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  • 1
    Language: English
    In: Organic Geochemistry, March 2014, Vol.68, pp.71-81
    Description: The taphonomic and diagenetic processes by which organic substances are preserved in animal remains are not completely known and the originality of putative metazoan biomolecules in fossil samples is a matter of scientific discussion. Here we report on biomarker information preserved in a fossil whale bone from an Oligocene phosphatic limestone (El Cien Fm., Mexico), with a focus on fatty acyl compounds. Extracts were quantitatively analysed using gas chromatography–mass spectrometry (GC–MS) and, to identify macromolecular-linked remains, demineralised extraction residues were subjected to catalytic hydropyrolysis (HyPy). To better recognise potential authentic (i.e. animal-derived) lipids, the data from the ancient bone were compared with those obtained from (i) the adjacent host sediment of the fossil and (ii) a recent whale ( ) vertebra. In addition, the spatial distribution of organic and inorganic species was observed at the μm level by imaging MS (time-of-flight-secondary ion mass spectrometry, ToF-SIMS). Our results revealed a rather even distribution of hydrocarbon-, O- and N-containing ions in the trabecular network of the ancient bone. A different, more patchy arrangement of organic compounds was evident in the former marrow cavities that were partly cemented by clotted micrites of putative microbial origin. The concentration of fatty acids (FAs) in the ancient bone was in the permil range of the amount extracted from the recent whale vertebra. Endogenous compounds, including monoenoic -C and -C as well as branched FAs, were identified in the fossil bone by comparison with the host sediment. Ca. 80% of the prevalent -C and -C moieties in the ancient bone were extractable as FAs, whereas ca. 20% were covalently bound in the non-saponifiable kerogen fraction. Ample pyrite precipitates, distinctive 10-methyl branched FAs and microbial microborings (“tunneling”) indicate that sulfate reducers and collagen-degrading actinomycetes were central players in the microbial decomposition of the bone. Similarities with reported microbial FA patterns suggest that the FAs in the fossil bone were largely contributed by these microbial “last eaters”. The results highlight some of the degradation and preservation mechanisms during marine FA diagenesis in the “natural laboratory” of bones, and therefore the processes that lead to either degradation, preservation, or introduction of these widespread biomolecules in the fossils of ancient marine animals.
    Keywords: Geology
    ISSN: 0146-6380
    E-ISSN: 1873-5290
    E-ISSN: 21655987
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  • 2
    Language: English
    In: Biomaterials, September 2013, Vol.34(28), pp.6797-6803
    Description: Extracellular mimetic hydrogels formed from peptide crosslinkers and polyethylene glycol monomers permit cell-controlled invasion. The use of matrix metalloproteinase specific peptides might further allow for selective control of different cell-type invasion. In this study, the invasion of fibroblasts and vascular smooth muscle cells (VSMC) into hydrogels polymerised with either a peptide generally permissive for matrix metalloproteinase (MMP) degradation or peptides preferentially cleaved by MMP-14 or MMP-9 enzymes were compared. The two cell-types invaded the MMP permissive hydrogel equally. However, invasion of VSMC into MMP-14 selective peptide crosslinked hydrogels was diametrically opposite in nature to that of fibroblasts whereby VSMC showed a two-fold increase into these hydrogels relative to that observed in permissive hydrogels whilst fibroblasts had a relative two-fold decrease (  〈 0.01). These findings are suggestive that invasion and growth of different cell-types in engineered synthetic extracellular matrix mimics may be controlled selectively by the choice of protease specific peptide crosslinker and this could have general utility in tissue regenerative and engineering approaches.
    Keywords: Biomimetic Material ; Hydrogel ; Fibroblast ; Matrix Metalloproteinase ; Smooth Muscle Cell ; Medicine ; Engineering
    ISSN: 0142-9612
    E-ISSN: 1878-5905
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  • 3
    Language: English
    In: Journal of Biomechanics, 2011, Vol.44(14), pp.2525-2531
    Description: With the steady technological development enabling reduced device dimensions and new patient populations, detailed data on mechanical loads become increasingly important to ensure reliability of implantable medical devices. Based on an intra-species correlation of in-line and transverse force of the established previously for the Chacma baboon ( ), a simplified physiological model and a mechanical equivalent model were developed for a sub-muscular pectoral device implant considering , and rib cage. By assessing the morphometric and mechanical parameters of these musculo-skeletal structures and the associated model parameters, the intra-species correlation was shown to exhibit (a) robustness for a larger intra-species subject population and (b) linear scale variance allowing application for humans under consideration of the inter-species difference of the attachment angles of . The transfer function provides a basis for the prediction of patient-specific maximum mechanical loadings on a sub-muscular pectoral cardiac pacemaker implant through non- or minimal invasive measurements on the patient.
    Keywords: Scaling ; Transfer Function ; Mechanical Loading ; Pacemaker ; Medicine ; Engineering ; Anatomy & Physiology
    ISSN: 0021-9290
    E-ISSN: 1873-2380
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  • 4
    Language: English
    In: Biomaterials, 2010, Vol.31(32), pp.8484-8493
    Description: Knitted textiles have been used in medical applications due to their high flexibility and low tendency to fray. Their mechanics have, however, received limited attention. A constitutive model for soft tissue using a strain energy function was extended, by including shear and increasing the number and order of coefficients, to represent the non-linear warp-weft coupled mechanics of coarse textile knits under uniaxial tension. The constitutive relationship was implemented in a commercial finite element package. The model and its implementation were verified and validated for uniaxial tension and simple shear using patch tests and physical test data of uniaxial tensile tests of four very different knitted fabric structures. A genetic algorithm with step-wise increase in resolution and linear reduction in range of the search space was developed for the optimization of the fabric model coefficients. The numerically predicted stress–strain curves exhibited non-linear stiffening characteristic for fabrics. For three fabrics, the predicted mechanics correlated well with physical data, at least in one principal direction (warp or weft), and moderately in the other direction. The model exhibited limitations in approximating the linear elastic behavior of the fourth fabric. With proposals to address this limitation and to incorporate time-dependent changes in the fabric mechanics associated with tissue ingrowth, the constitutive model offers a tool for the design of tissue regenerative knit textile implants.
    Keywords: Constitutive Modeling ; Finite Element Analysis ; Mechanical Properties ; Surgical Mesh ; Tissue Ingrowth ; Medicine ; Engineering
    ISSN: 0142-9612
    E-ISSN: 1878-5905
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  • 5
    Language: English
    In: Soil Biology and Biochemistry, April 2019, Vol.131, pp.206-216
    Description: Microbial biomass turnover and the associated recycling of carbon (C ), nitrogen (N ) and phosphorus (P ) depend on their stoichiometric relationships and plays a pivotal role for soil fertility. This study examines the responses of C , N , P , the microbial respiration rate (CO efflux), and the total DNA content to C and nutrient addition in forest soils with very low (Low-P) and high P (High-P) contents. Both the Low-P and High-P soils were treated with a low and high level of C, N and P (5% and 200% of C , N and P ). Phosphorus ( P) was added before the addition of C ( C) and N ( N) to investigate the potential P limitation. We hypothesized two modes of microbial biomass C and nutrient turnover: 1) maintenance through intracellular metabolisms and/or 2) microbial growth and death through necromass reutilization. In Low-P soil, the 2-day-sooner increase of C and P compared to the increase of CO efflux and DNA content after high CN input showed the rapid initial uptake of C and limiting nutrients into microbial cells. It also demonstrated a lag period before microbial growth commenced. In High-P soil, however, the CO efflux and DNA content increased simultaneously with increases in microbial biomass, reflecting the microbial capacity for immediate growth. Afterwards, CO efflux and DNA content dropped to the level before CNP addition, with a decline of C and P in Low-P soil and a decline of N in High-P soil, suggesting a C and P limitation in Low-P soil and N limitation in High-P soil. Under low CNP addition, the microorganisms in High-P soil are ready to grow, while those in Low-P soil are mainly in maintenance mode. The microorganisms under maintenance in low-P soil can switch to growth/death mode after removing the nutrient limitation. High CNP input caused a non-homeostatic response of C : N : P stoichiometry from 691:105:1 to 33:1:1 in Low-P soil, mainly resulting from a higher storage of the limiting elements (C and P) in microbial biomass. The ratio remained stable under low CNP addition due to the endogenous metabolism of C and nutrient at maintenance. The C and nutrient were turnovered much faster by microorganisms in the growth/death mode, confirming a key principle of ecology: the stronger the limitation by an element, the more efficiently that element is retained within an organism, and the more intensively it is reused. The triple labeling approach linked with C : N : P stoichiometry helped to identify the dominant maintenance and growth/death modes of microbial biomass CNP turnover in nutrient-limited and -unlimited soil.
    Keywords: Microbial Stoichiometry ; Nutrient Turnover ; Microbial Maintenance ; Phosphorus Limitation ; Forest Soils ; Agriculture ; Chemistry
    ISSN: 0038-0717
    E-ISSN: 1879-3428
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  • 6
    Language: English
    In: Journal of Plant Nutrition and Soil Science, August 2016, Vol.179(4), pp.425-438
    Description: Understanding and quantification of phosphorus (P) fluxes are key requirements for predictions of future forest ecosystems changes as well as for transferring lessons learned from natural ecosystems to croplands and plantations. This review summarizes and evaluates the recent knowledge on mechanisms, magnitude, and relevance by which dissolved and colloidal inorganic and organic P forms can be translocated within or exported from forest ecosystems. Attention is paid to hydrological pathways of P losses at the soil profile and landscape scales, and the subsequent influence of P on aquatic ecosystems. New (unpublished) data from the German Priority Program 1685 “” were added to provide up‐to‐date flux‐based information. Nitrogen (N) additions increase the release of water‐transportable P forms. Most P found in percolates and pore waters belongs to the so‐called dissolved organic P (DOP) fractions, rich in orthophosphate‐monoesters and also containing some orthophosphate‐diesters. Total solution P concentrations range from ca. 1 to 400 µg P L, with large variations among forest stands. Recent sophisticated analyses revealed that large portions of the DOP in forest stream water can comprise natural nanoparticles and fine colloids which under extreme conditions may account for 40–100% of the P losses. Their translocation within preferential flow passes may be rapid, mediated by storm events. The potential total P loss through leaching into subsoils and with streams was found to be less than 50 mg P m a, suggesting effects on ecosystems at centennial to millennium scale. All current data are based on selected snapshots only. Quantitative measurements of P fluxes in temperate forest systems are nearly absent in the literature, probably due to main research focus on the C and N cycles. Therefore, we lack complete ecosystem‐based assessments of dissolved and colloidal P fluxes within and from temperate forest systems.
    Keywords: Forest Ecosystem ; Phosphorus ; Fluxes ; Soil ; Processes ; Hydrology
    ISSN: 1436-8730
    E-ISSN: 1522-2624
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  • 7
    Language: English
    In: Cardiovascular Engineering and Technology, 2010, Vol.1(4), pp.269-281
    Description: The structural integrity and arterial mechanics are important aspects for tissue regenerative vascular grafts with ingrowth permissible porous scaffolds. This paper presents a computational study of structural designs for a small-diameter vascular graft comprising porous polyurethane scaffold and knitted reinforcement mesh using Nitinol and polyurethane wire, respectively. Finite element models of the porous scaffold with the knitted mesh as embedded or external reinforcement were generated using validated constitutive models for porous polyurethane and Nitinol. Simulating a luminal pressure of up to 200 mmHg, deformations and stresses were recorded in porous scaffold and knitted mesh. The models predicted compliance between 1.2 and 15.7%/100 mmHg for the reinforced grafts and 65.1 and 106.4%/100 mmHg for the non-reinforced grafts. For the reinforced grafts, maximum stress was 97.0, 28.2, and 0.055 MPa in Nitinol wire, polyurethane wire, and porous polyurethane scaffold, respectively, at 120 mmHg. The corresponding maximum strain was 0.27, 5.0, and 22.5%. Stress and strain remained safe in the Nitinol mesh and the porous polyurethane but became critical in the polyurethane mesh between 120 and 200 mmHg. Despite compression due to luminal pressure load, the porous scaffold remained ingrowth permissible for cells, capillaries, and arterioles up to 200 mmHg. The outcomes of this study provided preliminary concepts for the structural designs for a tissue regenerative composite vascular graft toward improved mechanical performance and structural integrity. The implemented modeling approach can be used in the further development and optimization of small-diameter tissue-regenerating vascular grafts.
    Keywords: Blood vessel ; Vascular prosthesis ; Tissue engineering ; Finite element method ; Arterial mechanics
    ISSN: 1869-408X
    E-ISSN: 1869-4098
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  • 8
    Language: English
    In: The Journal of Thoracic and Cardiovascular Surgery, 2009, Vol.137(5), pp.1101-1108
    Description: Constrictive external mesh support of vein grafts was shown to mitigate intimal hyperplasia in animal experiments. To determine the degree of constriction required for the elimination of dimensional irregularities in clinically used vein grafts, a detailed anatomic study of human saphenous veins was conducted. In 200 consecutive patients having coronary artery bypass grafting, harvested saphenous veins (length 34.4 ± 10.8 cm) were analyzed regarding diameter irregularities, side branch distribution, and microstructure. The mean outer diameter of surgically distended saphenous veins was 4.2 ± 0.6 mm (men, 4.3 ± 0.6 mm vs women, 3.9 ± 0.5 mm; 〈 .0001). Although the outer diameter significantly decreased over the initial 18 cm (−7.6%; 〈 .0001), the overall increase between malleolus and thigh was not significant (+11.2%). Smaller-diameter veins (〈3.5 mm) had more pronounced diameter fluctuations than larger veins (31.8% ± 11.0% vs 21.2% ± 8.8%; 〈 .0001), with more than 71% of all veins showing caliber changes of more than 20%. There was 1 side branch every 5.4 ± 4.3 cm, with a significantly higher incidence between 20 and 32 cm from the malleolus ( 〈 .0001 to distal, 〈 .0004 to proximal). Generally, women had more side branches than men (0.30 ± 0.15 cm vs 0.25 ± 0.12 cm ; = .0190). Thick-walled veins (565.7 ± 138.4 μm) had a significantly higher number of large side branches ( 〈 .0001), and thin-walled veins (398.7 ± 123.2 μm) had significantly more small side branches ( 〈 .0001). Pronounced intimal thickening (“cushions”) was found in 28% of vessels (119.8 ± 28.0 μm vs 40.1 ± 18.2 μm; 〈 .0001). Although the preferential location of side branches may be addressed by the deliberate discarding of infragenicular vein segments, a diameter constriction of 27% on average would eliminate diameter irregularities in 98% of vein grafts.
    Keywords: 23 ; 33 ; BMI ; Cabg ; Od;
    ISSN: 0022-5223
    E-ISSN: 1097-685X
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  • 9
    Language: English
    In: Biomaterials, March, 2012, Vol.33(7), p.2060(7)
    Description: To link to full-text access for this article, visit this link: http://dx.doi.org/10.1016/j.biomaterials.2011.11.031 Byline: Karen Kadner (a), Stephan Dobner (a), Thomas Franz (a)(b)(c), Deon Bezuidenhout (a), Mazin S. Sirry (a), Peter Zilla (a), Neil H. Davies (a) Abstract: Biomaterials are increasingly being investigated as a means of reducing stress within the ventricular wall of infarcted hearts and thus attenuating pathological remodelling and loss of function. In this context, we have examined the influence of timing of delivery on the efficacy of a polyethylene glycol hydrogel polymerised with an enzymatically degradable peptide sequence. Delivery of the hydrogel immediately after infarct induction resulted in no observable improvements, but a delay of one week in delivery resulted in significant increases in scar thickness and fractional shortening, as well as reduction in end-systolic diameter against saline controls and immediately injected hydrogel at both 2 and 4 weeks post-infarction (p 〈 0.05). Hydrogels injected at one week were degraded significantly slower than those injected immediately and this may have played a role in the differing outcomes. The hydrogel assumed markedly different morphologies at the two time points having either a fibrillar or bulky appearance after injection immediately or one week post-infarction respectively. We argue that the different morphologies result from infarction induced changes in the cardiac structure and influence the degradability of the injectates. The results indicate that timing of delivery is important and that very early time points may not be beneficial. Author Affiliation: (a) Cardiovascular Research Unit, Chris Barnard Division of Cardiothoracic Surgery, University of Cape Town, Department of Health Sciences, Cape Town 7925, South Africa (b) Centre for Research in Computational and Applied Mechanics, University of Cape Town, Rondebosch, South Africa (c) Centre for High Performance Computing, Rosebank, South Africa Article History: Received 4 November 2011; Accepted 13 November 2011
    Keywords: Peptides ; Polyols ; Biological Products ; Heart Attack
    ISSN: 0142-9612
    Source: Cengage Learning, Inc.
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  • 10
    Language: English
    In: Journal of Biomechanics, July 2012, Vol.45, pp.S131-S131
    Keywords: Medicine ; Engineering ; Anatomy & Physiology
    ISSN: 0021-9290
    E-ISSN: 1873-2380
    Source: ScienceDirect Journals (Elsevier)
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