National Institute for Materials Science, Tsukuba 305-0047, Japan.
Sci Rep. 2011;1:157. doi: 10.1038/srep00157. Epub 2011 Nov 15.
Targeted hyperthermia treatment using magnetic nanoparticles is a promising cancer therapy. However, the mechanisms of heat dissipation in the large alternating magnetic field used during such treatment have not been clarified. In this study, we numerically compared the magnetic loss in rotatable nanoparticles in aqueous media with that of non-rotatable nanoparticles anchored to localised structures. In the former, the relaxation loss in superparamagnetic nanoparticles has a secondary maximum because of slow rotation of the magnetic easy axis of each nanoparticle in the large field in addition to the known primary maximum caused by rapid Néel relaxation. Irradiation of rotatable ferromagnetic nanoparticles with a high-frequency axial field generates structures oriented in a longitudinal or planar direction irrespective of the free energy. Consequently, these dissipative structures significantly affect the conditions for maximum hysteresis loss. These findings shed new light on the design of targeted magnetic hyperthermia treatments.
利用磁性纳米粒子进行靶向热疗是一种很有前途的癌症治疗方法。然而，在这种治疗中使用的大交变磁场中热量耗散的机制还没有得到阐明。在这项研究中，我们通过数值比较了在水介质中可旋转纳米粒子和固定在局部结构上的不可旋转纳米粒子的磁损耗。在前一种情况下，由于每个纳米粒子的磁易轴在大磁场中的缓慢旋转，除了由于快速奈尔弛豫引起的已知的主要最大值之外，超顺磁纳米粒子的弛豫损耗具有二次最大值。用高频轴向场辐照可旋转铁磁纳米粒子会产生纵向或平面方向的取向结构，而与自由能无关。因此，这些耗散结构显著影响了最大磁滞损耗的条件。这些发现为靶向磁热疗的设计提供了新的思路。
