AMC

AMC

The aging micromechanisms of alumina matrix composite (AMC) used in total hip arthroplasty.[Pubmed:28215505]

J Orthop Sci. 2017 May;22(3):524-530.

BACKGROUND: The aim of the present study is to simulate and better understand the long-term interplay between alumina matrix composite (AMC) femoral head and aqueous environment. In particular, we focused on clarifying the role of alumina grains on zirconia phase stability and mechanical equilibrium in AMC head during aging processes in a clinically-relevant time frame. METHODS: The tested AMC head consists of an alumina matrix (82 vol.%) reinforced by yttria-stabilized zirconia (17 vol.%), chromium oxide (0.5 vol.%), and strontium aluminate (0.5 vol.%). The accelerated hydrothermal aging testing (at 134 degrees C, 2-bars pressure) was conducted up to 20 h. According to ASTM standard, 1-h aging under these conditions corresponds approximately to 2 yrs in vivo exposure. Confocal Raman and fluorescence spectroscopy were applied to quantify surface tetragonal-to-monoclinic phase transformation of zirconia and surface stresses in the AMC head. The Mehl-Avrami-Johnson (MAJ) theory was applied, which allowed modeling the micromechanisms of nucleation and growth of monoclinic sites during the transformation process. The obtained results were compared to those of monolithic zirconia (3Y-TZP) femoral heads. RESULTS: The 3Y-TZP head showed a rapid increase of transformation rate beyond the aging time of 5 h (simulated as approximately 10 yrs in vivo), suggesting the initiation of the transformation cascade toward the neighboring zirconia grains (growth mechanism). On the other hand, MAJ analysis revealed that the growth mechanism was completely absent and the nucleation of the monoclinic phase was partially prevented in the AMC head even after the 20-h aging ( approximately 40 yrs in vivo). In addition, the stress accumulation in the AMC head was restricted at a quite low level throughout the aging simulation. CONCLUSION: Those results suggest that the presence of stable and hard alumina in the AMC can play a considerable role in slowing down the destabilization processes by spatially encompassing zirconia grains.

Theoretical study of actinide monocarbides (ThC, UC, PuC, and AmC).[Pubmed:28049300]

J Chem Phys. 2016 Dec 28;145(24):244310.

A study of four representative actinide monocarbides, ThC, UC, PuC, and AMC, has been performed with relativistic quantum chemical calculations. The two applied methods were multireference complete active space second-order perturbation theory (CASPT2) including the Douglas-Kroll-Hess Hamiltonian with all-electron basis sets and density functional theory with the B3LYP exchange-correlation functional in conjunction with relativistic pseudopotentials. Beside the ground electronic states, the excited states up to 17 000 cm(-1) have been determined. The molecular properties explored included the ground-state geometries, bonding properties, and the electronic absorption spectra. According to the occupation of the bonding orbitals, the calculated electronic states were classified into three groups, each leading to a characteristic bond distance range for the equilibrium geometry. The ground states of ThC, UC, and PuC have two doubly occupied pi orbitals resulting in short bond distances between 1.8 and 2.0 A, whereas the ground state of AMC has significant occupation of the antibonding orbitals, causing a bond distance of 2.15 A.

EZH2 is overexpressed in laryngeal squamous cell carcinoma and enhances the stem-like properties of AMC-HN-8 cells.[Pubmed:27446358]

Oncol Lett. 2016 Aug;12(2):837-846.

The enhancer of zeste 2 polycomb repressive complex 2 subunit (EZH2) histone methyltransferase is the catalytic subunit of polycomb repressive complex 2 (PRC2), which is important for epigenetic regulation. EZH2 is highly expressed in various types of tumors, and its high-level expression promotes the progression and invasion of certain tumors. However, the expression level of EZH2 and its functions in laryngeal squamous cell carcinomas are unknown. In the present study, the level of EZH2 expression in laryngeal squamous cell carcinomas was evaluated using immunochemical staining and reverse transcription-quantitative polymerase chain reaction. EZH2 was overexpressed in AMC-HN-8 cells with lentiviral transfection. Cell proliferation, apoptosis, cell-cycle, chemotherapy-sensitivity and in vivo tumorigenic assays were performed. The results indicated that EZH2 was highly expressed in laryngeal squamous cell carcinomas. Additionally, EZH2 overexpression promoted proliferation, accelerated cell-cycle progression and enhanced the tumorigenicity in laryngeal squamous cancer cells. More importantly, EZH2 enhanced the chemotherapy resistance of these cells. Overall, the results indicated that EZH2 promotes the progression of laryngeal squamous cell cancer and could be a potential chemotherapeutic target for the treatment of such cancer.