Biomimetic implant coatings.

Biomaterials and tissue engineering technologies are becoming increasingly important in biomedical practice, particularly as the population ages. Cellular responses depend on topographical properties of the biomaterial at the nanometer scale. Structures on biomaterial surfaces are used as powerful tools to influence or even control interactions between implants and the biological system [; ]. The influence of nanometer sized surface structures on osteoblastlike cell interactions was tested with niobium oxide coatings on polished titanium slices (cp-Ti grade 2). The aim of the study was to investigate the influence of nanoscopic surface structures on osteoblast interactions in order to support collagen I production and cell adhesion. The coatings were done by means of the sol-gel process. The surface structure was adjusted by annealing of the metaloxide ceramic coatings due to temperature depended crystal growth. The applied annealing temperatures were 450, 550 and 700 degrees C for 1 h, corresponding to Ra-numbers of 7, 15 and 40 nm. The surfaces were characterized by means of AFM, DTA/TG, diffractometry and white light interferometry. The cell reactions were investigated concerning adhesion kinetics, migration, spreading, cell adhesion, and collagen I synthesis. The smooth surface (Ra=7 nm) resulted in the fastest cell anchorage and cell migration. The closest cell adhesion was reached with the surface structure of Ra=15 nm. The roughest surface (Ra=40 nm) impedes the cell migration as well as a proper spreading of the cells. The best results concerning cell adhesion and spreading was reached with an intermediate surface roughness of Ra=15 nm of the niobium oxide coating on cp-titanium slices.

Nanostructured niobium oxide coatings influence osteoblast adhesion.

The interaction of osteoblasts was correlated to the roughness of nanosized surface structures of Nb(2)O(5) coatings on polished CP titanium grade 2. Nb(2)O(5) sol-gel coatings were selected as a model surface to study the interaction of osteoblasts with nanosized surface structures. The surface roughness was quantified by determination of the average surface finish (Ra number) by means of atomic force microscopy. Surface topographies with Ra = 7, 15, and 40 nm were adjusted by means of the annealing process parameters (time and temperature) within a sol-gel coating procedure. The observed osteoblast migration was fastest on smooth surfaces with Ra = 7 nm. The adhesion strength, spreading area, and collagen-I synthesis showed the best results on an intermediate roughness of Ra = 15 nm. The surface roughness of Ra = 40 nm was rather peaked and reduced the speed of cell reactions belonging to the adhesion process.

[Corrosion behaviour, metal release and biocompatibility of implant materials coated by TiO2-sol gel chemistry]. / Einfluss einer TiO2-beschichtung auf Biokompatibilität, Korrosions- und Auslaugverhalten verschiedener Implantatlegierungen.

Alloys based on titanium or cobalt have been used as implant materials for decades with good success. Because of their natural oxide layer these alloys reveal good corrosion behaviour. In contact with physiological solution metal release takes place, which can cause inflammation. Coatings can improve the corrosion behaviour. In this study Ti6Al4V and Co28Cr6Mo alloys, which are frequently used as implant materials, were tested. Polished discs of these alloys and polished discs, which were coated with TiO2-layers by sol-gel chemistry, were compared regarding their corrosion behaviour and metal ion releasing. The releasing of Al, V, Ti, Co, Cr and Mo was quantified by ICP-MS analysis. The TiO2-coating reduced the release of all ions except of the Al-ion. Both alloys showed a deviating kinetic of ion releasing. In addition, cell response (cell vitality, cell proliferation, endothelial marker CD31 and actin allocation) of osteoblasts and endothelial cells were investigated.

Biocompatible Nb2O5 thin films prepared by means of the sol-gel process.

Thin biocompatible oxide films with an optimised composition and structure on the surface of titanium and its alloys can improve the implant integration. The preparation of these thin oxide layers with the intended improvement of the surface properties can be realised by means of the sol-gel process. Nb2O5 is a promising coating material for this application because of its extremely high corrosion resistance and thermodynamic stability. In this study, thin Nb2O5 layers ( < 200 nm) were prepared by spin coating of polished discs of cp-titanium with a sol consisting of a mixture of niobium ethoxide, butanol and acetylacetone. The thickness, phase composition, corrosion resistance and the wettability of the oxide layers were determined after an optimisation of the processing parameters for deposition of oxide without any organic impurities. The purity of the oxide layer is an important aspect in order to avoid a negative response to the cell adhesion. The biocompatibility of the oxide layers which was investigated by in vitro tests (morphology, proliferation rate, WST-1, cell spreading) is improved as compared to uncoated and TiO2 sol-gel coated cp-titanium concerning the spreading of cells, collagen I synthesis and wettability.

Biocompatibility of beta-stabilizing elements of titanium alloys.

In comparison to the presently used alpha + beta titanium alloys for biomedical applications, beta-titanium alloys have many advantageous mechanical properties, such as an improved wear resistance, a high elasticity and an excellent cold and hot formability. This will promote their future increased application as materials for orthopaedic joint replacements. Not all elements with beta-stabilizing properties in titanium alloys are suitable for biomaterial applications-corrosion and wear processes cause a release of these alloying elements to the surrounding tissue. In this investigation, the biocompability of alloying elements for beta- and near beta-titanium alloys was tested in order to estimate their suitability for biomaterial components. Titanium (grade 2) and the implant steel X2CrNiMo18153 (AISI 316 L) were tested as reference materials. The investigation included the corrosion properties of the elements, proliferation, mitochondrial activity, cell morphology and the size of MC3T3-E1 cells and GM7373 cells after 7 days incubation in direct contact with polished slices of the metals. The statistical significance was considered by Weir-test and Lord-test (alpha = 0.05). The biocompatibility range of the investigated metals is (decreasing biocompatibility): niobium-tantalum, titanium, zirconium-aluminium-316 L-molybdenum.

[High incidence of total hip arthroplasty aseptic loosening with ion-coated titanium femoral heads]. / Fréquence élevée des descellements prothétiques aseptiques après utilisation d'un couple titane implanté-polyéthylène.

PURPOSE OF THE STUDY: The purpose of this study was to determine the frequency of aseptic loosening among a series of total hip arthroplasties evaluated at 84 months and to search for the cause. Two types of acetabular cups had been implanted. It was hypothesized that the ion coating of the titanium head could be involved in the deterioration of titanium/polyethylene implants. MATERIAL AND METHODS: Two non-cemented acetabular cups differing only by the presence or not of a hypoxyapatite coating were studied. Different types of femoral heads (stainless steal, chromium-cobalt, alumina, zincrona, nitrurated titanium, ion-coated titanium) and femoral stems (with or without cement) were implanted. Sixty-two ion-coated titanium heads were implanted and 47 patients with 52 heads were reviewed. Clinical outcome was assessed with the Postel-Merle-d'Aubigné score and the Livermoore method was used for radiological assessment of the bone-implant interface and polyethylene wear. The physico-chemical properties of one titanium head explanted after aseptic loosening were also studied. RESULTS: At 84 months follow-up, the mean clinical score was 15.8/18 points. Mean polyethylene wear was 0.18 mm/year. There were 13 revisions for aseptic loosening: two bipolar, nine acetabular and two femoral. Mean wear for the explanted implants was 0.34 mm/year. Metallosis was observed in eight cases. Arthroplasties with the same types of femoral stem and acetabular implants but with other types of heads (stainless steal, chromium-cobalt, alumina, zincrona, nitrurated titanium) led to only one case of aseptic loosening among 118 implantations. Electron microscopy demonstrated the presence of scratch lines, disappearance of the nitrogen ion layer, decreased hardness, and increased roughness of the titanium head. DISCUSSION: The poor friction properties of titanium are well known. To improve performance, ion coating has been proposed. This technique consists in projecting nitrogen ions onto the surface of the head to form a surface coating measuring about one micron. The high incidence of aseptic loosening, polyethylene wear, metallosis, and modifications of the head surface (disappearance of the nitrogen ion layer, scratch marks, etc.) suggest ion-coated titanium heads could be the cause of these aseptic loosenings. CONCLUSION: Ion-coating has not provided good protection of the titanium head. Patients with this type of head should be followed carefully in order to detect aseptic loosening or metallosis early.

Autologous osteoblasts enhance osseointegration of porous titanium implants.

The goal of this study was to assess the osseointegration of porous titanium implants by means of coating with autologous osteoblasts. Titanium implants (8 x 5 x 4 mm) having drill channels with diameters of 400, 500, and 600 microm were coated with autologous osteoblasts obtained from spongiosa chips. The implants were inserted into the distal femora of 17 adult Chinchilla Bastard rabbits (group I). Uncoated implants were inserted as controls in the contralateral femur (group II). The animals were sacrificed after 5, 11, and 42 days. Intravital fluorochrome labeling and microradiography were used for the assessment of bone ingrowth into the titanium channels. In both groups, no bone tissue was formed in the channels up to day 5. On day 11, group I exhibited significantly more (p<0.05) bone tissue (19.8+/-14.0% vs. 5.8+/-9.1%) with greater bone-implant contact (13.3+/-15.1% vs. 5.7+/-5.3%, p<0.05) at the channel mouths than group II. Bone tissue was formed mainly between day 15 and 30 in group I, in group II between day 25 and 40. Six weeks after implantation, bone tissue filled on an average 68.8+/-15.1% of the mouths of the drill channels in implants in group I, the filling for group II was 49.8+/-18.1% (p<0.05). The average bone-implant contact at the channel mouths after six weeks was 56.5+/-13.5% in group I, 40.2+/-21.9% in group II (p<0.05). 600-microm channels showed at this time point the best osseous integration (p<0.05). Coating with autologous osteoblasts accelerates and enhances the osseointegration of titanium implants and could be a successful biotechnology for future clinical applications.

Evaluation of the haemocompatibility of titanium based biomaterials.

The increased use of metallic biomaterials in contact with blood e.g. for the application as coronary stents leads to the development of new biomaterials. The main requirements for stents are high flexibility, high cold deformability and sufficient mechanical strength (static and dynamic), which can be obtained by strain hardening, radio-opacity and haemocompatibility. In order to investigate the properties of the metallic biomaterials in contact with blood, a comparison of the haemocompatibility of newly developed materials with established materials has been performed. To evaluate haemocompatibility without the influence of the geometry of the material, spherical powders produced by rotating electrode process (REP) were used in a dynamic test system with full human blood under two different stress conditions. The high shear stress simulates the arterial and the low shear stress simulates the venous situation. The use of a dimensionless score point (SP) system where the parameters of the haemocompatibility are determined with and without a material exposition allows an objective comparison of the materials used.

Electrochemical and cytocompatibility assessment of NiTiNOL memory shape alloy for orthodontic use.

Orthodontic arcs and wires are mostly realised from alloys and constitute the motor of dental shifting. Ti-base alloys rapidly replaced the formerly used stainless steel wires due to their excellent corrosion resistance, their high mechanical characteristics and their increased biocompatibility. NiTiNOL shape memory alloys add to these advantages their ability of deforming force. NiTiNOL, highly pure Nickel (hp-Ni) and commercially pure titanium (cp-Ti) were tested by electrochemical assays in artificial saliva and in vitro biological tests with L132 cells and HEPM cells. All tests gave concordant results: the electrochemical assays, the proliferation test, the colony forming method, and the inflammatory test clearly show, that nickel is a corrosive and a cytotoxic material. Ti and NiTiNOL are cytocompatible and in particular corrosion resistant. No significant differences are observed for both materials on the electrochemical and the biological level as well. The NiTiNOL shape memory alloy is a master trump for dental practitioners to repair occlusal defects by shifting teeth under optimal biological conditions. In spite of its high Ni-content, it is biocompatible. It considerably reduces the tune of therapeutic treatment, facilitate the occlusal concept and leads to a result of high clinical quality.

Cell orientation and cytoskeleton organisation on ground titanium surfaces.

A stable connection between the biomaterial surface and the surrounding tissue is one of the most important prerequisites for the long-term success of implants. Therefore, a strong adhesion of the cells on the biomaterial surface is required. Beside the surface composition the surface topography influences the properties of the adherent cells. The quality of the connection between the cell and the biomaterial is-among other factors-determined by the dimensions of the surface topography. Osteoblasts and fibroblast-like cells in contact with a ground biomaterial surface spread in the direction of the surface structures. These aligned cells provide a more favourable adhesion behaviour than a spherically shaped cell. To determine the influence of the surface structure on the cell alignment and cytoskeleton organisation or arrangement, substrate discs of cp-titanium were ground, producing different roughness of the substrates. The oriented cells had a higher density of focal contacts when they were in contact with the edges of the grooves and showed a better organisation of the cytoskeleton and stronger actin fibres. These changes of the aligned cells depend on the peak to valley height of the surface structures.

Interactions between cells and titanium surfaces.

The interaction between cells and implant materials is determined by the surface structure and/or surface composition of the material. In the past years, titanium and titanium alloys have proved their superiority over other implant materials in many clinical applications. This predominant behaviour is caused by a dense passive oxide layer which forms within milliseconds in oxidizing media. Titanium dioxide layers of 100 nm thickness were produced on the surface of cp-titanium grade 2, and on an experimental alloy of high vanadium content (Ti1.5Al25V) as a harmful control. The layers were produced by thermal and anodic oxidation and by coating by means of the sol-gel process. The resulting oxide layers were characterized with respect of their structure and chemical composition. In cell tests (proliferation, MTT, morphology, actin staining), the reaction of the cells was examined. It was shown that the sol-gel-produced titanium oxide layer is able to shield the cells from toxic alloying elements, with the result that the cell reaction is influenced only by the thin titanium oxide surface layer and not by the composition of the bulk material.

Migration, matrix production and lamellar bone formation of human osteoblast-like cells in porous titanium implants.

The goal of this study was to characterize growth, mineralization and bone formation of osteoblast-like cells in titanium pore channels of defined diameter. Titanium implants with continuous drill channels of diameters of 300, 400, 500, 600 and 1,000 microm were inserted into human osteoblast-like cell cultures. The ingrowth of the cells into the drill channels was investigated by transmitted-light microscopy and scanning electron microscopy. Immunofluorescence and histological analysis of 15-channel sections of each diameter were used to investigate the growth behavior and the matrix protein patterns. Mineralization was evidenced by Alizarin red staining and high-resolution microradiography. The ingrowth of human osteoblast-like cells in the drill channels occurred in a sequence of four characteristic stages. In stage 1, osteoblast precursor cells adhered to the wall of the channel and migrated three-dimensionally into the channel by forming foot-like protoplasmic processes. For all 15 sample drill channels that were investigated, the cell ingrowth over 20 days amounted on average to 793 microm (+/- 179) into 600-microm-diameter channels, where they migrated significantly faster than in all the other channels. In stage 2, approximately on day 5-7, the osteoblast-like cells began to anchor on the substrate wall by matrix proteins and to build up a dense network of matrix proteins in the drill channel. The mineralization of the extracellular matrix, while depending on cell stimulation, was initiated in stage 3, on average after 4 weeks. In drill channels of a diameter of 1,000 microm the cell growth was incomplete and no mineralization was found by radiological assessment. Starting in week 6, in the drill channels of diameters ranging from 300 to 600 microm, the network of extracellular matrix proteins and osteoblast-like cells began to form an osteon-like structure. Neither the highly developed migration behavior of osteoblastic cells nor the reorganization from a fiber-like matrix to a lamellar structure have so far been described for cell cultures.

Preparation of TiO(2) layers on cp-Ti and Ti6Al4V by thermal and anodic oxidation and by sol-gel coating techniques and their characterization.

The excellent biocompatibility of titanium and its alloys used, for example, for medical devices, is associated with the properties of their surface oxide. For a better understanding of the tissue reaction in contact with the oxide layer, knowledge of the chemical and physical properties of this layer is of increasing interest. In this study, titania films were produced on cp-Ti and Ti6Al4V substrates by thermal oxidation, anodic oxidation, and by the sol-gel process. The thickness and structure of the films produced under different conditions were determined by ellipsometry, infrared spectroscopy, and X-ray diffraction measurements. The corrosion properties of these layers were investigated by current density-potential curves under physiological conditions. The oxide layers produced on cp-Ti and Ti6Al4V by thermal oxidation consist of TiO(2) in the rutile structure. For the anodized samples the structure of TiO(2) is a mixture of amorphous phase and anatase. The structure of the coatings produced by the sol-gel process for a constant annealing time depends on the annealing temperature, and with increasing temperature successively amorphous, anatase, and rutile structure is observed. Compared to the uncoated, polished substrate with a natural oxide layer, the corrosion resistance of cp-Ti and Ti6Al4V is increased for the samples with an oxide layer thickness of about 100 nm, independent of the oxidation procedure.

[Malignant fibrous histiocytoma of bone 20 years after femoral fracture treated by plate-screw fixation: analysis of corrosion products and their role in malignancy]. / Histiocytofibrome malin de l'os 20 ans après ostéosynthèse par lame-plaque d'une fracture du fémur : analyse des produits de corrosion et de leur rôle dans la malignité

We report a case of malignant fibrous histiocytoma of the bone that developed 20 years after a femoral fracture treated by plate-screw fixation. Similar cases reported over the past fifteen years in the literature suggest the possible mechanisms of sarcomatous degeneration. The possible carcinogenic effect of corrosion products is emphasized. Dispersion energy spectrometry of intracellular particles on the periphery and at the center of the tumor demonstrated the presence of chromium, iron and nickel at different concentrations. The association with other elements clearly demonstrates that the corrosion products were metabolized. The presence of metallic components in tumoral cells suggests a possible relationship between metallic implants and malignancy. These observations emphasize the importance of creating a national, or even international, registry of malignant tumors that develop in contact with metallic implants in order to search for a possible cause and effect relationship.

[The in vitro biological behavior of TiNb30 alloy treated with hydroxyapatite and tricalcium phosphates]. / Le comportement biologique in vitro d'un alliage TiNb30 traité avec hydroxyapatite et phosphates tricalciques.

An in vitro study has been carried out in different cell systems to determine the biological response of TiNb30 alloy before and after a surface treatment with hydroxyapatite (HA) and tricalcium phosphate (TCP) by the sol-gel method. TiNb30 pure Ti induce favorable cell viability with respect to pure Ni showing a high cytotoxic effect. After surface treatment with HA or HA-TCP mixtures, no difference in cell proliferation can be observed between amorphous and cristalline forms. However, HA decreases (75 +/- 15%) and HA-TCP mixtures increase (133 +/- 11%) significantly cell proliferation compared with controls.

[The electrochemical behavior of TiTa30 and TiNb30 alloys for implantology]. / Etude du comportement électrochimique des alliages TiTa30 et TiNb30 pour l'implantologie.

The electrochemical behavior in artificial saliva of TiNb30 and TiTa30 alloys were compared with that of commercial pure titanium. The anodic potential, the current density, the passivation potential and the galvanic corrosion vs. Au were determined. Both alloys have a similar behavior to that of pure titanium. Crevace corrosion, which is very weak in pure Ti, is completely inhibited by the addition of Nb or Ta.

Influence of the surface structure of titanium materials on the adhesion of fibroblasts.

Of utmost importance for the successful use of an implant is a good adhesion of the surrounding tissue to the biomaterial. In addition to the surface composition of the implant, the surface topography also influences the properties of the adherent cells. The aim of this investigation was thus to study the influence of the surface structure of the substrate on the formation of focal contacts and on the orientation of cultivated gingival fibroblasts by means of fluorescence microscopy. A further goal was to determine the effect of the material composition on the cell shape, on the assumption that in each case a lengthening of the cells can be expected to provide a more favourable adhesion behaviour than a spherical cell shape. In order to describe the shape of the cell, a shape factor was defined which was calculated from the area covered by the cells and from their circumference. To determine the influence of the surface structure, substrate platelets of cp-titanium, TiAl6V4 and TiTa30 were ground. Onto these specimens human gingival fibroblasts of the 5th to 7th passages were cultivated. After a culture time of two days the cells were fixed and stained. The number of orientated cells was determined as a function of the surface roughness of the substrate. The number of orientated cells was shown to increase---independent of the material---with increasing roughness of the ground substrate. On a polished surface the number of orientated cells was 11% (average peak-to-valley height 0.04 microns); at a peak-to-valley height of 1.36 microns the number of orientated cells increased to 72%. It could be observed that the orientated cells had a higher density of focal contacts where they were in contact with the edges of the grinding grooves. In order to determine the effect of the surface composition, gingival fibroblasts were cultured for 14 d on polished substrate specimens of cp-titanium, TiAl6V4 and TiTa30 and examined for differences in shape. The cells grown on cp-titanium and on TiTa30 had shape factors of 1.76 and 1.58 respectively, whereas those grown on TiAl6V4 had a shape factor of 0.93. The unfavourable spherical shape of the fibroblasts (resulting in a poor adhesion) grown on TiAl6V4 after a culture period of 14 d may be the result of a locally increased vanadium concentration in the substrate, with an accompanying increase in the release of toxic vanadium ions.

Development of a titanium alloy suitable for an optimized coating with hydroxyapatite.

By means of the metallurgical method of alloying, the thermal expansion coefficient of commercially pure titanium was adapted to that of hydroxyapatite (HA) in order to produce a tailored composite material with a maximum adhesion strength of HA to the metallic material. The alloying element chosen was manganese, which is an important trace element in the human organism. With the alloy TiMn6 a good compromise concerning the expansion coefficient, the mechanical properties and the biocompatible behaviour was found. With this alloy coatings with an extremely high adhesion strength could be produced, especially when the sol-gel process was used for HA precipitation. In addition, these layers fulfil the requirements of favourable thin coatings according to theoretical considerations.

Development and functionality of isoelastic dental implants of titanium alloys.

Two types of isoelastic endosseous dental implants were produced and their functionality was tested. One type consisted of a porous sintered TiTa30 alloy, the other had a special surface structure consisting of titanium wire loops. Their mechanical properties were optimized by the production parameter (sintering and diffusion bonding, respectively). The functionality was tested after insertion into an artificial jaw which had properties corresponding to the natural mandibular. The elastic properties of both implants were similar to the properties of the bone. In addition the implants have a safe anchorage bone ingrowth. In animal experiments using the implant with surface loops it was observed that the bone entered the loops and even extremely small surface cavities in the wire loops.

Contribution to the functional surface structure of endosseous implants.

An endosseous implant that should allow osseointegration as well as fixation by connective tissue has been developed. A special surface structure consisting of titanium wire loops on a titanium implant was produced by diffusion bonding. The mechanical properties of this implant are investigated.