No abstract

Biofilm growth has been observed in Soviet/Russian (Salyuts and Mir), American (Skylab), and International (ISS) Space Stations, sometimes jeopardizing key equipment like spacesuits, water recycling units, radiators, and navigation windows. Biofilm formation also increases the risk of human illnesses and therefore needs to be well understood to enable safe, long-duration, human space missions. Here, the design of a NASA-supported biofilm in space project is reported. This new project aims to characterize biofilm inside the International Space Station in a controlled fashion, assessing changes in mass, thickness, and morphology. The space-based experiment also aims at elucidating the biomechanical and transcriptomic mechanisms involved in the formation of a “column-and-canopy” biofilm architecture that has previously been observed in space. To search for potential solutions, different materials and surface topologies will be used as the substrata for microbial growth. The adhesion of bacteria to surfaces and therefore the initial biofilm formation is strongly governed by topographical surface features of about the bacterial scale. Thus, using Direct Laser-Interference Patterning, some material coupons will have surface patterns with periodicities equal, above or below the size of bacteria. Additionally, a novel lubricant-impregnated surface will be assessed for potential Earth and spaceflight anti-biofilm applications. This paper describes the current experiment design including microbial strains and substrata materials and nanotopographies being considered, constraints and limitations that arise from performing experiments in space, and the next steps needed to mature the design to be spaceflight-ready.

Mineral-fouling induced corrosion and deterioration of marine vessels, aircraft, and coastal structures is due in part from structural intrusion of crystals grown from ocean-generated saline drops. As such, much work has explored surface treatments that induce hydrophobicity or introduce barriers for antifouling and corrosion prevention; however, the efficacy of these strategies will be altered by the underlying substrate texture. Here, we study the behavior of evaporating saline drops on superhydrophobic and liquid-impregnated surfaces as a function of surface texture. On superhydrophobic surfaces, four disparate regimes (which are not observed for particle-laden drops) emerge as a function of the substrate solid fraction: Cassie-pinning, Cassie-gliding, Cassie-Wenzel transition, and Wenzel. These regimes control the morphology of the resultant crystal deposits. In contrast to the superhydrophobic surfaces, spreading liquid-impregnated surfaces demonstrate minimal influence of solid fraction on evaporative crystallization. The area, area localization, timescale of evaporation, and deposit morphology are all normalized by the presence of the lubricating layer, thus introducing an efficient method of eliminating crystal "coffee rings" as well as reducing the potential for fouling and corrosion.

Trenbolone acetate metabolites are endocrine-active contaminants discharged into the aquatic environment in runoff from agricultural fields, rangelands, and concentrated animal feeding operations. To investigate the environmental fate of these compounds and their biotransformation mechanisms, the authors used inocula from a variety of different water sources and dosed biologically active microcosms with approximately 1400 ng/L of trenbolone acetate metabolites, including 17β-trenbolone, trendione, and 17α-trenbolone. To investigate aerobic biotransformation rates and interconversions between known trenbolone acetate metabolites, gas chromatography-tandem mass spectrometry was used to measure concentrations and assess product distributions as a function of time. High-resolution liquid chromatography-tandem mass spectrometry (LC-MS/MS) was used to characterize novel transformation products and potential transformation pathways. Kinetic analysis yields observed half-lives of approximately 0.9 d, 1.3 d, and 2.2 d for 17β-trenbolone, trendione, and 17α-trenbolone, respectively, at 20 °C, although colder conditions increased half-lives to 8.5 d and biphasic transformation was observed. Relative to reported faster attenuation rates in soils, trenbolone acetate metabolites are likely more persistent in aqueous systems. Product distributions indicate an enzymatic preference for biotransformation between trendione and 17β-trenbolone. The LC-MS/MS characterization indicates dehydrogenation products as the major detectable products and demonstrates that major structural elements responsible for bioactivity in steroids are likely retained during biotransformation.

Mineral or crystal fouling (the accumulation of precipitants on a material and damage associated with the same) is a pervasive problem in water treatment, thermoelectric power production, and numerous industrial processes. Growing efforts have focused on materials engineering strategies (e.g., superhydrophobicity) to prevent fouling. Here, we present a curious phenomenon in which crystals self-eject from heated, nanotextured superhydrophobic materials during evaporation of saline water drops. These crystal structures (crystal critters) have exceedingly minimal contact with the substrate and thus pre-empt crystal fouling. This unusual phenomenon is caused by cooperative effects of crystallization, evaporative flows, and nanoscale effects. The temperature dependence of the critter effect can be predicted using principles of mass conservation, and we demonstrate that self-propulsion can be generated via temperature gradients, which promote asymmetric growth. The insights on confinement-driven evaporative crystallization can be applied for antifouling by self-ejection of mineral foulants, for drop-based fluidic machines, or even for self-propulsion.

A diverse range of proteins can assemble into amyloid fibrils, a process that generally results in a loss of function and an increase in toxicity. The occurrence and rate of conversion is strongly dependent on several factors including molecular structure and exposure to hydrodynamic forces. To investigate the origins of shear-induced enhancement in the rate of fibrillization, a stable rotating Couette flow was used to evaluate the kinetics of amyloid formation under uniform shear for two similar insulin species (human and bovine) that demonstrate unique fibrillization kinetics. The presence of shear-induced nuclei predicted by previous studies is supported by observations of a lag between the consumption of soluble insulin and the precipitation of amyloid aggregates. The apparent fibrillization rate generally increases with shear. However, a two-parameter kinetic model revealed that the nucleation rate has a maximum value at intermediate shear rates. The fibril elongation rate increases monotonically with shear and is similar for both insulin variants, suggesting that increased elongation rates are related to mixing. Differences between human and bovine insulin kinetics under shear are attributable to the nucleation step.

Amyloidogenesis of proteins is of wide interest because amyloid structures are associated with many diseases, including Alzheimer's and type II diabetes. Dozens of different proteins of various sizes are known to form amyloid fibrils. While there are numerous studies on the fibrillization of insulin induced by various perturbations, shearing at fluid interfaces has not received as much attention. Here, we present a study of human insulin fibrillization at room temperature using a deep-channel surface viscometer. The hydrodynamics of the bulk flow equilibrates in just over a minute, but the proteins at the air-water interface exhibit a very slow development during which the surface (excess) shear viscosity deduced from a Newtonian surface model increases slightly over a period of a day and a half. Then, there is a very rapid increase in the surface shear viscosity to effectively unbounded levels as the interface becomes immobilized. Atomic force microscopy shows that fibrils appear at the interface after it becomes immobilized. Fibrillization in the bulk does not occur until much later. This has been verified by concurrent atomic force microscopy and circular dichroism spectroscopy of samples from the bulk. The immobilized interface has zero in-plane shear rate, however due to the bulk flow, there is an increase in the strength of the normal component of the shear rate at the interface, implicating this component of shear in the fibrillization process ultimately resulting in a thick weave of fibrils on the interface. Real-time detection of fibrillization via interfacial rheology may find utility in other studies of proteins at sheared interfaces.

Agitation of protein is known to induce deleterious effects on protein stability and structure, with extreme agitation sometimes resulting in complete aggregation into amyloid fibrils. Many mechanisms have been proposed to explain how protein becomes unstable when subjected to flow, including alignment of protein species, shear-induced unfolding, simple mixing, or fragmentation of existing fibrils to create new seeds. Here a shearing flow was imposed on a solution of monomeric human insulin via a rotating Couette device with a small hydrophobic fluid interface. The results indicate that even very low levels of shear are capable of accelerating amyloid fibril formation. Simulations of the flow suggest that the shear enhances fibrillization kinetics when flow inertia is non-negligible and the resulting meridional circulation allows for advection of bulk protein to the hydrophobic interface.