Synthesis and characterization of A Hybrid bio/synthetic biomimetic aggrecan Macromolecule for the treatment of Low Back Pain

Sumona Sarkar1 and Michele S. Marcolongo2

 1 Polymers Division, Material Measurement Laboratory, NIST, Gaithersburg MD 20899
2 Department of Materials Science and Engineering, Drexel University, Philadelphia PA 19104

 

Lower back pain resulting from intervertebral disc degeneration is one of the leading musculoskeletal disorders confronting our health system.  This irreversible process leads to loss of mechanical stability with the potential for disc herniation and nerve damage.  While disc degeneration is poorly understood, it has been shown that aggrecan content of the disc decreases with age and degeneration.  Aggrecan, is a bottle brush proteoglycan with a protein core and radiating negatively charged chondroitin sulfate (CS) bristles which are densely packed in order to impart hydrating and shock absorbing properties to the disc.

 

In order to mechanically stabilize the disc early in the degenerative cascade and prevent the need for invasive and costly surgeries, we investigated the synthesis of a biomimetic aggrecan macromolecule for injection into the disc in the early stages of degeneration. In this biomimetic approach, the protein core is replaced with a synthetic polymeric backbone in order to resist enzymatic degradation while natural CS bristles are maintained in their bottle brush arrangement. 

 

The “grafting-through” technique of bottle brush polymer synthesis was explored via epoxy-amine step-growth polymerization reactions of poly(ethylene glycol) diglycidyl ether with amine terminated CS.  Incorporation of a synthetic polymeric backbone at the terminal amine of CS was confirmed via biochemical assays, 1H-NMR and FTIR spectroscopy, and biomimetic aggrecan size was demonstrated to be higher than that of natural CS via gel permeation chromatography, transmission electron microscopy and viscosity measurements.  Further analysis of biomimetic aggrecan functionality indicated maintenance of natural CS properties such as high fixed charge density, high osmotic potential and low cytotoxicity with nucleus pulposus cells. 

These studies are the first attempt at the incorporation of natural CS into biomimetic bottle brush structures.  Biomimetic aggrecan synthesized via the methods developed in these studies may be utilized in the treatment and prevention of debilitating back pain as well as act as mimetics for other proteoglycans implicated in cartilage, heart valve, and nervous system tissue function.