Amongst different routes of drug delivery systems, ophthalmic drug delivery still requires a careful investigation and strict parameter measurements because the eyes are one of the most sensitive parts of the body and require special attention. The conventional systems for eyes lead to rapid elimination of formulation and hence very small contact time on the ocular epithelium. The current review article covers various types of polymers used in ocular drug delivery along with their applications/ limitations. Polymers are widely used by researchers in prodrug techniques and as a penetration enhancer in ocular delivery. This article covers the role and use of different polymeric systems which makes the final formulation a promising candidate for ophthalmic drug delivery. The researchers are still facing multiple challenges in order to maintain the therapeutic concentration of the drug in the eyes because of its complex structure. There are several barriers that further restrict the intraocular entry of the drug. In order to remove/reduce such challenges, these days various types of polymers are used for ocular delivery in order to develop different drug carrier systems for better efficacy and stability. The polymers used are highly helpful in increasing residence time by increasing the viscosity at the ocular epithelium layer. Such preparations also get easily permeated in ocular cells. The combination of different polymeric properties makes the final formulation stable with prolonged retention, high viscosity, high permeability, and better bioavailability, making the final formulation a promising candidate for ocular drug delivery.
Topical route of administration is the most commonly used method for the treatment of ophthalmic diseases. However, presence of several layers of permeation barriers starting from the tear film till the inner layers of cornea make it difficult to achieve the therapeutic concentrations in the target tissue within the eye. In order to circumvent these barriers and to provide sustained and targeted drug delivery, tremendous advances have been made in developing efficient and safe drug delivery systems. Liposomes due to their unique structure prove to be extremely beneficial drug carriers as they can entrap both the hydrophilic and hydrophobic drugs. The conventional liposomes had several drawbacks particularly their tendency to aggregate, the instability and leakage of entrapped drug and susceptibility to phagocytosis. Due to this reason, for a long time, liposomes as drug delivery systems did not attract much attention of researchers and clinicians. However, over recent years development of new generation liposomes has opened up new approaches for targeted and sustained drug delivery using liposomes and has rejuvenated the interest of researchers in this field. In this review we present a summary of current literature to understand the anatomical and physiological limitation in achieving adequate ocular bioavailability of topically applied drugs and utility of liposomes in overcoming these limitations. The recent developments related to new generation liposomes are discussed.
Stimuli-responsive bacterial cellulose-g-poly(acrylic acid) hydrogels were investigated for their potential use as an oral delivery system for proteins. These hydrogels were synthesized using electron beam irradiation without any cross-linking agents, thereby eliminating any potential toxic effects associated with cross-linkers. Bovine serum albumin (BSA), a model protein drug, was loaded into the hydrogels, and the release profile in simulated gastrointestinal fluids was investigated. Cumulative release of less than 10% in simulated gastric fluid (SGF) demonstrated the potential of these hydrogels to protect BSA from the acidic environment of the stomach. Subsequent conformational stability analyses of released BSA by SDS-PAGE, circular dichroism, and an esterase activity assay indicated that the structural integrity and bioactivity of BSA was maintained and preserved by the hydrogels. Furthermore, an increase in BSA penetration across intestinal mucosa tissue was observed in an ex vivo penetration experiment. Our fabricated hydrogels exhibited excellent cytocompatibility and showed no sign of toxicity, indicating the safety of these hydrogels for in vivo applications.