TISSUE ENGINEERING: FROM RESEARCH TO CLINICAL APPLICATION IN REGENERATIVE MEDICINE

Tissue engineering strategies have recently emerged as the most advanced therapeutic option presently available in regenerative medicine. Tissue engineering encompasses the use of cells and their molecules in artificial constructs that compensate for lost or impaired body functions. It is based upon scaffoldguided tissue regeneration and involves the seeding of porous, biodegradable scaffolds with donor cells, which become differentiated and mimic naturally occurring tissues. These tissue-engineered constructs are then implanted into the patient to replace diseased or damaged tissues. Our approach to regenerative medicine is based on hyaluronan derivative polymers. HYAFF® is a class of hyaluronan derivative polymers obtained by coupling reaction. The strategy behind the creation of these polymers was to improve the stability of the polymer by esterifying the free carboxyl group of glucuronic acid, frequently repeated along the hyaluronic acid chain, with different types of alcohols. Once esterification of the polymer has been obtained, the material can easily be processed to produce membranes, fibres, sponges, microspheres and other devices, by extrusion, lyophilization or spray drying. A broad variety of polymers can be subsequently generated either by changing the type of ester group introduced or the extent of the esterification. The benzyl esters of hyaluronan, termed HYAFF®-11, are one of the most characterized HYAFF® polymers, from both the physicochemical and biological viewpoints, produced starting from hyaluronan of about 200 KDa. The ideal scaffold for tissue engineering should provide an immediate support to cells and have mechanical properties matching those of the tissue being repaired. Gradually then the material should be resorbed, as the cells begin secreting their own extracellular matrix, thus allowing for an optimal integration between newformed and existing tissue. Extensive biocompatibility studies have demonstrated the safety of HYAFF® scaffolds and their ability to be resorbed in the absence of an inflammatory response. Moreover, when implanted tend to promote the recapitulation of the events that facilitate tissue repair. HYAFF®-11 three-dimensional matrices support the in vitro growth of highly viable chondrocytes and fibroblasts. Similarly, micro-perforated membrane supports the growth and differentiation of keratinocytes. These cells, previously expanded on plastic and hence seeded into the HYAFF® scaffold, produce a characteristic extracellular matrix rich in proteoglycans expressing the typical markers of the tissues of their origin. Hyaluronan presents a variety of multi-functional activity being both a structural and informational molecule. Investigation of hyaluronan synthesis and degradation, the identification of new receptors and binding proteins and the elucidation of hyaluronan-dependent signaling pathways keep providing novel insights into the true biological functions of this intriguing polymer. The possibility to elaborate this natural polymer in different physical forms, as HYAFF® biopolymers family is allowing to do, has given the opportunity to translate tissue engineering strategies in clinical practice providing a biomaterial that induces and modulates the sequence of events that lead to damage tissue restoration. The following chapter will report how tissue engineering approach and hyaluronic acid technology could improve the biological function of cell transplantation in the treatment of tissue defects, in particular for skin and cartilage tissue restoration.