Abstract
Optical tweezers (OT) have been widely applied in various fields ever since Arthur Ashkin successfully pioneered the optical trapping process with laser beam in the 1970s. OT can be utilized to trap and manipulate single or multiple particles, as well as to investigate the mechanical properties of complex fluids through microrheological approach. Collagen is a natural biomaterial; its biological properties can help prevent scarring during all stages of wound healing process in soft tissues. However, collagen products have to go through sterilization in the processing steps, which can cause structural damage of collagen, and in turns, undermine its bioactive and functional properties. In this paper, optical tweezers are used to study the viscoelasticity of collagen under UV-254 nm irradiation, and to gauge the damaging level of sterilization on collagen. In the experiment, we first test the Kramers-Kroning procedure using distilled water as Newtonian fluid. Next, 2-μm polystyrene beads are placed in the collagen solution at a polymeric concentration of 0.3 mg/ml. Then, OT are employed to trap and measure the viscoelastic moduli of the collagen polymeric solutions under UV-254 nm irradiation. Our results indicated that all solutions exhibit viscoelastic behavior. However, different exposure time of UV contributes to the variation in viscous and elastic responses. The viscoelasticity of the collagen goes down as the dosage of UV irradiation rises. Collagen’s elastic modulus and the viscosity decrease about 7 and 5 times, respectively, by sterilization process. We combined optical tweezers and microrheological technique to measure the viscoelastic properties of collagen solutions. This combination enabled us to extend the range of frequencies and reduced the cost of samples. In the experiment, the viscoelasticity of collagen was measured after a series of irradiations as the sterilization process. We suggested that collagen exposured to UV irradiation may lead to breakage of chemical bonds, thus compromised viscoelasticity and clotting ability. This study concluded the downward viscoelasticity of collagen by UV irradiation in sterilization process. Our results can be used on cosmetology and arthritis rehabilitation.