TEMPERATURE-RESPONSIVE CULTURE SURFACES FOR REGENERATIVE MEDICINE - Intelligent Scaffolds for Tissue Engineering and Regenerative Medicine - page 905

to 20 ◦ C, at which point the modified surfaces become hydrophilic
due to PIPAAm's hydration/dehydration transition at 32 ◦ C. In our
preliminary studies, the graft amount of PIPAAm on the surface has
a significant influence on cell adhesion behavior. Here, we focused
on the correlation of the thickness of PIPAAm-grafted (covalently)
layers on tissue culture polystyrene (TCPS) surfaces and cell adhe-
sion/detachment behavior. 18 For this purpose, we utilized limited
excimer laser ablation, time-of-flight secondary ion mass spectrom-
etry (TOF-SIMS) images, and atomic force microscopy (AFM) meth-
ods to determine the thicknessof PIPAAm-graftedlayers. 19 − 21
TwotypesofPIPAAm-graftedTCPSsurfaceswereevaluatedwith
respect to the graft amount of PIPAAm on the surfaces and the
surface thermo-responsive wettability behavior. The grafted poly-
mer amounts on two PIPAAm-grafted surfaces were determined by
attenuated total reflection Fourier transform infrared spectroscopy
(ATR/FT-IR) measurements, which were 1.4 ± 0.1 μ g/cm 2 ( n = 4)
and 2.9 ± 0.1 μ g/cm 2 ( n = 4), respectively. These two sur-
face types are abbreviated as PIPAAm-1.4 and PIPAAm-2.9, respec-
tively, hereafter. PIPAAm-grafted TCPS surfaces were ablated with
a UV excimer laser until the TCPS region was exposed for a sub-
sequent measurement of the graft layer thickness by means of
AFM. The ablated domains were stained with a hydrophobic fluo-
rescent dye, 1,1'-dioctadecyl-3,3,3',3'-tetramethylindocarbocyanine
perchlorate (DiIC18), to elucidate whether the hydrophobic TCPS
regions were exposed. With sharp contrast, the fluorescent dye
selectively and clearly stained the ablated domains with an increas-
ing number of laser shots. The fluorescent intensity for PIPAAm-1.4
is likely to be saturated with six laser shots. This result indicates
that the TCPS region is successfully exposed by six times the laser
ablation. Figure 44.2 shows AFM images and corresponding section
profiles of the ablated domains for PIPAAm-1.4 (a) and PIPAAm-
2.9 (b). The PIPAAm-1.4 surface was relatively smooth, and ablated
areas were clearly observed. This is in sharp contrast with the
relatively rough PIPAAm-2.9 surface. The root mean square (RMS)
valuesofthePIPAAm-1.4andPIPAAm-2.9surfacesbeforelaserabla-
tionwereapproximately7.7and16.5nm,whereasthoseofthenon-
ablated areas shown in Fig. 44.2 were approximately 6.0 nm and
17.2 nm, respectively. The equivalent RMS values before and after
laser ablation indicate that laser ablation with 10 and 20 mJ/cm 2