Advancements in 3D-Printed Bone Scaffolds and Intramedullary Nail Systems: In Vitro Evaluation and Rabbit Tibia Model Assessment

S. Saleemi, O. Oti, A. Haleem, A.A. Moussa, M. Khandaker
University of Central Oklahoma,
United States

Keywords: long bone defect, bioabsorbable material, 3D printing, implant


Using 3D-printing technology in orthopedic surgery has opened new avenues for developing biodegradable bone scaffolds and intramedullary nail systems. Our study focuses on two specific aims aimed at enhancing the performance and application of these implants. Our first aim was to comprehensively evaluate 3D-printed PCL-HA (Polycaprolactone-Hydroxyapatite) bone scaffolds and intramedullary nail systems in vitro. We conducted a series of assessments to measure biomechanical load sharing, bone marrow stem cell (BMSC) adhesion and proliferation, and biodegradation characteristics. We employed an established polymer casting technique to fabricate intramedullary nails, screws, and bone scaffolds. Our results demonstrated the successful creation of these implants. The PCL-HA scaffold exhibited desirable porosity, facilitating rapid degradation and early weight-bearing capability, surpassing traditional PCL materials. Importantly, the scaffold's porous structure allowed for efficient water infiltration. In vitro absorption and degradation tests confirmed excellent biodegradation profiles, aligning with potential in vivo performance. Mechanical characterization revealed that both PCL and PCL-HA scaffolds exhibited compressive strengths (9.51 ± 0.24 MPa) closely resembling the mechanical properties of cancellous bone (ranging from 1.5 to 12 MPa). We assessed the compatibility of the PCL-HA scaffold with BMSCs. Cell viability assays using Passage 4 (P4) Stem Pro™ BMSCs revealed promising results. Three scaffolds were seeded with 1,000,000 cells/mL, and the scaffolds without cells served as controls. Cell viability was tracked over 21 days, showing a temporary decline at day 7 followed by a gradual increase, indicating favorable conditions for cell adhesion and proliferation. Our second aim aimed to evaluate the effectiveness of a designed delivery system for the implantation of the PCL-HA bone scaffold and intramedullary nail systems using a rabbit tibia model. An ex-vivo study conducted on rabbit cadavers confirmed the potential of our targeting jig to accurately implant the developed bone scaffold and intramedullary nail while aligning the screws, addressing large bone defects in rabbit tibiae. The study, however, revealed challenges in delivering small-sized implants with the required mechanical strength. Achieving higher mechanical stability for increased weight-bearing capacity and matching compressive/shear properties with cortical bone were identified as goals for future improvement. To evaluate mechanical performance, we developed a computer model based on our experimental setup. Using ANSYS finite element software, our study indicated reduced stress on bone by the PCL-HA bone substitute compared to traditional titanium nails and screws. While the mechanical properties were similar, a 2% higher deformation was observed in screws compared to titanium screws. This study demonstrates the potential and qualification of our designed models for long bone repair. Our research represents a significant step forward in the development of 3D-printed PCL-HA bone scaffolds and intramedullary nail systems. These findings underscore the potential of these implants in orthopedic applications, and further refinements in design and mechanical properties are anticipated to enhance their performance in clinical practice. We are currently doing an animal study using a rabbit tibia model to evaluate our scaffold performance. Acknowledgment: This publication was made possible by Grant Number 5P20GM103447 from the National Institute of Health (NIH).