Fig. 1.

Engineering tubular structures starting from MDCK cell suspensions. (A) Schematic representation of PDMS fabrication. Designed patterns are converted into 3D plastic masters using stereolithography. Subsequently, extruded patterns of the master are replicated in the PDMS scaffolds through replica molding in four basic steps: (i) masters are treated with FOTS silane to prevent the PDMS from sticking; (ii) the PDMS prepolymer is poured on the masters and allowed to cure, forming PDMS replicas; (iii) replicas are then peeled off from the masters, and bonded to a 20 μm-thick prepolymer layer by thermal curing in order to close the bottom side; (iv) after cutting and demolding, PDMS scaffolds are ready to be sterilized and used. The same technical steps are followed to generate linear or branched open-top PDMS scaffolds with rectangular cross-sectional geometry. (B) Experimental design. MDCK cells are resuspended in collagen, seeded into PDMS scaffold by pipetting, and cultured in the presence of HGF for up to 2 days. (C) Immediately after seeding, the collagen containing cells fills the scaffold channel completely (day 0). At 1 day, tubular aggregates show marked shrinkage. At 2 days, branches emerge from the cavities, and a translucent area (middle panel, asterisk) bordered by darker edges (middle panel, arrows) is visible. (D) Ramified and (E) tree-like tubular structures at 2 days. (F) A multichannel scaffold containing microtubules at 2 days. Scale bars: 2 mm (C–E), 500 μm (F).