Alongkorn Pimpin

Microelectrostrictive Actuator With Large Out-of-Plane Deformation for Flow-Control Application

We have established methods for the design and fabrication of a novel MEMS actuator for flow control based on the electrostrictive principle. Patterned metal electrodes were employed in order to obtain large out-of-plane deformation. A series of finite-element method (FEM) analyses of the electrical and strain fields was performed in order to optimize the design parameters. The maximum deformation for 2-mm-diameter actuators reaches 112 mum, which is 5.6% of the actuator diameter and six times larger than that of the plain metal-electrode actuator. The elastic energy density reaches 29% of the stored electrostatic energy. The power consumption at the driving frequency of 100 Hz is estimated to be on the order of 100 muW. The present electrostrictive actuator has a fast response, and its operating frequency is up to several kilohertz. A synthetic jet issuing from a 0.4-mm orifice is successfully developed using the present electrostrictive actuator, and this demonstrates the viability of the present actuator in active flow control.

The development of malaria diagnostic techniques: a review of the approaches with focus on dielectrophoretic and magnetophoretic methods

The large number of deaths caused by malaria each year has increased interest in the development of effective malaria diagnoses. At the early-stage of infection, patients show non-specific symptoms or are asymptomatic, which makes it difficult for clinical diagnosis, especially in non-endemic areas. Alternative diagnostic methods that are timely and effective are required to identify infections, particularly in field settings. This article reviews conventional malaria diagnostic methods together with recently developed techniques for both malaria detection and infected erythrocyte separation. Although many alternative techniques have recently been proposed and studied, dielectrophoretic and magnetophoretic approaches are among the promising new techniques due to their high specificity for malaria parasite-infected red blood cells. The two approaches are discussed in detail, including their principles, types, applications and limitations. In addition, other recently developed techniques, such as cell deformability and morphology, are also overviewed in this article.

Fabrication and characterization of novel microneedles made of a polystyrene solution

Nowadays, microneedles are attracting a lot of attention because microneedles can deliver drugs, vaccines and hormones into the body without pain unlike conventional hypodermic needles. Furthermore, microneedles are safe for self-injection and disposal. This work aims to develop novel microneedles made of a solution of polystyrene (PS) in toluene. The mechanical properties of the fabricated PS microneedles were characterized in failure strength test and skin penetration test. According to the experimental results, a PS microneedle could withstand a large force up to 1.0 N without fracturing. Owing to the superior mechanical strength, the PS microneedles could penetrate the skin without any deterioration making them a promising alternative for commercial applications.

Investigation of Optimal Silk Film Thickness in Silk Microneedle Fabrication

Injection is one of the most commonly used methods for delivering drugs or vaccines into human bodies. It is rapid, low-cost and compatible with almost any drugs. However, the major drawbacks of the injection by hypodermic needles are the pain associated with the injection and the disposal of used needles. Microneedles have then received wide attention since they can overcome such drawbacks, especially dissolving microneedles. Recently, silk fibroin has been used to fabricate dissolving silk microneedles for transdermal drug delivery at low temperature. In the fabrication process, the quality of the silk microneedles relies on the solidification of silk fibroin solution. This research aims to study the role of silk fibroin concentration (silk film thickness) in the formation of silk microneedles. In the experiment, silk microneedles were fabricated using various concentrations of silk fibroin solution from 3 to 7% while the volume of the silk fibroin solution was fixed. According to the experimental resuls, it was found that the concentrations of 4-5% were suitable for producing silk microneedles (silk film thickness of 470 μm) while the concentrations of 6-7% caused wrinkles on microneedle patch due to mismatch of upper and lower layers of microneedles. Furthermore, the concentration of 3% had a problem with the demolding step of microneedles since it caused mold damage due to strong adhesion force between microneedles and mold.

Design, Fabrication and Evaluation of a Novel Electro Thermal Micro-Gripper for Handling of Head Gimbal Assembly

A development of a novel electro thermal micro-gripper for handling of Head Gimbal Assembly (HGA) is an ultimate goal of this study. The scope of this study covers a design, fabrication and performance evaluation of the electro thermal micro-gripper. ANSYS software was used to examine the magnitude of tip displacement, exerting force and induced stress to investigate the mechanism’s viability for handling of HGA. Electroplating of nickel was employed to construct the micro-gripper’s mechanisms with three different sizes, and their displacement and exerting force were then examined. From the experiments, each mechanism deflected between 100 to 220 μm while the exerting force was over 200 mN at 25 oC above room temperature. Therefore, the results suggested that the new electro thermal micro-grippers are viable for the HGA handling application.

Two-Step Electroplating Process in Fabrication of Thermal Bimorph Cantilever Actuator for Flow Control Application

This work proposes a novel and simple fabrication process of a nickel-copper thermal bimorph actuator. This new fabrication process employs only two-step electroplating technique that is easy, cheap and compatible for various materials. In this study, the total thickness of fabricated cantilever actuator is around 80 μm, i.e. 30±10 and 50±10 μm for nickel and copper, respectively, and its length is equal to 22.5 mm. For actuator’s width, it is varied as 258±7, 351±7 and 447±7 μm. After heating by applying current through the actuator’s structure, the actuator bends up due to the elongation mismatch between copper and nickel elements. It is found that the deflection becomes larger for a narrower actuator. From the experiments, the deflection at current of 2.5A for 258±7 μm wide actuator is approximately equal to 4 mm. In addition, the response of all actuators is faster than 1 Hz. With obtained large deflection and fast response, the fabricated actuators are viable to employ for flow control applications.

A novel patterning method for three-dimensional paper-based devices by using inkjet-printed water mask

Paper-based devices are continuing to grow rapidly. However, conventional paper patterning methods are mostly restricted to the fabrication of two-dimensional (2D) patterns. Here, we present a novel patterning method for the fabrication of 2D and 3D paper-based devices. For the first time, a 3D fluidic channel network with multiple crossings of fluidic channels is successfully fabricated on a layer of paper without sophisticated procedures. The proposed method utilizes a commercially available inkjet printer to print water pattern as a protective mask onto both sides of a paper substrate and followed by soaking the sample into a non-polar solution which contains a hydrophobic substance to form hydrophobic barriers on the paper substrate. The printed water mask helps preventing the adsorption of the non-polar solution into the printed water area resulting in the formation of hydrophobic and hydrophilic areas. This opens up a new route towards the development of 2D and 3D paper-based devices using low-cost equipment and a variety of materials.

The Viability of Single Cancer Cells after Exposure to Hydrodynamic Shear Stresses in a Spiral Microchannel: A Canine Cutaneous Mast Cell Tumor Model

Our laboratory has the fundamental responsibility to study cancer stem cells (CSC) in various models of human and animal neoplasms. However, the major impediments that spike our accomplishment are the lack of universal biomarkers and cellular heterogeneity. To cope with these restrictions, we have tried to apply the concept of single cell analysis, which has hitherto been recommended throughout the world as an imperative solution pack for resolving such dilemmas. Accordingly, our first step was to utilize a predesigned spiral microchannel fabricated by our laboratory to perform size-based single cell separation using mast cell tumor (MCT) cells as a model. However, the impact of hydrodynamic shear stresses (HSS) on mechanical cell injury and viability in a spiral microchannel has not been fully investigated so far. Intuitively, our computational fluid dynamics (CFD) simulation has strongly revealed the formations of fluid shear stress (FSS) and extensional fluid stress (EFS) in the sorting system. The panel of biomedical assays has also disclosed cell degeneration and necrosis in the model. Therefore, we have herein reported the combinatorically detrimental effect of FSS and EFS on the viability of MCT cells after sorting in our spiral microchannel, with discussion on the possibly pathogenic mechanisms of HSS-induced cell injury in the study model.

Development of Simple-Structure Magnetic Membrane Actuator for Synthetic Jet Application

In this work, a magnetic membrane actuator that involves simple fabrication process and low cost is developed based on electroplating technique, and its dynamic performance is examined. The magnetic actuator consists of an element of soft ferromagnetic material embedded in PDMS circular membrane. It is driven by attracting the soft ferromagnetic element using external magnet that is attached on a shaft of electrical motor. When the shaft is rotated, the magnet will move back and forth towards the membrane. In this study, the nickel element as a soft ferromagnetic material is designed as a simple circular disk with four straight arms, and it is fabricated into three different thicknesses, i.e. 49±3, 70±7 and 100±6 μm, while PDMS thickness is fixed at 280±33 µm. The dynamic performances of 2-cm membrane actuators are examined using a capacitive sensor in the actuating frequency range of 40-240 Hz. The experimental results show that there are two motion patterns, i.e. small and strong oscillations, where the transition frequency is approximately at 100 Hz. In addition, with the increment of nickel element’s thickness, gain and peak frequency, where gain peaks occur, increase while peak-to-peak amplitude decreases.