Dear Colleagues,

Over the past three decades, the rapid development of nanotechnology has resulted in the increased implementation of nanoparticles (NPs) in the field of biomedicine as vehicles for drug delivery, diagnostic imaging, and theranostic applications. Clinically approved and investigational nano-based drug formulations have been applied to a variety of indications, such as cancer, infectious diseases, neurodegenerative disorders, and tissue engineering. The application of nanomedicine formulations presents several advantages compared to conventional medicines. The unique abilities of nanoparticles to improve the solubility and the pharmacokinetic and toxicological properties of active pharmaceutical ingredients, and the possibility to synthetically tailor them for specific tissue/organ targeting led to the initial promise and enthusiasm in nanoparticle investigation. However, despite growing efforts, a relatively small number of nanoparticle-based formulations is currently used in clinical practice. Challenges such as improved characterization, possible toxicity, delivery efficacy, cost–benefit considerations, and regulatory ambiguities of nanomedicines still need to be improved and resolved. A wide variety of materials has been used so far in nano-drug design, including liposomes, metals or metal oxides, synthetic and natural polymers, and nanocrystals, to mention a few. The propensity of these materials to form stable nanostructures of well-defined shape, size, and surface chemistry under physiological conditions is deemed responsible for improved drug delivery and drug efficacy. A number of important pharmacokinetic parameters, such as specific tissue uptake and accumulation, biodistribution, and clearance mechanisms, was found to depend on nanoparticle properties. The small size of NPs, usually between 10 and 100 nm, is exploited to avoid physiological barriers such as the immune system, renal clearance, and mechanical degradation. The ability of liposomal NPs or polymer-based micelles to envelop hydrophobic drugs has been used to improve the bioavailability, efficacy, and delivery of a wide range of compounds with interesting biological properties. Additionally, the grafting of NP surfaces with polycations created a new application of NPs in combination therapy, enabling the delivery of conventional chemotherapeutic agents and polynucleotides (RNA, DNA) that form the basis of gene therapy. Furthermore, the surface of NPs can be modified for active tissue/cell targeting, resulting in enhanced therapeutic levels at a target site. The strategy is especially used for cancer treatment where the NP surface has been decorated with many ligands that selectively bind receptors overexpressed by cancer cells, which leads to increased accumulation and/or cancer cell uptake. A different approach to smart NP-based drug carriers is based on the design of stimuli-sensitive NPs, where external stimuli such as pH or redox conditions lead to drug release at the targeted site. Conversely, magnetic NPs, such as superparamagnetic iron oxide NPs, rely on an external magnetic field for controlled drug release.

Although most of the NP drug delivery systems are well-characterized in vitro and exhibit improved therapeutic efficacy compared to classical treatment with the free drug, in vivo clinical effects are not always encouraging and are often incomplete or lacking altogether. It is therefore of paramount importance to systemize and present the latest developments in the field of NPs in biomedical applications.

In this Special Issue, Nanoparticles for Biomedical Applications, in vitro and in vivo studies are highlighted and discussed.

It is my pleasure to invite you to submit a manuscript for this Special Issue. Full papers, communications, and reviews are all welcome.

Prof. Dr. Ana Figueiras
Prof. Dr. Francisco Veiga
Dr. Ivana Jarak
Guest Editors

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• nanoparticles
• biomedical applications
• drug delivery
• in vitro studies
• in vivo studies