Porous Polymeric Nanofilms for Recreating the Basement Membrane in an Endothelial Barrier-on-Chip

Organs-on-chips (OoCs) support an organotypic human cell culture in vitro. Precise representation of basement membranes (BMs) is critical for mimicking physiological functions of tissue interfaces. Artificial membranes in polyester (PES) and polycarbonate (PC) commonly used in in vitro models and OoCs do not replicate the characteristics of the natural BMs, such as submicrometric thickness, selective permeability, and elasticity. This study introduces porous poly(d,l-lactic acid) (PDLLA) nanofilms for replicating BMs in in vitro models and demonstrates their integration into microfluidic chips. Using roll-to-roll gravure coating and polymer phase separation, we fabricated transparent ∼200 nm thick PDLLA films. These nanofilms are 60 times thinner and 27 times more elastic than PES membranes and show uniformly distributed pores of controlled diameter (0.4 to 1.6 μm), which favor cell compartmentalization and exchange of large water-soluble molecules. Human umbilical vein endothelial cells (HUVECs) on PDLLA nanofilms stretched across microchannels exhibited 97% viability, enhanced adhesion, and a higher proliferation rate compared to their performance on PES membranes and glass substrates. After 5 days of culture, HUVECs formed a functional barrier on suspended PDLLA nanofilms, confirmed by a more than 10-fold increase in transendothelial electrical resistance and blocked 150 kDa dextran diffusion. When integrated between two microfluidic channels and exposed to physiological shear stress, despite their ultrathin thickness, PDLLA nanofilms upheld their integrity and efficiently maintained separation of the channels. The successful formation of an adherent endothelium and the coculture of HUVECs and human astrocytes on either side of the suspended nanofilm validate it as an artificial BM for OoCs. Its submicrometric thickness guarantees intimate contact, a key feature to mimic the blood-brain barrier and to study paracrine signaling between the two cell types. In summary, porous PDLLA nanofilms hold the potential for improving the accuracy and physiological relevance of the OoC as in vitro models and drug discovery tools.