Selective laser sintering of hydroxyapatite/poly-ε-caprolactone scaffolds

Szilvia Eosoly 1Dermot Brabazon 1Stefan Lohfeld 2Lisa Looney 1

1. School of Mechanical and Manufacturing Engineering, Dublin City University, Dublin Dublin9, Ireland
2. National University of Ireland, Galway (NUIG), University Road, Galway none, Ireland

Abstract

Selective Laser Sintering (SLS) has the potential to fabricate complex geometries with intricate and controllable internal architecture. Numerous polymeric biomaterials can be processed by SLS given that they are available in the form of powder. However to process calcium phosphate bioceramics a thermoplastic polymer functioning as a binder material is required. In this study hydroxyapatite and poly-ε-caprolactone were used with a weight ratio of 30/70. These materials are suitable for hard tissue engineering purposes. SLS process parameters were examined in the following ranges: outline laser power (3-7 W), laser fill power (8-12W), scan spacing (0.1-0.2 mm) and building direction (X, Y, Z). The effect of feature size (0.5-0.7 mm) was also included in the design. All factors except manufacturing direction were examined at five levels using a Box-Wilson Central Composite Design (CCD) frequently used for process optimization. Mathematical model for estimating the mechanical properties, surface roughness and accuracy was developed and used for the optimization where the measured responses were the objective functions. As laser power and scan spacing determine the delivered energy density, the design also enabled the examination of its effect on the response functions in the range of 0.008 -0.02 J/mm2. In general higher energy density resulted in better mechanical properties due to lower porosity in the designed solid regions, increased dimensions and decreased surface roughness due to lower polymer viscosity during processing. The accuracy of fabricated parts was poor as deviation from nominal dimensions could reach 50%. Compressive moduli for geometries with relative density of 0.25 were in the range 1 - 5 MPa and compressive collapse strengths were in range 0.2-1 MPa. These values do not qualify the fabricated scaffolds for load bearing application however mechanical properties can be improved by post processing.

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Presentation: Oral at E-MRS Fall Meeting 2008, Symposium L, by Szilvia Eosoly
See On-line Journal of E-MRS Fall Meeting 2008

Submitted: 2008-05-12 13:15
Revised:   2009-06-07 00:48
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