| Improvements to bone fusion employing biologically active and mechanically stable scaffolds remain a challenge. More specifically, current procedures for spinal fusion involve the use of titanium implants coupled with autograft bone harvested from the patient during surgery. While autografting remains the golden standard, it is associated with significant trauma. Common alternatives include cadaveric bone, often limited by available supply, and synthetic graft material for which associated costs are considerable. In each case, the graft material is only suitable as filler and does not manifest biomechanical integrity. As such, grafts are employed within traditional titanium implants for load sustainment. The metallic implants are prone to stress shielding of the contained graft material, thereby limiting fusion and remodeling of the surrounding bone. While 3D printed scaffolds for tissue engineering have been realized, clinical applications in spinal fusion have been limited due to the lack of physiological load sustainment and mismatched mechanical properties between the implant/bone interfaces. The hyperboloid shape of the vertebral body has been examined as an intrinsically optimal load bearing structure, capable of transmitting compressive, bending moment, and torsional forces as purely axial forces. It was hypothesized that through use of hyperbolic geometries, a strut based scaffold can be designed that will enable physiological load sustainment and a suitable biological environment for cellular activity. The novel, surgically sized scaffold was 3D printed from polylactic acid filament. Characterization of the scaffold mechanical integrity through static compression and cyclic fatigue loading profiles validated the strut geometry configuration for physiological load sustainment up to 4900N prior to compressive failure and 5 million loading cycles at 50% scaffold strain. Scaffold bioactivity was supported through cell cultures of human fetal osteoblast and human mesenchymal stem cells. Further, dynamic mechanical stimulation of human mesenchymal stem cell derived osteoblasts increased calcium deposition over a 28 day stimulation period, enhancing the mechanical properties of the scaffold/cell construct despite degradation of the bioresorbable polymer. The demonstration of mechanical integrity and bioactivity of the novel scaffold provides evidence for strut based geometries towards surgical sized implant devices and provides a basis for use of this scaffold as an implant. |
