The aim of the present study is to investigate the interactions between liposomes and proteins and to evaluate the role of liposomal lipid composition and concentration in the formation of protein corona. Liposomes composed of 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC) or hydrogenated soybean phosphatidylcholine (HSPC) with 1,2-dipalmitoyl-sn-glycero-3-phospho-(1'-rac-glycerol) (sodium salt) (DPPG), 1,2-dipalmitoyl-sn-glycero-3-phosphoethanolamine-N-[methoxy(polyethylene glycol)-3000] (DPPE-PEG 3000), cholesterol (CH) or mixtures of these lipids, were prepared at different concentrations by the thin-film hydration method. After liposomes were dispersed in HPLC-grade water and fetal bovine serum (FBS), their physicochemical characteristics, such as size, size distribution and ζ-potential, were determined using dynamic and electrophoretic light scattering. Aggregation of DPPC, HSPC, DPPC:CH (9:1 molar ratio) and HSPC:CH (9:1 molar ratio) in FBS was observed. On the contrary, liposomes incorporating DPPG lipids and cholesterol both in a molar ratio of 11% were found to be stable over time, while their size did not alter dramatically in biological medium. Liposomes containing cholesterol and PEGylated lipids retain their size in the presence of serum as well as their physical stability. In addition, our results indicate that the protein binding depends on the presence of polyethylene glycol (PEG), cholesterol, concentration and surface charge. In this paper, we introduce a new parameter, fraction of stealthiness (Fs), for investigating the extent of protein binding to liposomes. This parameter depends on the changes in size of liposomes after serum incubation, while liposomes have stealth properties when Fs is close to 1. Thus, we conclude that lipid composition and concentration affect the adsorption of proteins and the liposomal stabilization.

Liposomes are considered to be one of the most extensively investigated drug delivery nanosystems. Each drug can be loaded either in the liposomal hydrophilic core or within the lipidic bilayer and delivered eventually to the proper site into the organism. There are already many marketed approved liposomal products. The development of a liposomal product is a quite complicated process, while many critical parameters have to be investigated during the preparation process. The present study deals with the drug-to-lipid ratio (D/L ratio), which is a critical process parameter, expresses the actual capacity of the liposome to accommodate the drug and can play a key role at the optimization of every liposomal formulation. D/L ratio is affected by the composition, the different biomaterials and the loading method being used, so the improvement of D/L ratio can optimize the liposomal formulation. D/L ratio can be used as an index of the effectiveness of the preparation method too. Furthermore, D/L ratio influences the therapeutic efficacy of the liposomal product, expressing the actual dose of the drug being administrated. There is a variety of analytical methods, quantifying the drug and the lipids and estimating eventually the D/L ratio. According to the regulatory framework of nanomedicine, about the development of nanosimilars, D/L ratio is a necessary element for the nanosimilar product description and the statement of product comparability.

Lipid nanoparticles (LNPs) are the first approved nanomedicines and the most well-studied class of nanocarriers for drug delivery. Currently, they are in the frontline of the pandemic fight as vaccine formulations and therapeutic products. However, even though they are so well-studied, new materials and new modifications arise every day that can improve their properties. Their dynamic nature, especially the liquid crystal state of membranes, is under constant investigation and it is that which many times leads to their complex biological behavior. In addition, newly discovered biomaterials and nanoparticles that possess promising effects and functionalities, but also toxicity and/or poor pharmacokinetics, can be combined with LNPs to ameliorate their properties. As a result, many promising theranostic applications have emerged during the past decade, proving the huge potential of LNPs in the field. In the present review, we summarize some of the most prominent classes of LNPs for nanotheranostic purposes, and present state-of-the-art research examples, with emphasis on the utilized biomaterials and the functionality that they confer to the resultant supramolecular nanosystems, in relation to diagnostic and therapeutic modalities. Although there has been unprecedented progress in theranostics, the translational gap between the bench and the clinic is undeniable. This issue must be addressed by experts in a coordinated way, in order to fully exploit these nanomedicines for the benefit of the society.