**2. Wettability on TiO2 nanostructures by electrochemical anodization**

Wettability of solid surfaces is a very important property of solid surface. Surfaces with extreme wetting properties, e.g. superhydrophilic and superhydrophobic, can be prepared by introducing certain rough structures on the originally "common" hydrophilic and hydrophobic surfaces. Various ways of preparing TiO2 semiconductor films on the different solid substrates have been developed, including sol-gel technique (Shen et al., 2005), sputtering (Takeda et al., 2001), chemical vapor deposition (Rausch & Burte, 1993), liquid phase deposition (Katagiri et al., 2007), hydrothermal (Yun et al., 2008), and electrochemical anodizing. Among them, the electrochemical anodizing is verified to be a convenient technique for fabricating nanostructured TiO2 films on titanium substrates (Lai et al., 2004, 2008b, 2009c; Gong et al., 2003). Moreover, the conductive titanium support substrate can be an advantage for fabricating functional material composites through electrochemical depositions to further improve their photoelectrochemical activities.

Figure 1a shows a typical FESEM image of the titanium substrate before electrochemical anodization. The surface of the substrate was relatively smooth, with features of parallel polished ridges and grooves at the micron scale (Lai et al., 2010a). Figure 1b shows the top view SEM image of the typical TiO2 nanotube array film by anodizing under 20 V for 20 min. After anodization, shallow cavities as large as several micrometers in diameter were present on the surface of the sample. This is probably due to the anisotropic oxidation of the underlying Ti grains (Crawford & Chawla, 2009; Yasuda et al., 2007). From the high magnification image (Fig. 1c), it can be seen that vertically aligned TiO2 nanotubes with inner diameter of approximately 80 nm covered the entire surface including the shallow polygonal micropits. The side view image shows that the self-assembled layers of the TiO2 nanotubes were open at the top and closed at the bottom with thickness about 350 nm (inset of Fig. 1c). Water droplet can quickly spread and wet the as-grown vertically aligned TiO2 nanostructure film due to capillary effect caused by the rough porous structure, indicating such TiO2 structure film by electrochemical anodizing is superhydrophilic. A more hydrophobic behaviour, on the other hand, was obtained after coating the TiO2 film with fluoroalkyl silane. The inset of Fig. 1b shows the intrinsic contact angle (CA) on the asprepared vertically aligned TiO2 nanotube surface and its corresponding 1*H*,1*H*,2*H*,2*H*perfluorooctyltriethoxysilane (PTES, Degussa Co., Ltd.) modified surface is nearly 0o (superhydrophilic) and 156o (superhydrophobic), respectively. However, the CA for the "flat" TiO2 surface and its corresponding PTES modified sample is about 46o (hydrophilic) and 115o (hydrophobic), respectively. From these results, we know the top surface of the vertically aligned nanotubes has an amplification effect to make hydrophilic and hydrophobic surfaces become superhydrophilic and superhydrophobic, respectively. After UV irradiation for 30 min, the water CA on the TiO2 nanotube film and "flat" TiO2 film decreased to 0o and 26o, as a consequence of the photocatalytic activity of TiO2 films (Balaur et al., 2005; Lai et al., 2010a). Moreover, the sample showed hydrophobic character once again when it was treated with PTES. Therefore the surface can be reversibly switched between superhydrophobic and superhydrophilic by alternating SAM and UV photocatalysis on the rough TiO2 nanotube arrays (shown in Fig. 1d). Compared with the large wettability contrast on this type of rough surface (larger than 150o), the wettability of a "flat" TiO2 film can only be reversibly changed within the small range between 26o and 115o.

Extremely Wetting Pattern by Photocatalytic Lithography and Its Application 595

from concave to convex (Figure 3a). This could result in an increased volume of air sealed in each nanotube by the liquid/air interface. According to Boyle's law (West, 1999), there is an inverse relationship between the volume (V) and pressure (P) for an ideal gas under the conditions of constant temperature and quality. Therefore, this expansion of air would result in the formation of a negative pressure (ΔP). In this case, the volume of air sealed in the nanotubes was varied by their depths, so longer tubes would be expected to have lower air-expansion ratios (ΔV/V), thus lesser negative pressures. For a fixed nanotube diameter, a longer nanotube would therefore require a smaller pulling-off force, and the total surface

Fig. 2. Schematic models, SEM images and corresponding water behavior on three types of superhydrophobic porous-nanostructure with water adhesive forces ranging from high to low. (a) Superhydrophobic NPA with high adhesion. (b) Superhydrophobic NTA with controllable adhesion. (c) Superhydrophobic NVS with extremely low adhesion.

Figure 3b shows the curves of the water CAs and adhesive forces with respect to the diameter of individual nanotube. When the nanotube diameter decreases, the force drastically increased, while the CA slightly decreased. When the diameter was tuned from 78 nm down to 38 nm, the surface adhesive force of the superhydrophobic NTA film increased 2.06 times, while the decline in magnitude of the water CA was not more than 2%, showing that the negative pressure caused by the volume change of air sealed in the nanotubes could effectively tune the surface adhesive force. The NTA structures in this study had variable length, with values of (0.35 ± 0.04) µm, (0.76 ± 0.05) µm, (1.18 ± 0.07) µm, while their diameter (~80 nm) was fixed. Figure 3c shows the curves for water CAs and adhesive forces obtained with PTES-modified NTA-nanostructure surfaces differing in nanotube length. With lengths extending from 0.35 µm to 0.76 µm and 1.18 µm, the CA change was very small, not more than 2%, which could be due to the minor variation in nanotube diameter. However, the adhesive force linearly decreased from 21.5 µN down to 16.7 µN and 12.2 µN for the above increases in length, respectively. It was evident that the water adhesive force of the superhydrophobic NTA-nanostructure surfaces could be tuned by varying the diameters and also lengths of the nanotubes. These findings are valuable to deepen insight into the roles of nanostructures in tailoring surface water-repellent and

adhesive properties for exploring new applications.

adhesive force would be smaller.

Fig. 1. SEM images of the mechanically polished and cleaned titanium substrate (a), low magnification of a nanotube structured TiO2 film (b), and a higher magnification of the TiO2 nanotube array film (c). Reversible surface wettability on a ''flat'' TiO2 film and rough nanotube TiO2 film by alternating SAM and UV photocatalysis (d). The inset of (b) shows the shape of a water drop on the PTES-modified and UV-irradiated TiO2 nanotube array film. The inset of (c) shows the side view of a TiO2 nanotube array film.

Recently, we designed three types of superhydrophobic nanostructure models consisting of a nanopore array (NPA), a nanotube array (NTA), and a nanovesuvianite structure (NVS) apply a facile electrochemical process (Figure 2) (Lai et al., 2009a). Based on basic principles of roughness-enhanced hydrophobicity and capillary-induced adhesion, these different porous structures were expected to create interfaces with decreasing adhesive forces. The surface adhesive forces could be effectively tuned by solid–liquid contact ways at the nanoscale and air-pocket ratio in open and sealed systems. The magnitude of the adhesive force of a droplet for a superhydrophobic surface descends in the order "area-contact" > "line-contact" > "point-contact". A continuous three-phase (solid–air–liquid) contact line (TCL) generates serious CA hysteresis and surface adhesion, while a discrete TCL is energetically advantageous to drive a droplet off a superhydrophobic surface, showing lower surface adhesion. Therefore, the water droplet behavior on these superhydrophobic surfaces could be greatly changed from pinning to sliding by adjusting the solid-liquid contact way.

Capillary adhesive force plays a dominant role in imparting adhesive behavior on NPA and NTA nanostructures will sealed cells, while the open NVS nanostructure, which had extremely low adhesion capacity for water, acted solely by van der Waals attraction between water and PTES molecules. A possible explanation is as follows. As the droplet gradually retracted from the sample surface, the meniscus on each nanotube nozzle would be changed

Fig. 1. SEM images of the mechanically polished and cleaned titanium substrate (a), low magnification of a nanotube structured TiO2 film (b), and a higher magnification of the TiO2 nanotube array film (c). Reversible surface wettability on a ''flat'' TiO2 film and rough nanotube TiO2 film by alternating SAM and UV photocatalysis (d). The inset of (b) shows the shape of a water drop on the PTES-modified and UV-irradiated TiO2 nanotube array

Recently, we designed three types of superhydrophobic nanostructure models consisting of a nanopore array (NPA), a nanotube array (NTA), and a nanovesuvianite structure (NVS) apply a facile electrochemical process (Figure 2) (Lai et al., 2009a). Based on basic principles of roughness-enhanced hydrophobicity and capillary-induced adhesion, these different porous structures were expected to create interfaces with decreasing adhesive forces. The surface adhesive forces could be effectively tuned by solid–liquid contact ways at the nanoscale and air-pocket ratio in open and sealed systems. The magnitude of the adhesive force of a droplet for a superhydrophobic surface descends in the order "area-contact" > "line-contact" > "point-contact". A continuous three-phase (solid–air–liquid) contact line (TCL) generates serious CA hysteresis and surface adhesion, while a discrete TCL is energetically advantageous to drive a droplet off a superhydrophobic surface, showing lower surface adhesion. Therefore, the water droplet behavior on these superhydrophobic surfaces could be greatly changed from pinning to sliding by adjusting the solid-liquid

Capillary adhesive force plays a dominant role in imparting adhesive behavior on NPA and NTA nanostructures will sealed cells, while the open NVS nanostructure, which had extremely low adhesion capacity for water, acted solely by van der Waals attraction between water and PTES molecules. A possible explanation is as follows. As the droplet gradually retracted from the sample surface, the meniscus on each nanotube nozzle would be changed

film. The inset of (c) shows the side view of a TiO2 nanotube array film.

contact way.

from concave to convex (Figure 3a). This could result in an increased volume of air sealed in each nanotube by the liquid/air interface. According to Boyle's law (West, 1999), there is an inverse relationship between the volume (V) and pressure (P) for an ideal gas under the conditions of constant temperature and quality. Therefore, this expansion of air would result in the formation of a negative pressure (ΔP). In this case, the volume of air sealed in the nanotubes was varied by their depths, so longer tubes would be expected to have lower air-expansion ratios (ΔV/V), thus lesser negative pressures. For a fixed nanotube diameter, a longer nanotube would therefore require a smaller pulling-off force, and the total surface adhesive force would be smaller.

Fig. 2. Schematic models, SEM images and corresponding water behavior on three types of superhydrophobic porous-nanostructure with water adhesive forces ranging from high to low. (a) Superhydrophobic NPA with high adhesion. (b) Superhydrophobic NTA with controllable adhesion. (c) Superhydrophobic NVS with extremely low adhesion.

Figure 3b shows the curves of the water CAs and adhesive forces with respect to the diameter of individual nanotube. When the nanotube diameter decreases, the force drastically increased, while the CA slightly decreased. When the diameter was tuned from 78 nm down to 38 nm, the surface adhesive force of the superhydrophobic NTA film increased 2.06 times, while the decline in magnitude of the water CA was not more than 2%, showing that the negative pressure caused by the volume change of air sealed in the nanotubes could effectively tune the surface adhesive force. The NTA structures in this study had variable length, with values of (0.35 ± 0.04) µm, (0.76 ± 0.05) µm, (1.18 ± 0.07) µm, while their diameter (~80 nm) was fixed. Figure 3c shows the curves for water CAs and adhesive forces obtained with PTES-modified NTA-nanostructure surfaces differing in nanotube length. With lengths extending from 0.35 µm to 0.76 µm and 1.18 µm, the CA change was very small, not more than 2%, which could be due to the minor variation in nanotube diameter. However, the adhesive force linearly decreased from 21.5 µN down to 16.7 µN and 12.2 µN for the above increases in length, respectively. It was evident that the water adhesive force of the superhydrophobic NTA-nanostructure surfaces could be tuned by varying the diameters and also lengths of the nanotubes. These findings are valuable to deepen insight into the roles of nanostructures in tailoring surface water-repellent and adhesive properties for exploring new applications.

Extremely Wetting Pattern by Photocatalytic Lithography and Its Application 597

Fig. 4. Schematic outline of the procedures to fabricate nanostructured patterning film by electrochemical deposition based on superhydrophilic-superhydrophobic micropattern (a). Survey-scan X-ray photoelectron spectra of the PTES modified nanotube TiO2 films before (1) and after (2) 20 min UV irradiation (b). The high-resolution spectra of Si2*p* and C1*s*

Figure 5 shows the optical micrograph of the as-obtained superhydrophilic– superhydrophobic pattern by focusing on the droplet within the superhydrophilic regions. A uniform pattern is formed due to the site-selective wetting by water droplets within the superhydrophilic regions (Fig. 5a). A light dot array (inset of Fig. 5a) is seen when focusing on the top of the droplets, indicating that the confined droplet has a hemispherical dome. To further verify the resulting micropatterns with an extreme wettability contrast, fluorescein sodium was used as a probe to label the surface of the films. Figure 5b shows the fluorescent micrograph of the resultant superhydrophilic–superhydrophobic micropatterns on the TiO2 nanotube array films. As shown, geometrically identical square superhydrophilic regions and dark superhydrophobic regions transferred well from the photomask to form a welldefined pattern. The UV-irradiated regions become superhydrophilic owing to the photocatalytic cleavage of the PTES molecule and the enhanced roughness of the nanotube structure, while the non-irradiated parts remain superhydrophobic without any change. Because the difference in the water CA between the irradiated and non-irradiated regions is larger than 150°, the liquid containing the fluorescent probe selectively appears only on the uniform superhydrophilic grids and not on the neighboring superhydrophobic regions. Therefore, a clear, well-defined fluorescent pattern in line with the dimensions of the Cu grid can be obtained. These results indicate that the micropatterned template composed of

superhydrophilic and superhydrophobic regions was fabricated successfully.

The UV irradiation times had a great effect on the quality of the resulting pattern. For example, it cannot exhibit a sufficient wettability contrast between the irradiated and nonirradiated regions to form a well-defined pattern within 5 min. This is attributed to the hydrophobic fluoroalkyl chain in the PTES molecule that was not efficiently cleaved under a short-time UV irradiation. However, with a long-time UV irradiation (i.e., 60 min), the

regions (c).

Fig. 3. (a) Capillary adhesion arises when a water droplet sitting on the tube nozzle is gradually drawn upwards because the convex air/liquid interface produces an inward pressure ΔP. (b,c) The curves of water contact angles and adhesive force on the superhydrophobic NTA nanostructures with respect to the diameter and length of nanotubes.

#### **3. Wetting pattern by photocatalytic lithography**

A novel approach for constructing superhydrophilic-superhydrophobic micropattern on the nanotube structured TiO2 films has developed by using photocatalytic lithography (Figure 4a) (Lai et al., 2008a). At the first step, the as-prepared amorphous TiO2 nanotubes by electrochemical anodizing of titanium sheets were calcinated at 450oC to form anatase phase, then treated with a methanolic solution of hydrolyzed 1 wt% PTES for 1 h and subsequently heated at 140oC for 1 h, and at the second step, the superhydrophobic film is selectively exposed to UV light through a copper grid (photomask) to photocatalytically cleave the fluoroalkyl chain. It is noteworthy, from the characterization of chemical composition before and after UV irradiation by X-ray photoelectron spectroscopy, that the intensities of the F1*s* and F*KLL* are decreased greatly and those of the Ti2*p* and O1*s* are increased after exposing the PTES modified surface to UV light for 20 min (Fig. 4b). From the inset high-resolution spectra (Fig. 4c), the peaks of -CF2 (at 291.8 eV) and -CF3 (at 294.1 eV) are obviously vanished after UV light irradiation, while the strength of silicon peaks in the XPS spectra remains unchanged but shifts from 102.8 to 103.3 eV, suggesting that Si-O-Si networks have already formed due to UV irradiation. According to these results, we believe that the hydrophobic fluoroalkyl chains have been completely decomposed and removed by the photocatalytic reactions at TiO2 nanotube films. Similarly, a serial of fluoroalkyl silane monolayer pattern (e.g. heptadecafluorodecyltrimethoxysilane, octadecyltriethoxysilane, and methyltriethoxysilane) can be successfully fabricated in our case. Although various monolayer patterns can be prepared with a resolution about micro-scale or submicro-scale under optimal condition, we will focus on the application of the PTES micro-pattern with a general TEM copper grid as a photomask by photocatalytic lighography.

Fig. 3. (a) Capillary adhesion arises when a water droplet sitting on the tube nozzle is gradually drawn upwards because the convex air/liquid interface produces an inward

A novel approach for constructing superhydrophilic-superhydrophobic micropattern on the nanotube structured TiO2 films has developed by using photocatalytic lithography (Figure 4a) (Lai et al., 2008a). At the first step, the as-prepared amorphous TiO2 nanotubes by electrochemical anodizing of titanium sheets were calcinated at 450oC to form anatase phase, then treated with a methanolic solution of hydrolyzed 1 wt% PTES for 1 h and subsequently heated at 140oC for 1 h, and at the second step, the superhydrophobic film is selectively exposed to UV light through a copper grid (photomask) to photocatalytically cleave the fluoroalkyl chain. It is noteworthy, from the characterization of chemical composition before and after UV irradiation by X-ray photoelectron spectroscopy, that the intensities of the F1*s* and F*KLL* are decreased greatly and those of the Ti2*p* and O1*s* are increased after exposing the PTES modified surface to UV light for 20 min (Fig. 4b). From the inset high-resolution spectra (Fig. 4c), the peaks of -CF2 (at 291.8 eV) and -CF3 (at 294.1 eV) are obviously vanished after UV light irradiation, while the strength of silicon peaks in the XPS spectra remains unchanged but shifts from 102.8 to 103.3 eV, suggesting that Si-O-Si networks have already formed due to UV irradiation. According to these results, we believe that the hydrophobic fluoroalkyl chains have been completely decomposed and removed by the photocatalytic reactions at TiO2 nanotube films. Similarly, a serial of fluoroalkyl silane monolayer pattern (e.g. heptadecafluorodecyltrimethoxysilane, octadecyltriethoxysilane, and methyltriethoxysilane) can be successfully fabricated in our case. Although various monolayer patterns can be prepared with a resolution about micro-scale or submicro-scale under optimal condition, we will focus on the application of the PTES micro-pattern with a

pressure ΔP. (b,c) The curves of water contact angles and adhesive force on the superhydrophobic NTA nanostructures with respect to the diameter and length of

general TEM copper grid as a photomask by photocatalytic lighography.

**3. Wetting pattern by photocatalytic lithography** 

nanotubes.

Fig. 4. Schematic outline of the procedures to fabricate nanostructured patterning film by electrochemical deposition based on superhydrophilic-superhydrophobic micropattern (a). Survey-scan X-ray photoelectron spectra of the PTES modified nanotube TiO2 films before (1) and after (2) 20 min UV irradiation (b). The high-resolution spectra of Si2*p* and C1*s* regions (c).

Figure 5 shows the optical micrograph of the as-obtained superhydrophilic– superhydrophobic pattern by focusing on the droplet within the superhydrophilic regions. A uniform pattern is formed due to the site-selective wetting by water droplets within the superhydrophilic regions (Fig. 5a). A light dot array (inset of Fig. 5a) is seen when focusing on the top of the droplets, indicating that the confined droplet has a hemispherical dome. To further verify the resulting micropatterns with an extreme wettability contrast, fluorescein sodium was used as a probe to label the surface of the films. Figure 5b shows the fluorescent micrograph of the resultant superhydrophilic–superhydrophobic micropatterns on the TiO2 nanotube array films. As shown, geometrically identical square superhydrophilic regions and dark superhydrophobic regions transferred well from the photomask to form a welldefined pattern. The UV-irradiated regions become superhydrophilic owing to the photocatalytic cleavage of the PTES molecule and the enhanced roughness of the nanotube structure, while the non-irradiated parts remain superhydrophobic without any change. Because the difference in the water CA between the irradiated and non-irradiated regions is larger than 150°, the liquid containing the fluorescent probe selectively appears only on the uniform superhydrophilic grids and not on the neighboring superhydrophobic regions. Therefore, a clear, well-defined fluorescent pattern in line with the dimensions of the Cu grid can be obtained. These results indicate that the micropatterned template composed of superhydrophilic and superhydrophobic regions was fabricated successfully.

The UV irradiation times had a great effect on the quality of the resulting pattern. For example, it cannot exhibit a sufficient wettability contrast between the irradiated and nonirradiated regions to form a well-defined pattern within 5 min. This is attributed to the hydrophobic fluoroalkyl chain in the PTES molecule that was not efficiently cleaved under a short-time UV irradiation. However, with a long-time UV irradiation (i.e., 60 min), the

Extremely Wetting Pattern by Photocatalytic Lithography and Its Application 599

different wettabilities were fabricated on the titania film. The adsorption behavior of bovine serum albumin (BSA) on the above two templates was investigated using fluorescent labeling (FITC) in buffer solution with different pH values. The results showed that, for the PTES template with great wettability differences, BSA would preferentially adsorb on the superhydrophilic regions. For the APTS-PTES template with smaller differences in wettability, competitive adsorption phenomenon on the super-hydrophobic regions was found due to the hydrophobic interaction force between the albumin and the surface. As the pH value decreased to 2.5, the phenomenon of competitive adsorption was prominent with the albumin adsorbed in the super-hydrophobic areas. The adsorption feature of the albumin may be closely related to the wettability and surface energy of the materials. This technique has promising applications in bio-compatible coatings where drugs could be

encapsulated in specific areas of the coating using simple microfabrication methods.

helpful to develop various micropatterned functional nanostructured materials.

Figure 7 shows an optical microscopy image of the TiO2 nanotube micropattern produced using a grid micropattern with different wet etching times (Lai et al., 2009b). A patterning with a clear outline was formed in a short time for 30 s (Fig. 7a). With an increase in the wet etching time (Fig. 7b and c), identical micropatterns with higher aspect ratios can be fabricated. When the etching was prolonged to 240 s (Fig. 7d), the size of the grids increased slightly, indicating that the PTES-SAM layer at the edge of the superhydrophobic lines is more easily etched as compared to the inner superhydrophobic area. This is due to the loose and disordered SAMs resulting from the scattered UV light photocatalytic degradation and the transfer of the active hydroxyl radicals at the edge of the grids. Moreover, the isotropic etching of the Ti substrate underneath the boundary leads to the collapse of the upper nanotube array structures. Therefore, the pattern can be obtained with a clear boundary in a short time after the wet etching in the aqueous solution, and the depth of the etching can be

Uniform self-assembly of functional inorganic nanomaterials is a fundamental challenge. Nature adopts a superior approach in biomineralization, where "matrix" macromolecules induce nucleation of inorganic crystals at specific locations with controlled size and morphology, and sometimes even with defined growth orientation. We apply the biomimetic principles derived from liquid phase processes to the assembly of nanoscale functional materials into microscale systems. We carefully control surface wettability to promote etching or heterogeneous nucleation at designated superhydrophilic regions while completely suppress these processes elsewhere (superhydrophobic regions), therefore enable the controlled top-down or bottom-up assembly of inorganic nanomaterials directly from solution. Following this principle, arrays of crystalline TiO2 nanotube, ZnO nanorods, CdS semiconductor materials and octacalcium phosphate (OCP) biomaterials were nucleated and assembled directly from solution onto Ti substrates at the desired precise locations and then fabricated into arrays of photodetector or matrix devices for large-area microelectronic applications. This strategy of micropatterned nanocomposites will be

**4. Application of wetting pattern** 

**4.1 Template for preparing functional pattern** 

controlled simply by adjusting the etching time.

adjacent PTES molecule covered by the Cu grid can be remotely oxidized by a TiO2 nanotube photocatalyst or the diffusion, scattering, and diffraction of the incident light (Haick & Paz, 2001; Kubo et al., 2004). Therefore, to obtain a higher pattern resolution, the optimized UV irradiated time in our case was controlled in the range of 10-30 min.

Fig. 5. (a) Optical micrograph of the as-obtained superhydrophilic-superhydrophobic pattern by focusing on the water droplet within the superhydrophilic regions. (b) Fluorescence microscopy image of the fluorescein probes on the as-prepared superhydrophilic-superhydrophobic micropattern.

Fig. 6. Fluorescence microscope images generated by blue light excitation on the different micropatterned templates with the adsorption of FITC-BSA, (a-1, a-2, a-3) the PTES template with a pH value of 7.5, 4.5 and 2.5, respectively; (b-1, b-2, b-3) the PTES-APTS template with a pH value of 7.5, 4.5 and 2.5, respectively.

Based on the molecular self-assembly and photocatalytic lithography techniques, micropatterned templates of PTES or PTES-APTS(3-aminopropyltriethoxysilanes) with different wettabilities were fabricated on the titania film. The adsorption behavior of bovine serum albumin (BSA) on the above two templates was investigated using fluorescent labeling (FITC) in buffer solution with different pH values. The results showed that, for the PTES template with great wettability differences, BSA would preferentially adsorb on the superhydrophilic regions. For the APTS-PTES template with smaller differences in wettability, competitive adsorption phenomenon on the super-hydrophobic regions was found due to the hydrophobic interaction force between the albumin and the surface. As the pH value decreased to 2.5, the phenomenon of competitive adsorption was prominent with the albumin adsorbed in the super-hydrophobic areas. The adsorption feature of the albumin may be closely related to the wettability and surface energy of the materials. This technique has promising applications in bio-compatible coatings where drugs could be encapsulated in specific areas of the coating using simple microfabrication methods.
