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Biomedical subjects

Peter Greil

Publications and source records attributed to Peter Greil.

13 recordsLinked to original sources
PubMed2006

Hydroxyapatite growth on anodic TiO2 nanotubes.

In the present work, we study the growth of hydroxyapatite formation on different TiO(2) nanotube layers. The nanotube layers were fabricated by electrochemical anodization of titanium in fluoride-containing electrolytes. To study various nanotube lengths, layers with an individual tube diameter of 100 nm were grown to a thickness of approximately 2 mum or 500 nm. The ability to form apatite on the nanotube layers was examined by immersion tests combined with SEM, XRD and FT-IR investigations. For reference, experiments were also carried out on compact anodic TiO(2) layers. The results clearly show that the presence of the nanotubes on a titanium surface enhances the apatite formation and that the 2-mum thick nanotube layer triggers deposition faster than the thinner layers. Tubes annealed to anatase, or a mixture of anatase and rutile are clearly more efficient in promoting apatite formation than the tubes in their "as-formed" amorphous state.

Coated Materials, Biocompatible↗
PubMed2006

Cellulose-based scaffold materials for cartilage tissue engineering.

Non-woven cellulose II fabrics were used as scaffolds for in vitro cartilage tissue engineering. The scaffolds were activated in a saturated Ca(OH)(2) solution and subsequently coated with a calcium phosphate layer precipitated from a supersaturated physiological solution. Chondrocyte cell response and cartilage development were investigated. The cell adherence was significantly improved compared to untreated cellulose fabrics, and the proliferation and vitality of the adhered chondrocytes were excellent, indicating the biocompatibility of these materials. A homogeneous distribution of the seeded cells was possible and the development of cartilageous tissue could be proved. In contact with a physiological chondrocyte solution, calcium is expected to be leached out from the precipitated layer, which might lead to a microenvironment that triggers the development of cartilage in a way similar to cartilage repair in the vicinity of subchondral bone.

Animals↗
PubMed2006

Transfer of metallic debris after dislocation of ceramic femoral heads in hip prostheses.

INTRODUCTION: Main reasons for the early revision of total hip arthroplasties are aseptic loosening as a result of wear debris caused by polyethylene particles, and postoperative dislocations. In revision arthroplasty of the hip metallic deposits were frequently found on femoral heads after dislocation or repositioning in total hip arthroplasties with metal back acetabular components. MATERIALS AND METHODS: In this study we examined ceramic femoral heads from alumina-on-alumina and alumina-on-polymer pairings, respectively. All the heads resulted from revision of total hip replacement with a titanium containing acetabular component and showed metallic deposit on their surface. The metallic deposit was characterized by environmental scanning electron microscopy, energy dispersive X-ray spectroscopy and laser scanning microscopy. RESULTS: The metallic deposits covered areas between 5 mm(2) and 8 cm(2) and reached a maximum height of 30 mum. They were shown to consist of titanium, and thus resulted from contact between the femoral head and the posterior part of the metal back. In case of twofold dislocated alumina-on-alumina pairings the titanium deposits showed different roughness profiles, whereas no differences were detectable for alumina-on-polymer pairings. CONCLUSION: From the obtained results it can be concluded, that titanium deposited onto a femoral head during dislocation will be abraded within the harder alumina-on-alumina bearing couple during normal gait and will subsequently be released into the body by synovial fluid. In case of a ceramic-on-polymer bearing the deposited metal seems to be more harmful. The increased surface roughness of the femoral head within the tribological pairing probably initiates damage of the polymeric acetabular inlay and increases the wear of the bearing surface through a third-body wear mechanism resulting in the release of high amounts of PE.

Adult↗
PubMed2006

Engineering of vascularized transplantable bone tissues: induction of axial vascularization in an osteoconductive matrix using an arteriovenous loop.

INTRODUCTION: Vascularization remains an obstacle to engineering of larger volume bone tissues. Our aim was to induce axial vascularization in a processed bovine cancellous bone (PBCB) matrix using an arteriovenous (AV) loop (artery, vein graft, and vein). METHODS: Custom-made PBCB discs (9 x 5 mm) were implanted into rats. In group A (n = 19), the matrices were inserted into microsurgically constructed AV loops between the femoral vessels using a vein graft from the contralateral side. In group B (n = 19), there was no vascular carrier. The matrices were encased in isolation chambers. After 2, 4, and 8 weeks, the animals were perfused with India ink via the abdominal aorta. Matrices were explanted and subjected to histological and morphometric analysis. Results were compared with intravital dynamic micro & magnetic resonance imaging and scanning electron microscopy images of vascular corrosion replicas. RESULTS: In group A, significant vascularization of the matrix had occurred by the 8th week. At this time, vascular remodeling with organization into vessels of different sizes was evident. Blood vessels originated from all 3 zones of the AV loop. Group A was significantly superior to group B in terms of vascular density and vascularization kinetics. DISCUSSION: This study demonstrates for the first time successful vascularization of solid porous matrices by means of an AV loop. Injection of osteogenic cells into axially prevascularized matrices may eventually create functional bioartificial bone tissues for reconstruction of large defects.

Animals↗
PubMed2005

Photoluminescence of annealed biomimetic apatites.

Biomimetic apatite coatings are widely used in orthopaedic applications to provide bioinert material surfaces with bioactive behaviour by means of initiating bone growth at the implant surface. In this study we manufactured biomimetic calcium phosphate coatings consisting of a calcium deficient carbonated apatite by immersing activated titanium platelets into simulated body fluid. The development of the crystal phases was monitored by X-ray diffractometry in addition to Fourier-transform infrared spectroscopy. The microstructure of the biomimetic apatites and phase composition was analysed using scanning and transmission electron microscopy as well as attached energy dispersive X-ray spectrometry. The samples were annealed in air yielding in an inherent luminescence of the biomimetic apatite up to temperatures of 600 degrees C. The photo-induced emission spectra were recorded in the range from 400 to 750 nm at excitation wavelengths ranging 310-450 nm. A blue (437 nm) and a green (561 nm) emission were found between 200 and 600 degrees C visually appearing white. Photoluminescence of annealed biomimetic apatites might be of interest for histological probing and monitoring of bone re-modelling. The results are discussed in terms of chemical and crystallographic changes in the calcium phosphate layer during heat treatment.

Apatites↗
PubMed2004

Toughening of dental glass ionomer cements with reactive glass fibres.

A fibre reinforced glass ionomer cement (FRGIC) for dental applications was loaded with 20 vol% short fibres (430 microm) with a glass composition in the system SiO(2)-Al(2)O(3)-CaF(2)-Na(3)AlF(6). The fracture toughness and the total energy release rate were examined. A 20% anisotropic fibre alignment was observed, perpendicular to the loading direction. An increase of fracture toughness of 140% and of total energy release rate of 440% was achieved compared to the unreinforced glass ionomer cement. Matrix-fibre interface reaction is supposed to exert the major influence on mechanical behaviour of FRGIC by controlling fibre pull-out and thus the total energy release rate.

Anisotropy↗
PubMed2003

Application of the method of images on electrostatic phenomena in aqueous Al2O3 and ZrO2 suspensions.

A new solution for the Poisson equation for the diffuse part of the double layer around spherical particles will be presented. The numerical results are compared with the solution of the well-known DLVO theory. The range of the diffuse layer differs considerably in the two theories. Also, the inconsistent representation of the surface and diffuse layer charge in the DLVO theory do not occur in the new theory. Experimental zeta potential measurements were used to determine the charge of colloidal Al2O3 and ZrO2 particles. It is shown that the calculated charge can be interpreted as a superposition of independent H+ and OH- adsorption isotherms. The corresponding Langmuir adsorption isotherms are taken to model the zeta potential dependence on pH. In the vicinity of the isoelectric point the model fits well with the experimental data, but at higher ion concentrations considerable deviations occur. The deviations are discussed. Furthermore, the numerical results for the run of the potential in the diffuse part of the double layer were used to determine the electrostatic interaction potential between the particles in correlation with the zeta potential measurements. The corresponding total interaction potentials, including the van der Waals attraction, were taken to calculate the coagulation half-life for a suspension with a particle loading of 2 vol%. It is shown that stability against coagulation is maintained for Al2O3 particles in the pH region between 3.3 and 7 and for ZrO2 only around pH 5. Stability against flocculation can be achieved in the pH regime between 4.5 and 7 for Al2O3, while the examined ZrO2 particles are not stable against flocculation in aqueous suspensions.

Journal Article↗
PubMed2003

Reactive fibre reinforced glass ionomer cements.

The mechanical properties of glass ionomer cements used in restorative dentistry reinforced by chopped glass fibres were investigated. Reactive glass fibres with a composition in the system SiO(2)-Al(2)O(3)-CaF(2)-Na(3)AlF(6) and a thickness of 26 microm were drawn by a bushing process. The manufacturing parameters were optimized with respect to maximum strength of the glass fibre reinforced ionomer cements. Powder to liquid ratio, pre-treatment of the glass, grain size distribution and fibre volume fraction were varied. Glass fibre and cement were characterized by X-ray diffraction, transmission electron microscopy and energy dispersive spectroscopy techniques, respectively. The highest flexural strength of the reinforced cement (15.6 MPa) was found by compounding 20 vol% reactive fibres and extending the initial dry gelation period up to 30 min. Microscopic examination of the fractured cements indicated a distinct reactive layer at the fibre surface. A pronounced fibre pull out mode gives rise to an additional work-of-fracture contributed by pulling the fibres out of the fracture surface.

Compressive Strength↗
PubMed2002

Lifetime prediction of CAD/CAM dental ceramics.

The dynamic fatigue method was used to obtain subcritical crack growth parameters n and A for a commercial feldspathic dental porcelain and for a lanthanum-glass-infiltrated alumina glass ceramic. Five stress rates d sigma/dt ranging from 50 to 0.01 MPa s(-1) were applied. The inert strength values were calculated with the use of Weibull statistics and maximum-likelihood approaches for the Weibull parameter m. Strength-probability-time (SPT) diagrams were derived for both materials. The alumina glass composite showed a high fracture strength sigma(0) (442 MPa) at a failure probability of P(F) = 63.2% and a high resistance against subcritical crack growth (n = 36.5). The development of strength under fatigue conditions was calculated for exemplary 1 year. The strength of the alumina glass material dropped to 228 MPa within this period. This fact is due to a low content of infiltrated lanthanum glass phase in the composite material (25 wt%). In contrast, for the high-silica-glass-containing porcelain a distinct decrease of strength sigma(0) from initial 133 to 47 MPa after 1 year was predicted. This, mainly because of a low crack growth resistance (n = 16.8) of the feldspathic porcelain. Much lower strength values were calculated, assuming a failure probability of P(F) = 5%. The decrease is mainly caused by the sensitivity of high-glass-containing ceramics against water corrosion.

Aluminum Oxide↗
PubMed2002

Hydroxyapatite formation on alkali-treated titanium with different content of Na+ in the surface layer.

Titanium can form a bone-like apatite layer on its surface in SBF when it is treated in NaOH. When pre-treated titanium is exposed to SBF, the alkali ions are released from the surface into the surrounding fluid. The Na+ ions increase the degree of supersaturation of the soaking solution with respect to apatite by increasing pH. On the other hand, the released Na+ cause an increase in external alkalinity that triggers an inflammatory response and leads to cell death. Therefore, it would be beneficial to decrease the release of Na+ into the surrounding tissue. The purpose of this study was to evaluate the hydroxyapatite formation on alkali-treated titanium with different content of Na+ in the surface layer. Using SEM, gravimetric analysis and measurement of calcium and phosphate concentration, it was found that the rate of apatite formation was not significantly influenced by a lower amount of Na+ in the surface layer. Titanium with the lowest content of Na+ could be more suitable for implantation in the human body. The amount of alkali ions released in the surrounding tissue is lower and the rate of apatite formation is identical to titanium with the highest content of Na+ in the surface layer.

Alkalies↗
PubMed2002

Mechanical properties and in vitro cell compatibility of hydroxyapatite ceramics with graded pore structure.

In order to improve the mechanical strength of hydroxyapatite (HA) ceramics used as osteoimplants and to enhance cellular penetration functionally graded ceramics with a transition in porosity from the surface towards the centre were designed. The multilayer structures were prepared by multiple tape casting based on an aqueous HA slurry containing polybutylmethacrylate (PBMA) spheres with diameters ranging from 100 to 300 microns. After burning out the PBMA, pores of 70-200 microns were generated. The pore-graded laminates were sintered at temperatures between 1250 degrees C and 1450 degrees C. Bending strength of the pore-graded ceramics was approximately 50% higher as compared to HA of the same pore volume fraction but without gradient structure. The materials were tested in vitro for attachment and activity of osteoblast-like MC3T3-E1 cells over a period of 3 weeks. Cells formed confluent layers on the ceramic surface, penetrated into the graded porosity ranging from 100-150 microns to 250-300 microns in size and showed increasing alkaline phosphatase activity over 3 weeks. The results demonstrated initial in vitro cell compatibility of the functionally graded HA materials and their potential as osteoimplants.

3T3 Cells↗
PubMedDate not supplied

Biomimetic apatite formation on chemically treated titanium.

Titanium treated in NaOH can form hydroxycarbonated apatite (HCA) after exposition in simulated body fluid (SBF). Generally, titanium is covered with a passive oxide layer. In NaOH this passive film dissolves and an amorphous layer containing alkali ions is formed on the surface. When exposed to SBF, the alkali ions are released from the amorphous layer and hydronium ions enter into the surface layer, resulting in the formation of Ti-OH groups in the surface. The released Na(+) ions increase the degree of supersaturation of the soaking solution with respect to apatite by increasing pH, and Ti-OH groups induce apatite nucleation on the titanium surface. The acid etching of titanium in HCl under inert atmosphere was examined as a pretreatment to obtain a uniform initial titanium surface before alkali treatment. Acid etching in HCl leads to the formation of a micro-roughened surface, which remains after alkali treatment in NaOH. It was shown by SEM, gravimetric and solution analysis that the apatite nucleation was uniform and the thickness of precipitated HCA layer increased continuously with time. The treatment of titanium by acid etching in HCl and subsequently in NaOH is a suitable method for providing the metal implant with bone-bonding ability.

Apatites↗