Publication InformationDoyle, H., Lohfeld, S., McHugh, P.E. (2013) 'Predicting the elastic properties of selective laser sintered PCL/b-TCP bone scaffold materials using computational modelling'. Annals Of Biomedical Engineering, 42 (3):661-677. Publisher SpringerLink to publisher's version http://link.springer.com/article/10.1007%2Fs10439-013-0913-4Item record http://hdl.handle.net/10379/5524 DOI http://dx.doi.org/10.1007/s10439-013-0913-4Accepted manuscript, published in Annals of Biomedical Engineering 09/2013; 42(3), pp 661-677. The final publication is available at Springer via http://dx.doi.org/10.1007/s10439-013-0913-4Title: Predicting the elastic properties of selective laser sintered PCL/β-TCP bone scaffold materials using computational modelling. AbstractThis study assesses the ability of finite element models to capture the mechanical behaviour of sintered orthopaedic scaffold materials. Individual scaffold struts were fabricated from a 50:50 wt% poly-ε-caprolactone (PCL) /β-tricalcium phosphate (β-TCP) blend, using selective laser sintering (SLS). The tensile elastic modulus of single struts was determined experimentally. High resolution finite element models of single struts were generated from micro-CT scans (28.8µm resolution) and an effective strut elastic modulus was calculated from tensile loading simulations. Three material assignment methods were employed: (1) homogeneous PCL elastic constants, (2) composite PCL/ β-TCP elastic constants based on rule of mixtures, and (3) heterogeneous distribution of micromechanically-determined elastic constants. In comparison with experimental results, the use of homogeneous PCL properties gave a good estimate of strut modulus; however it is not sufficiently representative of the real material as it neglects the β-TCP phase. The rule of mixtures method significantly overestimated strut modulus, while there was no significant difference between strut modulus evaluated using the micromechanically-determined elastic constants and experimentally evaluated strut modulus. These results indicate that the multi-scale approach of linking micromechancial modelling of the sintered scaffold material with macroscale modelling gives an accurate prediction of the mechanical behaviour of the sintered structure.Keywords: selective laser sintering; polycaprolactone, B-tricalcium phosphate; micromechanical modelling; bone tissue engineering; mechanical properties; finite element analysis.3 IntroductionThe purpose of bone tissue engineering scaffolds is to fill defects and support mechanical loading while providing a template on which new bone will form. The remodelling of native bone in response to mechanical loading occurs when cells convert mechanical stimuli to chemical signals to direct the formation of new tissue or resorption through mechanotransduction 30,44 . The mechanical stimuli that influence bone formation in vivo are a combination of both fluid shear over the cells 36,55 and mechanical loading of the cells 16,24,58 , therefore it is important to be able to acc...

No abstract

In bone tissue engineering, both geometrical and mechanical properties of a scaffold play a major part in the success of the treatment. The mechanical stresses and strains that act on cells on a scaffold in a physiological environment are a determining factor on the subsequent tissue formation. Computational models are often used to simulate the effect of changes of internal architectures and external loads applied to the scaffold in order to optimise the scaffold geometry for the prospective implantation site. Finite element analysis (FEA) based on computer models of the scaffold is a common technique, but would not take into account actual inaccuracies due to the manufacturing process. Image based FEA using CT scans of fabricated scaffolds can provide a more accurate analysis of the scaffold, and was used in this work in order to accurately simulate and predict the mechanical performance of bone tissue engineering scaffolds, fabricated using selective laser sintering (SLS), with a view to generating a methodology that could be used to optimise scaffold design. The present work revealed that an approach that assumes isotropic properties of SLS fabricated scaffolds will lead to inaccurate predictions of the FE model. However, a dependency of the grey value of the CT scans and the mechanical properties was discovered, which may ultimately lead to accurate FE models without the need of experimental validation.

No abstract

A multiscale modelling methodology to predict the macroscale stiffness of selective laser sintered polycaprolactone (PCL)/β-tricalcium phosphate (β-TCP) materials is evaluated. The relationship between a micromechanics-evaluated composite material elastic modulus (E eff) and segment grey-value (GVave) is established for a 90/10 wt% PCL/β-TCP material and compared to the previously established E eff vs. GVave relationship for a 50/50 wt% PCL/β-TCP material. The increase in E eff with GVave was found to be greater for the 90/10 wt% material than for the 50/50 wt% material. Differences in the material microstructures are visible with greater local conglomerations of β-TCP in the 90/10 wt% material compared to the 50/50 wt% material. These results indicate that the relationship between E eff and GVave is material-specific and that one definition cannot be used to describe both materials. We have used the E eff and GVave relationship specific to the 90/10 wt% material to assign element-specific elastic properties in a high resolution macroscale strut finite element model to successfully predict the experimentally-evaluated strut effective stiffness of the 90/10 wt%. These results combined indicate that this multiscale modelling methodology reasonably predicts the effective elastic modulus of selective laser sintering struts with different material configurations, and that it can be used to determine the material-specific definition of the relationship between E eff and GVave for a particular material.