(348h) STEP Enabled Isodiameteric Design Space for Ordered Deposition and Characterization of Polymeric Micro/Nanofiber Arrays

Polymeric nanofibers are finding increasing number of applications and hold the potential to revolutionize diverse fields such as tissue engineering, smart textiles, sensors, and actuators. Aligning and producing long smooth, uniform and defect-free fibers with control on fiber dimensions at the submicron and nanoscale has been challenging due to fragility of polymeric materials. Besides fabrication, the other challenge lies in the ability to characterize these fibers for material properties. Using our previously reported Spinneret based Tunable Engineered Parameters (STEP) technique; we are able to fabricate and deposit high aspect ratio (length/diameter) fiber arrays of different polymeric systems (Diameter: sub-50 nm-sub-micron and Length: several mm-cm) in single and multiple layers at tunable geometrical spacing's. In the proposed fabrication strategy, polymeric solution is continuously pumped through a glass micropipette which is collected in the form of aligned fiber arrays on a rotating substrate. Using this approach, we demonstrate single and multi-layer architectures of several polymeric systems such as Polystyrene (PS), Poly(methyl methacrylate) (PMMA), Poly lactic acid (PLA), and poly(lactic-co-glycolic acid) (PLGA). We demonstrate that uniform diameter fiber formation occurs at molecular entanglements corresponding to the onset of semi-dilute entangled domains, which is significantly lower than the predictions from electrospinning methods. The scaling laws developed for estimating fiber diameter from solution rheologies are used to map isodiameters (20-2000 nm) on the solution rheology design space for the first time. The proposed technology expandable to other polymeric systems is extremely attractive to a wide range of researchers and is envisioned to be instrumental in building hierarchical 3D polymeric fibrous structures for engineering ultra high strength textiles, biological scaffolds and sensor systems, besides enhancing our understanding of soft material behavior at nanoscale. Secondly, we demonstrate successful mechanical characterization of fabricated fibers with diameters as small as 34 nm using an Integrated Approach. In this approach, the fibers are first deposited on commercially available Transmission Electron Microscopy (TEM) grids in aligned configurations and are mapped for accurate locations under the TEM. Subsequently, the fibers are carefully placed under the AFM and mechanically characterized for flexural modulus using lateral force microscopy (LFM). Finally, accurate fiber dimensions are determined under the Scanning Electron Microscope (SEM). The unique advantage of this approach lies in the ability to deposit a large number of fibers with tunable diameters in aligned configurations with fixed-fixed boundary conditions and requires no external manipulation. The methods developed in this study will greatly aid in increasing our fundamental knowledge of polymeric materials at reduced lengthscales and allow integration of these one-dimensional building blocks in bottom-up assembly environments. This fundamental research presented here is expected to contribute to a paradigm shift in the nano-manufacturing and hierarchical assembly of functional materials and will potentially revolutionize approaches in drug delivery, drug testing platforms for pharmaceutical companies, ballistic armors, antifouling coatings, and batteries through nanostructured materials.