"The oral route of drug inclusion is the most convenient for the patient. In addition to ease of use, this method of drug inclusion has such advantages as non-invasiveness of inclusion, absence of complications during injection; comparative safety for the organism due to the passage of the active substance and auxiliary compounds through the gastrointestinal tract; the possibility of introducing larger doses of the drug at one time. However, despite the obvious advantages, the oral route of inclusion has a number of significant disadvantages that significantly limit its use for a number of drugs. Among them are: relatively slow therapeutic action of the drug with this route of inclusion; the aggressive effect of a number of drugs (for example, antibiotics) on the gastrointestinal tract; low bioavailability of a number of substances (especially high molecular weight hydrophilic compounds), caused by poor permeability of the intestinal epithelium for hydrophilic and large molecules, as well as enzymatic and chemical degradation of the active substance in the gastrointestinal tract. There are various approaches used in the development of oral drug delivery systems. In particular, for the targeted delivery of drugs, it is proposed to use nano- and microcapsules with mucoadhesive properties. Among the polymers used for the synthesis of these microparticles, it is preferable to use pH-dependent, gelable biopolymers that change their structure depending on the acidity of the environment. Microcapsules obtained from compounds with the above properties are capable of protecting the active substance (or from the active substance) in the stomach environment and ensuring its release in the intestine. These properties are possessed by such polysaccharides as alginate, pectin, carrageenan, xylan, etc. The listed biopolymers are non-toxic, biocompatible, and biodegradable, which makes microparticles containing these polysaccharides promising as oral drug delivery systems. To impart mucoadhesive properties to nanoparticles, complexes of the listed polymers with chitosan are used. In this research, pectin, a polysaccharide formed mainly by residues of galacturonic acid, was used as a structural polymer. The concentrations of substances in the initial solutions were selected that were optimal for the synthesis of microcapsules. The main parameters for evaluating the resulting microparticles were the size of the capsules (less than 1 μm for oral inclusion), the zeta-potential, showing the tendency of the microparticles to stick together, and the completeness of the binding of the microparticles to chitosan. It was found that the optimal solutions for the synthesis of microparticles are: 15.7 ml of a solution of pectin 0.093% by weight, 3.3 ml of a solution of chitosan 0.07% by weight and 1.0 ml of a solution of CaCl2 20 mM. The diameter of the microparticles obtained by this method was 700-800 nm, and the value of their zetta-potential, equal to - (34 ± 3) mV, does not cross the particle adhesion threshold. It was also found that the synthesis of microparticles at these concentrations of calcium chloride provides the most complete binding of chitosan to their surface, which increases the mucoadhesive properties of microparticles."
Implantable Polymeric Drug Delivery Devices: Classification, Manufacture, Materials, and Clinical Applications
