Biomedical subjects

H Worch

Publications and source records attributed to H Worch.

9 recordsLinked to original sources

PubMed2007

Surface modification of titanium-based alloys with bioactive molecules using electrochemically fixed nucleic acids.

A new method of surface modification for titanium (alloys) with bioactive molecules was developed with the intention of providing a new basis of implant adaptation for particular requirements of certain medical indications. Nucleic acid single strands are fixed electrochemically via their termini (regiospecifically) by growing an oxide layer on Ti6Al7Nb anodically. It could be shown that they are accessible to subsequent hybridization with complementary strands at physiological pH. Amount of nucleic acids immobilized and hybridized were determined radioanalytically using 32P-labelled nucleic acids. Stable fixation was attained at and above potentials of 4 V(SCE). Up to 4 pmol/cm2 of nucleic acid single strands could be immobilized and hybridization efficiencies up to 1.0 were reached. Hybridization efficiency was found to depend on surface density of immobilized oligonucleotides, while hybridization rates increased when MgCl2 was added. A conjugate consisting of an oligonucleotide complementary to the immobilized strand and the hexapeptide GRGDSP with RGD as an integrin recognition site was synthesized. This conjugate was able to bind to integrins on osteoblasts. It was shown that this conjugate binds to the anchor strand fixed on Ti6Al7Nb to an extent comparable with the unconjugated complementary strand.

Animals↗

PubMed2004

Comparison of microfocus- and synchrotron X-ray tomography for the analysis of osteointegration around Ti6Al4V implants.

Micro-computed tomography (microCT) provides quantitative three-dimensional information of bone around titanium implants similar to classical histology. The study, based on an animal model, containing cuboid-shaped biofunctionalised Ti6Al4V implants with surrounding bone after 4 weeks, is performed using 3 microCT-systems with X-ray tubes, one synchrotron-radiation-based microCT-system (SRmicroCT), and classical histology. Although the spatial resolution of the microCT-systems is comparable, only the results of SRmicroCT agree with results of classical histology. The X-ray tube sources give rise to huge artefacts in the tomograms (interface scattering, beam hardening), which impaired the quantitative analysis of bone up to about 200microm from the implant surface. Due to the non-destructive character of microCT the specimens can be subsequently examined by classical histology without restriction. The quantitative comparison of bone formation uncovers the strong dependence of the newly formed bone from the selected slice. This implies the necessity of 3D analysis. SRmicroCT and classical histology prove that surface modifications of the titanium implant significantly influence the bone formation. Using SRmicroCT, the preparation artefacts due to cutting and polishing are excluded.

Animals↗

PubMed2003

Electrochemically assisted deposition of thin calcium phosphate coatings at near-physiological pH and temperature.

An electrochemical method for the deposition of calcium phosphate phases on titanium surfaces using the galvanostatic mode is presented. Deposition was performed in a (Ca(2+) / H(x)PO(4) ((3-x)-))-containing electrolyte near physiological conditions with regard to pH (6.4) and temperature (36 degrees C). Cathodic alkalization leads first to the formation of a thin homogeneous layer that shows a nanoscale surface topography of alternating wall-like elevations and channels. It is thought that these channels in the calcium phosphate prelayer are formed as pathways for hydroxyl ions and hydrogen. Upon this layer, spheres of amorphous calcium phosphate (ACP) are formed as indicated by Fourier transform infrared spectroscopy (FTIR) and transmission electron microscopy. According to transmission electron microscopy images, these spheres consist of small clusters of calcium phosphate (approximately 30 nm) and can grow up to 300 nm in diameter. Characteristic for this ACP is a high water content as seen by FTIR. As a function of current density, the ACP is then transformed into crystalline hydroxyapatite (HAP), which was identified using FTIR and X-ray diffraction. The morphology of the HAP crystals can be described as needles with dimensions of <500-nm length and <60-nm width. By choice of different electrochemical parameters, a homogeneous coating of either ACP, HAP, or the intermediate phase can be achieved, as shown in a kinetic phase diagram, thus allowing the formation of coatings with different properties in solubility and morphology.

Alloys↗

PubMed2003

Transforming growth factor beta1 immobilized adsorptively on Ti6Al4V and collagen type I coated Ti6Al4V maintains its biological activity.

Titanium and titanium alloys are often used for orthopedic and dental implants. Osseointegration of Ti6Al4V may be improved not only by precoating of the surface with extracellular matrix proteins like collagen type I but also by additional immobilization of growth factors. In the present study, transforming growth factor beta1 (TGF-beta1) which is known as an inducer of collagen synthesis was immobilized adsorptively on uncoated and collagen type I coated Ti6Al4V surfaces. TGF-beta1 was found immobilized slightly faster to collagen type I coated than to uncoated Ti6Al4V and released slower from the collagen coated material. Immobilized TGF-beta1 is biologically active for at least 3 weeks storage at 4 degrees C. Sterilization by ethylene oxide inactivates immobilized TGF-beta1. In osteoblasts cultured on implants with adsorptively immobilized TGF-beta1, mRNA level and specific catalytic activity of alkaline phosphatase as well as accumulation of calcium and phosphate were found reduced, whereas procollagen alpha1(I) mRNA level and the rate of collagen synthesis were increased.

Adsorption↗

PubMed2002

Proliferation and differentiation of rat calvarial osteoblasts on type I collagen-coated titanium alloy.

Several attempts have been made to improve osseointegration of titanium alloy as an implant material by modification of its surface. In the present study, proliferation, differentiation, and mineralization of osteoblasts on type I collagen-coated Ti6Al4V were investigated. The activity of alkaline phosphatase and the accumulation of calcium by osteoblasts grown on titanium alloy were significantly higher compared to cells grown on polystyrene. Precoating of the implant surface with type I collagen did not extensively affect proliferation, the activity of alkaline phosphatase, collagen synthesis, calcium accumulation, or the mRNA levels for collagen I alpha1, osteopontin, osteocalcin, MMP-2, and TIMP-2. Maximum collagen synthesis by osteoblasts was observed at day 4 of culture independent of the type of implant material. The specific activity of alkaline phosphatase reached its maximum at day 18 of culture. Accumulation of calcium and elevated mRNA levels for osteocalcin were found at day 22. These results indicate that collagen-coating alone is not sufficient to accelerate differentiation of rat calvarial osteoblasts on Ti6Al4V.

Alloys↗

PubMed2002

Electrochemical behavior of titanium-based materials - are there relations to biocompatibility?

For biomedical applications the physico-chemical properties of oxide layers, always present in titanium-based materials, are of special interest because the biological system is in direct contact only with these oxides. Using electrochemical impedance spectroscopy and galvanostatic polarization it is shown that the different compositions of c.p.-titanium, Ti6Al4V, and Ti6Al7Nb result in different physico-chemical properties of air formed passive layers and anodic oxide layers. This may have a direct impact on the biocompatibility of these materials. Results of impedance spectroscopy distinctly differ in the flatband potentials as well as in the donor densities of air-formed passive layers with Ti6Al7Nb showing an approximately 50% smaller donor density than the other materials. Anodic galvanostatic polarization results in voltage-charge density curves with distinct differences in the Faraday efficiency epsilon of the oxide formation between Ti6Al7Nb and c.p.-titanium/Ti6Al4V, especially for low current densities. These effects correlate strongly with the donor densities in the air formed passive films of the examined materials. SEM-images of anodic oxide layers show a blister containing surface morphology of the outer part of the oxide layers for all materials. This morphology is probably caused by oxygen evolution, a process which relies on the transfer of electrons through the growing anodic oxide layers and strongly depends on the donor density in the air formed passive layers. Again, the much more pronounced morphology on c.p. titanium/Ti6Al4V agrees with the different donor densities in the air formed passive layers on the materials. These findings correlate with the good biocompatibility of Ti6Al7Nb and suggest that conduction mechanisms, in air formed passive layers and anodic oxide layers, contribute to processes that determine the biocompatibility of these materials.

Journal Article↗

PubMed2001

Titanium powder sintering for preparation of a porous functionally graded material destined for orthopaedic implants.

This work focuses on basic research into a P/M processed, porous-surfaced and functionally graded material (FGM) destined for a permanent skeletal replacement implant with improved structural compatibility. Based on a perpendicular gradient in porosity the Young's modulus of the material is adapted to the elastic properties of bone in order to prevent stress shielding effects and to provide better long-term performance of the implant-bone system. Using coarse Ti particle fractions the sintering process was accelerated by silicon-assisted liquid-phase sintering (LPS) resulting in a substantial improvement of the neck geometry. A novel evaluation for the strength of the sinter contacts was proposed. The Young's modulus of uniform non-graded stacks ranged from 5 to 80 GPa as determined by ultrasound velocity measurements. Thus, the typical range for cortical bone (10-29 GPa) was covered. The magnitude of the Poisson's ratio proved to be distinctly dependent on the porosity. Specimens with porosity gradients were successfully fabricated and characterized using quantitative description of the microstructural geometry and acoustic microscopy.

Journal Article↗

PubMed2000

Collagen type I-coating of Ti6Al4V promotes adhesion of osteoblasts.

The initial contact of osteoblasts with implant surfaces is an important event for osseointegration of implants. Osseointegration of Ti6Al4V may be improved by precoating of its surface with collagen type I. In this study, the adhesion of rat calvarial osteoblasts to uncoated and collagen type I-coated titanium alloy was investigated over a period of 24 h. Collagen type I-coating accelerates initial adhesion of osteoblasts in the presence of fetal calf serum. One hour after plating, no differences in the percentage of adherent cells between the surfaces investigated were found. Adhesion of osteoblasts to uncoated surfaces was reduced by the GRGDSP peptide by about 70%, whereas adhesion to collagen type I-coated surfaces remained unaffected by treatment of the cells with the peptide. Cell adhesion to coated materials was reduced by about 80% by anti-integrin beta1 antibody. The integrin beta1 antibody did not influence the adhesion to uncoated titanium alloy. The results suggest that osteoblasts adhere to collagen type I-coated materials via integrin beta1 but not by interacting with RGD peptides, whereas adhesion to uncoated titanium alloy is mediated by RGD sequences but not via integrin beta1. Fibronectin does not seem to be involved in the adhesion of osteoblasts to either coated or uncoated titanium alloy.

Adsorption↗

PubMedDate not supplied

Biomimetic coatings functionalized with adhesion peptides for dental implants.

A complete biological integration into the surrounding tissues (bone, gingiva) is a critical step for clinical success of a dental implant. In this work biomimetic coatings consisting either of collagen type I (for the gingiva region) and hydroxyapatite (HAP) or mineralized collagen (for the bone interface) have been developed as suitable surfaces regarding the interfaces. Additionally, using these biomimetic coatings as a matrix, adhesion peptides were bound to further increase the specificity of titanium implant surfaces. To enhance cell attachment in the gingiva region, a linear adhesion peptide developed from a laminin sequence (TWYKIAFQRNRK) was bound to collagen, whereas for the bone interface, a cyclic RGD peptide was bound to HAP and mineralized collagen using adequate anchor systems. The biological potential of these coatings deduced from cell attachment experiments with HaCaT human keratinocytes and MC3T3-E1 mouse osteoblasts showed the best results for collagen and laminin sequence coating for the gingiva region and mineralized collagen and RGD peptide coatings for regions with bone contact. Our concept opens promising approaches to improve the biological integration of dental implants.

Journal Article↗