Researchers at the University of Georgia (UGA; Athens, USA), the University of Texas (UT; Austin, USA), Baylor School of Medicine (Houston, TX, USA) and other institutions are working to create a dynamic putty-like material containing stem cells, which--when packed in or around a compound bone fracture--provides full load-bearing capabilities within days, creates an osteoconductive bone-like internal structure, and degrades over time to harmless resorbable by-products as the normal bone regenerates. The "Fracture Putty" could thus rapidly restore a patient to ambulatory function while normal healing ensues, with dramatically reduced rehabilitation time.
The “Fracture Putty” is composed of adenoviral delivery of modified human BMP2 gene (AdBMP2)-transduced stem cells which are microencapsulated within poly(ethylene) glycol diacrylate (PEGDA) hydrogel microspheres. Bone formation is rapid and extensive, and in rat femur fracture models appeared in many cases to be integrated with the skeletal bone as early as two weeks. Upon radiologic and histologic examination, the integrated bone appeared to be well fused to the adjacent skeletal bone, with contiguous cartilage and bone within the defect site.

Further biomechanical analysis showed that the stiffness and strength of the repair bone were even greater than the contralateral control femur, as early as 3 weeks postsurgery. In some cases, the external fixator was removed to confirm that the substantial well-mineralized bone, as determined by X-ray, was able to support weight bearing and normal daily activity. In these experiments, the rats were able to ambulate normally, and no apparent additional fractures occurred in the callus region. The study was presented at the annual meeting of the American Society for Bone and mineral Research (ASBMR), held during September 2011 in San Diego (CA, USA).

“Complex fractures are a major cause of amputation of limbs for US military men and women,” said study coauthor Steven Stice, PhD, director of the UGA Regenerative Bioscience Center, who is helping to develop the adult stem cells that will rapidly form bone. “For many young soldiers, their mental health becomes a real issue when they are confined to a bed for three to six months after an injury; this discovery may allow them to be up and moving as fast as days afterward.”

“The small-animal work has progressed, and we are making good progress in large animals,” added study coauthor John Peroni, PhD, an associate professor of large animal surgery in the UGA College of Veterinary Medicine. “The next step is to show that we can rapidly and consistently heal fractures in a large animal, then to convert it to clinical cases in the UGA [veterinary] clinics where clinicians treat animals with complex fractures all the time.”

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