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Developing a novel functional disc emulator to investigate the nucleus pulposus replacement

doi: 10.1007/s10856-021-06492-z.

Affiliations

Free PMC article

Hassan M Raheem et al. J Mater Sci Mater Med. .

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Abstract

We have developed a simple, inexpensive and innovative device for reproducing the global mechanical behavior of spinal motion segments and the local mechanical environment experienced by lumbar intervertebral discs. The device has several broad functions: (1) exploration of the basic mechanics underlying this complex skeletal system, (2) connecting changes in tissue characteristics with overall motion segment function, and (3) evaluation of strategies for repair and replacement of disc components. This “disc emulator” consists of three main parts: (1) an artificial annulus fibrosus (AAF), made out of silicone, with lumbar disc geometry and adjustable material properties, (2) a hydrogel nucleus pulposus (NP) also with lumbar disc geometry and adjustable material properties, and (3) simulated vertebral bodies 3D printed with trabecular bone simulated by a rigid polymer (Acrylonitrile Butadiene Styrene, ABS) and end plates crafted from a compliant polymer (Thermoplastic Polyurethane, TPU). Mechanical compression experiments have been conducted using the disc emulator under similar protocols to published studies of human cadaver samples. Bulging of the artificial annulus fibrosus was examined under axial compression loads using digital image correlation (DIC), and results show close agreement. We see this approach of using anatomical geometry and multiple adjustable components as a useful means of creating accurate local stress/strain environments for preliminary material evaluation, without the variability and difficulty inherent indirect testing of cadaveric materials.

Conflict of interest statement

The authors declare no competing interests.

Figures

Fig. 1

Fig. 1

A The disc emulator assembly. a Artificial vertebral bodies of ABS plastic with a 2 mm layer at the surface of TPU. b Artificial annulus fibrosus of RTV 630 silicon (c) cavity for nucleus pulposus simulation materials (B) annulus fibrosus component denucleated (left) and with a hydrogel nucleus pulposus (right) (C) mold for casting hydrogel NP components (left) and an example (right)

Fig. 2

Fig. 2

The experimental setup

Fig. 3

Fig. 3

The average stress- strain data of 1.5 wt. % agarose and 4 wt. % agarose samples under unconfined compression

Fig. 4

Fig. 4

Comparison between the disc emulator data under compression load without NP and reported data of Joshi et al. [4] for the denucleated human motion segment

Fig. 5

Fig. 5

The disc emulator data under compression test without nucleus pulposus NP and with nucleus pulposus, as a reference for comparison (1.5 wt.%, 4 wt.% agarose, A1.5, and A4, respectively)

Fig. 6

Fig. 6

Comparison of the compression response of the disc emulator (4 w/o NP) with literature results: (b) is Brown et al. [3] for segments L2/L3 to L4/L5; (k) is Kulak et al. [7] finite element results; (J) and (J2) are Joshi et al. [4] data for intact human motion segment and implanted hydrogel for NP

Fig. 7

Fig. 7

The bulging in the artificial annulus fibrosis disc under a 500 N compressive load, the disc without NP (a), the disc with the A4 as an NP (b). The big two arrows show the posterior (P) and posterolateral (PL) regions in the disc

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doi: 10.1007/s10856-021-06492-z. Affiliations Affiliations 1 Faculty of Engineering, Mechanical Department, University of Kufa, Najaf, Iraq. enghas25@gmail.com. 2 Ministry of Oil, Midland Refineries Company, Karbala Refinery, Karbala, Iraq. enghas25@gmail.com. 3 School of Chemical, Biological, and Environmental Engineering, Oregon State University, Corvallis, OR, USA. 4 School of Mechanical, Industrial, and Manufacturing Engineering, Oregon State University, Corvallis, OR,…

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