TiO2 Nanocomposite Films on Polystyrene for Light-Induced Cell

Xiaozhao WangZun ChenBeibei ZhouXiyue DuanWenjian WengKui ChengHuiming WangJun Lin. ACS Applied Materials & Interfaces 2018 10 (14), 11508- ...
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SiO2/TiO2 Nanocomposite Films on Polystyrene for Light-Induced Cell Detachment Application Zhiguo Cheng, Kui Cheng,* and Wenjian Weng* School of Materials Science and Engineering, State Key Laboratory of Silicon Materials, Cyrus Tang Center of Sensor Materials and Applications, Zhejiang University, Hangzhou 310027, China

ABSTRACT: Light-induced cell detachment shows much potential in in vitro cell culture and calls for high-performance lightresponsive films. In this study, a smooth and dense SiO2/TiO2 nanocomposite thin film with thickness of around 250 nm was first fabricated on H2O2 treated polystyrene (PS) substrate via a low-temperature sol−gel method. It was observed that the film could well-adhere on the PS surface and the bonding strength became increasingly high with the increase of SiO2 content. The peeling strength and shear strength reached 3.05 and 30.02 MPa, respectively. It was observed the surface of the film could transform into superhydrophilic upon 20 min illumination of ultraviolet with a wavelength of 365 nm (UV365). In cell culture, cells, i.e., NIH3T3 and MC3T3-E1 cells, cultured on SiO2/TiO2 nanocomposite film were easily detached after 10 min of UV365 illumination; the detachment rates reached 90.8% and 88.6%, respectively. Correspondingly, continuous cell sheets with good viability were also easily obtained through the same way. The present work shows that SiO2/TiO2 nanocomposite thin film could be easily prepared on polymeric surface at low temperature. The corresponding film exhibits excellent biocompatibility, high bonding strength, and good light responses. It could be a good candidate for the surface of cell culture utensils with light-induced cell detachment property. KEYWORDS: SiO2/TiO2, nanocomposite films, polystyrene, light induced, cell detachment TiO2 films,17,18 since TiO2 had good biocompatibility,19 chemical stability,20 nontoxicity,21,22 and ultraviolet light (365 nm, UV365) changeable wettability.23,24 Also, the mechanism of such light-induced detachment was ascribed to protein conformation modulations through light responses of TiO2.3,17,25 Since such cell harvesting is based on conformation variations on materials surfaces, it is reasonable to consider that other biocompatible materials could also make contributions. E.g., SiO2 also has excellent biocompatibility,26−28 and it is reported that the incorporation of SiO2 into TiO2 could improve the light responses of TiO2.29−32 Therefore, it is interesting to investigate the effect of SiO2 incorporation on the light-induced cell detachment performance of TiO2. Moreover, since most of the cell culture utensils are polystyrene, if such

1. INTRODUCTION Currently, in vitro cell culture is one of the most prevalent ways to obtain various species of cells for scientific researches. Due to the fact that cells are generally grown to confluency on tissue culture polystyrene dishes, the harvesting of them becomes a key issue. Conventionally, chelating agents EDTA and proteolytic enzymes, such as Dispase or trypsin, have been used to harvest the cells.1,2 However, these treatments were invasive, which means, cell-to-cell junctions were disrupted and extracellular matrix proteins attached to the culture surface were also damaged. That may affect the proper function of the cells. In some cases, e.g., cell sheets engineering,3−6 a complete cell sheet is even needed. Therefore, cell culture surfaces with easy cells enzyme-free cell release ability may have much potential. In order to harvest cells and cell sheets without compromising their functions, thermoresponsive,7−9 pHresponsive,10,11 magnetism-induced12−14 and electricity-induced15,16 methods are developed. In our previous study, a light-induced cell detachment method was developed based on © XXXX American Chemical Society

Received: November 5, 2016 Accepted: December 27, 2016 Published: December 27, 2016 A

DOI: 10.1021/acsami.6b14182 ACS Appl. Mater. Interfaces XXXX, XXX, XXX−XXX

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Figure 1. SEM images of original PS substrate (a), H2O2 treated PS (b), TiO2 film on H2O2 treated PS substrate (c), HSTN film (inset, EDS spectrum) (d), STN film (e), and the cross-section image of HSTN film (Si/Ti = 0.2) (f).

films are directly fabricated on polystyrene, cell culture utensils with enzyme-free cell release ability could be expected. In this study, a new route was developed to prepare SiO2/ TiO2 nanocomposite films on polystyrene. The effects of SiO2 existence and H2O2 pretreatment on film properties, as well as the light-induced cell detachment performance of the films, were investigated and discussed.

including peeling strength and shear strength, was measured by universal testing machine with 3 M adhesive tapes (Minnesota Mining and Manufacturing, 3M610). Three replicated samples were characterized for all films. The chemical composition of the composite film was characterized by energy dispersive spectroscopy attached on the SEM and X-ray photoelectron spectroscopy (XPS, Kratos AXIS ULtra DLD; Al Kα, 1486.6 eV). For XPS characterization, detailed scans for O, Si, and Ti were also carried out and calibrated with C 1s peak (284.6 eV). The data obtained were further analyzed with the software of XPS Peak 4.1. 2.3. Cell Culture. Mouse NIH3T3 and preosteoblastic MC3T3-E1 cells were used as the model cells. Subconfluent NIH3T3 and MC3T3-E1 on PS dishes were harvested with 0.25% trypsin/EDTA (Gibco) and were subcultured on HSTN films or on PS substrates with Dulbecco’s modified eagle medium (DMEM, Gibco) and Alpha modified minimum essential medium (MEM; Alpha, Gibco), supplemented with 10% fetal bovine serum (FBS; PAA, Morningside, QLD, Australia), 1% antibiotic solution containing 10,000 units/(mL of penicillin), 10,000 mg/(mL of streptomycin) (Gibco), 1% sodium pyruvate (Gibco), and 1% MEM nonessential amino acids (Gibco). The cell culture was carried out in a humidified atmosphere with 5% CO2 at 37 °C. For cell culture, the films were washed three times with ethanol and deionized water, and then sterilized for 1 h with 254 nm ultraviolet irradiation. The films were placed into a 24-well culture plate; then NIH3T3 and MC3T3-E1 cells were seeded on the films at a cell density of 5 × 104 cells/cm2, respectively. The cells were further incubated in Dulbecco’s modified eagle medium (DMEM) at 37 °C under a humidified 5% CO2 atmosphere. After culturing for 1, 3, and 5 days, Cell Counting Kit-8 (CCK-8, Dojingdo Laboratories, Kumamoto, Japan) solution was added in the wells at a concentration ratio of 1/10 with the culture solution. Three hours later, the optical OD value was measured at 450 nm with a microplate reader. As a control, cells seeded on blank PS substrates were also tested for OD value. 2.4. Cell Detachment Assay. NIH3T3 and MC3T3-E1 cells were seeded on HSTN films (1 mm × 1 mm) and PS substrates at a final cell density of 5 × 104 cells/cm2 and cultured for 24 h, respectively. A ultraviolet source (365 nm, 2.0 mW/cm2) was used to illuminated the samples from the back, and its transmittance power was also measured to be 1.4 mW/cm2. Before UV365 illumination, the samples were observed with a phase contact microscope (CKX41, Olympus, Tokyo) and then rinsed gently three times with phosphate buffered saline (PBS). Then the 24 h cultured samples were placed above the UV365 illumination for 5, 10, 15, and 20 min, respectively. After that, the samples were rinsed gently with PBS again and transferred to another 24-well plate. Then, 500 μL of fresh culture medium was added to each well, followed by a 50 μL of Cell Counting Kit-8 (CCK-8, Dojingdo Laboratories) solution addition. Samples were placed in the incubator for 3 h at 37 °C, and 120 μL culture medium was dispensed into a 96-well plate; then colorimetric measurement was displayed on

2. EXPERIMENTAL SECTION 2.1. Film Preparation. The polystyrene substrates (PS, Nanteng Co., Shenzhen, China; 10 mm × 10 mm) were washed twice with deionized water and ethanol. Then, the substrates were ultrasonically cleaned in deionized water for 20 min. After that, the substrates were immersed in H2O2 solution (Sinopharm Chemical Reagent; AR, 30 wt %) for 12 h for surface activation.33 SiO2/TiO2 nanocomposite films were prepared on H2O2 treated PS substrate (HSTN) through a sol−gel based method. Briefly, a SiO2 precursor sol was prepared with the following procedure: a mixture of 2 mL of tetraethyl orthosilicate (TEOS; Aladdin; GC, >99%), 10 mL of tetrahydrofuran (THF; Sinopharm; AR, ≥99.0%), 0.2 mL of HNO3 (Sinopharm; AR, 65−68%) was put into a flask to stir for 15 min; a mixture of 0.9 mL of deionized water and 4.6 mL of ethanol was then added to that mixed solution and further stirred for 60 min, aged for 2 days to be the Si precursor. After that, Si precursor sol and TiO2 collosol (Hunan Taitang Nano Technology Co. Ltd.; 20 wt %) with different Si/Ti molar ratios were mixed to be the final mixed precursor sol. For film preparation, the mixed precursor sol was spin-coated on H2O2 treated PS substrate with a rate of 7000 rpm for 40 s. Then the coated substrates were placed in an oven held at 70 °C in order to remove volatile tetrahydrofuran, which is harmful for cells. After 24 h, the film (HSTN) was ready for further characterization. SiO2/TiO2 nanocomposite films were also prepared on PS substrates without H2O2 treatment to be the control (STN). 2.2. Film Characterization. The morphologies and the surface roughness of original PS substrate, H2O2 treated substrate, TiO2, STN and HSTN film were analyzed with scanning electron microscope (SEM; Hitachi, Su-70) and atomic force microscopy (AFM; NTEGRA Spectra, NTMDT). The final mixed precursor sols were dried following the same process as that of the films, and then the X-ray diffraction (XRD) patterns were examined with X-ray diffractometer (PANalytical, X’Pert PRO) to identify the crystalline phase of the films. Raman spectra were also taken on the HSTN samples (Thermo Fisher Scientific, DXR532, with a 532 nm laser). The static water contact angles of the surfaces were measured with a contact angle meter (Dataphysics, OCA20). Before measurement, all of the samples were stored in vacuum and kept in the dark for 8 h at 70 °C. For the contact angle after ultraviolet illumination, an ultraviolet lamp with wavelength of 365 nm was used to illuminate the films for 20 min. The overall bonding of the films was evaluated through a water rinsing method. The bonding strength between film and substrates, B

DOI: 10.1021/acsami.6b14182 ACS Appl. Mater. Interfaces XXXX, XXX, XXX−XXX

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ACS Applied Materials & Interfaces the microplate reader at 450 nm. The detachment ratio of cells could be calculated from the fitting curve. For cell sheets, cells with a density of 1 × 105 cells/cm2 were seeded on the samples in tissue culture dishes. After culturing for 3 days, the confluent cell sheet was obtained. Then through UV365 illumination for 10 min, the detached cell sheet was acquired readily. This UV-light detachment method was carried out gently and quickly, and it did not damage the cell-to-cell junction. A freshly harvested cell sheet surface was analyzed for viability by using a live−dead stain. For live and dead evaluation, the cell sheet was placed in the live−dead solution for 20 min after rinsing three times with PBS buffer solution. The live−dead solution consisted of calceinAM and propidium iodide (PI).34,35 After washing three times with PBS again, the cell sheet was examined by using the fluorescence microscope (1 × 81; Olympus, Tokyo, Japan). Live cells were stained by the calcein-AM with fluorescent green color, and the dead cells were stained by PI with fluorescent red color. As a negative control, another piece of peeled cell sheet was also tested after using 3 min cytocidal treatment in ethanol by following the same procedure.

dimensional representation of the surface morphology was shown in Figure 2. The measured average roughness values for original PS substrate (Figure 2a), H2O2 treated substrate (Figure 2b), TiO2 film (Figure 2c), HSTN film (Figure 2d), and STN film (Figure 2e) were found to be 2.2, 1.1, 10.2, 5.3, and 4.6 nm, respectively. These results further confirmed the effects of H2O2 treatment of the substrate and SiO2 presence in the films. Figure 3 showed the XRD patterns of PS, STN, and HSTN. In Figure 3a, PS displayed an amorphous region centered at 19.47° which could be assigned to the existence of hard aromatic ring segments in the polystyrene. The XRD patterns of STN (Figure 3b) and HSTN (Figure 3c) were obtained from dried gel powders (STN and HSTN). The peaks at 25.35°, 37.83°, and 48.08° were clearly observed, and wellindexed to the (101), (004,) and (200) lattices of the anatase phase of TiO2. However, to the best of our knowledge, there were still several peaks on the XRD patterns of STN film and HSTN film that remain unknown. Probably, they were complex compounds containing organics. In Figure 4, the anatase phase of TiO2 could be also identified through Raman spectrum. The strong peak at 144 cm−1 represented Eg mode of the anatase phase according to the literature.18 Such Raman results were consistent with the XRD pattern. Nevertheless, both the XRD patterns and Raman spectrum showed no obvious signal of SiO2. That might be ascribed to the low content or the amorphous state of SiO2 in the films.31 3.2. Surface Chemical Groups and Property. As a cell culture surface, the surface will be in contact with cells directly. The surface composition would be more important in controlling cellular responses. Therefore, the chemical composition of the HSTN film surface was further characterized. In Figure 5a, it was found that the film contained Si, Ti, O, and C; no other elements were found, which was wellconsistent with the EDS result. However, Figure 5b showed that the H2O2 treated PS substrate promoted a significant decrease of the O 1s content, compared with the original PS substrate. That also demonstrated the effective removal of organic contaminants. Panels c and d of Figure 5 showed the XPS high-resolution spectra of Si 2p and Ti 2p of HSTN film. The Si 2p XPS spectrum of the film showed three distinct peaks. The peaks at 101.51 and 102.51 eV were ascribed to Si−O−H and Si−O−C, respectively,36 while the peak at 100.75 eV was attributed to Si−O−Si chain, indicating the existence of SiO2. For the Ti 2p XPS spectrum, four distinct peaks, which mean two different chemical states of Ti atoms, were observed. The peaks at 459.62 and 465.18 eV were attributed to 2p3/2 and 2p1/2 of Ti3+, and the peaks at 457.80 and 463.39 eV were attributed to 2p3/2 and 2p1/2 of Ti4+,37 indicating the presence of TiO2 on the surface of HSTN. Based on the XPS results, the atomic percentages of the surface are as follows: 5.7% for Si, 17.8% for Ti, 46.3% for O, and 29.2% for C. That means the majority of the HSTN film surface is a composite of SiO2 and TiO2. However, in comparison with the EDS result in Table 1, the surface composition showed significant decrease of O content. The reason is assumed to be that there might be some unhydrolyzed TEOS molecules residual that existed inside the film, or hydroxyl groups adsorption at the film−substrate interface. There were many reports that the surface of TiO2 could turn into superhydrophilic after ultraviolet illumination. As shown in

3. RESULTS AND DISCUSSIONS 3.1. Films Morphology and Crystalline Phase. Topography micrographs of different samples were shown in Figure 1. The original polystyrene substrate (Figure 1a) was rough, and after H2O2 treatment, as shown in Figure 1b, it became smooth and flat. That indicated the surface adsorption, including organic contaminants adhered on the surface, was removed. The reason is ascribed to that H2O2 decomposition could produce hydroxyl radicals with strong oxidizing ability. That will oxidize most of the organic contaminants and remove them, leading to a smooth and flat surface.33 In Figure 1c, it was observed that no continuous film formed on PS with TiO2 collosol. That is attributed to the hydrophobicity of the PS surface. The poor wetting between hydrophilic TiO2 collosol and PS surface makes it difficult to obtain smooth TiO2 film directly. In comparison with that, both of the HSTN (Figure 1d) and STN films (Figure 1e) were continuous and compact. That is owing to the mixed Si/Ti precursor sol. The existence of TEOS and tetrahydrofuran can improve the wettability between sol and the PS surface. That allows better wetting behavior of the sol. As a result, as shown in the cross-section micrographs of HSTN film (Figure 1f), it was found that SiO2/ TiO2 nanoparticles closed attached on the PS substrate. The thickness of the HSTN film was about 250 nm. The typical EDS spectrum of the HSTN film (inset of Figure 1d) showed that elements of Si, Ti, O, and C were observed, and the chemical composition results of all samples with different Si/Ti molar ratios were tabulated in Table. 1. Since the Ti amount was higher than that of Si, the film was actually a SiO2/TiO2 nanocomposite film with TiO2 as the main part. It is noteworthy that the O content is higher than it should be in SiO2 and TiO2. That will be discussed later. The topographical image and average roughness of these samples surfaces were also captured using AFM. The threeTable 1. Typical Chemical Composition of HSTN Films (Si/ Ti = 0.05, 0.1, 0.15, and 0.2) atomic percentage (%) sample (Si/Ti)

C

O

Si

Ti

0.05 0.1 0.15 0.2

73.04 77.52 77.55 77.53

25.22 21.1 21.08 21.11

0.99 0.14 0.19 0.26

1.66 1.24 1.18 1.1 C

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Figure 2. AFM images of original PS substrate (a), H2O2 treated PS (b), TiO2 film on H2O2 treated PS substrate (c), HSTN film (d), and STN film (e).

surface. However, when Si/Ti molar ratio reached 0.2, the WCA of composite film after ultraviolet irradiation remained at over 10°. The reason was ascribed to PS occupying more sites on the surface of the film, which, in turn, reduced the total amount of light-induced hydroxyl groups. As a result, the lightinduced hydrophilic transition became weaker. Such a result indicates the amount of light-induced hydroxyl groups could be well-tailored through film composition and subsequent UV365 illumination. That may potentially provide better control of the cellular responses. 3.3. Bonding Strength of the Films. In Figure 7, after rinsing, quite different morphology of the films was observed. In Figure 7a, almost nothing was left for TiO2 films, while, for HSTN film in Figure 7b, one was hardly able to find any changes. That means the bonding strength of the HSTN films is much higher than that of TiO2 film. In order to further evaluate the bonding strength of the films, the peeling and shear strength of the films were tested. The typical profiles of them were shown in Figure 8. For films with increasing Si/Ti molar ratio, the corresponding peeling strengths were measured to be 0.83 MPa for Si/Ti = 0.05 without H2O2 treatment, 1.39 MPa for Si/Ti = 0.05 with H2O2 treatment, and 3.05 MPa for Si/Ti = 0.2 with H2O2 treatment. For the shear strength, they were 24.49 MPa for Si/Ti = 0.05 without H2O2 treatment, 29.47 MPa for Si/Ti = 0.05 with H2O2 treatment, and 30.02 MPa for Si/Ti = 0.2 with H2O2 treatment, respectively. Clearly, both the peeling strength and shear strength follow the same trend: higher Si/Ti molar ratio and H2O2 treatment are beneficial for higher bonding strength of the films. That was mainly attributed to the following reasons: (1) Increased Si/Ti ratio means more Si precursor sol and more tetrahydrofuran. Polystyrene is somehow soluble in tetrahydrofuran. During the preparation, some PS molecules may be dissolved and then separate out. That promotes some TiO2 and SiO2 nanoparticles to be embedded in polystyrene surface and then enhances the interlocking between the films and substrate. Such interlocking may eventually improve the bonding. (2) H2O2 is oxidative; it is supposed that some contaminant adsorbed on the surface will be oxidized and then removed. Polarized groups, such as hydroxyl groups may then be adsorbed on the surface and lead to improved hydrophilicity. Such improvement could effectively reinforce the bonding between the film and PS substrate. 3.4. Cytocompatibility and Cell Detachment Assay. Since such composite films are developed for biomedical application, the cellular responses are very important. In fact,

Figure 3. XRD patterns of PS (a), STN film (b), and HSTN film (c).

Figure 4. Raman spectrum of HSTN film.

Figure 6, the initial water contact angle (WCA) of HSTN films before UV-light illumination increased with increasing Si/Ti molar ratio. That could be ascribed to minor PS could exist on the surface due to dissolution of PS in tetrahydrofuran (the contact angle of PS is around 90 o). Since higher Si/Ti ratio will lead to more tetrahydrofuran in the precursor sol, more PS could be dissolved and then separated out at the surface. That will increase the water contact angle. After ultraviolet irradiation, films with Si/Ti molar ratio of 0.05, 0.1, and 0.15 turned into superhydrophilic. The increase of hydrophilicity of these films could be attributed to formation of the polar functional groups, i.e., a light-induced hydroxyl group on a TiO2 D

DOI: 10.1021/acsami.6b14182 ACS Appl. Mater. Interfaces XXXX, XXX, XXX−XXX

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Figure 5. Typical XPS spectra of different samples: survey scan of HSTN film with Si/Ti = 0.2 (a), detailed scan of PS substrate before and after H2O2 treatment (b), Si 2p (c), and Ti 2p (d) of HSTN film.

MC3T3-E1 cells on the films characterized with CCk-8 kits. Similar adhesion was observed on HSTN film and bare PS substrate (1 day). As for proliferation, the initial proliferation was similar for HSTN film and bare PS substrate (3 days), while improved cell proliferation was observed on HSTN film at elongated time (5 days). That means, HSTN film coated PS substrate could show similar or even better cellular responses in comparison with bare PS. In general, in view of the good bonding strength and cellular responses of HSTN film, it could be a good candidate for PS based cell culture utensils with improved cellular responses. Cells attached and spread very well on the HSTN after culturing for 24 h. Figure 10 showed that the detachment ratios of NIH3T3 and MC3T3-E1 cells on HSTN was very high only after a short period of UV365 illumination (10 min); they could reach 90.8% and 88.6%, respectively, while further elongated UV365 illumination time had few changes on the cells detachment ratio. In fact, the cells detachment ratio at 90.8%

Figure 6. Water contact angles of HSTN film with different Si/Ti molar ratios before and after ultraviolet irradiation.

PS is the most commonly used materials in in vitro cell culture. Figure 9 showed the adhesion and proliferation of NIH3T3 and

Figure 7. SEM images displaying the morphology of TiO2 film (a) and HSTN film (b) after 1 min water rinsing. Insets indicated the corresponding morphology before rinsing. E

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Figure 8. Schematic diagram of peeling strength characterization (a), typical HSTN film peeling strength curve (b), SEM micrograph of postpeeling HSTN film (c), schematic diagram of shear bond strength characterization (d), typical HSTN film shear strength curve (e), and SEM micrograph of postshearing HSTN film (f). The Si/Ti ratio of typical HSTN film was 0.2.

Figure 9. CCK-8 results of HSTN film with Si/Ti = 0.2. NIH3T3 (a) and MC3T3-E1 (b).

Figure 10. Light-induced cell detachment from HSTN film with different UV365 illumination times: NIH3T3 (a) and MC3T3-E1 (b).

extracellular matrix detached from the HSTN surface spontaneously. The detached cell sheets were further assessed by live−dead staining method. In Figure 11, obviously, in contrast with the ethanol treated cell sheets, both NIH3T3 and MC3T3-E1 cell sheets detached from HSTN films showed the cells to be alive and had good activity. That means the HSTN

or 88.6% is comparable to that with trypsin treatment, which is usually around 85%. For cell sheet harvesting, the confluent NIH3T3 and MC3T3-E1 cell sheets were formed after culturing cells on HSTN for 3 days, respectively. After 10 min UV365 illumination, these continuous, intact cell sheets with F

DOI: 10.1021/acsami.6b14182 ACS Appl. Mater. Interfaces XXXX, XXX, XXX−XXX

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Figure 11. Viability of detached cell sheets demonstrated by live−dead staining: NIH3T3 (a) and MC3T3-E1 (b).

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film could be well-utilized in cell sheets harvest through light illumination.

(1) Yamato, M.; Akiyama, Y.; Kobayashi, J.; Yang, J.; Kikuchi, A.; Okano, T. Temperature-responsive Cell Culture Surfaces for Fegenerative Medicine with Cell Sheet Engineering. Prog. Polym. Sci. 2007, 32, 1123−1133. (2) Yang, J.; Yamato, M.; Kohno, C.; Nishimoto, A.; Sekine, H.; Fukai, F.; Okano, T. Cell Sheet Engineering: Recreating Tissues without Biodegradable Scaffolds. Biomaterials 2005, 26, 6415−6422. (3) Hong, Y.; Yu, M. F.; Weng, W. J.; Cheng, K.; Wang, H. M.; Lin, J. Light-induced Cell Detachment for Cell Sheet Technology. Biomaterials 2013, 34, 11−18. (4) Byambaa, B.; Konno, T.; Ishihara, K. Cell Adhesion Control on Photoreactive Phospholipid Polymer Surfaces. Colloids Surf., B 2012, 99, 1−6. (5) Byambaa, B.; Konno, T.; Ishihara, K. Detachment of Cells Adhered on the Photoreactive Phospholipid Polymer Surface by Photoirradiation and Their Functionality. Colloids Surf., B 2013, 103, 489−495. (6) Patel, N. G.; Zhang, G. Responsive Systems for Cell Sheet Detachment. Organogenesis 2013, 9, 93−100. (7) Yang, J.; Yamato, M.; Shimizu, T.; Sekine, H.; Ohashi, K.; Kanzaki, M.; Ohki, T.; Nishida, K.; Okano, T. Reconstruction of Functional Tissues with Cell Sheet Engineering. Biomaterials 2007, 28, 5033−5043. (8) Hatakeyama, H.; Kikuchi, A.; Yamato, M.; Okano, T. Biofunctionalized Thermoresponsive Interfaces Facilitating Cell Adhesion and Proliferation. Biomaterials 2006, 27, 5069−5078. (9) Elloumi Hannachi, I.; Itoga, K.; Kumashiro, Y.; Kobayashi, J.; Yamato, M.; Okano, T. Fabrication of Transferable Micropatternedco-cultured Cell Sheets with Microcontact Printing. Biomaterials 2009, 30, 5427−5432. (10) Chen, Y. H.; Chung, Y. C.; Wang, I. J.; Young, T. H. Control of Cell Attachment on pH-responsive Chitosan Surface by Precise Adjustment of Medium pH. Biomaterials 2012, 33, 1336−1342. (11) Guillaume-Gentil, O.; Semenov, O. V.; Zisch, A. H.; Zimmermann, R.; Voros, J.; Ehrbar, M. pH-controlled Recovery of

4. CONCLUSIONS In this study, SiO2/TiO2 nanocomposite films were prepared on PS substrate at low temperature. It was found that the bonding strength between the films and PS substrate becomes increasingly high with the increase of Si content. Moreover, H2O2 treatment effectively improved the bonding strength. The highest peeling strength and shear strength reached 3.05 and 30.02 MPa, respectively. NIH3T3 and MC3T3-E1 cells could well-attach and proliferate on such films. The corresponding cell sheets with good function could easily detach from the film through 10 min UV365 illumination. Such films show much potential in in vitro cell culture and tissue engineering application.

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REFERENCES

AUTHOR INFORMATION

Corresponding Authors

*(K.C.) E-mail: [email protected]. *(W.W.) E-mail: [email protected]. ORCID

Wenjian Weng: 0000-0002-9373-7284 Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS This work is financially supported by the National Natural Science Foundation of China (Grant Nos. 51372217, 31570962, 51472216, and 51272228), The Key Science Technology Innovation Team of Zhejiang Province (Grant No. 2013TD02), and Zhejiang Provincial Natural Science Foundation (Grant No. LY15E020004). G

DOI: 10.1021/acsami.6b14182 ACS Appl. Mater. Interfaces XXXX, XXX, XXX−XXX

Research Article

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DOI: 10.1021/acsami.6b14182 ACS Appl. Mater. Interfaces XXXX, XXX, XXX−XXX