An interesting article in the April 2018 issue of “The Scientist”. Title:  ‘Spermbots to the Rescue” .  see:  https://www.the-scientist.com/?articles.view/articleNo/52081/title/Researchers-Develop-Sperm-Robot-Hybrids-to-Deliver-Drugs–Assist-Fertilization/

Paper’s discussion is around idea that tiny motorized harnesses might be attached to sperm. Scientists could control where the sperm swim for purposes of IVF, drug delivery, etc.  References of published papers given in article.