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Design and manufacturing of bone analog models for the mechanical evaluation of custom medical implants
Abstract and Figures
The performance of orthopedic implants is often evaluated using cadaveric bone specimens. The high inter-specimen variability of cadaveric bone properties requires large sample sizes to obtain statistical significance. With recent focus on custom implants manufactured using direct metal freeform fabrication techniques, the need for a customized bone analog model is recognized. Data for bone geometry and internal structure were obtained from computed-tomography imaging. Traditional rapid prototyping techniques are then used to generate the rapid tooling from which composite bones that mimic the properties of the real bone can be duplicated. This work focused on the manufacturing process of bone analog models.
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... Sci. 2021, 11, 9961 2 of 10 Horn [19] polyurethane foam is a good alternative for human cancellous bone as it displays similar mechanical properties and may be used as a medium for implant testing. Horak et al. [17] conducted experimental studies to evaluate its mechanical properties (temperature, strain and density) and reported that it is not only suitable for mechanical investigations but also for investigations involving surgical instruments that generate heat. ...
... Polyurethane (PUR) foam blocks have been commonly used in experimental studies replacing cadaver or animal bone specimens [4,7,[12][13][14][15][16][17]. According to Schim [18] and Horn [19] polyurethane foam is a good alternative for human cancellous bone as it displays similar mechanical properties and may be used as a medium for implant testing. Horak et al. [17] conducted experimental studies to evaluate its mechanical properties (temperature, strain and density) and reported that it is not only suitable for mechanical investigations but also for investigations involving surgical instruments that generate heat. ...
The aim of this experimental study was to verify thermal diffusion differences, by measuring the maximum temperature achieved with different drill shapes. Synthetic bone blocks of type I density made from solid rigid polyurethane (PUR) foam were used to perform the drilling procedures. The experiment was conducted at three different rotation speeds: 800, 3000 and 5000 rpm. Conical drills (with and without an internal cooling hole) were compared with horizontal drills and disc drills. The temperature during drilling for implant bed preparation was estimated with the use of thermocouples and an infrared (IR) camera. The temperature during drilling with disc cutters for lateral basal implants did not exceed 33 ∘C and the temperature decreased in proportion to higher drill speed. The results indicate that the tested design is safe and will not cause bone overheating.
As a way of enhancing the mechanical properties of photopolymer-based parts produced by layered manufacturing (LM) techniques, the use of short glass-fibre reinforcements has been recently explored in the literature. This paper proposes a novel methodology that utilizes a modified rule-of-mixtures model for the prediction of the mechanical properties of such layered composites. The prediction process employs empirical data on (i) the fibre-matrix interface, (ii) the fibres’ geometrical arrangement within the specimens (i.e. fibre-orientation distribution), and (iii) the fibre-length distribution. The effects of the fibre-orientation and fibre-length distributions are accounted for in the prediction model by the fibre-length-correction and orientation-efficiency factors. Comparison of extensive experimental results and model-based predictions of mechanical properties of layered composites demonstrated the effectiveness of the proposed estimation methodology.
▪ Abstract The term bone refers to a family of materials, all of which are built up of mineralized collagen fibrils. They have highly complex structures, described in terms of up to 7 hierarchical levels of organization. These materials have evolved to fulfill a variety of mechanical functions, for which the structures are presumably fine-tuned. Matching structure to function is a challenge. Here we review the structure-mechanical relations at each of the hierarchical levels of organization, highlighting wherever possible both underlying strategies and gaps in our knowledge. The insights gained from the study of these fascinating materials are not only important biologically, but may well provide novel ideas that can be applied to the design of synthetic materials.
IntroductionLiterature ReviewElectron Beam Melting TechnologyDirect Fabrication of Titanium Orthopedic ImplantsSummary and Conclusions
References
GENERAL CONSIDERATIONS Basic Composition and Structure of Bone -E. Bonucci Basic Concepts of Mechanical Property Measurement and Bone Biomechanics -Y. H. An and W. R. Barfield and R. A. Draughn Mechanical Properties of Bone -Y.H. An Factors Affecting Mechanical Properties of Bone -P. Zioupos, C. W. Smith, and Y. H. An Basic Facilities and Instruments for Mechanical Testing of Bone -C.V. Bensen and Y.H. An Methods of Evaluation for Bone Dimensions, Densities, , Morphology, and Structures -Y.H. An, W. R. Barfield and I. Knets General Considerations of Mechanical Testing -Y.H. An and C.V. Bensen A Hierarchical Approach to Exploring Bone Mechanical Properties -C. E. Hoffler, B. R. McCreadie, E. A. Smith, and S. A. Goldstein Nondestructive Mechanical Testing of Cancellous Bone -F. Linde and I. Hvid Synthetic Materials and Structures Used as Models for Bone -J. A. Szivek METHODS OF MECHANICAL TESTING OF BONE Tensile and Compression Testing of Bone -T. S. Keller and M. A. Liebschner Bending Tests of Bone -M. J. Lopez and M. D. Markel Torsional Testing of Bone -B. Furman and S. Saha Indentation Testing of Bone -B. E. McKoy, Q. Kang and Y. H. An Penetration Testing of Bone Using an Osteopenetrometer -I. Hvid and F. Linde Microhardness Testing of Bone -S. S. Huja, T. R. Katona, and W. E. Roberts Nanoindentation Testing of Bone -J. Y. Rho and G. M. Pharr Single Osteon Micromechanical Testing -M. G. Ascenzi, A. Benvenuti, and A. Ascenzi Micromechanical Testing of Single Trabeculae -P. L. Mente Strain Gauge Measurements from Bone Surfaces -J. A. Szivek and V. M. Gharpuray Screw Pullout Test for Evaluating Mechanical Properties of Bone -M. S. Crum, F. A. Young, Jr., and Y. H. An Viscoelastic Properties of Bone and Testing Methods -N. Sasaki Observation of Material Failure Mode Using a SEM with a Built-in Mechanical Testing Device -R. M. Wang and Y. H. An Ultrasonic Methods for Evaluating Mechanical Properties of Bone -J. Y. Rho Evaluating Mechanical Properties of Bone Using Scanning Acoustic Microscopy -C. H. Turner and J. L. Katz Peripheral Quantitative Computed Tomography for Evaluating Structural and Mechanical Properties of Small Bone -J. L. Ferretti Computer Modeling for Evaluating Trabecular Bone Mechanics -R. Saxena and T. S. Keller METHODS OF MECHANICAL TESTING OF THE BONE-IMPLANT INTERFACE Factors Affecting the Strength of the Bone-Implant Interface -B. E. McKoy, Y. H. An and R. J. Friedman Implant Pushout and Pullout Test -A. Berzins and D. R. Sumner The Validity of a Single Pushout Test -W. J. A. Dhert and J. A. Jansen Tensile Testing of Bone-Implant Interface -T. Nakamura and S. Nishiguchi Fracture Toughness Tests of the Bone-Implant Interface -X. Wang, K. A. Athanasiou, and C. M. Agrawal In Vitro Measurements of Implant Stability -A. Berzins and D. Sumner In Vitro Testing of the Stability of Acetabular Components -J. R. Davis, R. A. Lofthouse, and R. H. Jinnah In Vitro Testing of the Stability of Femoral Components -S. H. Naidu, F. M. Khoury and J. M. Cuckler Screw Pullout Test -L. A. Ferrara and T. C. Ryken Finite Element Analysis for Evaluating Mechanical Properties of the Bone-Implant Interface -K. R. Williams Fatigue Testing of Bioabsorbable Screws in a Synthetic Bone Substrate -W. S. Pietrzak, D. R. Sarver, and D. H. Kohn Testing Intervertebral Stability after Spinal Fixation -K. S. James and A. U. Daniels
An analysis is made of the effect of orientation of the fibres on the stiffness and strength of paper and other fibrous materials. It is shown that these effects may be represented completely by the first few coefficients of the distribution function for the fibres in respect of orientation, the first three Fourier coefficients for a planar matrix and the first fifteen spherical harmonics for a solid medium. For the planar case it is shown that all possible types of elastic behaviour may be represented by composition of four sets of parallel fibres in appropriate ratios. The means of transfer of load from fibre to fibre are considered and it is concluded that the effect of short fibres may be represented merely by use of a reduced value for their modulus of elasticity. The results of the analysis are applied to certain samples of resin bonded fibrous filled materials and moderately good agreement with experimental results is found.
The design of custom or tailored implant components has been the subject of research and development for decades. However, the economic feasibility of fabricating such components has proven to be a challenge. New direct metal fabrication technologies such as Electron Beam Melting (EBM) have opened up new possibilities. This paper discusses the design and fabrication of titanium implant components having tailored mechanical properties that mimic the stiffness of bone to reduce stress shielding and bone remodeling. Finite Element Analysis was used to design the tailored structures, and results were verified using mechanical testing.
This paper addresses foams which are known as non-stochastic foams, lattice structures, or repeating open cell structure foams. The paper reports on preliminary research involving the design and fabrication of non-stochastic Ti–6Al–4V alloy structures using the electron beam melting (EBM) process. Non-stochastic structures of different cell sizes and densities were investigated. The structures were tested in compression and bending, and the results were compared to results from finite element analysis simulations. It was shown that the build angle and the build orientation affect the properties of the lattice structures. The average compressive strength of the lattice structures with a 10% relative density was 10 MPa, the flexural modulus was 200 MPa and the strength to density ration was 17. All the specimens were fabricated on the EBM A2 machine using a melt speed of 180 mm/s and a beam current of 2 mA. Future applications and FEA modeling were discussed in the paper.