Local joule heating and electric force on biological membrane during electro-microinjection

Significance 

Microinjection technology has extensively revolutionized the way of introducing foreign materials in inaccessible intracellular environments. A good example is its use in cryopreservation of fish eggs where fish eggs and embryos are loaded with cryoprotective agents due to its hard-external shell. Being a key technology for realizing productive and sustainable aquaculture, the need to develop advanced microinjection with enhancing sensing systems and precise force control is highly desirable. Unlike conventional microinjections, recently developed electro-microinjection(2) electrically punctures the rigid eggshell without using a mechanical force. Despite this method having numerous advantages such as being capable of piercing without fatal damages to the eggshell, its mechanism has not been fully explored to allow optimization of piercing parameters and potential configurations. Recently, researchers have identified electric and thermal analysis of fish egg during electro-microinjection as a promising solution.

To this note, scientists from the University of Tokyo: Sikai Wang and Professor Ryo Shirakashi studied the mechanism of electro-microinjection by determining the electric and thermal fields on the biological membrane. To achieve this, electrical and thermal fields were numerically calculated using reliable electric properties of medaka fish egg. The work is published in the International Journal of Heat and Mass Transfer.

Fundamentally, the time domain finite element method model was developed and used for solving unsteady heat transfer equations including Joule heat source and Maxwell’s equations. In this case, the magnetic fields were neglected due to the minimal required pulse strength piercing condition experimentally determined in their past study. Based on the calculation results, the authors evaluated the maximum temperature around the needle electrode tip and electric force to elucidate the electro-microinjection which was then compared to conventional mechanical piercing.

Results indicated that the electro-microinjection may use the local joule heat for reducing the rapture stress of a hard shell and stress focusing near the tip of the needle. For example, in situations where fish eggs are pierced with a long-duration pulse, the local joule heat was noted to play a significant role. The local-temperature is normally extremely high in the region near the tip of the needle electrode. This high temperature denatures the chorion protein thus decreasing its rupture stress which further lowers the minimal pulse strength for piercing. This clearly indicated that the denaturation as a result of the temperature rise should be the main mechanism of electro-microinjection particularly in cases involving long-duration and low-strength pulse piercing.

According to the authors, the Joule heating remains a crucial consideration in the effective designing of devices for electro manipulation and more so the sharp electrodes. Furthermore, the observed phenomena during electro-microinjection may be useful in other manipulations involving tiny regions, short rise in temperature and high local electric force.

In a summary, Professor Ryo Shirakashi in a statement to Advances in Engineering, noted that the proposed numerical model with reliable electric properties in addition to piercing mechanisms is a promising approach for obtaining the electric and temperature fields in biological cells for general electro-microinjection manipulations.

References

Wang, S., & Shirakashi, R. (2019). Local Joule heating and electric force on biological membrane during electro-microinjection. International Journal of Heat and Mass Transfer, 140, 798-806.

Go To International Journal of Heat and Mass Transfer

Shirakashi, R., Yasui, T., Memmel, S. & Sukhorukov, V. L. (2015) Electro-microinjection of fish eggs with an immobile capillary electrode. Biomicrofluidics, 9, 064109.

Go To Biomicrofluidics

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