  (light techno music)
 - [Voiceover] This is a
 RepRap, a popular open source
  3D printer in the lab at the
  University of Pennsylvania.
It's being used to print
blood vessel networks
   out of sugar for research
   in regenerative medicine.
  Scientists can
  create small samples
  of organ tissue in the lab.
But before they can
make human sized organs,
  they need a way to keep the
  cells on the inside alive.
 Living organs are
 fed by blood vessels,
 which branch and grow to meet
 cells' nutritional needs.
 Cell biologists can't yet
 grow networks of blood vessels
 in a block of tissue, so
 bioengineers from Penn and MIT
 turned the problem inside out.
  Using the RepRap 3D printer,
  they craft templates
 of blood vessel
 networks out of sugar.
 The printer builds up
 the walls of a mold,
then draws the sugar
across it in filaments.
  When the sugar has hardened,
  the researchers pour
  cells suspended in
  a gel into the mold,
   surrounding the filaments.
   After the gel solidifies,
   the researchers dissolve
 the sugar, which flows
 out of the tissue
through the vessels it created.
 In one experiment,
 the researchers pumped
 nutrient-filled liquid
 through the tissue.
   They found that the cells
   on the inside survived
  and improved their function
  when these networks
 were in place.
  This 3D printing
  method makes it easy
   to experiment with
   different network designs.
It can produce templates
that are stable enough
   to ship to cell biologists
   around the world.
  (light techno music)
