The synthesis of iron oxide nanoparticles (NPs) by thermal decomposition of iron precursors using oleic acid as surfactant has evolved to a state-of-the-art method to produce monodisperse, spherical ...NPs. The principles behind such monodisperse syntheses are well-known: the key is a separation between burst nucleation and growth phase, whereas the size of the population is set by the precursor-to-surfactant ratio. Here we follow the thermal decomposition of iron pentacarbonyl in the presence of oleic acid via in situ X-ray scattering. This method allows reaction kinetics and precursor states to be followed with high time resolution and statistical significance. Our investigation demonstrates that the final particle size is directly related to a phase of inorganic cluster formation that takes place between precursor decomposition and particle nucleation. The size and concentration of clusters were shown to be dependent on precursor-to-surfactant ratio and heating rate, which in turn led to differences in the onset of nucleation and concentration of nuclei after the burst nucleation phase. This first direct observation of prenucleation formation of inorganic and micellar structures in iron oxide nanoparticle synthesis by thermal decomposition likely has implications for synthesis of other NPs by similar routes.
Abstract Biocompatibility is a key issue in the development of new implant materials. In this context, a novel class of biodegrading Mg implants exhibits promising properties with regard to ...inflammatory response and mechanical properties. The interaction between Mg degradation products and the nanoscale structure and mineralization of bone, however, is not yet sufficiently understood. Investigations by synchrotron microbeam x-ray fluorescence (μXRF), small angle x-ray scattering (μSAXS) and x-ray diffraction (μXRD) have shown the impact of degradation speed on the sites of Mg accumulation in the bone, which are around blood vessels, lacunae and the bone marrow. Only at the highest degradation rates was Mg found at the implant–bone interface. The Mg inclusion into the bone matrix appeared to be non-permanent as the Mg-level decreased after completed implant degradation. μSAXS and μXRD showed that Mg influences the hydroxyl apatite (HAP) crystallite structure, because markedly shorter and thinner HAP crystallites were found in zones of high Mg concentration. These zones also exhibited a contraction of the HAP lattice and lower crystalline order.
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Understanding the implant–bone interaction is of prime interest for the development of novel biodegrading implants. Magnesium is a very promising material in the class of biodegrading ...metallic implants, owing to its mechanical properties and excellent immunologic response during healing. However, the influence of degrading Mg implants on the bone nanostructure is still an open question of crucial importance for the design of novel Mg implant alloys. This study investigates the changes in the nanostructure of bone following the application of a degrading WZ21 Mg implant (2wt% Y, 1wt% Zn, 0.25wt% Ca and 0.15wt% Mn) in a murine model system over the course of 15months by small angle X-ray scattering. Our investigations showed a direct response of the bone nanostructure after as little as 1month with a realignment of nano-sized bone mineral platelets along the bone–implant interface. The growth of new bone tissue after implant resorption is characterized by zones of lower mineral platelet thickness and slightly decreased order in the stacking of the platelets. The preferential orientation of the mineral platelets strongly deviates from the normal orientation along the shaft and still roughly follows the implant direction after 15months. We explain our findings by considering geometrical, mechanical and chemical factors during the process of implant resorption.
The advancement of surgical techniques and the increased life expectancy have caused a growing demand for improved bone implants. Ideally, they should be bio-resorbable, support bone as long as necessary and then be replaced by healthy bone tissue. Magnesium is a promising candidate for this purpose. Various studies have demonstrated its excellent mechanical performance, degradation behaviour and immunologic properties. The structural response of bone, however, is not well known. On the nanometer scale, the arrangement of collagen fibers and calcium mineral platelets is an important indicator of structural integrity. The present study provides insight into nanostructural changes in rat bone at different times after implant placement and different implant degradation states. The results are useful for further improved magnesium alloys.
Higher animals typically rely on calcification to harden certain tissues such as bones and teeth. Some notable exceptions can be found in invertebrates: The fangs, teeth, and mandibles of diverse ...arthropod species have been reported to contain high levels of zinc. Considerable quantities of zinc also occur in the jaws of the marine polychaete worm Nereis sp. High copper levels in the polychaete worm Glycera dibranchiata recently were attributed to a copper-based biomineral reinforcing the jaws. In the present article, we attempt to unravel the role of zinc in Nereis limbata jaws, using a combination of position-resolved state-of-the-art techniques. It is shown that the local hardness and stiffness of the jaws correlate with the local zinc concentration, pointing toward a structural role for zinc. Zinc always is detected in tight correlation with chlorine, suggesting the presence of a zinc-chlorine compound. No crystalline inorganic phase was found, however, and results from x-ray absorption spectroscopy further exclude the presence of simple inorganic zinc-chlorine compounds in amorphous form. The correlation of local histidine levels in the protein matrix and zinc concentration leads us to hypothesize a direct coordination of zinc and chlorine to the protein. A comparison of the role of the transition metals zinc and copper in the jaws of two polychaete worm species Nereis and Glycera, respectively, is presented.
Biominerals are widely exploited to harden or stiffen tissues in living organisms, with calcium-, silicon-, and iron-based minerals being most common. In notable contrast, the jaws of the marine ...bloodworm Glycera dibranchiata contain the copper-based biomineral atacamite$Cu_{2}(OH)_{3}Cl$. Polycrystalline fibers are oriented with the outer contour of the jaw. Using nanoindentation, we show that the mineral has a structural role and enhances hardness and stiffness. Despite the low degree of mineralization, bloodworm jaws exhibit an extraordinary resistance to abrasion, significantly exceeding that of vertebrate dentin and approaching that of tooth enamel.
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•Environmental influences on properties of adhesive anchors (epoxy and vinylester).•Water desorption of vinylester vs. water adsorption of epoxy at 23 °C and 53% RH.•Post curing leads ...to increasing tensile strength with increasing temperature.•High-temperature XRD investigations: Cement phases stay inert inside the matrix.
The long-term performance of adhesive anchor systems is largely determined by the time-dependent mechanical properties. As polymer-based composite materials, the properties of adhesives change during their service life dependent on environmental factors. Therefore, the influence of aging time on Young’s modulus and tensile strength of two different industrially produced materials (epoxy, vinylester) with a high filler content (20–50 vol%) were investigated considering that most literature is focused on neat resins. Mechanical properties of the vinylester based material increased with time and curing temperature. While the strength of the epoxy system increased at higher post-curing temperatures, the modulus slightly decreased, which is in contrast to most literature studies and interpreted as relaxation effect. Changes in the weight of the specimens were monitored. In contrast to other hydrolytic aging studies on submerged specimens a comparably low amount of moisture absorption of the epoxy was found when aged under realistic conditions and desorption of water of the vinylester was observed, which is an uncommon behavior. The reactivity of cement as a filler material was studied by X-ray diffraction (XRD), revealing inert cement phases even at higher temperatures and the presence of water. The results are discussed and compared to available data from literature.
•In-situ orientation of MWCNT and CNF during a hot curing process of a CFRP.•Remarkable improvement of mechanical and electrical performance.•Applicable procedure towards production of advanced ...functional composites.
A simple route for the in-situ orientation of carbon nanofillers applied during the curing process of a carbon fiber reinforced polymer (CRFP) in a hot press, is demonstrated. Neat MWCNT, amine-functionalized MWCNT (MWCNT-NH2) and CNF were dispersed in an epoxy resin using a three-roll-mill (TRM) to ensure good dispersion. The process leads to a hierarchically structured functional composite where MWCNT/CNF are aligned in the z-direction (out-of-plane) of the carbon fiber plies, giving rise to improved mechanical and electrical performance. Our results demonstrate that aligned carbon nanofillers yield significantly more pronounced improvements than non-oriented fillers. An applicable processing route towards advanced functional composite materials with major practical importance is presented in this study.
Most organisms consist of a functionally adaptive assemblage of hard and soft tissues. Despite the obvious advantages of reinforcing soft protoplasm with a hard scaffold, such composites can lead to ...tremendous mechanical stresses where the two meet. Although little is known about how nature relieves these stresses, it is generally agreed that fundamental insights about molecular adaptation at hard/soft interfaces could profoundly influence how we think about biomaterials. Based on two noncellular tissues, mussel byssus and polychaete jaws, recent studies suggest that one natural strategy to minimize interfacial stresses between adjoining stiff and soft tissue appears to be the creation of a “fuzzy” boundary, which avoids abrupt changes in mechanical properties. Instead there is a gradual mechanical change that accompanies the transcendence from stiff to soft and vice versa. In byssal threads, the biochemical medium for achieving such a gradual mechanical change involves the elegant use of collagen-based self-assembling block copolymers. There are three distinct diblock copolymer types in which one block is always collagenous, whereas the other can be either elastin-like (soft), amorphous polyglycine (intermediate), or silk-like (stiff). Gradients of these are made by an incrementally titrated expression of the three proteins in secretory cells the titration phenotype of which is linked to their location. Thus, reflecting exactly the composition of each thread, the distal cells secrete primarily the silk− and polyglycine−collagen diblocks, whereas the proximal cells secrete the elastin− and polyglycine−collagen diblocks. Those cells in between exhibit gradations of collagens with silk or elastin blocks. Spontaneous self-assembly appears to be by pH triggered metal binding by histidine (HIS)-rich sequences at both the amino and carboxy termini of the diblocks. In the polychaete jaws, HIS-rich sequences are expanded into a major block domain. Histidine predominates at over 20 mol % near the distal tip and diminishes to about 5 mol % near the proximal base. The abundance of histidine is directly correlated to transition metal content (Zn or Cu) as well as hardness determined by nanoindentation. EXAFS analyses of the jaws indicate that transition metals such as Zn are directly bound to histidine ligands and may serve as cross-linkers.
An electrochemical synthesis strategy for the production of nanostructured films was developed by combining self-assembly of surfactant−inorganic aggregates at solid−liquid interfaces and an ...electrodeposition process. Through this approach high quality nanostructured ZnO films were cathodically deposited from a plating solution containing 0.1 wt % of sodium dodecyl sulfate (SDS). The resulting ZnO films possess lamellar structures with two different repeat distances, d 001 = 31.7 Å and d 001* = 27.5 Å, both of which feature well-defined long range order. Due to kinetically controlled surfactant−inorganic assembly during the deposition process, the film exhibits a wide distribution of the stacking directions of the ZnO layers, which will allow facile access of the guest molecules and analytes to the interlayers. The synthetic mechanism used here can be generalized to generate nanostructured films of other semiconducting and metallic materials with architectures that cannot be assembled by other means.
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