Microemulsion hydrogels - properties and current applications in drug delivery

Abstract

The current research in cutaneous and percutaneous drug delivery is focused on design of advanced carriers with enhanced applicability, stability, drug-loading capacity, and drug penetration/permeation ability. Microemulsion hydrogels (MHs) are carriers which attract the attention of a growing number of researchers who aimed to enhace dermal or transdermal delivery of drugs which are common therapeutics for different skin disorders or systemic deseases such as infections, androgenic alopecia, rheumatoid arthritis, osteoarthritis, and spondylitis, respectively. Microemulsion hydrogels is a heterogeneous group of the drug delivery systems which usually represent thermodynamically stable systems comprising dispersed oil phase within a continuous aqueous phase which is thickened with a suitable hydrophilic polymer. This chapter summarises a novel observations regarding physicochemical properties, physical and chemical stability, and drug delivery potential of this type of drug delivery systems, based on comprehensive review of the research results from the relevant scientific publications. Particularly, the chapter describes the rheological behaviour of microemulsion hydrogels and elucidates the role of the most commonly used synthetic and natural hydrophilic polymers (such as carbomers, hydroxypropyl cellulose (HPC), hydroxypropyl methylcellulose (HPMC), xanthan gum, poloxamers) as gelling agents. Furthermore, the recently established models of the complex structure of different microemulsion hydrogels, the in vitro drug release profiles, the ex vivo permeation profiles, and the in vivo drug delivery availability of different drug molecules from the investigated systems, are described. The skin compatibility and skin irritation potential aspect of the selected hydrogel-thickened microemulsion systems is commented. The most important findings of the selected studies on microemulsion hydrogels were presented in order to illustrate their potential for achievement of topical, regional or transdermal drug delivery, including sustained drug delivery, as well as to compare to that of conventional hydrogels, microemulsions, and creams.