Scientists around the world are investigating whether living cells can be used to print replacement organs and tissues through 3-D printers, according to CNN.

The game changing 3-D printers are currently being used or explored for printing toys and automotive parts to meat and even houses, according to CNN. In medicine, they are already used to print prosthetic limbs and make patient-specific models of body parts that surgeons can use as guides during reconstructive surgery.

3-D printing is an exciting technology that is expected to play a significant role as scientists expand their ability to engineer tissues and organs in the lab, CNN reported.

Before any organ can be engineered, scientists must determine not only what types of cells to use, but how to expand them in the lab and how to keep them alive and viable throughout the engineering process, according to CNN.

Scientists on multiple teams have already demonstrated that lab-built organs can function quite well in patients, CNN reported. Engineered airways, bladders, blood vessels and urine tubes have been successfully implanted.

3-D printers offer the opportunity to very precisely combine cells and materials into the desired shape so the replacement tissue or organ can be designed on a computer using a patient's medical scans, according to CNN.

The printers give the option of using two or more different cell types and placing them exactly where they need to be, something not possible by hand, CNN reported.

3-D printers also have the flexibility of using a variety of biomaterials so that cells can be printed in either gel-like or rigid scaffolds, or printed without scaffolds, according to CNN.

Even when printed structures are made with living cells, they must "incubate" in the body to become fully functional, CNN reported. A major challenge in tissue engineering is to supply these structures with oxygen while they integrate with the body.

"While there are many challenges to solve, I believe the printing of complex organs will become reality, but not for decades," said Dr. Anthony Atala is director of the Wake Forest Institute for Regenerative Medicine in Winston-Salem, North Carolina.