The asymmetric giant magnetoimpedance (GMI) profile has been realized in weak-field-annealed Co-based amorphous ribbon at the annealing temperature of 380 °C in open air. Asymmetric GMI profiles with respect to applied field become profound as the annealing field increases over 500 mOe. The asymmetric GMI profile at the frequencies of ac current over 0.5 MHz is well ascribed for by the rotational transverse magnetization of single domain under a uniaxial anisotropy in amorphous core and a unidirectional anisotropy due to the exchange coupling with the bias field in the crystalline layer, underlying surface oxidation layer developed during the annealing in open air.
In a Comment [D. X. Chen, L. Pascual, and A. Hernando, Appl. Phys. Lett. 77, 1727 (2000)] on our recent letter [C. G. Kim, K. J. Jang, D. Y. Kim, and S. S. Yoon, Appl. Phys. Lett. 75, 2114 (1999); 76, 1345 (2000)] Chen et al. claimed that the unidirectional anisotropy due to bias field is unphysical one for the description of asymmetric giant magnetoimpedance (GMI) profiles. The symmetric two peaks of GMI profiles measured in the normal sample with an uniaxial anisotropy, allow one to take the minimum energy condition which assumes a jump of magnetization under the field from a metastable state to a stable one. However, the divergence in a calculated GMI profile should appear even in case of a uniaxial anisotropy of normal sample where there is no jump. Divergence indicates the asymmetry and hysteresis in GMI profile. The analysis of this calculation in Chen et al.’s Comment is simply a matter of hysteresis in GMI profile for the increasing and decreasing field, even in a normal sample with uniaxial anisotropy. Even though the hysteresis is ignored by taking the minimum energy condition, the asymmetric profiles with the negligible hysteresis are well ascribed by the model with two kinds of anisotropy fields, as proposed in our previous letter [C. G. Kim, K. J. Jang, D. Y. Kim, and S. S. Yoon, Appl. Phys. Lett. 75, 2114 (1999); 76, 1345 (2000)]. In this model the bias field is quite physical, and is based on the observed experimental results in a specially prepared sample.
Many attempts have been made to reduce complications of bone implant, such as pedicle screw loosening. To address this problem, the authors suggest a new concept of boneto-bone biologic fixation using recombinant human bone morphogenetic protein-2 (rhBMP-2)-loaded cannulated pedicle screws. Recombinant human bone morphogenetic protein-2 is an osteoinductive cytokine. Four types of titanium pedicle screws were tested (uncannulated, cannulated with no loading, beta-tricalcium phosphate (TCP)-loaded, and TCP/BMP2 loaded) using 16 miniature pigs. Radiological evaluation was conducted to assess the fusion and loosening of pedicle screws. Twelve weeks after implantation, peak torsional extraction torque was measured, and the pedicle screw and bone interface was evaluated by micro-computed tomography (µCT) and histologic examination. The mean value of the radiological score was significantly greater in the TCP/BMP2 loaded group at 12 weeks post-operation compared to those in the other groups. CT images showed distinct bone formation surrounding TCP/BMP2 loaded cannulated pedicle screws compared to the other groups. Mean extraction torsional peak torque at 12 weeks postoperative was more than 10-fold higher in the TCP/BMP2 loaded pedicle screw group than in the other groups. Bone surface and bone volume, as quantitated through µCT, were higher in the TCP/BMP2 loaded group. Histologic examination revealed bone-to-bone fixation at the interface of pedicle screws and pre-existing bone. Bone-to-bone biologic fixation through the holes of TCP/BMP2 loaded pedicle screws significantly increased fixation strength and represents a novel method that can be applied to osteoporotic or tumour spine surgeries.
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