Resumen de Injectable biodegradable carriers for the delivery of therapeutic agents and tissue engineering
Riccardo Levato
The design of smart biomaterial devices plays a key role to improve the way conventional therapies are being delivered, and to promote the development of new approaches for advanced therapies, such as regenerative medicine and targeted drug release. Injectable biodegradable materials, such as those consisting of suspensions of polymeric particles, are highly versatile devices that can be delivered through minimally-invasive injections. The physic-chemical properties of the particles can be engineered to obtain smart scaffolds for tissue engineering, carriers for drug release and cell therapy. The aim of this Thesis is to develop a novel class of biodegradable and injectable particulate carriers based on polylactic acid (PLA), that are capable to trigger and guide specific responses from the cells and the biological milieu. First, a novel route to fabricate PLA-based microcarriers (MCs) was set and characterized. The production method involved green, non-harmful chemicals and it is easy to scale-up. Such technique allowed tuning MC size and size distribution in the range suitable for drug and cell delivery applications. The favorable regulatory status of the materials and reagents may also be beneficial for the translation of the MCs from bench to bedside. The principles guiding the fabrication procedure can inspire techniques to generate nanocarriers for controlled drug delivery. Recent studies point out the importance of drug-loaded and submicron-sized materials in the treatment of severe clinical conditions, such as persistent biofilm infections. These nanoparticles (NPs) can be endowed with smart functionalities to enhance drug delivery within the biofilm matrix. In this way, NPs encapsulating the antibiotic ciprofloxacin were produced and functionalized with DNase I. The NPs improved the antimicrobial activity of the encapsulated drug and promoted biofilm eradication, targeting and degrading directly the biofilm matrix. On the other hand, larger particles such as MC, display a high surface area for cell expansion. MCs can also deliver cells with therapeutic potential as ¿living drugs¿, ideally in a spatio-temporal controlled fashion. This is especially important, as, in standard cell therapies, direct injection of cells is accompanied by massive cell mortality that renders the treatment ineffective. PLA MCs suitable for Mesenchymal Stromal Cells (MSCs) homing have been produced and modified with different functionalization approaches. The physic-chemical properties of the MCs and bioactive coatings modulated cell adhesion, proliferation, and migratory potential in response to chemokines that regulate MSC tissue localization, like SDF-1a. The results highlight the importance of carriers design to control cell delivery, and provide important guidelines to instruct a new generation of efficient biomaterial carriers. Another exciting application of injectable, cell-laden MCs is to use them as building blocks to fabricate living tissues in vitro. Combining MC technology and bioprinting is an appealing strategy to generate tissues grafts with controlled architectures. The suspension of injectable PLA cell-laden MCs within gelatin-based hydrogels formed an extrudable, composite bioink. MCs acted as mechanical reinforcement for soft gels and as means for cell expansion to encapsulate high cell payload. MSCs were shown to form MC-MSCs aggregates, with enhanced cell-to-cell contact on surface functionalized PLA MCs, and differentiated towards the osteogenic lineage. This result suggests potential applications of MC-MSCs laden bioinks for bone tissue engineering, and the composite bioink is proposed as component to build multimaterial, 3D-printed osteochondral graft models. Taken together, the injectable devices developed in the Thesis constitute promising and highly versatile biomaterial platforms for biomedical applications, and can be employed in a wide array of tissue engineering, and cell and drug delivery strategies.
