The human microbiome includes trillions of bacteria, many of which play a vital role in host physiology. Numerous studies have now detected bacterial DNA in first-pass meconium and amniotic fluid ...samples, suggesting that the human microbiome may commence
. However, these data have remained contentious due to underlying contamination issues. Here, we have used a previously described method for reducing contamination in microbiome workflows to determine if there is a fetal bacterial microbiome beyond the level of background contamination. We recruited 50 women undergoing non-emergency cesarean section deliveries with no evidence of intra-uterine infection and collected first-pass meconium and amniotic fluid samples. Full-length 16S rRNA gene sequencing was performed using PacBio SMRT cell technology, to allow high resolution profiling of the fetal gut and amniotic fluid bacterial microbiomes. Levels of inflammatory cytokines were measured in amniotic fluid, and levels of immunomodulatory short chain fatty acids (SCFAs) were quantified in meconium. All meconium samples and most amniotic fluid samples (36/43) contained bacterial DNA. The meconium microbiome was dominated by reads that mapped to
. Aside from this species, the meconium microbiome was remarkably heterogeneous between patients. The amniotic fluid microbiome was more diverse and contained mainly reads that mapped to typical skin commensals, including
and
spp. All meconium samples contained acetate and propionate, at ratios similar to those previously reported in infants.
reads were inversely correlated with meconium propionate levels. Amniotic fluid cytokine levels were associated with the amniotic fluid microbiome. Our results demonstrate that bacterial DNA and SCFAs are present
, and have the potential to influence the developing fetal immune system.
The ability to control wave propagation in highly deformable layered media with elastic instability-induced wrinkling of interfacial layers is presented. The onset of a wrinkling instability in ...initially straight interfacial layers occurs when a critical compressive strain is achieved. Further compression beyond the critical strain leads to an increase in the wrinkle amplitude of the interfacial layer. This, in turn, gives rise to the formation of a system of periodic scatterers, which reflect and interfere with wave propagation. We demonstrate that the topology of wrinkling interfacial layers can be controlled by deformation and used to produce band gaps in wave propagation and, hence, to selectively filter frequencies. Remarkably, the mechanism of frequency filtering is effective even for composites with similar or identical densities, such as polymer-polymer composites. Since the microstructure change is reversible, the mechanism can be used for tuning and controlling wave propagation by deformation.
Inspired by the imbricated scale-tissue flexible armor of elasmoid fish, we design hybrid stiff plate/soft matrix material architectures and reveal their ability to provide protection against ...penetration while preserving flexibility. Indentation and bending tests on bio-inspired 3D-printed prototype materials show that both protection and flexibility are highly tunable by geometrical parameters of the microstructure (plate inclination angle and volume fraction). We show that penetration resistance can be amplified by a factor of 40, while flexibility decreases in less than 5 times. Different deformation resistance mechanisms are found to govern flexibility (inter-plate matrix shear) versus penetration resistance (localized plate bending) for this microstructural architecture which, in turn, enables separation of these functional requirements in the material design. These experiments identify the tradeoffs between these typically conflicting properties as well as the ability to design the most protective material architecture for a required flexibility, providing new design guidelines for enhanced flexible armor systems.
Materials science. Bioinspired structural materials Ortiz, Christine; Boyce, Mary C
Science (American Association for the Advancement of Science),
2008-Feb-22, 20080222, Letnik:
319, Številka:
5866
Journal Article
Co‐continuous polymer composite materials are designed and fabricated to achieve enhancements in stiffness, strength, and energy dissipation. The mutual constraints between two phases of the ...co‐continuous structure enable enhanced dissipation by spreading of the plastic deformation and by containing cracking leading to a multitude of non‐catastrophic dissipative events, which also provides damage tolerance of the co‐continuous composites.
Suture interfaces with a triangular wave form commonly found in nature have recently been shown to exhibit exceptional mechanical behavior, where geometric parameters such as amplitude, frequency, ...and hierarchy can be used to nonlinearly tailor and amplify mechanical properties. In this study, using the principle of complementary virtual work, we formulate a generalized, composite mechanical model for arbitrarily-shaped interdigitating suture interfaces in order to more broadly investigate the influence of wave-form geometry on load transmission, deformation mechanisms, anisotropy, and stiffness, strength, and toughness of the suture interface for tensile and shear loading conditions. The application of this suture interface model is exemplified for the case of the general trapezoidal wave-form. Expressions for the in-plane stiffness, strength and fracture toughness and failure mechanisms are derived as nonlinear functions of shape factor β (which characterizes the general trapezoidal shape as triangular, trapezoidal, rectangular or anti-trapezoidal), the wavelength/amplitude ratio, the interface width/wavelength ratio, and the stiffness and strength ratios of the skeletal/interfacial phases. These results provide guidelines for choosing and tailoring interface geometry to optimize the mechanical performance in resisting different loads. The presented model provides insights into the relation between the mechanical function and the morphological diversity of suture interface geometries observed in natural systems.
► A general mechanical model for arbitrarily-shaped suture interfaces is formulated. ► Stiffness, strength, toughness and damage tolerance of wavy sutures are quantified. ► Triangular wave shows highest tensile and shear stiffness, strength and toughness. ► Anti-trapezoidal wave-form provides interlocking for flaw tolerance. ► Insights into the morphological diversity of biological interfaces are provided.
Geometrically structured interfaces in nature possess enhanced, and often surprising, mechanical properties, and provide inspiration for materials design. This paper investigates the mechanics of ...deformation and failure mechanisms of suture interface designs through analytical models and experiments on 3D printed polymer physical prototypes. Suture waveforms with generalized trapezoidal geometries (trapezoidal, rectangular, anti-trapezoidal, and triangular) are studied and characterized by several important geometric parameters: the presence or absence of a bonded tip region, the tip angle, and the geometry. It is shown that a wide range (in some cases as great as an order of magnitude) in stiffness, strength, and toughness is achievable dependent on tip bonding, tip angle, and geometry. Suture interfaces with a bonded tip region exhibit a higher initial stiffness due to the greater load bearing by the skeletal teeth, a double peak in the stress–strain curve corresponding to the failure of the bonded tip and the failure of the slanted interface region or tooth, respectively, and an additional failure and toughening mechanism due to the failure of the bonded tip. Anti-trapezoidal geometries promote the greatest amplification of properties for suture interfaces with a bonded tip due the large tip interface area. The tip angle and geometry govern the stress distributions in the teeth and the ratio of normal to shear stresses in the interfacial layers, which together determine the failure mechanism of the interface and/or the teeth. Rectangular suture interfaces fail by simple shearing of the interfaces. Trapezoidal and triangular suture interfaces fail by a combination of shear and tensile normal stresses in the interface, leading to plastic deformation, cavitation events, and subsequent stretching of interface ligaments with mostly elastic deformation in the teeth. Anti-trapezoidal suture interfaces with small tip angles have high stress concentrations in the teeth and fail catastrophically by tooth failure, whereas larger tip angles exhibit a shear failure of the interfaces. Therefore, larger tip angles and trapezoidal or triangular geometries promote graceful failure, and smaller tip angles and anti-trapezoidal geometries promote more brittle-like failure. This dependence is reminiscent of biological systems, which exhibit a range of failure behaviors with limited materials and varied geometry. Triangular geometries uniquely exhibit uniform stress distributions in its teeth and promote the greatest amplification of mechanical properties. In both the bonded and unbonded cases, the predictions from the presented analytical models and experimental results on 3D printed prototypes show excellent agreement. This validates the analytical models and allows for the models to be used as a tool for the design of new materials and interfaces with tailored mechanical behavior.
The elastic–plastic behavior of the polymer electrolyte membrane (PEM) Nafion is characterized via monotonic and cyclic uniaxial tension testing as a function of strain rate, temperature, and ...hydration. Dynamic mechanical analysis shows that, under dry (30%RH) conditions, the material begins to transition from the glassy to the rubbery state at 75
°
C, with a glass transition of 105
°
C. DMA reveals the fully hydrated state to be significantly more compliant than the dry state, with a glass transition beginning at 40
°
C. Large strain monotonic tensile tests find the rate-dependent stress–strain behavior to be highly dependent on temperature and hydration. The dry state transitions from an elastic–plastic behavior at 25
°
C to an increasingly more compliant behavior and lower yield stress as temperature is increased through the glass transition, until exhibiting a rubbery-like behavior at 100
°
C. At 25
°
C, the stress–strain behavior remains elastic-plastic for all hydrated states with the stiffness and yield stress decreasing with increasing hydration. Increasing hydration at all temperatures acts to decrease the initial elastic stiffness and yield stress. Unloading from different strains reveals the elastic-plastic nature of the behavior even for the elevated temperature and hydrated states. Cyclic loading-unloading-reloading excursions to different strains show significant nonlinear recovery at all strains past yield with a highly nonlinear reloading behavior which rejoins the initial loading path. A micromechanically motivated constitutive model consisting of an intermolecular resistance in parallel with an elastic network resistance is shown to be capable of capturing the rate, temperature, and hydration dependence of the monotonic stress-strain behavior. The intermolecular resistance captures the local intermolecular barriers to initial elastic deformation and also captures the thermally activated nature of yield; these intermolecular barriers are modeled to decrease with increasing temperature and hydration, in particular mimicking the reduction in these barriers as the material approaches and enters the glass transition regime, successfully capturing the strong temperature and hydration dependence of the stress-strain behavior. The highly nonlinear post-yield unloading and reloading suggest the development of a back stress during inelastic deformation which aids reverse plastic flow during unloading. Inclusion of a back stress which saturates after reaching a critical level provides an ability to capture the highly nonlinear cyclic loading stress response. Hence, the proposed model provides the capability to describe the complex evolution of stress and strain that occurs in PEM membranes due to the constrained hygrothermal cyclic swelling/deswelling characteristic of membranes in operating fuel cells.
Submicron diameter fibers of polystyrene are electrospun from solutions in dimethylformamide (DMF). When electrospun in a high-humidity environment, the interior of these fibers was found to be ...highly porous rather than consolidated, despite the smooth and nonporous appearance of the fiber surfaces. The formation of interior porosity is attributed to the miscibility of water, a nonsolvent for the polymers in solution, with DMF. The resulting morphology is a consequence of the relatively rapid diffusion of water into the jet, leading to a liquid−liquid phase separation that precedes solidification due to evaporation of DMF from the jet. When electrospun in a low-humidity environment, the fibers exhibit a wrinkled morphology that can be explained by a buckling instability. Understanding which morphology forms under a given set of conditions is achieved through the comparison of three characteristic times: the drying time, the buckling time, and the phase separation time. The morphology has important consequences for the properties of the fibers such as their mechanical strength and stiffness.
Short-chain fatty acids (SCFAs) are increasingly being monitored to elucidate the link between gut health and disease. These metabolites are routinely measured in faeces, but their determination in ...serum is more challenging due to their low concentrations. A method for the determination of eight SCFAs in serum is described here. High-resolution mass spectrometry and gas chromatography were used to identify the presence of isomeric interferences, which were then overcome through a combination of chromatographic separation and judicious choice of MS fragment ion. The SCFAs were derivatised to form 3-nitrophenylhydrazones before being separated on a reversed-phase column and then detected using liquid chromatography tandem mass spectrometry (LC-QQQ-MS). The LODs and LOQs of SCFAs using this method were in the range 1 to 7 ng mL
−1
and 3 to 19 ng mL
−1
, respectively. The recovery of the SCFAs in serum ranged from 94 to 114% over the three concentration ranges tested.
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