During the fabrication of the microfluidic chamber (check its structure in the file, a 5x2.4mm microfluidic chamber with height of 20 μm), the ceilings of the chamber often collapse when bonding pdms slice to the glass, the already pillar to support the ceiling from collapsing, but wont help out well, is there any other methods i could use to prevent the collapse, with no change to the origin geometric dimension of the chip.
If you can't change the material, the only solution is to add more pillars. They can be much smaller than the one you have. I would fill the chamber with 20-30 small round or elliptical pillars of about 100 µm width.
You seem to be satisfied by Markus' answer. Other readers may be interested in alternatives, though? Thus allow me to suggest further solutions allowing to keep your present chip design:
1. Expand the channel by slight over pressure. Then put 20 µm magnetic beads in the channel with a homogeneous magnetic field perpendicular to the channel. Then release pressure and the beads will support the top wall of your channel.
2. An even simpler, though more demanding solution would be to provide a permanent slight excess pressure with respect to the environment. This may also hinder the collapse. The flow can be controlled by changing inlet and outlet pressures with respect to the mentioned excess pressure.
Precise enough pressure controllers for that can be found at our company or at our competitors.
Cheers, Claus