Development of a novel biodegradable porous iron-based implant for bone replacement.

Bone replacement and osteosynthesis require materials which can at least temporarily bear high mechanical loads. Ideally, these materials would eventually degrade and would be replaced by bone deposited from the host organism. To date several metals, notably iron and iron-based alloys have been identified as suitable materials because they combine high strength at medium corrosion rates. However, currently, these materials do not degrade within an appropriate amount of time. Therefore, the aim of the present study is the development of an iron-based degradable sponge-like (i.e. cellular) implant for bone replacement with biomechanically tailored properties. We used a metal powder sintering approach to manufacture a cylindrical cellular implant which in addition contains phosphor as an alloying element. No corrosion inhibiting effects of phosphorus have been found, the degradation rate was not altered. Implant prototypes were tested in an animal model. Bone reaction was investigated at the bone-implant-interface and inside the cellular spaces of the implant. Newly formed bone was growing into the cellular spaces of the implant after 12 months. Signs of implant degradation were detected but after 12 months, no complete degradation could be observed. In conclusion, iron-based open-porous cellular biomaterials seem promising candidates for the development of self-degrading and high load bearing bone replacement materials.

Molybdenum - A biodegradable implant material for structural applications?

Molybdenum as a potentially new biodegradable material was investigated. Degradation behavior of commercially high purity molybdenum was observed in simulated physiological salt solutions (Kokubo's SBF with/without TRIS-HCl, Cu2+ addition and 0.9% NaCl solution). Potentiodynamic polarization, immersion mass loss and ion concentration measurements paired with REM/EDX analysis reveal gradual dissolution of molybdenum in the proper order of magnitude for stent application, associated with formation of thin, non-passivating corrosion products. The underlying corrosion mechanism is discussed as well as a comparison to literature data. However, formation of calcium phosphates (CaP) in SBF significantly decreases corrosion rates. In-situ polarization was found to be a potential way for overcoming this problem and simultaneously enhancing corrosion above the benchmark for a degradable stent material. STATEMENT OF SIGNIFICANCE: Biodegradable metals have the potential to overcome severe complications common to orthopedic and cardio-vascular implants. However, the need for a material with moderate and predictable degradation, high strength and toughness as well as MRI suitability must be satisfied. Molybdenum as potential new biodegradable material may just fulfill these requirements. An overall positive picture of molybdenum as an interesting alternative to recently discussed metallic biodegradable materials can be concluded from the herein presented results and from literature data, showing directions for future research on the topic.

Preparation of high-quality ultrathin transmission electron microscopy specimens of a nanocrystalline metallic powder.

This article explores the achievable transmission electron microscopy specimen thickness and quality by using three different preparation methods in the case of a high-strength nanocrystalline Cu-Nb powder alloy. Low specimen thickness is essential for spatially resolved analyses of the grains in nanocrystalline materials. We have found that single-sided as well as double-sided low-angle Ar ion milling of the Cu-Nb powders embedded into epoxy resin produced wedge-shaped particles of very low thickness (<10 nm) near the edge. By means of a modified focused ion beam lift-out technique generating holes in the lamella interior large micrometer-sized electron-transparent regions were obtained. However, this lamella displayed a higher thickness at the rim of ≥30 nm. Limiting factors for the observed thicknesses are discussed including ion damage depths, backscattering, and surface roughness, which depend on ion type, energy, current density, and specimen motion. Finally, sections cut by ultramicrotomy at low stroke rate and low set thickness offered vast, several tens of square micrometers uniformly thin regions of ∼10-nm minimum thickness. As major drawbacks, we have detected a thin coating on the sections consisting of epoxy deployed as the embedding material and considerable nanoscale thickness variations.