Liposomes have come a long way since their conception in the 1960s, when they were envisioned primarily for drug delivery. Besides serving the important function of the delivery of a variety of drugs, liposomes offer a platform for the co-delivery of a range of therapeutic and diagnostic agents with different physicochemical properties. They are also amenable to the addition of various targeting moieties such as proteins, sugars, and antibodies for selective targeting at a desired site, including tumors. Currently, the design of stimuli-sensitive liposomes for drug delivery is a lively area of research. Compared to conventional liposomes, stimuli-sensitive nanoplatforms respond to local conditions that are characteristics of the pathological area of interest, allowing the release of active agents at the targeted site. Acidic pH, abnormal levels of enzymes, temperature, altered redox potential, and external magnetic field are examples of internal and external stimuli exploited in the design of stimuli-sensitive liposomes. The penetration of the liposomes into the cells can be enhanced with the help of a variety of cell penetrating peptides, which can be incorporated into the liposomes with the help of various lipid-polymer conjugates. Liposomes are now being employed in diagnostics as well. Imaging of a tumor can be made easier by the inclusion of fluorescent probes. They can also be used for gamma or MR imaging using chelated reporter metals and incorporating them either into the core of the liposome or in the lipid bilayer facing outwards. In this chapter, we discuss methods that are commonly used for the preparation of liposomes with a vast range of functions to meet a variety of needs in diagnostics and drug delivery.
Keywords: Cell-penetrating; Liposomes; Long-circulating; MMP-sensitive; Magnetically sensitive; Multifunctional; Redox-sensitive; Temperature-sensitive; Tumor-targeting; pH-sensitive.