The present work describes an approach for layered manufacturing (LM) of porous objects using an appropriate modelling scheme, a pre-processing algorithm for slicing and a raster tool path generation based on the porosity information. Initially an overall framework of modelling and data transfer that includes controlled porosity information apart from the external geometry of porous objects and its transfer for LM is presented. A novel raster path generation methodology using space-filling fractal curves for LM of porous models is presented later. Specifically, the geometry and space-filling characteristics of fractal curves are studied for application to raster tool path generation in LM. Finally, boundary-constrained raster patterns are generated based on the surface geometry. The resulting data can be translated into a machine language file that can be imported by an LM system. Case studies are presented to illustrate the efficacy of this approach.
Thermal osteonecrosis of bone in drilling procedure is caused by improper parameters which can lead to poor bone-implant integration and loss of fixation. In this study, Taguchi technique for parameter optimization and multiple regression models for temperature prediction were employed. The main aim of the study was to determine the optimal parameters of bone drilling to control the temperature rise below the thermal osteonecrosis threshold (47[Formula: see text]C) in respect of the bone density variations at different drilling directions. A 32 full factorial design with nine sets of parameters was used in the study. Drilling operations were performed along the longitudinal, radial and circumferential directions at the proximal-diaphysis, mid-diaphysis and distal-diaphysis regions of the 10 adult cadaveric femurs with different feed rates (40, 60 and 80[Formula: see text]mm/min) and spindle speeds (500, 1000 and 1500[Formula: see text]rpm) using 3.2[Formula: see text]mm diameter surgical drill bit. The in-situ drilling temperatures were measured with T-type thermocouple. The optimum drilling parameters for each drilling direction were determined from signal to noise ratios and the effect of each parameter was determined using analysis of variance. By using computed tomography scan data of patients, the proposed method is able to predict the temperature rise at the bone-drilling sites, optimal parameters and possibility for the occurrence of thermal osteonecrosis. This important tool could assist in reducing localized temperature induced from surgical drilling by up to 32% and 18[Formula: see text]C and as such significantly reduce associated osteonecrosis and improve patient outcome and quality of life.
Tissue engineering scaffolds with intricate and controlled internal structure can be realized using computer-aided design (CAD) and layer manufacturing (LM) techniques. Design and manufacturing of scaffolds for load-bearing bone sites should consider appropriate biocompatibile materials with interconnected porosity, surface properties, and sufficient mechanical properties that match the surrounding bone, in order to provide adequate support, and to mimic the physiological stress-strain state so as to stimulate new tissue growth. The authors have previously published methods for estimating subject- and site-specific bone modulus using computed tomography (CT) data, CAD, and process planning for LM of controlled porous scaffolds. This study evaluates the mechanical performance of the designed porous hydroxyapite scaffolds in load-bearing sites using a finite element (FE) approach. A subject-specific FE analysis using femoral, defect site geometry and anisotropic material assignment based on CT data is employed. Mechanical behaviour of the femur with scaffold in stance-phase gait loading, which has been shown experimentally to produce clinically relevant results, is analysed. The comparison of results with simulation of healthy femur shows an overall correspondence in stress and strain state which will provide optimized mechanical properties for avoiding stress shielding, and adequate strength to avoid failure risk and for active bone tissue regeneration.
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