Hierarchical Hydrogel Drug Delivery System Enables Controlled Release of Adeno-Associated Viruses for Gene Therapy

This paper describes a drug delivery system (DDS) to release Adeno-associated viruses (AAVs) for gene therapy. Our system has two-level hierarchical structures made of different hydrogel materials: (i) Calcium alginate hydrogel microparticles ( $\sim 100\ \mu \mathrm{m}$ in diameter) that can properly immobilize AAVs inside and release them for gene transfection triggered by enzymatic degradation, and (ii) a millimeter-scale collagen sheet that encapsulates those alginate microparticles with AAVs for stable fixation to even a tiny and complicated diseased site in our body, such as an inner ear for the treatment of hereditary hearing loss (Figure 1). We fabricated the AAVs-immobilized hydrogel microparticles and evaluated their AAV releasing functions by measured the gene transfection ratio to cultured HeLa cells. In addition, we also demonstrated that the controlled release of AAVs immobilized in the alginate microparticles embedded in the millimeter-scale collagen sheet can be externally triggered from the outside. We envision that our developed composite hydrogel DDS could be an essential and general tool for gene therapy in practical medical scenes, especially in the treatment at complicated internal sites.