Biomedical Engineering Reference
In-Depth Information
a
PDMS
PDMS
Si water
PFOCTS layer
Plasma bonding
PDMS
PDMS
PDMS
Detach
PDMS gel
Si water
PDMS
Loading
Plastic plate
PDMS
PDMS
Si water
Repeat that process,
multilayer could be achieved
Heat
PDMS
Detach
PDMS
Si water
b
c
d
e
5
6
5
5
5
6
6
4
4
4
6
4
3
3
1
1
1
3
2
1
3
2
2
2
FIGURE 3.18
Fabrication. of. complex. multilevel. microluidics.. (From. Mengying. Zhang,. Jinbo. Wu,.
Limu.Wang,.Kang.Xiao,.and.Weijia.Wen,.“A.simple.method.for.fabricating.multi-layer.PDMS.struc-
tures. for. 3D. microluidic. chips,”.
Lab Chip
. 10,. 1199-1203,. 2010.. Reproduced. with. permission.
from The.Royal.Society.of.Chemistry.)
monomers are commercially available. he thickness of adhesive required to obtain bonding is
so small that it is compatible with the fabrication/bonding of 200-nm-wide channels.
Fortunately, CVD is not the only route to achieve good bonding. Nae Yoon Lee's group at
Kuyngwon University in Korea has developed a simple, silane-based room temperature pro-
cess to bond PDMS to plastics (PMMA, polycarbonate, polyimide, and PET;
Figure 3.20
). he
PDMS and plastic surfaces are derivatized with aminosilane SAM (APTES) and epoxysilane
SAM (GPTES), respectively, and allowed to react at 25°C for 1 hour—simple! he fact that it
takes 1 whole hour for the bonding to complete is advantageous, as it allows the experimenter
to bring the two surfaces into contact and, if there is a misalignment, there is plenty of time for
a retry (by comparison, oxygen plasma activation of PDMS only allows for a few minutes, at
most). Noting that SU-8 has abundant unreacted epoxy groups on the surface even ater expo-
sure, Gaozhi Xiao's group from the Institute for Microstructural Science in Ontario, Canada has
demonstrated an elegant simpliication of the previous process based on the use of a nitrogen
plasma (because oxygen plasma was being used for PDMS activation before APTES derivatiza-
tion anyways) to introduce surface nitrogen groups on the PDMS: up to 1.9% nitrogen can be
introduced to the PDMS surface in the form of C-NH
2
, C-NRH-, N-C-N, and C=N-, as con-
irmed by X-ray Photoelectron Spectroscopy (XPS) analysis. hese groups then slowly react at
room temperature with the unreacted SU-8 epoxy groups, allowing for the fabrication of hybrid
SU-8/PDMS devices. he Mathies laboratory from the University of California at Berkeley has
fabricated PMMA/PDMS hybrid microvalves (PDMS membrane sandwiched/bonded between
two PMMA slabs) using a very simple PDMS-to-PMMA bonding procedure: exposure of PDMS
and PMMA to a UV ozone cleaner.
