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ORIGINAL RESEARCH
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Four-dimensional-printed personalized shape memory NiTi implant for minimally invasive delivery in cavitary bone defect reconstruction

Zhuangzhuang Li1,2# ,  Minxun Lu1,2# ,  Shanfang Zou3 ,  Ruicheng Liu3 ,  Haoyuan Lei4 ,  Yitian Wang1,2 ,  Yuqi Zhang1,2 ,  Yong Zhou1,2 ,  Changchun Zhou4 ,  Yi Luo1,2* ,  Li Min1,2* ,  Chongqi Tu1,2*
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1 Department of Orthopedics, Orthopedic Research Institute, West China Hospital, Sichuan University, Chengdu, Sichuan, China
2 Model Worker and Craftsman Talent Innovation Workshop of Sichuan Province, Chengdu, Sichuan, China
3 Tianqi Additive Manufacturing Co., Ltd, Chengdu, Sichuan, China
4 National Engineering Research Centre for Biomaterials, Sichuan University, Chengdu, Sichuan, China
BMT, 00009 https://doi.org/10.12336/bmt.25.00009
Submitted: 2 March 2025 | Revised: 6 April 2025 | Accepted: 15 April 2025 | Published: 28 May 2025
Copyright © 2025 by the Author(s). This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution–NonCommercial–ShareAlike 4.0 License.
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Abstract

Integrating 4D printing technology in medical implants offers promising advancements for minimally invasive delivery (MID) and personalized orthopedic solutions. This study presents a 4D-printed shape memory nickel-titanium (NiTi) mesh implant for cavitary bone defect reconstruction, enabling a time-dependent shape transformation. Fabricated through selective laser melting (80 W laser power, 600 mm/s scanning speed, 70 μm hatch spacing, 25 μm layer thickness), the implant can be compressed during implantation and recover its original shape. Micro-computed tomography analysis confirmed high geometric fidelity (D50 = 58 μm), while scanning electron microscopy-energy dispersive spectroscopy analysis revealed a uniform microstructure and confirmed the homogeneous distribution of Ni/Ti across the mesh implant. Phase transformation testing showed that the austenite finish temperatures (austenite finish) of the as-built sample and the acid-washed sample were below the 37°C physiological threshold. Compression testing indicated that a force of 156 N was required for 30% deformation, with complete recovery to its pre-defined shape. Clinically, the implant reduced cortical bone fenestration by 20%. Post-operative imaging at 6 and 12 months showed excellent osseointegration and minimal residual cavities. Functional assessments at 12 months indicated excellent recovery, with a Musculoskeletal Tumor Society score of 29. In the present study, the clinical use of the 4D-printed mesh implant demonstrated not only satisfactory osteointegration but also a practical advantage in surgical handling. The shape recovery of the implant from a compressed state to its pre-designed shape allowed for MID and precise fit to the defect contour.

Keywords
4D printing
Shape memory effect
Nickel–titanium alloy
Selective laser melting
Minimally invasive surgery
Orthopedic implants
Funding
This work was supported by the Natural Science Foundation of Sichuan Province (2024NSFSC7665, 2023NSFSC1589) and the National Natural Science Foundation of China (82402816).
Conflict of interest
Shanfang Zou and Ruicheng Liu are employees of Tianqi Additive Manufacturing Co., Ltd. However, they were not involved in any activities that could constitute a conflict of interest in relation to this study.
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