BIOS Lab-on-a-Chip Group, MESA+ Institute for Nanotechnology, MIRA Institute for Biomedical Technology and Technical Medicine, University of Twente , Enschede, The Netherlands.
Biomacromolecules. 2015 Dec 14;16(12):3802-10. doi: 10.1021/acs.biomac.5b01104. Epub 2015 Nov 19.
To date, optical lithography has been extensively used for in situ patterning of hydrogel structures in a scale range from hundreds of microns to a few millimeters. The two main limitations which prevent smaller feature sizes of hydrogel structures are (1) the upper glass layer of a microchip maintains a large spacing (typically 525 μm) between the photomask and hydrogel precursor, leading to diffraction of UV light at the edges of mask patterns, (2) diffusion of free radicals and monomers results in irregular polymerization near the illumination interface. In this work, we present a simple approach to enable the use of optical lithography to fabricate hydrogel arrays with a minimum feature size of 4 μm inside closed microchips. To achieve this, we combined two different techniques. First, the upper glass layer of the microchip was thinned by mechanical polishing to reduce the spacing between the photomask and hydrogel precursor, and thereby the diffraction of UV light at the edges of mask patterns. The polishing process reduces the upper layer thickness from ∼525 to ∼100 μm, and the mean surface roughness from 20 to 3 nm. Second, we developed an intermittent illumination technique consisting of short illumination periods followed by relatively longer dark periods, which decrease the diffusion of monomers. Combination of these two methods allows for fabrication of 0.4 × 10(6) sub-10 μm sized hydrogel patterns over large areas (cm(2)) with high reproducibility (∼98.5% patterning success). The patterning method is tested with two different types of photopolymerizing hydrogels: polyacrylamide and polyethylene glycol diacrylate. This method enables in situ fabrication of well-defined hydrogel patterns and presents a simple approach to fabricate 3-D hydrogel matrices for biomolecule separation, biosensing, tissue engineering, and immobilized protein microarray applications.
迄今为止，光学光刻技术已经被广泛应用于各种规模的水凝胶结构的原位图案化，其范围从数百微米到数毫米。限制更小的水凝胶结构特征尺寸的两个主要因素是：（1）微芯片的上玻璃层保持着光掩模和水凝胶前体之间较大的间距（通常为 525μm），导致掩模图案边缘的紫外光衍射；（2）自由基和单体的扩散导致在光照界面附近聚合不规则。在这项工作中，我们提出了一种简单的方法，使光学光刻技术能够在封闭的微芯片中制造最小特征尺寸为 4μm 的水凝胶阵列。为了实现这一目标，我们结合了两种不同的技术。首先，通过机械抛光来减薄微芯片的上玻璃层，从而减小光掩模和水凝胶前体之间的间距，进而减小掩模图案边缘的紫外光衍射。抛光过程将上玻璃层的厚度从约 525μm 降低到约 100μm，平均表面粗糙度从 20nm 降低到 3nm。其次，我们开发了一种间歇式光照技术，由短的光照周期和相对较长的暗周期组成，从而减少了单体的扩散。这两种方法的结合使得可以在大面积（cm2）上以高重复性（约 98.5%的图案化成功率）制造小于 10μm 的亚 10μm 尺寸的水凝胶图案。这种图案化方法通过两种不同类型的光聚合水凝胶进行了测试：聚丙烯酰胺和聚乙二醇二丙烯酸酯。该方法能够实现水凝胶图案的原位制造，并为生物分子分离、生物传感、组织工程和固定化蛋白质微阵列应用提供了一种简单的制造 3D 水凝胶基质的方法。
