Tissue mechanics of piled critical size biomimetic and biominerizable nanocomposites: Formation of bioreactor-induced stem cell gradients under perfusion and compression.
BACKGROUND
Perfusion bioreactors are used to solve problems in critical size bone tissue engineering. Biominerizable and biocompatible nanocomposites are suitable scaffold materials for this purpose because they offer mineral components in organic carriers. Human adipose derived stem cells (ASCs) can potentially be used to increase bone healing.


METHODS
Electrospun nanocomposite disks of poly-lactic-co-glycolic acid and amorphous calcium phosphate nanoparticles (PLGA/a-CaP) were seeded with ASCs and eight disks were stacked in a bioreactor running with normal culture. Under perfusion and uniaxial cyclic compression, load-displacement curves as a function of time were assessed. Stiffness and energy dissipation were recorded. Moreover, stem cell densities in the layers of the piled scaffold were determined as well as their morphologies and differentiation status.


RESULTS
While the stiffness of the cell free constructs increased over time based on the transformation of the a-CaP nanoparticles into flake-like apatite, ASC-seeded constructs showed a constant stiffness. Stem cell density gradients had a linear increase from the bottom to the top of the pile (r(2)>0.95). Stem cells were getting more roundish at higher flow rates. Some osteogenesis was found upon osteopontin immunostaining, while no endothelial cell differentiation and no chondrogenesis was triggered.


CONCLUSIONS
The fabrication of a critical size bone graft is presented based on a biominerizable bone-biomimetic nanocomposite with preserved stiffness when seeded with ASCs. The cell densities of ASCs inside the piled construct varied with a linear gradient. Beginning osteogenesis was triggered by the dynamic culture conditions including perfusion and compression.
Division of Plastic and Hand Surgery, University Hospital Zurich, Rämistrasse 100, CH-8091 Zurich, Switzerland.
Walter
W
Baumgartner
Division of Plastic and Hand Surgery, University Hospital Zurich, Rämistrasse 100, CH-8091 Zurich, Switzerland.
Manfred
M
Welti
Institute for Chemical and Bioengineering, Department of Chemistry and Applied Biosciences, ETH Zurich, CH-8093 Zurich, Switzerland.
Nora
N
Hild
Institute for Chemical and Bioengineering, Department of Chemistry and Applied Biosciences, ETH Zurich, CH-8093 Zurich, Switzerland.
Samuel C
SC
Hess
Institute for Chemical and Bioengineering, Department of Chemistry and Applied Biosciences, ETH Zurich, CH-8093 Zurich, Switzerland.
Wendelin J
WJ
Stark
Division of Plastic and Hand Surgery, University Hospital Zurich, Rämistrasse 100, CH-8091 Zurich, Switzerland.
Gabriella Meier
GM
Bürgisser
Division of Plastic and Hand Surgery, University Hospital Zurich, Rämistrasse 100, CH-8091 Zurich, Switzerland.
Pietro
P
Giovanoli
Division of Plastic and Hand Surgery, University Hospital Zurich, Rämistrasse 100, CH-8091 Zurich, Switzerland. Electronic address: johanna.buschmann@usz.ch.
Johanna
J
Buschmann
D000273:Adipose Tissue / Q000166:cytology; D040761:Biomimetic Materials / Q000737:chemistry / Q000494:pharmacology*; D019149:Bioreactors; D002130:Calcium Phosphates / Q000737:chemistry; D002452:Cell Count; D002454:Cell Differentiation / Q000187:drug effects; D049109:Cell Proliferation / Q000187:drug effects; D006801:Humans; D019344:Lactic Acid / Q000737:chemistry; D008903:Minerals / Q000378:metabolism*; D053761:Nanocomposites; D053758:Nanoparticles / Q000737:chemistry; D010477:Perfusion; D011100:Polyglycolic Acid / Q000737:chemistry; D000077182:Polylactic Acid-Polyglycolic Acid Copolymer; D013234:Stem Cells / Q000166:cytology* / Q000187:drug effects* / Q000378:metabolism; D023822:Tissue Engineering; D054457:Tissue Scaffolds / Q000737:chemistry; D016474:Weight-Bearing
D002130:Calcium Phosphates; D008903:Minerals; D000077182:Polylactic Acid-Polyglycolic Acid Copolymer; D011100:Polyglycolic Acid; D019344:Lactic Acid; C020243:calcium phosphate
Adipose-derived stem cell; Amorphous calcium phosphate; Apatite; Bone; Composite; Nanoparticle; PLGA; Stiffness