MECHANICAL AND BIOLOGICAL CHARACTERIZATION OF 3D. PRINTED POLYMER LATTICES FOR BONE TISSUE ENGINEERING. Paul F. Egan (1), Xiuyu ...
MECHANICAL AND BIOLOGICAL CHARACTERIZATION OF 3D PRINTED POLYMER LATTICES FOR BONE TISSUE ENGINEERING Paul F. Egan (1), Xiuyu Wang (1), Helen Greutert (1), Kristina A. Shea (2), Karin Würtz-Kozak (1), and Stephen J. Ferguson (1)
1. Institute for Biomechanics, ETH Zurich, Switzerland; 2. Engineering Design and Computing Laboratory, ETH Zurich, Switzerland
Introduction Advances in additive manufacturing are enabling the design and fabrication of complex 3D printed structures suitable as biomaterials for tissue engineering, such as beam-based lattices [Wild et al, 2017]. Beam-based lattices have favourable mechanical properties due to greater mechanical efficiency at a given porosity when compared to more common foam-based scaffolds [Egan, Ferguson, Shea, 2017]. Experiments and simulation are necessary for characterizing diverse lattice designs to determine their performance as biomaterials for bone tissue engineering.
Figure 1: Cube/FX-BC topologies; panels (clockwise) show CAD design, 3D prints, structural microscopy, and 6 week SAOS-2 tissue growth.
Methods Lattices were designed with python scripting and Abaqus software to generate structures with controlled beam diameters, unit cell size, and porosity. Lattices were manufactured with a Stratasys Objet Connex polyjet printer with MED610 material. Support material was removed from structures chemically to reduce structural damage during cleaning. Scaffolds were sterilized and seeded with SAOS-2 cells that are representative of a bone tissue engineering environment [Sobral et al, 2011]. Light microscopy and confocal laser scanning microscopy were used to image scaffold structure and cell growth. Tissue growth simulations were conducted in a voxel environment representing one eighth of a lattice unit cell of 50% porosity. A scanning mask was used to calculate local curvature, tissue voxels were added in locations with positive curvature, and the simulation ran until structures were filled [Bidan et al, 2013]. Finite element analysis (FEA) for properties relative to the base polymer used beam-based models in Abaqus [Egan et al, 2017].
Results Scaffolds were designed with 500µm beam diameters and 500µm diameter interconnectivity pores. Manufactured beams diameters were measured in the range of 400µm-600µm. Tissue grew on surfaces for both topologies (Fig. 1). Simulations suggest the FX-BC topology facilitates faster tissue growth and has a higher shear modulus, but lower elastic modulus than the Cube topology (Fig. 2)
Figure 2: Tissue growth simulation and plots for Cube/FX-BC topologies with percent filled tissue p. FEA for Elastic/shear moduli of p=0 structures.
Discussion Both topologies were manufacturable and supported tissue growth, thus suggesting their suitability as tissue scaffolds. Simulations suggest lattices of different topologies provide contrasting properties that influence mechanical and biological performance. Further experiments are required to determine manufacturing/simulation accuracy and support lattice optimization as biomaterials.
References Bidan et al, Comp Meth Biomech, 16:1056, 2013. Egan, Ferguson, Shea, J M Des, 139:061401, 2017. Sobral et al, Acta Biomat, 7: 1009, 2011. Wild et al, 3DP and Add Manu, 4:143, 2016.
