Fabrication of Microfluidic Chips using Xurography

Jordon Gilmore and Rodrigo Martinez-Duarte
Multiscale Manufacturing Laboratory
Department of Mechanical Engineering
Clemson University

Xurography is the use of a cutting blade to pattern a material. A cutter plotter is commonly used to implement it. Bartholomeusz and coworkers originally proposed xurography in 2005 as an alternative technique for forming microstructures in microfluidics [1]. A cutter plotter was used to pattern a film of adhesive with channels and chambers. This film was then adhered to a piece of plastic, which is usually drilled to provide inlets and outlets for the channel. The possibility to pattern each of the adhesive and plastic layers, together with the stacking process, allows for the fabrication of complex 3D networks. The device is ultimately sealed using a rolling press, which does not necessarily need to be hot [1]. Figure 1 below shows a schematic for microfluidic chip assembly with xurography.

Figure 1. Schematic of the entire fabrication process of a microfluidic chip by xurography [2]

Islam et al. reported that xurography is capable of producing leak-free devices able to handle a few milliliters per second in channels as small as 100 µm high and 1 mm wide [2]. However, smaller channel dimensions are possible if the flow rate can be reduced. Cutter plotters are commercially available and relatively inexpensive with resolutions in the sub-mm range. Applications such as gradient generators and DEP have been accomplished. Figure 2 displays a gradient generator fabricated by this technique. Perhaps the most important advantage of this technique is that the cleanroom can be completely avoided and new devices can be fabricated from conception in a matter of minutes. Furthermore, the infrastructure required can be acquired for approximately 2000 USD and inexpensive pressure-sensitive adhesive films can be purchased with a number of thicknesses and features from providers such as FlexCON and Adhesives Research.

Figure 2. (a) Gradient generator developed through xurography, (b-e) variations in gradient were generated by changes in flow rate through the serpentine network of microchannels [2].

Xurography has been explored widely in the last decade. Greer and colleagues compared the effectiveness of microfluidic chips made using xurography to those made by glass etching. Her group demonstrated that the signal-to-noise ratio (SNR) of the xurographic chips was comparable the glass etched chips, with a 20-fold decrease in manufacturing cost and four fold reduction in manufacturing time [3]. Atencia and coworkers demonstrated a diffusion-based gradient generator for biochemical assays using xurography [4]. In electrophoresis applications, researchers such as Pessoa de Santana have used xurography to manufacture microchannels on glass slides [5], thereby keeping the advantages for electrophoresis on glass while minimizing the cost associated with the usual techniques (i.e. photolithography).

While low manufacturing cost and speed of development are key advantages of xurography, the resolution and precision of features made with this method are highly dependent on the type and quality of the cutter plotter, pressure-sensitive adhesive material, and blade angle being used. This group found that a commercially inexpensive plotter with an advertised resolution of 25 µm was only able to achieve straight channel widths of 200 µm with acceptable resolution and precision [2]. While more expensive plotters may claim even higher resolution (~10 µm), the results from this group suggest that actual resolution may be far from this value. Additionally, blade angle plays a major role in the precision and accuracy of cuts, especially when making cuts under 700 µm. There was a significant difference between both the accuracy (discrepancy from target dimension) and precision (standard deviation of identical cuts) for straight channels cut with a 45° blade angle versus a 30° angle. The 30° blade angle produced more accurate and more precise cuts, with an increasingly significant benefit under 500 µm target dimensions [2].

Finally, other limitations or considerations for xurography center on the orientation of the blade during cutting. This group, as well as other researchers [6], have documented higher cut quality in one of the dimensions in a 2-dimensional system. This is due to the fixed orientation of the blade, which allows for guided cutting along a rail or track in one direction, but less precise cutting is achieved in the other dimension because the adhesive must be pushed against the blade using a series of rollers. Build-up of sticky debris on the blade as complex cuts are made may also contribute to a loss of precision or accuracy over time [2].

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