Editorial [Hot Topic: Innovative Technologies for Drug Delivery Applications: From Biopolymers and Nanocapsules to Inorganic Materials (Guest Editor: Helder A. Santos)]

Over the past few decades, micro and nanomaterials for drug delivery applications have received tremendous experimental attraction in almost every field of biosciences. These materials hold great promise in biomedical applications for earlydiagnostics, noninvasive imaging and targeting delivery of therapeutics, as well as combined multifunctions and simultaneous therapy and monitoring of the diseases (theranostics). More than ever there are combined efforts from many scientists all over the World with different backgrounds to develop efficient and promising drug delivery systems (DDS) for the future. Currently, the field of drug delivery and biomaterials is a rather interdisciplinary and rapidly growing one. For example, efficient drug delivery, targeting and diagnostics can be achieved by employing advanced natural and synthetic biopolymers, new generation of lipid-based formulations (e.g. solid lipid nanoparticles) and even by using outstanding inorganic materials, such as porous silica- and silicon-based materials. These biomaterials are produced by novel technologies based on top-down and bottom-up approaches. It is well recognized that many of the new developed drug molecules encompass potent biological activity, but still exhibit poor pharmacokinetic properties that hinder their effective delivery to the intended site of action. These problems can be overcome by means of DDS. The great advantage of these systems is that in most cases they are non-toxic and biodegradable, which render them great promising in the future when moving from pre-clinical to clinical trials. In addition, the incorporation of therapeutic compounds in DDS enables not only the improvement of the dissolution rate, solubility and bioavailability of the compounds and the drug formulation stability, but also to effectively and selectively carrier the therapeutics to the specific site in a controlled manner. The DDS are also expected to be suitable to the specific application (e.g. biodegradable and pH sensitive) and attain a particular degree of drug loading and release kinetics (e.g. slow or fast). Importantly, the tissue/cellmaterial interactions have to be carefully considered to ensure the biocompatibility of DDS. It is well-known that there are many factors affecting the biofate of the drug carriers when in contact with cell/tissues, e.g. their surface chemistry, topology, and biocompatibility. The biodistribution, accumulation and cellular uptake of biomaterial-based delivery systems may also occur through several different pathways depending on the properties of the DDS, such as particle size, shape, surface charge, etc. Therefore, the safety of novel DDS requires a total understanding of the physicochemical properties that account for adverse biological responses before coming to clinical trials. In this special issue of Current Drug Discovery Technologies several examples of innovative technologies for drug delivery applications will be illustrated, ranging from biopolymers, nanocapsules, liposomes, solid nanoparticles, to inorganic silicon- and silica-based materials. Eight review papers and one original research article will highlight and describe in more detail some of the most recent innovative technologies and strategies used to design different DDS and demonstrate their potential in biomedical applications. The introductory review paper by Andrade et al. describes the recent potentialities and advantages of chitosan- based pharmaceutical dosage forms used in the development of formulations for therapeutic proteins, as well as their interaction with biological moieties and the effect on protein absorption pathways. Besides chitosan, other biodegradable polymers used for preparing nanocapsules are considered in the review paper by Rong et al., which also presents the most common methods of preparation of polymeric nanocapsules and also describes the applications of polymeric nanocapsules as carriers of therapeutics. In the subsequent review paper, Hirsjarvi et al. presents several nanocarrier systems based on polymer micelles, nanoparticles/polymer-drug conjugates and liposomes used for passive and active tumor targeting. Similarly, the review paper by Kolhatkar et al. further discusses the in vitro binding and in vivo pharmacokinetics of dendrimers, copolymers and liposomes modified with folic acid, integrin and transferring for targeting delivery applications. In addition, the review paper by Keck et al. reviews the 20 years work on solid lipid nanoparticles, including the state of production, regulatory aspects, the important questions of nanotoxicity, the different administration routes, as well as presents the potential of solid lipid nanoparticles for optimized delivery and pharmaceutical product developments. The subsequent review paper by Santos et al. highlights the potential applications of porous silicon materials in biomedical applications and presents examples on the most recent in vitro and in vivo studies, including the biocompatibility of these materials, their potential as carriers for delivery of therapeutics and as platforms for drug targeting and noninvasive imaging. A similar approach continues in the review paper by Simovic et al. which describes the most recent milestones in the research of silica-based materials for controlled drug delivery, emphasizing e.g. their fabrication processes, biocompatibility aspects, their anticancer therapy and stimuli-responsive applications. The review paper by Cheng and Lo continues presenting the current application of silica-based materials, gold and iron oxide as nanodelivery systems, in particular for enhanced photodynamic cancer treatment. The last article, an original research paper by Sandri et al., presents the results of an in situ gelling formulation based on Poloxamer 407 and sodium alginate, and demonstrates that such formulation is a suitable extemporaneous vehicle to deliver platelet lysate on buccal mucosa to treat oral mucositis. The reports presented here highlight great potential of the described DDS for safety, controlled, and targeted delivery of therapeutics and emphasize that more advanced or modified systems will emerge in the future with multifunctional applications towards the clinical trials. By taking advantage of the valuable properties of the DDS, such as increased surface area, improved solubility of therapeutics, possibility to encapsulate and protect therapeutics from degradation with reduced immunogenic potential and toxicological effect, new tuneable and targeted drug delivery technologies can be development to improve the clinical arsenal for numerous diseases. Moreover, many references can be found at the end of the individual reviews, which make this thematic issue useful to a wide range of scientists working in various fields of research, thus emphasizing the high scientific standing of the issue. All together, this issue will hopefully provide knowledge on the advances in DDS, biomaterials, and bio-nanotechnology, as well as demonstrate that they can be used for improving and/or delivery of therapeutics, potentially leading to new and effective DDS in the very near future. Finally, I would like to express my grateful thanks, as the Guest Editor of the special issue of Current Drug Discovery Technologies, to all the contributing authors and reviewers for their efforts in putting together this special issue.