Effects of Flow Shear Stress 2and Mass Transport o
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Currently, a tissue-engineered bone is usually constructed using a perfusion bioreactor in vitro. In the perfusion
culture, fluid flow can exert shear stress on the cells seeded on scaffold, improving the mass transport of the cells.
This experiment studied the effects of flow shear stress and mass transport, respectively, on the construction of a
large-scale tissue-engineered bone using the critical-sized b-tricalcium phosphate scaffold seeded with human
bone marrow–derived mesenchymal stem cells (hBMSCs). This was done by changing flow rate and adding
dextran into the media, thus changing the media’s viscosity. The cells were seeded onto the scaffolds and were
cultured in a perfusion bioreactor for up to 28 days with different fluid flow shear stress or different mass
transport. When the mass transport was 3mL=min, the flow shear stress was, respectively, 0.005 Pa (0.004–
0.007 Pa), 0.011 Pa (0.009–0.013 Pa), or 0.015 Pa (0.013–0.018 Pa) in different experiment group obtained by simulation
and calculation using fluid dynamics. When the flow shear stress was 0.015 Pa (0.013–0.018 Pa), the mass
transport was, respectively, 3, 6, or 9mL=min. After 28 days of culture, the construction of the tissue-engineered
bone was assessed by osteogenic differentiation of hBMSCs and histological assay of the constructs. Extracellular
matrix (ECM) was distributed throughout the entire scaffold and was mineralized in the perfusion culture after
28 days. Increasing flow shear stress accelerated the osteogenic differentiation of hBMSCs and improved the
mineralization of ECM. However, increasing mass transport inhibited the formation of mineralized ECM. So,
both flow shear stress and transport affected the construction of the large-scale tissue-engineered bone. Moreover,
the large-scale tissue-engineered bone could be better produced in the perfusion bioreactor with 0.015 Pa
(0.013–0.018 Pa) of fluid flow shear stress and 3mL=min of mass transport.
Introduction
Currently, clinical treatments for osseous defects
and anomalies mainly include autografts, allografts, and
metallic implants.1 However, the drawbacks to these methods
are the limited availability and donor-site morbidity of
autografts, as well as issues on the immune responses from
allografts and metallic implants.2,3 Therefore, they remain
unsatisfactory for the treatment of large-scale bone defects.
Studies on the construction of the tissue-engineered bone
in vitro are gradually increasing with the goal of overcoming
the problems mentioned. Through the combination of the
tissue-engineering paradigm’s different essential components
(specifically the biomaterial scaffolds, cells, and bioactive
molecules), the microenvironment of normal tissue
development in vivo may be mimicked to recreate functional
and structural tissues in vitro.4
Traditional tissue engineering is the static culture of cellseeded
three-dimensional (3D) scaffolds. However, this static
culture pattern typically produces thin tissue growth localized
to the construct periphery.5 This phenomenon has resulted
mainly from the lack of mass transport inside the
construct. Hence, improving in vitro mass transport is a critical
challenge in the production of thick cellular constructs.
Many groups have developed bioreactors that perfuse cellseeded
constructs, and that have demonstrated the beneficial
effects of perfusion on cell survival, proliferation, and tissue
formation in the scaffold.6–9 However, most of these studies
are about the construction of a small-size tissue-engineered
bone. To simulate the long bone structure and to aid in the
1Department of Orthopedic Surgery, Ninth People’s Hospital, Shanghai Jiao Tong University School of Medicine, Shanghai, P.R. China.
2Orthopedic Cellular and Molecular Biology Laboratory, Institute of Health Sciences, Chinese Academy of Sciences and Shanghai Jiao
Tong University School of Medicine, Shanghai, P.R. China.
3Shanghai Bio-lu Biomaterials Company Limited, Shanghai, P.R. China.
4Engineering Research Center of Digital Medicine, Ministry of Education PRC, Shanghai, P.R. China.
TISSUE ENGINEERING: Part A
Volume 15, Number 00, 2009
a Mary Ann Liebert, Inc.
DOI: 10.1089=ten.tea.2008.0540
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