At Penn State, engineers and chemists have crossed a threshold in regenerative medicine — teaching living cells, arranged in precise three-dimensional patterns, to rebuild what the body can no longer repair on its own. By programming stem cells with genetic switches that guide them toward either bone formation or blood vessel growth, the team has created printed scaffolds that address one of tissue engineering's oldest dilemmas: bone cannot survive without the vascular network to feed it. Tested in mice, the approach restored 93 percent of damaged tissue where the body alone managed only 35 pe