oa Editorial [Hot Topic: New Formulative Strategies for Lipid Nano and Microparticles Preparation (Guest Editor: L. Battaglia and M. Gallarate)]

INTRODUCTION Owing to lipid biocompatibility and versatility, lipid nanoparticles showed many advantages over polymeric nanoparticles and liposomes, and have been widely used for the preparation of nanoparticles for drugs and actives delivery [1]. The most known formulation in this field are solid lipid nanoparticles (SLN) [2]. Lipid nanoparticles of new generation have been lately exploited and patented, including nanostructured lipid carriers (NLC) [3] and lipid drug conjugates (LDC) [4]: all these lipid nanoparticles are produced mainly according to hot homogenisation method, which generally implies the use of an high pressure homogeniser (HPH). Many applications have been developed and patented regarding solid lipid nanoparticles: some of them are in cosmetic field, since the time-to-market is very short for these products [5-7]. Anyway, other applications are in emerging challenges of pharmaceutical field [8-11]. An innovative reformulation of a drug could extend its patent life: new delivery systems for out of patent molecules could lead to reduced side effects, achieving a more effective therapy [12]. Recently, the need of overcoming the critical process parameters of hot homogenisation technique (high temperatures, high pressures and cavitation forces) led to develop new methods to prepare lipid nanoparticles. Different techniques based on microemulsion templates have been worked out [13,14]; coacervation has been proposed for the preparation of fatty acid nanoparticles [15,16]; the potential application of phase inversion temperature has been exploited for lipid nanocapsules production [17]. Solvent based methods have been proposed, too, even if their future perspectives are limited by toxicity issues: solvent injection method [18,19], solvent evaporation method [20] and solvent diffusion method [21] have been extensively studied in literature. Also supercritical fluid (SCF) technology, in particular supercritical fluid extraction from emulsion (SFEE), has gained increasing interest for lipid nanoparticles suspension preparation [22]. Lipid nanoparticles are usually in the form of water suspensions; however, in order to comply the need of anhydrous delivery systems for various pharmaceutical applications, powdered lipid nano and microparticles have been engineered, too, according to different methods: spray-drying [23], spray-congealing [24-26], electrohydrodynamic atomisation [27, 28], cryogenic micronisation [29], rapid expansion of supercritical solutions (RESS), supercritical anti-solvent, particles from gas-saturated solutions/suspensions (PGSS) [30-32]. Currently, one of the major challenges for nanoparticles is the delivery of complex molecules, like proteins, peptides and nucleic acids (plasmid DNA, antisense oligonucleotides, short interfering RNA), with relevant stability and bioavailability problems. Naked nucleic acids are easily digested by enzymes in vivo and are not internalised by cells: lipid nanoparticles can protect them in biological fluids and have shown to enter into the cells by endocytosis [33], but suitable strategies are necessary to load these macromolecules within nanoparticles, most of them regarding the use of cationic lipids or nanoparticles with a positive surface charge [34-37]. Therapeutic application of peptides and proteins is restricted by their high molecular weight, their hydrophilic character and limited chemical stability, which cause low bioavailability, poor transfer across biological membranes and low stability in the bloodstream: lipid nanoparticles can stabilise loaded peptides and promote peptide absorption through biological membranes [38]. Different strategies have been implemented and patented for peptide and protein loading into lipid nanoparticles [38-41], including hydrophobic ion pairing technique [42]. SLN can be useful also as adjuvant for vaccine therapy [43,44]. In this issue, Attama examines the most important applications regarding SLN, NLC and LDC, while Lai et al. review the most innovative techniques, apart from hot homogenisation, for the preparation of lipid nanoparticles. Berton et al. provide a description of the methods and pharmaceutical challenges of lipid nano and microparticles in powdered form. Finally Del Pozo- Rodriguez et al. analyse two of the most important future outcomes of lipid nanoparticles: nucleic acid and protein delivery. This special issue aims to discuss, for academics as well as industrial practitioners, the recent patents on core topics of lipid nano and microparticles technology, thereby evidencing the potential economic impact of this research field. ACKNOWLEDGEMENTS We kindly acknowledge Dr. Lucia Gastaldi (Universita degli Studi di Torino - Dipartimento di Scienza e Tecnologia del Farmaco) for the supervision of the manuscripts.....