Influence of flow rate and scaffold pore size on cell behavior during mechanical stimulation in a flow perfusion bioreactor

Abstract

FJ. Influence of flow rate and scaffold pore size on cell behavior during mechanical stimulation in a flow perfusion bioreactor. Biotechnology and Bioengineering. 2012;109(6):1583-1594.-Use LicenceAttribution-Non-Commercial-ShareAlike 1.0 You are free:• to copy, distribute, display, and perform the work.• to make derivative works. Under the following conditions:• Attribution -You must give the original author credit.• Non-Commercial -You may not use this work for commercial purposes.• AbstractMechanically stimulating cell-seeded scaffolds by flow-perfusion is one approach utilised for developing clinically applicable bone graft substitutes. A key challenge is determining the magnitude of stimuli to apply that enhances cell differentiation but minimises cell detachment from the scaffold. In this study we employed a combined computational modelling and experimental approach to examine how the scaffold mean pore size influences cell attachment morphology and subsequently impacts upon cell deformation and detachment when subjected to fluid-flow. Cell detachment from osteoblast-seeded collagen-GAG scaffolds was evaluated experimentally across a range of scaffold pore sizes subjected to different flow-rates and exposure times in a perfusion bioreactor. Cell detachment was found to be proportional to flow-rate and inversely proportional to pore size. Using this data, a theoretical model was derived that accurately predicted cell detachment as a function of mean shear stress, mean pore size and time. Computational modelling of cell deformation in response to fluid flow showed the percentage of cells exceeding a critical threshold of deformation correlated with cell detachment experimentally and the majority of these cells were of a bridging morphology (cells stretched across pores). These findings will help researchers optimise the mean pore size of scaffolds and perfusion bioreactor operating conditions to manage cell detachment when mechanically simulating cells via flow perfusion.

Quantification of fluid shear stress in bone tissue engineering scaffolds with spherical and cubical pore architectures

“…p=90%). For example, a dynamic cell culture study, in which bone cells seeded in a collagen-GAG scaffold were exposed to fluid perfusion (1mL/min), suggested that larger pore sizes (d=325µm) were preferable for mechanical stimulation for a better cell attachment, and an average WSS of 17.6mPa resulted in the scaffold (McCoy et al 2012). If the scaffolds were fabricated by rapid prototyping with spherical or cubical pores of 325µm, an average WSS of 12.7mPa and 8.2mPa would result for spherical and cubical architectures (p=90%) under a similar flow rate (1mL/min).…”

“…architecture, pore size and porosity) and the precise contribution of each toward resulting mechanical stimulation within a scaffold is difficult to characterise due to the range of interacting parameters. While previous studies have characterised WSS as a function of architecture, pore-size or porosity, the range of parameters considered in many of these studies is limited, with studies perhaps only considering a single pore-size (McCoy et al 2012) or porosity (Melchels et al 2011), for example.…”

“…Several computational models have been developed that characterise mechanical stimulation within TE scaffolds under a range of experimental culture conditions (Hendrikson et al 2014;Jungreuthmayer et al 2009a;Jungreuthmayer et al 2009b;Marin and Lacroix 2015;McCoy et al 2012;Porter et al 2005;Tuan and Hutmacher 2005). For instance, a computational fluid dynamics (CFD) study showed that the wall shear stress (WSS) in collagen-glycosaminoglycan (GAG) scaffold (porosity= 99%) was almost three-fold greater than that of a calcium phosphate (CP) scaffold (porosity=60%) and this could be explained by the difference in scaffold geometries (collagen-GAG pore size d≈96µm, CP pore size d≈350µm) (Jungreuthmayer et al 2009a).…”

“…For instance, a computational fluid dynamics (CFD) study showed that the wall shear stress (WSS) in collagen-glycosaminoglycan (GAG) scaffold (porosity= 99%) was almost three-fold greater than that of a calcium phosphate (CP) scaffold (porosity=60%) and this could be explained by the difference in scaffold geometries (collagen-GAG pore size d≈96µm, CP pore size d≈350µm) (Jungreuthmayer et al 2009a). To study the effect of scaffold pore size and applied loading on WSS at cellular level, McCoy et al (McCoy et al 2012) developed a fluid structure interaction (FSI) model for collagen-GAG scaffolds with pore sizes of 85µm, 120µm or 325µm under applied fluid flow stimulation in the range of 0.05mL/min -5mL/min.…”

Integration of mechanotransduction concepts in bone tissue engineering

“…Most of the knowledge gathered in mechanotransduction studies has mainly been translated in the development of bioreactor to produce in vitro artificial tissues, e.g. (Sikavitsas et al 2003;McCoy et al 2012). Indeed for clinical applications, bone scaffolds are often facing load-bearing situations.…”