Professor Wei Tao, Chinese University of Hong Kong, Dr. Liu Wei: new hydrogel materials characterization methods
Star polyethylene glycol (PEG) hydrogel due to their unique viscoelastic, biocompatible, and hydrophilic, is widely used in biomaterials, tissue engineering and drug delivery and other biomedical applications. Traditionally characterization of the rheological properties of the hydrogel material is typically dependent on the macro rheometer, i.e. the viscosity is detected, the complex modulus and other rheological parameters by measuring the stress-strain response. However, one drawback is that it is difficult to capture fast dynamic gelation kinetics, can not further characterize the structure of colloids anisotropic behavior. 
Recently, Department of Chemistry University of Hong Kong Chinese professor Dr. Wei Taohu Liu Wei proposed A method of characterizing an interface based on the rheological properties of the hydrogel near micron sized magnetic probe method, more Effect of group structure of the cluster of small scale, faster and more accurate to observe early local precision forming PEG hydrogel gelled viscoelastic properties , and drawn in the overlap colloid concentration ([123 ] c *) the two-dimensional anisotropic dynamic map nearby. Using the new method is not only a useful addition to the conventional hydrogel materials rheological characterization means, can be more thoroughly reveal the inner relation between the mechanical properties of materials and topologies soft matter. Work related to \”Probing Sol-Gel Matrices and Dynamics of Star PEG Hydrogels Near Overlap Concentration\” was published in Macromolecules on the Dr. Liu Wei for the paper the first author, Professor Wei Tao, and academician Wu Qi as a co-corresponding author of this article.
Figure 1: new workflow micro rheological characterization methods. a) The independent research group set up multi-level magnetic tweezers and total internal reflection microscopy combined use group 8 for actuating an electromagnetic embodiment of a three-dimensional micrometric superparamagnetic beads, pellets and using the scattering intensity of the evanescent field real nanoscale observation. b) the probe beads in the four-arm PEG hydrogel network perturbation schematic, red and blue, respectively, a partial structure of regions of different degree of crosslinking. c) dynamic tracking the trajectory of the ball and force, displacement and to obtain information through ball and analytical methods differIts viscoelastic properties of the microenvironment.
FIG. 2: PEG hydrogel rheological characterization early gelation process. a) less than the local cluster c * and nearly linear and schematic view of the mesh when c *. b) the degree of crosslinking near the gel point ([epsilon]) and about of time ([tau]) correlation at different concentrations. c) elastic modulus (G \’) and loss modulus (G \”) in the overlap behavior difference c * before and after, reveal the viscoelastic properties of the hydrogel group structure and concentration of the strong dependence of the local cluster 2.d) gel point tg and Gg (defined as G \’and G \”and the time point when the modulus of the cross) concentration dependence of the index, which showed a stronger Gg exponential growth behavior after c *.
Figure 3: accurate positioning during rapid gelling of the gel point and the local anisotropic behavior of colloidal structures near the c *. a) G \’and G. \”obtained during the actual measurement spectrum wherein the top view of the small numerals starting point of each measurement; double exponential in the coordinate system, G\” values of the frequency of the linear fit only defining critical exponent (Δ, G \’~ G \”~ ωΔ) ranges between 0.70-0.78; right side is obtained by using the Hill equation G\’ and G\” at any time of the analog values at different frequencies. b) a more accurate continuous spectrum distribution G \’and G \”values plotted analog can be given the exact value of the critical exponent 0.75.c) colloidal structures anisotropic behavior in the vicinity of the local c * wherein the white arrow the G \’or G \”behavior due to fluctuations in a partial structure resulting from uneven; Also c * compared to longitudinal, visible G\’ and G\” c * performance near the two-dimensional distribution smoother, discloses star PEG the hydrogel is more likely to form a uniform network structure in the overlap concentration