Preliminary Investigation of a Sacrificial Process for Fabrication of Polymer Membranes with Sub-Micron Thickness
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Preliminary Investigation of a Sacrificial Process for Fabrication of Polymer Membranes with Sub-Micron Thickness Luke A. Beardslee1, Dimitrius A. Khaladj1, Magnus Bergkvist1 1 SUNY College of Nanoscale Science & Engineering, Albany NY. ABSTRACT Here we present a single mask sacrificial molding process that allows ultrathin 2dimensional membranes to be fabricated using biocompatible polymeric materials. For initial investigations, polycaprolactone (PCL) was chosen as a model material. The process is capable of creating 250-500 nm thin, through-hole PCL membranes with various geometries, pore-sizes and spatial features approaching 2.5 micrometers using contact photolithography. The technique uses a mold created from two layers of lift-off resist (LOR). The upper layer is patterned, while the lower layer acts as a sacrificial release layer for the polymer membrane. For mold fabrication, photoresist on top of the layers of lift-off resist is patterned using conventional photolithography. During development the mask pattern is transferred onto the first LOR layer and the photoresist is removed using acetone, leaving behind a thin mold. The mold is filled with a solution of the desired polymer. Subsequently, both the patterned and lower LOR layers are dissolved by immersion in an alkaline solution. The membrane can be mounted onto support structures pre-release to facilitate handling. INTRODUCTION Scaffold structures comprised of extracellular matrix (ECM) proteins provide cellular support and function within biological systems, particularly as basement layers for epithelial and endothelial cell sheets [1, 2]. They are often highly permeable membrane layers with micrometer to nanometer thickness [3, 4], where the Descemet’s membrane within the cornea of the eye, and the basement membrane of the vascular endothelium are two examples. Proper formation of such basement membranes during in-vitro cell culture can help to facilitate growth of functional artificial tissue from primary or stem cell cultures. To support in-vitro growth of functional tissue and to promote basement membrane formation, a thin pore containing scaffold material with suitable geometries is desirable. In this work, we present lithographically fabricated molds for the creation of ultrathin micropatterned scaffolds for tissue engineering. Many different methods are possible for the creation of patterned/structured biomaterials systems, including electrospinning [5], direct photopatterning of hydrogels [6, 7], photocrosslinking of polymers [810], soft lithography [11-13], stamping [14], etching [15], UV crosslinking of hydrogels through a PDMS mold [16], and two photon polymerization [17]. Direct photopatterning is an attractive and a relatively straight forward approach that can work well. For example, radical crosslinking of hydrogels [6] and bioplastics [9] has been demonstrated. However, such techniques typically require synthesis of unique precursor molecules. A common alternative method to create textured polymer structures is soft lithography [6, 8-
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