Magnetic nanoparticles are widely applied in biochemical applications due to their diverse functionalization and fast response to external magnetic fields. However, when actuated by magnetic fields, magnetic nanoparticles have a natural tendency to form clusters due to the induced magnetic attractive forces. In this study, we propose a strategy to controllably disassemble and spread magnetic nanoparticle clusters on uneven surfaces using dynamic magnetic fields. Magnetic nanoparticle clusters are disassembled into short nanoparticle chains, and the lengths of chains are controlled by adjusting the field parameters. To prevent reassembly, the separation distance between chains are enlarged by exploiting magnetic chain-chain repulsive forces, resulting in an increased coverage area of nanoparticles. Additionally, the induced tumbling motion of nanoparticles chains enables them to further spread on patterned surfaces. We demonstrate that the proposed disassembly and spreading strategy is effective on an uneven surface of organ ex vivo (bladder of swine). The disassembled nanoparticles are capable of regathering again, and this spreading-regathering process can be monitored using ultrasound imaging in real time. Our strategy shows great potential for increasing reproducibility and effectiveness of magnetic nanoparticle-based applications which requires high surface-to-volume ratio, and provides support to fundamentally understand collective behavior at the small scales.

磁性纳米粒子由于其多样化的功能性和对外部磁场的快速响应而被广泛应用于生化应用。然而，当通过磁场致动时，由于诱导的磁性吸引力，磁性纳米粒子具有形成簇的自然趋势。在这项研究中，我们提出了使用动态磁场可控地在不平坦表面上可控制地分解和散布磁性纳米粒子簇的策略。磁性纳米粒子簇被分解成短的纳米粒子链，并且通过调节场参数来控制链的长度。为了防止重新组装，通过利用磁链-链排斥力来扩大链之间的分离距离，从而增加了纳米颗粒的覆盖面积。此外，纳米粒子链的诱导翻滚运动使它们能够进一步在图案化的表面上扩散。我们证明了拟议的拆卸和散布策略在器官表面不平整上是有效的离体（猪膀胱）。分解后的纳米颗粒能够再次聚集，并且可以使用超声成像实时监测这种扩散-聚集过程。我们的策略显示出提高基于磁性纳米粒子的应用程序的可重复性和有效性的巨大潜力，该应用程序要求高的表面体积比，并为从根本上了解小规模的集体行为提供了支持。