Abstract
Athur Ashkin first performed the trapping of particles by optical pressure nearly 40 years ago. Since then, single gradient optical tweezers have been developed and broadly applied in fields of biology and physics. In an aging society, health care and cosmetics are now a rapidly growing industry. Collagen is one of the most abundant proteins in the human body, and is a main building material in tissue engineering and for other biomaterials. Similar to most proteins, collagen is sensitive to high thermal conditions, denaturing at about 40 °C. This research applies a self-assembled optical trapping system, modified with a piezo-stage for nanometer resolutions, to measure the thermal denaturing effect on the viscosity of collagen Type I. Calibration of the voltage-displacement coefficient was completed by two methods and compared. Rat tail collagen Type I was diluted with various buffers and additives, collagen samples are then heated to target temperatures before cooling down to room temperature (27 °C) for measurement. Viscosities of collagen samples were then determined by measuring the thermal motion of polystyrene microspheres (d = 1.78 μm) immersed within the samples. The measurement of viscosity is not real time, therefore different heating rates and incubation times were applied, but both results had minor effect on the denaturation temperature. Our results indicate that collagen Type I has best thermal resistance at neutral pH 6, a slight delay of denaturation temperature of ? 1 °C is discovered. As the pH of collagen samples approach neutral, the aggregation of collagen fibrils causes the viscosity to increase significantly, restricting the thermal motion of the microsphere. This result makes it impossible to measure viscosity at pH 7, but the addition of glucose inhibits collagen aggregation, and the denaturation temperature is measured to have a ? 2 °C increase when compared to pH 6. The addition of glycerol in acidic environments can also raise the denaturation temperature up to 3 °C. In this research, pH environments and additives are compared to conclude the best conditions for the protection of collagen Type I against thermal denaturation.