RESUMO
Understanding metal-to-insulator phase transitions in solids has been a keystone not only for discovering novel physical phenomena in condensed matter physics but also for achieving scientific breakthroughs in materials science. In this work, we demonstrate that the transport properties (i.e., resistivity and transition temperature) in the metal-to-insulator transitions of perovskite nickelates are tunable via the epitaxial heterojunctions of LaNiO3 and NdNiO3 thin films. A mismatch in the oxygen coordination environment and interfacial octahedral coupling at the oxide heterointerface allows us to realize an exotic phase that is unattainable in the parent compound. With oxygen vacancy formation for strain accommodation, the topmost LaNiO3 layer in LaNiO3/NdNiO3 bilayer thin films is structurally engineered and it electrically undergoes a metal-to-insulator transition that does not appear in metallic LaNiO3. Modification of the NdNiO3 template layer thickness provides an additional knob for tailoring the tilting angles of corner-connected NiO6 octahedra and the linked transport characteristics further. Our approaches can be harnessed to tune physical properties in complex oxides and to realize exotic physical phenomena through oxide thin-film heterostructuring.
RESUMO
BACKGROUND CONTEXT: Hydroxyapatite (HA) is considered to be useful because of its high affinity for recombinant human bone morphogenetic protein (rhBMP), mechanical resistance to compressive force, and possible reduction of rhBMP dose. PURPOSE: To evaluate the osteoinductivity of Escherichia coli-derived rhBMP-2 and the suitability of porous HA as an rhBMP-2 carrier. STUDY DESIGN: In vivo study using microcomputerized tomography (micro-CT) scanning. PATIENT SAMPLE: Seventy-six New Zealand white male rabbits were randomized into a single control group (n=14) without rhBMP-2 and four experimental groups (10 µg, 50 µg, 200 µg, and 500 µg of rhBMP-2; n=14 in each group). The subjects were divided into 3- and 6-week groups. OUTCOME MEASURES: Outcome was evaluated by radiography, bending test, three-dimensional micro-CT, and histologic examinations. METHODS: Bilateral posterolateral fusion was carried out, and rhBMP-2 (0, 10, 50, 200, 500, 1,000, and 2,000 µg) was implanted into the bilateral transverse processes using HA as a carrier. RESULTS: The fusion rates of the 3-week group were 83.3% for 50 and 200 µg of rhBMP-2 and 100% for 500 µg. The improved fusion rates of the 50 µg or higher groups compared with those of control were statistically significant. The fusion rates of the 6-week group were 75% for 10 µg of rhBMP-2 and 100% for 50 µg or higher. Similarly, the improved fusion rates of the 10 µg or higher groups compared with those of control were statistically significant. Significantly higher percent volumes were observed in the 3-week 200 µg of rhBMP-2 group and 6-week 200 µg of rhBMP-2 group than the 3-week HA group and 6-week HA group, respectively. Trabecular thickness was significantly higher in the 3-week 200 µg of rhBMP-2 group than the 3-week HA group. Histologic analysis of the 10 µg group showed bone tissues within the pores from 3 weeks, and this was observed more vividly in the 50, 200, and 500 µg groups. The 6-week 10 µg and 50 µg of rhBMP-2 groups had lower amounts of new tissue but higher portions of complete bone tissue within the HA specimen, along with higher formation of completely reconstituted bone tissues outside HA. CONCLUSIONS: Injection of 50 µg or more of E. coli-derived rhBMP-2 into a HA carrier induced earlier bone fusion in the intertransverse process of rabbits, which confirms the excellent bone forming ability of E. coli-derived rhBMP-2 and the suitability of HA as a carrier of rhBMP-2.
