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.