Abstract
The popularity of hydrogels as biomaterials lies in their tunable physical properties, ability to encapsulate small molecules and macromolecular drugs, water holding capacity, flexibility, and controllable degradability. Functionalization strategies to overcome the deficiencies of conventional hydrogels and expand the role of advanced hydrogels such as DNA hydrogels are extensively discussed in this review. Different types of cross-linking techniques, materials utilized, procedures, advantages, and disadvantages covering hydrogels are tabulated. The application of hydrogels, particularly in buccal, oral, vaginal, and transdermal drug delivery systems, are described. The review also focuses on composite hydrogels with enhanced properties that are being developed to meet the diverse demand of wound dressing materials. The unique advantages of hydrogel nanoparticles in targeted and intracellular delivery of various therapeutic agents are explained. Furthermore, different types of hydrogel-based materials utilized for tissue engineering applications and fabrication of contact lens are discussed. The article also provides an overview of selected examples of commercial products launched particularly in the area of oral and ocular drug delivery systems and wound dressing materials. Hydrogels can be prepared with a wide variety of properties, achieving biostable, bioresorbable, and biodegradable polymer matrices, whose mechanical properties and degree of swelling are tailored with a specific application. These unique features give them a promising future in the fields of drug delivery systems and applied biomedicine.
Highlights
Incorporation of hydrohydrophobic binding sites within polymer networks with simple methods such as solid molecular dispersion would allow more loading of poorly soluble drugs while preventing drug recrystallization, when exposed to aqueous environments [62]. Vesicular carriers such as liposomes, microspheres, nanoparticles, and niosomes incorporated within the hydrogel matrix have the ability to extend and control the release of drug while eliminating or minimizing the burst release typically associated with these particle-based drug delivery systems [63]
Nanocarriers loaded into hydrogels are used for from various ionic and non-ionic (PVA, hydroxyethyl cellulose (HEC), hydroxypropyl methylcellulose (HPMC)) mubuccal delivery to improve the residence time and bioavailability, and to protect the drug coadhesive hydrogel polymers
A vaginal drug delivery system was prepared with flexible propylene glycol-constituting liposomes loaded with metronidazole or clotrimazole dispersed in carbopol hydrogel
Summary
The physical interactions and chemical cross-linking of hydrogels can contribute towards both structural and physical integrity [1]. Apart from other published literature, the present article provides a comprehensive overview on the recent advances of hydrogels in diverse drug delivery systems. Hydrogels can be broadly classified based on the characteristics of side groups (ionic or non-ionic), structural aspects (homo or copolymer), physical nature (crystalline, amorphous, supramolecular), and responsiveness to various external stimuli such as temperature, pH, light, ionic strength, ultrasound, electromagnetic radiation, glucose, and proteins. In order to impart adequate mechanical strength to hydrogels besides biodegradability, various types of physical and chemical cross-linking methods are currently being employed.
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