Advanced Engineering Materials

The background image confirms the irregular amorphous structure of a bulk metallic glass in a false-color transmission electron micrograph (scale: 10 nanometer horizontally across the page). Atomic rearrangements at the glass transition were studied in real time by in-situ high energy X-ray diffraction. A two-dimensional pattern showing the typical broad rings scattered by the amorphous material is represented in the center, from which average atomic distances can be concluded accurately. Further details can be found in the article by D. D. Qu, K.-D. Liss et. al. on page 861.

The central image displays neutron diffraction patterns of Zr-2.5Nb, horizontal, evolving in time and increasing temperature, vertical. A phase transition takes place, seen by vanishing and increasing intensity lines. Some of the lines strongly shift due to the change of composition, which can be evaluated by Vegard's law. The background image is the microstructure in false colors (scale across the page ∼10 micrometer). Further details can be found in the article by K. Yan, et. al. on page 882.

The Cover shows direct writing of biodegradable polymers and bioactive composites using electric field printing methods. Further details can be found in the article by M. Edirisinghe et al. on page B296.

Thermal expansion in bulk metallic glass, as measured on an atomic scale by in situ high energy X-ray diffraction, occurs differently regarding the first and second nearest neighbors. This discrepancy leads inevitably to local stresses, which yield at the glass transition. The findings give an atomistic explanation for the correlation between mechanical yield strength and the glass transition temperature.

By using ultrafine grained Cu with homogeneous microstructures as initial modal materials and low-temperature oil-bath annealing, we successfully prepared bimodal Cu (see figure) with homogeneous distribution of different-volume-fraction recrystallized micro-grains within the ultrafine grained matrix. Tensile results and microstructural analyses indicate that both yield strength and uniform elongation of the bimodal Cu follow the rule-of-mixtures, with interesting results related to volume fraction. Our work provides a pathway for optimizing the mechanical properties of multiscale materials with bimodal grain size distribution.

In this study, we describe a novel indirect process for producing topologically-ordered, porous magnesium (Mg) scaffolds for application as degradable metallic orthopaedic biomaterials. The process involved printing of arapid prototyped mould, NaCl infiltration, and liquid Mg casting techniques. Using a range of characterization methods, we demonstrated that Mg scaffolds were manufactured with a high level of accuracy and with controlled pore architecture.

In situ neutron diffraction has been used to characterize the phase transformation process of the nuclear structural material Zr-2.5Nb (mass%) while subjected to heating and cooling cycles. The shift of diffraction peaks, as shown in the image, has been evaluated by Vegard's law to track the change of Nb concentrations in the β-Zr(Nb) phase, which reveals the system kinetics for approaching equilibrium.

Two aluminium alloys with 6wt% titanium diboride (TiB₂) particles have been studied. TiB₂ particles play an important role in the nucleation of the different phases of the alloys during solidification, and in the reduction of grain size and porosity. This study analyses the solidification patterns and microstructure of Al-Si₇Mg_0.3+TiB₂ (6wt%) and Al-Cu₅MgTi+TiB₂ (6wt%) materials compared to their corresponding non-reinforced alloys.

Aero engine high-pressure compressors undergo high thermal and heavy mechanical loads. Therefore, high temperature and strength resistant alloys such as Ti6246 are used. Mechanical surface treatments enhance their performance. In this context similar shot peening treatments with ceramic and steel on Ti6246 specimen are performed, evaluated, and discussed.

The effect of microwave hybrid heating on the sintering behavior and thermal gradient is studied. The results are obtained by a novel method specifically prepared for this task. The method permits simultaneous monitoring of the temperature distribution and shrinkage without contact during heating in microwave environment (see image).

A novel method of the in situ formation of carbon nanotubes (CNTs) in a porous polymer derived ceramic (PDC) is presented. The approach combines the pore formation in the PDC, the catalyst formation at the inner surface of the pores, and the CNT formation in the polymer derived ceramic in one thermal step in inert atmosphere.

Scaffolds based on methacrylated oligolactones, urethanes, and hydrogel forming poly(ethylene glycol) with adjustable spatial dimensions over a wide range and well defined microstructures were microstructured by two-photon polymerization (2PP). Their properties as well as their cytocompatibility make them attractive for implantation, tissue engineering and microsystem technology.

Photopolymerizable methacrylates based on synthetic oligomers (poly(ethylene) glycol, polyglycerine) and natural polymers (dextran, hyaluronan) are synthesized and characterized by their chemical structures and application-relevant properties including photopolymerization behavior, mechanical stability, cytocompatibility, and in vitro degradation. In an initial study, the substances are evaluated for their processability in 2-photon-polymerization to fabricate three-dimensionally structured, biodegradable hydrogel matrices usable in soft and cartilage tissue engineering.

Poly(ethyleneimine) (PEI) is known to be a potentially cytotoxic polymer, however, it is frequently used as an adhesion promoter in polymer multilayers. It is, therefore, important to investigate the biocompatibility of PEI used as nanometer thin single layer on biomaterials surfaces. It was shown for the first time that PEI layers with nanometer thickness do not affect the bone cell reaction negatively compared to native titanium.

Novel biomedical structures are written directly using electrohydrodynamic print-patterning which is an advantageous method for preparing ordered topographies. By combining this controlled deposition method with solvent evaporation, novel topographies and potential scaffolds are formed. To demonstrate this a biodegradable polymer and its composites have been used to generate 3D structures with control on size, shape and porosity.

Bonding of ZrO₂ toughened Al₂O₃ (ZTA) to acrylic bone cement (BC) was improved by a PAA film, formed in H₂C₂O₄ or H₃PO₄ by electrochemical anodization of a sputtered Al-layer on the ZTA substrate. Compared to unmodified interface (≈ 30 MPa), the PAA modified specimens achieved a significantly higher interface bonding strength (≈ 60 MPa), due to mixed mode fracture with part of the crack propagation along the PAA/BC interface and part through BC.

This study investigates the in vitro degradation behavior of magnesium alloys with varying alloying elements and the effect of coatings (MgF₂ and bioglass). The alloys were subjected to a simulated body fluid and were analyzed based on mass loss, pH changes, volume loss, and their mechanical properties. Regarding to its degradation behaviour, Nd2 could be an interesting option for biomedical applications.

A light triggered release system is developed employing a photocleavable 6-nitroveratryloxycarbonyl (NVOC) labeled FhuA variant embedded into liposome membranes. Protein engineering efforts demonstrate that lysine 556 in combination with the NVOC label is the main responsible to control compound release. The latter enables us to design channel plugs with tunable release kinetics that can be resized to the compounds of interest.