Biomimetic functionalized graphene for biodegradable bone implants

Abstract

Event Abstract Back to Event Biomimetic functionalized graphene for biodegradable bone implants Anne Arnold1*, Brian Holt1, Zoe Wright1 and Stefanie Sydlik1 1 Carnegie Mellon University, Chemistry, United States Introduction: Bone, like other tissues in the body, is constantly being remodeled[1], making it well equipped to heal minor injuries even into adulthood. However, bone’s regenerative ability diminishes when defects occur above a critical size, resulting in nonunion[2],[3] that can lead to severe pain and loss of function[4],[5]. Currently, autologous tissue transplantation or implantation of prosthetic devices are used as a therapeutic treatment for large defect areas; yet, both methods pose significant health issues for the patient[6]-[8]. Tissue engineering has been attempting to address the challenges associated with current bone replacement therapies, but a material that matches the unique mechanical properties and biochemical milieu of bone that is also biocompatible has yet to be realized[9]. Considering this, our laboratory’s goal is to use the principles of molecular design to generate a material that mimics the chemical, biological, and mechanical properties of native bone to create a biodegradable bone implant for the treatment of large defects. Using graphene oxide (GO) as a scaffold, polyphosphate functionalities that mimic the hydroxyapatite component of bone can be polymerized onto the basal plane of GO via modified Arbuzov chemistry (Figure 1)[10]. In addition, the chemistry to control the identity of the counter ion in the resulting phosphate graphene (PG) has generated an exciting new class of materials that exhibit similar mechanical properties to that of bone, making the materials an ideal candidate for a novel, biodegradable bone implant. Materials and Methods: GO was synthesized from graphite powder using a modified Hummer’s method. PG was synthesized with Arbuzov chemistry: GO was dissolved in an excess of triethyl phosphite with a Lewis Acid catalyst and metal bromide salt (Li, Ca, Mg, K, or Na). The reaction was refluxed at 160°C for 72 hours and then filtered and washed. The powder product was further processed via mold casting at 200°C and 10,000 PSI for 1 minute to form 3.86x1.5 mm pellets. Results and Discussion: Characterization of PG via FTIR spectroscopy, TGA, and XPS (Figure 2) indicated the presence of polyphosphate functionalities on graphene oxide. The FTIR stretch at 1080 cm-1 is indicative of phosphate moieties and the disappearance of the hydroxyl peak of GO at 3400 cm-1 further validates a reduction of the starting material. TGA also displayed a 15-25% degradation by mass percent of the materials at 310-340°C, a degradation peak not observed in GO, while XPS confirmed the presence of covalently attached phosphate groups. Lastly, dynamic mechanical analysis (DMA) of the processed material demonstrated PG’s viscoelastic compression properties were similar to that of bone (Figure 3). Interestingly, the identity of the counter ion seems to effect the mechanical behavior of the material; however, calcium PG was the most optimal material in terms of mechanical behavior, which is advantageous since calcium is present in large quantities in native bone. Conclusion: Considering the success of the Arbuzov chemistry on GO and the promising mechanical and cytocompatibility results of the material, PG could serve as an alternative material for bone implants, generating a biodegradable therapeutic rather than a permanent implant fixture. Further inclusion of biological moieties that promote osteogenesis could be included due to the controllable surface chemistry of GO.