Experimental samples can be a bit of a logistical nightmare to get back from space, currently they have to hitch a ride on a returning cargo or crew craft, but this only happens at regular intervals a few times a year. On top of this, every ounce of space is generally already taken up. This causes a problem for time sensitive experimental samples that can't wait to get back to earth.
Intuitive Machines have designed a Terrestrial Return Vehicle, to return experimental samples and other time sensitive supplies back to earth. It's scheduled to fly in 2016
Source (Intuitive Machines)