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The effects of regional variations in oxygen and temperature levels with depth were assessed for the metabolism and hypoxia tolerance of dominant euphausiid species. The physiological strategies employed by these species facilitate prediction of changing vertical distributions with expanding oxygen minimum zones and inform estimates of the contribution of vertically migrating species to biogeochemical cycles. The migrating species from the Eastern Tropical Pacific (ETP), Euphausia eximia and Nematoscelis gracilis, tolerate a Partial Pressure (PO2) of 0.8 kPa at 10 8C (15 mM O2) for at least 12 h without mortality, while the California Current species, Nematoscelis difficilis, is incapable of surviving even 2.4 kPa PO2 (32 mM O2) for more than 3 h at that temperature. Euphausia diomedeae from the Red Sea migrates into an intermediate oxygen minimum zone, but one in which the temperature at depth remains near 22 8C. Euphausia diomedeae survived 1.6 kPa PO2 (22 mM O2) at 228C for the duration of six hour respiration experiments. Critical oxygen partial pressures were estimated for each species, and, for E. eximia, measured via oxygen consumption (2.1 kPa, 10 8C, n¼2) and lactate accumulation (1.1 kPa, 10 8C). A primary mechanism facilitating low oxygen tolerance is an ability to dramatically reduce energy expenditure during daytime forays into low oxygen waters. The ETP and Red Sea species reduced aerobic metabolism by more than 50% during exposure to hypoxia. Anaerobic glycolytic energy production, as indicated by whole-animal lactate accumulation, contributed only modestly to the energy deficit. Thus, the total metabolic rate was suppressed by 49–64%. Metabolic suppression during diel migrations to depth reduces the metabolic contribution of these species to vertical carbon and nitrogen flux (i.e., the biological pump) by an equivalent amount. Growing evidence suggests that metabolic suppression is a widespread strategy among migrating zooplankton in oxygen minimum zones and may have important implications for the economy and ecology of the oceans. The interacting effects of oxygen and temperature on the metabolism of oceanic species facilitate predictions of changing vertical distribution with climate change.
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An Integrated Approach to Control the Penetration Depth of 3D-Printed Hollow Microneedles
A variety of hollow microneedle (HMN) designs has emerged for minimally invasive therapies and monitoring systems. In this study, a design change limiting the indentation depth of the (3D) printed custom microneedle assembly (circular array of five conical frusta with and without a stopper, aspect ratio = 1.875) fabricated using stereolithography has been experimentally validated and modeled in silico. The micro-indentation profiles generated in confined compression on 1 mm ± 0.073 mm alginate films enabled the generation of a Prony series, where displacement ranged from 100 to 250 µm. These constants were used as intrinsic properties simulating experimental ramp/release profiles. Puncture occurred on two distinct hydrogel formulations at the design depth of 150 µm and indentation rate of 0.1 mm/s characterized by a peak force of 3.5 N (H = 31 kPa) and 8.3 N (H = 36.5 kPa), respectively. Experimental and theoretical alignments for peak force trends were obtained when the printing resolution was simulated. Higher puncture force and uniformity inferred by the stopper was confirmed via microscopy and profilometry. Meanwhile, poroviscoelasticity characterization is required to distinguish mass loss vs. redistribution post-indentation through pycnometry. Results from this paper highlight the feasibility of insertion-depth control within the epidermis thickness for the first time in solid HMN literature.
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- Award ID(s):
- 2216061
- PAR ID:
- 10524970
- Publisher / Repository:
- mdpi
- Date Published:
- Journal Name:
- Applied Mechanics
- Volume:
- 5
- Issue:
- 2
- ISSN:
- 2673-3161
- Page Range / eLocation ID:
- 233 to 260
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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- Free Publicly Accessible Full Text
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Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.3390/applmech5020015
