微磁性粒子於彷生工程應用研究

Abstract

由於磁性粒子在微機電系統(MEMS)及生物醫學之領域具有潛在應用價值，於 近年來旋轉磁場下之操控機制及力學探討，已有廣泛的研究。而粒子串在擺動 磁場下之研究，亦可很簡易地的應用到微機電系統或生物晶片等領域。其中一 項具體之應用為在微小的流道中加上外加磁場，粒子因此受磁化作用而串接成 鏈條狀，若粒子受到外加的擺動磁場時，液體中的粒子串也回隨著磁場的方向 改變而進行擺動的運動型態。此類簡易型微粒子串比起利用DNA 串接磁性粒 子串具有更簡易製作、成本低廉且粒子重覆使用性之優點。 此類利用磁場操控之微粒子串，可被用於進行多種類之仿生機構或生物醫學相關 研究，除較廣為人知之微游泳器外，亦可應用於仿生磁感細菌（magnetotactic bacteria 或簡稱 MTB）及人造微纖毛(Cilia)。磁感細菌為生活在水中以及水底爛泥 裡之微生物，這些細菌體內有一串約大小在35~120 奈米之磁性晶體形成的鏈狀構 造，構成了一微型羅盤，以做為運動時定位方向之用，磁感細菌於1975 年為論文 報導以來，即廣受生物界研究，包含以生物及生態觀點之研究、生醫應用研究以及 工程應用研究。另一方面，纖毛(Cilia)為附著於微生物或組織表面之似微毛髮般之 微細結構，其直徑約為1 微米，長度則介於5 至50 微米間。纖毛之拍動可提供微 生物或組織推動力與攫取所須養份。人造仿生微纖毛研究除其對生物組織之價值 外，亦具有於Lab-on-a-chip 系統中做為致動器與混合器之應用。 本研究計畫預計以3 年期時程，應用前期之[磁性粒子操控之力學探討與於微奈米 系統之應用]計畫發展成果，進行更深入及廣泛之探討。研究目的為應用所謂智慧 型之磁性粒子串結構，施以外加動態磁場加以操控，針對3 大類型之生物組織(游 泳生物、磁感細菌及纖毛)進行仿生運動研究。同時為有效瞭解粒子運動過程及串 接型態受磁牽引力、流體阻力之影響，將改良前期之校簡單之模擬方式，套用進階 商用軟體Fluent 之流固偶合(Fluid-Solid Interaction, FSI)模組，加以使用者定義功 能(User Defined Function, UDF)，進行流固偶合流場模擬，以期可提供詳盡之阻力 分佈與仿生運動體之可能型變狀態，達到有效操控仿生運動體所須之必要資訊。

Micrometer-sized magnetic beads contained in magneto-rheological (MR) suspension are applicable to reversible devices in micro-electro-mechanical-systems (MEMS) or Lap-on-a Chip. The beads could form chains under the influences of an external field. The particle chains can then be manipulated in various ways by properly adjusting the field distributions. These controllable particle chains possess great potentials for applications in nano-micro-systems, such as mixers, valves, pumps etc. In addition, if the motions of the chains can be well controlled similar to the oscillations of a fish body or fin, the chains can be driven just as a micro-swimmer. In addition, the micro-magnetic particle chains can also be manipulated to mimic the motion of magnetotactic bacteria and cilia. Nevertheless, to achieve above applications in bionics, well understandings to the formation of chains and the mechanisms acting on them are essential. The goals of the present proposed 3-year project are to study, both experimentally and numerically, the manipulations of micrometer-sized superparamagnetic bead chains and their applications to in bionics, such as the artificial micro-swimmer, artificial magnetotactic bacteria and artificial magnetic cilia. In the first year, the efforts will mainly be devoted on artificial micro-swimmers regarding their better swimming efficiency as well as the understandings of steering techniques. In addition, numerical simulations incorporated with fluid-solid interaction model between the oscillating chain and the surrounding flow will also be conducted to give better understandings of the forces acting on the swimmers. The knowledge obtained from the numerical simulations will be applied to optimize manipulations of the swimmer, including their propulsive efficiency and steering control. Artificial magnetotactic bacteria will be the subject of study in the second year. A fundamental research in the interfacial dynamics of the magnetic bead driven by an external field against the interface between the carrier fluid of artificial magnetotactic bacteria surrounding fluid will be started first, followed by a practical condition of the motion of artificial magnetotactic bacteria in surrounding fluid. In the final year, focus will be shifted to artificial magnetic cilia. The flow field and induced force by the beating of cilia will be investigated thoroughly both by experiments and simulations. The results will provide important information to sustain a stable chaining structure to effectively manipulate the artificial cilia.