Min Liu,1,2 Bo Liu,2 Ziyang Liu,3 Zhen Yang,2 Thomas J Webster,4 Huan Zhou,2 Lei Yang2 

1School of Materials Science and Engineering, Hebei University of Technology, Tianjin, People’s Republic of China; 2Center for Health Science and Engineering, Hebei Key Laboratory of Biomaterials and Smart Theranostics, School of Health Sciences and Biomedical Engineering, Hebei University of Technology, Tianjin, 300131, People’s Republic of China; 3Department of Orthopedics, Tianjin Hospital, Tianjin, People’s Republic of China; 4School of Engineering, Saveetha University, Chennai, India

Correspondence: Huan Zhou; Lei Yang, Center for Health Science and Engineering, School of Health Sciences and Biomedical Engineering, Hebei University of Technology, Tianjin, 300131, People’s Republic of China, Email zhouhuan@hebut.edu.cn; ylei@hebut.edu.cn

Introduction: Lumbar interbody fusion is widely employed for both acute and chronic spinal diseases interventions. However, large incision created during interbody cage implantation may adversely impair spinal tissue and influence postoperative recovery. The aim of this study was to design a shape memory interbody fusion device suitable for small incision implantation.
Methods: In this study, we designed and fabricated an intervertebral fusion cage that utilizes near-infrared (NIR) light-responsive shape memory characteristics. This cage was composed of bisphenol A diglycidyl ether, polyether amine D-230, decylamine and iron oxide nanoparticles. A self-hardening calcium phosphate-starch cement (CSC) was injected internally through the injection channel of the cage for healing outcome improvement.
Results: The size of the interbody cage is reduced from 22 mm to 8.8 mm to minimize the incision size. Subsequent NIR light irradiation prompted a swift recovery of the cage shape within 5 min at the lesion site. The biocompatibility of the shape memory composite was validated through in vitro MC3T3-E1 cell (osteoblast-like cells) adhesion and proliferation assays and subcutaneous implantation experiments in rats. CSC was injected into the cage, and the relevant results revealed that CSC is uniformly dispersed within the internal space, along with the cage compressive strength increasing from 12 to 20 MPa.
Conclusion: The results from this study thus demonstrated that this integrated approach of using a minimally invasive NIR shape memory spinal fusion cage with CSC has potential for lumbar interbody fusion.

Keywords: shape memory, interbody fusion cage, NIR responsive, calcium phosphate cement, minimally invasive