NANOINDENTATION BASED APPROACH FOR THE MECHANICAL CHARACTERIZATION OF POLYMERIC MICROSPHERES FOR DRUG DELIVERY

Polymeric microspheres are largely studied for biomedical applications as, e.g., embolic agents to treat hyper-vascular tumors [1], or in tissue engineering [2]. The possibility to produce an ad hoc drug delivery system is the mostly studied characteristic of these type of microspheres. The class of polymeric microspheres used for biomedical applications are mainly composed by hydrophilic polymers, because of their biocompatibility. The polymers chosen for this study are Gelatin and Chitosan. Due to the instability of these two polymers in aqueous environment a natural cross-liker (genipin) is added. Here the mechanical properties of a new design of polymeric microspheres to be used as carriers for local release of drugs and grow factors, are investigated. The rationale of the study is understand how the used polymers and the presence of the cross-linker influence the mechanical properties of the microspheres and therefore the effectiveness in properly release drugs. Technically, nanoindentation was applied on microspheres of size in the range 20-70 µm. The mechanical characterization highlighted a viscous-elastic behavior of microspheres, with an increasing area of the characteristics hysteresis loops when the genipin concentration increases. Moreover, on measured load-displacement data, the Hertz model was applied to estimate the Young’s Modulus. A protocol for the mechanical characterization of polymeric microspheres used for drug delivery will allow: (1) to support their design phase and (2) to improve their effectiveness in targeting the release of drugs.