Processing of a porous titanium alloy from elemental powders using a solid state isothermal foaming technique

The authors have conducted a preliminary investigation with regard to the potential to manufacture porous titanium alloys for biomedical applications using toxic-free elemental powders, i.e., Ti, Nb, Ta, Zr, in combination with the pressurised gas bubble entrapment method and in contrast to standard processing routes that generally utilise prealloyed powder containing potentially toxic elements. Elemental powder compacts were either hot isostatic pressed (HIP-ed) at 1000°C and then foamed at 1150°C or else HIP-ed at 1100°C and foamed at 1350°C. Porous α + β alloys containing up to 45 vol% of porosity in the size range 20–200 μm were successfully produced, thus highlighting the potential of this manufacturing route. It was expected that further optimisation of the processing route would allow full development of the preferred β-Ti phase (from the point of view of elastic modulus compatibility between implant and bone) with this being the subject of future work by the authors.     

Schweißen von Hohlstrukturen und offenporösen Metallschäumen für den Einsatz in Kombi‐Kraftwerken

Welding of Hollow Structures and Open‐Porous Metal Foams for Application in Combined Cycle Power Plants For applications within the scope of novel cooling concepts joining technologies for sandwich composites and open‐porous metal foams are researched in the context of the Collaborative Research Centre 561 “Thermally highly loaded, porous and cooled multi‐layer systems for combined cycle power plants”. The research motivation and application fields of the different structures are defined. Welding processes and strategies for manufacturing these structures are specified as well as the joining technologies’ characteristics. Planned future works for enhancements of the processes and structures are listed.     

Mechanical examinations on dental implants with porous titanium coating

Due to its good biocompatibility, porous titanium is an interesting material for biomedical applications. Bone tissue can grow inside the porous structure and maintain a long and stable connection between the implant and the human bone. To investigate its long term stability, the mechanical behavior of porous titanium was tested under static and dynamic conditions and was compared to human bone tissue. A promising application of this material is the coating of dental implants. A manufacturing technique was developed and implants were produced. These implants were fatigue tested according to modified ISO 14801 and the micro structural change was examined. The fatigue test was statically modeled using finite element analysis (FEA). The results show that the implants resist a continuous load which is comparable to the loading conditions in the human jaw. The experiments show that the porous titanium has bone-like mechanical properties. Additionally the porous titanium shows an anisotropic behavior of its mechanical properties depending on the alignment of the pores. Finally, other potential applications of porous titanium are outlined.     

Manufacturing and processing of NiTi implants: A review

NiTi is categorized as a shape memory alloy that found interesting applications in vast areas of engineering from aerospace to biomedical; the latter applications are due to its biocompatibility in addition to its unique properties. The unique properties such as shape memory and pseudoelasticity make NiTi an excellent candidate in many functional designs. However, the manufacturing and processing complications of this alloy pose impediments to widespread applications. This paper discusses challenges and opportunities in making NiTi parts for biomedical applications such as implants. To this end, common manufacturing processes for NiTi from casting and powder metallurgy to machining are discussed. Also, new opportunities in additive manufacturing processes such as laser and electron beam techniques towards making 3D components from NiTi are described. Finally, the challenges in heat treatment and shape-setting of NiTi parts in order to attain desired shape memory properties are reviewed.     

High‐Porosity Titanium,Stainless Steel,and Superalloy Parts

The production of highly porous parts from titanium, stainless steel, and nickel‐based superalloys is of increasing interest in lightweight constructions. A new space‐holder method uses carbamide (urea) and ammonium hydrogen carbonate to produce samples with porosities between 60 and 80 %. Depending on the shape and size distribution of the space holder, spherical and angular pores in the range of 0.1–2.5 mm were obtained.     

Combinatorial Synthesis of Macromolecular Arrays by Microchannel Cantilever Spotting (µCS)

Surface‐bound microarrays of multiple oligo‐ and macromolecules (e.g., peptides, DNA) offer versatile options in biomedical applications like drug screening, DNA analysis, or medical diagnostics. Combinatorial syntheses of these molecules in situ can save significant resources in regard to processing time and material use. Furthermore, high feature densities are needed to enable high‐throughput and low sample volumes as generally regarded in combinatorial chemistry. Here, a scanning‐probe‐lithography‐based approach for the combinatorial in situ synthesis of macromolecules is presented in microarray format. Feature sizes below 40 µm allow for the creation of high‐density arrays with feature densities of 62 500 features per cm². To demonstrate feasibility of this approach for biomedical applications, a multiplexed array of functional protein tags (HA‐ and FLAG‐tag) is synthesized, and selective binding of respective epitope recognizing antibodies is shown. This approach uses only small amounts of base chemicals for synthesis and can be further parallelized, therefore, opening up a route to flexible, highly dense, and cost‐effective microarrays.     

Development of a Net Shape Manufacturing Method for Ventilated Brake Discs in Single Piece Design

Carbon fibre reinforced ceramic matrix composites (CMC), originally developed for lightweight heat shields of spacecraft, are used for high performance brake discs in sports cars from different manufacturers. In contrast to the CMC materials for space applications, based on woven fabrics and costly manufacturing methods, these low cost friction materials are produced by liquid silicon infiltration of porous Carbon/Carbon (C/C) preforms, based on short fibre reinforced CFRP green bodies manufactured via warm press technique. In this work, different manufacturing methods for ventilated CMC brake discs are compared to each other, and the development of a new technology for the manufacture of single piece C/C‐SiC brake discs in net shape technique is presented.     

Ultralong‐Discharge‐Time Biobattery Based on Immobilized Enzymes in Bilayer Rolled‐Up Enzymatic Nanomembranes

Glucose biofuel cells (GBFCs) are highly promising power sources for implantable biomedical and consumer electronics because they provide a high energy density and safety. However, it remains a great challenge to combine their high power density with reliable long‐term stability. In this study, a novel GBFC design based on the enzyme biocatalysts glucose dehydrogenase, diaphorase, and bilirubin oxidase immobilized in rolled‐up titanium nanomembranes is reported. The setup delivers a maximum areal power density of ≈3.7 mW cm^?2 and a stable power output of ≈0.8 mW cm^?2. The power discharges over 452 h, which is considerably longer than reported previously. These results demonstrate that the GBFC design is in principle a feasible and effective approach to solve the long‐term discharge challenge for implantable biomedical device applications.     

Neue Kapseltechnik für Diamantverbundwerkstoffe mittels PVD‐Verfahren

Novel encapsulation technique for diamond composites using PVD‐process For machining of mineral materials diamond tools consisting of a steel body combined with diamond impregnated segments are used. Frequently, these segments are hot pressed. Other process routes are pressureless sintering of green compacts partly combined with hot isostatic pressing and hot isostatic pressing of encapsulated powder mixtures. The compaction effect of hot isostatic pressing require a low porosity of sintered components realized by using ultra‐fine metal powder or an impermeable capsule made of metal or glass. The Institute of Materials Engineering pursues a novel process route by physical vapor deposition of a coating on pressureless sintered composites. The thin coating acts as a capsule and guarantees the pressure transfer in the following hot isostatic pressing process. Although bronze powders with particle sizes up to 90 μm are used, the manufacturing of diamond composites with low porosities is possible. In comparison to conventional encapsulation‐techniques the main advantages of this novel process route are the use of comparatively coarse metal powders and a larger geometric flexibility.     

Induktive Erwärmung von partikelverstärkten Stahlpresslingen in den thixotropen Temperaturbereich

The producers of powder metallurgy components are constantly making efforts to improve manufacturing processes and to extend the present ranges of their applications. One way to increase the complexity of powder metallurgy components is the combination of powder metallurgy and thixoforging. In contrast to the conventional process route, the powder‐pressed raw parts are heated up to the thixotropic temperature range in order to realise complex components in one process step. Additionally, the powder metallurgy combined with ceramic particles allows to produce Metal Matrix Composite (MMC) materials with improved mechanical properties compared to conventional materials. In this work basic experiments of the pressing and inductive heating of particle‐reinforced steel parts are examined.     

Tough,Self‐Healing Hydrogels Capable of Ultrafast Shape Changing

Achieving multifunctional shape‐changing hydrogels with synergistic and engineered material properties is highly desirable for their expanding applications, yet remains an ongoing challenge. The synergistic design of multiple dynamic chemistries enables new directions for the development of such materials. Herein, a molecular design strategy is proposed based on a hydrogel combining acid–ether hydrogen bonding and imine bonds. This approach utilizes simple and scalable chemistries to produce a doubly dynamic hydrogel network, which features high water uptake, high strength and toughness, excellent fatigue resistance, fast and efficient self‐healing, and superfast, programmable shape changing. Furthermore, deformed shapes can be memorized due to the large thermal hysteresis. This new type of shape‐changing hydrogel is expected to be a key component in future biomedical, tissue, and soft robotic device applications.     

生物医用多孔钛及钛合金激光快速成形研究进展

多孔钛及钛合金具有良好的生物相容性和与人骨更匹配的力学性能,是人体理想的替代材料,因此其制备技术及相关性能研究引起了广泛关注。激光快速成形是一项先进的制造技术,在制备生物多孔金属材料时具有独特的优势。介绍了激光快速成形的工作原理和技术特征,根据成形工艺特点简要回顾了4种代表性激光快速成形技术(选择性激光烧结、选择性激光熔化、激光近净成形和激光立体成形)的国内外发展现状,并重点论述了这几种技术在制备生物医用多孔钛及钛合金方面的最新研究进展,最后指出了今后在该领域的主要研究工作。     

Biomedical Applications of Layer‐by‐Layer Assembly: From Biomimetics to Tissue Engineering

The design of advanced, nanostructured materials at the molecular level is of tremendous interest for the scientific and engineering communities because of the broad application of these materials in the biomedical field. Among the available techniques, the layer‐by‐layer assembly method introduced by Decher and co‐workers in 1992 has attracted extensive attention because it possesses extraordinary advantages for biomedical applications: ease of preparation, versatility, capability of incorporating high loadings of different types of biomolecules in the films, fine control over the materials' structure, and robustness of the products under ambient and physiological conditions. In this context, a systematic review of current research on biomedical applications of layer‐by‐layer assembly is presented. The structure and bioactivity of biomolecules in thin films fabricated by layer‐by‐layer assembly are introduced. The applications of layer‐by‐layer assembly in biomimetics, biosensors, drug delivery, protein and cell adhesion, mediation of cellular functions, and implantable materials are addressed. Future developments in the field of biomedical applications of layer‐by‐layer assembly are also discussed.     

Laserstrahlschweißen von Mikrodrähten aus Nickel‐Titan‐Formgedächtnislegierungen und austenitischem Stahl

Laserwelding of microwires made of nickel‐titanium shape memory alloys and austenitic steel The special properties of nickel‐titanium shape memory alloys are currently used in micro engineering and medical technology. In order to integrate nickel‐titanium components into existing parts and modules, they often need to be joined to other materials. For this reason, the present contribution deals with the laser welding of thin pseudoelastic nickel‐titanium wires (100 μm) with a neodymium‐doped Yttrium Aluminium Garnet laser. Based on extensive parameter studies, joints without defects were produced. This study deals with the microstructure in the fusion and heat‐affected zones, the performance of the joints in static tensile tests and their functional fatigue. It can be shown that nickel‐titanium/nickel‐titanium joints reach about 75 % of the ultimate tensile strength of pure nickel‐titanium wires. In case of welding nickel‐titanium to steel no interlayer was used. The dissimilar nickel‐titanium/steel joints provide a bonding strength in the fusion and heat‐affected zones higher than the plateau stress level. Nickel‐titanium/steel joints of thin wires, as a new aspect, enable the possibility to benefit from the pseudoelastic properties of the nickel‐titanium component.     

金属泡沫材料研究进展

综述了金属泡沫材料的各种制备方法。液相法制备金属泡沫材料包括气体吹入法、固体发泡剂法和固体—气体共晶凝固法、熔模铸造法、渗流铸造法、喷射沉积法以及粉末加压熔化法等制备方法。采用金属粉末烧结法、浆料发泡法等制备工艺可以从固相制备金属泡沫材料。电沉积法以及气相沉积法可用于制备高孔隙率的金属泡沫材料。最后简要总结了金属泡沫材料的应用。     

Stretchable,Large‐area Organic Electronics

Stretchability will significantly expand the application scope of electronics, particularly large‐area electronics—displays, sensors, and actuators. If arbitrary surfaces and movable parts could be covered with stretchable electronics, which is impossible with conventional electronics, new classes of applications are expected to emerge. A large hurdle is manufacturing electrical wiring with high conductivity, high stretchability, and large‐area compatibility. This Review describes stretchable, large‐area electronics based on organic field‐effect transistors for applications to sensors and displays. First, novel net‐shaped organic transistors are employed to realize stretchable, large‐area sensor networks that detect distributions of pressure and temperature simultaneously. The whole system is functional even when it is stretched by 25%. In order to further improve stretchability, printable elastic conductors are developed by dispersing single‐walled carbon nanotubes (SWNTs) as dopants uniformly in rubbers. Further, we describe integration of printable elastic conductors with organic transistors to construct a rubber‐like stretchable active matrix for large‐area sensor and display applications. Finally, we will discuss the future prospects of stretchable, large‐area electronics with delineating a picture of the next‐generation human/machine interfaces from the aspect of materials science and electronic engineering.     

Powder Metallurgical Near‐Net‐Shape Fabrication of Porous NiTi Shape Memory Alloys for Use as Long‐Term Implants by the Combination of the Metal Injection Molding Process with the Space‐Holder Technique

A new method was developed for producing highly porous NiTi for use as an implant material. The combination of the space‐holder technique with the metal injection molding process allows a net‐shape fabrication of geometrically complex samples and the possibility of mass production for porous NiTi. Further, the porosity can be easily adjusted with respect to pore size, pore shape, and total porosity. The influence of the surface properties of powder metallurgical NiTi on the biocompatibility was first examined using human mesenchymal stem cells (hMSCs). It was found that pre‐alloyed NiTi powders with an average particle size smaller than 45 μm led to the surface properties most suitable for the adhesion and proliferation of hMSCs. For the production of highly porous NiTi, different space‐holder materials were investigated regarding low C‐ and O‐impurity contents and the reproducibility of the process. NaCl was the most promising space‐holder material compared to PMMA and saccharose and was used in subsequent studies. In these studies, the influence of the total porosity on the mechanical properties of NiTi is investigated in detail. As a result, bone‐like mechanical properties were achieved by the choice of Ni‐rich NiTi powder and a space‐holder content of 50 vol% with a particle size fraction of 355–500 μm. Pseudoelasticity of up to 6% was achieved in compression tests at 37 °C as well as a bone‐like loading stiffness of 6.5 GPa, a sufficient plateau stress σ₂₅ of 261 MPa and a value for σ₅₀ of 415 MPa. The first biological tests of the porous NiTi samples produced by this method showed promising results regarding proliferation and ingrowth of mesenchymal stem cells, also in the pores of the implant material.     

Bioinspired Peptoid Nanotubes for Targeted Tumor Cell Imaging and Chemo‐Photodynamic Therapy

Substantial progress has been made in applying nanotubes in biomedical applications such as bioimaging and drug delivery due to their unique architecture, characterized by very large internal surface areas and high aspect ratios. However, the biomedical applications of organic nanotubes, especially for those assembled from sequence‐defined molecules, are very uncommon. In this paper, the synthesis of two new peptoid nanotubes (PepTs1 and PepTs2) is reported by using sequence‐defined and ligand‐tagged peptoids as building blocks. These nanotubes are highly robust due to sharing a similar structure to those of nontagged ones, and offer great potential to hold guest molecules for biomedical applications. The findings indicate that peptoid nanotubes loaded with doxorubicin drugs are promising candidates for targeted tumor cell imaging and chemo‐photodynamic therapy.     

Stabilization of Polymer‐Hydrogel Capsules via Thiol–Disulfide Exchange

Polymer hydrogels are used in diverse biomedical applications including drug delivery and tissue engineering. Among different chemical linkages, the natural and reversible thiol–disulfide interconversion is extensively explored to stabilize hydrogels. The creation of macro‐, micro‐, and nanoscale disulfide‐stabilized hydrogels commonly relies on the use of oxidizing agents that may have a detrimental effect on encapsulated cargo. Herein an oxidization‐free approach to create disulfide‐stabilized polymer hydrogels via a thiol–disulfide exchange reaction is reported. In particular, thiolated poly(methacrylic acid) is used and the conditions of polymer crosslinking in solution and on colloidal porous and solid microparticles are established. In the latter case, removal of the core particles yields stable, hollow, disulfide‐crosslinked hydrogel capsules. Further, a procedure is developed to achieve efficient disulfide crosslinking of multilayered polymer films to obtain stable, liposome‐loaded polymer‐hydrogel capsules that contain functional enzymatic cargo within the liposomal subcompartments. This approach is envisaged to facilitate the development of biomedical applications of hydrogels, specifically those including fragile cargo.     

Cooling‐Triggered Shapeshifting Hydrogels with Multi‐Shape Memory Performance

Heating‐triggered shape actuation is vital for biomedical applications. The likely overheating and subsequent damage of surrounding tissue, however, severely limit its utilization in vivo. Herein, cooling‐triggered shapeshifting is achieved by designing dual‐network hydrogels that integrate a permanent network for elastic energy storage and a reversible network of hydrophobic crosslinks for “freezing” temporary shapes when heated. Upon cooling to 10 °C, the hydrophobic interactions weaken and allow recovery of the original shape, and thus programmable shape alterations. Further, multiple temporary shapes can be encoded independently at either different temperatures or different times during the isothermal network formation. The ability of these hydrogels to shapeshift at benign conditions may revolutionize biomedical implants and soft robotics.