Development of Biomedical Dynamometer for Measurement of Grip Strength in Mice Modeled with Cerebral Palsy

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This research aimed to develop a biomedical dynamometer capable of measuring the grip strength of the forepaws of laboratory mices to verify the posterior phase, the effect of modeled cerebral palsy in the animal. The equipment was developed using a stainless steel blade, two double strain gages, a signal conditioning circuit that was connected to a software for acquisition, processing and plotting of graphs and tables in Excel. The metal blade has a length of 18.5 cm, a width of 1.5 cm and a thickness of 2 mm and a double strain gage model pa-09-125ha-350-l8 from Excel Sensors (Brazil), was glued to each face. The two double strain gages were connected in a Wheatstone bridge, which produces an analog response due to mechanical deformation of the blade, with force applied by the mice. This response was submitted to a signal conditioning circuit developed with Arduino that modulated the input wave, generated 10000 times amplification and performed filtering 4th order using Butterworth filter. Finally, a software developed in Labview 2019 of National Instruments (USA) was used for acquisition, processing and plotting of graphs and tables in Excel of the measurements performed. In the next step, the dynamometer was calibrated for sequential loading of masses of 0, 15.48 g, 31.53 g, 46.88 g to 62.47 g and also for sequential unloading of the same masses. For this, the masses were hung on a nylon string that was attached to the free end of the metal sheet. The final test was to measure the response time of the dynamometer with a stopwatch, when hanging a mass of 62.47 g on the nylon thread that was cut abruptly with scissors. Some of the main results of the calibration were as follows: 15.48 g generated 3.70 V, 31.53 g generated 7.48 V and 62.47 g gene rated 14.80 V and the response time was 0.3 s. These answers show that the dynamometer can be used to measure the grip strength of mice and can be modified for use in humans.