Monolithic total disc replacement made of polyurethane lattice based on anatomical features

Abstract

Lower back pain (LBP) is included in the top 10 contributors to the overall disease burden. One of the etiologies of LBP is the intervertebral disc (IVD) degeneration, which in some cases, needs to be replaced with an artificial disc, the so-called total disc replacement (TDR). Unfortunately, TDR might provide post-surgical complications, including the failure in the metal-polymer assembly of TDR. The failure was argued due to the rigidity of the metal part and the shape of TDR that was not fully compliant with the anatomical features. Due to these complications, we proposed PU and monolithic construct to be alternative materials and comply with anatomical relevance. This study designed and developed a monolithic TDR made of PU lattices based on anatomical features. We focused on the IVDs in the lumbar section of the spine. The design step consisted of 3 phases: segmentation of DICOM files of IVDs using a 3D Slicer software, alignment using an Autodesk Meshmixer software, and lattice design using an Autodesk Inventor software. The manufacturing step started with a configuration setup in Simplify3D, software for computer-aided manufacturing (CAM) in 3D printing. The lattice features were fabricated using a Creality CP01 3D printer with two types of PU filaments: TPU 87A and TPU 95A. The printing results were able to construct the external curvature of the IVDs. Unfortunately, the microscopic measurement results showed that struts and holes' dimensions deviated from the design, which must be resolved in the next studies.

Anatomically and Biomechanically Relevant Monolithic Total Disc Replacement Made of 3D-Printed Thermoplastic Polyurethane

“…The segmentation was performed using open-source software, namely the 3D Slicer image computing platform. The detailed segmentation procedures were elaborated in our previous study [ 33 ]. The IVD segmentation results were exported in a standard tessellation (STL) file format.…”

“…The lattice structure comprised a pattern of struts with in-between gaps making a webbing-like mesh, referring to the design used by Christiani et al [ 17 ] that was also used in our previous MTDR study [ 33 ]. The lattice structure was designed using an Autodesk Inventor 2021 software (Autodesk, Inc., San Rafael, CA, USA) and distinguished into two configurations: a full lattice configuration (FLC) and anatomy-based configuration (ABC).…”

“…Our group proposed a monolithic total disc replacement (MTDR) made of thermoplastic polyurethane (TPU) that was based on the anatomical and biomechanical features of IVDs. The MTDR was reconstructed from the magnetic resonance imaging (MRI) results of IVDs in the lumbar segment and subsequently featured a lattice structure [ 33 ]. The lattice-structured MTDR was fabricated using a 3D printing approach in the form of fuse filament fabrication (FFF) [ 33 ], an emerging technology for developing personalized orthopedic implants and scaffolds [ 34 , 35 , 36 ], thereby complying with the anatomical features of the patients [ 34 , 35 ].…”

“…The MTDR was reconstructed from the magnetic resonance imaging (MRI) results of IVDs in the lumbar segment and subsequently featured a lattice structure [ 33 ]. The lattice-structured MTDR was fabricated using a 3D printing approach in the form of fuse filament fabrication (FFF) [ 33 ], an emerging technology for developing personalized orthopedic implants and scaffolds [ 34 , 35 , 36 ], thereby complying with the anatomical features of the patients [ 34 , 35 ]. PU was chosen because the material has been widely used for spine treatments including TDRs [ 37 ] due to the biocompatibility, load-bearing ability, and cushion capability [ 38 ].…”

“…This is such a waste of potential for PU, considering that PU filaments were proven to be biocompatible and could be fabricated into various shapes using an FFF machine [ 39 , 40 , 41 ]. Continuing from our previous study [ 33 ], this study aims to evaluate the physical, mechanical, and cytotoxicity properties of the MTDR in accordance with the anatomy and biomechanics of native IVDs.…”