Muscle and bone from an ink-jet printer

A Pittsburgh-based research team has created and used an innovative ink-jet system to print "bio-ink" patterns that direct muscle-derived stem cells from adult mice to differentiate into both muscle cells and bone cells.

The results, which could revolutionize the design of replacement body tissues, will be presented Sunday, Dec. 10 at the 46th annual meeting of the American Society for Cell Biology in San Diego by Julie (Jadlowiec) Phillippi, a Carnegie Mellon University post-doctoral research fellow supported by the Pittsburgh Tissue Engineering Initiative.

This report is the first describing a system that can pattern the formation of multiple cell types within the same vessel from a single population of adult stem cells. The new preclinical advance in the field of regenerative medicine could one day benefit millions of people whose tissues are damaged from a variety of conditions, including fatal genetic diseases like Duchenne Muscular Dystrophy (DMD), wear and tear associated with aging joints, accidental trauma, and joint deterioration due to autoimmune disorders.

The custom-built ink-jet printer, developed at Carnegie Mellon's Robotics Institute, can deposit and immobilize growth factors in virtually any design, pattern or concentration, laying down patterns on native extracellular matrix-coated slides (such as fibrin). These slides are then placed in culture dishes and topped with muscle-derived stem cells (MDSCs). Based on pattern, dose or factor printed by the ink-jet, the MDSCs can be directed to differentiate down various cell-fate differentiation pathways (e.g. bone- or muscle-like).

"Previously, researchers have been limited to directing stem cells to differentiate toward multiple lineages in separate culture vessels. This is not how the body works: the body is one vessel in which multiple tissues are patterned and formed. The ink-jet printing technology allows us to precisely engineer multiple unique microenvironments by patterning bio-inks that could promote differentiation towards multiple lineages simultaneously," explained Phil Campbell, research professor at Carnegie Mellon's Institute for Complex Engineered Systems.

"Controlling what types of cells differentiate from stem cells and gaining spatial control of stem cell differentiation are important capabilities if researchers are to engineer replacement tissues that might be used in treating disease, trauma or genetic abnormalities," said Lee Weiss, research professor at Carnegie Mellon's Robotics Institute.

"This system provides an unprecedented means to engineer replacement tissues derived from muscle stem cells," said Johnny Huard, professor of orthopedic surgery at the University of Pittsburgh School of Medicine and director of the Stem Cell Research Center at Children's Hospital of UPMC. Huard has long-standing research findings that show how muscle-derived stem cells (MDSCs) from mice can repair muscle in a model for Duchenne Muscular Dystrophy, improve cardiac function following heart failure, and heal large bone and articular cartilage defects.

Weiss and Campbell, along with graduate student Eric Miller, previously demonstrated the use of ink-jet printing to pattern growth factor "bio-inks" to control cell fates. For their current research, they teamed with Phillippi, Huard and biologists of the Stem Cell Research Center at Children's Hospital to gain experience in using growth factors to control differentiation in populations of MDSCs from mice.

The Carnegie Mellon scientists used computer-vision feedback to calibrate how bio-inks were jetted onto their targets with micrometer precision to facilitate subsequent image analysis. They stained the MDSC cultures for cell markers to confirm that muscle and bone-like lineages "lined-up" in register with engineered bio-ink patterns that were initially printed onto the slides with the ink-jet printer.

"Our findings showed that we successfully engineered MDSCs to become subpopulations of muscle or bone-like cells that were patterned using our bio-ink-jet system," said Phillippi. "This experiment represents a key first step in demonstrating the potential of this technology to learn more about not only the basic biology of how multiple cell types are patterned in the body during development, repair and regeneration, but also for translating adult stem cells into real therapies for patients in the future."

The team, along with Alan Waggoner, professor of biological sciences and director of Carnegie Mellon's Molecular Biosensor Imaging Center, is now developing novel biosensors and fluorescent-based techniques to visualize stem cell differentiation in response to the bio-ink patterns.

Because the ink-jet system employs such precision, it could be used one day to co-culture multiple MDSC lineages - including bone, muscle and other cell types - in complex, patterned configurations that could be incorporated directly into specific areas of the body in need of repair of multiple tissue types, according to the investigators.

The Pittsburgh team envisions the ink-jet technology as potentially useful for engineering stem cell-based therapies for repairing defects where multiple tissues are involved, such as joints where bone, tendon, cartilage and muscle interface. Patients afflicted with conditions like osteoarthritis might benefit from these therapies, which incorporate the needs of multiple tissues and may improve post-treatment clinical outcomes.

The long-term promise of this new technology could be the tailoring of tissue-engineered regenerative therapies. In preparation for preclinical studies, the Pittsburgh researchers are combining the versatile ink-jet system with advanced real-time live cell image analysis developed at the Robotics Institute and Molecular Biosensor and Imaging Center to further understand how stem cells differentiate into bone, muscle and other cell types.

Source: Carnegie Mellon University

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