Effects of silane on the interfacial fracture of a parylene film over a stainless steel substrate

Parylene can be coated on stainless steel substrates with and without γ-methacryloxypropyltrimethoxysilane (γ-MPS) as an adhesion promoter. In order to study the effects of silane (γ-MPS) on the adhesion and mixed-mode interfacial fracture performance between parylene C and 316L stainless steel, this paper presents the results of a combined experimental and theoretical approach. Atomic force microscopy (AFM) was used to obtain pull-off forces between parylene coated AFM tips with or without γ-MPS and 316L substrates. A combination of adhesion theories and fracture mechanics models was then used to obtain estimates of the fracture energy release rates over a wide range of mode mixities between pure mode I and pure mode II. The trends in the estimates were shown to be in good agreement with experimental measurements of interfacial fracture toughness obtained from Brazil nut tests coated with parylene C in the presence or absence of γ-MPS over the same range of mode mixities. The study determined that the contribution of silane to the adhesion of parylene C to 316L steel was modest.     

类金刚石薄膜在不锈钢表面结合强度及耐腐蚀性研究

类金刚石(DLC)薄膜与不锈钢的结合强度是DLC薄膜应用于血管支架表面改性的关键技术问题.利用磁过滤阴极真空弧源沉积方法在316L不锈钢表面沉积DLC薄膜,研究沉积时基体偏压、薄膜厚度以及钛过渡层对DLC薄膜与基体结合强度的影响.研究结果表明,316L表面制备相同厚度的DLC薄膜,采用-1000V脉冲偏压制备的薄膜结合强度明显优于-80V直流偏压下制备的DLC薄膜;随着DLC薄膜厚度的增大,DLC薄膜与316L基体的结合力下降;316L不锈钢表面制备一层100nm的钛过渡层之后可以改善DLC薄膜的结合状况,并且经过20%的拉伸变形后,DLC薄膜完整,耐蚀性优于未表面处理的316L不锈钢.以上研究结果表明,磁过滤阴极真空弧源方法制备DLC薄膜与316L结合强度高,可以有效的提高316L的耐腐蚀性,是一种具有应用前景的血管支架表面改性方法.     

Adhesive B-doped DLC films on biomedical alloys used for bone fixation

The long-term failure of the total hip and knee prostheses is attributed to the production of wear particles at the articulating interface between the metals, ceramics and polymers used for surgical implants and bone-fixtures. Therefore, finding an adhesive and inert coating material that has low frictional coefficient should dramatically reduce the production of wear particles and hence, prolong the life time of the surgical implants. The novel properties of the non-toxic diamond-like carbon (DLC) coatings have proven to be excellent candidates for biomedical applications. However, they have poor adhesion strength to the alloys and biomaterials. The addition of a thin interfacial layer such as Si, Ti, TiN, Mo and Cu/Cr and/or adding additives such as Si, F, N, O, W, V, Co, Mo, Ti or their combinations to the DLC films has been found to increase the adhesion strength substantially. In our study, grade 316L stainless steel and grade 5 titanium alloy (Ti-6Al-4V) were used as biomaterial substrates. They were coated with DLC films containing boron additives at various levels using various Si interfacial layer thicknesses. The best film adhesion was achieved at 8% and 20% on DLC coated Ti-6Al-4V and grade 316L substrates, respectively. It has been demonstrated that doping the DLC with boron increases their adhesion strength to both substrates even without silicon interfacial layer and increases it substantially with optimum silicon layer thickness. The adhesion strength is also correlated with the hydrogen contents in the B-DLC films. It is found to reach its maximum value of 700 kg/cm² and 390 kg/cm² at 2/7 and 3/6 for CH₄/Ar partial pressures (in mTorr ratio) for Ti-6Al-4V and 316L substrates, respectively.     

Synthesis and properties of metal matrix composite foams based on austenitic stainless steels –titanium carbonitrides

Metal matrix composite foams based on 316L stainless steel and reinforced with TiC0.7N0.3 were produced by the replication method using polyurethane sponge as a template. The rheological properties of the slurry appeared to be the key issue in the preparation of the composite foams. A homogeneous distribution of TiC0.7N0.3 particles throughout the 316L matrix and a good interaction between the 316L matrix and TiC0.7N0.3 reinforcement particles were obtained. Compression strength results showed that TiC0.7N0.3 particles acted as the real reinforcement medium. The values of the compressive yield strength and the elastic modulus of the metal matrix composite foams increased significantly with increasing TiC0.7N0.3 content when compared to the open cell 316L stainless steel foams.     

Reducing Staphylococcus aureus biofilm formation on stainless steel 316L using functionalized self-assembled monolayers

Stainless steel 316L (SS316L) is a common material used in orthopedic implants. Bacterial colonization of the surface and subsequent biofilm development can lead to refractory infection of the implant. Since the greatest risk of infection occurs perioperatively, strategies that reduce bacterial adhesion during this time are important. As a strategy to limit bacterial adhesion and biofilm formation on SS316L, self-assembled monolayers (SAMs) were used to modify the SS316L surface. SAMs with long alkyl chains terminated with hydrophobic (? CH₃) or hydrophilic (oligoethylene glycol) tail groups were used to form coatings and in an orthogonal approach, SAMs were used to immobilize gentamicin or vancomycin on SS316L for the first time to form an “active” antimicrobial coating to inhibit early biofilm development. Modified SS316L surfaces were characterized using surface infrared spectroscopy, contact angles, MALDI-TOF mass spectrometry and atomic force microscopy. The ability of SAM-modified SS316L to retard biofilm development by Staphylococcus aureus was functionally tested using confocal scanning laser microscopy with COMSTAT image analysis, scanning electron microscopy and colony forming unit analysis. Neither hydrophobic nor hydrophilic SAMs reduced biofilm development. However, gentamicin-linked and vancomycin-linked SAMs significantly reduced S. aureus biofilm formation for up to 24 and 48 h, respectively.     

Si3N4和52100钢对磨副材料对CrN薄膜干摩擦学行为的影响

利用阴极电弧离子镀技术在316L不锈钢基体上制备了CrN薄膜。采用扫描电子显微镜(SEM)、X射线衍射仪(XRD)、纳米压痕仪对CrN薄膜的形貌、成分和力学性能进行了表征。为了研究Si_3N_4和52100钢对磨副材料对CrN薄膜和316L不锈钢干摩擦行为的影响,在2N、5N、8N三种载荷下,将CrN薄膜和316L不锈钢基体与Si_3N_4陶瓷球和52100钢球分别进行了往复式滑动干摩擦实验。采用扫描电子显微镜观察了磨痕的微观形貌,并对CrN薄膜和316L不锈钢基体的磨损机制进行了分析。结果表明:CrN薄膜表面平整,缺陷较少;CrN薄膜的纳米硬度约为28GPa,弹性模量约为350GPa;与Si_3N_4陶瓷球相比,CrN薄膜与52100钢球摩擦时摩擦因数相对较小(保持在0.7左右)且更加稳定;316L不锈钢的摩擦因数远大于CrN薄膜且波动较大;对磨球为Si_3N_4陶瓷球时,CrN薄膜的主要磨损机制为磨粒磨损,伴有少量的氧化和黏着磨损,316L不锈钢的磨损机制主要为磨粒磨损和塑性变形,伴有少量的氧化和黏着磨损;对磨球为52100钢球时,CrN薄膜的主要磨损机制为黏着磨损,伴有少量的氧化,316L不锈钢的磨损机制主要为黏着磨损,伴有少量的氧化和磨粒磨损。CrN薄膜与两种对磨球的磨损量均小于316L不锈钢基体的磨损量,说明CrN薄膜有效提高了基体的耐磨性。     

Measuring bone cell adhesion on implant surfaces using a spinning disc device

The adhesion behaviour of osteoblastic cells on implant surfaces is a main focus during the development of osteoconductive implant surfaces. Therefore, besides cell spreading and proliferation on surfaces the adhesion strength of cells to the substrate is of high interest. There are different approaches to determine cell adhesion but only few quantitative methods. For this purpose, we have developed an adhesion device based on the spinning disc principle in conjunction with an inverse confocal laser scanning microscope (LSM). Mirror polished disc‐shaped test samples made of titanium‐ (Ti6Al4V) and cobalt‐alloys (Co28Cr6Mo), as well as stainless steel (316L), were seeded with osteoblasts, stained with a fluorescent dye, at defined radial positions and were incubated for 18 h in cell culture medium (DMEM). After incubation the test samples were placed into the adhesion chamber filled with DMEM. By means of a computer controlled motor the test samples were rotated for 3 min. Using the LSM the detachment of the cells at defined radial positions was determined and the cell count was recorded before and after rotation with the help of imaging software. An average shear stress of 47.1 N/m², 53.2 N/m² and 49.4 N/m² was assessed for the mirror polished Ti6Al4V, Co28Cr6Mo and 316L surfaces respectively. The technique is suitable for studying bone cell adhesion strength on orthopaedic implant materials. Future investigations will focus on different bioactive and anti‐infectious implant surfaces, as well as soluble bioactive factors.     

Compatibility of ferritic and duplex stainless steels as implant materials: in vitro corrosion performance

The pitting corrosion, crevice corrosion and accelerated leaching of iron, chromium and nickel of super-ferritic and duplex stainless steels, and for effective comparison the presently used 316L stainless steel, have been studied in an artificial physiological solution (Hank's solution) by the potentiodynamic anodic polarization method. The results of the above studies have shown the new super-ferritic stainless steel to be immune to pitting and crevice corrosion attack. The pitting and crevice corrosion resistances of duplex stainless steel were found to be superior to those of the commonly used type 316L stainless steel implant materials. The accelerated leaching study conducted for the above alloys showed very little tendency for the leaching of metal ions when compared with 316L stainless steel. Thus the present study indicated that super-ferritic and duplex stainless steels can be adopted as implant materials due to their higher pitting and crevice corrosion resistance.     

医用316L不锈钢表面改性的研究进展

316L不锈钢作为生物医用材料在近20年内被广泛应用在矫形外科植入物、牙种植体和冠状动脉支架等领域。分析了目前医用316L不锈钢在临床应用中存在的主要问题,指出生物相容性、耐腐蚀性和耐磨损性有待提高和表面改性是改善上述问题的有效途径。综述了医用316L不锈钢表面改性的各种途径及研究成果,并展望了316L不锈钢表面改性的研究趋势。     

In vitro study of platelet adhesion on medical nickel-free stainless steel surface

A new nickel-free austenitic stainless steel, named BIOSSN4, has been recently developed to avoid the sensitivity to Ni ions. In the present study, the blood compatibility of the nickel-free stainless steel was evaluated in vitro by the platelet-rich plasma adhesion test with comparison to 316L stainless steel. The result shows that the nickel-free stainless steel only causes less activation of platelets, which was indicated by their morphology and low spreading. The result suggests that the nickel-free stainless steel should have better blood compatibility compared with 316L stainless steel and, as a bio-material, it should have obvious advantage and potential applications.     

Ti和TiO2薄膜在血管支架表面附着状况的研究

采用非平衡磁控溅射法在316L不锈钢制成的血管支架表面制备Ti以及TiO2薄膜,初步研究了Ti薄膜厚度、TiO2薄膜沉积速率对薄膜在血管支架表面附着状况的影响.结果表明,支架表面较薄的Ti薄膜附着状况较厚的Ti薄膜好;低沉积速率制备的TiO2薄膜在支架表面附着状况好于高沉积速率制备的TiO2薄膜;对于Ti/TiO2复合薄膜,Ti层厚度过大不利于Ti/TiO2复合薄膜在支架表面附着.     

Metallurgical investigation of a failure in 316L stainless steel orthopaedic implant

An orthopaedic implant (nail for shinbone) made of 316L stainless steel (SS) that failed prematurely was examined to determine the root cause for the fracture. Detailed scanning electron microscopy was carried out to conclusively establish the evidence(s). Based on the results of extensive fracture surface analysis as well as the background information provided on the implant, it was determined that the implant (stainless steel nail) failed by the mechanism of predominantly ductile fracture facilitated by the presence of non-metallic inclusions.     

脉冲电流处理对轧制316L不锈钢的快速强化

目的 探究不同参数的脉冲电流处理(EPT)对轧制316L不锈钢拉伸性能、显微硬度及微观组织的影响。方法 将轧制的316L不锈钢作为原始样,调节流过样品的脉冲电流密度,分别为130、170、190、260、310 A/mm²,分析脉冲电流密度与其拉伸性能和显微硬度的关系。结果 轧制316L不锈钢的抗拉强度和显微硬度随着脉冲电流密度的增大呈现先增大后减小的趋势,其中当脉冲电流密度为170 A/mm²时达到峰值,抗拉强度由1 485 MPa提升到1 625 MPa,同时显微硬度也由431HV增大到473HV。通过电子背散射衍射分析微观组织可知,与原始样相比,经过脉冲电流处理的样品晶粒尺寸明显减小,马氏体含量明显增多,脉冲电流处理可以促使微观组织快速均匀化。结论 脉冲电流处理可以在短时间内实现轧制316L不锈钢组织的均匀化调控,有效改善轧制316L不锈钢的微观组织,减少轧钢形变织构,促使参与的奥氏体转变为马氏体,使微观组织趋于稳定,同时还可以使轧制316L不锈钢晶粒快速细化,达到细晶强化的效果,有效提高整体抗拉强度和显微硬度。     

In vitro testing of surface-modified biomaterials

The influence of surface modification treatments such as ion implantation and sputter coating on an in vitro rat bone-marrow cell culture was studied by scanning electron microscopy and X-ray microanalysis. 316 L stainless steel, Ti–6Al–4V and Ti–5Al–2.5Fe were nitrogen ion-implanted with three fluences: 1015, 1016 and 1017 ion cm-2 with an energy beam of 40 keV. Both nitrogen and carbon sputter-coated 316 L stainless steel samples were also studied. Polished 316 L stainless steel, Ti–6Al–4V, Ti–5Al–2.5Fe and ThermanoxTM were also studied, in order to give comparative information. The materials were inoculated with a droplet of cell suspension and were maintained for 3 wk. A mineralized extracellular matrix was formed on all materials except on nitrogen sputter-coated 316 L stainless steel. The morphology of the cell cultures obtained on nitrogen-ion implanted materials was similar to those obtained on the untreated materials and ThermanoxTM. The observation of the interface between the cell layer and the substrata showed the presence of calcium- and phosphorus-rich globular deposits associated with collagen fibres. A higher density of these globular deposits was observed on the ion-implanted materials.     

Bacterial adhesion reduction on a biocompatible Si+ ion implanted austenitic stainless steel

The colonization of an implant surface by bacteria is an extremely important medical problem, which often leads to the failure of medical devices. Modern surface modification techniques, such as ion implantation, can confer to the surfaces very different properties from those of the bulk underlying material. In this work, austenitic stainless steel 316 LVM has been superficially modified by Si⁺ ion implantation. The effect of surface modification on the biocompatibility and bacterial adhesion to 316 LVM stainless steel has been investigated. To this aim, human mesenchymal stem cells (hMSCs), as precursor of osteoblastic cells, and bacterial strains relevant in infections related to orthopedic implants, i.e., Staphylococcus aureus and Staphylococcus epidermidis, have been assayed. For the understanding of changes in the biological response associated to ion implantation, variations in the chemical surface composition, topography, surface Gibbs energy, isoelectric point and in vitro corrosion behavior have been evaluated. hMSCs adhesion, viability and differentiation to the osteoblastic lineage were unaffected by Si⁺ ion implantation. On the other hand, Si⁺ ion implantation diminished the number of attached bacteria in static conditions and led to smaller adhesion rates and retention strength. The ability of implanted surfaces to reduce the bacterial adhesion was higher for Staphylococcus epidermidis than for Staphylococcus aureus. This study proposes Si⁺ ion implantation as an effective way of reducing bacterial adhesion on 316 LVM stainless steel surfaces without compromising its good biocompatibility.     

Development of nitrogen-containing nickel-free austenitic stainless steels for metallic biomaterials—review

Metallic biomaterials—such as 316L stainless steel and cobalt-based alloys—have been used as biomaterials mainly because of their excellent mechanical and corrosion properties. However, the release of nickel trace elements—which cause toxicity—has prompted the development of nitrogen-containing nickel-free austenitic stainless steels. This paper reviews their development, traces the history of 316L stainless steel, and the improvement of properties by nitrogen addition. These steels are now available for production of implant devices such as bone plates and screws. Such production requires special techniques with nitrogen absorption treatment.     

Evaluation of hydroxyapatite coatings on borate passivated 316L SS in Ringer's solution

Surgical grade stainless steel (316L SS) is one of the widely used implant material in orthopedic surgeries. But often the release of metal ions is evidenced from the implants and subsequently a second surgery is required to remove the implant material. One way to control this release of metal ions is to coat the implant material with a biocompatible material like hydroxyapatite. In this paper we have reported a successful coating of hydroxyapatite over borate passivated 316L SS by a dip coating method. The coatings were characterized by electrochemical techniques such as potentiodynamic polarization, electrochemical impedance and cyclic voltammetry (CV). Also X-ray diffraction (XRD) and scanning electron microscopic (SEM) studies were performed to confirm the quality of the coatings. Results of accelerated leach out characteristics by inductively coupled plasma–atomic emission spectroscopy (ICP–AES) and the evaluation of shear strength are also presented to support the corrosion resistant nature of the coatings. The enhanced bio-resistivity of the as-formed HAP coatings on passivated 316L SS is attributed to the protective passive layer formed by borate buffer solution at selected potentials.     

Mechanical properties and corrosion behavior of selective laser melted 316L stainless steel after different heat treatment processes

Irregular grains, high interfacial stresses and anisotropic properties widely exist in 3D-printed metallic materials, and this paper investigated the effects of heat treatment on the microstructural, mechanical and corrosion properties of 316 L stainless steel fabricated by selective laser melting. Sub-grains and low-angle boundaries exist in the as-received selective laser melted (SLMed) 316 L stainless steel. After heat treatment at 1050 °C, the sub-grains and low-angle boundaries changed slightly, and the stress state and strength decreased to some extent due to the decrease of dislocation density. After heat treatment at 1200 °C, the grains became uniform, and the dislocation cells vanished, which led to a sharp decline in the hardness and strength. However, the ductility was improved after recrystallization heat treatment. The passive film thickness and corrosion potential of the SLMed 316 L stainless steel decreased after heat treatment, and the pitting potential also decreased due to the accelerated transition from metastable to steady-state pitting; this accelerated transition was caused by the presence of weak passive films at the enlarged pores after heat treatment, especially for an adequate solid solution treatment.     

Effect of porosity and density on the mechanical and microstructural properties of sintered 316L stainless steel implant materials

In this study, the microstructure and mechanical properties of sintered AISI 316L stainless steel implant materials produced by powder metallurgy (P/M) method were investigated as a function of porosity amount. AISI 316L stainless steel powders were cold-pressed with 800 MPa pressure and sintered at 1200 °C, 1250 °C and 1300 °C for 30 min in a nitrogen atmosphere. The mechanical properties of the 316L implant samples were determined by tensile, fatigue and microhardness tests. Metallographic studies such as pore formation, and fractured surface analyses were performed by Scanning Electron Microscopy (SEM) and Light Optical Microscopy (LOM). The results of this study indicate that, irregular pore formation tendencies increase with an increase in porosity (%). Furthermore, an increase in porosity was shown to decrease the mechanical properties of sintered AISI 316L stainless steel. Sintering temperature is important parameter in decreasing the porosity of P/M materials.