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The adhesion strengths of a viscoelastic adhesive were measured on various substrates that were prepared by grafting silanes bearing organic functional groups to silicon wafers. Conventional theories predict that adhesion should be proportional to the surface free energy of the substrate; but adhesion on a fluorocarbon surface was significantly greater than on some of the hydrocarbon surfaces, although the fluorocarbon surface has the lowest surface free energy. This result could be explained by invoking a model of adhesion based on the slippage of the adhesive at the interface.

We have developed a simple Marangoni flow-induced method for self-assembling nanoparticles (NPs) into both hexagonal and stripelike patterns. First, a NPs/ethanol suspension was spread on a slightly nonwettable and a wettable silicon oxide substrate. The Marangoni flow, induced by simultaneous evaporation of ethanol and condensation of water, leads to the formation of the corresponding hexagonal distributed circular NP rings and dotted stripes. The inter-ring spacing and ring size of the hexagonal patterns can be tuned by varying the relative humidity of the N2 stream blown over the slightly nonwettable substrate. Hexagonal patterns of circular NP patches can also be fabricated by lowering the evaporation of the condensed water droplets. On the wettable substrate, complex patterns result when the humidity of the N2 stream changes.

Gradient surfaces are widely employed in biological studies for protein adsorption and cell attachment and growth. They also offer great potential in the areas of fluid flow and combinatorial experimental design for obtaining material properties and behaviors. Gradient surfaces are created with organosilanes by using the diffusion techniques proposed by Ewling and modified by Chaudhury. However, these techniques have limitations. They either generate a significant amount of organic waste or require well-controlled deposition conditions. In this paper, we propose a fast, convenient, reproducible, and inexpensive method that generates gradient surfaces with minimum waste generation. Particularly, we have adopted Whitesides's contact-printing technique to achieve a gradient by gradually varying the contact time over the contacted area using octadecyltrichlorosilane. Elastomeric stamps with different geometries and various radii of curvature are used to generate gradient surfaces at both millimeter and micrometer scales. With this approach, we are able to generate micrometer-scaled gradient surfaces with a gradient steepness 1−3 orders of magnitude higher than those generated using diffusion-based techniques. The energy gradient on these surfaces is verified by the dewetting of polymer (e.g., polystyrene) thin films and by the movement of picoliter and nanoliter water droplets on the surface devoid of other driving forces such as gravity, temperature gradients, or a pressure drop.

Bacterial Cellulose (BC) synthesized by Acetobacter xylinum has been a promising candidate for medical applications. Modifying BC to possess the properties needed for specific applications has been reported. In this study, BCs functionalized by organosilanes were hypothesized to improve the attachment and spreading of Normal Human Dermal Fibroblast (NHDF). The BC gels obtained from biosynthesis were dried by either ambient-air drying or freeze drying. The surfaces of those dried BCs were chemically modified by grafting methyl terminated octadecyltrichlorosilane (OTS) or amine terminated 3-aminopropyltriethoxysilane (APTES) to expectedly increase hydrophobic or electrostatic interactions with NHDF cells, respectively. NHDF cells improved their attachment and spreading on the majority of APTES-modified BCs (∼70-80% of area coverage by cells) with more rapid growth (∼2.6-2.8× after incubations from 24 to 48h) than on tissue culture polystyrene (∼2×); while the inverse results (< 5% of area coverage and stationary growth) were observed on the OTS-modified BCs. For organosilane modified BCs, the drying method had no effect on in vitro cell attachment/spreading behaviors.

The development of mechanically tough and biocompatible polymer hydrogels has great potential and promise for many applications. Herein, we synthesized a new type of hybrid physically-chemically crosslinked Agar/PAM double network (DN) hydrogel using a simple, one-pot method. Agar/PAM gels are designed with desirable/balanced mechanical properties by varying the network-forming parameters.Among them, a strong Agar/PAM DN gel achieves the highest tensile stress of 3.3 MPa at failure strain of 2400%, while a tough DN gel achieves the tensile strain of 3700% at failure stress of 2.8 MPa. Besides excellent mechanical properties, Agar/PAM DN hydrogels exhibited excellent antifouling properties to highly resist protein adsorption, cell adhesion, and bacterial attachment, as well as the free shapeable property to form any complex shapes. The relationship between mechanical properties and antifouling performance was discussed. We hope that the combination of the mechanical and antifouling properties in Agar/PAM gels will make them as promising ''biomimetic'' materials for many bio-inert applications.

Thin films of polymer blends are molded into strips for investigating the influence of lateral confinement on phase separation. The strip has a width and thickness of 17 µm and 1.0 µm, respectively, and contains a 50/50 blend of poly(methyl methacrylate) (PMMA) and poly(styrene-ran-acrylonitrile) (SAN). Upon annealing, the strip profile rapidly becomes bell-shaped, forming a contact angle of 3°with the substrate. The dynamics of phase separation is investigated using confocal microscopy and atomic force microscopy. The early stage is characterized by an interconnected morphology and symmetric wetting of the PMMA-rich phase at the substrate and surface. The PMMA-rich domains grow from the surface toward the substrate during the early intermediate stage and eventually connect with the wetting layer covering the substrate to begin the late intermediate stage. The domain diameter increases rapidly (early), slows down (intermediate), and then decreases (late) during phase separation. During the late stage the PMMA-rich domains heal, leaving behind an elliptical SAN-rich core encapsulated by PMMA-rich wetting layers. These studies demonstrate that confinement directs the formation of a self-assembled core/shell morphology, which has potential applications for encapsulating drugs or creating microwires.

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