Evaluation of the Growth Environment of a Hydrostatic Force Bioreactor for Preconditioning of Tissue-Engineered Constructs

Abstract

Bioreactors have been widely acknowledged as valuable tools to provide a growth environment for engineering tissues and to investigate the effect of physical forces on cells and cell-scaffold constructs. However, evaluation of the bioreactor environment during culture is critical to defining outcomes. In this study, the performance of a hydrostatic force bioreactor was examined by experimental measurements of changes in dissolved oxygen (O 2 ), carbon dioxide (CO 2 ), and pH after mechanical stimulation and the determination of physical forces (pressure and stress) in the bioreactor through mathematical modeling and numerical simulation. To determine the effect of hydrostatic pressure on bone formation, chick femur skeletal cell-seeded hydrogels were subjected to cyclic hydrostatic pressure at 0-270 kPa and 1 Hz for 1 h daily (5 days per week) over a period of 14 days. At the start of mechanical stimulation, dissolved O 2 and CO 2 in the medium increased and the pH of the medium decreased, but remained within human physiological ranges. Changes in physiological parameters (O 2 , CO 2 , and pH) were reversible when medium samples were placed in a standard cell culture incubator. In addition, computational modeling showed that the distribution and magnitude of physical forces depends on the shape and position of the cell-hydrogel constructs in the tissue culture format. Finally, hydrostatic pressure was seen to enhance mineralization of chick femur skeletal cell-seeded hydrogels.

Pluripotent Stem Cells and Their Dynamic Niche

“…However, ESC-derived EB exhibit downregulation of chondrogenic markers when subjected to the same stimulation regime [197]. It is also under investigation whether mechanical cues provided by bioreactors alone or in combination with other cues can induce lineage commitment in PSC [287,288].…”

“…stress, strain, shear, compression, hydrostatic pressure) are greatly influencing the cell morphology, cell adhesion, proliferation and gene regulation [214,289]. In order to provide physiological relevant growth environments for cells and tissue-engineered constructs, various types of bioreactors have been developed [287,290]. Bioreactors are devices that utilise mechanical forces to influence biological processes under closely controlled and monitored conditions [291,292].…”

“…They offer biophysical cues encouraging cells to differentiate or/and produce ECM prior to implantation in vivo [293]. In general, bioreactors meet the following applications in regenerative medicine-1: they provide spatially uniform cell distribution, 2: they deliver physiological relevant concentrations of oxygen and carbon dioxide as well as nutrients in the culture medium, 3: they support mass transport to the core of the tissue engineered construct facilitating cell survival throughout tissue-engineered constructs, 4: they provide physical stimuli to regulate stem cell differentiation and proliferation, 5: they facilitate tissue development and accelerate construct maturation [287,[294][295][296][297]. Studies utilising mechanical forces for the direction of stem cell fate and tissue development are summarised in Table 4.…”

“…Professor El Haj's group has developed a novel hydrostatic bioreactor allowing for ease of handling and scale up of sample numbers that can be mechanically stimulated simultaneously [287,288] (Figure 8). This bioreactor system is composed of a sealed aluminium chamber suitable for standard tissue culture well plates.…”

“…Hence, strategies including novel bioreactor technologies have been developed. By replicating the in vivo environment, bioreactors allow the study of mechanical stimuli in combination with chemical and biological signals on cell-cell and cell-biomaterial constructs [12].…”