Evaluating Compressive Properties and Morphology of Expandable Polyurethane Foam for use in a Synthetic Paediatric Spine

An expandable rigid PU foam can turns into complex shapes, with a shell like structure onthe outside and honeycomb structure on the inside, which can be easily shaped to a vertebraform. The present study aims to determine whether expandable rigid polyurethane foamwas an appropriate substitute for rigid block polyurethane foam to model the trabecularbone. Static compression tests were performed to determine compressive moduli and yieldstresses on three polyurethane foam densities namely 0.16 g/cm3, 0.24 g/cm3and 0.42 g/cm3.Morphology of the PU foams for all densities was also observed. The compressive modulusfor 0.16 g/cm3and 0.24 g/cm3were found varied from 40 to 43 MPa and 83 to 92 MPa whileyield stress ranged from 2.1 to 2.3 MPa and 3.4 to 4.8 MPa respectively. As for 0.42 g/cm3, thecompressive modulus and yield stress varied from 240 to 256 MPa and 38 to 40 MPa. Based onthese results, the compressive modulus and yield stress of 0.24 g/cm3compared favourablywith rigid block PU foam and human cadavers presented in the literatures. Hence, the find-ings of this study could potentially be used in developing a synthetic vertebral trabecularbone of paediatric spine for biomechanical testing

Design and Development of Artificial Spinal Ligaments for Paediatric Synthetic Spine

A synthetic spine is a model fabricated from artificial materials consisting of the vertebrae, intervertebral discs and ligaments for spinal testing. The synthetic spine overcomes many difficulties associated with biological specimens such as handling, biohazard concerns, high costs, and limited availability of specimens, quality and large inter-specimen variability. This paper presents the design and development of spinal ligaments to mimic the stiffness of the paediatric ligaments for use in the synthetic spine. Spinal ligaments are uniaxial structures in the spine that carry tensile loads along the direction of the fibres. Early in the research, silicone materials were used to cover the whole spinal unit, but it became apparent that the material responses were inadequate. The synthetic spine was revised to use fibreglass tape to more closely simulate the natural spinal structures. The composite design applied in this paper consisted of soft silicone rubber and fibreglass tape to obtain the natural stiffness that normally occurred in the spinal ligaments

Experimental Analysis of Fabricated Synthetic Midthoracic Paediatric Spine as Compared to the Porcine Spine Based on Range of Motion (ROM)

The present study is aimed at investigating the mechanical behaviour of fabricated synthetic midthoracic paediatric spine based on range of motion (ROM) as compared to porcine spine as the biological specimen. The main interest was to ensure that the fabricated synthetic model could mimic the biological specimen behaviour. The synthetic paediatric spine was designed as a 200% scaled-up model to fit into the Bionix Servohydraulic spine simulator. Biomechanical tests were conducted to measure the ROM and nonlinearity of sigmoidal curves at six degrees of freedom (DOF) with moments at ±4 Nm before the specimens failed. Results were compared with the porcine spine (biological specimen). The differences found between the lateral bending and axial rotation of synthetic paediatric spine as compared to the porcine spine were 18% and 3%, respectively, but was still within the range. Flexion extension of the synthetic spine is a bit stiff in comparison of porcine spine with 45% different. The ROM curves of the synthetic paediatric spine exhibited nonlinearities for all motions as the measurements of neutral zone (NZ) and elastic zone (EZ) stiffness were below 1. Therefore, it showed that the proposed synthetic paediatric spine behaved similarly to the biological specimen, particularly on ROM

Modelling of a Cable-driven Ankle Rehabilitation Robot

Ankle injury is one of physical injury that commonly occurs in sports or domestic-related activities. Presently, there are various established treatments for ankle rehabilitation in hospital or rehabilitation clinic. This involves a range of motion treatment exercise and endurance treatment exercise. However, current treatment requires patients to frequently visit to the hospital which is tedious and also repetitive. One of the solutions to deal with the repetitiveness of the treatment is to introduce an automated device such as a robot that can help the therapist to perform this repetitive task on the patients. A concept design for a cable driven ankle rehabilitation robot has been proposed for this task. The reason for selecting cable-based design is the design is lighter than a rigidly based robot. This adds up its potential for mobility and portability which allows convenience to the users. The focus of this paper is to present inverse kinematics analysis and modelling of the proposed concept design of the robot which aimed to determine the feasibility of the concept design. Overall, the modelling of the cable-based ankle rehabilitation robot using inverse kinematics is feasible to project or to predict the trajectory paths of the moving platform of the robot. This will be useful for planning suitable dimension for fabrication of the robot

Fracture prediction on patient-specific tibia model with osteogenesis Imperfecta under various loading direction

This study aims to predict the fracture of bone with osteogenesis imperfecta (OI) by considering the homogenization properties of real patient. A Type-III of osteotomy in OI femur was used as bone specimen. Nine representative volume element (RVE) models were developed based on μCT-images of bone specimen. Homogenized properties particularly the Young's moduli of the RVEs was obtained based on homogenization theory in Voxelcon software. The obtained homogenized properties were then assigned to the OI patient-specific model that was developed from CT-images of real patient. The fracture of OI bone was predicted based on linear static analysis and finite element method under loadings of activity daily living (ADL). The results found that the fracture might be happen to the patient under jumping load case, whereas the subject is expected to be safe under standing still and walking load case

Ratchetting of composite pipes

The uniaxial ratchetting characteristics of fibre glass reinforced epoxy laminate have been investigated in the present project. The specimens were subjected to cyclic axial stress with a constant mean stress of 40 MPa and a varying amplitude stress of 26.67 MPa and 53.33 MPa. Tests were also performed on 50 mm diameter, Glass fibre Reinforced Epoxy (GRE) straight pipe. The pipe was subjected to a constant internal pressure of 1.875 MPa and a cyclic axial load. The finite element model in ABAQUS has also been simulated in similar loading case. The comparisons between experiment and simulation results were observed. The effect of fibre orientation on the rate of ratchetting was also investigated at the present project. The uniaxial and biaxial ratchetting strain was observed to increase with a number of cycles but decreased the rate of ratchetting. The specimen showed no further ratchetting rate and exhibited shakedown after some strain accumulation. On the basis of experiment and simulation, it appears that ratchetting would occur in the circumferential direction for a composite pipe subjected to constant internal pressure and cyclic displacement with no ratchetting observed in axial direction. A direction in fibre orientation seemed to have effect on the rate of ratchetting. Thus, the increasing of fibre angle from the axial load axis will increase the rate of ratchetting

Stochastic multi-scale analysis of homogenised properties considering uncertainties in cellular solid microstructures using a first-order perturbation

Randomness in the microstructure due to variations in microscopic properties and geometrical information is used to predict the stochastically homogenised properties of cellular media. Two stochastic problems at the micro-scale level that commonly occur due to fabrication inaccuracies, degradation mechanisms or natural heterogeneity were analysed using a stochastic homogenisation method based on a first-order perturbation. First, the influence of Young's modulus variation in an adhesive on the macroscopic properties of an aluminium-adhesive honeycomb structure was investigated. The fluctuations in the microscopic properties were then combined by varying the microstructure periodicity in a corrugated-core sandwich plate to obtain the variation of the homogenised property. The numerical results show that the uncertainties in the microstructure affect the dispersion of the homogenised property. These results indicate the importance of the presented stochastic multi-scale analysis for the design and fabrication of cellular solids when considering microscopic random variation