Diffusion studies of nanomedicines within increasing complexity tissue models
Many solid tumors develop biological characteristics different from those which characterize the healthy tissues; compared to normal tissues, tumoral main features include blood vessels with fenestration and a higher rigidity of extracellular matrix (ECM) that, with its architecture, influence drug delivery and diffusion to the tumoral mass   playing a leading role on the effectiveness of the therapy . Living cells are always surrounded by extracellular matrix, which can be understood
... s a three-dimensional structured filter; no substance can pass directly from the bloodstream to cell and vice versa, but must reach the cell over the ECM. The nanocarriers are the most important drug transporters to whom the researchers always pose attention for overcoming biological barriers to enabling the drug reach the pathological site. They can carry hydrophilic and/or hydrophobic drugs, protecting them from degradation, providing a drug controlled release and reducing toxic effects to the healthy tissues  . Particles movement in tissues depends on their size, charge, and configuration and these features can be modified in order to optimize particles delivery to cancer cells. As well as from particle features, particle movements depend also on ECM properties; it is necessary to understand the best way how these particles diffuse in the ECM . Drug and particles transport through interstitial tissue is ruled by a diffusive flux due to concentration gradient and a convective flux due to fluid movement even if high interstitial fluid pressure makes the transport of drugs dependent only by the diffusion  . Drug delivery depends also on the cells that form the tumor mass and on the matrix 4 structure . It is of fundamental importance to understand how these barriers interfere with the drugs transport to improve even more the transport of therapeutic molecules  . For this purpose, in this work it has been developed a Tissue Chamber Chip that represents a tool to investigate the diffusion of different nanoparticles (NPs) in an extravascular space modeled by collagen, the main component of the extracellular matrix. Before clinical trials and food and drug administration (FDA) approval, drugs and delivery mechanisms need to be tested to determine their effectiveness and toxicity. Here, six different nanocarriers, almost similar in size but with different surface decoration were tested. The found results highlight that the surface PEGylation promotes diffusion by acting as a lubricant agent. In particular, it has been found that the greater the percentage of PEG on the surface, the greater the mobility of these nanovectors within the ECM. The particles covered with hyaluronic acid, instead, showed a different behavior: their diffusion was hampered proportionally to the molecular weight of this glycosaminoglycan. To demonstrate the generality of our approach, the same NPs were tested on murine brain tissue. The results obtained provide the same trend that can be seen from collagen alone, even if the order of magnitude of the diffusivity is different because of the tissue architecture and complexity. Collectively, these results suggest that the procedure adopted for the nanomedicine diffusion studies, regardless of the tissue, is solid. And, in particular, this suggests that the Tissue Chamber chip can be used as a predictive model of NPs behavior within a biological environment. 5 Finally, to further increase the translational characteristic of our platform, the same collagen matrix was used as a nutritional environment for a 3D culture of cells derived from colorectal cancer. The in vivo tumor tissue has been recreated in vitro in order to potentially allow patient-specific drug screening and the development of personalized This work demonstrated that our device can be efficiently used to test the extravascular transport of NPs and, moreover, it can be modified increasing its complexity to get closer to a real model. In addition, this project could continue using patient-derived 3D culture to effectively test drugs and NPs to make clinical trials increasingly oriented and well targeted.