Kristin Wall
Feb 28, 2012

Patented injectable bone polymer heals fractures

Remember that scene in the Harry Potter books where Harry falls off his broom and breaks his arm, and the nurse gives him Skele-gro to heal his breaks? This new patent, assigned to Drexel University, is kind of like that.

These clever scientists are using hydrogel polymer systems to fix bone fractures, and reinforce and resurface bones. J.K. Rowling wasn’t quite so specific in her potion’s chemical processes, but she had the right general idea.

The prior art already teaches options for alleviating pain due to vertebral fracture through use of vertebroplasty and kyphoplasty, which involve inserting balloons into the vertebral space to expand and compress the trabecular bone tissue and create a central cavity within the vertebra. Polymethylmethacrylate (PMMA), an acrylic bone cement, is then injected into the cavity using percutaneous techniques. Sounds simple enough.

This process works to alleviate pain by restoring the mechanical integrity of the vertebral body by stabilizing the trabecular fractures. But it has some drawbacks. The PMMA cement causes increased rigidity of the vertebrae body as compared to surrounding bone tissue, which can lead to stress inconsistencies along the length of the spine. This strength differential has been known to lead to subsequent fractures. Even worse, some patients have suffered pulmonary embolisms leading to cardiac failure, believed to be caused by the PMMA leaching from the injection site into the patient’s body.

Thus, there was an unmet need for an alternative cementing material to PMMA. The scientists at Drexel University met this need by producing an injectable, bioactive material having a compression modulus similar to that of vertebral trabecular bone, and having suitable material-bone interfacial properties. This novel hydrogel comprises poly(N-alkylacrylamide), poly(alkyleneglycol)di-acrylate or methacrylate, a cross-linking agent, a source of calcium ions and water.

This real-life Skele-gro has multiple applications. It may be used to repair vertebral fractures by injecting the hydrogel into the vicinity of the fracture. It may also be used to reinforce vertebral bone structures in patients with a higher risk of fracture, for example those with osteoporosis, trauma, or certain types of cancer. Furthermore, the hydrogel may be used to resurface articulating joints by providing a bearing surface that can bond to the underlying bone tissue, as in a knee joint.

The hydrogel may also be used in conjunction with PMMA to provide reduced stress concentration to the surrounding tissues by providing more of a modulus transition between the PMMA bone cement and the adjacent tissues, as in end plates, intervertebral discs and adjacent vertebrae. Further embodiments envision a mixture of the hydrogel and medicaments, osteoclastic inhibitors (to down-regulate the activity of bone cells that remove bone tissue), pain relievers and chemotherapeutic agents, to name a few. Additional embodiments include inserting imaging materials into the hydrogel, such as radiopacifiers, radiomarkers or radiopaque materials, so that the hydrogel may be visualized after injection.