That and possible dimensional anchors. If teleporting one end of string, the other end stays intact and it can be pulled through freely like dental floss. Once the string leaves the teleporter, then the teleportation closes. Oddly enough, once a string is in place, no more energy needs to be added to keep it open or close it safely. However, walking into the teleportation field when the string exists on both sides will scramble your atoms on both sides of the teleportation system. Trial by error, unfortunately. More tests are being done to investigate this interesting property.
EDIT:
The properties have been investigated where more than one string is moved within the teleportation field. When experimenting with three or more strings, it has been found that stretching these strings in a shape with more than 3 sides, it keeps the teleportation field open and safe to travel through within this area. Fascinating enough, the scientists looking through one side of the teleporter were able to see the scientists on the other side. When travelling through this field, nothing seems to have changed. Ladies and Gentlemen. Portals have been born.
It is planned to cover the inside of the teleporter frames with Invincium fabric to create a portal to walk through as if the doorway was a simple door to another side of the galaxy~ Oh wait... It is.