Penn State Team 3D Prints Bone Tissue That Grows Its Own Blood Vessels

A Penn State team has used genetic switches inside 3D-printed cell clusters to produce bone tissue that grows its own blood vessel networks, moving regenerative medicine closer to practical implants for severe bone loss.

The researchers, from the departments of biomedical engineering and engineering science and mechanics, introduced two strands of microRNA into stem cells before assembling them into spheroids. Those tiny cell clusters were then printed into hydrogel scaffolds using aspiration-assisted bioprinting, a technique that places each spheroid at a precise location.

The microRNA strands act like on-off switches. miR-148b pushes cells toward bone growth. miR-210 drives vascularization, the formation of new blood vessels. Without blood vessels, thick bone tissue cannot survive. That gap has kept bioprinted implants from moving beyond very small experimental grafts.

How the Scaffold Performed in Mice

The team tested several scaffold designs over six weeks in mice with bone damage. Mice that received no treatment regenerated bone across roughly 35% of the injured area. Mice that received scaffolds with spheroids containing both microRNA strands showed markedly better results, with higher bone density and more complete coverage.

The combination group also showed stronger expression of CD31, a protein found on the inner lining of blood vessels. That signal suggested the engineered spheroids were not just helping bone form, but were actively supporting the micro-vasculature those new bone cells need to survive.

From Lab Curiosity to Clinical Path

The work is not ready for human trials. The team still needs to understand how vascularization and bone growth influence each other over longer periods, and whether mixed spheroid populations cooperate as well in larger animals as they do in mice. But the proof-of-concept is clear: you can pre-program cell clusters with genetic instructions before printing them, and those instructions still function after the scaffold is implanted.

For trauma patients, cancer survivors, and people with severe infections that destroy bone, that distinction matters. Current treatments for large bone defects rely on grafts from the patient's own skeleton, which creates a second surgical site and limits how much bone can be harvested. A bioprinted scaffold that encourages the body to rebuild its own tissue in the exact shape needed would change that calculation entirely.

The study, led by co-corresponding authors Ibrahim Ozbolat and Daniel Hayes, is available in Chemical Engineering Journal. The team plans follow-up work in larger models and is continuing to refine the microRNA combinations and spheroid placement patterns that deliver the most reliable vascularized bone.