Publications by authors named "Carsten Gundlach"

15 Publications

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Evaluation of 2D super-resolution ultrasound imaging of the rat renal vasculature using ex vivo micro-computed tomography.

Sci Rep 2021 Dec 21;11(1):24335. Epub 2021 Dec 21.

Department of Biomedical Sciences, University of Copenhagen, 2200, Copenhagen, Denmark.

Super-resolution ultrasound imaging (SRUS) enables in vivo microvascular imaging of deeper-lying tissues and organs, such as the kidneys or liver. The technique allows new insights into microvascular anatomy and physiology and the development of disease-related microvascular abnormalities. However, the microvascular anatomy is intricate and challenging to depict with the currently available imaging techniques, and validation of the microvascular structures of deeper-lying organs obtained with SRUS remains difficult. Our study aimed to directly compare the vascular anatomy in two in vivo 2D SRUS images of a Sprague-Dawley rat kidney with ex vivo μCT of the same kidney. Co-registering the SRUS images to the μCT volume revealed visually very similar vascular features of vessels ranging from ~ 100 to 1300 μm in diameter and illustrated a high level of vessel branching complexity captured in the 2D SRUS images. Additionally, it was shown that it is difficult to use μCT data of a whole rat kidney specimen to validate the super-resolution capability of our ultrasound scans, i.e., validating the actual microvasculature of the rat kidney. Lastly, by comparing the two imaging modalities, fundamental challenges for 2D SRUS were demonstrated, including the complexity of projecting a 3D vessel network into 2D. These challenges should be considered when interpreting clinical or preclinical SRUS data in future studies.
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http://dx.doi.org/10.1038/s41598-021-03726-6DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC8692475PMC
December 2021

The STRYDE limb lengthening nail is susceptible to mechanically assisted crevice corrosion: an analysis of 23 retrieved implants.

Acta Orthop 2021 Oct 8;92(5):621-627. Epub 2021 Jun 8.

Orthopaedic Reconstruction and Children's Orthopaedics, Aarhus University Hospital, Aarhus, Denmark.

Background and purpose - We noted several adverse events in patients in whom the first version of the STRYDE limb-lengthening nail (NuVasive Specialized Orthopaedics, San Diego, CA) had been implanted. Pain, osteolysis, periosteal reactions, and cortical hypertrophy at the nail junction were noted. Here, we present the analysis of 23 retrieved STRYDE implants.Materials and methods - We undertook visual inspection of the retrieved nails and screws, mechanical evaluation of the junction, micro-CT analyses, microscopic inspection of the bushing, screws, screw holes, and separated parts of the implants. Positive material identification (PMI) and energy-dispersive X-ray spectroscopy (EDS) were used to analyze the chemical composition. The hardness of the material was also investigated.Results - 20/23 retrieved nails had visible signs of corrosion, i.e., discoloration at the telescopic junction. Micro-CT verified corrosion attacks in 12/12 scanned bushings. Corrosion, predominantly mechanically assisted crevice corrosion, was observed at the locking screws and screw holes in 20/23 nails. Biological material inside the nail was observed in addition to oozing from the junction of 2 nails during hardware removal, which was experimentally reproducible. Notably, the mechanical construction of the bushing changed from PRECICE P2 to STRYDE nails.Interpretation - STRYDE nails are not hermetically sealed, and liquid can pass the bushing. Biodur 108 itself is corrosion resistant; however, mechanically assisted crevice corrosion of the bushing, locking screws, and screw holes may be aggravated due to manufacturing aiming for increased strength and hardness of the alloy.Observing several adverse events, we recently published a nationwide cross-sectional analysis of all 30 STRYDE limb- lengthening nails (NuVasive, Specialized Orthopedics, San Diego, CA) that were implanted in Denmark (Rölfing et al. 2021a). 27/30 STRYDE nails have now been removed and we present data from metallurgical analysis of 23 of the retrieved implants.
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http://dx.doi.org/10.1080/17453674.2021.1927506DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC8519523PMC
October 2021

X-ray Imaging for Gastrointestinal Tracking of Microscale Oral Drug Delivery Devices.

ACS Biomater Sci Eng 2021 06 15;7(6):2538-2547. Epub 2021 Apr 15.

The Danish National Research Foundation and Villum Foundation's Center for Intelligent Drug Delivery and Sensing Using Microcontainers and Nanomechanics (IDUN), Department of Health Technology, Technical University of Denmark, 2800 Kongens Lyngby, Denmark.

Microscale devices are promising tools to overcome specific challenges within oral drug delivery. Despite the availability of advanced high-quality imaging techniques, visualization and tracking of microscale devices in the gastrointestinal (GI) tract is still a challenge. This work explores the possibilities of applying planar X-ray imaging and computed tomography (CT) scanning for visualization and tracking of microscale devices in the GI tract of rats. Microcontainers (MCs) are an example of microscale devices that have shown great potential as an oral drug delivery system. Barium sulfate (BaSO) loaded into the cavity of the MCs increases their overall X-ray contrast, which allows them to be easily tracked. The BaSO-loaded MCs are quantitatively tracked throughout the entire GI tract of rats by planar X-ray imaging and visualized in 3D by CT scanning. The majority of the BaSO-loaded MCs are observed to retain in the stomach for 0.5-2 h, enter the cecum after 3-4 h, and leave the cecum and colon 8-10 h post-administration. The imaging approaches can be adopted and used with other types of microscale devices when investigating GI behavior in, for example, preclinical trials and potential clinical studies.
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http://dx.doi.org/10.1021/acsbiomaterials.1c00225DOI Listing
June 2021

Flexible and Green Electronics Manufactured by Origami Folding of Nanosilicate-Reinforced Cellulose Paper.

ACS Appl Mater Interfaces 2020 Oct 9;12(42):48027-48039. Epub 2020 Oct 9.

Department of Health Technology, Institute of Biotherapeutic Engineering and Drug Targeting, Center for Intestinal Absorption and Transport of Biopharmaceuticals, Technical University of Denmark, 2800 Kgs. Lyngby, Denmark.

Today's consumer electronics are made from nonrenewable and toxic components. They are also rigid, bulky, and manufactured in an energy-inefficient manner via CO-generating routes. Though petroleum-based polymers such as polyethylene terephthalate and polyethylene naphthalate can address the rigidity issue, they have a large carbon footprint and generate harmful waste. Scalable routes for manufacturing electronics that are both flexible and ecofriendly (Fleco) could address the challenges in the field. Ideally, such substrates must incorporate into electronics without compromising device performance. In this work, we demonstrate that a new type of wood-based [nanocellulose (NC)] material made via nanosilicate (NS) reinforcement can yield flexible electronics that can bend and roll without loss of electrical function. Specifically, the NSs interact electrostatically with NC to reinforce thermal and mechanical properties. For instance, films containing 34 wt % of NS displayed an increased young's modulus (1.5 times), thermal stability (290 → 310 °C), and a low coefficient of thermal expansion (40 ppm/K). These films can also easily be separated and renewed into new devices through simple and low-energy processes. Moreover, we used very cheap and environmentally friendly NC from American Value Added Pulping (AVAP) technology, American Process, and therefore, the manufacturing cost of our NS-reinforced NC paper is much cheaper ($0.016 per dm) than that of conventional NC-based substrates. Looking forward, the methodology highlighted herein is highly attractive as it can unlock the secrets of Fleco electronics and transform otherwise bulky, rigid, and "difficult-to-process" rigid circuits into more aesthetic and flexible ones while simultaneously bringing relief to an already-overburdened ecosystem.
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http://dx.doi.org/10.1021/acsami.0c15326DOI Listing
October 2020

Monitoring the influx of new species through citizen science: the first introduced ant in Denmark.

PeerJ 2020 8;8:e8850. Epub 2020 Apr 8.

Section for Ecology and Evolution, Department of Biology, University of Copenhagen, Copenhagen, Denmark.

Climate change and invasive species threaten biodiversity, yet rigorous monitoring of their impact can be costly. Citizen science is increasingly used as a tool for monitoring exotic species, because citizens are geographically and temporally dispersed, whereas scientists tend to cluster in museums and at universities. Here we report on the establishment of the first exotic ant taxon () in Denmark, which was discovered by children participating in The Ant Hunt. The Ant Hunt is a citizen science project for children that we ran in 2017 and 2018, with a pilot study in 2015. was discovered in the Botanical Garden of the Natural History Museum of Denmark in 2015 and confirmed as established in 2018. This finding extends the northern range boundary of by almost 460 km. Using climatic niche modelling, we compared the climatic niche of in Europe with that of based on confirmed observations from 2006 to 2019. and had a 13% niche overlap, with showing stronger occurrence in warmer and drier areas compared to . Mapping the environmental niches onto geographic space identified several, currently uninhabited, areas as climatically suitable for the establishment of . was sampled almost three times as often in areas with artificial surfaces compared to , suggesting that may not be native to all of Europe and is being accidentally introduced by humans. Overall, citizen scientists collected data on ants closer to cities and harbours than scientists did and had a stronger bias towards areas of human disturbance. This increased sampling effort in areas of likely introduction of exotic species naturally increases the likelihood of discovering species sooner, making citizen science an excellent tool for exotic species monitoring, as long as trained scientists are involved in the identification process.
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http://dx.doi.org/10.7717/peerj.8850DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7150537PMC
April 2020

Critical Phenomena in the Gravitational Collapse of Electromagnetic Waves.

Phys Rev Lett 2019 Oct;123(17):171103

CENTRA, Departamento de Física, Instituto Superior Técnico IST, Universidade de Lisboa UL, Avenida Rovisco Pais 1, 1049 Lisboa, Portugal.

We numerically investigate the threshold of black-hole formation in the gravitational collapse of electromagnetic waves in axisymmetry. We find approximate power-law scaling ρ_{max}∼(η_{*}-η)^{-2γ} of the maximum density in the time evolution of near-subcritical data with γ≃0.145, where η is the amplitude of the initial data. We directly observe approximate discrete self-similarity in near-critical time evolutions with a log-scale echoing period of Δ≃0.55. The critical solution is approximately the same for two families of initial data, providing some evidence of universality. Neither the discrete self-similarity nor the universality, however, are exact. We speculate that the absence of an exactly discrete self-similarity might be caused by the interplay of electromagnetic and gravitational wave degrees of freedom, or by the presence of higher-order angular multipoles, or both, and discuss implications of our findings for the critical collapse of vacuum gravitational waves.
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http://dx.doi.org/10.1103/PhysRevLett.123.171103DOI Listing
October 2019

Biodegradable microcontainers - towards real life applications of microfabricated systems for oral drug delivery.

Lab Chip 2019 09 1;19(17):2905-2914. Epub 2019 Aug 1.

The Danish National Research Foundation and, Villum Foundation's Center for Intelligent Drug Delivery and Sensing Using Microcontainers and Nanomechanics (IDUN), Denmark and National Centre for Nano Fabrication and Characterization, DTU Nanolab, Technical University of Denmark, 2800 Kgs. Lyngby, Denmark.

Microfabrication techniques have been applied to develop micron-scale devices for oral drug delivery with a high degree of control over size, shape and material composition. Recently, microcontainers have been introduced as a novel approach to obtain unidirectional release to avoid luminal drug loss, enhance drug permeation, protect drug payload from the harsh environment of the stomach, and explore the ability for targeted drug delivery. However, in order to eventually pave the way for real life applications of these microfabricated drug delivery systems, it is necessary to fabricate them in biodegradable materials approved for similar applications and with strategies that potentially allow for large scale production. In this study, we for the first time evaluate biodegradable microcontainers for oral drug delivery. Asymmetric poly-ε-caprolactone (PCL) microcontainers with a diameter of 300 μm and a volume of 2.7 nL are fabricated with a novel single-step fabrication process. The microcontainers are loaded with the model drug paracetamol and coated with an enteric pH-sensitive Eudragit® S100 coating to protect the drug until it reaches the desired location in the small intestine. In vitro dissolution studies are performed to assess the drug load and release profile of the PCL microcontainers. Finally, in vivo studies in rats showed a higher bioavailability compared to conventional dosage forms and confirm the potential of biodegradable microcontainers for oral drug delivery.
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http://dx.doi.org/10.1039/c9lc00527gDOI Listing
September 2019

Polymeric Lids for Microcontainers for Oral Protein Delivery.

Macromol Biosci 2019 05 2;19(5):e1900004. Epub 2019 Apr 2.

Department of Health Technology, Technical University of Denmark, Ørsteds Plads 345C, Kgs. Lyngby, 2800, Denmark.

Oral delivery of proteins and peptides is one of the main challenges in pharmaceutical drug development. Microdevices have the possibility to protect the therapeutics until release is desired, avoiding losses by degradation. One type of microdevice is polymeric microcontainers. In this study, lysozyme is chosen as model protein and loaded into microcontainers with the permeation enhancer sodium decanoate (C10). The loaded microcontainers are sealed and functionalized by applying polymeric lids onto the cavity of the devices. The first lid is poly(lactic-co-glycolic) acid (PLGA) and on top of this either polyethylene glycol (PEG) or chitosan is applied (PLGA+PEG or PLGA+chitosan, respectively). The functionalization is evaluated in vitro for morphology, drug release, and mucoadhesive properties. These are coupled with in vitro and ex vivo studies using Caco-2 cells, Caco-2/HT29-MTX-E12 co-cultures, and porcine intestinal tissue. PLGA+chitosan shows slower release compared to PLGA+PEG or only PLGA in buffer and the transport of lysozyme across cell cultures is not enhanced compared to the bulk powder. Microcontainers coated with chitosan or PEG demonstrate a three times stronger adhesion during ex vivo mucoadhesion studies compared to samples without coatings. Altogether, functionalized microcontainers with mucoadhesive properties and tunable release for oral protein delivery are developed and characterized.
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http://dx.doi.org/10.1002/mabi.201900004DOI Listing
May 2019

From concept to in vivo testing: Microcontainers for oral drug delivery.

J Control Release 2017 Dec 18;268:343-351. Epub 2017 Oct 18.

Department of Micro- and Nanotechnology, Technical University of Denmark, Ørsteds Plads 345C, 2800 Kgs. Lyngby, Denmark.

This work explores the potential of polymeric micrometer sized devices (microcontainers) as oral drug delivery systems (DDS). Arrays of detachable microcontainers (D-MCs) were fabricated on a sacrificial layer to improve the handling and facilitate the collection of individual D-MCs. A model drug, ketoprofen, was loaded into the microcontainers using supercritical CO impregnation, followed by deposition of an enteric coating to protect the drug from the harsh gastric environment and to provide a fast release in the intestine. In vitro, in vivo and ex vivo studies were performed to assess the viability of the D-MCs as oral DDS. D-MCs improved the relative oral bioavailability by 180% within 4h, and increased the absorption rate by 2.4 times compared to the control. This work represents a significant step forward in the translation of these devices from laboratory to clinic.
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http://dx.doi.org/10.1016/j.jconrel.2017.10.013DOI Listing
December 2017

Scene reassembly after multimodal digitization and pipeline evaluation using photorealistic rendering.

Appl Opt 2017 Sep;56(27):7679-7690

Transparent objects require acquisition modalities that are very different from the ones used for objects with more diffuse reflectance properties. Digitizing a scene where objects must be acquired with different modalities requires scene reassembly after reconstruction of the object surfaces. This reassembly of a scene that was picked apart for scanning seems unexplored. We contribute with a multimodal digitization pipeline for scenes that require this step of reassembly. Our pipeline includes measurement of bidirectional reflectance distribution functions and high dynamic range imaging of the lighting environment. This enables pixelwise comparison of photographs of the real scene with renderings of the digital version of the scene. Such quantitative evaluation is useful for verifying acquired material appearance and reconstructed surface geometry, which is an important aspect of digital content creation. It is also useful for identifying and improving issues in the different steps of the pipeline. In this work, we use it to improve reconstruction, apply analysis by synthesis to estimate optical properties, and to develop our method for scene reassembly.
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http://dx.doi.org/10.1364/AO.56.007679DOI Listing
September 2017

Critical Collapse of Rotating Radiation Fluids.

Phys Rev Lett 2016 Jun 3;116(22):221103. Epub 2016 Jun 3.

Mathematical Sciences, University of Southampton, Southampton SO17 1BJ, United Kingdom.

We present results from the first fully relativistic simulations of the critical collapse of rotating radiation fluids. We observe critical scaling both in subcritical evolutions-in which case the fluid disperses to infinity and leaves behind flat space-and in supercritical evolutions, which lead to the formation of black holes. We measure the mass and angular momentum of these black holes, and find that both show critical scaling with critical exponents that are consistent with perturbative results. The critical exponents are universal: they are not affected by angular momentum, and are independent of the direction in which the critical curve, which separates subcritical from supercritical evolutions in our two-dimensional parameter space, is crossed. In particular, these findings suggest that the angular momentum decreases more rapidly than the square of the mass, so that, as criticality is approached, the collapse leads to the formation of a nonspinning black hole. We also demonstrate excellent agreement of our numerical data with new closed-form extensions of power-law scalings that describe the mass and angular momentum of rotating black holes formed close to criticality.
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http://dx.doi.org/10.1103/PhysRevLett.116.221103DOI Listing
June 2016

Balancing power density based quantum yield characterization of upconverting nanoparticles for arbitrary excitation intensities.

Nanoscale 2013 Jun 22;5(11):4770-5. Epub 2013 Apr 22.

Division of Atomic Physics, Department of Physics, Lund University, P. O. Box 118, S-221 00 Lund, Sweden.

Upconverting nanoparticles (UCNPs) have recently shown great potential as contrast agents in biological applications. In developing different UCNPs, the characterization of their quantum yield (QY) is a crucial issue, as the typically drastic decrease in QY for low excitation power densities can either impose a severe limitation or provide an opportunity in many applications. The power density dependence of the QY is governed by the competition between the energy transfer upconversion (ETU) rate and the linear decay rate in the depopulation of the intermediate state of the involved activator in the upconversion process. Here we show that the QYs of Yb(3+) sensitized two-photon upconversion emissions can be well characterized by the balancing power density, at which the ETU rate and the linear decay rate have equal contributions, and its corresponding QY. The results in this paper provide a method to fully describe the QY of upconverting nanoparticles for arbitrary excitation power densities, and is a fast and simple approach for assessing the applicability of UCNPs from the perspective of energy conversion.
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http://dx.doi.org/10.1039/c3nr00469dDOI Listing
June 2013

Critical Phenomena in Gravitational Collapse.

Living Rev Relativ 2007 11;10(1). Epub 2007 Dec 11.

Institut d'Astrophysique de Paris CNRS & Université Pierre et Marie Curie, 98 bis boulevard Arago, 75014 Paris, France.

As first discovered by Choptuik, the black hole threshold in the space of initial data for general relativity shows both surprising structure and surprising simplicity. Universality, power-law scaling of the black hole mass, and scale echoing have given rise to the term "critical phenomena". They are explained by the existence of exact solutions which are attractors within the black hole threshold, that is, attractors of codimension one in phase space, and which are typically self-similar. Critical phenomena give a natural route from smooth initial data to arbitrarily large curvatures visible from infinity, and are therefore likely to be relevant for cosmic censorship, quantum gravity, astrophysics, and our general understanding of the dynamics of general relativity.
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http://dx.doi.org/10.12942/lrr-2007-5DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5256106PMC
December 2007

Formation and subdivision of deformation structures during plastic deformation.

Science 2006 May;312(5775):889-92

Center for Fundamental Research: Metal Structures in Four Dimensions, Materials Research Department, Risø National Laboratory, DK-4000 Roskilde, Denmark.

During plastic deformation of metals and alloys, dislocations arrange in ordered patterns. How and when these self-organization processes take place have remained elusive, because in situ observations have not been feasible. We present an x-ray diffraction method that provided data on the dynamics of individual, deeply embedded dislocation structures. During tensile deformation of pure copper, dislocation-free regions were identified. They showed an unexpected intermittent dynamics, for example, appearing and disappearing with proceeding deformation and even displaying transient splitting behavior. Insight into these processes is relevant for an understanding of the strength and work-hardening of deformed materials.
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http://dx.doi.org/10.1126/science.1124141DOI Listing
May 2006

Critical Phenomena in Gravitational Collapse.

Authors:
Carsten Gundlach

Living Rev Relativ 1999 22;2(1). Epub 1999 Dec 22.

Enrico Fermi Institute, University of Chicago, 5640 S Ellis Avenue, Chicago, IL 60637 USA.

As first discovered by Choptuik, the black hole threshold in the space of initial data for general relativity shows both surprising structure and surprising simplicity. Universality, power-law scaling of the black hole mass, and scale echoing have given rise to the term "critical phenomena". They are explained by the existence of exact solutions which are attractors within the black hole threshold, that is, attractors of codimension one in phase space, and which are typically self-similar. This review gives an introduction to the phenomena, tries to summarize the essential features of what is happening, and then presents extensions and applications of this basic scenario. Critical phenomena are of interest particularly for creating surprising structure from simple equations, and for the light they throw on cosmic censorship and the generic dynamics of general relativity.
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http://dx.doi.org/10.12942/lrr-1999-4DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5253925PMC
December 1999
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