Switchable Adhesion

A fully reversible adhesive based on magnetic switching of nickel cantilevers (10 [xm X 130 xm) coated with vertically aligned polymeric nanorods was demonstrated by Northen et al. [71]. The cantilevers were able to reorient under a magnetic field, such that the tips rotated away from the counter-surface, decreasing the adhesion force [71]. 

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Rolli, C. G. Nakayama, H. Yamaguchi, K. Spatz, J. P Kemkemer, R. Nakanishi, J. Switchable adhesive substrates revealing geometry dependence in collective cell behavior. Biomaterials 2012, 33, 2409-2418. 

Northen, M.T, Greiner, C., Arzt, E., and Turner, K.L. (2006) A hierarchical gecko-inspired switchable adhesive. Presented at Solid-State Sensors, Actuators, and Microsystems Workshop, Hilton Head Island, SC, USA. 

Since changes on the enviroimient can significantly affect the thermodynamics at the surface level structural reorganization may occur. Hence, reversible changes on the surface properties of these materials can be easily accomplished, thus, creating switchable materials with controlled surface wettability, charge, adhesion, and chemical functionality. 

Beyond the examples discussed above, which use the synthetic polymer block of bioconjugates to suppress cell adhesion, other selective polymer functions can be exploited, for example, to generate switchable surfaces modifications. 

Biomimetics is an important strategy for the fabrication of modern biomaterials that provides solutions which closely resemble those of living systems. In the area of biomimetic supramolecular chemistry, a surface-grafted PMOEP polymer has recently been found to impart mesoporous silica with switchable ion channel transport properties. This was enabled by the dual protonation and Ca chelation ability of the polymer phosphate groups. A series of studies made use of PMAEP-based copolymers in the fabrication of biomimetic adhesives which were inspired by the sandcastle worm that produces peptide polyelectrolytes rich in phosphorylated serine. These adhesives were aimed at providing molecular solutions to... 

Another typical photoresponsive material for preparation of switchable surfaces is the spiropyran-merocyanine system. The spiropyran isomerizes to zwitterionic merocyanine conformation by UV exposure, and the reverse reaction can be triggered by irradiation with visible light as well as azobenzene. The changes in hydrophilic/hydrophobic properties through the isomerization of spiropyran groups also enable the control of cell adhesion/ detachment. Edahiro et al. reported photoresponsive cell culture substrates grafted... 

FIGURE 12.16 Schematic representation of the electrically switchable surface, (a) The surface is composed by an RGD and EG6-sulfonate mixed SAM and (b) by an RGD and EG6-ammonium mixed SAM. The two portions are able to switch from cell adhering to cell repellent in response to a potential applied. A positive potential of -E0.3 V will determine the attachment of cells in (a) while a negative potential of —0.3 V will determine the adhesion of cells in (b) [220]. 

Grundke, K. Nitschke, M. Minko, S. Stamm, M. Froeck, C. Simon, F. Uhlmann, S. Poschel, K. Motornov, M. Merging Two Concepts Ultrahydrophobic Polymer Surfaces and Switchable Wettability. In Contact Angle, Wettability and Adhesion Mittal, K. L., Ed. VSP Utrecht, The Netherlands, 2003 Vol. 3, 267-291. 

Another route towards biomolecular functionalisation of switchable cell culture carriers was proposed by Gramm et al. (2011). The thermo-responsive polymer poly (vinyl methyl ether) was blended with a small amount of the alternating copolymer of vinyl methyl ether and maleic anhydride. After electron beam cross-linking, stable films with a dry thickness of up to 70 nm were obtained. The introduced anhydride moieties allow for subsequent protein or peptide immobilization without toxic coupling agents. This concept was applied and further developed by Teich-mann et al. (2013). The impact of different adhesion-promoting molecules immobilised in different concentrations to the thermo-responsive coating was evaluated and compared. 

Schmidt, S., Zeiser, M., Hellweg, T., Duschl, C., Eery, A., Hwald, M., et al. (2010). Adhesion and mechanical properties of PNIPAM microgel films and their potential use as switchable cell culture substrates. Advanced Functional Materials, 20, 3235-3243. 

Wischerhoff, E., Uhlig, K., Lankenau, A., Bomer, H. G., Laschewsky, A., Duschl, C., et al. (2008). Controlled cell adhesion on PEG-based switchable surfaces. Angewandte Chemie International Edition in English, 47, 5666-5668. 

Depending on the application, the surface of the biomaterial should promote cell adhesion (e.g., in an implant) or promote cell detachment (e.g., in cell sheet engineering) (Gil and Hudson, 2004 Roy et al., 2010). Responsive surfaces with cell adhesive properties which are switchable in response to an external stimulus have been extensively applied in the design of smart systems for TE. 

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