Liposomes are consolidated and attractive biomimetic nanocarriers widely used in the field of drug delivery. The structural versatility of liposomes has been exploited for the development of various carriers for the topical or systemic delivery of drugs and bioactive molecules, with the possibility of increasing their bioavailability and stability, and modulating and directing their release, while limiting the side effects at the same time. Nevertheless, first-generation vesicles suffer from some limitations including physical instability, short in vivo circulation lifetime, reduced payload, uncontrolled release properties, and low targeting abilities. Therefore, liposome preparation technology soon took advantage of the possibility of improving vesicle performance using both natural and synthetic polymers. Polymers can easily be synthesized in a controlled manner over a wide range of molecular weights and in a low dispersity range. Their properties are widely tunable and therefore allow the low chemical versatility typical of lipids to be overcome. Moreover, depending on their structure, polymers can be used to create a simple covering on the liposome surface or to intercalate in the phospholipid bilayer to give rise to real hybrid structures. This review illustrates the main strategies implemented in the field of polymer/liposome assembly for drug delivery, with a look at the most recent publications without neglecting basic concepts for a simple and complete understanding by the reader.

The present study aimed to develop and optimize liposome formulation for the colonic delivery of biologically active compounds. A strategy to facilitate such targeting is to formulate liposomes with a polymer coating sensitive to the pH shifts in the gastrointestinal tract. To this end, liposomes encapsulating curcumin—chosen as the biologically active compound model—and coated with the pH-responsive polymer Eudragit S100 were prepared and characterized. Curcumin was encapsulated into small unilamellar vesicles (SUVs) by the micelle-to-vesicle transition method (MVT) in a simple and organic solvent-free way. Curcumin-loaded liposomes were coated with Eudragit S100 by a fast and easily scalable pH-driven method. The prepared liposomes were evaluated for size, surface morphology, entrapment efficiency, stability, in vitro drug release, and curcumin antioxidant activity. In particular, curcumin-loaded liposomes displayed size lower than 100 nm, encapsulation efficiency of 98%, high stability at both 4 °C and 25 °C, high in vitro antioxidant activity, and a cumulative release that was completed within 200 min. A good Eudragit S100 coating which did not alter the properties of the curcumin-loaded liposomes was obtained. The present work therefore provides a fast and solvent-free method to prepare pH-responsive polymer-coated liposomes for the colonic delivery of biologically active compounds.

Curcumin is a natural polyphenol with strong antioxidant activity. However, this molecule shows a very poor bioavailability, instability, and rapid metabolism in vivo. In this work curcumin was loaded in Eudragit-coated liposomes to create a gastroresistant carrier, able to protect its load from degradation and free it at the site of absorption in the colon region. Small unilamellar vesicles were prepared and coated with Eudragit by a pH-driven method. The physico-chemical properties of the prepared systems were assessed by light scattering, transmission electron microscopy, infrared spectroscopy, and differential scanning calorimetry. The uptake of vesicles by Caco-2 cells and the anti-oxidant activity in cells were evaluated. The produced vesicles showed dimensions of about forty nanometers that after covering with Eudragit resulted to have micrometric dimensions at acid pH. The experiments showed that at pH > 7.0 the polymeric coating dissolves, releasing the nanometric liposomes and allowing them to enter Caco-2 cells. Delivered curcumin loaded vesicles were then able to decrease significantly ROS levels as induced by H₂O₂ in Caco-2 cells. The proposed work showed the possibility of realizing effective gastroresistant curcumin liposome formulations for the delivery of antioxidant molecules to Caco-2 cells, potentially applicable to the treatment of pathological conditions related to intestinal oxidative stress.