CROSS-REFERENCE TO RELATED APPLICATION

[0001] The present application is claiming priority from U.S. Provisional Application No. 63/358,909 filed July 7, 2022, the content of which is hereby incorporated by reference in its entirety.

TECHNICAL FIELD

[0002] The present description relates to bioreactors for ex vivo characterization of biological structures such as intervertebral discs.

BACKGROUND ART

[0003] Back pain is often linked to intervertebral disc (IVD) pathology, as wear, degeneration and other diseases of the IVD may affect its functionality and in some cases allow nearby physiological structures to impinge on nervous pathways. The mechanical loading conditions to which IVDs may be subjected are complex, and even some deemed typical of normal, daily activity are recognized as significant contributing factors behind IVD diseases. To understand these diseases and develop effective therapies, means for assessing the response of IVDs to such complex loads have been developed, for example ex vivo mechanical testing of biological samples, and computer- based simulations of geometrical models of IVDs bound by constitutive relations and subjected to loading conditions intended to reproduce in vivo behaviour. Though the biological and mechanical response of IVDs has been studied extensively via either means, developments in the field may assist in further characterization of the physiological and pathological mechanisms associated to IVDs.

[0004] There is thus a need to be provided with means to characterize biological structures such as intervertebral discs.

SUMMARY

[0005] In an aspect of the present technology, there is provided a biomechanical characterization system comprising: a perfusion system including a culture chamber, a first and a second endplate disposed opposite one another inside the culture chamber, and a loading system kinematically coupled to the first endplate such that the first endplate is controllably displaceable inside the culture chamber.

[0006] In some embodiments, the first endplate and the second endplate are arranged so as to define a gap therebetween, at least one of the first endplate and the second endplate having an inlet conduit in fluid communication between upstream of the culture chamber and the gap.

[0007] In some embodiments, the at least one of the first endplate and the second endplate has a gap-facing surface defining channels extending radially outwardly from the inlet conduit, the channels in fluid communication between the inlet conduit and outside the gap.

[0008] In some embodiments, the first endplate is disposed above the second endplate and the culture chamber includes a base disposed below the second endplate, the base having an outlet conduit in fluid communication between inside the culture chamber and downstream thereof.

[0009] In some embodiments, the loading system includes an end effector connected to the first endplate and an actuator arrangement operatively connected to the end effector, the actuator arrangement controllably operable to displace the end effector with the first endplate.

[0010] In some embodiments, the culture chamber includes a dynamic seal defining an opening inward the culture chamber, and the end effector is sized to extend from outside the culture chamber to inside thereof via the dynamic seal.

[0011] In some embodiments, the loading system is a parallel manipulator, the actuator arrangement including a plurality of linear actuators operatively connected to the end effector.

[0012] In some embodiments, the actuator arrangement includes six linear actuators having a connector joined to the end effector and displaceable with the end effector between a retracted position and an extended position defining a stroke range of about 50.8 mm, the linear actuators arranged to be at a first angle of about 99 degrees relative to the end effector when in the retracted position and at a second angle of about 97 degrees when in the extended position.

[0013] In some embodiments, the biomechanical characterization system further comprises a second loading system kinematically coupled to the second endplate such that the second endplate is controllably displaceable inside the culture chamber.

[0014] In another aspect of the present technology, there is provided a method of ex vivo characterization of an intervertebral disc comprising: connecting an end effector between the intervertebral disc inside a culture chamber and an actuator to kinetically couple the intervertebral disc to the actuator; controlling the actuator to displace the end effector to a desired position corresponding to a desired loading condition to be imparted to the intervertebral disc including at least one of compression, torsion and bending; sensing a response position of the actuator after displacing the end effector, and determining a biomechanical response of the intervertebral disc based on the response position of the end effector.

[0015] In some embodiments, the sensing of the response position of the actuator is delayed by a response duration upon the end effector attaining the desired position.

[0016] In some embodiments, the method further comprises imparting a predetermined load to the end effector via the actuator for the response duration upon the end effector attaining the desired position, the response position being indicative of a creep response of the intervertebral disc.

[0017] In some embodiments, the method further comprises disengaging the actuator for the response duration upon the end effector attaining the desired position, the response position being indicative of a stress relaxation response of the intervertebral disc.

[0018] In some embodiments, the method further comprises perfusing the intervertebral disc with a flow of cell culture medium as the end effector is displaced. [0019] In some embodiments, the method further comprises controlling an upstream flow rate of the flow of cell culture medium and sensing a downstream flow rate of the flow of cell culture medium, a rate difference between the upstream and downstream flow rate being indicative of a permeability of the intervertebral disc.

[0020] In some embodiments, the method further comprises injecting an intervertebral nucleus pulposus substitute composition in the intervertebral disc prior to displacing the end effector to the desired position.

[0021] In some embodiments, the method further comprises determining the desired position.

BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Fig. 1 is a perspective view taken from a top, rear, left side of a spinal functional unit comprising two vertebrae and an intervertebral disc;

[0023] Fig. 2 is a perspective view of an exemplary embodiment of a bioreactor in accordance with an aspect of the present technology;

[0024] Fig. 3 is a top planar view of a portion of a loading system of the bioreactor of Fig. 2, shown isolated from a remainder of the bioreactor;

[0025] Fig. 4 is a section view of the loading system of Fig. 2, taken along line 4-4 of Fig. 3, and

[0026] Fig. 5 is a perspective view of a perfusion system of the bioreactor of Fig. 2 shown isolated from a remainder of the bioreactor.

DETAILED DESCRIPTION

[0027] In the present disclosure, unless specified otherwise, position, orientation and movement is described with respect to three-dimensional spatial coordinate systems in which axes X, Y and Z are orthogonal to one another. Such coordinate systems may be defined globally, for example relative to an enclosure in which an IVD may be disposed, or more locally, for example relative to a spinal functional unit 2 including an IVD 4 and its adjacent cranial 6 and caudal 8 vertebrae, as shown in Fig 1. Although the forthcoming description focuses on loading conditions and implementations of the present technology pertaining to anatomy and biomechanics of the human kind, it may also apply, mutatis mutandis, to those of several animal species, references to which are omitted from the present disclosure merely for the sake of brevity. Hence, in Fig. 1 , a local coordinate system Xi, Yi, Zi of the IVD 4 located at a cranial cartilaginous endplate (CE) 4a of the IVD 4. This system is conventionally defined by landmarks of the adjacent cranial vertebra 6, and can be used to describe loading conditions applicable to the IVD 4 at this interface. Conversely, a similar coordinate system located at a caudal CE 4b of the IVD 4 can be defined by the caudal vertebra 8.

[0028] Still referring to Fig. 1, an origin of the local coordinate system is at a centroid of a caudal bony endplate 6b of the cranial vertebra 6. The Xi and Yi axis extend perpendicularly to one another from the origin, defining a plane in which lays the caudal bony endplate 6b. The Zi axis is normal to the Xi-Yi plane and extends away from the origin toward a cranial bony endplate 6a opposite the caudal bony endplate 6b. Tension (and compression) may be imparted by loading the IVD 4 with a force along the Zi axis and away from (or toward) the origin. Shear may be imparted along either of the Xi and Yi axes. Left and right bending may be imparted respectively clockwise and counter clockwise about the Xi axis. Flexion and extension may be imparted respectively counter clockwise and clockwise about the Yi axis. Finally, torsion may be imparted to the IVD 4 with a moment about the Zi axis. The spinal functional unit 2 has been schematically depicted for clarity. For example, the IVD 4 has been provided with a symmetrical shape with respect to planes Xi-Yi, Xi-Zi, Yi-Zi, with its CEs 4a, 4b parallel to one another.

[0029] With respect to Figs. 2-5, there is provided a bioreactor in accordance with an aspect of the present technology, an exemplary embodiment of which is shown at 10 in Fig 2. The bioreactor 10 may also be referred to as a biomechanical characterization system. As will later be described hereinbelow, the present technology also provides, in another aspect thereof, a method of ex vivo characterization of biomaterials, such as the IVD 4. [0030] The bioreactor 10 generally comprises an enclosure 12, a loading system 14 and a perfusion system 16. In embodiments, the bioreactor 10 also comprises a control system, schematically represented at 18, by way of which operations of the bioreactor 10 can be controlled. The enclosure 12 is structurally connected to the loading and perfusion systems 14, 16, forming a framework for orienting and stabilizing the latter. For instance, the enclosure 12 may be structured so as to define a first, global reference coordinate system of the bioreactor 10 (axes X1, Y1, Z1). The enclosure 12 may also be structured so as to exhibit adequate rigidity and vibration dampening properties. Indeed, the enclosure 12 may be adapted to mitigate propagation of vibration to and from other components of the bioreactor 10, whether such vibration originates from outside the enclosure 12 or from inside thereof, as may be the case during its operation. The enclosure 12 may also be shaped to define a clearance volume inside which the loading and perfusion systems 14, 16 are operable unhindered. The enclosure 12, the loading system 14 and the perfusion system 16 may be said to be arranged with respect to one another such that their components are generally accessible for manual operation, maintenance or replacement. Shown in an exemplary implementation, the enclosure 12 comprises beams 20, corner brackets 22 linking the beams 20 to one another in a prismatic arrangement defining six generally open sides of the enclosure 12, and plates 24 disposed along top (24a) and bottom (24b) sides, interfacing their corresponding beams 20. Fasteners are used to mechanically attach the corner brackets 22 and the plates 24 to the beams 20. The plates 24a, 24b are positioned and oriented parallel of the X1-Y1 plane and thus perpendicular to the Z1 axis. Components of the loading system 14 are mechanically linked to the top plate 24a around the Z1 axis and extend generally toward the bottom plate 24b. Components of the perfusion system 16 are joined to the bottom plate 24b and extend generally toward the top plate 24a (and thus the loading system 14) along the Z1 axis. In mounting the IVD 4 to the bioreactor 10, the IVD 4 may be positioned with respect to the perfusion system 16 such that its axes Xi, Yi, Zi generally align with the corresponding axes X1, Y1 , Z1 of the enclosure 12. The loading system 14 may then be positioned with respect to the IVD 4 such that its axes X2, Y2, Z2 align with the corresponding axes Xi, Yi, Zi of the IVD 4. The foregoing is merely an exemplary one of many suitable arrangements for the enclosure 12 and positional configurations of the IVD 4 with respect to the bioreactor 10.

[0031] Referring to Figs 3 and 4, the loading system 14 generally comprises actuators 40 and a platform 50 kinematically coupled thereto, and may be generally described as a parallel manipulation robot having a sole end effector (i.e., the platform 50) and multiple individually-controllable linkages (i.e., the actuators 40) operatively connected to the end effector. It should be understood that the term “parallel” is merely used to distinguish the side-by-side configuration of the actuators 40 from serial (or end- to-end) configurations, and that geometrical parallelism between any two components of the loading system 14 is not to be inferred unless stated or shown explicitly.

[0032] Each actuator 40 generally includes a driving body 42 and a driven member 44 linearly displaceable relative to the driving body 42 along a stroke axis 40’. The driving body 42 has a sleeve 42a extending along the stroke axis 40’ and in this case houses an electric motor. The driven member 44 has a shaft 44a collinear to the sleeve 42a and mechanically connected to the driving body 42 so as to be displaceable (or driven) thereby along the stroke axis 40’. The actuator 40 may be referred to as an electromechanical actuator, although other types of actuators (e.g., pneumatic, hydraulic, electromagnetic) are encompassed. In any case, the actuator 40 is arranged to generate and bear loads via the shaft 44a in either direction along the stroke axis 40’. In the depicted embodiment, the sleeve 42a and the shaft 44a have complementary shapes cooperable with one another to hinder rotation of the shaft 44a relative to the sleeve 42a about the stroke axis 40’. Hence, the sleeve 42a and the shaft 44a may be said to form a prismatic joint, imparting the actuator 40 with a sole degree of freedom, i.e., linear displacement along the stroke axis 40’. In other embodiments, rotation of the shaft 44a relative to the sleeve 44b about the stroke axis 40’ is unhindered by their respective shapes, and such rotation may be actuable by the driving body 42 under control by the control system 18.

[0033] An end connector 44b of the driven member 44 is provided as a means for the actuator 40 to interface the platform 50. The end connector 44b is mounted to a distal end of the shaft 44a and displaceable therewith along the stroke axis 40’ between a retracted position and an extended position relative to the driving body 42, in this case relative to a body connector 42b of the driving body 42 located opposite the end connector 44b. A distance between the retracted and extended positions may be referred to as a stroke of the actuator 40, which may be of about 50 mm, for example 50.8 mm as per the present embodiment. In other embodiments, one or more of the actuators 40 may have a different stroke. It is contemplated that any of the actuators 40 may, in some implementations, have a pair of driven members that are controllably displaceable in opposite directions independently from one another. For instance, in some such implementations, the connectors 42b, 44b may be provided at the ends of both driven members. Further, the driven members may respectively form part of two separate actuators paired in series to form the actuator 40.

[0034] In the depicted embodiment, six actuators 40 are provided, and hence the platform 50 joined thereto may be referred to as a hexapod (also known as Stewart) platform. This arrangement provides the loading system 14 with six-axis kinematics. Stated otherwise, the loading system 14 has the capacity to effect motion with respect to either one of the axes X1, Y1 , Z1, whether in translation or rotation, without there being any other motion coupled thereto. In other embodiments, other arrangements of more or less actuators 40 may be used, and in some instances including actuators of different types (e.g., linear and rotary actuators), provided that they impart the loading system 14 with kinematics consistent with the present description. The platform 50 has an actuator-side 50a surface which bears platform connectors 52 respectively paired to one of the end connectors 44b of the actuators 40 to form a proximal rotatable joint. Each proximal rotatable joint imparts two or three degrees of freedom to the platform 50 relative to its corresponding driving body 42 in addition to those inherited from the connection between the driving body 42 and the driven member 44. In any case, the resulting degrees of freedom imparted to the platform 50 by each proximal rotatable joint includes rotation about three orthogonal axes including the stroke axis 40’ of the corresponding actuator 40. The proximal rotatable joints are in this case spherical joints. Opposite the end connectors 44b, the body connectors 42b are paired with complementary enclosure connectors 26 to form distal rotatable joints, also provided in the form of spherical joints. The enclosure connectors 26 are held in position relative to the enclosure 12. Each actuator 40 is thus joined to the enclosure 12 and to the platform 50 such that it is rendered orientable relative to the enclosure 12. Various suitable types of spherical joints may be used, such as several ball joint types, lubricant- free or not. In some cases, for example in certain embodiments of the bioreactor 10 provided with more than six actuators 40, one or both rotatable joints along a same stroke axis 40’ may be a universal joint provided to hinder rotation of the corresponding actuator 40 about the axis 40’.

[0035] Each distal rotatable joint may be said to define an origin of a spherical coordinate system (R, 0 <j>) according to which an orientation of its corresponding actuator 40 may be described. The origin lays in an azimuth plane parallel to the X1-Y1 plane and is intercepted by an inclination axis I parallel to the Z1 axis. A projection of the actuator 40 and its stroke axis 40’ in the azimuth plane is at an azimuthal angle <j> (Fig. 3). The stroke axis 40’ extends away from the origin at an inclination angle 0 relative to the azimuth plane (Fig. 4). A distance between the end connector 44b of the actuator 40 and the origin may be referred to as a radial distance R. Upon the end connectors 44b of the actuators 40 being at matching positions along their respective stroke axes 40’, and hence at a same radial distance R, the actuators 40 are constrained at a same inclination angle 0 and the platform 50 is constrained in an orientation parallel to the X1-Y1 plane. Under such circumstances, the platform 50 may be said to be in a hanging position, wherein the platform 50 is constrained at a same angle a with respect to every actuator 40. For instance, as shown in Fig. 4, the platform 50 is in a first hanging position at a first angle a1 when each actuator 40 is in the retracted position and in a second hanging position at a second angle a2 when each actuator 40 is in the extended position. The radial distance R of the end connector 44b in each position is schematically shown at R1 (retracted position) and R2 (extended position). The first and second angles a1, a2 may be of 99 degrees and 97 degrees respectively as in the present embodiment, although other angles a may be suitable for other implementations of the loading system 14. [0036] Despite the constraints described above, the end connectors 44b are displaceable unhindered to and from any position between their retracted and extended positions to produce various combinations of radial distances R, thereby effecting various displacements of the platform 50 consistent with the ranges of motion (ROMs) described hereinbelow. For this purpose, the rotatable joints are configured to have suitable ranges of rotation. In one exemplary configuration, the platform connector 52 of each proximal rotatable joint is indirectly attached to the platform 50, in this case by way of a block 54, so as to define a clearance between the platform connector 52 and the platform 50. The platform connector 52 is spaced away from the actuator-side surface 50a along the Z2 axis by its corresponding block 54, and spaced away from the block 54 along a direction D by a stem-like spacer. The platform connector 52 connects to the end connector 44b along a connection axis C collinear to the direction D. A similar configuration is provided, mutatis mutandis, for each distal rotatable joint.

[0037] It should be noted that the rotational joints are configured to ensure that operational limits of the rotational joints are not reached upon displacing the platform 50. Such operational limits include azimuthal and inclination rotation ranges being limited to maximums of less than 90 degrees. Such maximums may for example be both of about 54 degrees. To this end, any one of the enclosure and platform connectors 26, 52 may the arranged such that its direction D is at an angle in the vicinity of 90 degrees relative to the corresponding inclination axis I upon the platform 50 being in one of its hanging positions. In some embodiments, the directions D of the enclosure and platform connectors 26, 52 of a same actuator 40 may be respectively parallel to the X1-Y1 plane and to the X2-Y2 plane. Further, as per the present embodiment, the enclosure and platform connectors 26, 52 of a same actuator 40 may be positioned relative to the enclosure 12 and to the platform 50 such that their directions D and corresponding inclination axis I are generally coplanar whenever the platform 50 is in one of its hanging positions. An exemplary structural arrangement for achieving such a spatial relationship will now be described with respect to the platform 50. A track 56 defined inward the actuator-facing surface 50a of the platform 50 extends along a specific orientation. The block 54 is slidably received by the track 56, and a fastener 58 (Fig. 4) is used to fasten the block 54 to the platform 50 at a specific position along the track 56. The fastener 58 is in this case a screw received in a platform bore (in this case having a counterbore) extending through the platform 50 in an orientation parallel to the Z2 axis. The block 54 has a tapped bore and is positioned in the track 56 such that the tapped bore is collinear to the platform bore. The fastener 58 has a head that is oversized relative to the platform bore (and in this case sized to fit inside the counterbore of the platform bore) and a threaded shank projecting from the head and sized to extend through the platform bore and into the tapped bore to secure the block 54 in place. The block 54 and the track 56 have complementary shapes cooperating to hinder displacement of the block 54 relative to the platform 50, for instance rotation of the block 54 about the axis of the platform bore. Further, the block 54 and the track 56 may be said to hinder loosening of the fastener 58 which may otherwise result from torques borne by the blocks 54 during operation of the loading system 14. The aforementioned spatial and functional relationships may be achieved by way of this structural arrangement or by any suitable alternative being provided for the platform connector 52 and the enclosure connector 26 of a same actuator 40.

[0038] In embodiments, one or more of the actuators 40 may be provided with a sensor arrangement configured to sense at least one kinematic property of its end connector 44b. The property may be either of a position, orientation, speed, acceleration and movement direction of the end connector 44b. The sensor arrangement may thus include a potentiometer, an accelerometer, a gyroscope and the like. In some embodiments, the sensor arrangement is configured to sense a load property of the end connector 44b, i.e., a load imparted or borne thereby. The sensor arrangement may thus include a load cell suitable for sensing a compression, tension or torque. The sensor arrangement may be connected to the control system 18 to send one or more signals indicative of sensed properties. In certain implementations, some part or all of the sensor arrangement may instead be external to the actuator 40 and be part of the control system 18.

[0039] Opposite the actuators 40, a stem-like end effector E (Figs. 2 and 5) of the loading system 14 extends away from the effector-side 50b surface of the platform 50. A second, local reference coordinate system (axes X2, Y2, Z2) of the bioreactor 10 is defined by the platform 50. The actuator-side 50a and effector-side 50b surfaces are each generally normal to the Z2 axis and parallel to the X2-Y2 plane, and the end effector E is generally parallel to the Z2 axis. Upon the actuators 40 being in their respective retracted positions, the platform 50 is in a neutral position in which the X2-Y2 plane is generally parallel to the X1-Y1 plane of the global reference system and, conversely, the Z2 axis and the end effector E are generally parallel to the Z1 axis. As the CEs 4a, 4b of the IVD 4 be at an angle relative to one another, mounting the caudal CE 4b onto the second endplate 64b so as to be generally parallel to the X1-Y1 plane and normal to the Z1 axis may position the cranial CE 4a at an angle relative to the X1- Y1 plane. Under such circumstances, the actuators 40 may be controlled to move the end effector E with the first endplate 64a to a baseline position in which the cranial CE 4a is mounted to the first endplate 64a absent any significant load imparted by the end effector E to the IVD 4. In the baseline position, the axes of the second coordinate system (X2, Y2, Z2) are in general alignment with the corresponding ones of the IVD coordinate system (Xi, Yi, Zi). The baseline position may be one of the hanging positions of the platform 50. In some embodiments, the first endplate 64a is integral to the end effector E. In some embodiments, at least one of the first endplate 64a and the second endplate 64b is provided with a load cell configured for sensing a load borne by either endplate 64a, 64b. The load may thus be indicative of that imparted to the IVD 4 if present between the plates 64a, 64b.

[0040] The actuators 40 and the platform 50 are arranged such that the end effector E is provided with ranges of motion (ROMs) and capable of imparting loads encompassing those typically observable in vivo with respect to healthy or pathological intervertebral discs, at either one or both of its cartilaginous endplates or adjacent vertebrae. Exemplary ROMs will now be provided with respect to the global coordinate system of the enclosure 12, followed by corresponding physiological loading terminology in parentheses. The platform 50 may be displaced along either of the X1 and Y1 axes by about 20 mm in either of their respective directions (to impart shear), along the Z1 axis by up to about 50 mm toward the origin (to impart compression) or away therefrom (to impart tension), pivoted about the Y1 axis by up to about 15 degrees either counter clockwise (to impart flexion) or clockwise (to impart extension), pivoted about the X1 axis by up to about 10 degrees either clockwise or counter clockwise (to impart lateral bending), and about the Z1 axis by up to about 40 degrees (to impart torsion). Resolutions of displacement within the above ROMs may be of about 0.2 mm along either of the X1 , Y1, Z1 axes, 0.2 degree about either of the X1 and Y1 axes, and 0.4 degree about the Z1 axis. Moreover, exemplary loading conditions that may be imparted by the end effector E include up to about 3000 N along the Z1 axis, up to about 135 Nm about the Y1 axis, up to about 164 Nm about the X1 axis, and up to about 40 Nm about the Z1 axis, whether alone or in combination. Loading conditions may be imparted statically to maintain a constraint in the IVD 4 over time, which may allow to determine, for example, a creep response of the IVD 4. The loading system 14 also provides for kinematic loading conditions of various types, amplitudes and frequencies, which may correspond to typical in vivo conditions borne by the IVD 4, for example over the course of a 24-hour day. Loading conditions for the IVD 4 may be determined ad hoc, for example according to a sought disc constraint, deformation or other response, or according to a previously determined response of the IVD 4.

[0041] In some embodiments, the bioreactor 10 comprises a pair of loading systems disposed opposite one another with a perfusion system disposed therebetween, respectively corresponding, mutatis mutandis, to the loading system 14 and perfusion system 16 described hereinabove.

[0042] The control system 18 may include a control unit 80 (or microcontroller) located either inside or outside the housing 12. The control unit 80 may be arranged to receive a signal indicative of one or more of the kinematic and loading properties described hereinabove, and to send a corresponding signal to the given actuator 40 for it to operate accordingly. By way of an inverse kinematics method (or algorithm) implemented on a computer such as the control unit 80, a position of the platform 50 is relatable to that of any one of the actuators 40. The actuators 40 are mutually constrained relative to the enclosure 12 and the platform 50 such that each position of the platform 50 corresponds to a sole position for each actuator 40. Stated otherwise, the actuators 40 are arranged such that for the platform 50 to be in a desired position, each one of the actuators 40 must be in a specific, predetermined position. The respective predetermined positions of the actuators 40 together form a combination of positions corresponding to the desired position of the platform 50. A position of the first endplate 64a is inherited from that of the platform 50 and is relatable to that of the second endplate 64b. Hence, with the IVD 4 disposed between the endplates 64a, 64b, the desired position of the platform 50 may be relatable to a desired deformation of the IVD 4.

[0043] The control of the bioreactor rely on inverse kinematics. First, the desired deformations of the IVD serve as the input signals, and the position of the upper plane of the IVD can be calculated accordingly. Then, since the connections between the IVD upper plane and the manipulator platform are rigid, the position of the manipulator platform can then be calculated. For each linear actuator, it has two connection points: one on the fixed base platform, the other on the mobile manipulator platform. The connection points on the fixed base platform do not change during operation, whereas, the connection points on the manipulator platform change with the position and orientation of the manipulator platform. With the coordinates of both sides of the connection point known, the vector of each linear actuator with length and orientation can be calculated. This length signal from the previous calculated vector can then serve as the output signal for each linear actuator, achieving the control of the whole bioreactor. Since the six linear actuators are mutually constrained by the parallel robot structure, given one input signal, only one length combination of the six actuators will result.

[0044] In some implementations, any one of the actuators 40 may be a servo unit, i.e., an actuator provided with its own control unit. Hence, in some such implementations, the control unit 80 may be omitted.

[0045] Turning now to Fig. 5, the perfusion system 16 generally includes a culture chamber 60, a perfusion circuit 62 (not shown in detail) in fluid communication therewith and a pair of endplates 64 (i.e., a first 64a and a second 64b endplate) disposed inside the culture chamber 60. In this embodiment, the culture chamber 60 is shown as having a cylindrical shape, although other shapes may be implemented. The culture chamber 60 is constructed of biocompatible and sterilizable materials, and so are other components of the bioreactor 10 interfacing therewith. For example, end portions (i.e., a cap 60a and a base 60b) of the culture chamber 60 and the endplates 64 may be made of a polymeric material such as polytetrafluoroethylene (PFTE) or polyether ether ketone (PEEK), whereas a peripheral wall 60c of the culture chamber 60 may be made of borosilicate glass. It should be noted that materials graded for long-term culture are used or contemplated for any component in fluid communication with inside the culture chamber 60, and that suitably strong materials are used or contemplated for any loadbearing component. On a side facing generally toward the loading system 14, the culture chamber 60 defines an opening 60d into the culture chamber 60 inward which the end effector E extends. In some embodiments, the opening 60d may be defined by a dynamic seal. The end effector E and the dynamic seal may be fitted to one another such that a sealing engagement is achieved therebetween and maintained across the ROMs described hereinabove. The dynamic seal is one exemplary means to achieve sealing of the culture chamber 60. In embodiments, the cap 60a has an annular shape extending radially inward of the peripheral wall 60c and surrounding the opening 60d (and the dynamic seal, as the case may be). In other embodiments, the dynamic seal is omitted, and sealing engagement may be achieved otherwise, such as between the component of the culture chamber 60 defining the opening 60d and to which the end effector E is suitably fitted.

[0046] The perfusion circuit 62 is used to provide a flow of nutrient-enriched fluid to the cell chamber 60, ultimately to nourish cells of a biological structure contained therein. In implementations, the perfusion circuit 62 generally includes an upstream line 62a and a downstream line 62b respectively upstream and downstream of the culture chamber 60, and a pressurized source 62c of cell culture fluid connected between the lines 62a, 62b. Opposite the source 62c, the lines 62a, 62b are in fluid communication with inside the culture chamber, albeit indirectly via the endplates 64, as will be described. In some embodiments, the perfusion circuit 62 is located inside the enclosure 12. The perfusion circuit 62 may otherwise be standard, and will thus not be described at length in the interest of brevity. [0047] The endplates 64 may be deemed analogous to a pair of consecutive vertebrae located on either side of an intervertebral disc, i.e., to two vertebrae that belong, with the IVD located therebetween, to a same spinal functional unit. The first endplate 64a and the second endplate 64b are arranged so as to define a gap 66 (or space) therebetween. The gap 66 may correspond to an intervertebral space of the functional unit. The endplates 64 both have a gap-facing surface 64c corresponding to an endplate surface of one of the vertebrae. Such vertebral surfaces engage a cartilaginous plate of the IVD, a structure considered as an instrumental pathway for supplying the IVD with fluid-borne nutrients (Ghosh, P. (1988). The Biology of the intervertebral disc, Vol. 1). In this respect, the endplates 64 are provided with perfusion pathways 68 in fluid communication between the upstream line 62a and the gap 66. The perfusion pathway 68 of each endplate 64 includes a perfusion conduit 68a extending therethrough toward the gap-facing surface 64c, as well as perfusion channels 68b defined inward the gap-facing surface 64c. The channels 68b are in fluid communication between the conduit 68a and an interior space of the culture chamber 60 surrounding the endplate 64. In the depicted embodiment, both of the first and second endplates 64a, 64b are traversed by their respective perfusion conduit 68a, from which corresponding perfusion channels 68b extend radially. To supply the endplates 64 with the flow of cell culture medium, a first inlet conduit 68c defined inside the end effector E connects the upstream line 62a to the perfusion pathway 68a of the first endplate 64a, whereas a second inlet conduit 68d defined in the base 60b of the culture chamber 60 connects the upstream line 62a to the perfusion pathway of the second endplate 64b. The base 60b defines an outlet conduit 68e connected between the culture chamber 60 and the downstream line 62b. Depending on the implementation, the base 60b may be arranged to gravitationally drain the culture chamber 60 toward the outlet conduit 68e, and the downstream line 62b may impart a suction to the outlet conduit 68e. In this embodiment, the first inlet conduit 68c and the second inlet conduit 68d respectively align with the X2 axis and the X1 axis. However, this alignment may be undone upon a a torsion moment M being applied about the Z2 axis (Fig. 5), rotating the effector E and the first endplate 64a with the cranial CE 4a of the IVD 4. [0048] In some embodiments, an upstream flow of cell culture fluid provided to the culture chamber 60 may be controlled by way of the control system 18. In further embodiments, an upstream rate of the flow is thus controllable. Also, the perfusion system 16 may be provided with means for sensing one or more flow rates, for example the upstream rate or a downstream rate of the flow downstream of the culture chamber 60. Under certain circumstances, the downstream rate may differ from the upstream rate as a function of a fluid intake of the IVD 4.

[0049] For the preservation of in v/ o-like properties of the IVD 4 upon its placement inside the culture chamber 60, it is generally desirable that certain environmental conditions be maintained therein. For instance, a desired temperature inside the culture chamber 60 may be of about 37 C. In the depicted embodiment, the bioreactor 10 is configured such that a heat flux generated by an exterior heat source may be transferred to inside the culture chamber 60 to maintain the desired temperature. In this case, the bioreactor 10 is sized to be receivable inside an incubator and arranged such that heat may be transferred from the incubator to the culture chamber 60 via one or more of radiation, conduction and convection. In some embodiments, the bioreactor 10 is provided with a heat source (not shown) controllable by way of the control system 18 to transfer heat to the culture chamber 60 as needed to maintain the desired temperature. The heat source may be internal, for example when mounted to the enclosure 12 or to the culture chamber 60. In such embodiments, the bioreactor 10 may be arranged to limit heat transfer away from the culture chamber 60 by insulating the heat source and the culture chamber 60. A flexible insulation membrane may be provided between the platform 50 and the culture chamber 60, through which the end effector E may extend and be movable unhindered. The enclosure 12 may be closed on all sides, at least one of which being openable by way of a door or a removable panel. The heat source may otherwise be external, for example when mounted to a portion of the perfusion circuit 62 located outside the enclosure 12. Various types and arrangements of heat sources are contemplated.

[0050] In view of the foregoing, methods of ex vivo characterization of IVDs, for example methods involving operation of a bioreactor, will now be described. As encompassed herein, the method comprises a step of connecting an end effector between the IVD located inside a culture chamber and an actuator located outside the culture chamber to kinetically couple the intervertebral disc to the actuator. This step may include mounting the IVD to the bioreactor. For example, the IVD may be confined in a culture chamber having first and second endplates opposite one another, with the first endplate connected to the end effector, the second endplate connected to a base of the culture chamber, and the IVD disposed between the first and second endplates.

[0051] In another step, the method comprises controlling the actuator to displace the end effector to a desired position. In displacing the end effector to this position, the end effector imparts a desired loading condition to the IVD which includes shear, compression, torsion and bending as described hereinabove, whether alone or in combination.

[0052] In a subsequent step, i.e., after displacing the end effector, the method comprises sensing a response position of the actuator. As the response position is relatable to a position of the end effector, and thus to a deformation of the IVD, an inverse kinematics method (or algorithm implemented for example on a control unit 80 of the control system 18 or on another computer) can be used to determine a biomechanical response of the IVD based on the response position.

[0053] In some embodiments, the method may include delaying the sensing of the response position of the actuator by a response duration starting once the end effector has attained the desired position.

[0054] In further embodiments, the method allows to determine a creep response of the IVD. In one step, the method comprises imparting a predetermined load to the end effector via the actuator for the response duration upon the end effector attaining the desired position. In this case, the creep response of the IVD may be determined as a function of the response position.

[0055] The method may also include, in some embodiments, disengaging the actuator (i.e., allowing the end effector to move under a load imparted thereto by the IVD without active opposition from the actuator) upon the end effector attaining the desired position, and for a certain period of time (e.g., the response duration). The response position may thus be indicative of a stress relaxation response of the IVD.

[0056] In some embodiments, the method may include perfusing the IVD with a flow of cell culture medium, at least as the end effector is displaced. This may allow some of the fluid to enter the IVD, which may increase a fluid content of the IVD, or to restore any fluid that may have been lost during loading and/or displacement. In another embodiment, the method further includes controlling an upstream flow rate of the flow of cell culture medium and sensing a downstream flow rate of the flow of cell culture medium. A rate difference between the upstream and downstream flow rate may allow to determine a fluid intake of the IVD and/or to assess a permeability of the IVD.

[0057] As encompassed herein, the method provided may further comprise injecting an intervertebral nucleus pulposus substitute composition inside the IVD prior to displacing the end effector to the desired position to load the IVD. The desired position may be predetermined, for example according to a desired biomechanical property for the IVD sought as a result of the injection. The method may in some embodiments include determining a quantity to inject based on a previously determined response of the IVD.

[0058] While the present technology has been described in connection with specific embodiments thereof, it will be understood that it is capable of further modifications and this application is intended to cover any variations, uses, or adaptations of the technology following, in general, the principles of the technology and including such departures from the present disclosure as come within known or customary practice within the art to which the present technology pertains and as may be applied to the essential features hereinbefore set forth, and as follows in the scope of the appended claims.