  Stereolithographic 3D-printing (SLA) permits facile fabrication of
high-precision microfluidic and lab-on-a-chip devices. SLA photopolymers often
yield parts with low mechanical compliancy in sharp contrast to elastomers such
as poly(dimethyl siloxane) (PDMS). On the other hand, SLA-printable elastomers
with soft mechanical properties do not fulfill the distinct requirements for a
highly manufacturable resin in microfluidics (e.g., high-resolution
printability, transparency, low-viscosity). These limitations restrict our
ability to print microfluidic actuators containing dynamic, movable elements.
Here we introduce low-viscous photopolymers based on a tunable blend of
poly(ethylene glycol) diacrylate (PEGDA, Mw~258) and poly(ethylene glycol
methyl ether) methacrylate (PEGMEMA, Mw~300) monomers. In these blends, which
we term PEGDA-co-PEGMEMA, tuning the PEGMEMA-to-PEGDA ratio alters the elastic
modulus of the printed plastics by ~400-fold, reaching that of PDMS. Through
the addition of PEGMEMA, moreover, PEGDA-co-PEGMEMA retains desirable
properties of highly manufacturable PEGDA such as low viscosity, solvent
compatibility, cytocompatibility and low drug absorptivity. With
PEGDA-co-PEGMEMA, we SLA-printed drastically enhanced fluidic actuators
including microvalves, micropumps, and microregulators with a hybrid structure
containing a flexible PEGDA-co-PEGMEMA membrane within a rigid PEGDA housing.
These components were built using a custom "Print-Pause-Print" protocol,
referred to as "3P-printing", that allows for fabricating high-resolution
multimaterial parts with a desktop SLA printer without the need for
post-assembly. SLA-printing of multimaterial microfluidic actuators addresses
the unmet need of high-performance on-chip controls in 3D-printed microfluidic
and lab-on-a-chip devices.
