Polylactic acid (PLA) and graphene reinforced polylactic acid (PLA‐graphene) composites have been fabricated by three‐dimensional (3D) fused deposition modeling (FDM) printing. Indentation creep resistance was analyzed in terms of the strain‐rate sensitivity index of PLA (0.11) and PLA‐graphene (0.21). Enhanced creep resistance in PLA‐graphene is attributed to the restriction of the polymeric chains by graphene, caused by low strain rates identified during secondary creep. The tribological properties of PLA and PLA‐graphene composites were evaluated by ball‐on‐disk wear tests. Wear resistance was increased by a 14% in PLA‐graphene as compared to PLA. A two‐stage coefficient of friction (COF) behavior has been observed for PLA‐graphene. Initially, PLA‐graphene exhibits a 65% decrease in COF as compared to PLA. During the second stage, PLA‐graphene approached similar COF behavior and value of PLA (∼0.58). PLA‐graphene composites have shown significant improvement in creep and wear resistance demonstrating 3D printing to be a novel manufacturing route. POLYM. COMPOS., 39:3877–3888, 2018. © 2017 Society of Plastics Engineers

Morphological and chemical transformations in boron nitride nanotubes under high temperature atmospheric conditions is probed in this study. We report atmospheric oxygen induced cleavage of boron nitride nanotubes at temperatures exceeding 750 °C for the first time. Unzipping is then followed by coalescence of these densely clustered multiple uncurled ribbons to form stacks of 2D sheets. FTIR and EDS analysis suggest these 2D platelets to be Boron Nitride Oxide platelets, with analogous structure to Graphene Oxide, and therefore we term them as “White Graphene Oxide” (WGO). However, not all BNNTs deteriorate even at temperatures as high as 1000 °C. This leads to the formation of a hybrid nanomaterial system comprising of 1D BN nanotubes and 2D BN oxide platelets, potentially having advanced high temperature sensing, radiation shielding, mechanical strengthening, electron emission and thermal management applications due to synergistic improvement of multi-plane transport and mechanical properties. This is the first report on transformation of BNNT bundles to a continuous array of White Graphene Oxide nanoplatelet stacks.

Graphene foam-based hierarchical polyimide composites with nanoengineered interface are fabricated in this study. Damping behavior of graphene foam is probed for the first time. Multiscale mechanisms contribute to highly impressive damping in graphene foam. Rippling, spring-like interlayer van der Waals interactions and flexing of graphene foam branches are believed to be responsible for damping at the intrinsic, interlayer and anatomical scales, respectively. Merely 1.5 wt% graphene foam addition to the polyimide matrix leads to as high as ≈300% improvement in loss tangent. Graphene nanoplatelets are employed to improve polymer-foam interfacial adhesion by arresting polymer shrinkage during imidization and π-π interactions between nanoplatelets and foam walls. As a result, damping behavior is further improved due to effective stress transfer from the polymer matrix to the foam. Thermo-oxidative stability of these nanocomposites is investigated by exposing the specimens to glass transition temperature of the polyimide (≈400 °C). The composites are found to retain their damping characteristics even after being subjected to such extreme temperature, attesting their suitability in high temperature structural applications. Their unique hierarchical nanostructure provides colossal opportunity to engineer and program material properties.

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Ultra-long Boron Nitride Nanotubes (100-200 mm) based layered Al-BNNT-Al composites are fabricated by spark plasma sintering, followed by cold rolling. The BNNT mat is sputter coated with Al to engineer strong metal-nanotube interface. The BNNTs exhibit perfect alignment along the cold rolling direction. The tensile strength of the composite is found to be 200 MPa, which is 400% greater than the strength of pure Al (%40 MPa). Young's modulus of this sandwich composite (%134 GPa) is found to be double the modulus of pure Al (%70 GPa) (with standard deviations less than 10%). Strengthening is explained by three major mechanisms: superior load transfer for long BNNT reinforcement, improvement in matrix-nanotube bonding due to trace amount of interfacial product formation, and crack bridging by directionally aligned long nanotubes.

Biomimetic on-chip tissue models serve as a powerful tool for studying human physiology and developing therapeutics; however, their modeling power is hindered by our inability to develop highly ordered functional structures in small length scales. Here, we demonstrate how high-precision fabrication can enable scaled-down modeling of organ-level cardiac mechanical function. We use two-photon direct laser writing (TPDLW) to fabricate a nanoscale-resolution metamaterial scaffold with fine-tuned mechanical properties to support the formation and cyclic contraction of a miniaturized, induced pluripotent stem cell–derived ventricular chamber. Furthermore, we fabricate microfluidic valves with extreme sensitivity to rectify the flow generated by the ventricular chamber. The integrated microfluidic system recapitulates the ventricular fluidic function and exhibits a complete pressure-volume loop with isovolumetric phases. Together, our results demonstrate a previously unexplored application of high-precision fabrication that can be generalized to expand the accessible spectrum of organ-on-a-chip models toward structurally and biomechanically sophisticated tissue systems.

Boron Nitride Nanotube (BNNT) is a promising reinforcement for developing strong and lightweight metal matrix composites due to its brilliant mechanical properties and excellent high-temperature oxidation resistance. In this study, layered composites of aluminum and BNNT are fabricated by a multistep process comprising of hot pressing, rolling, and annealing. Less than 0.1 wt% of ultra-long nanotubes (up to 200 μm in length) are used to induce superior strengthening. For achieving enhanced mechanical properties, nanotubes are de-agglomerated and chemically dispersed in an aqueous solution before introducing between the layers of aluminum sheets. Application of pressure (up to 10 MPa) and temperatures (up to 300 C) during rolling and hot pressing induces a bonding between aluminum sheets and nanotubes. Scanning electron microscopy reveals that the nanotubes survive these conditions, suggesting superior thermal and mechanical endurance of BNNT. The nanohardness and elastic modulus of the composites are found to improve by 52% and 17%, respectively, by merely 0.045 wt% BNNT addition. BNNT reinforced composites exhibit up to 13% improvement in ultimate tensile strength. The improvement in mechanical properties is ascribed to effective load transfer from the aluminum matrix to the long nanotubes via interfacial shear stress and enhancement of dislocation density.

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