Posterior segment eye diseases (PSEDs) including age macular degeneration (AMD) and diabetic retinopathy (DR) are amongst the major causes of irreversible blindness worldwide. Due to the numerous barriers encountered, highly invasive intravitreal (IVT) injections represent the primary route to deliver drugs to the posterior eye tissues. Thus, the potential of a more patient friendly topical route has been widely investigated. Mucoadhesive formulations can decrease precorneal clearance while prolonging precorneal residence. Thus, they are expected to enhance the chances of adherence to corneal and conjunctival surfaces and as such, enable increased delivery to the posterior eye segment. Among the mucoadhesive polymers available, chitosan is the most widely explored due to its outstanding mucoadhesive characteristics. In this review, the major PSEDs, their treatments, barriers to topical delivery, and routes of topical drug absorption to the posterior eye are presented. To enable the successful design of mucoadhesive ophthalmic drug delivery systems (DDSs), an overview of mucoadhesion, its theory, characterization, and considerations for ocular mucoadhesion is given. Furthermore, chitosan-based DDs that have been explored to promote topical drug delivery to the posterior eye segment are reviewed. Finally, challenges of successful preclinical to clinical translation of these DDSs for posterior eye drug delivery are discussed.

The preparation of acid‐responsive degradable oligomers with active agents in their main chains is described. Dichlorophene (DCP), an effective anticestodal agent, and the corrosion inhibitor 4‐(2‐pyridylazo)resorcinol (PAR) are reacted to form polymerizable bisacrylate derivatives. The derivatives are then copolymerized with aliphatic and aromatic dithiols by thiol‐Michael addition to obtain a polymer backbone with cleavable thiopropionate groups. Low molecular weight (M n < 10 000 g mol−1) linear oligomers are obtained, which can be used for the preparation of poly(ester‐urethane)s. Polymer nanoparticles from both oligo(thioether‐ester) and poly(ester‐urethane)s are fabricated by the miniemulsion‐solvent evaporation method. The polymers in solution and dispersion can be gradually degraded in acidic media. The degraded products of the degradation of PAR containing polymers can be detected in the presence of copper ions.

The goal of this research was to prepare drug‐encapsulated polymeric micelles for delivery to the posterior segment of the eye. Solutions of surface active PF127 at the critical micellar concentration (CMC) were prepared in deionized water (DI water) and phosphate buffer (PBS). The CMC of PF127 solution in DI water and PBS solution were found to 0.21 ± 0.04 and 0.16 ± 0.05% (w/v), respectively. In addition, the micellization of the PF127 was observed around 25 and 21°C in DI water and PBS solution, respectively by DSC analysis. The hydrodynamic diameter of the PF127 micelles were found to range between 3 and 4 nm with polydispersity indices ranging between 0.35 ± 0.22 and 0.96 ± 1.52. Curcumin (CUR), a natural dietary compound having an anti‐VEGF properties, was successfully loaded into PF127 copolymers by the thin‐film hydration method. The CUR‐loaded PF127 micelles were confirmed by several characterization techniques including DLS and HPLC. A detailed study of the effect of experimental conditions on both the particle size and drug encapsulation efficiency (%EE) of the CUR micelles was also carried out. CUR‐loaded PF127 micelles with small particle sizes (around 15 nm, PDI = 0.19 ± 0.13) and %EE around 10% were observed at high centrifugation speed. Also, increasing the copolymer‐to‐drug ratio resulted in higher %EE (>90%). Additionally, the CUR‐loaded PF127 micelles were easy to reconstitute in water by manual shaking after lyophilization. These results suggest that PF127 micelles are a promising carrier for delivery of CUR to the eye. Future work will study in more detail about the physicochemical properties and the ability of these micelles to transport CUR across ocular barriers in ex vivo and in vivo trials.