Master of Science in Mechanical Engineering (MSME)


Mechanical Engineering

Document Type



The goal of the present study was to fabricate perforated membrane structures in polymers with the pore diameter ranging from 10 ìm down to the sub ìm scale. The perforated membrane structure plays an important role in many biological systems. Thus the ability to reproduce such architecture will help with the study of biological systems by mimicking biological cell membrane-like structures and open new vistas in the study of transport behavior in cell biology and the separation of biological vesicles. Such structures also have potential uses as components in polymer optics and modular micro/nanofluidic devices. Use of polymer substrates is desirable due to the variety of materials and properties available, their biocompatibility and low manufacturing cost. In order to realize low cost production of the membrane structures, a single step imprinting process was employed, which was combined with a sacrificial layer technology and semiconductor micromachining processes. The stamps with micrometer-scale features were fabricated using photolithography on a resist-coated Si wafer, followed by deep reactive ion etching into substrate Si. Prior to imprinting, the stamp surface was treated with a fluorinated silane in the vapor phase in an in house chemical vapor deposition (CVD) chamber to improve the demolding process. SU-8 was used as an imprint resist and either poly(methyl-methacrylate) (PMMA), or a lift off resist (LOR) as a sacrificial layer. Optimal imprinting conditions for SU-8 imprinting were found at 135°C and 4 MPa. Demolding performed at (60 ± 5)°C showed minimal or no damage to both stamps and imprinted structures. UV curing of SU-8 lead to sufficient mechanical strength of the resist to enable it to form free standing membrane after lift-off of the sacrificial layer. In order to demonstrate the application of the perforated membrane structures, selective formation of lipid vesicles was demonstrated in SU-8 membranes by using Poly(L-Lysine)-poly(ethylene glycol) (PLL-PEG) to selectively pattern the membrane surface providing a nonspecific adsorption of the lipid vesicles in the non-porous areas. The pores showed formation of lipid bi-layer as confirmed by optical micrographs of the membrane surface showing faint traces of Trypan-blue dye used to the stain the lipid solution.



Document Availability at the Time of Submission

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Committee Chair

Sunggook Park