Hydrogels
Hydrogel based controlled release formulations: Designing considerations, characterization techniques and applications.
Abstract
Hydrogels have evolved over the last decade as materials of choice in varied biomedical applications. This is associated with the inherent biocompatible nature of the hydrogels. The modulation of the properties of the hydrogels is easily possible due to the availability of polymers of varied chemistry and physical properties. This review discusses the pharmaceutical aspects of the controlled release of bioactive agents from hydrogel based formulations.
1. Introduction
A gel may be defined as a 3-dimensional matrix of a solid component, having the ability to immobilize a liquid component.[1-2] Depending on the miscibility of the liquid component, the gels may be categorized either as hydrogels (water-miscible) or organogels (water-immiscible)
(Figure 1).[2] The present review will discuss about the designing strategies, mechanisms of drug release, methods for characterization and applications of hydrogel-based controlled release formulations. Hydrogel is a 3-dimensional network structure made up of hydrophilic polymers.[3-4] It has the ability to absorb and hold water within its structure. Even though the hydrogel absorbs a large amount of water, the 3-dimensional network does not get dissolved.
This is either due to the formation of junction points by chemical reactions or entanglement of the polymer chains or presence of crystallite domains associated with the physical interactions.[5-6] The polymer matrix devoid of the water phase is known as xerogel. In other words, a xerogel is a polymer matrix, which when placed in an aqueous media will absorb water and undergo swelling to form hydrogel.[7] The absorption of water by the xerogel is a thermodynamically favorable process.[8] When a xerogel is placed within water, the water starts to interact with the hydrophilic molecules of the polymers. This results in the
Abstract
Hydrogels have evolved over the last decade as materials of choice in varied biomedical applications. This is associated with the inherent biocompatible nature of the hydrogels. The modulation of the properties of the hydrogels is easily possible due to the availability of polymers of varied chemistry and physical properties. This review discusses the pharmaceutical aspects of the controlled release of bioactive agents from hydrogel based formulations.
1. Introduction
A gel may be defined as a 3-dimensional matrix of a solid component, having the ability to immobilize a liquid component.[1-2] Depending on the miscibility of the liquid component, the gels may be categorized either as hydrogels (water-miscible) or organogels (water-immiscible)
(Figure 1).[2] The present review will discuss about the designing strategies, mechanisms of drug release, methods for characterization and applications of hydrogel-based controlled release formulations. Hydrogel is a 3-dimensional network structure made up of hydrophilic polymers.[3-4] It has the ability to absorb and hold water within its structure. Even though the hydrogel absorbs a large amount of water, the 3-dimensional network does not get dissolved.
This is either due to the formation of junction points by chemical reactions or entanglement of the polymer chains or presence of crystallite domains associated with the physical interactions.[5-6] The polymer matrix devoid of the water phase is known as xerogel. In other words, a xerogel is a polymer matrix, which when placed in an aqueous media will absorb water and undergo swelling to form hydrogel.[7] The absorption of water by the xerogel is a thermodynamically favorable process.[8] When a xerogel is placed within water, the water starts to interact with the hydrophilic molecules of the polymers. This results in the