A 3D‑scaffold of PLLA induces the morphological differentiation and migration of primary astrocytes and promotes the production of extracellular vesicles

The present study analyzed the ability of primary rat astrocytes to colonize a porous scaffold, mimicking the reticular structure of the brain parenchyma extracellular matrix, as well as their ability to grow, survive and differentiate on the scaffold. Scaffolds were prepared using poly-L-lactic acid (PLLA) via thermally-induced phase separation. Firstly, the present study studied the effects of scaffold morphology on the growth of astrocytes, evaluating their capability to colonize. Specifically, two different morphologies were tested, which were obtained by changing the polymer concentration in the starting solution. The structures were characterized by scanning electron microscopy, and a pore size of 20 µm (defined as the average distance between the pore walls) was detected. For comparison, astrocytes were also cultured in the traditional 2D culture system that we have been using since 2003. Then the effects of different substrates, such as collagen I and IV, and fibronectin were analyzed. The results revealed that the PLLA scaffolds, coated with collagen IV, served as very good matrices for astrocytes, which were observed to adhere, grow and colonize the matrix, acquiring their typical morphology. In addition, under these conditions, they secreted extracellular vesicles (EVs) that were compatible in size with exosomes. Their ability to produce exosomes was also suggested by transmission electron microscopy pictures which revealed both EVs and intracellular structures that could be interpreted as multivesicular bodies. The fact that these cells were able to adapt to the PLLA scaffold, together with our previous results, which demonstrated that brain capillary endothelial cells can grow and differentiate on the same scaffold, could support the future use of 3D brain cell co-culture systems.