Spinal Motion Segments — II: Tuning and Optimisation for Biofidelic Performance

Most commercially available spine analogues are not intended for biomechanical testing, and the few that are suitable for using in conjunction with implants and devices to allow a hands-on practice on operative procedures are very expensive and still none of these offers patient-specific analogues that can be accessed within reasonable time and price range. Man-made spine analogues would also avoid the ethical restrictions surrounding the use of biological specimens and complications arising from their inherent biological variability. Here we sought to improve the biofidelity and accuracy of a patient-specific motion segment analogue that we presented recently. These models were made by acrylonitrile butadiene styrene (ABS) in 3D printing of porcine spine segments (T12−L5) from microCT scan data, and were tested in axial loading at 0.6 mm·min −1 (strain rate range 6×10 −4 s −1 –10×10 −4 s −1 ). In this paper we have sought to improve the biofidelity of these analogue models by concentrating in improving the two most critical aspects of the mechanical behaviour: the material used for the intervertebral disc and the influence of the facet joints. The deformations were followed by use of Digital Image Correlation (DIC) and consequently different scanning resolutions and data acquisition techniques were also explored and compared to determine their effect. We found that the selection of an appropriate intervertebral disc simulant (PT Flex 85) achieved a realistic force/displacement response and also that the facet joints play a key role in achieving a biofidelic behaviour for the entire motion segment. We have therefore overall confirmed the feasibility of producing, by rapid and inexpensive 3D-printing methods, high-quality patient-specific spine analogue models suitable for biomechanical testing and practice.