Characterization of a direct-write method for fabricating three-dimensional polymer microfibers and construction of microscale platforms.

摘要

A number of polymer fiber-based microdevices have emerged which capitalize on the unique and customizable properties of polymers to maximize performance. However, current limitations on three-dimensional fabrication and placement of these fibers have impeded the development of complex 3D systems. The purpose of this investigation is to develop a direct-write technique for fabricating arrays of suspended, 3D-oriented polymer fibers, then demonstrate the applicability of these arrays in the areas of microelectronics, microfluidics, and tissue engineering.;An automated, micromanipulator-controlled syringe was used to deposit and stretch droplets of viscous polymer solutions into precisely-positioned filaments. These filaments then thin, via surface tension-driven necking, and dry to form solidified fibers. This procedure was characterized, and a generalized, empirical model was constructed to relate fiber diameter to fundamental system parameters including viscosity, surface tension, solvent drying rate, and filament stretching velocity. Fibers were produced from three different categories of polymer solutions, each relevant to a specific application. First, carbon nanotube (CNT)-doped poly(methyl methacrylate) (PMMA) was directly-written into fibers and electrical transport through these structures was quantified. Next, pure PMMA fibers were utilized as sacrificial structures in the production of electrokinetic (EK) microchannels by coating the fibers with borosilicate glass and Parylene, and then dissolved the PMMA to yield hollow microchannels. Lastly, microscale biodegradable fibers were employed as biomimetic scaffolds for in vitro directed-growth of endothelial cells (EC) into microvascular-like configurations.;Characterization of the direct-write system suggested that microfiber diameter is controllable through modulation of system geometry and/or polymer solution properties. Furthermore, the relationship between fiber diameter and the aforementioned fundamental system parameters appeared to be relatively conserved from polymer to polymer, with the condition that viscous strain-thinning must be considered for highly non-Newtonian systems, including CNT composites. Some CNT-doped PMMA fibers exhibited conductivities exceeding 0.1 S/m, but these values proved erratic as aggregation prevented consistent percolation of the CNTs within the polymer matrix. EK transport of charged microparticles was successfully induced in sacrificial-PMMA microchannels, and these structures exhibited similar (2% difference) EK mobilities compared with conventionally-fabricated microchannels. ECs were successfully cultured on the scaffolds to >80% confluency and it was observed that cells completely enveloped the fiber circumferences.