Although optical lithography or photolithography is one of the most well-established techniques for micro, nano-fabrication, its usage with proteins and cells is restricted by steps that must be carried out in harsh organic solvents. Here, we present simple methods for cell-micropatterning using poly(dimethylsiloxane) (PDMS) as a mold. Cell non-adhesive surface or nonfouling surface providing a physico-chemical barrier to cell attachment was introduced for biomaterial pattering, where cells fail to interact with the surface over desired periods of time determined by each application. Poly(ethylene glycol) (PEG) was selected as nonfouling material to inhibit protein adsorption from biological media. The fouling resistance of PEG polymer is often explained by a steric repulsion interaction, resulting from the compression of PEG chains as proteins approach the surface. We also chose fibronectin to direct cell attachment because it is an extracellular matrix protein that is involved in the adhesion and spreading of anchorage-dependent cells. In our experiment, we propose two methods by application of micromolding in capillary (MIMIC) method based on UV polymerization to obtain a surface of alternating PEG and fibronectin. First to fabricate PEG microstructure via MIMIC method, a pre-patterned PDMS mold is placed on a desired substrate, and then the relief structure in the mold forms a network of empty channels. A drop of ethylene glycol monomer solution containing initiator for UV polymerization is placed at the open ends of the network of channels, which is then polymerized by exposure to UV light at room temperature. Once PEG microstructure is fabricated, incubation of the patterned surface in a fibronectin-containing solution allows back-filling of only the bare regions with fibronectin via adsorption. In the alternative method, a substrate is first incubated in a fibronectin-containing solution, leading to the adsorption of fibronectin over the entire surface, and the fibronectin-adsorbed substrate is then micropatterned with the PEG by MIMIC based on UV polymerization. Both methods create reproducible alternating PEG and fibronectin patterns applicable to cell-surface interactions on the microscale.
This article presents a microfabrication technology of 3D microstructures via the soft-imprint technique using poly(dimethylsiloxane) (PDMS) mold attached with a screen mask, TEM grid. A prepolymer and monomer mixture, after short UV exposure, rises only up to the open spot of TEM grid, sequentially into the groove of the PDMS mold, then, 3D microstructures are formed in one-step process. The unreacted remaining monomer enables the viscous prepolymer mixture to fill the cavity of TEM grid and the PDMS mold, and the conformal contact of the PDMS mold with TEM grid also prevents the permeation of sticky prepolymer into the interface of PDMS mold and TEM grid. The proposed technique is an inexpensive, simple, and reliable method to fabricate 3D microstructures without expensive and complex lithographic tools. Thus, using this 3D microfabrication method, various 3D microstructures of the combination of TEM grid pattern and PDMS mold groove are easily generated with good pattern fidelity.