Hydrogels for the Replacment of Spinal Discs

Hydrogels for the Replacement of Spinal Discs

Wyatt Self, Marissa Thierheimer, Allison Lind, Gabby Fief, and Skip Rochefort

Polymer Laboratory, School of Chemical, Biological, and Environmental Engineering

Oregon State University

Corvallis, OR 97331

Every year millions of people experience back pain. Back pain can be caused from a variety of sources, such as thinning, herniated, ruptured and compressed discs. The purpose of this project was to determine a suitable replacement for damaged spinal discs that could be injected directly into the spine.  Current procedures are invasive and often leave the patient with pain or limited mobility. Finding a hydrogel which could be injected directly into the spine to replace the damaged nucleus pulposus would result in a less costly and possibly more effective solution. In order to evaluate a hydrogels potential for use in the spine two types of testing were performed. The first test was a dynamic oscillatory frequency test which changes the frequency at which a gel sample was being twisted while the amount it is twisted remains constant. An AR2000ex rheometer is used to complete this test. The second test was completed using a Bose ELF 3200. This test compressed the gel by lowering a plate onto the gel at a constant rate. The purpose of the frequency testing was to determine the viscous and elastic properties of the gel; compression testing finds the strain and stress that a gel can withstand. Based on the results of these tests, as well as qualitative findings, such as how the gel broke, we could determine which gels would be suitable for replacing spinal discs. In order to make these gel discs, powdered gel was added to 90°C water. When all added powdered was dissolved into the water, the liquid was injected into a mold and allowed to solidify. Each gel was 25 mm in diameter and approximately 5 mm thick to mimic the size of an adult spinal disc. Four different polymers were used to form these gels, including, Agarose, Kelcogel F, Kelcogel LT100 and Gelzan CM. To begin understanding the various properties of these gels, each gel was tested as the sole component of the hydrogel, using different weight percents to observe differences at lower and higher percentages. After running these pure samples it was determined that each gel had very unique properties that could be combined to improve the quality of a hydrogel. Agarose displayed a solid structure but was very brittle and handled compression poorly. Kelcogel F didn’t display any positive properties as it was soft and broke easily however, it could be added to Agarose to slightly improve Agarose’s brittle nature. Kelcogel LT100 was very different than the other gels mentioned. This gel was very elastic and would stretch greatly before breaking or tearing; unfortunately it wasn’t very structured and would slowly stop returning to its original shape. Gelzan CM proved that it had potential to be the only polymer in a hydrogel why still producing acceptable results. . It had a very high compression value and was much more resilient to tearing than the first two gels mentioned. With knowledge of these characteristics it was possible to begin testing combinations of multiple polymers. Gelzan wasn’t available when testing first began resulting in lower compression values during the first two weeks of testing. After several tests, it was determined that total weight percents should be between 2.75 and 3.5%; less than this range caused the gel to lack structure and fall apart easily however, higher than this range caused the hydrogel to become ridged, lacking flexibility. Combinations consisting of Gelzan CM and LT100 proved to be the most effective, offering extremely high breaking points and sufficiently high percent strain values at breaking. To further this research, dynamic compression testing would be beneficial to more closely compare hydrogels qualities to the stresses that a spine undergoes daily. Testing the properties of other hydrogels could also lead to advancements in this research.