News Release

Penn researchers develop injectable microtissue to preserve muscle function in rats with severed sciatic nerves

The microtissue “babysits” regenerative pathways and muscle while nerves regrow, and shows promise to improve recovery of sensory and motor function after peripheral nerve injuries

Peer-Reviewed Publication

University of Pennsylvania School of Medicine

TE-NMI In Vitro and Muscle Reinnervation after Delayed Repair

image: A TE-NMI in vitro and reinnervated muscle fiber after delayed nerve repair following TE-NMI excision. view more 

Credit: Penn Medicine

PHILADELPHIA— Researchers engineered the first injectable microtissue containing motor and sensory neurons encased in protective tissue, called tissue engineered neuromuscular interfaces (TE-NMIs). The TE-NMI neurons provide a source of axons to muscles in rats who suffered nerve injuries, and “babysit” the muscles to prevent degeneration and loss of function, while the damaged nerve regrows, according to researchers at the Perelman School of Medicine at the University of Pennsylvania. Their findings were published in Bioactive Materials.

The TE-NMIs are comprised of nerve cells encapsulated in a protective hydrogel, and the entire microenvironment is injected in close proximity to muscles. This “ship in a bottle” method protects the neurons and increases the likelihood that a greater quantity of axons will connect with the muscle and maintain regenerative pathways.

Researchers severed the sciatic nerve in rats, and injected them with either a TE-NMI or a microtissue without any neurons. In the group that received TE-NMIs, researchers were able to electrically stimulate the nerve stump being “babysat” by the TE-NMI and record a muscle response up to five months after the tissue was implanted. No muscle response was detected in the control group.

“There are hundreds of thousands of patients who undergo surgery to repair nerve injuries every year, and even if a surgeon performs a perfect procedure, they can’t make axons regrow faster than about one inch per month. For nerve injuries in the upper arm or upper leg, regeneration could take years; however, the pathway leading to the muscle and the muscle itself will irreparably degenerate after six to 12 months without connections from axons, resulting in permanent loss of motor and sensory function,” said senior author D. Kacy Cullen, PhD, an associate professor of Neurosurgery. “By increasing the time window for a patient’s axons to reconnect to muscle, this research has potential to improve the extent of recovery for patients without causing further damage.”

For example, patients who suffer from a brachial plexus injury – a nerve root avulsion where nerves are pulled away from the spinal cord – may regain elbow function, but will likely never regain function of their hand. In these cases, a neurosurgeon would typically split a healthy nerve near the hand, and reroute it to stimulate the hand muscles to restore partial function while the nerve regrows. TE-NMIs would potentially do a more thorough job, without having to damage a patient’s healthy nerve, researchers suggest.

“Working closely with clinicians at Penn’s Nerve Center, we identified a potential surgical paradigm that would be most helpful to them and their patients,” said first author Justin Burrell, PhD, a postdoctoral research fellow in the Department of Neurosurgery and the Institute for Translational Medicine and Therapeutics. “What’s more, as we continue to test and reaffirm our findings, we will continue our partnership with the Nerve Center to ensure that our research is providing them with the technology they need to provide the best possible care for patients.”

This study was primarily supported by the U.S. Department of Defense (W81XWH-16-1-0796, W81XWH-19-1-0867), the National Institutes of Health (R44-NS108869, TL1-TR001880), and the Department of Veteran Affairs (I01-BX003748).

Editor’s Note: Dr. Cullen is a co-founder of Axonova Medical, LLC, and Innervace, Inc., which are both University of Pennsylvania (Penn) spinout companies focused on the translation of advanced regenerative therapies to treat nervous system disorders. Dr. Cullen’s laboratory at Penn receives sponsored research funding from Axonova Medical.  Penn and Dr. Cullen each own equity interests in both companies, have received license-related financial consideration and may receive additional financial consideration in the future related to the licensing of certain Penn intellectual property to these companies.



Penn Medicine is one of the world’s leading academic medical centers, dedicated to the related missions of medical education, biomedical research, and excellence in patient care. Penn Medicine consists of the Raymond and Ruth Perelman School of Medicine at the University of Pennsylvania (founded in 1765 as the nation’s first medical school) and the University of Pennsylvania Health System, which together form a $9.9 billion enterprise.

The Perelman School of Medicine has been ranked among the top medical schools in the United States for more than 20 years, according to U.S. News & World Report's survey of research-oriented medical schools. The School is consistently among the nation's top recipients of funding from the National Institutes of Health, with $546 million awarded in the 2021 fiscal year.

The University of Pennsylvania Health System’s patient care facilities include: the Hospital of the University of Pennsylvania and Penn Presbyterian Medical Center—which are recognized as one of the nation’s top “Honor Roll” hospitals by U.S. News & World Report—Chester County Hospital; Lancaster General Health; Penn Medicine Princeton Health; and Pennsylvania Hospital, the nation’s first hospital, founded in 1751. Additional facilities and enterprises include Good Shepherd Penn Partners, Penn Medicine at Home, Lancaster Behavioral Health Hospital, and Princeton House Behavioral Health, among others.

Penn Medicine is powered by a talented and dedicated workforce of more than 52,000 people. The organization also has alliances with top community health systems across both Southeastern Pennsylvania and Southern New Jersey, creating more options for patients no matter where they live.

Penn Medicine is committed to improving lives and health through a variety of community-based programs and activities. In fiscal year 2021, Penn Medicine provided more than $619 million to benefit our community.

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