Rheological measurement of biological fluids by a portable differential dynamic microscopy-based device

Elementary function of fluids in being able to flow and deform continuously is an important field of study variously known as rheology. Understanding of such characteristics provides benefits for not only being able to control and understand fluid dynamics following an exposure to force. In a simple fluid, a shear stress exposed on a small fluid element causes the fluid to deform. The rate of the deformation that is proportional to the shear stress is referred to as Newtonian fluid. This rheological response reflects the intrinsic structure of the fluid from internal friction amongst the fluid. Unlike simple fluid, mechanical responses of many biological fluids are more complex due to their heterogeneity in structure. In addition, these mechanical behaviours are often relevant to the biological functionality of the fluids. For example, human whole blood exhibits a shear-thinning characteristic in which its viscosity decreases according to a progressive rate of change in velocity or shear rate. When the blood is at rest, viscosity dramatically increases due to ongoing coagulation processes to prevent and stop bleeding injuries. Several methodologies have previously been developed and demonstrated in measuring of such rheological characteristics. This thesis exploits the emerging technique of differential dynamic microscopy (DDM) for quantitative rheological assessment of biological fluids using simple implementation of passive microrheological measurements. Improvements have been carried out to achieve and quantify reliable results. Firstly, time-stamps of every acquiring images associated more accurate dynamic (time-based) information for the typical DDM to analyse. In addition, the use of a near-infrared illumination source allowed human whole blood experiment (overcoming visible light absorbance of the blood.) Finally, the thesis implemented a direct conversion approach to eliminate high frequency artefacts of the obtained viscoelastic moduli from using generalised Stokes-Einstein relation. In order to determine the fluid viscosity the Cox-Merz relationship was adopted. Apart from rheological measurement, the developed device was successfully use to also determine particle size distribution of both colloidal particles and cells from the measurement data, applying a numerical inversion which was a non-negative least square approach

High-Quality Large-Magnification Polymer Lens from Needle Moving Technique and Thermal Assisted Moldless Fabrication Process.

The need of mobile microscope is escalating as well as the demand of high quality optical components in low price. We report here a novel needle moving technique to fabricate milli-size lens together with thermal assist moldless method. Our proposed protocol is able to create a high tensile strength structure of the lens and its base which is beneficial for exploiting in convertinga smart phone to be a digital microscope. We observe that no bubble trapped in a lens when this technique is performed which can overcome a challenge problem found in a typical dropping technique. We demonstrate the symmetry, smoothness and micron-scale resolution of the fabricated structure. This proposed technique is promising to serve as high quality control mass production without any expensive equipment required

A relationship of lens focal length and fabricated temperature.

<p>Measured focal length depends on the surface temperature and the volume of the polymer. Upon temperature increasing, the focal length decreases.</p

A Lens geometry study.

<p>(a) Three-dimensional surface geometry of the fabricating lens, (b) demonstrating symmetry in both x and y axes.</p

A needle moving technique.

<p>Schematic representation of (a) flat base formation using free fall drop of PDMS from a needle with distance Z_b away from a glass slide under thermal assisted at 200°C for 20 seconds, and (b) lens fabrication with high tensile strength between lens and its base generated by the proposed moving needle technique.</p

An infrared photo of lens formation.

<p>(a) Heat transfer from the hot surface into the polymer during 8 seconds of the lens formation, obtained by heating the surface at 180°C, and 20 μl of polymer droplet. Numerical simulation of heat transfer using shows temperature distribution at (b) 0, (c) 2, and (d) 8 seconds during lens formation.</p

A high tensile lens created by different needle position.

<p>(a) The needle moving technique with the depth h inside the polymer droplet creates a lens which has the radius R₂ and height H, whereas the typical dropping technique gives a lens with smaller radius R₁. (b) Experimental data shows that the ratio R₂to R₁ depends mainly on the depth h, when H, R₁ and D are controlled parameters.</p

An image quality testing.

<p>Line profile plots and images of a standard USAF 1951 pattern: (a) group 8–3 and (b) 8–4. The white dash lines indicate the region of obtaining the intensity data.</p

A mobile microscope.

<p>Optical photographs of (a) nauplius larvae and (b) aquatic nematodes taken by (c) an iPhone 4S attached with our PDMS lens with its base on the camera. Photographs of RGB pixels demonstrate field of view of (d) 50x and (e) 100x magnification of our preparing lens.</p