(187j) Radiopaque Composite Pin for Fixation of Fractures

Orthopedic Fixation Devices such as screws, plates and pins are essential for stabilizing fractured bone fragments and providing structural support during healing. While traditional metallic devices have been widely used, they present notable drawbacks such as stress shielding, the need for revision surgery, and growth inhibition in pediatric patients. These limitations have driven the development of resorbable orthopedic implants, which degrade naturally in the body, eliminating the need for surgical removal and minimizing long-term complications. A critical limitation of most current resorbable implants—particularly those based on polylactic acid (PLA)—is their lack of radiopacity.

Radiopacity is vital for accurate intraoperative placement and postoperative monitoring, enabling surgeons to visualize the implant position clearly under imaging. The absence of radiographic visibility can lead to improper implant placement, migration, and other complications, ultimately affecting treatment outcomes. Therefore, developing mechanically robust and radiopaque resorbable fixation devices is essential for improving the precision and safety of orthopedic interventions.

Bone pins, a type of Orthopedic fixation device, are widely employed for the fixation of small bone fragments and must exhibit adequate mechanical strength, biocompatibility, and surface grip. Commercially available resorbable bone pins are primarily fabricated from polylactic acid (PLA), which suffers from poor radiopacity and limited mechanical strength for load-bearing applications such as femoral fracture fixation. To overcome these shortcomings, this study investigates PLA-based composites enhanced with a radiopaque salt (S, 0–15 wt%) and a bioactive ceramic (C, 0–15 wt%) to improve both radiographic visibility and mechanical performance. The composites (PLA/S/C) were melt-mixed using a twin-screw extruder and fabricated into cylindrical pins of 3mm diameter with a tapered tip to facilitate suitable insertion.

Mechanical testing demonstrated that the PLA/S/C composites exhibited a notable enhancement in mechanical performance, with the bending modulus increasing from 4000 MPa for neat PLA to 6000 MPa in the optimized formulation, along with a corresponding improvement in bending strength. Radiographic analysis done by digital X-Ray demonstrated that the composite pins displayed radiopacity comparable to commercially used metallic implants, ensuring enhanced intraoperative and postoperative visibility. In-vitro cytocompatibility, evaluated using the MTT assay with SaOS-2 osteosarcoma cells, indicated that PLA/15%S/15%C composites supported the highest cell viability, confirming their non-cytotoxic nature. Furthermore, Alizarin Red staining showed enhanced biomineralization of the optimized composite, indicating improved osteointegration due to the incorporation of bioactive fillers.

Thus, a composite radiopaque pin was developed, which has significantly improved mechanical properties and biocompatibility with Osteosarcoma cells compared to PLA pins. Future work involves investigating in vitro degradation behavior and conducting in vivo studies to assess biological performance in an appropriate animal model.

References

1. Emonde, Crystal Kayaro, Max-Enno Eggers, Marcel Wichmann, Christof Hurschler, Max Ettinger, and Berend Denkena. 2024. “Radiopacity Enhancements in Polymeric Implant Biomaterials: A Comprehensive Literature Review.” ACS Biomaterials Science & Engineering 10(3): 1323–34. doi:1021/acsbiomaterials.3c01667
2. Park, J., Kim, B. J., Hwang, J. Y., Yoon, Y. W., Cho, H. S., Kim, D. H., Lee, J. K., & Yoon, S. Y. (2018). In-VitroMechanical Performance Study of Biodegradable Polylactic Acid/Hydroxyapatite Nanocomposites for Fixation Medical Devices. Journal of nanoscience and nanotechnology, 18(2), 837–841. https://doi.org/10.1166/jnn.2018.14884