Bicontinuous cubic liquid crystals as sustained delivery systems for peptides and proteins

Importance of the field: Self-assembling lipid-based liquid crystalline systems are a broad and active area of research. Of these mesophases, the cubic phase with its highly twisted bilayer and two non-intersecting water channels has been investigated extensively for drug delivery. The cubic phase has been shown to accommodate and control the release of drugs with varying physicochemical properties. Also, the lipids used to prepare these delivery systems are generally cheap, safe and biodegradable, making these systems highly attractive. Early research investigating the potential of cubic phases as delivery systems showed that several peptides or proteins entrapped within these gel-based systems showed retarded release. Furthermore, entrapment within the cubic phase protected the selected peptide or protein from chemical and physical degradation with its native confirmation and bioactivity retained. Areas covered in this review: In this review, the literature pertaining to the delivery of various bioactives from cubic liquid crystalline phases is examined, with a particular focus on peptides and proteins. The scope and limitations of the cubic phases in this respect and the future of cubic liquid crystalline systems as sustained delivery systems are highlighted. What the reader will gain: The reader will be able to gain an understanding of the properties of the bicontinuous cubic phase and how its structural attributes make these systems desirable for sustained delivery of bioactives, in particular peptides and proteins, but also how these same structural properties have hindered progress towards clinical applications. Current strategies to overcome these issues will also be discussed. Take home message: The bicontinuous cubic phase offers great potential in the field of peptide and protein delivery, but limited research in this area precludes definite conclusions to its future in this respect.