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.

G. Saravana Kumar

Department of Engineering Design

CONTROLLED POROSITY

FRACTAL CURVES

MACHINE LANGUAGES

Path Generation

POROUS MODEL

POROUS OBJECT

POROUS OBJECTS

PRE-PROCESSING ALGORITHMS

RASTER TOOL PATHS

Space-filling

SURFACE GEOMETRIES

Tool Path Generation

TOOLPATHS

Computational geometry

Data transfer

Lagrange multipliers

Layered manufacturing

Scanning

Fractals

IIT Madras is a public technical and research university located in Chennai, Tamil Nadu. Founded in 1959, it is recognised as an Institute of National Importance.

IIT Madras has been ranked as the top engineering institute in India for four years in a row by the National Institutional Ranking Framework of the MHRD

It currently offers undergraduate, postgraduate and research degrees across 16 disciplines in Engineering, Sciences, Humanities and Management. About 596 faculty belonging to science and engineering departments and centres of the Institute are engaged in teaching, research and industrial consultancy.

IIT Madras

Fractal raster tool paths for layered manufacturing of porous objects

Virtual and Physical Prototyping

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.

Fulltext

Proceedings of the Institution of Mechanical Engineers, Part H: Journal of Engineering in Medicine

Finite element analysis of a personalized femoral scaffold with designed microarchitecture

The scaffolds for bone tissue engineering should consider the functional requirements such as the external shape of the replacement, porosity for vessel and nutrient conduit, and stiffness in order to avoid stress shielding and to stimulate growth of the new tissue. Layered manufacturing (LM) has shown great promise in fabricating such porous bone scaffold. The present work proposes a biomimetic design and LM of patient- and site-specific controlled porosity scaffolds for optimised mechanical properties for repair and regeneration of bone. Correlation models between porosity and modulus for bone, and known biomaterials processable by LM are used to estimate the site-specific porosity requirements in the scaffold model. A novel method for generating a tool path using space-filling fractal curves eliminates representation difficulties associated with LM of porous objects. A representative study of a hydroxyapatite scaffold for a cortical bone defect site in human femur is presented to illustrate the methodology. © 2009 Taylor & Francis.

Personalised bone tissue engineering scaffold with controlled architecture using fractal tool paths in layered manufacturing

Mechanics of Functionally Graded Material Structures

Beams Made of Functionally Graded Material

The International Journal of Advanced Manufacturing Technology

Modeling of porous structures for rapid prototyping of tissue engineering scaffolds

Biomaterials

Fabrication of three-dimensional polycaprolactone/hydroxyapatite tissue scaffolds and osteoblast-scaffold interactions in vitro

Temperature and stress analysis and simulation in fractal scanning-based laser sintering

Computer-Aided Design

Heterogeneous object modeling: A review

Journal	Virtual and Physical Prototyping
ISSN	17452759
Open Access	No