Bioreactors with hydrostatic pressures imitating physiological environments in intervertebral discs

Abstract

Intervertebral discs are normally exposed to a variety of loads and stresses but hydrostatic pressure (HP) could be the main biosignal for chondrogenic cell differentiation and maintenance of this tissue. Although there are simple approaches to intermittently expose cell cultures to HP in separate material testing devices, utilization of biomimetic bioreactors aiming to provide in vitro conditions mimicking those found in vivo, attracts special attention. However, design of such bioreactors is complex due to the requirement of high HP magnitudes (up to 3 MPa) applied in different regimes mimicking pressures arising in intervertebral disc during normal daily activities. Furthermore, efficient mass transfer has to be facilitated to cells within 3D scaffolds, and the engineering challenges include avoidance or removal of gas bubbles in the culture medium before pressurization as well as selection of appropriate, biocompatible construction materials and maintenance of sterility during cultivation. Here, we review approaches to induce HP in 2D and 3D cell cultures categorized into 5 groups: (I) discontinuous systems with direct pressurization of the cultivation medium by a piston, (II) discontinuous systems with indirect pressurization by a compression fluid, (III) continuous systems with direct pressurization of the cultivation medium, static culture, (IV) continuous systems with culture perfusion, and (V) systems applying HP in conjunction with other physical signals. Although the complexity is increasing as additional features are added to the systems, the need to understand HP effects on cells and tissues in a physiologically relevant, yet precisely controlled, environment together with current technological advancements are leading towards innovative bioreactor solutions.

Hydrostatic Pressure Modulates Intervertebral Disc Cell Survival and Extracellular Matrix Homeostasis via Regulating Hippo-YAP/TAZ Pathway

“…There are still some contradictions in the prior studies about the effects of different pressure loading methods or intensities on the biological behavior of the IVD. The majority holds that the cells in NP and inner AF tissues mainly suffered hydrostatic pressure, because when a compressive force is applied to the IVD, the hydrostatic pressure within NP and inner AF is increased [9,27]. Hence, in the present study, we used the self-developed hydrostatic pressure bioreactor based on a pressure-transmitting mode achieved by a slight deformation of a flexible membrane in a completely sealed stainless steel chamber, to imitate in vivo microenvironment for NP and inner AF tissues.…”

“…However, the conclusions of the studies are not entirely consistent, due to the different quality of hydrostatic loading devices and observing methods used in the studies. It has been reported that the "physiological intensity (0.35-0.75 MPa)" of hydrostatic pressure acts as an anabolic factor for NP and AF cells, owing to the stimulation of proteoglycan synthesis [7][8][9]. In contrast, excessive pressure aggravates the catabolic metabolism of proteoglycan in NP and AF cells [7][8][9].…”

“…It has been reported that the "physiological intensity (0.35-0.75 MPa)" of hydrostatic pressure acts as an anabolic factor for NP and AF cells, owing to the stimulation of proteoglycan synthesis [7][8][9]. In contrast, excessive pressure aggravates the catabolic metabolism of proteoglycan in NP and AF cells [7][8][9]. Another study reported that the proteoglycan synthesis is inhibited at 0.35 MPa compared to atmospheric pressure for both NP and AF cells harvested from the lumbar IVD tissue of dogs [10].…”

Biomaterials-Induced Stem Cells Specific Differentiation Into Intervertebral Disc Lineage Cells

“…Some studies have emphasized the importance of bionic micromechanical characteristics (Wan et al, 2016). More specifically, biomaterials with natural NP and AF structures have been recommended for IVD reconstruction (Zvicer and Obradovic, 2018). Nevertheless, the complex modulus of the NP is 22 kPa (Bron et al, 2009), and the AF extra-fibrillar matrix modulus ranges from 10 to 50 kPa (Cortes et al, 2013), which is much greater than the modulus that favors IVD cell differentiation.…”

Compressive Stress Enhances Invasive Phenotype of Cancer Cells via Piezo1 Activation

“…Several methods exist to apply compressive stress to cells such as using a microfluidic platform 6,44 or a hydrostatic pressure system 45,46 . However, a system that exerts a constant contact compressive force is more suitable to simulate uncontrolled growth-induced mechanical compression found in solid tumor.…”