Electrical stimulation of sample, we're building understanding

posted Dec 21, 2012, 12:04 PM by Tiberius Brastaviceanu   [ updated Dec 21, 2012, 2:07 PM ]
This week we made some progress at Phil's lab. I remind you that the end goal is to characterize the Mosquito and to obtain some meaningful results on animal muscle samples. The project was scheduled to end on December 02, but we accumulated some delay. I think SENSORICA made a lot of progress during the 6 months time of the project, so the delay does not apply to our overall situation, but other activities got in the way of Phil's project. 
For the characterization experiments, we installed a piezo micromanipulator prototype made by Jonathan and used Tibi's LabView program to drive it. The video below shows the piezo in action during the first trials in Phil's lab. 


Tibi integrated the piezo with the Mosquito program, one running on the NI DAQ and the other one running on the LabJack. This allows script-based automation of characterization experiments. The script language was created and tested.

Ivan mounted the optical fiber-based transducer on the blue micromanipulator and Tibi made some preliminary tests by pushing the  transducer with the piezo under the microscope.  

Piezo stack attatched by Ivan to the blue micromanipulator in Phil's lab

This piezo prototype is still very limited, its range is only approx. 40 microns. Moreover, as you can see in the video above, it takes a long time to relax when the voltage is reduced, which means that motion in both directions cannot be at the same speed. This limits the type of tests we can perform using this particular prototype, to those that are more static in nature, i.e. sensitivity, resolution... Tests like fatigue and time response require back and forth motion of the piezo, and cannot be done with this prototype.

Biological experiments

In parallel, we advanced the biological part of the project. Ivan, Phil, James and Tibi participated in this last effort to understand why our samples could not be electrically activated/stimulated. We performed our experiments with fresh mouse diaphragm muscles. See sample preparation and solutions below.

The picture below shows our initial setup, using the bath designed by
Ivan.

Bath with carbon electrodes

The red arrows in the picture below point to the graphite electrodes used to stimulate the sample. The white blob on top is silver conductive glue, attaching these electrodes to the metallic wire. See more pictures in this album. The sample sits in the middle of the bath, attached to the two hooks sitting inside of the darker circle in the center of the picture.

Graphite electrodes in the bath.

The picture below shows a muscle sample attached to the two hooks, as described above. In this case the carbon electrodes are not in the bath.
Muscle sample in the bath, The bath has temperature control system and electrical stimulation electrods.
 


For the electrical stimulation we used Jame's electronic circuit, driven with a NI DAQ card, and powered by a power supply. Tibi's LabView program (still undocumented) was used to generate the electrical pulse pattern. A max of 17 Volt could be supplied to the sample. This arrangement produced results only once.

The picture below shows the front panel of the LabView program used for the Stimulation, in conjunction with James' electronic circuit.

The Stimulator - a LV program that works with James muscle cell stimulation circuit.


We turned to a second electrical stimulator which could supply up to 40 Volt. This was still not enough to stimulate the sample in the same bath, but worked very well when the sample was placed in the different type of bath with very large surface graphite electrodes. 

James' bath with large carbon electrods

These results eliminated other hypothesis that we have made, related to the sample preparation and chemical solutions. It seams that the orientation and the strength of the electrical field generated between the electrodes is the main factor. We need to increase the surface of our electrodes and/or place them closer to the sample, and make sure that the sample sits well in between the electrodes. The voltage adjustment/optimization is another issue. 

Conclusion

For the characterization tests, we are now ready to start acquiring data for sensitivity and resolution. Dynamic tests must wait for a better piezo system.

For the biological tests we will test different types of electrodes.

Sample preparation

to come...

Solutions

to come...

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