Human fibroblast reactions to standard and electropolished titanium and Ti-6Al-7Nb, and electropolished stainless steel

Stainless steel (SS), titanium (cpTi), and Ti-6Al-7Nb (TAN) are frequently used metals in orthopedic internal fracture fixation. Although reactivity to SS and cpTi are noted in reference, the soft tissue compatibility of TAN has not been comprehensively studied. This study focuses on the in vitro soft tissue compatibility of TAN in comparison to SS and cpTi using a human fibroblast model. The industrial standard surface finishes of these three materials vary considerably in view of their use in similar applications. To distinguish between material parameters of topography and chemistry, we have included electropolished (e.p) counterparts of the standard preparations of cpTi and TAN in the study (standard SS is e.p). All materials were characterized using atomic force microscopy, profilometry, and scanning electron microscopy. Our findings demonstrate that cell morphology and growth rate was similar for SS, and e.p. cpTi and TAN, with cells well spread and forming a confluent monolayer by 10 days. Cell growth on standard cpTi was similar to the electropolished samples; however, they showed a less spread morphology with more filopodia and surface ruffling present. Cell morphology on standard TAN was rounded or elongated and proliferation was inhibited at all time points, with possible cell necrosis by day 10. We found evidence of endocytosis of beta-phase particles originating from the standard TAN surface. We believe that the particle uptake coupled with the characteristic surface topography contribute to the noncytocompatibility of fibroblasts on standard TAN.     

Cell adhesion and proliferation are reduced on stainless steel coated with polysaccharide-based polymeric formulations

Hydromer's polymeric formulations F200 and F202 were evaluated after application to a synthetic substrate for effects on cell adhesion and proliferation. A significant reduction in cell adhesion was observed when cells grown on medical-grade stainless steel coated with these polymers were stained and examined under a fluorescence microscope. This reduction in cell adhesion/proliferation was confirmed when cells were isolated and analyzed by the MTS cell proliferation assay. The rate of growth of cells on F200- and F202-coated stainless steel monitored over a period of 7 days was significantly less than that observed on uncoated stainless steel, suggesting that the rate of growth of cells was reduced. The adhesion/proliferation of human umbilical vein endothelial cells (HUVEC) to coated substrates was also decreased significantly, indicating that the reduction in cell adhesion/proliferation is not restricted to only fibroblasts. Additional studies have indicated that the adhesion/proliferation of murine fibroblasts and human endothelial cells to stainless coated with a modified formulation exhibiting a high degree of lubricity was also significantly reduced. This lubricious formulation was also observed to be effective in reducing platelet adhesion, data supporting the view that lubricity also contributes to a reduction in cell and platelet adhesion. The application of these polymeric coatings on devices designed for medical implantation may not only prevent thrombus formation but may also retard the process of restenosis.     

Preparation and evaluation of polyurethane surfaces containing immobilized plasminogen

Plasminogen has been immobilized onto a segmented polyurethane containing amino groups, using glutaraldehyde as coupling agent. It was also aspecifically adsorbed, for sake of comparison, onto polyurethane films containing different functional groups and, in particular, ε-amino caproic acid and lysine residues. The differently immobilized plasminogen has been converted to plasmin by activation with urokinase, and the percentage of active plasmin obtained for the various polymer films was determined using a tripeptide (S-2251) as a synthetic substrate. The biological behaviour of the differently treated polymer films has been evaluated in vitro by measurements of partial thromboplastin time (PTT) and platelet adhesion.     

Corrosion of stainless steel surgical implants

In the light of examination of a series of failed stainless steel implants, the paper suggests that much material currently used for orthopaedic prostheses is not of a sufficiently high metallurgical quality for its purpose.     

Sol-gel hydroxyapatite coatings on stainless steel substrates.

Thin film hydroxyapatite deposits onto sandblasted 316L stainless steel substrates were prepared using water-based sol-gel technique recently developed in our lab. The coatings were annealed in air at 375 degrees C, 400 degrees C, and 500 degrees C. Phase formation, surface morphology, interfacial microstructure, and interfacial bonding strength of the coatings were investigated. Apatitic structure developed within the coatings while annealing at temperatures > or = 400 degrees C, while those heat-treated at 375 degrees C showed poor crystallinity. The coatings were dense and firmly attached to the underlying substrates, reaching an average bonding strength (as determined through the pull-out test) of 44 MPa. Nano-porous structure was found for the coatings annealed at 500 degrees C, believed to result from grain growth, and causing a slight decrease in the bonding strength. Surface microcracking, although not extensive, occurred after annealing at temperatures > or = 400 degrees C, and was linked to non-uniform thickness of the coating due to roughness of the substrate. A contraction of the coatings as a result of sintering, and phase transition from amorphous (or poor crystalline) to reasonably good crystalline apatite, may be responsible for the loss of structural integrity of the thicker sections of the coatings. It seems quite promising that a dense and adhesive apatite coating can be achieved through water-based sol gel technology after short-term annealing at around 400 degrees C in air.     

Reduction of bacterial adhesion on ion-implanted stainless steel surfaces

The high incidence of infections caused by the use of biomedical devices has a severe impact on human health. An approach to reduce the complications is to modify the surface properties of biomedical devices. In this paper, stainless steel disks were implanted with N(+), O(+) and SiF(3)(+), respectively, by an ion implantation technique. The surface properties of the ion-implanted surfaces were characterized, including their surface chemical composition, roughness, topography, wettability and surface energy. Bacterial adhesion of Staphylococcus epidermidis and Staphylococcus aureus, which frequently cause medical device-associated infections was evaluated. The experimental results showed that these implanted stainless steels, particularly SiF(3)(+) implanted stainless steel performed much better than untreated stainless steel control on reducing bacterial attachment.     

Surface characterization and platelet adhesion studies on polyurethane surface immobilized with C60.

Due to its distinctive molecular configuration, C60 and its derivatives have been the research focus in exploring its electrical, mechanical, optical, and even biological applications during the past decades. In this investigation, C60 molecules are grafted onto the polyurethane surface, which is pretreated with oxygen plasma activation, through amine-terminated silane coupling agents. ESCA analysis indicates that the C60 molecules spontaneously grafted onto the amine-terminated PU substrate through nucleophilic additions to the fullerene double bonds which fuse two six-membered rings. More amine functional groups are formed on the PU surface if 4-aminobutyldimethylmethoxysilane is used as the coupling agent. In vitro platelet adhesion assay shows the C60 grafted PU are more platelets activating than the nontreated PU control. This might be attributed to the synergistic effect of the grafted C60 molecules and the few residual amine functional groups which are left after the C60 grafting reaction. Further applications using these C60 grafted polyurethane surfaces as the cell adhesion and cell growth substrates are currently under exploration.     

Flame-sprayed alumina on stainless steel for possible prosthetic application.

Various methods of roughening type 316 stainless steel substrate surfaces for flame-spraying alumina (Al2O3) were investigated and tested for the best alumina-to-metal bond strength. Best strength values were obtained by means of roughening via anodic polarization pitting of the stainless steel. Subsequent in vitro testing indicated a severe loss in bond strength following exposure to aerated Ringer's solution. It is suggested that the utilization of flame-sprayed devices has potential in orthopedic prostheses, but precautions must be observed.     

新型医用无镍不锈钢的生物相容性评价

背景：BIOSSN4无镍不锈钢是一种奥氏体医用不锈钢材料,在中国药品生物制品检定所通过了标准的溶血实验、细胞毒性实验和致敏实验。 目的：评价新型医用BIOSSN4无镍不锈钢的体外细胞毒性及抗腐蚀性。 方法：将小鼠L929成纤维细胞悬液以1×108 L-1的浓度接种于96孔板,分5组培养,分别加入BIOSSN4无镍不锈钢浸提液、316L不锈钢浸提液、金合金浸提液、铅材料浸提液(阳性对照)及RPMI1640培养液(阴性对照)。培养1,2,3 d,观察细胞形态,采用MTT法检测各组吸光度值,计算细胞相对增殖率,评价毒性分级。在模拟口腔环境中,检测BIOSSN4无镍不锈钢、316L不锈钢及金合金的自腐蚀电位、自腐蚀电流密度及极化电阻。 结果与结论：培养3 d内,铅材料浸提液组细胞皱缩,细胞数量明显减少,细胞相对增殖率低于其余4组(P < 0.05);其余4组细胞形态良好,增殖旺盛,细胞相对增殖率均在75%以上。BIOSSN4无镍不锈钢浸提液、316L不锈钢浸提液与金合金浸提液的毒性均为1级,铅材料浸提液的毒性为2至3级,表明BIOSSN4无镍不锈钢具有良好的生物相容性。BIOSSN4无镍不锈钢的抗腐蚀性高于316L不锈钢,低于金合金。 中国组织工程研究杂志出版内容重点：生物材料;骨生物材料; 口腔生物材料; 纳米材料; 缓释材料; 材料相容性;组织工程     

316L不锈钢血管支架材料的电化学抛光工艺

用直流电化学抛光技术,研究了316L不锈钢血管支架材料电化学抛光液中各成分的作用及操作条件对抛光质量的影响。通过优化,用实验得到的工艺能很快获得光亮平整的抛光表面。     

No genotoxicity of a new nickel-free stainless steel

Stainless steel is a metallic alloy largely employed in orthopedics, maxillofacial surgery and orthodontic therapy. However, the presence in its composition of a high quantity of nickel, an agent known to trigger toxic, allergic and cancerogenous responses in humans, is cause of some concern. In this study, we have investigated the in vitro mutagenicity and genotoxicity of a new nickel-free stainless steel, namely P558, in comparison to the conventional stainless steel AISI 316L. The cytogenetic effects were evaluated by studying the frequency of Sister Chromatid Exchanges (SCE) and chromosomal aberrations. Ames test was performed to detect the mutagenic activity. Both P558 and AISI 316L did not cause any significant increase in the average number of SCE and in chromosomal aberrations, either with or without metabolic activation. Furthermore, the Ames test showed that the extracts of both P558 and of AISI 316L are not mutagenic. Overall, these findings prove that P558 is devoid of genotoxicity and mutagenicity. The present results, together with other previous interesting observations that P558 promotes osseointegration, suggest that this new nickel-free stainless steel can represent a better alternative to other conventional steel alloys.     

Effect of stainless steel corrosion products on in vitro biomineralization.

Osteoblast-like cell cultures have been used as in vitro models to study the interactions of bone tissue with biomaterials and their degradation products. This work reviews the effects of AISI 316L stainless steel (SS) corrosion products on the osteoblastic behavior of rat and human bone cell cultures. Results suggest that such products affect, in a dose-dependent manner, the proliferation and differentiation of osteoblastic cells; these effects depend on the developmental stage of the osteoblastic cells. Above certain nonlethal concentrations, SS corrosion products prevent the mineralization of the extracellular matrix, a process that reflects the complete expression of the osteoblastic phenotype.     

Preparation of hydroxyapatite-nanocrystal-coated stainless steel, and its cell interaction

Calcined nanocrystals of hydroxyapatite (HAp) having spherical or rod-shaped morphologies were coated through covalent linkage on a type 316L stainless steel substrate, which was chemically modified by the graft polymerization of gamma-methacryloxypropyl triethoxysilane (MPTS) at 70-110 degrees C. The grafting of poly(MPTS) on the substrate was confirmed by X-ray photoelectron spectroscopy (XPS) and attenuated total reflection Fourier transform infrared spectroscopy (ATR FT-IR). In order to coat the substrate with the HAp crystals through covalent linkage, the reactionbetween the alkoxysilyl groupsin the poly (MPTS) grafted on the substrate and the OH groups on the HAp crystals was conducted at 80 degrees C. The poly(MPTS)-grafted substrate was strongly coated with the HAp nanocrystals, although the HAp crystals adsorbed physically on the original substrate without poly(MPTS) grafting were removed by ultrasonic treatment. Human umbilical vein endothelial cells (HUVEC) adhered in larger numbers on the HAp-coated stainless steel substrate as compared with the original substrate after 24 h of initial incubation. The number of HUVEC adhered on the rod-shaped HAp-coated substrate was not significantly different from that on the spherical HAp-coated substrate under the present conditions.     

Preparation and characterization of polymeric coatings with combined nitric oxide release and immobilized active heparin

A new dual acting polymeric coating is described that combines nitric oxide (NO) release with surface-bound active heparin, with the aim of mimicking the nonthrombogenic properties of the endothelial cell (EC) layer that lines the inner wall of healthy blood vessels. A trilayer membrane configuration is employed to create the proposed blood compatible coating. A given polymeric substrate (e.g., the outer surface of a catheter sleeve, etc.) is first coated with a dense polymer layer, followed by a plasticized poly(vinyl chloride) (PVC) or polyurethane (PU) layer doped with a lipophilic N-diazeniumdiolate as the NO donor species. Finally, an outer aminated polymer layer is applied. Porcine heparin is then covalently linked to the outer layer via formation of amide bonds. The surface-bound heparin is shown to possess anti-coagulant activity in the range of 4.80-6.39 mIU/cm2 as determined by a chromogenic anti-Factor Xa assay. Further, the surface NO flux from the underlying polymer layer containing the diazeniumdiolate species can be controlled and maintained at various levels (from 0.5 to 60 x 10(-10) mol cm(-2)min(-1)) for at least 24 h and up to 1 week (depending on the flux level desired) by changing the chemical/polymer composition of the NO release layer. The proposed polymeric coatings are capable of functioning by two complementary anti-thrombotic mechanisms, one based on the potent anti-platelet activity of NO, and the other the result of the ability of immobilized heparin to inhibit Factor Xa and thrombin (Factor IIa). Thus, the proposed polymeric coatings are expected to exhibit greatly enhanced thromboresistivity compared to polymers that utilize either immobilized heparin or NO release alone.     

Constructing thromboresistant surface on biomedical stainless steel via layer-by-layer deposition anticoagulant

Multilayer films consisting of polyethylenimine (PEI) and heparin were successfully prepared on biomedical 316L stainless steel surface via electrostatic self-assembly (ESA) of the PEI and heparin. The process of ESA of PEI/heparin was monitored by static contact angle, electrochemical impedance spectroscopy (EIS), reflection adsorption spectroscopy and X-ray photoelectron spectroscopy data. The contact angle and EIS data revealed that the multilayer coating was stable in Tris-HCl (pH 7.35) buffer solution for 21 days. The static platelet adhesion and static clotting time experiments indicated that the PEI/heparin-deposited stainless steel could resist the platelet adhesion and prolong the static clotting time effectively. Such an easy processing and shape-independent method may have good potential for surface modification of cardiovascular devices.     

Thin films with chemically graded functionality based on fluorine polymers and stainless steel

Thin films of stainless steel and poly(tetrafluoroethylene) were co-deposited, by radiofrequency magnetron sputtering, in an inert atmosphere in order to produce a functionally graded material as a coating on a traditional biomaterial, where non-ferromagnetic characteristics and improved wettability must be ensured. These thin films are intended to modify the surface of SS316L used in stents, where the bulk/thin film couple should be regarded as a single material. This requires excellent adhesion of the coating to the substrate. All coatings were deposited with an average thickness of 500 nm. The chemical and phase characterization of the surface revealed that, with the increase in F content, the thin film evolves from a ferritic phase (alpha) to an amorphous phase with dispersion of a new crystalline ceramic phase (FeF(2)). For intermediate F content values, an austenitic (111) phase (gamma) was present. Bearing in mind the envisaged application, the best results were attained for thin films with a fluorine content between 10 and 20 at.%.     

Repassivation of a high chromium stainless steel orthopaedic alloy

The repassivation of Ortron90, a high chromium stainless steel alloy, was studied to assess the effect of passive layer removal on corrosion levels. Cathodic dissolution of the passive layer followed by potentiostatic experiments within the passive region were employed to study the repassivation process. The scratch method, carried out for comparison purposes, yielded current densities similar to those obtained by cathodic dissolution.The detailed analysis of the slopes of plots of log I/log t indicated that the repassivation did not follow any of the existing growth models. It also suggested that the slope depended on the extent of repassivation and reached a minimum when three to five monolayers of oxide were completed. The virtual potentiodynamic plots suggested the presence of some form of protective layer within 5-10 seconds and the change in open circuit potential vs time indicated that the passive layer present after 10 seconds of repassivation continued to evolve for about 1000 to 1500 seconds possibly representing a transition between two different forms such as oxide and a oxyhydroxides. Estimation of the effect of localized removal of passive layer on the corrosion indicated a dramatic increase in local corrosion density. These results show that a fast repassivation rate is an important requirement for biocompatibility of alloys used to manufacture dental and orthopaedic devices.     

Quantification of fibrinogen adsorption onto 316L stainless steel

Adsorption of the plasma protein fibrinogen (Fb) onto 316L stainless steel (316L SS) was observed and quantified using both in situ and ex situ atomic force microscopy techniques. Industry standard mechanical and electrochemical polishing techniques were used to prepare bulk alloy 316L SS samples, rendering the surfaces flat enough to directly observe and measure Fb adsorption. The data were analyzed kinetically using a Langmuir model. Largely irreversible adsorption was found on the 316L SS surface with an adsorption rate constant (k(o)) of 1.9 x 10(-4) mL microg(-1) s(-1) using the ex situ method and 1.7 x 10(-4) mL microg(-1) s(-1) using the in situ method. Additionally, protein conformation and assembly orientation on these surfaces were documented, where the adsorption pattern appeared random. Complete area coverage was never obtained. That is, after adsorption for over 5 time constants (5tau), voids in the structure were always observed.     

聚二甲基硅氧烷／聚氨酯共混体系的表面结构和抗凝血性能

本文用光电子能谱（ＸＰＳ）、衰减全反射红外光谱（ＡＴＲ）及扫描电子显微镜（ＳＥＭ），研究了一系列不同结构聚二甲基硅氧烷／聚氨酯（ＰＤＭＳ／ＰＵ）共混体系的表面化学组成和表面形态结构．研究结果表明：共混物具有织态状微相分离结构；在垂直表面方向上化学组成具有不均匀性，软段和聚二甲基硅氧烷在表面富集，氧原子优先在表面层中分布．对吸附血小板形态观察及再钙化时间的测定表明，聚二甲基硅氧烷／聚氨酯共混物的抗凝血性能优于聚氨酸，和共混物的表面形态结构和化学组成相关。