Towards the development of multiaxial loading bioreactor for intervertebral disc studies: validation of an ex vivo organ model and customized sample holder

Jun 29, 2022, 4:00 PM
10m
Room: S1

Room: S1

Speaker

Šećerović, Amra (AO Research Institut Davos)

Description

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Introduction
The intervertebral disc (IVD) distributes multiaxial loads applied to the spine, namely axial compression, tension, lateral bending, and torsion. The effect of mechanical loading on IVD health and degeneration is commonly investigated in bioreactors used for ex vivo culture of IVD organ models. Currently available bioreactors have mainly integrated one or two degrees of freedom (DOF), while thus far developed multiaxial simulators with 6 DOF lack control of biological conditions. A new generation of bioreactors will integrate both six DOF loading and sterile culture of IVD organ models. Such a multiaxial system requires the implementation of the holding mechanism that must enable proper transmission of the loads from the bioreactor onto the specimen and sufficient nutrition through the cartilaginous endplate. We developed and validated a sample holder and new ex vivo IVD organ model according to the requirements for multiaxial bioreactor culture.

Methodology
A customized, circular IVD holder with a central cross pattern was designed. An ex vivo bovine caudal IVD organ model was adjusted to maintain more vertebral bone than the standard model (5-6 mm instead of 0.5 mm) to machine the cross counterpart and a central hole for nutrient access. The new and standard models were compared for long-term maintenance in a bioreactor under physiological conditions by alternating cyclic compressive uniaxial loading (0.02-0.2 MPa, 0.2 Hz, 2h/day) and overnight free swelling recovery. The disc height changes were measured daily, and cell viability was assessed with histology after 1, 2 and 3 weeks of culture (n= 2 for each time point) in comparison to day 0 samples (n= 3). The interface of the new IVD model and sample holder was enhanced with tightening of side screws onto the bone, or a combination of side screws and top screws, or side screws and adhesive, and was tested for failure point in compression, tension, torsion, and lateral bending (n=3 for each test).

Results
The new model retained a high level of cell viability during three weeks of in vitro culture (standard versus new model after 3 weeks: outer annulus fibrosus 82% and 84%, inner annulus fibrosus 69% and 64%, nucleus pulposus 75% and 73%). In both models, the decrease in IVD height after loading was in the range of typical physiological conditions (≤ 10%). When differently directed motions were applied, the holder-IVD interface with side screws transmitted compression and torsion above reference values (average obtained values were 320.37 N and 1.64 Nm, respectively), while the combination of side and top screws improved the resistance to tension and bending compared to the targeted values (average obtained values were 431.86 N and 0.79 Nm, respectively).

Conclusion
We have developed a mechanically reliable holding system for application in a new generation of multiaxial bioreactors and demonstrated that the new ex vivo IVD organ model can be maintained in long-term culture. Additional studies are envisaged to validate the system in the new bioreactor. Such a unique bioreactor will enable overcoming the gap between preclinical in vitro cultures, animal models, and clinical trials."

20941829709

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