Publications by authors named "David McKenzie"

219 Publications

The role of mechanistic physiology in investigating impacts of global warming on fishes.

J Exp Biol 2021 Feb 24;224(Pt Suppl 1). Epub 2021 Feb 24.

Marine Biodiversity, Exploitation and Conservation (MARBEC), Université de Montpellier, CNRS, Ifremer, IRD, 34000 Montpellier, France.

Warming of aquatic environments as a result of climate change is already having measurable impacts on fishes, manifested as changes in phenology, range shifts and reductions in body size. Understanding the physiological mechanisms underlying these seemingly universal patterns is crucial if we are to reliably predict the fate of fish populations with future warming. This includes an understanding of mechanisms for acute thermal tolerance, as extreme heatwaves may be a major driver of observed effects. The hypothesis of gill oxygen limitation (GOL) is claimed to explain asymptotic fish growth, and why some fish species are decreasing in size with warming; but its underlying assumptions conflict with established knowledge and direct mechanistic evidence is lacking. The hypothesis of oxygen- and capacity-limited thermal tolerance (OCLTT) has stimulated a wave of research into the role of oxygen supply capacity and thermal performance curves for aerobic scope, but results vary greatly between species, indicating that it is unlikely to be a universal mechanism. As thermal performance curves remain important for incorporating physiological tolerance into models, we discuss potentially fruitful alternatives to aerobic scope, notably specific dynamic action and growth rate. We consider the limitations of estimating acute thermal tolerance by a single rapid measure whose mechanism of action is not known. We emphasise the continued importance of experimental physiology, particularly in advancing our understanding of underlying mechanisms, but also the challenge of making this knowledge relevant to the more complex reality.
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http://dx.doi.org/10.1242/jeb.238840DOI Listing
February 2021

Mapping solar magnetic fields from the photosphere to the base of the corona.

Sci Adv 2021 Feb 19;7(8). Epub 2021 Feb 19.

Institute for Solar Physics, Department of Astronomy, Stockholm University, AlbaNova University Centre, SE-106 91, Stockholm, Sweden.

Routine ultraviolet imaging of the Sun's upper atmosphere shows the spectacular manifestation of solar activity; yet, we remain blind to its main driver, the magnetic field. Here, we report unprecedented spectropolarimetric observations of an active region plage and its surrounding enhanced network, showing circular polarization in ultraviolet (Mg ii & and Mn i) and visible (Fe i) lines. We infer the longitudinal magnetic field from the photosphere to the very upper chromosphere. At the top of the plage chromosphere, the field strengths reach more than 300 G, strongly correlated with the Mg ii line core intensity and the electron pressure. This unique mapping shows how the magnetic field couples the different atmospheric layers and reveals the magnetic origin of the heating in the plage chromosphere.
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http://dx.doi.org/10.1126/sciadv.abe8406DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7895431PMC
February 2021

Evaluating CNVII Recovery after Reconstruction with Vascularized Nerve Grafts: A Retrospective Case Series.

Plast Reconstr Surg Glob Open 2021 Jan 22;9(1):e3374. Epub 2021 Jan 22.

Section of Plastic Surgery, Department of Surgery, University of Calgary, Calgary, Alberta, Canada.

Few studies have evaluated vascularized nerve grafts (VNGs) for facial nerve (CNVII) reconstruction. We sought to evaluate long-term outcomes for CNVII recovery following reconstruction with VNGs. A retrospective review of all patients at a tertiary centre who underwent radical parotidectomy and immediate CNVII reconstruction with VNGs was performed (January 2009-December 2019). Preoperative demographics, perioperative factors (flap type, source of VNGs), and postoperative factors [complications, adjuvant therapy, revisionary procedures, length of follow-up, and CNVII function via the House-Brackmann scale (HB)] were collected. Data were summarized qualitatively. Twelve patients (M = 53 ± 18 years) with a mean follow-up of 33 (± 23) months were included. Six patients underwent reconstruction with a radial forearm flap and dorsal sensory branches of the radial nerve. Six patients underwent reconstruction with an anterolateral thigh flap and only deep motor branches of the femoral nerve to the vastus lateralis (n = 4) or combined with the lateral femoral cutaneous nerve (n = 2). Two patients regained nearly normal function (HB = 2). Eight patients regained at least resting symmetry (HB = 3 for n = 7; HB = 4 for n = 1). One patient regained a flicker of movement (HB = 5). One patient did not regain function (HB = 6). Six patients had static revision procedures to improve symmetry. Five patients had disease recurrence; 3 died from their disease. VNGs offer a practical and viable addition to the CNVII reconstruction strategy, and result in good functional recovery with acceptable donor site deficits. The associated adipofascial component of these flaps can also augment the soft tissue defect left after tumor ablation.
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http://dx.doi.org/10.1097/GOX.0000000000003374DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7861610PMC
January 2021

Use of an Omental Flow-Through Flap for Recipient Vessels in the Reconstruction of a Lumbar Spine Defect: A Case Report.

JBJS Case Connect 2020 Dec 4;10(4):e20.00156. Epub 2020 Dec 4.

Section of Plastic Surgery, Department of Surgery, University of Calgary, Calgary, Alberta, Canada.

Case: Spine reconstruction after en bloc spondylectomy is challenging and may require multidisciplinary intervention. En bloc spine tumor resection with embolization of local recipient vessels for tumor control limits reconstructive options. Herein, we describe a case where combined efforts from orthopaedic, general, and plastic surgery teams permitted the successful reconstruction of a multilevel lumbar vertebral defect.

Conclusion: A fibula-free flap within a titanium cage construct anastomosed to the left gastroepiploic vessels via a pedicled omental flow-through flap is a viable and novel method for reconstruction of a multilevel vertebral defect.
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http://dx.doi.org/10.2106/JBJS.CC.20.00156DOI Listing
December 2020

Imaging prior to radiotherapy impacts survival.

Phys Imaging Radiat Oncol 2020 Oct 28;16:138-143. Epub 2020 Nov 28.

VectorLAB, Radiation Oncology, Chris O'Brien Lifehouse, Missenden Rd, Camperdown, Sydney, NSW 2050, Australia.

Background And Purpose: Cone Beam Computed Tomography (CBCT) is routinely used in radiotherapy to identify the position of the target volume. The aim of this study was to determine whether the CBCT dose, when followed by the treatment, influences the therapeutic outcomes as determined by in-vitro clonogenic cell survival in a radiobiological experiment.

Materials And Methods: Human cell lines, four cancer and one normal, were exposed to a 6 MV photon beam, produced by a linear accelerator. For half of each sample, a prior imaging dose was delivered using the on-board CBCT. A sample size of n = 103 was used to achieve statistical power.

Results: The experimental group of cell lines exposed to CBCT imaging prior to treatment exhibited a reduction in mean cancer cell survival of ~17 times (p = 0.02) greater than predicted from the average dose response and equivalent to more than 5% of the therapeutic dose, compared to 11 times greater than predicted for normal cells (n.s.).

Conclusion: The greater than predicted reduction in survival resulting from the additional CBCT dose is consistent with radiation-induced bystander effects.
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http://dx.doi.org/10.1016/j.phro.2020.11.003DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7807556PMC
October 2020

Intraspecific variation in tolerance of warming in fishes.

J Fish Biol 2020 Nov 20. Epub 2020 Nov 20.

Department of Zoology, University of British Columbia, Vancouver, British Columbia, Canada.

Intraspecific variation in key traits such as tolerance of warming can have profound effects on ecological and evolutionary processes, notably responses to climate change. The empirical evidence for three primary elements of intraspecific variation in tolerance of warming in fishes is reviewed. The first is purely mechanistic that tolerance varies across life stages and as fishes become mature. The limited evidence indicates strongly that this is the case, possibly because of universal physiological principles. The second is intraspecific variation that is because of phenotypic plasticity, also a mechanistic phenomenon that buffers individuals' sensitivity to negative impacts of global warming in their lifetime, or to some extent through epigenetic effects over successive generations. Although the evidence for plasticity in tolerance to warming is extensive, more work is required to understand underlying mechanisms and to reveal whether there are general patterns. The third element is intraspecific variation based on heritable genetic differences in tolerance, which underlies local adaptation and may define long-term adaptability of a species in the face of ongoing global change. There is clear evidence of local adaptation and some evidence of heritability of tolerance to warming, but the knowledge base is limited with detailed information for only a few model or emblematic species. There is also strong evidence of structured variation in tolerance of warming within species, which may have ecological and evolutionary significance irrespective of whether it reflects plasticity or adaptation. Although the overwhelming consensus is that having broader intraspecific variation in tolerance should reduce species vulnerability to impacts of global warming, there are no sufficient data on fishes to provide insights into particular mechanisms by which this may occur.
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http://dx.doi.org/10.1111/jfb.14620DOI Listing
November 2020

Oxygen uptake, heart rate and activities of locomotor muscles during a critical swimming speed protocol in the gilthead sea bream Sparus aurata.

J Fish Biol 2020 Nov 20. Epub 2020 Nov 20.

Marbec, Université Montpellier, CNRS, Ifremer, IRD, Montpellier, France.

Oxygen uptake, heart rate and contraction frequencies of slow oxidative (SO) and fast glycolytic (FG) muscle were measured simultaneously in gilthead seabream Sparus aurata submitted to stepwise increases in current speed in a swimming respirometer. Variation in oxygen uptake was closely related to variation in heart rate, over initial steps these rose in concert with an increase in contraction frequency of SO muscle. There was an asymptote in oxygen uptake and heart rate at high speeds that reflected a transition from exclusive use of aerobic SO muscle to a combination of SO and anaerobic FG muscle, and which preceded fatigue.
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http://dx.doi.org/10.1111/jfb.14621DOI Listing
November 2020

Investigation of Room Temperature Formation of the Ultra-Hard Nanocarbons Diamond and Lonsdaleite.

Small 2020 Dec 4;16(50):e2004695. Epub 2020 Nov 4.

Research School of Physics, The Australian National University, Canberra, ACT, 2601, Australia.

Diamond is an attractive material due to its extreme hardness, high thermal conductivity, quantum optical, and biomedical applications. There is still much that is not understood about how diamonds form, particularly at room temperature and without catalysts. In this work, a new route for the formation of nanocrystalline diamond and the diamond-like phase lonsdaleite is presented. Both diamond phases are found to form together within bands with a core-shell structure following the high pressure treatment of a glassy carbon precursor at room temperature. The crystallographic arrangements of the diamond phases revealed that shear is the driving force for their formation and growth. This study gives new understanding of how shear can lead to crystallization in materials and helps elucidate how diamonds can form on Earth, in meteorite impacts and on other planets. Finally, the new shear induced formation mechanism works at room temperature, a key finding that may enable diamond and other technically important nanomaterials to be synthesized more readily.
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http://dx.doi.org/10.1002/smll.202004695DOI Listing
December 2020

Remote-learning, time-use, and mental health of Ecuadorian high-school students during the COVID-19 quarantine.

World Dev 2021 Feb 22;138:105225. Epub 2020 Oct 22.

HEC Paris, France.

The COVID-19 pandemic has closed schools around the world, forcing school systems and students to quickly attempt remote learning. We conducted a rapid response phone survey of over 1500 high school students aged 14 to 18 in Ecuador to learn how students spend their time during the period of quarantine, examine their access to remote learning, and measure their mental health status. We find 59 percent of students have both an internet connection at home and a computer or tablet, 74 percent are engaging in some online or telelearning, and 86 percent have done some schoolwork on the last weekday. Detailed time-use data show most students have established similar daily routines around education, although gender and wealth differences emerge in time spent working and on household tasks. Closure of schools and social isolation are the two main problems students say they face, and while the majority are mostly happy, 16 percent have mental health scores that indicate depression.
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http://dx.doi.org/10.1016/j.worlddev.2020.105225DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7581322PMC
February 2021

Social dynamics obscure the effect of temperature on air breathing in catfish.

J Exp Biol 2020 Nov 12;223(Pt 21). Epub 2020 Nov 12.

Institute of Biodiversity, Animal Health and Comparative Medicine, College of Medical, Veterinary and Life Sciences, University of Glasgow, Glasgow G12 8QQ, UK

In some fishes, the ability to breathe air has evolved to overcome constraints in hypoxic environments but comes at a cost of increased predation. To reduce this risk, some species perform group air breathing. Temperature may also affect the frequency of air breathing in fishes, but this topic has received relatively little research attention. This study examined how acclimation temperature and acute exposure to hypoxia affected the air-breathing behaviour of a social catfish, the bronze corydoras , and aimed to determine whether individual oxygen demand influenced the behaviour of entire groups. Groups of seven fish were observed in an arena to measure air-breathing frequency of individuals and consequent group air-breathing behaviour, under three oxygen concentrations (100%, 60% and 20% air saturation) and two acclimation temperatures (25 and 30°C). Intermittent flow respirometry was used to estimate oxygen demand of individuals. Increasingly severe hypoxia increased air breathing at the individual and group levels. Although there were minimal differences in air-breathing frequency among individuals in response to an increase in temperature, the effect of temperature that did exist manifested as an increase in group air-breathing frequency at 30°C. Groups that were more socially cohesive during routine activity took more breaths but, in most cases, air breathing among individuals was not temporally clustered. There was no association between an individual's oxygen demand and its air-breathing frequency in a group. For , although air-breathing frequency is influenced by hypoxia, behavioural variation among groups could explain the small overall effect of temperature on group air-breathing frequency.
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http://dx.doi.org/10.1242/jeb.222133DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7673363PMC
November 2020

Covalent Immobilization of -Acetylcysteine on a Polyvinyl Chloride Substrate Prevents Bacterial Adhesion and Biofilm Formation.

Langmuir 2020 11 20;36(43):13023-13033. Epub 2020 Oct 20.

Department of Infectious Diseases and Immunology, School of Medical Science, The University of Sydney, Camperdown 2006, Australia.

Biofilm formation and antimicrobial resistance at surgical implant sites result in high morbidity and mortality. Identifying novel molecules that inhibit biofilm formation to coat surgical biomaterials is essential. One such compound is -acetylcysteine (NAC), a potent antioxidant precursor for glutathione, necessary in mammalian cells and known to disrupt/prevent biofilms. In this study, NAC was covalently immobilized onto functionalized polyvinyl chloride surfaces using plasma immersion ion implantation (PIII) treatment that achieves covalent binding without the need for linker groups. NAC immobilization was characterized using water contact angles, Fourier-transform infrared, and X-ray photoelectron spectroscopy techniques. Bacterial viability and biofilm formation on NAC surfaces were assessed using resazurin assays, phase contrast microscopy, and colony counting experiments. Effect of NAC on bacterial polysaccharide production and DNA cleaving was investigated using the phenol-sulfuric acid method and the Qubit fluorometer. Surface thermodynamics between the NAC coating and bacterial cells were measured using the Lewis acid-base method. Surface characterization techniques demonstrated superficial changes after PIII treatment and subsequent covalent NAC immobilization. NAC-coated surfaces significantly reduced biofilm viability and the presence of Gram-negative and Gram-positive bacteria. NAC also decreased polysaccharide production and degraded DNA. This led to unfavorable conditions for biofilm formation on NAC-coated surfaces, as demonstrated by surface thermodynamic analysis. NAC-coated surfaces showed no cytotoxicity to human fibroblast cells. This study has successfully utilized NAC as an antibiofilm coating, which may pave the way for improved prophylactic coatings on medical implant devices in the future.
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http://dx.doi.org/10.1021/acs.langmuir.0c02414DOI Listing
November 2020

Cancer treatment with gas plasma and with gas plasma-activated liquid: positives, potentials and problems of clinical translation.

Biophys Rev 2020 Aug 5;12(4):989-1006. Epub 2020 Aug 5.

VectorLAB, Chris O'Brien Lifehouse, Camperdown, NSW, 2050, Australia.

Gas plasmas, created in atmospheric pressure conditions, both thermal (hot) and non-thermal (cold) are emerging as useful tools in medicine. During surgery, hot gas plasmas are useful to reduce thermal damage and seal blood vessels. Gas plasma pens use cold gas plasma to produce reactive chemical species with selective action against cancers, which can be readily exposed in surgery or treated from outside of the body. Solutions activated by cold gas plasma have potential as a novel treatment modality for treatment of less readily accessible tumours, or those with high metastatic potential. This review summarises the preclinical and clinical trial evidence currently available, as well as the challenges for translation of direct gas plasma and gas plasma-activated solution treatment into regular practice.
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http://dx.doi.org/10.1007/s12551-020-00743-zDOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7429664PMC
August 2020

Atmospheric Pressure Plasma Jet Treatment of Polymers Enables Reagent-Free Covalent Attachment of Biomolecules for Bioprinting.

ACS Appl Mater Interfaces 2020 Aug 11;12(34):38730-38743. Epub 2020 Aug 11.

School of Physics, The University of Sydney, Sydney, New South Wales 2006 Australia.

Three-dimensional (3D) bioprinting, where cells, hydrogels, and structural polymers can be printed layer by layer into complex designs, holds great promise for advances in medicine and the biomedical sciences. In principle, this technique enables the creation of highly patient-specific disease models and biomedical implants. However, an ability to tailor surface biocompatibility and interfacial bonding between printed components, such as polymers and hydrogels, is currently lacking. Here we demonstrate that an atmospheric pressure plasma jet (APPJ) can locally activate polymeric surfaces for the reagent-free covalent attachment of proteins and hydrogel in a single-step process at desired locations. Polyethylene and poly-ε-caprolactone were used as example polymers. Covalent attachment of the proteins and hydrogel was demonstrated by resistance to removal by rigorous sodium dodecyl sulfate washing. The immobilized protein and hydrogel layers were analyzed using Fourier transform infrared and X-ray photoelectron spectroscopy. Importantly, the APPJ surface activation also rendered the polymer surfaces mildly hydrophilic as required for optimum biocompatibility. Water contact angles were observed to be stable within a range where the conformation of biomolecules is preserved. Single and double electrode designs of APPJs were compared in their characteristics relevant to localized surface functionalization, plume length, and shape. As a proof of efficacy in a biological context, APPJ-treated polyethylene functionalized with fibronectin was used to demonstrate improvements in cell adhesion and proliferation. These results have important implications for the development of a new generation of 3D bioprinters capable of spatially patterned and tailored surface functionalization performed during the 3D printing process .
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http://dx.doi.org/10.1021/acsami.0c07169DOI Listing
August 2020

The impact of a quality management program for patients undergoing head and neck resection with free-flap reconstruction: longitudinal study examining sustainability.

J Otolaryngol Head Neck Surg 2020 Jun 23;49(1):42. Epub 2020 Jun 23.

Section of Otolaryngology Head & Neck Surgery, Department of Surgery, University of Calgary Cumming School of Medicine, 3280 Hospital Drive NW, Calgary, Alberta, T2N 4Z6, Canada.

Background: Care pathways (CPs) are helpful in reducing unwanted variation in clinical care. Most studies of CPs show they improve clinical outcomes but there is little known about the long-term impact of CPs as part of a sustained quality management program. Head and neck (HN) surgery with free flap reconstruction is complex, time-consuming and expensive. Complications are common and therefore CPs applied to this patient population are the focus of this paper. In this paper we report outcomes from a 9 year experience designing and using CPs in the management of patients undergoing major head and neck resection with free flap reconstruction.

Methods: The Calgary quality management program and CP design is described the accompanying article. Data from CP managed patients undergoing major HN surgery were prospectively collected and compared to a baseline cohort of patients managed with standard care. Data were retrospectively analyzed and intergroup comparisons were made.

Results: Mobilization, decannulation time and hospital length of stay were significantly improved in pathway-managed patients (p = 0.001). Trend analysis showed sustained improvement in key performance indicators including complications. Return to the OR, primarily to assess a compromised flap, is increasing.

Conclusions: Care pathways when deployed as part of an ongoing quality management program are associated with improved clinical outcomes in this complex group of patients.
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http://dx.doi.org/10.1186/s40463-020-00437-2DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7310531PMC
June 2020

Designing and integrating a quality management program for patients undergoing head and neck resection with free-flap reconstruction.

J Otolaryngol Head Neck Surg 2020 Jun 23;49(1):41. Epub 2020 Jun 23.

Section of Otolaryngology Head & Neck Surgery, Department of Surgery, University of Calgary Cumming School of Medicine, 3280 Hospital Drive NW, Calgary, Alberta, T2N 4Z6, Canada.

Background: Care pathways (CPs) offer a proven method of systematically improving patient care. CPs are particularly helpful in complex clinical conditions where variation in care is a problem such as patients undergoing major head and neck resection with free flap reconstruction. Although CPs have been used to manage this patient group, most CPs are implemented as part of relatively short-term quality improvement projects. This paper outlines a detailed methodology for designing and delivering a quality management program sustained for 9 years.

Methods: We describe a change management approach informed by Kotter's "8 Step Process" that provided a useful framework to guide program development and implementation. We then provide a detailed, step by step description of how such a program can be implemented as well as a detailed summary of time and costs for design, implementation and sustainability phases. An approach to design and delivery of a measurement, audit and feedback system is also provided.

Results: We present a summary of resources needed to design and implement a head and neck surgery quality management program. The primary result of this study is a design for a sustainable quality management program that can be used to guide and improve care for patients undergoing major head and neck resection with free flap reconstruction.

Conclusions: A change management approach to design and delivery of a head and neck quality management program is practical and feasible.
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http://dx.doi.org/10.1186/s40463-020-00436-3DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7310437PMC
June 2020

Covalent Biofunctionalization of the Inner Surfaces of a Hollow-Fiber Capillary Bundle Using Packed-Bed Plasma Ion Implantation.

ACS Appl Mater Interfaces 2020 Jul 2;12(28):32163-32174. Epub 2020 Jul 2.

School of Physics, University of Sydney, Sydney, New South Wales 2006, Australia.

Hollow-fiber capillary bundles are widely used in the production of medical devices for blood oxygenation and purification purposes such as in cardiopulmonary bypass, hemodialysis, and hemofiltration, but the blood interfacing inner surfaces of these capillaries provide poor hemocompatibility. Here, we present a novel method of packed-bed plasma ion implantation (PBPII) for the modification of the inner surfaces of polymeric hollow-fiber bundles enclosed in a cassette. The method is simple and can be performed on an intact hollow-fiber bundle cassette by the placement of a hollow cylindrical electrode, connected to a negative high-voltage pulse generator, around the cassette. The method does not require the insertion of electrodes inside the capillaries or the cassette. Nitrogen gas is fed into the capillaries inside the cassette by connecting the inlet of the cassette to a gas source. Upon the application of negative high-voltage bias pulses to the electrode, plasma is ignited inside the cassette, achieving the surface modification of both the internal and external surfaces of the capillaries. Fourier transform infrared-attenuated total reflectance spectroscopy of the PBPII-treated capillaries revealed the formation of aromatic C═C bonds, indicating the progressive carbonization of the capillary surfaces. The PBPII treatment was found to be uniform along the capillaries and independent of the radial position in the cassette. Atomic force microscopy of cross sections through the capillaries revealed that the increased stiffness associated with the carbonized layer on the inner surface of the PBPII-treated capillary has a depth (∼40 nm) consistent with that expected for ions accelerated by the applied bias voltage. The modified internal surfaces of the capillary bundle showed a greatly increased wettability and could be biofunctionalized by covalently immobilizing protein directly from the buffer solution. The direct, reagent-free protein immobilization was demonstrated using tropoelastin as an example protein. Covalent binding of the protein was confirmed by its resistance to removal by hot sodium dodecyl sulfate detergent washing, which is known to disrupt physical binding.
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http://dx.doi.org/10.1021/acsami.0c07070DOI Listing
July 2020

Gas chromatography-mass spectrometry analyses of encapsulated stable perovskite solar cells.

Science 2020 06 21;368(6497). Epub 2020 May 21.

Australian Centre for Advanced Photovoltaics, School of Photovoltaic and Renewable Energy Engineering, University of New South Wales, Sydney, NSW 2052, Australia.

Although perovskite solar cells have produced remarkable energy conversion efficiencies, they cannot become commercially viable without improvements in durability. We used gas chromatography-mass spectrometry (GC-MS) to reveal signature volatile products of the decomposition of organic hybrid perovskites under thermal stress. In addition, we were able to use GC-MS to confirm that a low-cost polymer/glass stack encapsulation is effective in suppressing such outgassing. Using such an encapsulation scheme, we produced multi-cation, multi-halide perovskite solar cells containing methylammonium that exceed the requirements of the International Electrotechnical Commission 61215:2016 standard by surviving more than 1800 hours of the Damp Heat test and 75 cycles of the Humidity Freeze test.
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http://dx.doi.org/10.1126/science.aba2412DOI Listing
June 2020

Using aerobic exercise to evaluate sub-lethal tolerance of acute warming in fishes.

J Exp Biol 2020 05 7;223(Pt 9). Epub 2020 May 7.

Department of Physiological Sciences, Federal University of São Carlos, 13565-905 São Carlos, SP, Brazil.

We investigated whether fatigue from sustained aerobic swimming provides a sub-lethal endpoint to define tolerance of acute warming in fishes, as an alternative to loss of equilibrium (LOE) during a critical thermal maximum (CT) protocol. Two species were studied, Nile tilapia () and pacu (). Each fish underwent an incremental swim test to determine gait transition speed (), where it first engaged the unsteady anaerobic swimming mode that preceded fatigue. After suitable recovery, each fish was exercised at 85% of their own and warmed 1°C every 30 min, to identify the temperature at which they fatigued, denoted as CT Fish were also submitted to a standard CT, warming at the same rate as CT, under static conditions until LOE. All individuals fatigued in CT, at a mean temperature approximately 2°C lower than their CT Therefore, if exposed to acute warming in the wild, the ability to perform aerobic metabolic work would be constrained at temperatures significantly below those that directly threatened survival. The collapse in performance at CT was preceded by a gait transition qualitatively indistinguishable from that during the incremental swim test. This suggests that fatigue in CT was linked to an inability to meet the tissue oxygen demands of exercise plus warming. This is consistent with the oxygen and capacity limited thermal tolerance (OCLTT) hypothesis, regarding the mechanism underlying tolerance of warming in fishes. Overall, fatigue at CT provides an ecologically relevant sub-lethal threshold that is more sensitive to extreme events than LOE at CT.
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http://dx.doi.org/10.1242/jeb.218602DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7225124PMC
May 2020

Interactive effects of mercury exposure and hypoxia on ECG patterns in two Neotropical freshwater fish species: Matrinxã, Brycon amazonicus and traíra, Hoplias malabaricus.

Ecotoxicology 2020 May 12;29(4):375-388. Epub 2020 Mar 12.

Department of Physiological Sciences, Federal University of São Carlos (UFSCar), São Carlos, São Paulo, Brazil.

Hypoxia and mercury contamination often co-occur in tropical freshwater ecosystems, but the interactive effects of these two stressors on fish populations are poorly known. The effects of mercury (Hg) on recorded changes in the detailed form of the electrocardiogram (ECG) during exposure to progressive hypoxia were investigated in two Neotropical freshwater fish species, matrinxã, Brycon amazonicus and traíra, Hoplias malabaricus. Matrinxã were exposed to a sublethal concentration of 0.1 mg L of HgCl in water for 96 h. Traíra were exposed to dietary doses of Hg by being fed over a period of 30 days with juvenile matrinxãs previously exposed to HgCl, resulting in a dose of 0.45 mg of total Hg per fish, each 96 h. Both species showed a bradycardia in progressive hypoxia. Hg exposure impaired cardiac electrical excitability, leading to first-degree atrioventricular block, plus profound extension of the ventricular action potential (AP) plateau. Moreover, there was the development of cardiac arrhythmias and anomalies such as occasional absence of QRS complexes, extra systoles, negative Q-, R- and S-waves (QRS complex), and T wave inversion, especially in hypoxia below O partial pressures (PO) of 5.3 kPa. Sub-chronic dietary Hg exposure induced intense bradycardia in normoxia in traira, plus lengthening of ventricular AP duration coupled with prolonged QRS intervals. This indicates slower ventricular AP conduction during ventricular depolarization. Overall, the data indicate that both acute waterborne and sub-chronic dietary exposure (trophic level transfer), at sublethal concentrations of mercury, cause damage in electrical stability and rhythm of the heartbeat, leading to myocardial dysfunction, which is further intensified during hypoxia. These changes could lead to impaired cardiac output, with consequences for swimming ability, foraging capacity, and hence growth and/or reproductive performance.
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http://dx.doi.org/10.1007/s10646-020-02186-4DOI Listing
May 2020

Atomic-Scale Patterning of Arsenic in Silicon by Scanning Tunneling Microscopy.

ACS Nano 2020 Mar 12;14(3):3316-3327. Epub 2020 Mar 12.

London Centre for Nanotechnology, University College London, London WC1H 0AH, U.K.

Over the past two decades, prototype devices for future classical and quantum computing technologies have been fabricated by using scanning tunneling microscopy and hydrogen resist lithography to position phosphorus atoms in silicon with atomic-scale precision. Despite these successes, phosphine remains the only donor precursor molecule to have been demonstrated as compatible with the hydrogen resist lithography technique. The potential benefits of atomic-scale placement of alternative dopant species have, until now, remained unexplored. In this work, we demonstrate the successful fabrication of atomic-scale structures of arsenic-in-silicon. Using a scanning tunneling microscope tip, we pattern a monolayer hydrogen mask to selectively place arsenic atoms on the Si(001) surface using arsine as the precursor molecule. We fully elucidate the surface chemistry and reaction pathways of arsine on Si(001), revealing significant differences to phosphine. We explain how these differences result in enhanced surface immobilization and in-plane confinement of arsenic compared to phosphorus, and a dose-rate independent arsenic saturation density of 0.24 ± 0.04 monolayers. We demonstrate the successful encapsulation of arsenic delta-layers using silicon molecular beam epitaxy, and find electrical characteristics that are competitive with equivalent structures fabricated with phosphorus. Arsenic delta-layers are also found to offer confinement as good as similarly prepared phosphorus layers, while still retaining >80% carrier activation and sheet resistances of <2 kΩ/square. These excellent characteristics of arsenic represent opportunities to enhance existing capabilities of atomic-scale fabrication of dopant structures in silicon, and may be important for three-dimensional devices, where vertical control of the position of device components is critical.
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http://dx.doi.org/10.1021/acsnano.9b08943DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7146850PMC
March 2020

Bubble-positive expiratory pressure device and sputum clearance in bronchiectasis: A randomised cross-over study.

Physiother Res Int 2020 Jul 29;25(3):e1836. Epub 2020 Feb 29.

Faculty of Health Sciences, Discipline of Physiotherapy, The University of Sydney, Lidcombe, New South Wales, Australia.

Objectives: The bubble-positive expiratory pressure (PEP) device may be used for sputum clearance in people with daily sputum production. However, this device has never been studied in people with bronchiectasis. Hence, the objective of this study was to compare the effect of bubble-PEP device, the active cycle of breathing technique (ACBT) and no intervention (control) on sputum clearance in people with bronchiectasis.

Methods: This was a prospective, randomised cross-over trial with concealed allocation, assessor blinding and intention-to-treat analysis. Adult participants with stable bronchiectasis and productive of sputum daily were recruited. Participants performed 30-min of bubble-PEP, ACBT or control in random order whilst sitting, followed by 60-min of quiet sitting, on three separate days at the same time within a 10-day period. Primary outcome measure was wet weight of expectorated sputum during 30-min intervention, 60-min post intervention and total wet weight (30 min plus 60 min).

Results: Thirty-five-participants (11 males, mean [standard deviation] age 75 [8] years, forced expiratory volume in 1 s 72 [20] % predicted) were recruited and 34 completed the study. There was no significant difference in sputum wet weight between bubble-PEP and ACBT during 30-min intervention (mean difference [95% confidence interval]) -0.59 g [-1.37, 0.19] and total wet weight (0.74 g [-0.54, 2.02]). Sputum wet weight was significantly greater in bubble-PEP than ACBT at 60-min post intervention (1.33 g [0.19, 2.47]).

Conclusion: Sputum wet weight was significantly greater with bubble-PEP than control at all time periods, and greater than ACBT at 60-min-post. Bubble-PEP could be considered an alternative sputum clearance technique to ACBT.
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http://dx.doi.org/10.1002/pri.1836DOI Listing
July 2020

Sustained treatment of retinal vascular diseases with self-aggregating sunitinib microparticles.

Nat Commun 2020 02 4;11(1):694. Epub 2020 Feb 4.

The Center for Nanomedicine, The Wilmer Eye Institute, Johns Hopkins University School of Medicine, Baltimore, MD, USA.

Neovascular age-related macular degeneration and diabetic retinopathy are prevalent causes of vision loss requiring frequent intravitreous injections of VEGF-neutralizing proteins, and under-treatment is common and problematic. Here we report incorporation of sunitinib, a tyrosine kinase inhibitor that blocks VEGF receptors, into a non-inflammatory biodegradable polymer to generate sunitinib microparticles specially formulated to self-aggregate into a depot. A single intravitreous injection of sunitinib microparticles potently suppresses choroidal neovascularization in mice for six months and in another model, blocks VEGF-induced leukostasis and retinal nonperfusion, which are associated with diabetic retinopathy progression. After intravitreous injection in rabbits, sunitinib microparticles self-aggregate into a depot that remains localized and maintains therapeutic levels of sunitinib in retinal pigmented epithelium/choroid and retina for more than six months. There is no intraocular inflammation or retinal toxicity. Intravitreous injection of sunitinib microparticles provides a promising approach to achieve sustained suppression of VEGF signaling and improve outcomes in patients with retinal vascular diseases.
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http://dx.doi.org/10.1038/s41467-020-14340-xDOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7000758PMC
February 2020

Impact of respiratory muscle training on respiratory muscle strength, respiratory function and quality of life in individuals with tetraplegia: a randomised clinical trial.

Thorax 2020 03 14;75(3):279-288. Epub 2020 Jan 14.

Neuroscience Research Australia, Sydney, New South Wales, Australia.

Background: Respiratory complications remain a leading cause of morbidity and mortality in people with acute and chronic tetraplegia. Respiratory muscle weakness following spinal cord injury-induced tetraplegia impairs lung function and the ability to cough. In particular, inspiratory muscle strength has been identified as the best predictor of the likelihood of developing pneumonia in individuals with tetraplegia. We hypothesised that 6 weeks of progressive respiratory muscle training (RMT) increases respiratory muscle strength with improvements in lung function, quality of life and respiratory health.

Methods: Sixty-two adults with tetraplegia participated in a double-blind randomised controlled trial. Active or sham RMT was performed twice daily for 6 weeks. Inspiratory muscle strength, measured as maximal inspiratory pressure (PImax) was the primary outcome. Secondary outcomes included lung function, quality of life and respiratory health. Between-group comparisons were obtained with linear models adjusting for baseline values of the outcomes.

Results: After 6 weeks, there was a greater improvement in PImax in the active group than in the sham group (mean difference 11.5 cmHO (95% CI 5.6 to 17.4), p<0.001) and respiratory symptoms were reduced (St George Respiratory Questionnaire mean difference 10.3 points (0.01-20.65), p=0.046). Significant improvements were observed in quality of life (EuroQol-Five Dimensional Visual Analogue Scale 14.9 points (1.9-27.9), p=0.023) and perceived breathlessness (Borg score 0.64 (0.11-1.17), p=0.021). There were no significant improvements in other measures of respiratory function (p=0.126-0.979).

Conclusions: Progressive RMT increases inspiratory muscle strength in people with tetraplegia, by a magnitude which is likely to be clinically significant. Measurement of baseline PImax and provision of RMT to at-risk individuals may reduce respiratory complications after tetraplegia.

Trial Registration Number: Australian New Zealand Clinical Trials Registry (ACTRN 12612000929808).
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http://dx.doi.org/10.1136/thoraxjnl-2019-213917DOI Listing
March 2020

Identifying adverse outcome pathways (AOP) for Amsterdam city fish by integrated field monitoring.

Environ Toxicol Pharmacol 2020 Feb 21;74:103301. Epub 2019 Nov 21.

Biosciences, University of Birmingham, B15 2TT, Birmingham, United Kingdom.

The European City Fish project aimed to develop a generic methodology for ecological risk assessment for urban rivers. Since traditional methods only consider a small fraction of substances present in the water cycle, biological effect monitoring is required for a more reliable assessment of the pollution status. A major challenge for environmental risk assessment (ERA) is the application of adverse outcome pathways (AOP), i.e. the linking of pollutant exposure via early molecular and biochemical changes to physiological effects and, ultimately, effects on populations and ecosystems. We investigated the linkage between responses at these different levels. Many AOP aspects were investigated, from external and internal exposure to different classes of micropollutants, via molecular key events (MKE) the impacts on organs and organisms (fish physiology), to changes in the population dynamics of fish. Risk assessment procedures were evaluated by comparing environmental quality standards, bioassay responses, biomarkers in caged and feral fish, and the impact on fish populations. Although no complete AOP was observed, indirect relationships linking pollutant exposure via MKE to impaired locomotion were demonstrated at the most polluted site near a landfill for chemical waste. The pathway indicated that several upstream key events requiring energy for stress responses and toxic defence are likely to converge at a single common MKE: increased metabolic demands. Both fish biomarkers and the bioanalytical SIMONI strategy are valuable indicators for micropollutant risks to fish communities.
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http://dx.doi.org/10.1016/j.etap.2019.103301DOI Listing
February 2020

Evolutionary and cardio-respiratory physiology of air-breathing and amphibious fishes.

Acta Physiol (Oxf) 2020 03 13;228(3):e13406. Epub 2019 Nov 13.

Department of Integrative Biology, University of Guelph, Guelph, ON, Canada.

Air-breathing and amphibious fishes are essential study organisms to shed insight into the required physiological shifts that supported the full transition from aquatic water-breathing fishes to terrestrial air-breathing tetrapods. While the origin of air-breathing in the evolutionary history of the tetrapods has received considerable focus, much less is known about the evolutionary physiology of air-breathing among fishes. This review summarizes recent advances within the field with specific emphasis on the cardiorespiratory regulation associated with air-breathing and terrestrial excursions, and how respiratory physiology of these living transitional forms are affected by development and personality. Finally, we provide a detailed and re-evaluated model of the evolution of air-breathing among fishes that serves as a framework for addressing new questions on the cardiorespiratory changes associated with it. This review highlights the importance of combining detailed studies on piscine air-breathing model species with comparative multi-species studies, to add an additional dimension to our understanding of the evolutionary physiology of air-breathing in vertebrates.
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http://dx.doi.org/10.1111/apha.13406DOI Listing
March 2020

Muscle bioenergetics of two emblematic Mediterranean fish species: Sardina pilchardus and Sparus aurata.

Comp Biochem Physiol A Mol Integr Physiol 2019 09 17;235:174-179. Epub 2019 Jun 17.

MARBEC, Université de Montpellier, CNRS, Ifremer, IRD, Avenue Jean Monnet, 34203 Sète Cedex, France.

We investigated links between swimming behavior and muscle bioenergetics in two emblematic Mediterranean fish species that have very different ecologies and activity levels. European sardines Sardina pilchardus are pelagic, they swim aerobically, school constantly and have high muscle fat content. Gilthead seabream Sparus aurata are bentho-pelagic, they show discontinuous spontaneous swimming patterns and store less fat in their muscle. Estimating the proportion of red and white muscle phenotypes, sardine exhibited a larger proportion of red muscle (~10% of the body mass) compared to gilthead seabream (~5% of the body mass). We firstly studied red and white muscle fiber bioenergetics, using high-resolution respirometers, showing a 4-fold higher oxidation capacity for red compared to white muscle. Secondly, we aimed to compare the red muscle ability to oxidize either lipids or carbohydrates. Sardine red muscle had a 3-fold higher oxidative capacity than gilthead seabream and a greater capacity to oxidize lipids. This study provides novel insights into physiological mechanisms underlying the different lifestyles of these highly-prized species.
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http://dx.doi.org/10.1016/j.cbpa.2019.06.008DOI Listing
September 2019

Linker-protein G mediated functionalization of polystyrene-encapsulated upconversion nanoparticles for rapid gene assay using convective PCR.

Mikrochim Acta 2019 05 11;186(6):346. Epub 2019 May 11.

Department of Molecular Sciences, Macquarie University, Sydney, NSW, 2109, Australia.

The authors report on a simplified approach to encapsulate upconversion nanoparticles (UCNPs) in polystyrene spheres by mini-emulsion polymerisation. The resulting particles (PS-UCNP) are hydrophilic, stable and suitable for biomolecular recognition and biosensing applications. Also, a strategy was developed for bioconjugation of antibodies onto the surface of the PS-UCNPs by using the bifunctional fusion protein linker-protein G (LPG). LPG mediates the functionalisation of PS-UCNPs with antibodies against digoxigenin allowing for specific labelling of convective PCR (cPCR) amplicons. Lambda DNA was amplified using cPCR on a heat block for 30 min using the digoxigenin labelled forward and biotin labelled reverse primers. The antibody functionalised PS-UCNPs bind to the digoxigenin end of the cPCR amplicons. Finally, the streptavidin labelled magnetic beads were used to selectively capture the PS-UCNP-labelled cPCR amplicons and the upconversion signal was detected at 537 nm under 980 nm excitation. This sandwich approach enables direct recognition of the target lambda DNA with a detection limit of 10 copies μL. The upconversion signal decreased proportionally to the concentration of the lambda DNA with a linear response between 10 and 10 copies of DNA. Graphical abstract Schematic representation of polystyrene-encapsulated upconversion nanoparticles (PS-UCNPs) prepared by mini-emulsion polymerisation. The PS-UCNPs were functionalised with anti-digoxigenin antibody using the fusion protein linker-protein G (LPG). Detection of digoxigenin-labelled amplicons is achieved (a) by using the antibody-functionalised LPG@PS-UCNP labels; (b) magnetic separation, and (c) 980 nm laser light for detection of the green upconversion luminescence peaking at 537 nm.
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http://dx.doi.org/10.1007/s00604-019-3466-xDOI Listing
May 2019

Noisy waters.

Authors:
David J McKenzie

J Fish Biol 2019 05;94(5):691

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http://dx.doi.org/10.1111/jfb.13985DOI Listing
May 2019

Plasma ion implantation enabled bio-functionalization of PEEK improves osteoblastic activity.

APL Bioeng 2018 Jun 5;2(2):026109. Epub 2018 Jun 5.

Applied and Plasma Physics, School of Physics, The University of Sydney, NSW 2006, Australia.

Slow appositional growth of bone is a major problem associated with polyether ether ketone (PEEK) based orthopaedic implants. Early stage promotion of osteoblast activity, particularly bone nodule formation, would help to improve contact between PEEK implantable materials and the surrounding bone tissue. To improve interactions with bone cells, we explored here the use of plasma immersion ion implantation (PIII) treatment of PEEK to covalently immobilize biomolecules to the surface. In this study, a single step process was used to covalently immobilize tropoelastin on the surface of PIII modified PEEK through reactions with radicals generated by the treatment. Improved bioactivity was observed using the human osteoblast-like cell line, SAOS-2. Cells on surfaces that were PIII-treated or tropoelastin-coated exhibited improved attachment, spreading, proliferation, and bone nodule formation compared to cells on untreated samples. Surfaces that were both PIII-treated and tropoelastin-coated triggered the most favorable osteoblast-like responses. Surface treatment or tropoelastin coating did not alter alkaline phosphatase gene expression and activity of bound cells but did influence the expression of other bone markers including osteocalcin, osteonectin, and collagen I. We conclude that the surface modification of PEEK improves osteoblast interactions, particularly with respect to bone apposition, and enhances the orthopedic utility of PEEK.
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http://dx.doi.org/10.1063/1.5010346DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6481719PMC
June 2018

Tin oxide artificial synapses for low power temporal information processing.

Nanotechnology 2019 Aug 16;30(32):325201. Epub 2019 Apr 16.

School of Engineering, RMIT University, Melbourne VIC 3001, Australia.

Lateral memristors configured with inert Pt contacts and mixed phase tin oxide layers have exhibited immediate, forming-free, low-power bidirectional resistance switching. Activity dependent conductance and relaxation in the low resistance state resembled short term potentiation in biological synapses. After scanning probe microscopy, x-ray photoelectron spectroscopy and electrical measurements, the device characteristics were attributed to Joule heating induced decomposition of the minority SnO phase and formation of a SnO conducting filament with higher effective n-type doping. Finally, the devices recognized input voltage pulse sequences and spectral data by returning unique conductance states, suggesting suitability for bio-inspired pattern recognition systems.
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http://dx.doi.org/10.1088/1361-6528/ab19c9DOI Listing
August 2019