The development of a physical model of cancellous bone whose structure could be controlled would provide significant advantages over the study of in vitro samples, making…
Abstract
The development of a physical model of cancellous bone whose structure could be controlled would provide significant advantages over the study of in vitro samples, making repetitive or comparative testing possible. This would enable the relationship between the mechanical integrity (and hence fracture risk) of cancellous bone and its structural properties to be more exactly defined. Whilst the use of RP to generate these porous objects was a considerable challenge such objects would have been impossible to manufacture using any other approach. This short technical note describes how stereolithography was used to create over 25 accurate models, which were required to perform physical experiments to validate the results of the FEA. The note highlights how problems associated with STL and SLC file formats, support generation and software limitations were overcome to produce stereolithography models of highly complex, naturally occurring three‐dimensional structures.
Details
Keywords
G. Sisias, R. Phillips, C.A. Dobson, M.J. Fagan and C.M. Langton
A set of algorithms has been developed and evaluated for 3D and 21/2D rapid prototyping replication of 3D reconstructions of cancellous bone samples. The algorithms replicate a…
Abstract
A set of algorithms has been developed and evaluated for 3D and 21/2D rapid prototyping replication of 3D reconstructions of cancellous bone samples. The algorithms replicate a voxel map without any loss of fidelity, so as to increase the validity of the comparison of mechanical tests on the 3D reconstructed models with those predicted by finite element analyses. The evaluation is both in terms of algorithmic complexity and the resultant data set size. The former determines the feasibility of the conversion process, whereas the latter the potential success of the manufacturing process. The algorithms and their implementation in PC software is presented.
Details
Keywords
Shuangyan Lei, Matthew C. Frank, Donald D. Anderson and Thomas D. Brown
The purpose of this paper is to present a new method for representing heterogeneous materials using nested STL shells, based, in particular, on the density distributions of human…
Abstract
Purpose
The purpose of this paper is to present a new method for representing heterogeneous materials using nested STL shells, based, in particular, on the density distributions of human bones.
Design/methodology/approach
Nested STL shells, called Matryoshka models, are described, based on their namesake Russian nesting dolls. In this approach, polygonal models, such as STL shells, are “stacked” inside one another to represent different material regions. The Matryoshka model addresses the challenge of representing different densities and different types of bone when reverse engineering from medical images. The Matryoshka model is generated via an iterative process of thresholding the Hounsfield Unit (HU) data using computed tomography (CT), thereby delineating regions of progressively increasing bone density. These nested shells can represent regions starting with the medullary (bone marrow) canal, up through and including the outer surface of the bone.
Findings
The Matryoshka approach introduced can be used to generate accurate models of heterogeneous materials in an automated fashion, avoiding the challenge of hand-creating an assembly model for input to multi-material additive or subtractive manufacturing.
Originality/value
This paper presents a new method for describing heterogeneous materials: in this case, the density distribution in a human bone. The authors show how the Matryoshka model can be used to plan harvesting locations for creating custom rapid allograft bone implants from donor bone. An implementation of a proposed harvesting method is demonstrated, followed by a case study using subtractive rapid prototyping to harvest a bone implant from a human tibia surrogate.
Details
Keywords
Manak Jain, Sanjay Dhande and Nalinaksh Vyas
Congenital telipes equinovarus (CTEV) or club foot is a historical foot deformity where the foot is turned in and pointing down causing the subject to walk on the outside edges of…
Abstract
Purpose
Congenital telipes equinovarus (CTEV) or club foot is a historical foot deformity where the foot is turned in and pointing down causing the subject to walk on the outside edges of foot. The non‐surgical correction of this deformity is an unsolved challenging problem in the medical domain and it becomes interesting due to the increasing number of such patients. The purpose of this paper is to build a biomodel of this historical foot deformity in newborn babies and hence an attempt to develop a corrective procedure using rapid prototyping (RP).
Design/methodology/approach
Biomodeling is a new technology that allows medical scan data sets to generate solid plastic replicas of anatomical structures. The medical scan data sets of live club foot baby patients were acquired and after image processing, biomodels of four live unilateral club foot baby patients are developed in a fused deposition modeling RP system.
Findings
The paper shows the location and position of abnormal bones and abnormal tarsal joints and is useful for management of club foot deformity in newborn babies. On visual study, it is observed that the talus is underdeveloped, talar neck is shorter and deviated in the medial and planter direction.
Research limitations/implications
The major outcome of this paper is the detailed geometrical visualization of talus bone of club foot and normal foot that assists in diagnosis and better treatment of CTEV. In future, the developed biomodels of club foot help to develop a corrective device that assists in bringing the club to normal foot geometrys.
Practical implications
These developed biomodels of club foot help in deciding the best corrective procedure for surgeons. The geometrical comparison between normal and club foot helps in developing a non‐surgical corrective procedure of this historical foot deformity. A 3D representation of talus bone provides an opportunity to view talus and analyse the ankle joint geometry that develops a favorable condition for diagnosis and treatment of this deformity.
Originality/value
The first time developed biomodels of clubfeet helps orthopaedic surgeons in preoperative surgical planning and consequently in carrying out biomechanical studies of club foot. The presented research plays a major role in planning a non‐surgical corrective procedure of this historical deformity. It also provides a platform for finite element analysis of club foot.
Details
Keywords
John Richard McCardle and Joe Bunyan
This paper aims to investigate whether the trabecular architecture found in natural bone can be effectively replicated through the selective laser sintering process of Nylon P2200.
Abstract
Purpose
This paper aims to investigate whether the trabecular architecture found in natural bone can be effectively replicated through the selective laser sintering process of Nylon P2200.
Design/methodology/approach
Trabecular bone was idealised into a scaled up hexagonal cell proven to replicate the natural structure. The structure was modelled in Solidworks 2013 to form a network of interlinking cells. The specific property analysed was the structure toughness through the measurement of the energy absorbed before sample fracture.
Findings
It was found that the impact absorption can be increased with the integration of a greater number of trabecular cells producing a finer resolution and not necessarily by increasing the trabecular size. The information gained from this research may be useful in the design of impact and shock absorbing components, with an emphasis on efficient use of material mass.
Research limitations/implications
Designers and engineers may find biomimetic methods of absorbing shock and impact an efficient alternative consideration in design applications.
Practical implications
The trabecular architecture should be designed so as to be weaker than the bounding surfaces, ensuring that the individual trabecular experience failure first, maximising their energy absorbing capability through increasing the period of deceleration. The simplest way of doing this is to ensure the rod thickness is less than the bounding material thickness.
Originality/value
This work documents original testing of both the RP material and consolidated design of samples of idealised bone structures. It builds on previous work in the area and through the results of empirical testing, derives recommendations for further considerations in this area of design and manufacture of biomimetic structures.
Details
Keywords
Aleksandra Drizo and Joseph Pegna
To provide a comprehensive state of the art review of environmental impact assessment (EIA) of existing rapid prototyping (RP) and rapid tooling (RT), and identify prospective…
Abstract
Purpose
To provide a comprehensive state of the art review of environmental impact assessment (EIA) of existing rapid prototyping (RP) and rapid tooling (RT), and identify prospective research needs.
Design/methodology/approach
The sparse literature on the EIA of RP and RT is balanced by that of the comparatively mature field of industrial ecology (IE). Hence, the review emphasizes portable IE measurement and evaluations methods. As RP and RT can also be viewed as design tools and mass customization manufacturing, other EIA may be needed.
Findings
The scarcity of research to date combined with rapid technological advances leaves a large number of unresolved issues. In addition, the special character of RP and RT, as design and manufacturing enablers implies that future research is needed.
Research limitations/implications
This review is drawn from a technology in rapid evolution. Hence, unresolved issues focus on technologies that already are on the market and the research needs are formulated in terms of state of the art process research.
Practical implications
As technological advances multiply, so does the number of unresolved environmental problems. The review of unresolved issues points to a pressing need to assess the consequences of RP and RT while identified research needs point the way to anticipated areas where further assessment methods will be needed.
Originality/value
This paper intends to raise awareness about the potential environmental impacts from RP and RT, by presenting the problems associated with current methods for measuring environmental effects and discussing some of the most urgent unresolved issues, specifically with respect to materials. Indirect effects of other uses of RP and RT are discussed only briefly for lack of available data.