Micropatterning photopolymerizable hydrogels for diffusion studies using pillar arrays or photomasks

Abstract

In situ polymerization and micropatterning of hydrogels on-chip opens the potential for many applications such as tracking and controlling the diffusion of molecules, stimulants, inhibitors, as well as nutrients and drugs, from their source to a target. To enable such applications, we developed hydrogel-on chip platforms for molecular diffusion studies by refining PEGDA-PEG hydrogel in terms of micropatterning and diffusion properties. In the first platform that we introduce here, the design has multiple adjacent microfluidic channels separated with pillar arrays shaping the flow of our custom-prepared photopolymerizable hydrogels and thus enabling the localization of photopolymerization. In the second platform, a photomask formation has been achieved by coupling the micro-milling of 250-\textmu m thickness of PMMA substrate with Platinum (Pt)-coating onto the PMMA mask. In this way the design was obtained to have opaque and transparent regions for light-based polymerization of the PEGDA-PEG hydrogels. The developed method of in situ polymerization of the hydrogel on-chip through photomask has enabled direct transfer of the design of interest to the pre-hydrogel in channel. Next, the developed platforms will be further used to test various compositions of photopolymerizable hydrogels and track and control the diffusion of molecules across hydrogel interfaces. The micropatterning methods and platforms developed here could be tailored to device design and development needs in various application fields from molecular transport to biosensing to electronic devices.

Figures (10)

• Figure 1: Micropatterning methods used to design and fabricate master and devices, represented in two platforms. (a-c) Hydrogel-on-chip device used for controlling diffusion of molecules to the adjacent channels through barriers of custom-prepared hydrogel. (a) Optical microscope stitched images of Si/photoresist master developed for the design written with laser lithography. (b) Etched Si master fabricated using ICP-RIE. (c) PDMS device with hydrogel and DPBS (Dulbecco's Phosphate-Buffered Saline) loaded into corresponding channels. (d) Microfabricated PMMA mask. (e) Pt-coated PMMA mask. (f) PMMA master of microchannel. (g) PDMS channel bonded to 35-mm Fluorodish glass. (h) PEGDA-PEG hydrogel cylinders in situ formed in PDMS channel through the Pt-coated PMMA mask.
• Figure 2: LSCM images showing diffusion of fluorescent molecules and quantification. (a) Time lapse images showing diffusion of Bovine Serum Albumine (BSA) fluorescein across channels from source channel (top) to hydrogel in narrow channel between pillar arrays and to DPBS channel (bottom) over 2 hours, shown here as representative data. (b-c) Quantification of molecular diffusion from source channel to hydrogel and to DPBS channel for BSA (b) versus Dextran 70 kDa (c). Channel regions and ROIs used in quantification are shown in Supplementary Figure \ref{['SuppFig1']}(a).
• Figure 3: LSCM imaging and quantification of molecular diffusion from source channel to hydrogel and to DPBS channel by tile scanning and comparison of Dextran 70 kDa concentrations of (a) 0.2 mg/ml and (b) 1 mg/ml in DPBS for diffusion length.
• Figure 4: Imaging of hydrogel-on-chip structures. (a) SEM images of PEGDA-PEG hydrogel in the chip with PDMS pillars and in the chip with hydrogel cylinders, formed by polymerizing at 100% power (160 mW) and 12% power (15 mW), respectively. (b) Representative LSCM image (z-stack) of a chip with orthogonal projections. LSCM images of the hydrogel structure by reflection and the molecules inside gel by fluorescence mode.
• Figure 5: Diffusion of various molecules in hydrogel cylinders on-chip. (a) Diffusion and separation of a mixed form of Rhodamine 110 and Dextran 70 kDa. (b-c) Diffusion of Epirubicin hydrochloride and BSA into the gel cylinders. (d) The behavior of 100-nm spheres around the gel, by LSCM and SEM.