Klaus D Jandt

Universitätsklinikum Jena, Jena, Thuringia, Germany

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Publications (188)729.18 Total impact

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    ABSTRACT: Biodegradable calcium phosphate cements (CPCs) are promising materials for minimally invasive treatment of bone defects. However, CPCs have low mechanical strength and fracture toughness. One approach to overcome these limitations is the modification of the CPC with reinforcing fibers. The matrix-fiber interfacial shear strength (ISS) is pivotal for the biomechanical properties of fiber-reinforced CPCs. The aim of the current study was to control the ISS between a brushite-forming CPC and degradable PLGA fibers by oxygen plasma treatment and to analyze the impact of the ISS alterations on its bulk mechanical properties.
    No preview · Article · Feb 2016 · Journal of the Mechanical Behavior of Biomedical Materials
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    ABSTRACT: A polyzwitterion is synthesized by regioselective functionalization of cellulose possessing a uniform charge distribution. The positively charged ammonium group is present at position 6, while the negative charge of carboxylate is located at positions 2 and 3 of the repeating unit. The molecular structure of the biopolymer derivative is proved by NMR spectroscopy. This cellulose-based zwitterion is applied to several support materials by spin-coating and characterized by means of atomic force microscope, contact angle measurements, ellipsometry, and X-ray photoelectron spectroscopy. The coatings possess antimicrobial activity depending on the support materials (glass, titanium, tissue culture poly(styrene)) as revealed by confocal laser scanning microscopy and live/dead staining.
    No preview · Article · Dec 2015 · Macromolecular Bioscience
  • Stefan Maenz · Mike Mühlstädt · Klaus D. Jandt · Joerg Bossert
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    ABSTRACT: The aim of this study was to significantly reduce the curing time for glass fibre epoxy composites in industrial relevant dimensions without worsening of the mechanical properties. With the combination of microwave heating and resin transfer moulding (RTM), the time between filling the mould and demoulding the samples was reduced to only 1 h and 15 min compared to at least 6 h for conventional curing of the same material. Based on the different dielectric losses of cured and uncured resin a pulsed microwave process was developed. In this way homogenously cured samples were obtained. Tensile strength, flexural strength, flexural modulus of elasticity and Charpy impact strength of microwave cured samples were compared to conventionally cured samples. No statistically significant differences were found. Thus, microwave curing shows a high potential to improve the efficiency of fibre composite production while maintaining the mechanical properties.
    No preview · Article · Sep 2015 · Journal of Composite Materials
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    ABSTRACT: Self-assembled nanostructures of crystallizable block copolymers can be tuned by controlled crystal thickening during annealing. In this contribution, we present a strategy, based on time- and temperature-dependent DSC, SAXS and WAXS measurements, which enables to study, both, the mechanisms and kinetics of crystal thickening and the respective morphological development, exemplarily discussed for the soft-confined PB-b-PEO block copolymer. Thereby, DSC based PEO crystal thickness distributions yield qualitative information about the mechanisms during annealing. Conclusions on the kinetics and the absolute long-period growth due to crystal thickening can be drawn from the time- and temperature dependent SAXS investigations, by calculating the average long-period and its deviations from the SAXS reflection position and shape, respectively. By this combined study, three annealing regimes were observed. (i) At low annealing temperatures Ta, steady lamellae-thickening was found, due to defect healing of the PEO crystals. (ii) Thermal fractionation was observed at intermediate Ta, due to the exclusion of shorter PEO chains from the crystals. (iii) Annealing close to and above the peak melting temperature, self-nucleation of the molten PEO fractions dominates. The combination of the applied techniques provides deeper insights into the kinetics and ordering mechanisms of the controlled long-period growth by crystal thickening under variable confinements, which enables to tailor the morphology of the block copolymer within several nanometers, without changing the degree of polymerization.
    Full-text · Article · Apr 2015 · European Polymer Journal
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    ABSTRACT: Despite their various advantages, such as good esthetic properties, absence of mercury and adhesive bonding to teeth, modern dental composites still have some drawbacks, e.g., a relatively high rate of secondary caries on teeth filled with composite materials. Recent research suggests that microstructured biomaterials surfaces may reduce microbial adhesion to materials due to unfavorable physical material–microbe interactions. The objectives of this study were, therefore, to test the hypotheses that (i) different surface microstructures can be created on composites by a novel straightforward approach potentially suitable for clinical application and (ii) that these surface structures have a statistically significant effect on microbial adhesion properties.
    No preview · Article · Jan 2015 · Dental materials: official publication of the Academy of Dental Materials
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    ABSTRACT: Microstructured surfaces mimicking the endothelial cell (EC) morphology is a new approach to improve the blood compatibility of synthetic vascular grafts. The ECs are capable of changing their shapes depending on different shear conditions. However, the quantitative correlation between EC morphology and shear stress has not yet been investigated statistically. The aim of this study was to quantitatively investigate the morphology of ECs in dependence on the shear stress. Blood flow rates in different types of natural blood vessels (carotid, renal, hepatic and iliac arteries) originated from domestic pigs were first measured in vivo to calculate the shear stresses. The EC morphologies were quantitatively characterized ex vivo by imaging with high resolution scanning electron microscopy (SEM) and cross-sectioning of the cells using a state-of-the-art Focused Ion Beam (FIB). The relationships between EC geometrical parameters and shear stress were statistically analyzed and found to be exponential. ECs under high shear stress conditions had a longer length and narrower width, i.e. a higher aspect ratio, while the cell height was smaller compared to low shear conditions. Based on these results, suitable and valid geometrical parameters of microstructures mimicking EC can be derived for various shear conditions in synthetic vascular grafts to optimize blood compatibility.
    No preview · Article · Dec 2014 · Tissue and Cell
  • K Jandt · B Sigusch

    No preview · Article · Nov 2014 · ZWR - Das Deutsche Zahnärzteblatt
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    ABSTRACT: Carbon nanotubes (CNTs) and their polymer nanocomposites are interesting materials for future applications, for example in optics or electronics. Research faces two major challenges with these outstanding nanofillers: Control over dispersion and spatial arrangement within the nanocomposite, both required to achieve optimal structure and properties of CNT based nanocomposites. We report on novel self-assembled multi-wall CNT (MWCNT)/block copolymer (BCP) nanostructures realized by patterning MWCNTs with amphilphilic diblock copolymer micelles. A high molecular weight Poly(styrene)-b-poly(2-vinylpyridine) BCP which forms large micelles (250 nm) was chosen to facilitate the templating by reducing the bending energy induced in the MWCNTs. We tested the hypothesis, that it is possible to use an amphiphilic BCP as a dispersing agent and its spherical micelles as a template at the same time without modification of the CNTs. In thin films of the MWCNT/BCP micelles, highly separated MWCNTs were repeatedly observed which enveloped the core of the BCP micelles, i.e., the unfunctionalized MWCNTs segregated to the interface between the two BCP phases. Depending on the size of the MWCNTs, ring like (split-ring) or network forming structures were obtained. The MWCNT templating mechanism, i.e. the segregation to the interface, is explained by the interfacial tension within the BCP interface and the chain entropy. The reported new complex nanocomposite has potential to be applied for example as cost-effective split-ring resonators for metamaterials or for conductive polymer films with an extremely low percolation threshold.
    No preview · Article · Oct 2014 · Langmuir
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    ABSTRACT: The dynamics of adhesion and growth of bacterial cells on biomaterial surfaces play an important role in the formation of biofilms. The surface properties of biomaterials have a major impact on cell adhesion processes, eg the random/non-cooperative adhesion of bacteria. In the present study, the spatial arrangement of Escherichia coli on different biomaterials is investigated in a time series during the first hours after exposure. The micrographs are analyzed via an image processing routine and the resulting point patterns are evaluated using second order statistics. Two main adhesion mechanisms can be identified: random adhesion and non-random processes. Comparison with an appropriate null-model quantifies the transition between the two processes with statistical significance. The fastest transition to non-random processes was found to occur after adhesion on PTFE for 2-3 h. Additionally, determination of cell and cluster parameters via image processing gives insight into surface influenced differences in bacterial micro-colony formation.
    No preview · Article · Oct 2014 · Biofouling
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    ABSTRACT: Injectable, brushite-forming calcium phosphate cements (CPCs) have great potential as bone replacement materials due to enhanced degradability and long-term inclusion in bone remodeling. However, the use of such brushite-forming CPCs in load-bearing areas is limited by their low mechanical strength. One approach to overcome this limitation is the use of reinforcing fibers. Thus, an injectable, biodegradable, brushite-forming CPC based on beta-tricalcium phosphate/phosphoric acid with fiber reinforcement was developed for minimally invasive surgery. The fibers (diameter 25µm; length 0.25, 1 or 2mm) were extruded from poly(l-lactide-co-glycolide) acid (PLGA) and added to the CPC (2.5, 5 or 7.5% (w/w)). Independent of the fiber content, injectability of the CPC was retained up to a fiber length of 1mm. The addition of all PLGA fiber types increased diametral tensile strength, biaxial flexural strength, and flexural strength by up to 25% (p≤0.05 for the diametral tensile strength for the CPC with 5% (w/w) 1mm fibers and the biaxial flexural strength of the CPC with 5% (w/w) 0.25mm fibers). In contrast, the work of fracture strongly and significantly increased (p<0.01) by up to 12.5-fold. At constant fiber content, the mechanical properties of the fiber-reinforced CPC were mostly augmented with increasing fiber length. Also, the addition of PLGA fibers to the brushite-forming CPC (up to 7.5% (w/w)) only transiently delayed cell growth and did not decrease cell viability. Fiber reinforcement of CPCs thus augments their mechanical strength while preserving the injectability and biocompatibility required for their application in modern surgery.
    Full-text · Article · Aug 2014 · Journal of the Mechanical Behavior of Biomedical Materials
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    ABSTRACT: Objectives: Endodontic pathogens can penetrate deep into dentinal tubules and therefore survive the chemo-mechanical disinfection procedures. Bacterial penetration has been mainly studies using sliced infected human teeth which, besides creating artifacts, can hinder the observation of the inner tubules due to the dense and opaque dentin structure. The aim of the present study was to develop a standardized dentin model by using artificial SiO/SiO2-microtubes of different diameters and lengths to test the penetration ability of Enterococcus faecalis. Methods: E. faecalis was grown in Schaedler fluid media for 24h and thereafter cell density was settled to 10(3)cells/ml by addition of fresh media. The bacterial solution was then incubated for 2, 3, 5 and 10 days with the SiO/SiO2-microtubes of different diameters (2-5.5μm) and lengths (100-500μm). The colonization of the tubes was evaluated by phase-contrast microscopy and the amount of colonization was determined by using a colonization index (CI; 0-none, 1-mild, 2-moderate, 3-heavy). Results: The diameter of the tubes strongly influences the microbial colonization. After 2 days of cultivation the 5.5μm tubes showed a moderate to heavy colonization (CI 2-3). In comparison, the 2 and 3μm tubes were clearly less colonized at the same point in time. In detail: at day 3, only mild to moderate bacteria colonization (CI 1-2) were found in the 3μm tubes and at day 10 penetration of the 2μm tubes just started. The colonization of the 5.5μm tubes was also influenced by their length. In case of the longer microtubes, though, a smaller share of heavily colonized tubes was observed. Significance: Our results show that E. faecalis was able to penetrate and reproduce within the standardized SiO/SiO2-microtubes in a short time. To examine the mechanisms of bacterial adhesion and invasion into tubular structures the 2μm tubes could serve as a model system because the diameters are similar to those of dentinal tubules.
    No preview · Article · Jun 2014 · Dental materials: official publication of the Academy of Dental Materials
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    Dataset: C3RA47499B

    Full-text · Dataset · May 2014
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    ABSTRACT: An effective method for fabrication of long range ordered micro- and nanostructures on surfaces is to control the interactive crystallisation of block copolymers. In this study, the influence of different initial mesophases of a double crystalline polyethylene-block-poly (ethylene oxide) (PE-b-PEO) diblock co-oligomer on the interactive crystallisation process was studied using synchrotron radiation X-ray diffraction (SAXS/WAXD), in situ optical microscopy and differential scanning calorimetric analysis (DSC). According to the applied annealing procedure, different PE-b-PEO initial mesophases, i.e., disordered, cylindrical and spherical, have been induced. In all cases, the subsequent PEO crystallisation disrupted these initial microdomains and transformed them into crystalline lamellar morphologies with the same long periods. However, the different initial mesophases significantly affected the PEO crystallisation kinetics due to different topological confinements. An initial disordered mesophase induced the highest PEO crystallisation rate because PEO nucleation and crystal growth were limited only by chain diffusion. For an initial spherical or cylindrical mesophase, decreased PEO crystallisation rates were observed. Here, the chain diffusion was decreased by the microdomain structure. For an initial cylindrical mesophase, the earlier formed PE crystals act as a template for the subsequent PEO crystallisation and, thus, increased the PEO crystallisation as compared to the spherical mesophase where the PE was amorphous. This study demonstrates that the topological confinement of the block copolymer's initial mesophase strongly influences the crystallisation kinetics and, thus, the structures formed at the surface of drop-casted films.
    Full-text · Article · Apr 2014 · Polymer
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    ABSTRACT: Ferrihydrite (Fh) is a widespread poorly crystalline Fe oxide which becomes easily coated by natural organic matter (OM) in the environment. This mineral-bound OM entirely changes the mineral surface properties and therefore the reactivity of the original mineral. Here, we investigated the reactivity of 2-line Fh, Fh with adsorbed OM and Fh coprecipitated with OM towards microbial and abiotic reduction of Fe(III). As a surrogate for dissolved soil OM we used a water extract of a Podzol forest floor. Fh-OM associations with different OM-loadings were reduced either by Geobacter bremensis or abiotically by Na-dithionite. Both types of experiments showed decreasing initial Fe reduction rates and decreasing degrees of reduction with increasing amounts of mineral-bound OM. At similar OM-loadings, coprecipitated Fhs were more reactive than Fhs with adsorbed OM. The difference can be explained by the smaller crystal size and poor crystallinity of such coprecipitates. At small OM loadings this led to even faster Fe reduction rates than found for pure Fh. The amount of mineral-bound OM also affected the formation of secondary minerals: goethite was only found after reduction of OM-free Fh and siderite was only detected when Fhs with relatively low amounts of mineral-bound OM were reduced. We conclude that direct contact of G. bremensis to the Fe oxide mineral surface was inhibited when blocked by OM. Consequently, mineral-bound OM shall be taken into account besides Fe(II) accumulation as a further widespread mechanism to slow down reductive dissolution.
    Full-text · Article · Mar 2014 · Biogeosciences
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    ABSTRACT: We report here a facile strategy to fabricate three-dimensional (3D) hydroxyapatite (HA) architectures with well-defined long continuous interconnected pores by using electrospinning and biomimetic mineralization. To this end, a polymeric nanofiber (NF) scaffold with well-defined architecture was fabricated by electrospinning, and bone morphogenetic protein 2 (BMP2) was then adsorbed onto the chemically modified NFs through bio-conjugation. The 3D nanoporous HA architecture was finally fabricated by biomimetic mineralization of NF-BMP2 hybrid in simulated body fluids and subsequent dissolution of NFs in hexafluoroisopropanol. The formation of NF-BMP2 hybrid was identified by confocal laser scanning microscopy analysis. The crystal structure of HA crystals formed on NFs was examined by X-ray diffraction. The chemical composition and interconnected porous structure of the created 3D HA architectures were measured by X-ray photoelectron spectroscopy, focused ion beam scanning electron microscopy, and transmission electron microscopy, respectively. This bottom-up strategy based on electrospinning and biomimetic mineralization opens up a new way to prepare diverse porous HA-based hybrid materials and show great potentials in drug delivery, gene transfer and tissue engineering.
    Full-text · Article · Mar 2014 · RSC Advances
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    ABSTRACT: Thin film surface nanostructures of semicrystalline diblock copolymer are promising for the fabrication of photonic crystals and bioanalytical devices because they might be tailorable by controlled crystallization. One approach to systematically control polymer crystallization is a self-nucleation experiment. The self-nucleation experiment for block copolymers has only been reported for the bulk and so far not for thin films. Considering the versatility of a tailorable surface nanostructure, it is promising to apply the controlled crystallization of a bulk self-nucleation experiment to thin films of a diblock copolymer. In the current study we tested the hypothesis that within two self-nucleation experiments, i.e., in the bulk and thin film, the calorimetric bulk properties of a polybutadiene-block-poly(ethylene oxide) can be correlated to the resulting thin film surface nanostructures and to understand as well as predict their formation. The calorimetric bulk properties measured by differential scanning calorimetry in the bulk self-nucleation experiment were correlated to surface nanostructures measured by atomic force microscopy of the thin film self-nucleation experiment samples. In analogy to the bulk self-nucleation experiment, we introduced a crystalline standard for the thin film self-nucleation experiment where the crystalline lamellae consisted of once-folded chains. Annealing the thin film crystalline standard promoted the thickening of crystalline lamellae on the film surface which is explained by the formation of less folded chain crystals that obtain higher melting temperatures. The crystalline lamellae thickness was steplessly variable within the range of 8–16 nm. In analogy to the Hoffman–Weeks and Gibbs–Thomson plots, we derived a function which can be used to predict the lamellae thickness as a function of the annealing temperature. Bulk and thin film self-nucleation experiments were successfully related, since thin film surface nanostructures were consistently correlated to calorimetric results. We established the dual self-nucleation experiment as a powerful tool to predictably tailor thin film nanostructures in the range of several nanometers.
    No preview · Article · Mar 2014 · Macromolecules
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    Full-text · Dataset · Feb 2014
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    ABSTRACT: Various microstructures and phase morphologies of an amphiphilic poly(ethylene oxide)-block-polyethylene (PEO-b-PE) co-oligomer, controlled by topological restriction of PE segments on the tethered PEO chains, were characterized by differential scanning calorimetry (DSC), polarized optical microscopy (POM), scanning electron microscopy (SEM), and synchrotron radiation wide-angle/small-angle X-ray scattering (WAXS/SAXS) in drop-cast films. The crystallization processes were mediated by two pathways, a one-step crystallization process (I) and a sequential crystallization process (II). Results show that the thermal procedures have great influence on the microstructures and phase morphologies of PEO-b-PE co-oligomer, e.g., negative spherulites with radial stripes were detected in the one-step crystallization process (I), while crystalline texture, which contains a large number of crystals with reduced sizes, formed in the sequential crystallization process (II). Based on our experimental data, the topological restriction effect encountered by PEO chains depends on the hard confinement of PE crystals and the soft confinement of amorphous PE in the two crystallization procedures. The formation mechanisms of the long-range order structures within the co-oligomer were elucidated through morphology models. These nano-patterned structures make the double crystalline block copolymers outstanding candidates for surface modification, micromolding, and optoelectronic devices in nanotechnological and biomedical applications.
    Full-text · Dataset · Jan 2014
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    Full-text · Article · Jan 2014 · RSC Advances
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    ABSTRACT: Biomaterials-associated infections are primarily initiated by the adhesion of microorganisms on the biomaterial surfaces and subsequent biofilm formation. Understanding the fundamental microbial adhesion mechanisms and biofilm development is crucial for developing strategies to prevent such infections. Suitable in vitro systems for biofilm cultivation and bacterial adhesion at controllable, constant and reproducible conditions are indispensable. This study aimed (i) to modify the previously described constant-depth film fermenter for the reproducible cultivation of biofilms at non-depth-restricted, constant and low shear conditions and (ii) to use this system to elucidate bacterial adhesion kinetics on different biomaterials, focusing on biomaterials surface nanoroughness and hydrophobicity. Chemostat-grown Escherichia coli were used for biofilm cultivation on titanium oxide and investigating bacterial adhesion over time on titanium oxide, poly(styrene), poly(tetrafluoroethylene) and glass. Using chemostat-grown microbial cells (single-species continuous culture) minimized variations between the biofilms cultivated during different experimental runs. Bacterial adhesion on biomaterials comprised an initial lag-phase I followed by a fast adhesion phase II and a phase of saturation III. With increasing biomaterials surface nanoroughness and increasing hydrophobicity, adhesion rates increased during phases I and II. The influence of materials surface hydrophobicity seemed to exceed that of nanoroughness during the lag-phase I, whereas it was vice versa during adhesion phase II. This study introduces the non-constant-depth film fermenter in combination with a chemostat culture to allow for a controlled approach to reproducibly cultivate biofilms and to investigate bacterial adhesion kinetics at constant and low shear conditions. The findings will support developing and adequate testing of biomaterials surface modifications eventually preventing biomaterial-associated infections.
    Full-text · Article · Jan 2014 · PLoS ONE

Publication Stats

6k Citations
729.18 Total Impact Points

Institutions

  • 2007-2015
    • Universitätsklinikum Jena
      Jena, Thuringia, Germany
  • 2002-2015
    • Friedrich Schiller University Jena
      • • Institute of Organic Chemistry and Macromolecular Chemistry
      • • Faculty of Physics and Astronomy
      • • Department of Materials Science and Technology (IMT)
      • • Section of Dental Technological Materials Science
      Jena, Thuringia, Germany
  • 1993-2005
    • University of Bristol
      • School of Oral and Dental Sciences
      Bristol, England, United Kingdom
  • 1994-2004
    • Cornell University
      • Department of Materials Science and Engineering
      Ithaca, New York, United States
    • Technische Universität Dortmund
      Dortmund, North Rhine-Westphalia, Germany