Biomedical Engineering Reference
In-Depth Information
surfaces as a uniform surface treatment, or as patterns on
the surface with length scales of millimeters, microns or
even nanometers. There is much interest in deposition of
proteins and cells in surface patterns and textures in
order to control bioreactions (Section 3.2.16). Further-
more, devices ''on a chip'' frequently require patterning.
Such devices include microfluidic systems (''lab on
a chip''), neuronal circuits on a chip, and DNA diagnostic
arrays. An overview of surface patterning methods for
bioengineering applications has been published (Folch
and Toner, 2000).
Photolithographic techniques that were developed for
microelectronics have been applied to patterning of
biomaterial surfaces when used in conjunction with
methods described in this section. For example, plasma-
deposited films were patterned using a photoresist (PR)
lift-off method (Goessl
et al.
, 2001).
Microcontact printing (
m
CP) is a newer method per-
mitting simple modification. Basically, a rubber stamp is
made of the pattern that is desired on the biomaterial
surface (
Fig. 3.2.14-10
). The stamp can be ''inked'' with
thiols (to stamp gold), silanes (to stamp silicon), proteins
(to stamp many types of surfaces) or polymer solutions
(again, to stamp many types of surfaces). Spatial resolu-
tion of pattern features in the nanometer range has been
demonstrated, though most patterns are applied in the
micron range. Methods have been developed to accurately
stamp curved surfaces. An example of cells on laminin-
stamped lines is shown in
Fig. 3.2.14-11
. These laminin
lines were durable for at least 2 weeks of cell contact.
Durability remains a major consideration with patterns on
surface generated by this relatively simple method.
There are many other options to pattern biomaterial
surfaces. These include ion-beam etching, electron-beam
lithography, laser methods, inkjet printers, and stochastic
patterns made by phase separation of two components
(Takahara
et al.,
2000).
a
b
Fig. 3.2.14-11 (a) Microcontact printed lines of laminin protein
(fluorescent labeled) on a cell-resistant background. (b) Car-
diomyocyte cells adhering and aligning on the laminin printed lines
(see J. Biomed. Mater. Res. 60:472 for details) (used with the
permission of P. Stayton, C. Murry, S. Hauschka, J. Angello and
T. McDevitt).
Conclusions
Surface modifications are being widely explored to en-
hance the biocompatibility of biomedical devices and
improve other aspects of performance. Since a given
medical device may already have appropriate perfor-
mance characteristics and physical properties and be well
understood in the clinic, surface modification provides
a means to alter only the biocompatibility of the device
without the need for redesign, retooling for manufacture,
and retraining of medical personnel.
Silicon
a
f
Silanize
Silicon
Silicon
Coat with
silicon
elastomer
(PDMS)
Strip PDMS
from silicon
PDMS
Resist
Coat with resist,
expose
b
g
Silicon
Silicon
Acknowledgment
h
PDMS
c
Develop resist
The suggestions and assistance of Professor J. Lemons
have
Silicon
enhanced
this
section
and
are
gratefully
Ink the stamp
i
PDMS
appreciated.
protein
thiol
silane
polymer
d
Etch
Silicon
j
PDMS
Questions
e
Strip
Silicon
Stamp a
surface
1.
You are assigned the task of designing a proteomics
array for cancer diagnostics. Six hundred and twenty-
five proteins must be attached to the surface of
Fig. 3.2.14-10 Fabrication of a silicone elastomer stamp for mCP.
The sequence of steps is a-j.
