Biomedical subjects

M Epple

Publications and source records attributed to M Epple.

At least 19 recordsLinked to original sources

PubMed2005

Uniform magnetic properties for an ultrahigh-density lattice of noninteracting co nanostructures.

We report on the magnetic properties of two-dimensional Co nanoparticles arranged in macroscopically phase-coherent superlattices created by self-assembly on Au(788). Our particles have a density of 26 Tera/in2 (1 Tera=10(12)), are monodomain, and have uniaxial out-of-plane anisotropy. The distribution of the magnetic anisotropy energies has a half width at half maximum of 17%, a factor of 2 more narrow than the best results reported for superlattices of three-dimensional nanoparticles. Our data show the absence of magnetic interactions between the particles. Co/Au(788) thus constitutes an ideal model system to explore the ultimate density limit of magnetic recording.

Journal Article↗

PubMed2004

[Occlusion of central venous port catheters after simultaneous 24 h infusions of 5-FU and calcium-folinic acid in patients with gastrointestinal cancer].

Folinic acid-modulated 5-FU regimens are standard elements in several chemotherapy combinations like FOLFIRI, FOLFOX or AIO-regimen in the palliative treatment of patients with gastrointestinal cancer. When the simultaneous mixed infusion of 5-FU and calcium-folinic acid (Leucovorin) was authorized by the BfArM in 2002, we introduced this application regimen in the treatment of our cancer patients. 19 patients (AIO-regimen [5], FOLFIRI [12] and FOLFOX [2]) received a simultaneously mixed infusion of calcium-folinic acid and 5-FU over 24 hours with a total of 110 applications. 5-FU doses varied between 2000 and 2600 mg/m2, calcium-folinic acid was given with 500 mg/m2, infusion rate was 10 ml/hour using a 24 h pump. Central venous catheters employed included single Barth-Port in 18 cases, 1 patient had a Viggon-Port. In 3 out of the 19 patients catheter occlusion was noticed after 8-10 weekly applications of the mixed infusion. Heparine and subsequently urokinase were not successful in reversing the obstruction. All three catheters had to be explanted. Catheter tips in all cases showed a yellow cristalline precipitation. The crystallographic analysis exhibited calcium carbonate (CaCO3) in its polymorphic form (calcite). Thus, we confirmed calcite formation causing catheter occlusion as a frequent complication during a continuous 24 h-infusion of mixed high dose 5-FU and calcium-folinic acid. This reaction could not be avoided by increasing infusion volume and the application flow rate. As a result of our findings, recommending using calcium-folinic acid mixed with 5-FU has been withdrawn in the meantime.

Aged↗

PubMed2004

A novel method to produce hydroxyapatite objects with interconnecting porosity that avoids sintering.

Porous objects of carbonated apatite were prepared by mixing polyvinyl alcohol fibres (PVA) and sodium chloride as porogens with nanocrystalline carbonated apatite powder. After cold isostatic pressing (CIP) and dissolving the porogens, the bioceramic showed an interconnecting porosity with pore diameters in the range of 250-400 microm. The method can be transposed to any material that is insoluble in water (like many polymers). Such objects are promising for bone regeneration because the interconnecting porosity in carbonated apatite provides a good environment for bone attachment and ingrowth.

Biocompatible Materials↗

PubMed2004

A comparative study of clinically well-characterized human atherosclerotic plaques with histological, chemical, and ultrastructural methods.

Atherosclerotic plaques (six cases) with well-documented clinical history were analysed using histology, scanning electron microscopy (SEM), transmission electron microscopy (TEM), energy-dispersive X-ray (EDX) spectroscopy, infrared spectroscopy (IR), thermogravimetry (TG), and high-resolution synchrotron X-ray diffraction. All samples contained about 60-70 wt% biological carbonated apatite (in dry state) in a nanocrystalline form with particle sizes of about 20 nm. Structurally, there are strong similarities to bone mineral. Ultrastructural investigations documented typical calcospherites, mineralisation processes starting at collagen fibrils and ring-shaped crystalline mineralised structures. There were no significant ultrastructural or chemical differences between the calcifications of individual patients.

Aged↗

PubMed2004

A thorough physicochemical characterisation of 14 calcium phosphate-based bone substitution materials in comparison to natural bone.

Fourteen different synthetic or biological bone substitution materials were characterised by high-resolution X-ray diffractometry, infrared spectroscopy, thermogravimetry, and scanning electron microscopy. Thus, the main parameters chemical composition, crystallinity, and morphology were determined. The results are compared with natural bone samples. The materials fall into different classes: Chemically treated bone, calcined bovine bone, algae-derived hydroxyapatite, synthetic hydroxyapatite, peptide-loaded hydroxyapatite, and synthetic beta-TCP ceramics.

Animals↗

PubMed2003

An optimized synthetic substrate for orthodontic bond strength testing.

OBJECTIVE: The purpose of this study was to investigate the suitability of different synthetic calcium phosphate based substrates as a biomimetic enamel surface model for orthodontic bond strength testing. METHODS: Carbonated apatite, amorphous calcium phosphate and commercial hydroxyapatite specimens were prepared as substrates for orthodontic bond strength testing. Carbonated apatite specimens were prepared by pressing, sintering and treatment with NaF. The shear bond strength was measured with a universal testing machine. RESULTS: Hydroxyapatite, amorphous and cold pressed carbonated hydroxyapatite exhibited fractures within the substrate after debonding. Mean bond strength values for carbonated hydroxyapatite were 7.38 (1.75) MPa for specimens pressed at 300 degrees C and 9.55 (2.23) MPa for specimens pressed at 300 degrees C and then sintered at 600 degrees C. An additional NaF treatment after sintering resulted in lower bond strength measurements of on average 6.52 (1.03) MPa. SIGNIFICANCE: Hot pressed and sintered carbonated hydroxyapatite showed acceptable shear bond strength values and may represent a suitable biomimetic model for orthodontic bond strength testing.

Apatites↗

PubMed2003

Mechanically stable implants of synthetic bone mineral by cold isostatic pressing.

A calcium phosphate phase that is equivalent in composition (carbonate content) and crystallinity (nanocrystals) to the mineral phase of bone was prepared by a continuous precipitation method. The powder was compacted by cold isostatic pressing into desired shapes with high compressive strength (range of 20-50 MPa, depending on the geometry). It is concluded that such implant materials can be prepared with a fine-tuned biodegradability in combination with a high mechanical strength. The high mechanical strength of the objects also permits further mechanical shaping procedures like drilling or cutting.

Biocompatible Materials↗

PubMed2003

The remarkable difference between surface and step atoms in the magnetic anisotropy of two-dimensional nanostructures.

The original magnetic properties of nanometre-sized particles are due to the distinct contributions of volume, surface and step atoms. To disentangle these contributions is an ongoing challenge of materials science. Here we introduce a method enabling the identification of the remarkably different contributions of surface and perimeter atoms to the magnetic anisotropy energy of two-dimensional nanostructures. Our method uses the generally nonlinear relationship between perimeter length and surface area. Atomic-scale characterization of the morphology of ensembles of polydisperse nanostructures, combined with in situ measurements of their temperature-dependent magnetic susceptibility, gives access to the role played by the differently coordinated atoms. We show for Co nanostructures on a Pt(111) surface that their uniaxial out-of-plane magnetization is entirely caused by edge atoms having 20 times more anisotropy energy than their bulk and surface counterparts. Identification of the role of perimeter and surface atoms opens up unprecedented opportunities for materials engineering. As an example, we separately tune magnetic hardness and moment in bimetallic core-shell nanostructures.

Anisotropy↗

PubMed2002

Continuous synthesis of amorphous carbonated apatites.

Amorphous carbonated hydroxyapatite was prepared by rapid mixing of aqueous solutions of a continuous computer-controlled reactor. The variation of the carbonate content in the solid product is possible by adjustment of the ratios of phosphate to carbonate in the initial solution. The principal reaction parameters (temperature, pH, stirrer speed, solution composition and supersaturation) are controlled and monitored. By controlling these processing parameters, a non-stoichiometric hydroxyapatite with fine-tuned crystallinity, morphology, and carbonate content can be reproducibly prepared. The higher solubility under the conditions of osteoclastic resorption was tested in vitro at constant pH (4.4).

Apatites↗

PubMed2002

[A graded composite material for use in the area of the cranial and facial skull].

For the reconstruction of complex skull defects with individual prefabricated CAD/CAM-implants titanium is well established as bone substitution material. The aim of our studies was to optimize a composite material from polyesters and calcium phosphate. Therefore two different operating procedures (hot pressing and gas-flushing) were combined. As a result the graded composition and porosity of the implants allow a spatial guided degradation progress and cell ingrowth. First biocompatibility tests in vitro with primary human osteoblasts showed a much better pH-characteristic and a better biocompatibility of the composites in comparison with the pure polymers. Degradation experiments in vitro confirmed the different expected degradation rates of the composite materials. As a next step in vivo experiments in ovine skulls are in progress.

Animals↗

PubMed2002

[Rapid analysis of biocompatibility with graded test samples exemplified by Ni-NiTi-Ti].

The biocompatibility of nickel-titanium alloys was investigated by single-culture experiments on functionally graded samples with a stepwise change in composition from nickel to titanium, including NiTi shape memory alloy of a 50:50 mixture. This approach permitted a considerable decrease of experimental resources by simultaneously studying a full variation of composition. The results indicate a good biocompatibility for a nickel content up to about 50%. The cells used in the biocompatibility studies comprised human osteoblast-like osteosarcoma cells (SAOS-2, MG-63), primary human osteoblasts (HOB), and murine fibroblasts (3T3).

Animals↗

PubMed2001

Energetics of C-Cl, C-Br, and C-I bonds in haloacetic acids: enthalpies of formation of XCH2COOH (X=CI, Br, I) compounds and the carboxymethyl radical.

The standard molar enthalpies of formation of chloro-, bromo-, and iodoacetic acids in the crystalline state, at 298.15 K, were determined as deltafH(o)m(C2H3O2Cl, cr alpha)=-(509.74+/- 0.49) kJ x mol(-1), deltafH(o)m(C2H3O2Br, cr I)-(466.98 +/- 1.08) kJ x mol(-1), and deltafH(o)m (C2H3O2I, cr)=-(415.44 +/- 1.53) kJ x mol(-1), respectively, by rotating-bomb combustion calorimetry. Vapor pressure versus temperature measurements by the Knudsen effusion method led to deltasubH(o)m(C2H3O2Cl)=(82.19 +/- 0.92) kJ x mol(-1), deltasubH(o)m(C2H3O2Br)=(83.50 +/- 2.95) kJ x mol(-1), and deltasubH(o)m-(C2H3O2I) = (86.47 +/- 1.02) kJ x mol(-1), at 298.15 K. From the obtained deltafH(o)m(cr) and deltasubH(o)m values it was possible to derive deltafH(o)m(C2H3O2Cl, g)=-(427.55 +/- 1.04) kJ x mol(-1), deltafH(o)m (C2H3O2Br, g)=-(383.48 +/- 3.14) kJ x mol(-1), and deltafH(o)m(C2H3O2I, g)=-(328.97 +/- 1.84) kJ x mol(-1). These data, taken with a published value of the enthalpy of formation of acetic acid, and the enthalpy of formation of the carboxymethyl radical, deltafH(o)m(CH2COOH, g)=-(238 +/- 2) kJ x mol(-1), obtained from density functional theory calculations, led to DHo(H-CH2COOH)=(412.8 +/- 3.2) kJ x mol(-1), DHo(Cl-CH2COOH)=(310.9 +/- 2.2) kJ x mol(-1), DHo(Br-CH2COOH)=(257.4 +/- 3.7) kJ x mol(-1), and DHo(I-CH2COOH)=(197.8 +/- 2.7) kJ x mol(-1). A discussion of the C-X bonding energetics in XCH2COOH, CH3X, C2H5X, C2H3X, and C6H5X (X=H, Cl, Br, I) compounds is presented.

Journal Article↗

PubMed2001

Biologically and chemically optimized composites of carbonated apatite and polyglycolide as bone substitution materials.

We report on the development and characterization of a new composite material consisting of amorphous carbonated apatite, Ca(5)(PO(4), CO(3))(3)(OH), and microstructured poly(hydroxyacetic acid), polyglycolide (PGA). This material is able to keep the pH of a surrounding solution within the physiological range (7.2-7.6). This was achieved by chemical fine-tuning of the counterplay between the acidic degradation of the polyester and the basic dissolution of calcium phosphate. Microporous samples with pore sizes of <1 microm and compact samples were prepared. The biological behavior was assayed in vitro by long-term osteoblast culture. Morphological and biochemical analyses of cell differentiation revealed excellent biocompatibility, leading to cell attachment, collagen and osteocalcin expression, and mineral deposition. This material could be of use as a biodegradable bone substitution material and as a scaffold for tissue engineering.

Animals↗

PubMed2001

Simulating arterial wall calcification in vitro: biomimetic crystallization of calcium phosphates under controlled conditions.

OBJECTIVES: A method to simulate the biological and pathological crystallization of calcium phosphate in vitro is presented. BACKGROUND: The pathological crystallization of calcium phosphates during atherosclerosis is still poorly understood as it depends on a variety of external factors, e.g., the presence of biological molecules that act as crystallization promoters or inhibitors. METHODS: A computer-controlled double-diffusion device is presented that permits crystallization under constant external conditions (constant pH, constant concentrations of Ca2+ and PO4(3-)). RESULTS: The crystallization of hydroxyapatite occurs in a well-defined way. The presence of additives (cholesterol, magnesium) distinctively alters the morphology of the crystals. CONCLUSIONS: The simulation of pathological crystallization as in atherosclerosis is possible if the external conditions are kept strictly constant during the experiment. In order to obtain a meaningful insight into biological crystallization, this approach is essential as otherwise the external conditions change continuously during the experiment. The effect of additives can be conveniently studied.

Arteriosclerosis↗

PubMed2001

How much interdisciplinarity is required to understand vascular calcifications? Formulation of four basic principles of vascular calcification.

Four potential basic mechanisms of arterial wall calcification were identified: 1) loss of inhibitory action on crystallization of biological macromolecules, 2) nucleation of calcium phosphate precipitation by dead cells and/or their membranes, 3) autocatalytic nucleation of cholesterol by antibodies against cholesterol crystals, and 4) formation of bone-like structures in advanced atherosclerotic lesions. The relevance and interplay of these mechanisms has not yet been clarified. Their elucidation will require a concerted effort of natural scientists and medical specialists.

Animals↗

PubMed2001

Solid-state chemical methods to investigate the nature of calcified deposits.

Basics and application of three solid-state chemical techniques are presented that can be used to study calcified deposits, e.g., in atherosclerotic lesions: thermogravimetry (TG; giving the mineral content), X-ray diffractometry (XRD; identifying the mineral phase and giving its crystallinity), and X-ray absorption spectroscopy (EXAFS; allowing one to identify amorphous phases that do not show up in X-ray diffractometry).

Absorptiometry, Photon↗

PubMed2001

[Alternative bone replacement substances for preoperative design of individual CAD/CAM skull implants].

BACKGROUND: The preoperative manufacturing of individual skull implants using computer aided design (CAD) and computer aided manufacturing (CAM) is based on the use of titanium, although the use of other materials is also potentially possible. THE USE OF OTHER MATERIALS: The use of poly-(D,L-lactide) (PDLLA) as an implant material was investigated using an adult, formalin fixed sheep's head with a complex frontolateral defect. A standard individual titanium implant as well as a resection template made of aluminium were milled in order to allow bone resection and reconstruction within one operation. A mould was made of Teflon for the fabrication of the PDLLA implant using carbon dioxide at high pressure. This procedure allowed a critical comparison to be made of both implant materials and showed that the production of a biodegradable PDLLA implant is possible. At present the titanium implant is superior to the PDLLA implant, as PDLLA settled with slightly larger dimensions than the mould, although the structure itself was exact. DISCUSSION: The goal of the present research is the fabrication of a functionally graded material made of polylactide, polyglycolide, calcium phosphate and osteoinductive proteins using existing technology, which will meet all of the requirements for stability, resorption kinetics, biocompatibility, radiotranslucence and osteogenic potency of an ideal implant material.

Bone Substitutes↗

PubMed2000

Calcium carbonate modifications in the mineralized shell of the freshwater snail Biomphalaria glabrata.

The mineralized shell (consisting of calcium carbonate) of the tropical freshwater snail Biomphalaria glabrata was investigated with high resolution synchrotron X-ray powder diffractometry and X-ray absorption spectroscopy (EXAFS). Parts from different locations of the snail shell were taken from animals of different age grown under various keeping conditions. Additionally, eggs with ages of 60, 72, 120, and 140 hours were examined. Traces of aragonite were found as first crystalline phase in 120 h old eggs, however, Ca K-edge EXAFS indicated the presence of aragonitic structures already in the X-ray amorphous sample of 72 h age. The main component of the shell of adult animals was aragonite in all cases, but in some cases minor amounts of vaterite (below 1.5%) are formed. The content of vaterite is generally low in the oldest part of the shell (the center) and increases towards the mineralizing zone (the shell margin). In juvenile snails, almost no vaterite was detectable in any part of the shell.

Aging↗