Browsing by Author "Tozzi, Gianluca"

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    Evaluation of bone excision effects on a human skull model - I: Mechanical testing and digital image correlation.
    (Sage, 2019-12-06) Franceskides, Constantinos; Leger, Thibault; Horsfall, Ian; Tozzi, Gianluca; Gibson, Michael C.; Zioupos, Peter
    The mechanisms of skull impact loading may change following surgical interventions such as the removal of bone lesions, but little is known about the consequences in the event of subsequent head trauma. We, therefore, prepared acrylonitrile butadiene styrene human skull models based on clinical computed tomography skull data using a three-dimensional printer. Six replicate physical skull models were tested, three with bone excisions and three without. A drop tower was used to simulate the impact sustained by falling backwards onto the occipital lobe region. The impacts were recorded with a high-speed camera, and the occipital strain response was determined by digital image correlation. Although the hole affected neither the magnitude nor the sequence of the fracture pattern, the digital image correlation analysis highlighted an increase in strain around the excised area (0.45%–16.4% of the principal strain). Our approach provides a novel method that could improve the quality of life for patients on many fronts, including protection against trauma, surgical advice, post-operative care, advice in litigation cases, as well as facilitating general biomechanical research in the area of trauma injuries.
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    Spinal Motion Segments — I: Concept for a Subject-specific Analogue Model
    (Springer, 2020-06-24) Franceskides, Constantinos; Arnold, Emily; Horsfall, Ian; Tozzi, Gianluca; Gibson, Michael C.; Zioupos, Peter
    Most commercial spine analogues are not intended for biomechanical testing, and those developed for this purpose are expensive and yet still fail to replicate the mechanical performance of biological specimens. Patient-specific analogues that address these limitations and avoid the ethical restrictions surrounding the use of human cadavers are therefore required. We present a method for the production and characterisation of biofidelic, patient-specific, Spine Motion Segment (SMS = 2 vertebrae and the disk in between) analogues that allow for the biological variability encountered when dealing with real patients. Porcine spine segments (L1–L4) were scanned by computed tomography, and 3D models were printed in acrylonitrile butadiene styrene (ABS). Four biological specimens and four ABS motion segments were tested, three of which were further segmented into two Vertebral Bodies (VBs) with their intervertebral disc (IVD). All segments were loaded axially at 0.6 mm·min−1 (strain-rate range 6×10−4 s−1–10×10−4 s−1). The artificial VBs behaved like biological segments within the elastic region, but the best two-part artificial IVD were ∼15% less stiff than the biological IVDs. High-speed images recorded during compressive loading allowed full-field strains to be produced. During compression of the spine motion segments, IVDs experienced higher strains than VBs as expected. Our method allows the rapid, inexpensive and reliable production of patient-specific 3D-printed analogues, which morphologically resemble the real ones, and whose mechanical behaviour is comparable to real biological spine motion segments and this is their biggest asset.
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    Spinal Motion Segments — II: Tuning and Optimisation for Biofidelic Performance
    (Springer, 2020-06-24) Franceskides, Constantinos; Arnold, Emily; Horsfall, Ian; Tozzi, Gianluca; Gibson, Michael C.; Zioupos, Peter
    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
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    A subject-specific analogue model for spinal motion segments
    (European Society of Biomechanics, 2017-07-05) Franceskides, Constantinos; Arnold, Emily; Horsfall, Ian; Tozzi, Gianluca; Zioupos, Peter
    Human cadaveric tissues are incredibly variable and difficult to preserve [1], thus making frequent biomechanical testing with these materials challenging. Available funds and ethical procedures will also limit their availability [2]. Due to these restrictions, animal bone models are often used. However, as all biological tissues, those models present variable mechanical properties depending on a number of factors [3]. For the above reasons subject-specific analogues are very attractive, particularly in the field of forensic and injury biomechanics. The analogue proposed in this study was 3D-printed from micro-CT (Computed Tomography) dataset of real bone, through generation of a 3D model. Both cadaveric and analogue segments were mechanically tested in axial compression. And surface displacement was computed via digital image correlation (DIC). The proposed protocol has the potential to be applied in the prediction and modelling of bone behaviour.