Permeability of Rapid Prototyped Artificial Bone Scaffold Structures

Abstract

<jats:p>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.</jats:p>

Numerical Evaluation and Prediction of Porous Implant Design and Flow Performance

“…In the meantime, as expected, higher permeabilities were recorded for larger pore sizes and porosity ( Figure 8 ). These results are quite consistent with S. Gómez' study [ 32 ], and previous numerical calculations also had confirmed experimental results which indicated that permeability increased with increasing pore sizes and porosity [ 41 ]. However, with the increasing of volume, surface area, and specific surface area, average permeability seemed to be decreased.…”

Evaluation of multi-scale mineralized collagen–polycaprolactone composites for bone tissue engineering

“…In the case of the CGCaP scaffold and PCL-CGCaP composite, a high degree of specific surface area was reflected in the significantly lower permeability compared to the PCL support alone (Figure 4). The relatively lower specific surface area and resultant increased permeability in the 3D printed PCL construct has been previously attributed to limitations in feature size (mm-scale, rather than micron-scale, pores) (Lipowiecki et al, 2014). The significance of specific surface area as a biomaterial design parameter has similarly been addressed (Harley and Gibson, 2008;O'Brien et al, 2007;O'Brien et al, 2005).…”

“…Permeability was measured as previously described (Lipowiecki et al, 2014;O'Brien et al, 2007;Weisgerber et al, 2013). Briefly, axial permeability was assessed with flow through using a custom polycarbonate rig and a constant pressure head (ΔP) of 26.7 cm of de-ionized water.…”

“…channels in current PCL constructs for a mandibular repair), resulting in low specific surface areas (surface area/volume) for cell attachment as well as pore sizes well above the 100 -500 µm range largely believed to be optimal for bone tissue engineering (Hulbert et al, 1970;Kuhne et al, 1994). So while 3D printed biomaterials offer mechanically robust, customizable implants, limits in printed feature size and low specific surface area represent critical dilemmas that must be addressed (Lipowiecki et al, 2014).…”

Influence of 3D printed porous architecture on mesenchymal stem cell enrichment and differentiation

“…Here we aimed to minimize the impact of pore size by designing the pores to be equivalent in size, and focus on the impact of pore geometry on cell behavior, a concept that has been much less studied. Trabecular bone has a macroporous structure, with open marrow space pores on the order of 1 mm in size [33]. Previous studies have shown that larger pore sizes (on the order of 1-3 mm) allow for greater interaction between cells and the underlying biomaterial, improving the osteogenic properties of the tissue and resulting in a thicker tissue formation along the material surface [34,35].…”