Nanocarriers in modern drug delivery systems

Introduction Nanotechnology consists in manufacturing nanometre-sized materials and structures, i.e. up to 100 nm. There is no doubt that it is one of the most dynamically developing branches of science and technology. This is a multidisciplinary branch, as it combines the elements of solid-state physics, chemistry, material science and molecular biology that interpenetrate each other. Nanotechnology is widely used in medical science. Reducing the size of a selected material to a nanometric scale makes it possible to utilise them in numerous potential applications. Drug carriers can be built of carbon, polymeric and magnetic materials, as well as of their combinations, thus creating complexes – core-shell structures. The main goals of nanopharmacology are the targeted therapy (TT) and the controlled drug delivery systems (DDS). The basic component of the DDS includes using an appropriate carrier that should not be toxic, should bind the drug properly, making it also possible to release it at the target site keeping the therapeutic concentration range. In addition, the role of nanoparticles (NP) used is to improve the therapeutic value of applied drugs by changing their solubility, retention time and the penetration of biological barriers [1]. The bioavailability enhanced by the above-mentioned mechanisms increases the therapy efficacy and minimises side effects resulting from a prolonged administration of medication. The conjugates of nanoparticle–drug offer a lot of advantages: they reduce therapy costs targeted at the proper site by guiding molecules (folic acid (FA), antibody (Ab) or RGD – the integrin recognising peptide αvβ3) – they reduce the general toxicity of pharmaceuticals and increase the drug tolerance in patients. The very process of drug nanoencapsulation increases the efficacy, specificity and the therapeutic index of immobilised active substances [2, 3]. This is not only the carrier biotransformation inside the body that counts, but also its size is of equal importance. The size of molecules affects all the stages of pharmacokinetics, e.g. while the drug penetrates cell membranes (blood vessel walls, epithelia) and is excreted from the body – avoiding accumulation and related side effects. Particular types of nanoparticles show different indications for use depending on the area of the body. As a result, nanocarriers should show specific features necessary to reach a predefined goal, i.e. a properly sized carrier, type of attaching the drug to the NP, surface properties (hydrophilicity/hydrophobicity), the presence of surface functional groups, biodegradability and physical properties because of environmental changes, such as pH, temperature and the features of the very carrier, including surface potential and magnetism [4]. Drug immobilization on nanocarriers is carried out by using physical processes: adsorption, absorption and encapsulation, and chemical processes: covalent bonds, ionic bonds and the van der Waals forces.