Chin Fhong Soon

Development of a novel liquid crystal based cell traction force transducer system.

Keratinocyte traction forces play a crucial role in wound healing. The aim of this study was to develop a novel cell traction force (CTF) transducer system based on cholesteryl ester liquid crystals (LC). Keratinocytes cultured on LC induced linear and isolated deformation lines in the LC surface. As suggested by the fluorescence staining, the deformation lines appeared to correlate with the forces generated by the contraction of circumferential actin filaments which were transmitted to the LC surface via the focal adhesions. Due to the linear viscoelastic behavior of the LC, Hookes equation was used to quantify the CTFs by associating Youngs modulus of LC to the cell induced stresses and biaxial strain in forming the LC deformation. Youngs modulus of the LC was profiled by using spherical indentation and determined at approximately 87.1±17.2kPa. A new technique involving cytochalasin-B treatment was used to disrupt the intracellular force generating actin fibers, and consequently the biaxial strain in the LC induced by the cells was determined. Due to the improved sensitivity and spatial resolution (∼1μm) of the LC based CTF transducer, a wide range of CTFs was determined (10-120nN). These were found to be linearly proportional to the length of the deformations. The linear relationship of CTF-deformations was then applied in a bespoke CTF mapping software to estimate CTFs and to map CTF fields. The generated CTF map highlighted distinct distributions and different magnitude of CTFs were revealed for polarized and non-polarized keratinocytes.

Biophysical characteristics of cells cultured on cholesteryl ester liquid crystals

This study aimed at examining the biophysical characteristics of human derived keratinocytes (HaCaT) cultured on cholesteryl ester liquid crystals (CELC). CELC was previously shown to improve sensitivity in sensing cell contractions. Characteristics of the cell integrin expressions and presence of extracellular matrix (ECM) proteins on the liquid crystals were interrogated using various immunocytochemical techniques. The investigation was followed by characterization of the chemical properties of the liquid crystals (LC) after immersion in cell culture media using Fourier transform infrared spectroscopy (FTIR). The surface morphology of cells adhered to the LC was studied using atomic force microscopy (AFM). Consistent with the expressions of the integrins α2, α3 and β1, extracellular matrix proteins (laminin, collagen type IV and fibronectin) were found secreted by the HaCaT onto CELC and these proteins were also secreted by cells cultured on the glass substrates. FTIR analysis of the LC revealed the existence of spectrum assigned to cholesterol and ester moieties that are essential compounds for the metabolizing activities of keratinocytes. The immunostainings indicated that cell adhesion on the LC is mediated by self-secreted ECM proteins. As revealed by the AFM imaging, the constraint in cell membrane spread on the LC leads to the increase in cell surface roughness and thickness of cell membrane. The biophysical expressions of cells on biocompatible CELC suggested that CELC could be a new class of biological relevant material.

Flicking technique for microencapsulation of cells in calcium alginate leading to the microtissue formation.

Microbeads have wide applications in biomedical engineering field that include drug delivery, encapsulation of biomolecules, tissue padding and tissue regeneration. In this paper, we report a simple, yet efficient, flicking technique to produce microcapsules of calcium alginate at a narrow distribution of size. The system consists of an infusion pump and a customised flicker that taps the syringe needle for dispersing microcapsules of sodium alginate that polymerised in the calcium chloride solution. The flow rate of the syringe pump and the velocity of the flicker were studied to achieve a well controlled and tunable size distribution of microbeads ranging from 200 to 400 μm. At a flow rate of 4 μl/min and flicking rate of 80 rpm, a narrow size distribution of microbeads were produced. Via this technique, HaCaT cells were encapsulated in calcium alginate microbeads that grown into microtissues with a size ranging from 100 to 300 μm after two weeks of culture. These microtissues could be potentially useful for pharmacological application.

A scaffoldless technique for self-generation of three-dimensional keratinospheroids on liquid crystal surfaces.

We describe a new scaffold-free three-dimensional (3D) cell culture model using cholesteryl ester based lyotropic liquid crystal (LC) substrates. Keratinocytes were deposited randomly on the LC surface where they self-assembled into 3D microtissues or keratinospheroids. The cell density required to form spheroids was optimized. We investigated cell viability using dead/live cell assays. The adhesion characteristics of cells within the microtissues were determined using histological sectioning and immunofluorescence staining. Fourier transform infrared spectroscopy (FTIR) was used to characterize the biochemistry of the keratinospheroids. We found that both cells and microtissues could migrate on the LC surface. The viability study indicated approximately 80% viability of cells in the microtissues up to 20 days of culture. Strong intercellular adhesion was observed in the stratification of the multi-layered microspheroids using field emission-scanning electron microscopy (FE-SEM) and histochemical staining. The cytoskeleton and vinculins of the cells in the microtissues were expressed diffusely, but the microtissues were enriched with lipids and nucleic acids, which indicates close resemblance to the conditions in vivo. The basic 3D culture model based on LC may be used for cell and microtissue migration studies in response to cytochemical treatment.

Effects of trypsin and cytochalasin-B treatments to cell traction forces

This study aimed at characterizing the responses and cell traction forces of keratinocytes after treated with trypsin and cytochalasin-B using a liquid crystal based cell traction force transducer. The physical restructuring of the cell and the deformation lines induced in the liquid crystal surface were profiled using phase contrast microscopy. The liquid crystal based cell traction force transducer allowed experiments involving the dissolution of the cytoskeleton via cytochalasin-B and trypsinization to identify clear differences in cell responses to the two treatments indicated that the attachment of the cells was mediated by integrins and enforced by actin filaments. This work indicates that the new liquid crystal based sensor can be used to interrogate the kinetic and cytoskeletal responses of cells to the infusion of compounds known to interact with the actin cytoskeleton and adhesion proteins.

Investigation of Cell Adhesion, Contraction and Physical Restructuring on Shear Sensitive Liquid Crystals

In this study, the nature of cell attachment and contraction on the surface of a shear sensitive cholesteryl ester liquid crystal (LC) was examined. This interaction has the potential to be utilized as a novel cell force transducing assay. Preliminary studies indicated that cells cultured on the LC induce deformations in the underlying LC layer. This study aimed at determining if those deformations resulted from the weight of the cell or from forces generated within the cell being transmitted to the LC surface by focal adhesions (FA). In order to study this cell-surface relationship, the forces generated within the cell by the actin cytoskeleton were inhibited by treatment with 30 ?M cytochalasin-B and cell surface attachment via integrins was broken by treatment of cells with, 0.25% Trypsin–EDTA. In the study of the morphology changes of cells and their interfacial interactions within the LC were investigated using fluorescence staining of the actin cytoskeleton and Widefield Surface Plasmon Resonance (WSPR) microscopy. Both cytochalasin-B and trypsin treatments caused deformations in the shear sensitive LC surface to decrease and disappear. This indicates that the deformations in the LC were induced by forces generated in the actin cytoskeleton being transmitted to the LC surface via FA. Fluorescent staining of the actin cytoskeleton and immunofluorescent vinculin staining indicated that cells cultured on the soft LC substrate developed a diffuse actin cytoskeleton and vinculin staining revealed FA around the periphery of the cells. These finding were confirmed by WSPR microscopy which indicated that cell surface attachments formed around the periphery of cells grown on the liquid crystals.

Tracking Traction Force Changes of Single Cells on the Liquid Crystal Surface

Cell migration is a key contributor to wound repair. This study presents findings indicating that the liquid crystal based cell traction force transducer (LCTFT) system can be used in conjunction with a bespoke cell traction force mapping (CTFM) software to monitor cell/surface traction forces from quiescent state in real time. In this study, time-lapse photo microscopy allowed cell induced deformations in liquid crystal coated substrates to be monitored and analyzed. The results indicated that the system could be used to monitor the generation of cell/surface forces in an initially quiescent cell, as it migrated over the culture substrate, via multiple points of contact between the cell and the surface. Future application of this system is the real-time assaying of the pharmacological effects of cytokines on the mechanics of cell migration.

Electrical and optical characteristics of atmospheric pressure plasma needle jet driven by neon trasformer

The atmospheric pressure plasma needle jet driven by double sinusoidal waveform of neon transformer is reported in this paper. The commercial neon transformer produces about 5 kV of peak sinusoidal voltages and 35 kHz of frequency. Argon gas has been used as discharge gas for this system since the discharge was easily developed rather than using helium gas. In addition, argon gas is three times cheaper than helium gas. The electrical property of the argon discharge has been analyzed in details by measuring its voltage, current and power during the discharge process. Interestingly, it has been found that the total power on the inner needle electrode was slightly lower than that of outer electrode. This may be due to the polarization charges that occurred at inner needle electrode. Then, further investigation to understand the discharge properties was carried out using optical emission spectroscopy (OES) analysis. During OES measurements, two positions of plasma discharge are measured by aligning the quartz optical lens and spectrometer fiber. The OH emission intensity was found higher than that of N2 at the plasma orifice. However, OH emission intensity was lower at 1.5 cm distance from orifice which may be due to penning ionization effect. These results and understanding are essential for surface modification and biomedical applications of atmospheric pressure plasma needle jet.

A study on the ergonomic assessment in the workplace

Ergonomics has gained attention and take into consideration by the workers in the different fields of works recently. It has given a huge impact on the workers comfort which directly affects the work efficiency and productivity. The workers have claimed to suffer from the painful postures and injuries in their workplace. Musculoskeletal disorders (MSDs) is the most common problem frequently reported by the workers. This problem occurs due to the lack of knowledge and alertness from the workers to the ergonomic in their surroundings. This paper intends to review the approaches and instruments used by the previous works of the researchers in the evaluation of the ergonomics. The two main assessment methods often used for ergonomic evaluation are Rapid Upper Limb Assessment (RULA) and Rapid Entire Body Assessment (REBA). Popular devices are Inertial Measurement Units (IMU) and Microsoft Kinect.

Hydrophilic property of glass treated by needle plasma jet for surface modification

The application of needle plasma jet using argon gas for surface modification is presented in this paper. The main objective is to modify the surface property of microscope slide glass from hydrophilic surface approximately to superhydrophilic surface. The power supply to the needle plasma jet was set to 400 kV and 1 kHz frequency with highly purity argon (Ar) gas as working gas to generate plasma condition. A copper wire was used as a powered electrode and needle. Water contact angle measurement was used to investigate the surface properties under the different period of treatment and storage time. As a result, we found that the sample of exposure for 300 seconds shows a great result in superhydrophilic surface until 6 hours of storage. This understanding is important in device fabrication application using the glass substrate.