A mechanical and chemical model of intervertebral disk (IVD) degeneration was developed by examining the enzymatic degradation of the nucleus pulposus (NP), and a gelatin-based restoration study was performed.
It was hypothesized that forced enzymatic degradation of the NP will mimic natural degeneration through the loss of disk height and that an injection of a gelatin solution will restore mechanical function.
Collagen and proteoglycans are essential for normal NP function. Their chemical destruction, combined with light mechanical loading, will mimic degeneration. Previous studies have determined that collagenase and matrix metalloproteinase-3 are directly implicated in IVD degradation; therefore, these enzymes were used in this model.
On the basis of preliminary testing, 0.5% collagenase, 1% collagenase, and 0.0025% metalloproteinase-3 in phosphate-buffered saline (PBS) were injected directly into the NP of various motion segments from a young bovine lumbar spine and subjected to light cyclic loading. To restore disk height and mechanical function, 20% gelatin in PBS at 70°C was injected into a degraded disk and subjected to the same loading conditions after an allotted hardening time.
Mechanical testing showed statistically significant changes in disk height between control segments, 1% collagenase, and 0.5% collagenase. 0.5% collagenase had the most accurate appearance and loading pattern of degeneration upon disk transection postloading. A trend in restoration of disk function, given by the lessened loss of disk height upon loading, was observed with injection of gelatin after degradation with 0.5% collagenase.
This study demonstrated the potential to create a degenerative model using enzymatic degradation of the NP and the possibility to restore function with an injectable therapy. Although gelatin is not a clinically viable option, it provides preliminary data for other injectable IVD therapies.
Department of Biomedical Engineering, Parks College of Engineering, Aviation, and Technology, Saint Louis University, Saint Louis, MO
The authors declare no conflict of interest.
Reprints: John Gary Bledsoe, PhD, Biomedical Engineering Building, 3507 Lindell Boulevard, Saint Louis 63103, MO (e-mail: firstname.lastname@example.org).
Received October 4, 2013
Accepted January 24, 2014