The extraordinary permeability and manufacturability of ultrathin silicon-based membranes are enabling devices with improved performance and smaller sizes in such important areas as molecular filtration and sensing, cell culture, electroosmotic pumping, and hemodialysis. Because of the robust chemical and mechanical properties of silicon nitride (SiN), several laboratories have developed techniques for patterning nanopores in SiN using reactive ion etching (RIE) through a template structure. These methods however, have failed to produce pores small enough for ultrafiltration (<100 nm) in SiN and involve templates that are prone to microporous defects. Here we present a facile, wafer-scale method to produce nanoporous silicon nitride (NPN) membranes using porous nanocrystalline silicon (pnc-Si) as a self-assembling, defect free, RIE masking layer. By modifying the mask layer morphology and the RIE etch conditions, the pore sizes of NPN can be adjusted between 40 nm and 80 nm with porosities reaching 40%. The resulting NPN membranes exhibit higher burst pressures than pnc-Si membranes while having 5× greater permeability. NPN membranes also demonstrate the capacity for high resolution separations (<10 nm) seen previously with pnc-Si membranes. We further demonstrate that human endothelial cells can be grown on NPN membranes, verifying the biocompatibility of NPN and demonstrating the potential of this material for cell culture applications.

Silicon nanomembranes are thin nanoporous films that are frequently used as separation tools for nanoparticles and biological materials. In such applications, increased differential pressure across the nanomembranes directly increases process throughput. Therefore, a predictive tool governing the macroscale failure of the porous thin films is fundamentally important in application areas where high differential pressures are desired. Although the deflections and stresses of the nanomembranes can be reliably predicted, a straightforward and prognostic failure model has yet to be outlined. In this publication, a brittle macroscale failure model is established and validated with experimental results. Theoretical agreement with experiments within 10% accuracy offers reliable failure predictions for square membrane dimensions from 60 µm to 1.5 mm through over 100 trials. The methodology relies on an effective fracture toughness from previously published work that is incorporated through Griffith's law. These developments will be useful in the selection of nanomembranes for particular applications and will help guide the design of materials with improved strength. The model should also prove useful for high-volume, in-line processing and inspection of nanomembranes as their role becomes more prominent in industry.

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Two major complications following tendon surgery are adhesion formation and re-rupture. There is a need to develop an ultrasound imaging system for non-invasive, non-destructive, longitudinal monitoring of tendon structure throughout a rehabilitation protocol to optimize restoration of range of motion and mechanical properties. Type I collagen is the primary extracellular matrix protein in tendon, and its organization impacts tendon function. The objective of the present study is to develop a high-frequency quantitative ultrasound spectral analysis technique to characterize collagen fiber alignment in murine tendon. This work tests the hypothesis that the integrated backscatter coefficient (IBC) will exhibit anisotropy in murine tendon with aligned structure, and isotropy in murine liver with inhomogeneous structure. Backscattered echoes from murine tail tendon and liver were acquired at varying insonification angles using 38-MHz and 55-MHz single-element transducers. B-mode and IBC parametric images were computed, and the average IBC value in a region of interest was determined at each insonification angle. The IBC was angular-dependent in tendon and isotropic in liver. These data suggest that the IBC can be used to detect collagen fiber alignment in murine tendon, and contribute to establishing the foundation for a dedicated device to non-invasively monitor collagen remodeling during tendon healing.