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Biomedical subjects

R Thull

Publications and source records attributed to R Thull.

51 records · Page 3Linked to original sources
PubMed1986

Electrochemistry of after-pacing potentials on electrodes.

Predictable electrochemical behavior of electrodes in physiologic pacemakers is desirable. The after-pacing potentials play a major role in determining precise sensing and pacing performance between both chambers. Ideally, pacemaker input impedance should be high (in relation to the electrode/blood interface), whereas the potential remaining on the electrode should be as low as possible. Both of these conditions are influenced by the electrode material, structure, and design. Results of in vivo and in vitro testing show that the after-pacing potential interference is directly related to the potential decay, and these values are in general considerably shorter than the blanking periods.

Electrochemistry↗
PubMed1982

Surface processes in artificial organs. An overview.

The area of contact between an artificial organ and the biological environment results from the inner and outer surface of the organ. The lifetime of the organ determines the properties of the material's surfaces in use. Reactions occur in both directions--from the surface to the body and vice versa, from the body to the surface. Centers of nucleation and points for destruction propagation due to attacks of body fluids are irregularities of the surface structure and gradients in the chemical composition of both material and fluid. Some of the mechanisms that occur are initiated or at least promoted by mechanical factors. Some of the body-surface interactions that take place are: adsorption, degradation, corrosion, calcification, fatigue, embrittlement, and wear; these limit the lifetime of artificial organs. The strength of the interaction depends on the substituted function, the design, and the locus of implantation.

Adsorption↗
PubMed1977

The long-term stability of metallic materials for use in joint endoprostheses.

In orthopedic implants, metals are permanently incorporated into bones and tissue. Usually the metals are not in the electrochemical equilibrium state immediately after implantation. The metal oxide forms itself only after hours up to weeks. In the meantime the metal releases ions into the tissue, much more than in the equilibrium state. On the other hand a passive layer can interchange mechanically with bones and implanted components. The resulting destruction of the surface leads equally to an increasing release of ions. As a consequence of these facts, perfect metals for application in implants must have a short repassivation period and mechanically indestructible surface oxides. To what extent the applied metals perform these conditions is tested for the stainless steel type 316 L, the multiphase alloy MP-35 N and TiAIV. A comparison of the rates of corrosion resulting from damage to, or destruction of, the passivating oxide layers, with the rates that can occur in connection with local forms of corrosion, shows that in joint implants, it is merely the repassivation properties of the metals employed that determine the concentration of ions in the tissue.

Alloys↗
PubMed1977

A multichannel telemetry system for long-term in vivo evaluation of implantable materials.

Long-term in vivo measurements of the corrosion potentials of various implantable metal materials are performed using an implantable multichannel telemetry system. The data acquisition system has been designed to achieve maximum ease of operation for routine tests in animal applications. A novel signal encoding technique offers advantageous properties in connection with a commercial audio cassette tape recorder for signal storage. The flexibility of the design extends the scope of application to include not only biomaterial testing but all low frequency data transmissions in biological research.

Animals↗
PubMedDate not supplied

[Comparative studies on the applicability of a new surface conditioning system (Airsonic Mini Sandblaster) in adhesive bridging technic].

The object of this work was to investigate a new surface conditioning system for hydrolysis-stable metal-polymer bonds in dental prosthetics. The application of the adhesive SiO2-interface layer was achieved tribochemically by the use of a miniaturised sand blasting instrument (Airsonic Mini Sandblaster, Co. Hager and Werken, Duisburg, Germany) using the SiO2 coated Rocatec blasting medium. An advantage of this instrument is the possibility of decreasing costs for dentist and patient and also the time of treatment by connecting the device to the dental chair. Evaluation of applicability was based on the composition and morphology of the coatings applied to different dental alloys (titanium, NiCr, CoCr). In addition, the strength of metal-polymer bonds prior to and after physiological ageing was determined by tensile shear testing. In all cases the Airsonic Mini Sandblaster coatings proved to be equivalent to the original Rocatec system in terms of the parameters tested, such as structure and composition of the coating, and adhesivity. Irrespective of the adhesive alloy-dependent adhesive strengths in the region of 24-30 MPa were achieved; no significant decrease in strength caused by degrading of the bonds occurred. Bonding strengths are within the range reported in the literature for the Rocatec system, and are appreciably above clinically required minimum strength of 10 MPa as enamel strength. The results demonstrate the applicability of the Airsonic Mini Sandblaster in practice. By employing the procedure at the dental chair the process of silicating and subsequent silanising can be transferred from the dental laboratory to the dentist's practice. In this way, a reduction in treatment time and costs is achieved, and the reliable handling of the coating system is also improved.

Adhesiveness↗
PubMedDate not supplied

[Model for immunologic testing of biomaterials].

Corrosion products and electric fields are capable of changing proteins to antigens, thus permitting the immunological system to identify the biomaterial as foreign. The reaction between corrosion products and a macro-molecule also leads to an antigen (carrier antigen), such as conformational changes of a macro-molecule, e.g. a protein, caused by the electric field at the implant surface (modified macro-molecule antigen). While the sensitivity to corrosion and the effectiveness of galvanic elements is measurable by electrochemical methods, suitable methods of determining the field strength in the vicinity of biomaterial surfaces are still unavailable. The influence of the double layer of uncoated and coated titanium surfaces on the conformation of proteins and their conversion to antigens are investigated with polyclonal antibodies capable of identifying the unchanged protein despite adsorption to the surface. 14C-marked Bovine Serum Albumin serves as a model protein. Determination of the total number of protein molecules adsorbed is effected via the detection of the emitted electrons. The quotient of the concentration of natural proteins to the concentration of adsorbed molecules gives the biocompatibility index, which is independent of the surface area, and gives an indication of the expected biocompatibility of the material. The results of the biological tests of titanium and two coating materials on titanium were confirmed in an animal experiment. It is possible that in the future immunological tests may replace experiments in animals.

Animals↗
PubMedDate not supplied

[Reducing NMR image artefacts by using optimized materials for diagnostic aids and implants].

Differences in magnetic susceptibility, as occur for example at the boundary between implant materials and the surrounding body tissue, result in artefacts and a signal loss in magnetic resonance imaging. By using materials with a magnetic susceptibility matched to the respective environment, it is possible to minimize both artefacts and signal loss. Such materials can be made by combining two materials of different magnetic susceptibility (e.g. diamagnetic and paramagnetic materials) in such a way that the resulting material has the desired effective magnetic susceptibility.

Artifacts↗
PubMedDate not supplied

[Standardized testing of bone implant surfaces with an osteoblast cell culture system. II. Titanium surfaces of different degrees of roughness].

The effect of titanium surfaces with different degrees of roughness on osteoblast proliferation and differentiation was investigated using a standardised cell culture system. Human foetal osteoblasts (hFOB 1.19) were cultured on polished (Ti pol), sandblasted (Ti sb) and sandblasted/heat treated (Ti sb-ht) titanium surfaces for 17 days. Cell culture quality polystyrene (Ps) was used as a control. Cell number and viability were determined for assessment of proliferation. Alkaline phosphatase activity, collagen I and osteocalcin production were measured as parameters for osteoblast differentiation. In the early phase, higher proliferation values were measured on Ti pol. However, on Ti sb and Ti sb-ht higher proliferation was found in the late phase. The activity of the early differentiation marker alkaline phosphatase was higher on Ti pol. No differences were seen for the late differentiation parameters collagen I and osteocalcin. The test system permits the influence of the surface structure on the dynamics of the osteoblast development cycle to be determined. The larger surface area of rough materials leads to an initially delayed, but then prolonged cell proliferation. This model correlates with recent in vivo findings, and confirms the use of rough surfaces for implants in direct contact with bone, even at the cellular level.

Cell Differentiation↗
PubMedDate not supplied

[Standardized testing of skeletal implant surfaces with an osteoblast cell culture system. IV. Specific gene expression during differentiation].

Successful osseointegration of an implant depends on the properties of the material of which it is made. A standardized cell culture system for the assessment of the biological effect of material surfaces has already been described. In the present study, this system has been extended to include the quantitative analysis of the material-dependent osteoblast gene expression. Human foetal osteoblasts (hFOB 1.19) were cultured for 3 weeks on titanium surfaces of varying roughness, and on surfaces of chromium-cobalt-molybdenum alloy (CrCoMo). Using a real time RT-PCR technique, expressions of alkaline phosphatase, collagen 1 and osteocalcin were determined as parameters of osteoblast differentiation. In comparison with CrCoMo, differentiation was accelerated on titanium. While the smooth titanium surface leads to earlier cell growth, the rough surface induces more prolonged and stronger cell proliferation. Our results confirm at the molecular level the excellent clinical biocompatibility of titanium surfaces. The real-time RT-PCR provides a new method for the quantitative assessment of material-dependent osteoblastic differentiation.

Cell Differentiation↗