Implode on a nested array

Implode on a nested array

I want to implode every "a_skill" in this array into a string. Usually I
would do implode(", ", $my_array); but this is nested. Is there an easy
way to handle this?
Array
(
[0] => Array
(
[email] => don.pinkus@gmail.com
[a_skill] => test
)
[1] => Array
(
[email] => don.pinkus@gmail.com
[a_skill] => testerrrr
)
)
From PHP's array docs, array_keys looks promising but I can't get it to work.