Development and characterization of polymer-based nano-complexes for cartilage regeneration

The repair of damaged articular cartilage, which rarely heals spontaneously and develops osteoarthritic complications, is a common clinical issue[1] and none of the available therapies can restore the hyaline cartilage surface beyond just fibrous repair. Over the last few years, polymer-based nanoparticles (NPs) have been in the limelight as a system for the encapsulation and delivery of drugs or active biomolecules, for the treatment of chronic wounds. Water-soluble, biodegradable, polyelectrolyte NPs offer numerous advantages over the conventional delivery forms, particularly so regarding the possibility to tune surface properties, high versatility to control the release profiles of loaded molecules and to interact with membrane receptors of cells, improved efficacy and patient compliance, and reduced toxicity. Polysaccharide-based NPs have, hitherto, been applied in the field of tissue engineering to enhance tissue regeneration by sustained and localized release of appropriate biological molecules, incorporated within the biodegradable nanostructure[2]. Starting from this point, this project is mainly focused on the development and characterization of polymer-based nano-complexes, as a first step in the fulfillment of an injectable composite material for cartilage regeneration. Among different polymers, hyaluronan (HA), Chitosan and its derivatives seem to be very promising for their structural and well established biological role. The two differently charged polymers were used for the preparation of a binary mixture solution by mixing different amounts of a HA solution and a Chitosan/derivatives solution, respectively, hence obtaining different HA weight fractions. The different formulations were prepared in the presence of different concentrations of NaCl to study the influence of ionic strength on the formation of complexes; the variation of pH and the used of HA with higher molecular weight were also investigated to find the best condition for NPs preparation. First, the Transmittance (T) of the different solutions was measured; then the same solutions were investigated by Dynamic Light Scattering (DLS) for the evaluation of Z-average size, zeta-potential, polydispersity index. After that, the best formulation was selected to evaluate the stability of complexes, first in water, and then changing the ionic strength and the pH up to physiological conditions. Overall, these nano-complexes appear as promising biomaterials with interesting biological and physical properties for cartilage regeneration.