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The colorimetric method is usually used to test the concentration of substances. However, this method has a big error since different people have different sensitivities to colors. In this paper, in order to solve the identification problem of the color and the concentration of the test paper, firstly, we found out that the concentration of substance is correlated with the color reading by using the Pearson's Chi-squared test method. And by the concentration coefficient of Pearson correlation analysis, the concentration of substance and color reading is highly correlated. Secondly, according to the RGB value of the paper image, the color moments of the image are calculated as the characteristics of the image, and the Levenberg–Marquardt (LM) neural network is established to classify the concentration of the substance. The accuracy of the training set model is 94.5%, and the accuracy of the test set model is 87.5%. The model precision is high, and the model has stronger generalization ability. Therefore, according to the RGB value of the test paper image, it is effective to establish the LM neural network model to identify the substance concentration. [ABSTRACT FROM AUTHOR]

Introduction: Extracellular vesicles (EV) derived from progenitor cells are a novel therapy for ischemic cardiomyopathy, with promise for "off-the-shelf" delivery. Clinical translation and timely delivery post-myocardial infarction (MI) requires assurance of EV stability after storage. Bioactivity studies of EVs after freezing are currently lacking and are necessary to establish quality standards for widespread clinical use of EVs. Hypothesis: We hypothesize that endothelial progenitor cell-derived EVs (EPC-EVs) can be frozen at -80 °C for at least 2 months without decrement of therapeutic effect when delivered intramyocardially to ischemic tissue. Methods: EVs were isolated from male Wistar rat bone marrow EPCs. Fresh preparations of EVs isolated from 700,000 EPCs were compared to frozen EVs stored in dPBS for 2-4 months at -80 °C. Particle size of EVs was analyzed via nanoparticle tracking analysis. In vitro angiogenesis was measured with Matrigel assay. A rat model of MI via left anterior descending artery ligation was used to assess EPC-EV function. Hemodynamics, scar thickness and vasculogenesis were assessed 4 weeks post-intramyocardial injection of EPC-EV within a shear-thinning gel (STG). Results: After 4 months' storage at -80 °C, frozen EVs had stable mean particle diameter. In vivo analysis demonstrated equivalent hemodynamic outcomes between fresh and 2-month frozen EVs (p=1.0), both of which had statistically significantly improved measures of contractility over PBS as measured by Ees (p=0.0001; p=0.0008) and dp/dt (p=0.01; p=0.03, respectively). Scar thickness was increased in fresh, but not frozen EVs vs PBS (0.68, 0.64 v 0.50; p=0.031, p=0.22). On IHC, fresh and frozen EVs had significantly increased vascular density vs PBS (Δ665.5, Δ907.5; p=0.05). Conclusions: EPC-EVs retain adequate functionality after 2 months of freezing to produce hemodynamic benefits equivalent to freshly prepared EPC-EVs when delivered in STG to ischemic myocardium. [ABSTRACT FROM AUTHOR]