Biomedical subjects

Frank A Müller

Publications and source records attributed to Frank A Müller.

6 recordsLinked to original sources

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

Preparation of SBF with different HCO3- content and its influence on the composition of biomimetic apatites.

The bioactivity of bone and dental implant materials is usually tested in vitro using simulated body fluid (SBF). The composition of common SBF differs from that of blood plasma in that it has a higher Cl- and a lower HCO3- concentration, which affects the composition of in vitro formed bone-like apatite. Five different SBFs with a composition of 142 Na+, 5 K+, 2.5 Ca2+, 1 Mg2+, 1SO4(2-), 1HPO4(2-), and 136 (Cl-+HCO3-) mmol/l were prepared with HCO3- concentrations ranging from 5 to 27 mmol/l. The SBF solutions were prepared by mixing stable concentrated solutions, which increase the reproducibility of in vitro tests due to negligible changes of pH during preparation. The high stability of thus prepared SBF enables the evaluation of hydroxyapatite formation on the surface of bioactive materials without the negative effect of spontaneous precipitation. Furthermore, the use of concentrated solutions offers a facile way to prepare SBF with different ionic contents and thus modify the composition of Ca-P layers precipitated on the surface of the bioactive materials exposed to the SBF solutions. The SBF solutions were shown to be supersaturated with respect to slightly carbonated apatite. The Fourier transform infrared (FT-IR), Raman and X-ray analyses of the precipitated layers indicate that the HCO3- content in SBF influences the composition and structure of the calcium phosphates obtained. It can be supposed that as long as the HCO3- concentration in the testing solutions is lower than 20 mmol/l, only B-type HCA precipitates. At higher HCO3- concentrations, it can be assumed that A-type HCA forms as well considering FT-IR, Raman and X-ray measurements.

Anions↗

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↗

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↗

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↗