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Design and operation of magnetophoretic systems at microscale: Device and particle approaches

Chong WH, Leong SS, Lim J

Electrophoresis, 2021 11;42(21-22):2303-2328.
PMID: 34213767 DOI: 10.1002/elps.202100081

Combining both device and particle designs are the essential concepts to be considered in magnetophoretic system development. Researcher efforts are often dedicated to only one of these design aspects and neglecting the interplay between them. Herein, to bring out importance of the idea of integration between device and particle, we reviewed the working principle of magnetophoretic system (includes both device and particle design concepts). Since, the magnetophoretic force is influenced by both field gradient and magnetization volume, hence, accurate prediction of the magnetophoretic force is relying on the availability of information on both parameters. In device design, we focus on the different strategies used to create localized high-field gradient. For particle design, we emphasize on the scaling between hydrodynamic size and magnetization volume. Moreover, we also briefly discussed the importance of magnetoshape anisotropy related to particle design aspect of magnetophoretic systems. Next, we illustrated the need for integration between device and particle design using microscale applications of magnetophoretic systems, include magnetic tweezers and microfluidic systems, as our working example. On the basis of our discussion, we highlighted several promising examples of microscale magnetophoretic systems which greatly utilized the interplay between device and particle design. Further, we concluded the review with several factors that possibly resulted in the lack of research efforts related to device and particle design integration.
Exploring the Impact of Surface Functionalization on the Reaction, Magnetophoretic, and Collective Transport Behavior of Nanoscale Zerovalent Iron

Ng WM, Chong WH, Abdullah AZ, Lim J

Langmuir, 2023 Dec 05;39(48):17270-17285.
PMID: 37976676 DOI: 10.1021/acs.langmuir.3c02358

This study provides a systematic analysis of the transport and magnetophoretic behavior of nanoscale zerovalent iron (nZVI) particles, both bare and surface functionalized by poly(ethylene glycol) (PEG) and carboxymethyl cellulose (CMC), after undergoing a chemical reaction. Here, a simple and well-investigated chemical reaction of methyl orange (MO) degradation by nZVI was used as a model reaction system, and the sand column transport and low-gradient magnetophoretic profiles of the nanoparticles were measured before and after the reaction. The results were compared over time and analyzed in the context of extended Derjaguin-Landau-Verwey-Overbeek (DLVO) theory to understand the particle interactions involved. The colloidal stability of both bare and functionalized nZVI particles was enhanced after the reaction due to the consumption of metallic Fe content, resulting in a significant drop in their magnetic properties. As a result, they exhibited improved mobility across the sand column and a slower magnetophoretic collection rate compared to the unreacted particles. Here, the colloidal filtration theory (CFT) was employed to analyze the transport behavior of nZVI particles across the packed sand column. It has been observed that the surface properties of the reacted functionalized particles changed, possibly due to the entrapment of degraded products within the polymer adlayer. Moreover, quartz crystal microbalance with dissipation (QCM-D) measurements were performed to reveal the viscoelastic contribution of the adlayer formed by both bare and functionalized nZVI particles after the reaction on influencing their transport behavior across the sand column. Finally, we proposed the implementation of a high-gradient magnetic trap (HGMT) to reduce the transport distance of the colloidally stable CMC-nZVI, both before and after the reaction. This study sheds light on the behavioral changes of iron nanoparticles after the reaction and highlights environmental concerns regarding the presence of reacted nanoparticles.
Navigating the microenvironment with flip and turn under quadrupole magnetophoretic steering control: Nanosphere- and nanorod-coated microbead

Chong WH, Chan DJC, Liu CZ, Lim J

Electrophoresis, 2024 Mar;45(5-6):357-368.
PMID: 38044267 DOI: 10.1002/elps.202300042

The spatiotemporal accuracy of microscale magnetophoresis has improved significantly over the course of several decades of development. However, most of the studies so far were using magnetic microbead composed of nanosphere particle for magnetophoretic actuation purpose. Here, we developed an in-house method for magnetic sample analysis called quadrupole magnetic steering control (QMSC). QMSC was used to study the magnetophoretic behavior of polystyrene microbeads decorated with iron oxide nanospheres-coated polystyrene microbeads (IONSs-PS) and iron oxide nanorods-coated polystyrene microbeads (IONRs-PS) under the influence of a quadrupole low field gradient. During a 4-s QMSC experiment, the IONSs-PS and IONRs-PS were navigated to perform 180° flip and 90° turn formations, and their kinematic results (2 s before and 2 s after the flip/turn) were measured and compared. The results showed that the IONRs-PS suffered from significant kinematic disproportion, translating a highly uneven amount of kinetic energy from the same magnitude of magnetic control. Combining the kinematic analysis, transmission electron microscopy micrographs, and vibrating sample magnetometry measurements, it was found that the IONRs-PS experienced higher fluid drag force and had lower consistency than the IONSs-PS due to its extensive open fractal nanorod structure on the bead surface and uneven magnetization, which was attributed to its ferrimagnetic nature.
Low-Gradient Magnetophoresis of Nanospheres and Nanorods through a Single Layer of Paper

Law JKC, Ng WM, Chong WH, Li Q, Zhang L, Khoerunnisa F, et al.

Langmuir, 2023 Apr 11;39(14):4904-4916.
PMID: 36992604 DOI: 10.1021/acs.langmuir.2c03164

The possible magnetophoretic migration of iron oxide nanoparticles through the cellulosic matrix within a single layer of paper is challenging with its underlying mechanism remained unclear. Even with the recent advancements of theoretical understanding on magnetophoresis, mainly driven by cooperative and hydrodynamics phenomena, the contributions of these two mechanisms on possible penetration of magnetic nanoparticles through cellulosic matrix of paper have yet been proven. Here, by using iron oxide nanoparticles (IONPs), both nanospheres and nanorods, we have investigated the migration kinetics of these nanoparticles through grade 4 Whatman filter paper with a particle retention of 20-25 μm. By performing droplet tracking experiments, the real-time stained area growth of the particle droplet on the filter paper, under the influences of a grade N40 NdFeB magnet, were recorded. Our results show that the spatial and temporal expansion of the IONP stain is biased toward the magnet and such an effect is dependent on (i) particle concentration and (ii) particle shape. The kinetics data were first analyzed by treating it as a radial wicking fluid, and later the IONP distribution within the cellulosic matrix was investigated by optical microscopy. The macroscopic flow front velocities of the stained area ranged from 259 μm/s to 16 040 μm/s. Moreover, the microscopic magnetophoretic velocity of nanorod cluster was also successfully measured as ∼214 μm/s. Findings in this work have indirectly revealed the strong influence of cooperative magnetophoresis and the engineering feasibility of paper-based magnetophoretic technology by taking advantage of magnetoshape anisotropy effect of the particles.
The Transport Behavior of a Biflagellated Microswimmer before and after Cargo Loading

Teng XJ, Ng WM, Chong WH, Chan DJC, Mohamud R, Ooi BS, et al.

Langmuir, 2021 08 03;37(30):9192-9201.
PMID: 34255525 DOI: 10.1021/acs.langmuir.1c01345

The changes in the transport behavior of a microswimmer before and after cargo loading are crucial to understanding and control of the motion of a biohybrid microbot. In this work, we show the change in swimming behavior of biflagellated microalgae Chlamydomonas reinhardtii picking up a 4.5 μm polystyrene microbead upon collision. The microswimmer changed from linear forward motion into helical motion upon the attachment of the cargo and swam with a decreased swimming velocity. We revealed the helical motion of the microswimmer upon cargo loading due to suppression of flagella by image analysis of magnified time-lapse images of C. reinhardtii with one microbead attached at the anterior end (between the flagella). Furthered suppression on the flagellum imposed by the loading of the second cargo has led to increased oscillation per displacement traveled and decreased swimming velocity. Moreover, the microswimmer with a microbead attached at the posterior end swam with swimming velocity close to free swimming microalgae and did not exhibit helical swimming behavior. The experimental results and analysis showed that the loading location of the cargo has a great influence over the swimming behavior of the microswimmer. Furthermore, the work balance calculation and mathematical analysis based on Lighthill's model are well consistent with our experimental findings.
The effect of hypoxic ischemic encephalopathy towards multi-organ complications and its early outcome at a Malaysian district hospital

Chong WH, Ong HY, Ooi JS, Eleen Khaw YY, Lim LM, Tew MM, et al.

Med J Malaysia, 2024 Mar;79(2):184-190.
PMID: 38553924

INTRODUCTION: Hypoxic ischemic encephalopathy (HIE) is a clinically defined syndrome of disturbed neurologic function in the newborn with evidence of perinatal asphyxia. Stages of HIE are categorised into mild, moderate or severe based on the Sarnat classification. Neurological dysfunction constitutes a part of the wide spectrum of hypoxic ischemic insult as affected infants can have co-existing multi-organ dysfunction which further contributes to morbidities and mortality. This study aims to determine the relationship between the severity of HIE with multi-organ complications and early clinical outcomes.
MATERIALS AND METHODS: All neonates who were admitted to the NICU at Hospital Sultan Abdul Halim between January 2018 to December 2022, who fulfilled the inclusion criteria were included. Demographic data, clinical course and investigation results were retrospectively obtained from the medical records.
RESULTS: From a total of 90 infants (n = 90) who fulfilled our inclusion criteria, 31 (34%) were mild, 31 (34%) were moderate and 28 (31%) were severe HIE. The mean maternal age was 27 years. Common antenatal issues include diabetes mellitus (37.8%) and anaemia (22.2%). The Apgar scores at 1 and 5 minutes, initial resuscitation requiring intubation, chest compression and adrenaline were associated with higher severity of HIE (p < 0.05). Coagulation dysfunction was the most common complication (79.7%), followed by respiratory dysfunction (33.3%), cardiac dysfunction (28.9%), renal dysfunction (16.1%), haematological dysfunction (15.6%) and hepatic dysfunction (12%). Respiratory and haematological dysfunctions were significantly associated with higher mortality (p < 0.05). There was a significant longer hospital stay (p = 0.023), longer duration of ventilation (p < 0.001) and increase in frequency of seizures (p < 0.001) when comparing moderate and severe HIE patients to mild HIE patients. With increasing severity of HIE, there was also statistically significant higher mortality (p < 0.001).
CONCLUSIONS: There is a significant relationship between multiorgan dysfunction, the severity of HIE and mortality. Early anticipation of multi-organ injury is crucial for optimal early management which would reduce the mortality and improve the neurological outcome of the patients.