Modell zur Analyse des knöchernen Anwachsverhaltens auf bioaktiv beschichteten Implantatoberflächen

Model to analyse the bone on‐growth on bioactive coated implant surfaces Especially on the field of bone regeneration, transient and permanent implants are an important method of therapy in the Orthopaedic Surgery. In this context, bioactive surfaces on metallic implants provide an improved contact to the surrounding bone. The goal of our study was to establish an in‐vitro test system to evaluate the on‐growth of bone‐derived cells on different surface coatings. Therefore, we invented a special kind of clamps made of commercially‐pure (c‐p) titanium and blasted with hydroxyapatite particles followed by electrochemically coating with calcium phosphate (BONIT®‐HA, BONIT®). Definite pieces of human cancellous bone were attached to these clamps, inserted onto tissue culture plates and cultivated in DMEM for ten days. Finally, the contact area between human cancellous bone and the implant surface was analyzed and the spreading of osteoblast‐like cells evaluated by scanning electron microscopy (SEM). A well‐spread morphology of bone cells was observed on the implant surfaces coated with calcium phosphate (CaP). In comparison the clamps without CaP coatings showed only a marginal growth of bone cells on the clamp surface. The presented newly in‐vitro test setup using titanium clamps coated with bioactive layers attached to human cancellous bone represents a well‐functioning model for qualitative evaluation of bone on‐growth.     

Influence of nickel ions on human multipotent mesenchymal stromal cells (hMSCs)

Nickel‐Titanium‐Shape‐Memory‐Alloys (NiTi‐SMA) are of biomedical interest due to an unusual range of pure elastic deformability (superelasticity) and the shape memory effect which allows this material to return to a predictable previously memorized shape after external changes in temperature. HMSCs (human multipotent mesenchymal stromal cells) are currently the most promising cell type for regenerative medicine and tissue engineering, due to the ability to differentiate into several tissues such as bone, tendon, cartilage or muscle. For tissue engineering newly developed porous NiTi‐SMA materials are evaluated preloaded with hMSCs. For biocompatibility testing the high nickel content (50 %at) of NiTi‐SMA plays a critical role. To analyse the influence of Ni‐ions on hMSCs viability and activation, cells were cultured with or without NiCl₂ for 24h and 7days. Cells were either seeded in media containing NiCl₂ or the NiCl₂ was later added to already adherent cells. Cell metabolism, proliferation and viability were analysed by alamarBlue^TM assay or fluorescence microscopy. Cytokine (IL‐6, 8, 11) release from hMSCs was determined by ELISA . NiCl₂ concentrations below 25 μg/ ml were well tolerated by the cells. A significant decrease in cell proliferation occurred at threshold values of 200 μg/ ml (24 h) and 25 μg/ ml (7 d). There was a significant, dose dependent increase in the release of IL‐8 from hMSCs cultured in the presence of sub toxic NiCl₂ concentrations. The present study demonstrates for the first time that high but non‐toxic concentrations of Ni²⁺ are capable to activate hMSCs. Thus high Ni²⁺ concentrations apart from allergen‐ or particle‐induced inflammation, may lead to tissue inflammation in the vicinity of a NiTi‐SMA implant in vivo and subsequently to implant failure e.g. due to implant loosening.     

On the electropolishing of NiTi braided stents – challenges and solutions

Nickel Titanium (NiTi) alloys possess special mechanical properties and good biocompatibility hence used as base material for the production of vascular stents. Normally, vascular stents are machined from NiTi tubes, using laser cutting processes. Braiding is a promising alternative for the machining of certain NiTi stents. However, a surface finish treatment, such as electropolishing of the braided stents, is still required in order to achieve a medical‐grade surface finish. The thermally‐grown oxide resulting from the shape‐setting heat treatment, following the braiding must be removed. Moreover, electropolishing is required to achieve optimum corrosion resistance. Therefore, the aim of this study is to find suitable parameters for the effective electropolishing of NiTi textile stents. Electropolishing of a device with such a complex geometry is challenging, hence a custom‐designed electrolytic cell was constructed and used in this study. We examined the stent surfaces before and after electropolishing, using scanning electron microscopy (SEM) and confocal laser scanning microscopy (CLSM). Potentiodynamic tests were performed in NaCl 0.9% solution for as‐received and electropolished samples. The results from the present study indicate an improvement in surface quality of the braided stents after electropolishing. Potentiodynamic tests revealed that electropolishing improves the corrosion resistance of the NiTi stents.     

Deposition of TiN coatings on shape memory NiTi alloy by plasma immersion ion implantation and deposition

An investigation has been carried out to study the effect of pulse negative bias voltage on the morphology, microstructure, mechanical, adhesive and tribological properties of TiN coatings deposited on NiTi substrate by plasma immersion ion implantation and deposition. The surface morphologies were relatively smooth and uniform with lower root mean square values for the samples deposited at 15 kV and 20 kV negative bias voltages. X-ray diffraction results demonstrated that the pulse negative bias voltage can significantly change the microstructure of TiN coatings. The intensity of TiN(220) peak increased with the increase of negative bias voltage in the range of 5-20 kV. When the negative bias voltage increased to 30 kV, the preferred orientation was TiN(200). Nanoindentation test indicates that hardness and elastic modulus increased with the increase of the negative bias voltage (5 kV, 15 kV and 20 kV), and then dropped sharply at 30 kV. The adhesion between the TiN and NiTi alloy and tribological properties of TiN coated NiTi alloy depend strongly on the bias voltage parameter; the sample deposited at 20 kV possesses good adhesion strength and excellent tribological property.     

Improving the biocompatibility of NiTi alloy by chemical treatments: An in vitro evaluation in 3T3 human fibroblast cell

The nearly equi-atomic nickel titanium alloy was coated with calcium phosphates by socking the chemically treated alloy in simulated body fluid in order to prepare bioactive NiTi implants. The biocompatibility of the calcium phosphates coated NiTi alloy was investigated by in vitro 3T3 human embryonic fibroblast cell culture tests. The cells attachment and morphologies were studied using phase contrast light microscope and environmental scanning electron microscope. The mechanically polished and the calcium phosphates coated NiTi samples were well tolerated by the cells, whereas, the controlled pure Ni samples exhibited strong toxicity to the cells. Furthermore, the calcium phosphates coated NiTi samples showed good osteoconductivity.     

Characteristics and in vitro biological assessment of (Ti, O, N)/Ti composite coating formed on NiTi shape memory alloy

In this investigation, plasma immersion ion implantation and deposition (PIIID) was used to fabricate a (Ti, O, N)/Ti coating on NiTi shape memory alloy (SMA) to improve its long-term biocompatibility and wear resistance. The surface morphology, composition and roughness of uncoated and coated NiTi SMA samples were examined. Energy dispersive X-ray elemental mapping of cross-sections of (Ti, O, N)/Ti coated NiTi SMA revealed that Ni was depleted from the surface of coated samples. No Ni was detected by X-ray photoelectron spectroscopy on the surface of coated samples. Furthermore, three-point bending tests showed that the composite coating could undergo large deformation without cracking or delamination. After 1 day cell culture, SaOS-2 cells on coated samples spread better than those on uncoated NiTi SMA samples. The proliferation of SaOS-2 cells on coated samples was significantly higher at day 3 and day 7 of cell culture.     

Tissue-engineered endothelial cell layers on surface-modified Ti for inhibiting in vitro platelet adhesion

Abstract

A tissue-engineered endothelial layer was prepared by culturing endothelial cells on a fibroblast growth factor-2 (FGF-2)–l-ascorbic acid phosphate magnesium salt n-hydrate (AsMg)–apatite (Ap) coated titanium plate. The FGF-2–AsMg–Ap coated Ti plate was prepared by immersing a Ti plate in supersaturated calcium phosphate solutions supplemented with FGF-2 and AsMg. The FGF-2–AsMg–Ap layer on the Ti plate accelerated proliferation of human umbilical vein endothelial cells (HUVECs), and showed slightly higher, but not statistically significant, nitric oxide release from HUVECs than on as-prepared Ti. The endothelial layer maintained proper function of the endothelial cells and markedly inhibited in vitro platelet adhesion. The tissue-engineered endothelial layer formed on the FGF-2–AsMg–Ap layer is promising for ameliorating platelet activation and thrombus formation on cardiovascular implants.     

不同等离子源形成的DLC涂层对NiTi合金腐蚀行为的影响

采用等离子浸没离子注入和沉积(PIIID)法分别以C2H2和石墨为等离子源在NiTi合金表面形成DLC涂层来提高该合金的耐腐蚀性.利用Raman光谱和扫描电镜分析膜层结构.利用电化学测试和原子吸收光谱测试涂层前后基体的耐腐蚀性和Ni离子析出.结果表明:采用等离子浸没离子注入和沉积法以乙炔和石墨为等离子源在NiTi合金表面形成均匀致密、结合力良好的DLC涂层.两种涂层都明显地提高了NiTi合金的耐腐蚀性能和有效地抑制了Ni离子的溶出.     

High‐Temperature Corrosion of NiTi‐Shape‐Memory Alloys

Semi‐finished products and components made of NiTi‐shape‐memory alloys (NiTi‐SMA) are often subjected to heat treatment after their fabrication. During this heat treatment, oxide layers begin to form which contain a high amount of titanium. In this investigation special attention was drawn to the selective oxidation of Ti because a TiO_X‐layer can represent a Ni‐barrier and may therefore be of special use for medical applications. A comparison of the following three samples was carried out: A sample oxidised at room temperature, another that was heat‐treated in ambient air (600 °C/1min) and a third sample that was subjected to a heat treatment (600 °C/1min) in an atmosphere that oxidises titanium but reduces NiO in order to achieve a selective oxidation of the titanium. The analysis of the oxide layers was carried out by means of x‐ray photoelectron spectroscopy (XPS). It was shown that the ratio of titanium to nickel in the oxide layer can be substantially increased when performing the annealing treatments in a partial reducing atmosphere. Furthermore, a thermo‐gravimetric investigation of the material was carried out at 600 °C in dry air in order to estimate the growth of the oxide layers.     

磷酸钙涂覆炭织物体外细胞毒性的评价

医用植人体的成功与否常常取决于器件植入后细胞与材料表面间的相互作用.采用生物体外测试法考察了声电化学法制备的磷酸钙涂层对炭织物的骨细胞附着、增殖能力的影响.借助MTS检测技术、扫描电子显微镜,选择人类成骨细胞(MG63)作为细胞模型,通过测定细胞与炭织物、磷酸钙涂覆炭织物、以及其各自的提取液作用后的存活能力,研究了细胞/材料的相互作用,并对基底材料的细胞毒性进行了评价.结果表明,炭织物、磷酸钙涂覆炭织物均不具有细胞毒性,且磷酸钙涂层可提高成骨细胞的附着和增殖.SEM图像显示,细胞形貌正常,与对照组相比较生长增殖情况相似.     

PM‐Composites with Nickel‐Titanium Shape Memory Alloys

Starting from NiTi‐powders, composites of nickel‐titanium shape memory alloys (NiTi‐SMA) and different stainless steels as well as of different NiTi‐SMAs were produced by using the process of hot isostatic pressing (HIP). Metallographic investigations focussed on the interface between NiTi‐SMA and stainless steel with special emphasis placed on the characterization of the typical structure of the diffusion zones in both components.     

Synthesis,Characterization and Bioactivity Evaluation of Porous Barium Titanate with Nanostructured Hydroxyapatite Coating for Biomedical Application

Nano phase hydroxyapatite (HA) bioceramics have gained importance in the biomedical field due to their superior biological properties. In this study, nanostructured HA coating was used to increase the bioactivity of a piezoelectric bioceramic, barium titanate (BT). Early reports on the influence of collagen piezoelectricity in remodeling of bone have attracted many researchers to piezoelectric bioceramics such as BT. Hence; porous BT was used as the matrix of a new bone graft composite and then coated with nanostructured HA. BT ceramic was foamed via a direct foaming method with a spray of polyurethane foam. The surface of the foam voids was coated with HA via sol–gel and dip‐coating methods. X‐ray diffraction (XRD), transmission electron microscopy (TEM), and scanning electron microscopy (SEM) techniques were used to characterize the prepared coated foam. XRD and TEM analysis showed that the HA coating had a nanostructure with crystallite size of 20–30 nm. SEM images of the prepared samples showed that the HA coating has about 25 µm thickness. The bioactivity of the prepared composite was evaluated in an in vitro study. The variation of Ca²⁺ and PO₄^3? ions versus time in simulated body fluid (SBF) solution were measured by inductively coupled plasma (ICP) analysis during 1 month and the results showed that the mineralization of calcium phosphate (Ca‐P) on HA coated porous samples was much more than that in non‐coated sample. The SEM micrographs and energy‐dispersive X‐ray spectroscopy (EDS or EDX) analysis of the samples after 1 month of immersing in SBF confirm that Ca‐P phase (bone‐like apatite) was significantly mineralized on HA coated porous BT samples. It was concluded that the nanostructured HA coating would improve the bioactivity of BT foam.     

Novel sol-gel derived calcium phosphate coatings on Mg4Y alloy

Calcium phosphates (CaPs) and silicon containing calcium phosphates (Si-CaPs) coatings on a biodegradable magnesium yttrium alloy (Mg4Y) were prepared by a sol-gel technique to improve the bioactivity of the alloy surface. The experimental results show that thick porous coatings comprised of nano-sized calcium phosphate particles can be prepared by heating the as dip coated substrates at 450 °C. The in vitro degradation results show that the coatings do not alter the degradation kinetics of the substrates significantly and the release of magnesium and yttrium ions at initial time points was very similar for both the coated and bare substrates. The cyto-compatibility studies using MC3T3-E1 osteoblasts show that the coated substrates were more bioactive than the uncoated substrates as the cells begin to grow and form a matrix on the coated substrates more easily than on the bare metal. These preliminary results collectively show the potential of use of sol-gel derived calcium phosphate coatings on magnesium based degradable scaffolds to improve their surface bioactivity.     

Dextran‐based coating system for the immobilization of cell adhesion promoting molecules on titanium surfaces

Immobilization of adhesive peptides interacting with cellular integrin receptors onto metallic implant surfaces represents a promising approach to improve osseointegration of implants into the surrounding tissue. In the present study, a functional dextran‐based coating system consisting of an amino titanate adhesion promoter with dendritic structure and a carboxymethyl dextran was established to bind an RGD‐containing adhesive peptide via a selective coupling methodology onto titanium surfaces. The three‐step reaction procedure was characterized by X‐ray photoelectron spectroscopy. In cell adhesion experiments it could be demonstrated that dextran coatings containing immobilized RGD promote attachment and spreading of fibroblast and pre‐osteoblastic cells compared to native as well as CMD‐coated titanium surfaces without RGD. The direct attachment of the RGD sequence to the metal surface via the amino titanate adhesion promoter did not increase pre‐osteoblastic cell spreading, whereas coupling of RGD to the polymeric carboxy­methyl dextran layer slightly enhanced spreading of the cells.     

PIIID-formed (Ti,O)/Ti, (Ti,N)/Ti and (Ti,O, N)/Ti coatings on NiTi shape memory alloy for medical applications

(Ti, O)/Ti, (Ti, N)/Ti and (Ti, O, N)/Ti composite coatings were fabricated on NiTi shape memory alloy via plasma immersion ion implantation and deposition (PIIID). Surface morphology of samples was investigated using atomic force microscopy (AFM) and scanning electron microscopy (SEM). Cross-sectional morphology indicated that the PIIID-formed coatings were dense and uniform. X-ray diffraction (XRD) was used to characterize the phase composition of samples. X-ray photoelectron spectroscopy (XPS) results showed that the surface of coated NiTi SMA samples was Ni-free. Nanoindentation measurements and pin-on-disc tests were carried out to evaluate mechanical properties and wear resistance of coated NiTi SMA, respectively. For the in vitro biological assessment of the composite coatings in terms of cell morphology and cell viability, osteoblast-like SaOS-2 cells and breast cancer MCF-7 cells were cultured on NiTi SMA samples, respectively. SaOS-2 cells attached and spread better on coated NiTi SMA. Viability of MCF-7 cells showed that the PIIID-formed composite coatings were noncytotoxic and coated samples were more biocompatible than uncoated samples.     

The effect of grain orientation on the tensile‐compressive asymmetry of polycrystalline NiTi shape memory alloy

The purpose of the present study is to thoroughly understand the influence of crystallographic texture on the stress‐strain asymmetric behavior of polycrystalline NiTi shape memory alloy under tension and compression. To do this, a 3D thermo‐mechanical model has been implemented in a finite element program and textured and untextured polycrystalline NiTi have been considered. In our polycrystalline finite element model, each element represents one grain and a set of crystal orientations which approximate the initial crystallographic texture of the NiTi are assigned to the elements. From the calculated results, it is found that the crystallographic texture is the important reason for the tension‐compression asymmetry. For the textured polycrystal, the tension‐compression asymmetry can be observed clearly, but for the polycrystal containing randomly oriented grains, the stress‐strain curves show low levers of asymmetry between tensile and compressive loading, and the evolutions of martensite volume fractions are similar under two stress states.     

Biocompatibility study of plasma-coated nitinol (NiTi alloy) stents

The authors aimed to assess the surface modification effects of plasma coatings on biocompatibility of nitinol intravascular stent in terms of anticoagulation, haemocytolysis rate, hydrophilicity, cytotoxicity and so on. In order to improve their surface adhesive properties to endothelial cells, NiTi alloy intravascular stents were treated and coated using a low-temperature plasma deposition technique. It was found that plasma coating changed the surface morphology of the stents to a micron-level surface roughness in the range of 1-5 microm. In comparison with the untreated control, the plasma-treated NiTi alloy intravascular stents showed increased surface hydrophilicity and enhanced anticoagulation property. Testing results on plasma-coated NiTi stents indicated that they complied with the standard of national biologic safety evaluation of medical apparatus and instrument (GB/T16886-1997, People's Republic of China) in terms of haemocytolysis rate, cytotoxicity and pyretogen.     

Controlled release of gentamicin from biomimetic calcium phosphate in vitro. Comparison of four different incorporation methods

Cylinders of biomimetic (nanocrystalline) calcium phosphate were loaded with gentamicin by four different methods: 1) dip‐coating, 2) impregnation followed by cold‐isostatic pressing, 3) co‐precipitation followed by cold‐isostatic pressing, and 4) coating of co‐precipitated particles with a biodegradable polymer PDLLA (poly‐D,L‐lactide), followed by uniaxial pressing. The release kinetics were studied in vitro over 10 days. The incorporation by methods 2), 3) and 4) showed a significantly higher long‐term release of active gentamicin than dip‐coating, although there was an initial burst during the first two days with all four methods. With method 4), there was an increase of the released gentamicin after 7 days, and the long‐term release was the highest of these four methods. The results are of considerable interest for the preparation of biodegradable bone implants which are loaded with biologically active substances.     

In vivo histological evaluation of bioactive NiTi alloy after two years implantation

This work is aimed at evaluating the in vivo histological performance of HA coated NiTi through chemical treatments and the untreated NiTi after two years implantation by animal model. A complete implant–bone interfacial osseointegration was observed after HA coated and untreated NiTi was implanted into the animal model for two years. However, the osseous lamella structure on HA coated NiTi was more mature and the osseous tissue was more compact as compared with that of untreated NiTi, which was ascribed to the differences resulted from nickel ion release from the alloy, cell adhesion ability and osteogenesis mechanism during the early stage of implantation. The bioactivity and biocompatibility of NiTi alloy are significantly improved by coating the alloy with HA through chemical treatment, though the untreated NiTi shows good biocompatibility after long time implantation.