An Investigaton On Measuring Young’s Modulus Of Low-elasticity Polyacrylamide Hydrogels

Mechanical environment of cells plays a crucial role in the regulation of cellular behavior, including cell migration, proliferation, differentiation and morphological adjustment. While many physiological and pathological processes are closely related with these behaviors. Therefore, in order to build a better in vitro cell culture model, not only biochemical factors but also biomechanical factors sholud be taken into consideration. A major drawback of now used cell culture substrates is that: as usually cultured on glass or plastic petri dishes, the stiffness of these substrates are much greater than that in vivo. Thus, reaearch results can not accurately reproduce the effect of biomechanical factors on cell, and causing great deviations between the results in vivo and in vitro. Therefore, it’s crucial to establish substrates with appropriate and controllable mechanical properties.Hydrogels have been widly used as biomedical materials as they exhibit good biocompatible and elastic properties, and their water content are very similar with native tissues, organs and macromolecular compounds in vivo. Meanwhile, the stiffness of hydrogels thatusually characterized as Young’s modulus is highly controllable. There are many kinds of methods measuring the Young’s modulus of hydrogels. However, there isn’t an acknowledged method of measuring Young’s modulus, especially for low elastic modulus hydrogels.In view of this, this paper will discuss several mostly used methods: improved tensile method, compression method and microsphere indentation method. And on the base of traditional methods we made some improvements. Main works of the thesis are as follows: firstly, I put the hydrogels into water instead of air in which way I can use buoyancy to decrease the errors caused by hydrogel self-weight; secondly, I use high-frequency oscillation compression method combined with data processing software Matlab to measure the Young’s modulus; finally, I established a measuring system of microsphere indentation, and improved the traditional formula which displayed great deviation. In this paper, I use polyacrylamide(PA) hydrogel as its stiffness has been well defined. I take the AFM(atomic force microscopy) measurements of Young’s modulus as the reference values. Results show that: comparing to reference values, measurements obtained from improved tensile method are reliable, and the operation method is feasible; when measuring low elasitc hydrogels such as 2 k Pa hydrogels using high frequency oscillation compression method, results show great errors, while the results are reliable when dealing with hydrogel with Young’s modulus more than 3 k Pa; in experimental results of microspheres indentation method, values calculated by traditional Hertz contact formula present great deviation, while the values calculated by the improved formula is much more accurate.