Poly(N-isopropylacrylamide-co-acrylamide) (PNIAM-co-AM)grafted surfaces have been reported to promote cell adhesion and detachment by a hydrophobic-to-hydrophilic transition triggered by temperature change. However, the surface uniformity and cell detachment consistency are still an issue. In this study, PNIAM-co-AM is prepared with spin coating to control the grafting density and the thickness and to achieve better cell detachment. The atomic force microscopy results indicate that the surface becomes smoother as the spin speed increases. The attenuated total reflection Fourier transform infrared results show a grafting density from 1.68 to 2.03 μg/cm 2 . Ellipsometry suggests that the thickness of the spin-coated PNIAM-co-AM layer is 11−21 nm. The grafted surfaces were tested with mouse preosteoblast MC3T3-E1 cells, which grew successfully. The detachment reached 100 percent with the samples prepared with 1.5 and 2 h ultraviolet exposure times without the use of a poly(vinylidene difluoride) membrane. The detached sheet was in good condition, as indicated by Live/Dead stains.
In this study, a novel temperature-responsive poly(N-isopropylacrylamide)-co-acrylamide was used to prepare a chondrocyte cell sheet. Chondrocytes were isolated from human articular cartilage and plated on the copolymer film grafted tissue culture plates. The cell attachment on the copolymer film was shown to be similar to that of the ungrafted surface. To harvest a cell sheet, the incubation temperature was reduced to 10°C for 30 minutes to allow the polymer chain to fully extend, changing the copolymer's phase from hydrophobicity to hydrophilicity. Additional incubation at 20°C for 60 minutes was necessary to activate the cellular metabolism required for cytoskeletal organization and cell detachment. A complete cell sheet recovery was achieved when a PVDF membrane was used as a cell sheet carrier. Unfortunately, the shrinkage of the cell sheet was observed. Nonetheless, the harvested cell sheet was shown to be viable and healthy.
Poly(N‐isopropylacrylamide‐co‐acrylamide) (PNIAM‐co‐AM) grafted onto tissue culture polystyrene surfaces (TCPSs) with different thicknesses and grafting densities were prepared by varying the spin‐coating speed and UV irradiation time for use in cell sheet engineering. The thickness of the PNIAM grafted surface, less than 30 nm, was believed to influence protein adhesion and cell attachment. However, methods for determining the thicknesses of a thin surface (nanometer scale) are still a challenge. In this study, a model was developed to relate the thickness of the PNIAM‐co‐AM film to its grafting density. Spectroscopic ellipsometry (SE) and attenuated total reflection‐Fourier transform infrared spectroscopy (ATR‐FTIR) with synchrotron radiation were used to quantify the thickness and the grafting density, respectively. The amount of the grafted copolymer was determined from quantitative ATR‐FTIR by relating the signals at wavenumber 1,654 to 1,600 cm−1 (A1,654/A1,600) to the known grafting density. A combination of SE and ATR‐FTIR was used to construct a linear model (h = 6.29σ + 2.24), to obtain the grafting density (σ) from the film thickness (h) with R2 = 0.93. To validate the model, random samples were prepared with different thicknesses and grafting densities. The linear model was used to predict the grafting density, which was nearly equal to the measured values.
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