Viral methods are just more efficient and give you a higher viability in the end. Electroporation works but you'll have a low yield of viable cells after. Here's a nice paper looking at the effects of buffer composition on cell viability/transfection efficiency: with the general take away being, if electroporation is working well enough to transfect the cells, it will also kill a fair percentage as well.

Hek cells in particular are pretty easy to transfect through viral methods for stable integration of your plasmid or Fugene/lipofectamine for transient expression.

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