) system with 5-fluorouracil (5-FU) with and without MMC for their ability to reduce fibrosis when attached to an Ahmed glaucoma valve (AGV) and implanted in a rabbit model.

METHODS

New Zealand albino rabbits (48) were divided into six equal groups, and AGVs, modified as described below, were implanted in the right eye of each rabbit. The groups included (1) PLGA alone; (2) P(HEMA) plus MMC (6.5 μg); (3) PLGA plus 5-FU (0.45 mg); (4) PLGA plus 5-FU (1.35 mg); (5) PLGA plus 5-FU and MMC (0.45 mg and 0.65 μg, respectively); (6) PLGA plus 5-FU and MMC (1.35 mg and 0.65 μg, respectively). The rabbits were followed for 3 months prior to euthanasia.

RESULTS

The bleb wall thickness was significantly less in groups 2, 5, and 6 compared to the rest. At 3 months, the PLGA polymer had completely disappeared, while the P(HEMA) polymer remained intact. There were no statistical differences in the degree of clinically graded conjunctival injection, histologic inflammation, or histologic fibrosis among the six groups.

CONCLUSIONS

We successfully created a sustained-release drug delivery system that decreased the postoperative fibrosis using both a nonbiodegradable P(HEMA) polymer and a biodegradable (PLGA) polymer. Both systems appear to work equally well with no side effects.

TRANSLATIONAL RELEVANCE

These results are supportive of the antifibrotic effect of the slow-release drug delivery system following glaucoma drainage device implantation, thus paving the way for human pilot studies.

Safety evaluation of poly(lactic-co-glycolic acid)/poly(lactic-acid) microspheres through intravitreal injection in rabbits

Poly(lactic-co-glycolic acid) (PLGA) and/or poly(lactic-acid) (PLA) microspheres are important drug delivery systems. This study investigated eye biocompatibility and safety of PLGA/PLA microspheres through intravitreal injection in rabbits. Normal New Zealand rabbits were randomly selected and received intravitreal administration of different doses (low, medium, or high) of PLGA/PLA microspheres and erythropoietin-loaded PLGA/PLA microspheres. The animals were clinically examined and sacrificed at 1, 2, 4, 8, and 12 weeks postadministration, and retinal tissues were prepared for analysis. Retinal reactions to the microspheres were evaluated by terminal deoxynucleotidyl transferase-mediated dUTP nick end staining and glial fibrillary acidic protein immunohistochemistry. Retinal structure changes were assessed by hematoxylin and eosin staining and transmission electron microscopy. Finally, retinal function influences were explored by the electroretinography test. Terminal deoxynucleotidyl transferase-mediated dUTP nick end staining revealed no apoptotic cells in the injected retinas; immunohistochemistry did not detect any increased glial fibrillary acidic protein expression. Hematoxylin and eosin staining and transmission electron microscopy revealed no micro- or ultrastructure changes in the retinas at different time points postintravitreal injection. The electroretinography test showed no significant influence of scotopic or photopic amplitudes. The results demonstrated that PLGA/PLA microspheres did not cause retinal histological changes or functional damage and were biocompatible and safe enough for intravitreal injection in rabbits for controlled drug delivery.

Evaluation of a prednisolone acetate-loaded subconjunctival implant for the treatment of recurrent uveitis in a rabbit model

AIM

To assess the efficacy of a biodegradable, prednisolone acetate implant in a rabbit uveitis model.

METHODS

Randomized, controlled study of biodegradable microfilms preloaded with prednisolone acetate (PA) in a rabbit uveitis model. Experimental uveitis was induced by unilateral intravitreal injection of Mycobacterium tuberculosis H37Ra antigen (50 ug; 1 ug/uL) in preimmunized rabbits. PA-loaded poly[d,l-lactide-co-ε-caprolactone] (PLC) microfilms (n = 10) and blank microfilms (n = 6) were implanted subconjunctivally. An estimate of PA release in vivo was calculated from measured residual PA amounts in microfilms after the rabbits were sacrificed. The eyes were clinically monitored for ocular inflammation for 28 days. Histopathological examination of the enucleated eyes was performed at the end of the study period.

RESULTS

In vitro studies revealed that sandwich PA-loaded microfilm formulations exhibited higher release kinetic compared to homogenous PA-loaded microfilms. The 60-40-60% microfilm released an average of 0.034 mg/day of PA over the period of 60 days in vitro; and we found that approximately 0.12 mg/day PA was released in vivo. Animals implanted with the PA-loaded microfilms exhibited significantly lowered median inflammatory scores when compared against the control group in this model for recurrent uveitis (P<0.001). The implants were clinically well tolerated by all the animals. Histology results showed no significant scarring or inflammation around the PA-loaded microfilms.

CONCLUSION

Our pilot study demonstrated that a subconjunctival PA-loaded implant is effective in suppressing inflammation in the rabbit model of uveitis, by providing therapeutic levels of PA that attenuated the inflammatory response even after a rechallenge. Longer term studies are now needed to establish the therapeutic potential of such a delivery system for treatment of ocular inflammation.

A new design and application of bioelastomers for better control of intraocular pressure in a glaucoma drainage device

Glaucoma drainage device (GDD) implantation is an effective method of lowering the intraocular pressure (IOP). Commonly used GDDs can be classified into nonvalved and valved. Although a stable IOP is critical, currently available devices often cause extreme IOP fluctuations: nonvalved GDDs suffer from a risk of hypotony (IOP<5 mmHg), whereas valved GDDs have a higher risk ocular hypertensive (IOP>22 mmHg). It is hypothesized that a GDD with a valve designed to open around the time of onset of the hypertensive phase, would minimize IOP fluctuation. Accordingly, a valve fabricated from a biodegradable polymer poly(L-lactide-co-ϵ-caprolactone) (PLC 70/30) is evaluated in vitro and in vivo. The pressure response is compared with its non-degradable counterpart in in vitro studies of IOP. It is also established that in vitro, the biodegradability of the valve is programmed to occur over 12 weeks. In vivo, a steady and low IOP is achieved with the biodegradable valve and the hypertensive phase is significantly attenuated compared with the commercial device. Fibrotic encapsulation of the device is also minimized with the biodegradable valve in vivo.

Engineering hybrid polymer-protein super-aligned nanofibers via rotary jet spinning

Cellular microenvironments are important in coaxing cells to behave collectively as functional, structured tissues. Important cues in this microenvironment are the chemical, mechanical and spatial arrangement of the supporting matrix in the extracellular space. In engineered tissues, synthetic scaffolding provides many of these microenvironmental cues. Key requirements are that synthetic scaffolds should recapitulate the native three-dimensional (3D) hierarchical fibrillar structure, possess biomimetic surface properties and demonstrate mechanical integrity, and in some tissues, anisotropy. Electrospinning is a popular technique used to fabricate anisotropic nanofiber scaffolds. However, it suffers from relatively low production rates and poor control of fiber alignment without substantial modifications to the fiber collector mechanism. Additionally, many biomaterials are not amenable for fabrication via high-voltage electrospinning methods. Hence, we reasoned that we could utilize rotary jet spinning (RJS) to fabricate highly aligned hybrid protein-polymer with tunable chemical and physical properties. In this study, we engineered highly aligned nanofiber constructs with robust fiber alignment from blends of the proteins collagen and gelatin, and the polymer poly-ε-caprolactone via RJS and electrospinning. RJS-spun fibers retain greater protein content on the surface and are also fabricated at a higher production rate compared to those fabricated via electrospinning. We measured increased fiber diameter and viscosity, and decreasing fiber alignment as protein content increased in RJS hybrid fibers. RJS nanofiber constructs also demonstrate highly anisotropic mechanical properties mimicking several biological tissue types. We demonstrate the bio-functionality of RJS scaffold fibers by testing their ability to support cell growth and maturation with a variety of cell types. Our highly anisotropic RJS fibers are therefore able to support cellular alignment, maturation and self-organization. The hybrid nanofiber constructs fabricated by RJS therefore have the potential to be used as scaffold material for a wide variety of biological tissues and organs, as an alternative to electrospinning.

Sustained release of triamcinolone acetonide from an episcleral plaque of multilayered poly-ε-caprolactone matrix

A subtenon injection of triamcinolone acetonide (TA) is a widely used treatment modality for various chorio-retinal diseases. Although it is less invasive than intravitreal injection, it can produce dose-associated ocular complications and has the disadvantages associated with systemic TA exposure. In this study we have developed and evaluated an episcleral film consisting of TA and poly-ε-caprolactone (PCL). The films were prepared by spraying a mixture of PCL in dichloromethane and TA in acetone. The films were produced as 6mm wide and 12 mm long episcleral plaques. X-ray diffraction demonstrated an even distribution of TA crystals in PCL, although the TA was less crystalized than a native TA control. Fourier transform infrared spectroscopy revealed effective integration of TA within the PCL matrix. An in vitro study of the release of TA from the episcleral plaques showed that TA release rate was only 40-50% that of the equivalent native TA control. An in vivo study demonstrated that the plaques were well tolerated in rabbit eyes with significantly less systemic TA exposure. The episcleral plaques provided therapeutic vitreous TA levels for 3 months, while TA levels in the vitreous were detectable for only 1 month following an equivalent dose by subtenon TA injection. The PCL-TA 30-60 episcleral plaque may be further developed as a better alternative treatment for many chronic vitreo-retinal diseases, providing longer and controlled release and fewer drug-associated complications than those associated with a conventional subtenon injection of TA.

Critical assessment of implantable drug delivery devices in glaucoma management

Glaucoma is a group of heterogeneous disorders involving progressive optic neuropathy that can culminate into visual impairment and irreversible blindness. Effective therapeutic interventions must address underlying vulnerability of retinal ganglion cells (RGCs) to degeneration in conjunction with correcting other associated risk factors (such as elevated intraocular pressure). However, realization of therapeutic outcomes is heavily dependent on suitable delivery system that can overcome myriads of anatomical and physiological barriers to intraocular drug delivery. Development of clinically viable sustained release systems in glaucoma is a widely recognized unmet need. In this regard, implantable delivery systems may relieve the burden of chronic drug administration while potentially ensuring high intraocular drug bioavailability. Presently there are no FDA-approved implantable drug delivery devices for glaucoma even though there are several ongoing clinical studies. The paper critically assessed the prospects of polymeric implantable delivery systems in glaucoma while identifying factors that can dictate (a) patient tolerability and acceptance, (b) drug stability and drug release profiles, (c) therapeutic efficacy, and (d) toxicity and biocompatibility. The information gathered could be useful in future research and development efforts on implantable delivery systems in glaucoma.

A biodegradable, sustained-released, prednisolone acetate microfilm drug delivery system effectively prolongs corneal allograft survival in the rat keratoplasty model

Frequent and long-term use of topical corticosteroids after corneal transplantation is necessary to prevent graft rejection. However, it relies heavily on patient compliance, and sustained therapeutic drug levels are often not achieved with administration of topical eye drops. A biodegradable drug delivery system with a controlled and sustained drug release may circumvent these limitations. In this study, we investigated the efficacy of a prednisolone acetate (PA)-loaded poly (d,l-lactide-co-ε-caprolactone) (PLC) microfilm drug delivery system on promoting the survival of allogeneic grafts after penetrating keratoplasty (PK) using a rat model. The drug release profiles of the microfilms were characterized (group 1). Subsequently, forty-eight PK were performed in four experimental groups: syngeneic control grafts (group 2), allogeneic control grafts (group 3), allogeneic grafts with subconjunctivally-implanted PA microfilm (group 4), and allogeneic grafts with PA eye drops (group 5; n = 12 in each). PA-loaded microfilm achieved a sustained and steady release at a rate of 0.006-0.009 mg/day, with a consistent aqueous drug concentration of 207-209 ng/ml. The mean survival days was >28 days in group 2, 9.9±0.8 days in group 3, 26.8±2.7 days in group 4, and 26.4±3.4 days in group 5 (P = 0.023 and P = 0.027 compared with group 3). Statistically significant decrease in CD4+, CD163+, CD 25+, and CD54+ cell infiltration was observed in group 4 and group 5 compared with group 3 (P<0.001). There was no significant difference in the mean survival and immunohistochemical analysis between group 4 and group 5. These results showed that sustained PA-loaded microfilm effectively prolongs corneal allograft survival. It is as effective as conventional PA eye drops, providing a promising clinically applicable alternative for patients undergoing corneal transplantation.

Intraocular lens as a drug delivery reservoir

PURPOSE OF REVIEW

To describe the development and use of intraocular lenses (IOLs) as drug delivery systems and to review the current literature on their application and efficacy.

RECENT FINDINGS

Many drugs have been loaded onto IOLs by coating or by attachment in a separate reservoir. With incorporation of polymeric materials either as a coating or by attachment as a separate reservoir, it is possible to achieve a sustained and controlled release of drugs. Experimental evidence in animal models has shown that IOL drug delivery systems are effective in the prevention and treatment of inflammation, infection and posterior capsule opacification after cataract surgery.

SUMMARY

The use of IOLs as drug delivery reservoirs appears to show great promise. Although excellent results with therapeutic potential have been reported in experimental animal studies, further studies are needed to reach clinical use.

Eye

The Eye chapter of the 3rd edition of Haschek and Rousseaux’s Handbook of Toxicologic Pathology brings a comprehensive description of pathological processes affecting the ocular tissues in the most commonly used laboratory animals and their correlations with human diseases of interest in toxicology. Also presented are detailed descriptions of the structure and function of the different ocular tissues, the most advanced techniques applied in the toxicological evaluation of the eye, useful animal models of human disease, and known mechanisms of ocular toxicity. The introductory sections of the chapter also feature such essential topics as ocular embryology, an overview of clinical ophthalmic evaluation, and eye-specific techniques of tissue processing.

Neo-vascularization of the stroke cavity by implantation of human neural stem cells on VEGF-releasing PLGA microparticles

Replacing the tissue lost after a stroke potentially provides a new neural substrate to promote recovery. However, significant neurobiological and biotechnological challenges need to be overcome to make this possibility into a reality. Human neural stem cells (hNSCs) can differentiate into mature brain cells, but require a structural support that retains them within the cavity and affords the formation of a de novo tissue. Nevertheless, in our previous work, even after a week, this primitive tissue is void of a vasculature that could sustain its long-term viability. Therefore, tissue engineering strategies are required to develop a vasculature. Vascular endothelial growth factor (VEGF) is known to promote the proliferation and migration of endothelial cells during angio- and arteriogenesis. VEGF by itself here did not affect viability or differentiation of hNSCs, whereas growing cells on poly(D,L-lactic acid-co-glycolic acid) (PLGA) microparticles, with or without VEGF, doubled astrocytic and neuronal differentiation. Secretion of a burst and a sustained delivery of VEGF from the microparticles in vivo attracted endothelial cells from the host into this primitive tissue and in parts established a neovasculature, whereas in other parts endothelial cells were merely interspersed with hNSCs. There was also evidence of a hypervascularization indicating that further work will be required to establish an adequate level of vascularization. It is therefore possible to develop a putative neovasculature within de novo tissue that is forming inside a tissue cavity caused by a stroke.

Ocular drug delivery for glaucoma management

Current glaucoma management modalities are hindered by low patient compliance and adherence. This can be due to highly complex treatment strategies or poor patient understanding. Treatments focus on the management or reduction of intraocular pressure. This is most commonly done through the use of daily topical eye drops. Unfortunately, despite effective therapies, glaucoma continues to progress, possibly due to patients not adhering to their treatments. In order to mitigate these patient compliance issues, many sustained release treatments are being researched and are entering the clinic. Conjunctival, subconjunctival, and intravitreal inserts, punctal plugs, and drug depots are currently in clinical development. Each delivery system has hurdles, yet shows promise and could potentially mitigate the current problems associated with poor patient compliance.

Evaluation of sustained release of PLC-loaded prednisolone acetate microfilm on postoperative inflammation in an experimental model of glaucoma filtration surgery

PURPOSE

To evaluate the effect of a biodegradable microfilm with sustained release of prednisolone acetate (PA) on postoperative wound healing after experimental glaucoma filtration surgery (GFS).

METHODS

Biodegradable microfilms composed of poly (D-, L-lactide-co-caprolactone) (PLC) were fabricated and then pre-loaded PA-20% total weight. Fourteen New Zealand White rabbits were randomly divided into 3 treatment groups: GFS alone (n=4), GFS with PLC microfilms (n=4) and GFS with PA-loaded microfilm (n=6). Microfilms were inserted subconjunctivally, adjacent to the filtering surgical site. We monitored all eyes with slit-lamp examination, bleb photography and anterior segment optical coherence tomography (AS-OCT). Histology with immunohistochemistry was performed to determine the presence of any inflammation.

RESULTS

Prednisolone acetate 20%-loaded microfilms exhibited steady, sustained release in vitro. Eyes implanted with PA-loaded microfilms showed a significantly better bleb survival (100% vs. 37.5%, p<0.001) and reduced bleb vascularity (58%; 95% CI 54-62% vs. 30%; 95% CI 23-37%, p=0.001) compared to the control at 30 days postoperatively. Histology and immunohistochemistry demonstrated less T-cell infiltration in the eye implanted with PA-loaded microfilms.

CONCLUSION

Subconjunctival insertion of a PA-loaded biodegradeable microfilm exhibit sustained release of PA to reduce postoperative inflammation and prolong bleb survival in rabbit GFS.