Permeability of rapid prototyped artificial bone scaffold structures

Abstract

Abstract.Fluid flow through a bone scaffold structure is an important factor in its ability to build up a living tissue. Permeability is often used as a measure of a structure's ability to allow for flow of nutrients and waste products related to the growth of new tissue. These structures also need to meet conflicting mechanical strength requirements to allow for load bearing. In this work, the effect of different bone structure morphologies on permeability were examined both numerically and experimentally. Cubic and hexagonal based three dimensional scaffold structures were produced via stereolithography and 3D printing techniques. In particular, porosity percentage, pore size, and pore geometry were examined. Porosity content was varied from 30% to 70% and pore size from 0.34 mm to 3 mm. An adapted Kozeny-Carmen numerical method was applied for calculation of permeability through these structures and an experimental validation of these results was performed via a standard permeability experimental testing set-up. From the results it was determined that increased permeability was provided with the cubic rather than hexagonal structure as well as by utilizing the larger pore size and higher levels of porosity. Stereolithography was found to be the better processing technique, not only for improved micrometer scale dimensional accuracy reasons, but also due to the increase wettability found on the produced surfaces. The appropriate model constants determined in this work will allow for analysis of new alternate structure designs on the permeability of rapid prototyped synthetic bone structures.

Relationship between the morphological, mechanical and permeability properties of porous bone scaffolds and the underlying microstructure

“…However, previous studies have found a highly linear correlation between the permeability derived from CFD analysis and the experimental results (with a factor of approximately 0.27), concluding that the CFD analysis is a reliable tool for estimating the scaffold permeability [50,51]. This is confirmed by the fact that the range of permeability (1.0×10 −10 m 2 to 1.0×10 −8 m 2 ) predicted in the present study agrees with the experimental data using the flow chambers [52,53].…”

Computationally designed lattices with tuned properties for tissue engineering using 3D printing

“…The modeled relative elastic modulus of the Octet topology agrees well with studies that have found its relative elastic modulus as E r ≈ 0.01 when its relative density is about 0.1 [ 27 , 67 ]. Permeability predictions agree with studies that have found permeability on the order of 1 × 10 −8 m 2 for scaffolds with similar porosities and pore sizes tested with unidirectional flow chambers [ 18 , 66 ] and simulated with computational fluid dynamics [ 36 , 58 ]. Surface-volume ratios found for scaffolds are highly similar to those of trabecular bone, that is estimated as 7.25 mm −1 when bone porosity is 0.8 [ 68 ].…”

“…Element diameter constraints may be introduced to ensure scaffolds are manufacturable with a desired process, such as selective laser sintering that is limited to a minimum beam diameter of 200μm [ 28 ]. Mechanical properties of fabricated structures are measurable with standard compression and shear loading tests [ 5 , 16 , 17 ], while permeability properties are measurable with unidirectional flow chambers [ 18 , 66 ].…”

“…Permeability k was determined with ANSYS fluent computational fluid dynamics software that simulated unidirectional fluid flow through a lattice. Walls were placed around four sides of a lattice consisting of 27 unit cells that represent a flow channel [ 10 , 18 , 63 ]. Navier-Stokes equations of continuity and momentum were solved with the finite volume method.…”

“…Recent studies have demonstrated the capacity for tissue growth on beam-based lattices that inform computational approaches for scaffold design [ 11 – 13 ]. Lattice properties linked to scaffold performance include tissue growth related morphological properties of porosity, pore size, and surface area [ 14 ], mechanically related properties of elastic modulus and shear modulus [ 15 – 17 ], and properties related to nutrient transport such as permeability [ 18 , 19 ]. Our aim is to computationally model lattices with designed properties suitable for tissue engineering, and provide a basis for comparing lattices as porous structures for bone growth, using a spinal interbody fusion cage application to inform lattice design decisions.…”