The Effect of Hydrophobic Patterning on Micromolding of Aqueous-Derived Silk Structures
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The Effect of Hydrophobic Patterning on Micromolding of Aqueous-Derived Silk Structures Konstantinos Tsioris1, Robert D White1, David L Kaplan2, and Peter Y Wong1 1 Mechanical Engineering, Tufts University, Medford, MA, 02155 2 Biomedical Engineering, Tufts University, Medford, MA, 02155 ABSTRACT A novel micromolding approach was developed to process liquid biopolymers with high aqueous solvent contents (>90% water). Specifically silk fibroin was cast into a well-defined scaffold-like structures for potential tissue engineering applications. A method was developed to pattern the hydrophilicity and hydrophobicity of the polydimethylsiloxane (PDMS) mold surfaces. The water based biopolymer solution could then be directly applied to the desired regions on the cast surface. The variations in degree of hydrophilicity and hydrophobicity on the PDMS surfaces were quantified through contact angle measurements and compared to the outcome of the molded silk structures. Through this method free-standing structures (vs. relief surfacepatterning) could be fabricated. INTRODUCTION Biopolymers, polymers synthesized by organisms, have many advantages including excellent biocompatibility and adjustable biodegradability [1]. Silk, for example, offers a wide spectrum of outstanding material properties such as good fracture toughness and excellent optical properties. Fabricating with biopolymers is also environmentally sound, since they can be processed in aqueous solutions. Due to these advantages biopolymers are often used as substrates in cell and tissue culture [1]. However they are rarely used in MEMS applications [2]. There is enormous potential for biopolymers in MEMS applications. In MEMS devices biopolymers could function as membranes or optical components. Devices which demand outstanding biocompatibility, such as implantable sensors, could be packed in or fully manufactured from biopolymers. The challenge today exists in understanding critical processing parameters in manufacturing structures with micron and submicron level features from biopolymers. In this research, the development of a micromolding technology, to produce microstructures from aqueous derived silk solutions was studied. In particular, well-defined cellular and tissue culture substrate (scaffold) fabrication was used as a model to study manufacturing methods. The most important aspect of the proposed technology is the ability to produce freestanding structures vs. relief surface patterns through micromolding. In particular, the manufacturing challenges consist of processing materials with a high solvent content (> 90% water), producing well-defined structures and demolding the delicate structures. In this study we are addressing the molding process with the innovative solution of controlling the hydrophilicity and hydrophobicity of the cast surface to control the deposition of the biopolymer only in the cast cavities and not on cast surface.
EXPERIMENT Soft lithography Soft lithography is a well established method to create elastomer rubber s
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