Abstract
Micro-contact printing, μCP, is a well-established soft-lithography technique for printing biomolecules. μCP uses stamps made of Poly(dimethylsiloxane), PDMS, made by replicating a microstructured silicon master fabricated by semiconductor manufacturing processes. One of the problems of the μCP is the difficult control of the printing process, which, because of the high compressibility of PDMS, is very sensitive to minute changes in the applied pressure. This over-sensitive response leads to frequent and/or uncontrollable collapse of the stamps with high aspect ratios, thus decreasing the printing accuracy and reproducibility. Here we present a straightforward methodology of designing and fabricating PDMS structures with an architecture which uses the collapse of the stamp to reduce, rather than enlarge the variability of the printing. The PDMS stamp, organized as an array of pyramidal micro-posts, whose ceiling collapses when pressed on a flat surface, replicates the structure of the silicon master fabricated by anisotropic wet etching. Upon application of pressure, depending on the size of, and the pitch between, the PDMS pyramids, an air gap is formed surrounding either the entire array, or individual posts. The printing technology, which also exhibits a remarkably low background noise for fluorescence detection, may find applications when the clear demarcation of the shapes of protein patterns and the distance between them are critical, such as microarrays and studies of cell patterning.Electronic supplementary materialThe online version of this article (doi:10.1007/s10544-016-0036-4) contains supplementary material, which is available to authorized users.
Highlights
IntroductionPatterning proteins on surfaces have multiple applications in the area of biomedical microdevices, such as microarrays (Allison et al 2006; Müller and Nicolau 2005), lab-on-achip (Chin et al 2012), biosensors and bioMEMS (Mujahid et al 2013), as well in the area of functional studies for cell and tissue development (Kane et al 1999; Nicolau et al 1996; Nicolau et al 1999a)
Biomed Microdevices (2016) 18: 9 contact-based printing, e.g., classical pin printing (Rowland et al 2012), dip pen lithography (Huo et al 2008), or microcontact printing, μCP (Bernard et al 1998; Kumar et al 1994). μCP has a special place in the panoply of direct deposition methods, because it is capable of very high resolution of printing, at a low cost of ownership, making it widely used in exploratory research (Delamarche et al 2003; Delamarche et al 1997; Kane et al 1999; Renault et al 2003)
Silicon master The silicon master was fabricated by photolithography, followed by anisotropic etching with a 28 % KOH solution along the crystallographic face of a silicon wafer, resulting in arrays of pyramidal wells (Ayeyard et al 2010)
Summary
Patterning proteins on surfaces have multiple applications in the area of biomedical microdevices, such as microarrays (Allison et al 2006; Müller and Nicolau 2005), lab-on-achip (Chin et al 2012), biosensors and bioMEMS (Mujahid et al 2013), as well in the area of functional studies for cell and tissue development (Kane et al 1999; Nicolau et al 1996; Nicolau et al 1999a). The patterning of proteins can be achieved by their immobilisation from solution in contact with surfaces presenting pre-fabricated patterns, using either selective covalent binding (Ivanova et al 2002; Lenci et al 2011; Nicolau et al 1998, 1999b), or more rarely selective adsorption (Lan et al 2005; Nicolau et al 1999b). Protein patterns can be created by direct deposition methods, such as projectionbased printing, e.g., ink-jet printing (Pardo et al 2003), or based on laser microablation (Dobroiu et al 2010), or
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