Patent Publication Number: US-2022218496-A1

Title: Expanding spinal fusion cage

Description:
FIELD 
     This disclosure relates to methods and devices for stabilizing spinal motion between two adjacent vertebrae and, more particularly, to such methods and devices that utilize an expanding spinal fusion cage, which can be inserted in a collapsed state into the intervertebral space and subsequently inflated or expanded within the intervertebral space. 
     BACKGROUND 
     Minimally invasive surgical (MIS) and/or microsurgical procedures are increasingly utilized to perform spinal surgeries, such as resection, decompression, and fusion. These procedures can have a number of advantages, including reduced risk of patient injury, faster recovery time, etc. Such procedures are typically performed using various access ports or retractors that provide a passageway from the skin surface to the spine and intervertebral disc space. These ports and retractors often provide passageways of minimal size, perhaps about 30 mm in diameter or less, in order to minimize tissue trauma and successfully traverse narrow anatomical passages, such as the anatomic window of Kambin&#39;s triangle in the spine. 
     These minimally invasive and/or microsurgical procedures can require new instruments, devices, and methods suitable for use in the limited size passageways provided by the various ports or retractors. By way of example, certain larger devices, whether implantable devices such as fusion cages or other associated instruments, cannot be passed through a narrow opening and therefore cannot be used in minimally invasive and/or microsurgical procedures. 
     Accordingly, there is a need for improved surgical devices and methods, including improved spinal fusion cages, that can be utilized in minimally invasive procedures that, e.g., require passing a device through a small or restricted passageway to a surgical site. 
     SUMMARY 
     The devices and methods disclosed herein address the above-noted need by providing devices that can have a collapsed and expanded state, thereby allowing introduction through a smaller working channel while in a collapsed state and subsequent expansion at a surgical site. More particularly, the devices and methods described herein leverage advances in the ability to 3D-print or additive manufacture highly complex geometries and encapsulated structures, as well as multiple materials within a single structure, to enable the design of disc replacement devices with advanced geometries or mechanisms for expanding uniformly into a complex or asymmetrical shape through a highly controlled process. 
     Certain aspects of the present disclosure provide for a 3D printed spinal fusion cage that expands to a pre-defined shape and size from a compressed size in order for the spinal fusion cage to be implanted in a patient&#39;s intervertebral space through minimally invasive methods. 
     Two example embodiments of the present disclosure include an expanding spinal fusion cage device utilizing elastic expansion and using meta-material expansion. Other example embodiments are within the scope of the present disclosure, including, for example, implementations utilizing both elastic expansion and meta-material expansion. Additionally, other expansion configurations are described herein, and the above two example embodiments are provided only as illustrations of the present disclosure and their distinctions are presented to help explain to overall concept. 
     Certain aspects of the elastic expansion cage devices include, for example, a single-piece structure that contains a particular geometry to ensure controlled expansion into a defined shape and structure. For example, a soft object that can be inserted between vertebrae using current MIS methods and that can be inflated with a gas, fluid, or semi-solid material blend to expand from a simple and compressed shape into a complex, structural, and stable cage device. 
     Certain aspects of the meta-material expansion cage devices include, for example, a multi-material system where a bag or pouch with a surrounding 3D-printed structure that provides structural stability and control is inserted between vertebrae and inflated. For example, a mesh bag where a collapsible 3D printed structure or scaffold has been directly printed onto that mesh material acting as a physical support to the inflation of the mesh bag or pouch. 
     One example embodiment of the present disclosure is an expandable cage assembly configured to expand from a collapsed state to an expanded state in an intervertebral space when inflated with a material. The expandable cage assembly includes an inflatable section defining an interior volume configured to receive the material and expand the interior volume in response to a pressure from the received material to cause the expandable cage assembly to transition from the collapsed state to the expanded state, and a stabilization section configured to restrain the inflatable section during inflation. 
     In some instances, the stabilization section at least partially surrounds the inflatable section, the stabilization section sized and shaped to define at least a portion of a periphery of the expandable cage assembly. 
     In some instances, the inflatable section surrounds the stabilization section and the stabilization section is coupled with the stabilization section for retaining inflatable section. 
     In some instances, at least one of the inflatable section and the stabilization section includes a 3D printed material. In some instances, wherein at least one of the inflatable section and the stabilization section includes a single-piece structure. In some instances, the single-piece structure includes a 3D printed material. In some instances, the inflatable section includes a woven substrate. In some instances, the stabilization section includes a 3D printed scaffold. In some instances, wherein the stabilization section includes tubular woven structures configured to be filled by the material. 
     In some instances, at least one of the inflatable section and the stabilization section includes a porous structure configured to allow interaction between the material and the intervertebral space. 
     In some instances, the expandable cage assembly defines one or more void channels, where each void channel is formed continuously though the stabilization section and the inflatable section. In some instances, the void channels are configured to receive bone graft material. 
     In some instances, the stabilization section includes a rigid structure. In some instances, the rigid structure defines one or more splits arranged to facilitate deflection or deformation of the stabilization section around the inflatable section when the inflatable section moves the expandable cage assembly from the collapsed state to the expanded state. In some instances, the rigid structure defines one or more sections arranged to telescopically expand when the inflatable section moves the expandable cage assembly from the collapsed state to the expanded state. 
     In some instances, at least one of the inflatable section and the stabilization section includes a bio re-absorbable material configured to be reabsorbed into the body after a time when fusion has taken place. 
     In some instances, at least one of the inflatable section and the stabilization section includes embedded organic materials configured to expedite osteointegration. In some instances, the embedded organic materials include at least one of: hyaluronic acids, collagens, proteins, patient cells from bone grafts. In some instances, at least one of the inflatable section and the stabilization section includes embedded materials configured to expedite osteointegration, for example, phosphate. 
     In some instances, at least one of the inflatable section and the stabilization section includes an embedded active pharmaceutical compound. 
     In some instances, the expandable cage assembly has an asymmetric shape in the expanded state. 
     In some instances, in the expanded state, a superior surface of the expandable cage assembly is oblique to an inferior surface of the expandable cage assembly. 
     In some instances, wherein the expandable cage assembly is formed from a plurality of materials. 
     In some instances, the inflatable section and the stabilization section are formed from different materials. 
     The intervertebral disc implant of claim  1 , wherein the inflatable section includes multiple chambers, wherein each of the multiple chambers is able to be filled with the material, and wherein the expanded shape of the intervertebral disc implant is a function of which of the multiple chambers is filled with material. 
     The intervertebral disc implant of claim  1 , including at least one additional structural component attached thereto, wherein the additional structural component is configured to improve fixation in the intervertebral space. 
     The intervertebral disc implant of claim  1 , wherein the inflatable section includes a core inflation area configured to be filled with the material and an outer inflation area that is configured to be filled with a biologically active material. 
     Another example embodiment is an intervertebral disc implant, including an expandable structure configured to elastically expand from a collapsed state to an expanded state in an intervertebral space when inflated with a material, the expandable structure including a sidewall, the sidewall defining an interior chamber configured to receive the material and expand at least a portion of the sidewall elastically in response to a pressure from the received material to cause the expandable structure to transition from the collapsed state to the expanded state. The sidewall has a variable thickness over the surface of the expandable structure configured to control differential expansion rates of the structure during expansion. In some instances, the implant includes a structured lattice configured to provide a conformal shape to the sidewall at least at a given pressure. In some instances, the implant includes a damping mechanism comprising one or more independently filled lattice channels of a structured lattice. 
     In some instances, the expandable structure includes a porous outer layer configured to allow interaction between the material and the intervertebral space. 
     In some instances, the expandable structure defines, in the expanded state, one or more void channels configured to receive bone graft material. 
     In some instances, an outer surface of the expandable structure defines protrusions configured to increase the fixation between the outer surface and surfaces of the intervertebral space. In some instances, the expandable structure is monolithic. 
     In some instances, the interior chamber includes multiple chambers, wherein each of the multiple chambers is able to be filled with the material, and wherein the expanded shape of the intervertebral disc implant is a function of which of the multiple chambers is filled with material. 
     In some instances, the intervertebral disc implant of includes at least one additional structural component attached thereto, wherein the additional structural component is configured to improve fixation in the intervertebral space. 
     In some instances, the interior chamber includes a core inflation area configured to be filled with the material and an outer inflation area that is configured to be filled with a biologically active material. 
     Yet another example embodiment is a surgical method, including inserting a spinal fusion cage into an intervertebral space of the patient while the cage is in a collapsed state, expanding the spinal fusion cage from the collapsed state to an expanded state by injecting a volume of a flowable material into an interior chamber of an inflatable section of the spinal fusion cage, and constraining a shape of the spinal fusion cage in the expanded state using a stabilization structure coupled to the inflatable section. 
     Still another example embodiment, is a method for manufacturing a surgical implant, including forming an expandable substrate from a first material, and forming a stabilization structure on the substrate from a second material using an additive manufacturing process that deposits a plurality of layers of the second material on one another. 
     In some instances, the expandable substrate is a woven tubular structure. In some instances, the woven tubular structure is elastically expanded over a mandrel prior to forming the stabilization structure thereon. In some instances, forming the expandable substrate is performed using an additive manufacturing process. In some instances, the additive manufacturing process is any of: jetting, extruding, and fused deposition modeling, powder bed fusion, vat photopolymerization, binder jetting, material extrusion, directed energy deposition, selective laser sintering, material jetting, and sheet lamination. 
     In some instances, the expandable structure includes a single-piece expanding structure. In some instances, expandable state defines a first expanded shape when the expandable structure is expanded in free space and a second expanded shape when the expandable structure is expanded the intervertebral space, the first expanded shape being at least a function of the expandable structure and the pressure of the material, and the second expanded shape being at least a function of the expandable structure, the pressure of the material, and properties of the intervertebral space. In some instances, the first expanded shape is a function of a target shape of the second expanded shape in the intervertebral space. In some instances, the first expanded shape defines a first face and a second face, and wherein an orientation between the first face and the second face is a function of a target orientation of the first face and the second face in the second expanded shape. 
     In some instances, some or all of the components of an expanding spinal fusion cage are 3D printed using a vat extrusion process, whereby a material is extruded into a vat of suspension. 
     In some instances, some or all of the components of an expanding spinal fusion cage are 3D printed using a fused deposition modelling process, whereby thermoplastics are extruded onto a variety of flat or multi-planar substrates. 
     In some instances, some or all of the components of an expanding spinal fusion cage are 3D printed using whereby a single or combination of elastomeric and solid materials is jetted onto a variety of substrates. 
     In some instances, an expanding spinal fusion cage includes a 3D woven structure that is fabricated in an initial digital weaving process then integrated into a 3D printing process as the substrate for printing. 
     Certain aspects of the present disclosure provide advantages to surgeons and patients. For example, aspects include a cage-like device with a smaller compressed/pre-insertion volume would reduce the required incision size and thus reduce required healing time. Some aspects provide a cage-like device that expands into a final form with multiple faces at varying angles e.g. lordotic, vertical, and horizontal. Some aspects provide a new and functionally superior expanding cage device that is sufficiently divergent from prior solutions (e.g., mechanically actuated cages) and could act as platform technology for future spinal and orthopedic products. 
     Some aspects of the present disclosure include an expanding cage device with bio re-absorbable materials. For example, certain implementations can include a cage device with some or all of the material constructing the device being reabsorbed into the body after a time when sufficient fusion would have taken place. This a benefit over prior spinal cage products that become useless once fusion has occurred and remain as a nonfunctioning foreign object in the patient&#39;s body. 
     Some aspects of the present disclosure include an expanding cage device with embedded organic materials to be used in the construction of all or part of the cage device. In some examples of both the elastic and meta-material embodiments, organic materials and compounds are formulated into the printed material and/or substrate. The embedded organic materials and compounds enable opportunities for the addition of beneficial organic compounds and molecules that, in some implementations, help expedite osteointegration, such as hyaluronic acids, collagens, proteins. In some implementations, the patient&#39;s own cells (grafts) can be formulated into the printed material that comprises their personal implant. In some implementations, inorganic material, such as calcium phosphate are embedded. 
     Some aspects of the present disclosure include an expanding cage device with embedded medical components and active pharmaceutical ingredients. In some examples of both the elastic and meta-material embodiments, active pharmaceutical ingredients, molecules, and compounds can be formulated into the printed material and/or substrate. Implementations including embedded medical components can enable an implant to possess a secondary function as a drug delivery platform for anti-inflammatories, antibiotics, or other pharmaceuticals with the aim of reducing risks of infection and improving overall recovery time. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
       This disclosure will be more fully understood from the following detailed description taken in conjunction with the accompanying drawings, in which: 
         FIGS. 1A  and B are illustrations of two different expanding spinal fusion cage embodiments according to aspects of the present disclosure; 
         FIGS. 2A and 2B  are illustrations of the collapsed and expanded states, respectively, of an elastically expanding cage device embodiment; 
         FIGS. 3A-3C  are illustrations of elastically expanding cage device embodiments having different shape profiles; 
         FIGS. 4A and 4B  are perspective and cross-sectional views of an elastically expanding cage device embodiment; 
         FIGS. 5A and 5B  are perspective and cross-sectional views of another elastically expanding cage device embodiment; 
         FIGS. 6A-6C  are illustrations of an alternate embodiment of an elastically expanding cage device; 
         FIGS. 7A-7D  are illustrations of an example procedure for replacing a spinal disc with an elastically expanding cage device; 
         FIGS. 8A-8D  are illustrations of a metamaterial cage device embodiment showing the expansion process; 
         FIGS. 9A-9D  are cross-sectional schematics of two alternative expanding cage device embodiments with an exterior stabilization structure; 
         FIGS. 10A-10D  are cross-sectional schematics of two alternative expanding cage device embodiments with an internal stabilization structure; 
         FIGS. 10E and 10F  are cross-sectional schematics of two alternative expanding cage device embodiments with multiple interior chambers. 
         FIG. 10G  is a cross-sectional schematic an alternative expanding cage device embodiment with additional structural components attached on the top and bottom face to improve fixation. 
         FIGS. 11A-D  are illustrations of an example procedure for replacing a spinal disc with a metamaterial expanding cage device; 
         FIGS. 12A-C  are illustrations of an example extrusion process for manufacturing an expanding cage device; 
         FIGS. 13A-C  are illustrations of an example material jetting process for manufacturing an expanding cage device; 
         FIGS. 14A and 14B  are illustrations of an example process for manufacturing a woven tubular structure for use in an expanding cage device; 
         FIGS. 15A-E  are illustrations of an example process for manufacturing an expanding cage device; and 
         FIGS. 16A-E  are illustrations of an example process for manufacturing an expanding cage device. 
     
    
    
     DETAILED DESCRIPTION 
     Certain exemplary embodiments will now be described to provide an overall understanding of the principles of the structure, function, manufacture, and use of the devices and methods disclosed herein. One or more examples of these embodiments are illustrated in the accompanying drawings. Those skilled in the art will understand that the devices and methods specifically described herein and illustrated in the accompanying drawings are non-limiting exemplary embodiments and that the scope of the present disclosure is defined solely by the claims. The features illustrated or described in connection with one exemplary embodiment may be combined with the features of other embodiments. Such modifications and variations are intended to be included within the scope of the present disclosure. 
     Certain aspects of the present disclosure provide for an expanding spinal fusion cage that expands to a pre-defined shape and size from a compressed size that enables the spinal fusion cage to be implanted through minimally invasive methods. 
     In some aspects, some or all of the components of an expanding spinal fusion cage are 3D printed. 3D printing the components, also referred to as additive manufacturing, enables the production of highly complex and/or encapsulated geometries that, in certain embodiments, provide added control to an expanding or inflating bag or balloon-like part of the expanding spinal fusion cage. Discussed in more detail below, 3D printing components of the expanding spinal cage device provides benefits, such as the production of multiple-materials at a high degree of precision within the same part and the ability to calibrate expansion behavior through variable elastic property control. Additionally, 3D printing systems can be reconfigured to print in multiple axis and on multiple substrates, which enables hybrid printing onto other functional devices, materials and substrates. 
     Overview 
     Two categories of embodiments are now described as example aspects of the present disclosure. The first category includes expanding spinal fusion cages with a structure that expands elastically. For example, a single-piece structure that contains a particular geometry to ensure the controlled expansion into a defined shape and structure. For example, a soft object that can be inserted between vertebrae using current MIS methods and that can be inflated with a gas, fluid, or semi-solid material blend to expand from a simple and compressed shape into a complex, structural, and stable cage device. The second category includes expanding spinal fusion cages that include a stabilizing structure arranged to allow the expansion of an expansion material (e.g., a woven bag or meta-material). For example, a multi-material system where a bag or pouch with a surrounding 3D-printed structure that provides structural stability and control is inserted between vertebrae and inflated. For example, a mesh bag where a collapsible 3D printed structure or scaffold has been directly printed onto that mesh material acting as a physical support to the inflation of the mesh bag or pouch. These two categories need not be distinct, and some aspects of the present disclosure include embodiments having features of both categories, for example, a stabilizing structure arranged to allow the expansion of an elastic material. 
     Certain aspects of the present disclosure include “two-part” systems, e.g., having an expanding spinal fusion cage/pouch element of the system, which is implanted and positioned intervertebrally, and a second major component and/or process, which is the inflation and final fixation of the device in the intervertebral space. In some instances, a secondary component can be an injectable medium used to inflate the expanding spinal fusion cage after insertion into the intervertebral space. The injectable medium can be used to provide required long-term stability and fixation of the cage (e.g., resistive force against intervertebral compression or collapse) and could be, for example, a bone cement or other suitable medium known by those skilled in the art, such as DePuy Synthes SMARTSET PMMA Bone Cement. Aspects of the present disclosure also include expanding spinal fusion cages configured to be used with the injectable mediums with added pharmaceutical compounds and/or antibiotics that increase functionality whilst potentially counter-acting any potential rejection/inflammation caused by the cage materials. Further, certain aspects include the use of 3D printed materials, in combination with elastic materials and complex geometries, to create structures that deform or expand in controlled ways. 
       FIGS. 1A  and B are illustrations of two different expanding spinal fusion cage embodiments according to aspects of the present disclosure.  FIG. 1A  shows an expanding spinal fusion cage  100  that includes a body  110  defining an interior volume  120 . The expanding spinal fusion cage  100  (herein also referred to as an expanding cage) is shown in an expanded state, whereby the body  110  has expanded from an initial collapsed state (not shown) as a result of an inflationary material being pumped into the interior volume  120 . The body  110  also defines an access port  140  to the interior volume  120  that enables an inflationary material (e.g., a bone cement, gas, liquid, etc.) to be delivered to the interior volume  120  during an inflation operation. In some instances, the body  110  of the expanding cage  100  is configured to elastically expand from the collapsed state to the expanded state. In some instances, the body  110  of the expanding cage  100  is constructed from a single material that is configured to elastically expand the expanding cage  100  from the collapsed state to the expanded state in the intervertebral space. 
       FIG. 1B  shows another expanding spinal fusion cage  200  having aspects of the present disclosure. The expanding spinal fusion cage  200  includes a textile substrate  230  that defines an interior volume  220  and a stabilization structure  210  that at least partially constrains the textile substrate  230  (e.g., an expanding structure) to define an exterior size and shape of the expanding cage  200 . The expanding cage  200  is shown in an expanded state, whereby the stabilization structure  210  and the textile substrate  230  has expanded from an initial collapsed state (not shown) as a result of an inflationary material being pumped into the interior volume  220 . The expanding cage  200  also includes an assess port  240  to the interior volume  220  that enables an inflationary material (e.g., a bone cement, etc.) to be delivered to the interior volume  220  during an inflation operation. 
     In operation, after the preparation of the patient&#39;s intervertebral space to receive an implant, the expanding cage  100 ,  200  can be inserted into the intervertebral space in a collapsed state in order to clear the limited spatial access dimensions to the intervertebral space. After insertion, the inflationary material can be injected into the interior volume  120 ,  220  of the expanding cage  100   200 , thereby deforming the expanding cage  100 ,  200  from the collapsed state to a final expanded state, where the final expanded state is not necessarily the initial expanded state of  FIG. 1A  because of the properties of the specific patient&#39;s intervertebral space. Instead,  FIGS. 1A and 1B  can illustrate one of both a “free” expansion state where the expanding cage  100 ,  200  is inflated outside of the intervertebral space or a “designed” expansion state, where the expanding cage  100 ,  200  illustrates a designed size and shape of the expanding cage  100 ,  200  when inflated in the intervertebral space. In some instances, the free expansion state and the designed expansion state can be different, but in other instances they can be similar. In operation, a true final shape of the expanding cage  100 ,  200  in the intervertebral space can be a combination of both the free and designed expansion states that depends on the geometry of the expanding cage  100 ,  200  and the materials the body  110  ( FIG. 1A ), scaffold  210 , and/or textile substrate  230  ( FIG. 1B ) are constructed from. 
     Examples of Elastically Expanding Cages 
       FIGS. 2A and 2B  are illustrations of the collapsed and expanded states, respectively, of an elastically expanding cage device embodiment.  FIG. 2A  shows an expanding cage  100  in a collapsed state and  FIG. 2B  shows expanding cage  100  of  FIG. 2A  in an expanded state. In this illustration, a height  118  of the body  110  of the expanding cage  100  in the collapsed state ( FIG. 2A ) is reduced compared to the height  119  of the body  110  in the expanded state ( FIG. 2B ). In operation, an inflationary material (e.g., bone cement, etc.) can be pumped into the interior volume  120  of the body  110  in the collapsed state and the pressure of the inflationary material can deform the body  110  from the collapsed state to the expanded state, as shown in  FIG. 2B . 
     In some instances, the body  110  can be made from a material with an elasticity sufficient to enable the expanding cage  100  to elastically expand from the collapsed state to the expanded state. In some instances, the body  110  can be constructed with a shape that allows the body  110  to be expanded and contracted with only a portion of the body being deformed. For example, the body  110  can have a bellows portion. In some instances, that body  110  can be constructed with one or more expansion joints, such that elasticity of the material of the body is not required to expand or contract the body  110 . In some instances, the body can be constructed with a material having an elasticity sufficient to enable the expanding cage  100  to elastically expand from the collapsed state to the expanded state. In some instances, the elastically expanding cage  100  can also define one or more void channels  170  though the body  110  that can enable material, such as a bone graft, to be integrated with the expanding cage  100 . Such channels can also permit natural growth of a patient&#39;s bone through the implant following a surgical procedure (e.g., promote the fusion process). 
     In some embodiments, the expanding cage  100  can be configured to be at an initially expanded state, deformed into a smaller collapsed state for insertion into an intervertebral space, and subsequently inflated into a new expanded state by the inflationary material. In some embodiments, the body  110  can be constructed with a material that is able to be elastically deformed to enable the expanding cage  100  to deformed (e.g., folded, rolled, squished, etc.) into the collapsed state. In some instances, the expanding cage  100  can be configured to be initially deformed from an initial expanded state to a collapsed state during insertion into the intervertebral space, and subsequently elastically expanded to a final expanded state that is at least partially beyond the size of the initial expanded state (e.g., at least part of the body  110  of the expanding cage  110  can be elastically expanded during an inflation operation to the final expanded shape). In some instances, the actual shape of the expanded cage  100  in the intervertebral space after the inflation operation is at least partially a function of the properties of the patient&#39;s spine (e.g., the body  110  will form to the volume and/or shape of the vertebrae), the final inflation pressure of the inflationary medium, and the material and geometric properties of the body  110  (e.g., thicker regions of the body  110  will expand less than relatively thinner region). 
       FIGS. 3A-C  are illustrations of elastically expanding cage device embodiments having different shape profiles. The size and shape of the expanding cages  100 ,  200  are able to be configured in many different ways. For example, an expanding cage  100 ,  200  can have a shape that is specifically designed for a patient&#39;s bony anatomy. Also, an expanding can  100 ,  200  can have an expanded shape that is designed to, for example, modify the intervertebral space upon inflation or interface with an existing implant or device that is present in the intervertebral space. The following are three examples that illustrate parameters of the expanding cages  100 ,  200  that can be modified, but aspects of the present disclosure can be modified in many different ways and the present embodiments are only non-limiting examples of the types of parameters that can be designed or customized for a given application or patient. In some instances, the expanding cages  100 ,  200  can have more than one chambers for inflation, which may or may not be connected to each other. This is shown in more detail in  FIGS. 10E and 10F . In some instances, multiple chambers can enable selectively filling certain of the multiple chambers to match or augment a particular shape of a patient&#39;s anatomy (e.g., their spine). 
       FIGS. 3A-3B  illustrate different aspects of the present disclosure for providing a range of lordotic, vertical, horizontal (footprint) and face angle options depending on patient need.  FIG. 3A , for example, shows an expanding cage  301  having a body  311  that is generally cylindrical in shape and defines a top face  351  and a bottom face  361  of generally the same size and orientation, with a height  318  of the body  311  spanning between the bottom face  361  and the top face  351 . The expanding cage  301  is shown in the expanded state, but compared with the height  119  of expanding cage  100  of  FIGS. 1A and 2B  in the expanded shape, the expanding cage  301  of  FIG. 3A  defines a reduced height  318  that may be, for example, designed to integrate with a patient having a reduced height in their intervertebral space. 
       FIG. 3B  shows an expanding cage  302  having a body  312  that is generally cylindrical in shape and defines a top face  352  and a bottom face  362  of generally the same size but different orientations, as compared to the arrangement in  FIG. 3A . In  FIG. 3B , the expanding cage  302  is shown in the expanded state and the top face  352  defines a sloped surface  382  that may be, for example, designed to integrate with adjacent vertebral surface of a patient having a similarly sloped angle with respect to the opposite vertebral surface (which would, for example, integrate with the bottom face  362  of the expanding cage  302 ). In other words, in some embodiments various surfaces or faces of expanding cages can be parallel with one another, while in other embodiments various surfaces or faces can be non-parallel, e.g., oblique, perpendicular, etc. to one another. In the illustrated example of  FIG. 3B , by way of example, the superior or top surface  352  of the cage  302  can be oblique to the inferior or bottom surface  362  of the cage. Further, in some embodiments the cage  302  can have an asymmetric shape, or a shape that is asymmetric in at least one respect. For example, the right half of the cage  302  in  FIG. 3B  is not symmetrical with the left half of the cage in the view of the figure. 
       FIG. 3C  shows an expanding cage  303  having a body  313  that is generally conical in shape and defines a top face  353  and a bottom face  363  of different sizes but similar orientations, as compared to the arrangement in  FIG. 3A . In  FIG. 3C , the expanding cage  303  is shown in the expanded state and defining a conical peripheral surface  338  that defines a corresponding size difference between the top face  353  and the bottom face  363 . 
     In some instances, one or more of the height  318 , slope  328 , or taper  338  (or another parameter readily known to those of skill in the art) of an expanding cage can be designed as a function of a specific patient&#39;s anatomy that can be, for example, measured or determined prior to insertion of the expanding cage in order to manufacture a custom expanding spinal fusion cage for the patient. 
       FIGS. 4A and 4B  are perspective and cross-sectional views of an elastically expanding cage device embodiment in an expanded state.  FIG. 4A  shows an elastically expanding spinal fusion cage  400  that includes a body  410  manufactured from a material with elastic properties that enable the elastically expanding cage  400  to elastically expand from a collapsed state (not shown) to the expanded state shown in  FIGS. 4A and 4B . The body  410  of the elastically expanding cage  400  defines a generally hexahedric shape with five flat faces  450  meeting at rounded corners and a sixth side defining an inflation valve  440  that is configured to permit inflationary material to be delivered to an interior volume  420  of the body  410 , as shown in  FIG. 4B .  FIG. 4B  shows the inflation valve  440  is connected to the interior volume  420  by an inflation channel the runs through the body  410 . The body  410  defines a plurality of internal wall projections  411  that form the interior volume  420 . The internal wall projections  411  define a variable thickness of the body  411 , and the variable thickness controls differential expansion rates of the elastically expanding cage  400  during an inflation operation. 
       FIGS. 5A and 5B  are perspective and cross-sectional views of another elastically expanding cage embodiment with additional features to enhance fixation of the expanding cage in the intervertebral space.  FIG. 5A  shows an elastically expanding cage  500  that includes a body  510  (e.g., a balloon) manufactured from a material with elastic properties that enable the elastically expanding cage  500  to elastically expand from a collapsed state (not shown) to the expanded state shown in  FIGS. 5A and 5B . The body  510  of the elastically expanding cage  500  defines a generally hexahedric shape with five flat faces meeting at rounded corners and a sixth side defining an inflation valve  540  that is configured to permit inflationary material to be delivered to an interior volume  520  of the body  510 , as shown in  FIG. 5B . A top face  550  and a bottom face ( 560  in  FIG. 5B ) of the body  510  include a plurality of crisscrossed protrusions  551  that define a texture in the surface of the top face  550  that can improve fixation and prevent migration of the cage after implantation (e.g., the textured surfaces can better grip or provide more friction with vertebral endplates against which they are disposed). The cage also includes a plurality of void channels  571  that span from the top face  550  to the bottom face ( 560  in  FIG. 5B ). As noted above, these void channels can be utilized to promote bone growth through the implant, thereby speeding fusion, as well as used to pack and deliver various osteoconductive or otherwise therapeutic agents. In some instances, the body  510  is configured to have additional structural components attached thereto and configured to improve fixation in the intervertebral space. For example, top and bottom plates, such as metal and plastic components, that are affixed to the corresponding top and bottom faces of the body  510 . 
       FIG. 5B  shows the inflation valve  540  is connected to the interior volume  420  by an inflation channel  541  the runs through the body  510 . The body  510  defines a plurality of internal wall projections  511  that form the interior volume  520 . The internal wall projections  411  define a variable thickness of the body  511 , and the variable thickness controls differential expansion rates of the elastically expanding cage  500  during an inflation operation. The body  510  also defines the plurality of void channels  571  that span between the top face  550  and the bottom face  560 . As noted above, the void channels  571  can enable a direct material connection to exist across the elastically expanding cage  500  in the intervertebral space, for example, between the two opposing vertebral faces. The direct material connection can be used to, for example, allow bone graft packing and delivery of the bone graft material to the intervertebral space in order to promote ossification around the elastically expanding cage  500  after being implanted. 
       FIGS. 6A-6C  are illustrations of an alternate embodiment of an elastically expanding cage device that includes a lattice structure in the center of an elastically expanding toroidal (e.g., donut shaped) body for controlling variable expansion rates and also allow eventual bone integration.  FIG. 6A  shows an elastically expanding spinal fusion cage  600  that includes a toroidal body  610  in a collapsed state. At the center of the body  610  is a lattice structure  680  that is coupled to the body  610 .  FIG. 6B  shows the elastically expanding cage  600  in the expanded state, where the body  610  has expanded elastically after being filled with an inflationary medium. In some embodiments, the lattice structure  680  can be stretched or otherwise deformed during the inflation process. 
     In operation, the structure and material properties of the lattice structure  680  can control the expansion rate and/or final shape of body  610  by, for example, allowing more vertical expansion than horizontal expansion, or some other combination of dynamic dimensional relationships that is a function of the latticework itself and/or the connection of the body  610  to the lattice work  680 .  FIG. 6C  shows a translucent view of the elastically expanding cage  600  with the interior volume  620  of the body being visible.  FIG. 6C  shows expansion of the latticework  680 —and the device generally—from the initial collapsed state of  FIG. 6A  has occurred in the vertical direction (V) with less (or negative) corresponding expansion of the latticework  680  in the horizontal direction (H). Other constraints on the expansion of the body  610  can be achieved by varying the properties or construction of the lattice structure  680 , for example, allowing horizontal expansion with limited vertical expansion. 
       FIGS. 7A-7D  are illustrations of an example procedure for replacing a spinal disc with an elastically expanding cage device.  FIG. 7A  shows a section of a patient&#39;s spine  790 , where degenerated disc material  799  is removed from the intervertebral space  791 . Next, as shown in  FIG. 7B , an elastically expanding spinal fusion cage  100  is implanted while in a collapsed or constrained state and positioned in the cleared intervertebral space  791  using an implant instrument  780 . Next, as shown in  FIG. 7C , an inflationary medium  719  (e.g., medical cement or bone cement) is pumped into the elastically expanding spinal fusion cage  100  to cause the elastic expansion of the expanding cage  100 . When the expanding cage  100  is filled with the inflationary medium  719 , it can provide a solid weight-bearing structure in the intervertebral space  791 .  FIG. 7D  shows the patient&#39;s spine  790  post-operatively, where the elastic material of the body  110  of the expanding cage  100  has bioreabsorbed over time and osteointegration has resulted in the patient&#39;s own bone matter  798  forming between the adjacent vertebrae using the cured cement  719  as a scaffold. 
     Example Materials 
     The choice of materials for the elastically expanding cage  100  embodiments is at least partially a function of the desired design requirements. For example, the material must withstand internal pressure, chemical, and heat from injected medium. In some instances, the expansion can produce up to 800N of pressure and in other instances up to 100N and others up to 1500N. In addition, the material must be elastically expandable to provide a desired expansion from the collapsed state to the expanded state. In some implementations, the body material for the elastic cage can be capable of expanding by a factor of up to about 280% without rupturing. In some instances, the elastically expanding cage  100  can be capable of withstanding up to about 25 bar of inflationary pressure. In some instances, the elastically expanding cage  100  can be capable of withstanding up to about 16,000N of pressure once in a final position and following curing of bone cement. In some instances, the materials can be less robust. For instance, the expanding cage  100  could be inflated under low pressure and then the inflation material (e.g., bone cement) is allowed to set. In this case, the expanding cage  100  would not need to withstand as high of an internal pressure as would be seen if the inflationary material were a fluid. In these cases, only the compressive stress capabilities of the material of a wall of the body would be tested as opposed to the structural integrity of the entire cage device. 
     In some implementations, the expanding body  110  can be configured to be manufactured in a collapsed state (e.g., a pre-expanded state) and then withstand inflation (e.g., expansion) to an expanded state without rupturing. In some implementations, the elastic body  110  can be configured to expand without rupturing when expanded in the intervertebral space. In some instances, the body  110  of the elastically expanding cage  100  can grow by more than twice the size (measured, for example, by volume or exterior linear dimensions). In some implementations, the body  110  can be configured to be manufactured in an expanded state and withstand compression into a collapsed state without splitting or otherwise failing. In some implementations, the material of the body  110  can be capable of withstanding any expected temperature or chemical factors (e.g., during sterilization) without degrading. In some implementations, the chemical factors can a function of the inflationary medium used with the body. In some implementations, the materials of the expanding cage  100  can be biocompatible, e.g., meeting the US Pharmacopeia (USP) Class VI standards for biocompatibility. 
     In some implementations, the material of the body  110  of the elastically expanding cage  100  can prevent the inflationary material from contaminating the implantation area or leaking uncontrollably. In some instances, the material of the body  110  can be configured to expose the inflationary medium to the body of the patient, requiring inflationary medium to be biocompatible. For example, the body  110  can include pores in the body  110  of the expanding cage  100 , or the material of the body  110  itself can be a porous material. 
     Exemplary materials for the expanding spinal fusion cage embodiments can include polymers, which can satisfy both medical and functional requirements for the devices. For example, polyisoprene (e.g., Cariflex Polyisoprene) can meet biocompatibility requirements and exhibit high elongation properties, thereby allowing for the required factor of expansion (e.g., up to about 280%). Polyisoprene (e.g., synthetic latex) can also exhibit sufficient Young&#39;s modulus for use in the expanding cage. In some instances, a polyisoprene body  110  of an expanding cage  100  can be 3D printed using Vat polymerization and/or material jetting techniques. 
     Additionally, in some instances, polyisoprene can be jetted using methods that print picodot size deposits, which enable the jetted polyisoprene of the body  110  to keep its mechanical properties. In some instances, a semi-porous geometric micro-structure can be constructed within the 3D jetted polyisoprene to better engineer a rate of bioreabsorption. Polyester and PET are other biocompatible and biodegradable materials commonly used in medical applications that could be utilized in various aspects and embodiments of the present disclosure. Examples include aliphatic polyesters (e.g., PLLA, PLA, PLGA, PGA, PDS, PCL, etc.) that are known to be biocompatible and absorbable. In some instances, the added materials that are included with the printed structure are able to create a response from the surrounding tissue such that the osteointegration of the cage device is improved or made to occur faster. In some instances, the added materials can be used in small quantities through the printing process and provide a positive effect, whereas if they were used in bulk they may create other issues such as biocompatibility. In some instances, photocurable constructs (e.g., acrylate scaffolds with urethane linkages, etc.) as well as silicone materials are used in combination with or in replacement of the above materials. 
     3D Printing Techniques 
     Certain aspects of the present disclosure include methods of 3D printing some or all of the structures of an expanding spinal fusion cage according to embodiments disclosed herein. With regard to the above-identified elastically expanding cages, multiple different 3D printing techniques can be used, including, but not limited to, vat extrusion, selective laser sintering, and material jetting and stereolithography. 
     Examples of Expanding Cages with Meta-Materials 
       FIGS. 8A-8D  are illustrations of one embodiment of a metamaterial cage (i.e., formed from or having hybrid characteristics of multiple materials) embodiment showing the expansion process.  FIG. 8A  shows an expanding cage  200  in a pre-expansion or collapsed state where the expanding cage  200  has a generally tubular shape with a minor diameter  280  that is about the same size as an inflation valve  240  disposed in the body of the expanding cage  200 . In this pre-expansion state, the expanding cage  200  is sized and shaped to be able to be inserted into the intervertebral space (e.g.,  791  of  FIG. 7A ) via existing minimally invasive surgical techniques. The expanding cage  200  can include an expanding structure that is shown as a textile substrate  230  and a stabilization structure wrapped around the textile substrate  230  that is shown as a network of 3D scaffolds  210 . In some instances, the textile substrate  230  can be a woven textile substrate. The textile substrate  230  defines an interior volume  220  that can be configured to receive and inflationary medium for expanding the textile substrate  230 . The textile substrate  230  can be capable of inflation to a larger size and the 3D scaffold  210  can be configured to either expand with the textile substrate  230  or otherwise allow the expansion of the textile substrate  230  until the 3D scaffold  210  constrains further expansion of the textile substrate  230 . 
     In the collapsed state, both of the textile substrate  230  and the 3D scaffold  210  can be compressed down into a small volume to enable the expanding cage  200  to be inserted into the intervertebral space and subsequently inflated to a larger size using an inflationary medium, as shown in  FIG. 8B . In some instances, the 3D scaffold can control the differential expansion rate of the textile substrate  230  during the inflation process. In some instances, the 3D scaffold can at least partially define a size and shape of the expanding cage  200  by restricting further expansion of the textile substrate  230 , as shown in  FIGS. 8C and 8D . 
     In  FIG. 8B , an inflationary medium is injected (as shown by arrows  271 ) into the interior volume  220  of the expanding cage  200 . The expanding cage  200  can be filled with the inflationary medium, and pressure from the inflationary medium can expand the textile substrate  220 . As the textile substrate  230  expands within the 3D scaffold  210 , the 3D scaffold also expands, grows, unfolds, or otherwise controls the expansion of the textile substrate  230 . In some instances, the expanding cage  200  includes a dual inflation system, including a core inflation area that is configured to be filled with an inflationary material and an outer inflation area that is configured to be filled with an anti-inflammatory or other media for providing a biological effect. 
       FIG. 8C  shows the expanding cage  200  in an expanded state where the pressure of the inflationary material pumped into the expanding cage  200  has reached a designed pressure and, as a result, the textile substrate  230  and 3D scaffold  210  has expanded to a designed sized and shape.  FIG. 8C  shows the expanding cage  200  having a given length scale  818  that is, in some instances, a function of the material properties and size and shape of the textile substrate and the 3D scaffold  210 , as well as the pressure of the inflation material. For example,  FIG. 8D  shows another expanding cage  201  with the same textile substrate  210  as the expanding cage  200  of  FIG. 8C , but with a different 3D scaffold  211  that results in a different length scale  819  of the expanding cage  201  in the expanded state. Any number of final shapes and sizes for the expanding cage  200  are possible depending on the particular construction of the textile substrate  230  and the 3D scaffold  210 . In some embodiments, there are pores in an outer surface of the expanding cage  200 , which, in some instances, do no open to allow material to exude into the intervertebral space until the pressure inside the expanding cage  200  reaches a threshold or final pressure. 
     In some instances, however, the 3D scaffold  230  can be a rigid stabilizing structure that can be configured to constrain, control, or otherwise limit the expansion and/or final shape and size of the expanding cage  200  depending on the required parameters of the expanding cage. In some instances, the textile substrate  230  can be an elastically expanding material. In some instances, the textile substrate  230  can be inelastic and can be configured to expand from a collapsed state to an expanded state by inflating from a ‘crumpled’ or otherwise compacted shape to a maximally volumetric shape. In some instances, the textile substrate  230  can be porous and can enable transfer of the inflationary medium across the textile substrate  230  in order to, for example, promote fusion in of the inflationary medium with the surfaces of the intervertebral space. 
       FIGS. 9A-9D  are cross-sectional schematics of two alternative expanding cage device embodiments with an exterior 3D scaffold formed as a rigid exterior stabilization structure.  FIG. 9A  shows an expanding cage  900  with a rigid external structure  910  that at least partially surrounds a woven textile substrate  230 . The rigid external structure  910  includes a rigid top container  918  and a rigid bottom container  919  that are able to expand away from each via extension coupling  910  when the woven textile substrate  230  is inflated, as shown in  FIG. 9B . In some instances, the rigid top and bottom containers  918 ,  919  are box-like structures that slide in a single degree of freedom with respect to each other during inflation of the woven textile substrate  230 , with the extension coupling  910  being the overlap between the box-like structures that is configured to prevent separation beyond, for example, the extension shown in  FIG. 9B . In some instances, the rigid top and bottom containers  918 ,  919  are top and bottom face members that are connected by two or more individual extension couplings  910  configured to at least constrain the rigid top and bottom containers  918 ,  919  in the single degree of freedom of extension show in  FIGS. 9A and 9B . 
       FIG. 9C  shows an expanding cage  901  embodiment with ridged exterior stabilization structure that includes a rigid top element  928  connected to a rigid bottom element  929  via two or more telescopic extension mechanisms  912 . The expanding cage  901  includes a woven textile substrate  230  between the rigid top and bottom elements  928 ,  929  that, during inflation, translates the rigid top and bottom elements  928 ,  929  away from each other via an extension of the telescopic extension mechanisms  912 , as shown in  FIG. 9D . In some instances, the telescopic extension mechanisms  912  can be made of three or more telescopic elements  913   a - c  to allow the rigid top and bottom elements  928 ,  929  to expand away from each other a distance more than twice a collapsed length of the telescopic extension mechanisms  912 , as shown. The telescoping elements can either be one rectangle in rectangle telescoping element on each side or multiple cylindrical telescoping elements on each side. 
       FIGS. 10A-10D  are cross-sectional schematics of two alternative expanding cage device embodiments with an internal stabilization structure in the form of a scaffold to constrain the expansion and shape of an exterior woven textile substrate.  FIG. 10A  shows an expanding cage  1000  that includes an interior expanding scaffold  1010  surrounded an exterior woven textile substrate  1030  in a collapsed state. The exterior woven textile substrate  1030  can be connected to the interior expanding scaffold  1010  by a plurality of threads  1060 . The interior expanding scaffold  1010  can be configured to expand by inflation of the exterior woven textile substrate  1030  until the interior expanding scaffold  1010  reaches a designed maximum extension size, as shown in  FIG. 10B .  FIG. 10B  shows the expanded exterior woven textile substrate  1030  being constrained in an expanded state by the fully expanded interior expanding scaffold  1010 . In operation, the shape of the fully expanded interior expanding scaffold  1010  can define the shape of the inflated exterior woven textile substrate  1030 . In some instances, the expansion of the interior expanding scaffold  1010  can be configured to control the overall expansion of the expanding cage  1000 . 
       FIG. 10C  shows an expanding cage  1001  that includes a fixed interior scaffold  1011  surrounded by an exterior woven textile substrate  1030  in a collapsed state. The exterior woven textile substrate  1030  can be connected to the fixed interior scaffold  1011  by a plurality of threads  1060 . The fixed interior scaffold  1011  can be configured to constrain the expansion of the exterior woven textile substrate  1030  at a designed maximum extension size, as shown in  FIG. 10C . In  FIG. 10C , the shape of the inflated exterior woven textile substrate  1030  can be a function of the shape of the fixed interior scaffold  1011  and the length of the threads  1060 . 
     In some instances, the threads  1060  can be inelastic. In other instances, the threads  1060  can be elastic and an inflated shape of the exterior woven textile substrate  1030  can also be a function of the elastic property of the threads  1060 . 
       FIGS. 10E and 10F  are cross-sectional schematics of two alternative expanding cage device embodiments with multiple interior chambers.  FIG. 10E  shows the inflatable portion of an expanding cage  1002  that includes an core inflatable structure  1031  and an exterior inflatable structure  1030 . The core inflatable structure  1031  can be configured to be filled with an inflationary material and the outer inflation structure  1030  can be configured to be filled with an anti-inflammatory or other media for providing a biological effect. 
       FIG. 10F  shows the inflatable portion of an expanding cage  1003  that includes an outer inflatable structure  1030  that includes a plurality a different chambers  1032   a - d  that can be inflated individually to change the overall shape of the outer inflatable structure  1030 . In some instances, the different chambers  1032   a - d  are in fluid communication with each other. In some instances, the different chambers  1032   a - d  are separate from each other. 
       FIG. 10G  is a cross-sectional schematic an alternative expanding cage device embodiment  1004  with additional structural components  1090  attached on the top and bottom face of an outer inflatable structure  1030  to improve fixation. The additional structural components  1090  can be removably attached to the outer inflatable structure  1030 . The additional structural components  1090  can be configured to engage with vertebral faces. 
       FIGS. 11A-11D  are illustrations of an example procedure for replacing a spinal disc with an expanding spinal fusion cage device  200  constructed using metamaterials (e.g., 3D scaffolds  210  and a woven textile substrate  230 ).  FIG. 11A  shows a section of a patient&#39;s spine  790 , where degenerated disc material  799  is removed from the intervertebral space  791 . Next, as shown in  FIG. 11B , the expanding spinal fusion cage  200  can be implanted and positioned in the cleared intervertebral space  791  using an implant instrument  780 . Next, as shown in  FIG. 11C , an inflationary medium  719  (e.g., medical cement or bone cement) can be pumped into the expanding spinal fusion cage  200  to cause the expansion of the expanding cage  200 . When the expanding cage  200  is filled with the inflationary medium  719  (and, in some embodiments, following curing of the inflationary medium), it can provide a solid weight-bearing structure in the intervertebral space  791 .  FIG. 11D  shows the patient&#39;s spine  790  post-operatively, where fusion and osteointegration have resulted in the patient&#39;s own bone matter  798  forming between the adjacent vertebrae using the woven textile substrate  230  and cured inflationary medium as a scaffold structure. 
     Example Materials 
     Existing 3D printing applications and technologies can enable 3D printing onto fabric substrates, allowing complex printed structures can be incorporated onto fabrics. For example, in the fashion industry, apparel can be 3D printed, where a combination of hard geometric shapes (e.g., 3D printed structures) and a soft, drape-able substrate (e.g., a fabric) can be combined to provide new ergonomic and aesthetic possibilities. Such techniques can allow, by way of further example, control of how a garment moves on the body through the precise design of, and interface between, the 3D printed and woven components. Additionally, such techniques can leverage 3D printing onto textiles to create programmable textiles, e.g., fabrics that have a form of shape memory. 
     By way of further example, in some embodiments material tracks can be printed at variable thicknesses onto a pre-stressed textile substrate. Once the textile is allowed to take its relaxed state, the printed geometry can constrain the contraction, thereby directing the fabric into a designed, pre-defined form. 
     In some instances, the materials for the meta-material solution can be a combination of woven polyester for the textile substrate (e.g., an expanding structure or the textile substrate  230  of  FIG. 8A-8D ) and a polyester composite or polyisoprene for the 3D printed scaffold (e.g., an stabilizing structure  210  or the 3D scaffold  210  of  FIGS. 8A-8D ). In some implementations, the materials can be biocompatible, e.g., meeting the US Pharmacopeia (USP) Class VI standards for biocompatibility (or can be formulated to meet such standards). 
     In some instances, cement can be used as a fixation method. For example, in some embodiment existing medical cements can be suitable. In some instances, a solid-setting compound such as medical bone cement can be used to fix the final expanded position of the expanding cage device in order to prevent maintaining a permanently inflated device in the body under pressure. In some instances, hydrogel and other gelatinous materials are used as fillers, which can be, for example, inserted at elevated temperatures and set at body temperature. In some instances, a phase change temperature of the filler material is tailored for the specific application. In some instances, an electronic device is added that heats the material to change the compressibility of the filler, which can be done, for example, in selective channels to change the local compressibility of the filler. 
     In some instances, the materials of the meta-material expanding cage  200  can be capable of being compressed, rolled, or folded into a small form-factor without compromising the 3D printed scaffold or without compromising the woven substrate. In some instances, the woven textile substrate  230  (e.g., the expanding structure) can be capable of expanding or unfolding at least about 280% in volume from the collapsed state to the expanded state. In some instances, the 3D printed scaffold (e.g., a stabilizing structure of the 3D scaffold  210  of  FIGS. 8A-8D ) can be sized and shaped to provide a degree of flexibility to allow for the expansion of the cage. 
     In some instances, the weave of the textile substrate (e.g., an expanding structure or the textile substrate  230  of  FIG. 8A-8D ) can be sized and shaped to allow for precise control over weave density to ensure that the injection of the inflationary medium (e.g., bone cement) does not escape rapidly or uncontrollably through the weave of the textile substrate. In some instances, the woven textile substrate can be constructed from polyester fibers. In some instances, the polyester fibers can have a tensile strength above about 580 MPa and an elongation factor of at least about 50% in order to support high pressures that can be experienced during the injection of bone cement. 
     3D Printing Techniques 
     Certain aspects of the present disclosure include methods of 3D printing some or all of the structures of an expanding spinal fusion cage according to embodiments disclosed herein. With regard to the above-identified metamaterial cage embodiments, multiple different 3D printing techniques can be used, including, but not limited to, fused deposition modelling, material jetting, and 3D digital weaving. Other 3D printing techniques described herein, or a combination thereof, can also be used to produce various structures of the expanding cages according to aspects of the present disclosure. 
     Kirchhoff-Plateau Surfaces 
     One example method of 3D printing for use in the manufacture of expanding spinal fusion cages, and in particular the metamaterial embodiments described above, includes the use of Kirchhoff-Plateau surfaces. In some instances, the textile substrates of the present disclosure (e.g.,  230  of  FIGS. 8A-8D ) with or without 3D scaffolds can define or utilize a Kirchhoff-Plateau surface. Example methods using Kirchhoff-Plateau include creating a 3D structure by engineering and 3D printing a programmable 2D net, or Kirchhoff-plateau surface. The methods can include simulating and flattening the 3D components of an expanding cage design to be 3D printed in a digital design environment into a 2D net structure. Afterwards, a 3D printed geometry or system of tracks (e.g., a 3D scaffold  230 ) can be set onto a woven substrate (e.g., a textile substrate  230 ) under tension. The 3D printed structure can control the contraction and deformation of the polyester substrate once released from tension. This deformation can be programmed and simulated during the initial computer aided design (CAD) stage. 
     One example method of manufacturing Kirchhoff-Plateau surfaces is flat knitting a 3D net, whereby a 2D manufacturing process creates a 3D structure. Because this method first manufactures a 2D material and then forms a 3D net, as opposed to directly manufacturing a 3D structure, it provides an alternate solution to 3D printing tracks onto a conformal woven substrate. In this instance, a 3D digital object (e.g., the expanding structure or stabilizing structure of the expanding spinal fusion cage) can be flattened into a net, followed by the 2D weaving of a conformal woven substrate. Three-dimensional tracks can then be printed onto the substrate in a programmable textiles process. In some examples, a 3D knitted structure can be fabricated by weaving a flat net shape, then pulling or forming the net into the final 3D product in a secondary process. In operation, a net can be 3D printed onto a flat textile substrate under tension, and the release of the substrate from tension can result in controlled deformation of the net into the desired 3D shape. A high degree of complexity can be achieved in terms of woven structures, mechanical behaviors, and 3D geometry from a 2D knitted net. 
     Another example method of manufacturing Kirchhoff-Plateau surfaces involves fused deposition of thermoplastics to 3D print a scaffold or track network onto a textile substrate. This method can provide another step in functionality with 2D net shapes by programming the 3D net to take its final form independent of external force or secondary processes. A high level of complexity can be achieved through the combination of 3D printed constraint tracks and a textile substrate under tension. 
     Yet another example method of manufacturing Kirchhoff-Plateau surfaces is with material jetting, whereby jets of ink or other materials are used to create 3D relief structures on fabrics. In some instances, the inks can be either jetted hot and solidify as they cool or contain photo-catalyzers and be cured solid from a UV light source. In some instances, one or more materials can be jet onto a polyester substrate to achieve extremely high layer height resolution (e.g., about 14 microns) and create the complex geometries, scaffolds, and tracks of certain aspects of the expanding spinal fusion cages of the present disclosure. 
     Tubular Knitted Structures 
     Another example method of 3D printing the structures of expanding spinal fusion cages includes the use of tubular knitted structures. In some instances, the expanding structure is a woven textile substrate  230  constructed from one or more tubular knitted structures and the stabilizing structure  210  is a scaffold that is 3D printed onto the tubular knitted structures. 
     One example method of producing the 3D scaffold structures onto a tubular knitted structure includes using a two-stage hybrid manufacturing approach. First, a 3D knitting machine can weave a tubular structure to create a conformal balloon or pouch that makes up the tubular knitted structure. In some instances, this tubular knitted structure can be made of polyester. Afterward, the tubular knitted structure can be removed from the 3D knitting system and placed onto a mandrel, whereby a secondary 3D printing process can print a geometry of 3D scaffolds across the tubular knitted structure. The 3D printed components (e.g., the 3D scaffolds or stabilization structures  210 ) can function as a mechanism to control and ensure the precise expansion of the tubular knitted structure (e.g., the expanding structure) as it is inflated through the injection of medical cement or other inflationary medium. 
     One example method of 3D printing scaffolds onto a textile substrate is material extrusion, whereby the textile substrate can be placed onto a mandrel and a fused deposition modeling head can extrude the geometry of the 3D scaffolds onto the textile substrate of the tubular knitted structure as it rotates. 
     Another example method of 3D printing scaffolds onto a textile substrate is using material jetting, whereby the extrusion head of the material extrusion method noted above can be substituted with a material jetting head. Material jetting methods can provide a greater degree of precision in material deposition, layer-height resolution, and printing speed. Furthermore, the material jetting process can print in multiple materials simultaneously, which can increase the functionality of the design by providing for printing of multiple embedded materials. 
     An example method of 3D printing a textile substrate is using digital weaving systems to create woven substrates. Three-dimensional weaving technologies provide an ability to design and manufacture a conformal tubular woven structure to function as a bag and substrate to a secondary 3D printed track component. For example, 3D looms and weaving machines can create complicated customized tubular meshes or structures by weaving multiple filaments in 3D space. By picking up or dropping stitches, the circumference of the tube can be varied over the length of a part, thereby enabling the design of complex tubular structures. Additionally, digital weaving methods can create multi-tube and multi-branch geometries, which enable multi-branching spinal cage designs to be manufactured. 
     In some instances, the complex nets or balloons of the textile substrate can be alternatively manufactured in 3D using 3D electrospinning as an alternative to the textile weaving methods described above. Electrospinning can involve creating an electrical potential between a mandrel (e.g., acting as a cathode) and a fiber emitter (e.g., acting as an anode) to deposit fibers (e.g., nanofibers) over the mandrel. Electrospinning can create bioscaffolds and very fine strong fibers suitable for use as the substrate of, for example, the textile substrate  230  of the expanding cage  200  of  FIGS. 8A-8D . Electrospinning a textile substrate in 3D can also enable the substitution of polyester fibers for wholly organic materials (e.g., as collagens and hyaluronic acid). 
     As described below, several embodiments of additive manufacturing over woven substrates can make use of a spinning mandrel to hold the substrate while additional material is deposited thereon. In some embodiments, rather than using a rotating cylinder, cuboid, or spherical shape to create an expandable section of a cage, 3D printing or additive manufacturing could be used to create a mandrel of a desired shape, e.g., a geometrically-complex mandrel that could be, e.g., asymmetric in some respect, etc. With reference to electrospinning in particular, a conductive layer could be added to the mandrel to create a cathode and enable fiber deposition. Use of 3D printed mandrels, with electrospinning or any of the other deposition techniques described herein, can allow more complex expandable section shapes. 
     3D Printing Processes 
     Below is exemplary description regarding various embodiments of 3D printing or additive manufacturing processes that can be used to manufacture the above-described embodiments of expanding cage devices. 
       FIGS. 12A-C  illustrate an example extrusion process for manufacturing an expanding cage device.  FIGS. 12A-C  show a production apparatus  1200  for an extrusion process, using a 3D printing system  1220  and a separate part cleaning station  1290 . The 3D printing system  1220  can include a build chamber  1207 , a suspension or support material  1206 , an extrusion apparatus  1204  contain polyisoprene  1203 , and a computer  1201  controlling the 3D printing system  1220 . In some instances, the 3D printing system  1220  can ensure that the support containments  1205  are within acceptable tolerances. 
     In operation, the computer  1201  can convert a CAD model to build instructions, which can be transmitted  1202  to the 3D printing system  1220 , where a printed part  1208  can be created. Afterwards, the extrusion apparatus  1204  can be removed  1209  and the completed part  1210  can be allowed to cure before being transferred to the cleaning station  1290 . In the cleaning station  1290 , remaining support material  1212  can be removed with a manual cleaning tool  1291  as well as with cleaning fluid  1293  dispensed from cleaning jet nozzles  1292 . 
       FIGS. 13A-C  illustrate an example material jetting process for manufacturing an expanding cage device.  FIGS. 13A-C  show a production apparatus  1300  for a material jetting process using a 3D printing system  1320  and a separate part cleaning station  1290 . The 3D printing system  1320  includes a build plate  1306 , a build material delivery apparatus  1303 , a support material delivery apparatus  1305 , a supply  1304  of the materials, and a computer  1201  controlling the 3D printing system  1320 . 
     In operation, the computer  1201  can convert a CAD model to build instructions, which can be transmitted via a connection  1202  to the 3D printing system  1320 , where a printed part  1308  can be created on the build plate  1306  using a material jetting method. Afterwards, the printed part  1308  can be removed  1309  and transferred to the cleaning station  1290 . 
       FIGS. 14A and 14B  illustrate an example process for manufacturing a woven tubular structure for use in an expanding cage device.  FIG. 14A  shows a tubular knitted structure  1402  being printed by a material jetting apparatus  1401  onto an inflated substrate  1403  in an expanded configuration.  FIG. 14B  shows the tubular knitted structure  1402  in a collapsed state after the substrate  1403  has been deflated in order to remove the tubular knitted structure  1402 . 
       FIGS. 15A-E  illustrate an example process for manufacturing an expanding cage device.  FIGS. 15A-E  show a 3D printing system  1501  for use in a meta-material jetting process  1500  that is designed to work with existing 3D weaving systems for fabricating a woven substrate  1502 . The 3D printing system  1501  includes a mandrel  1505  holding a woven substrate  1502  (e.g., a polyester substrate in some embodiments) and a printing apparatus including jetting heads  1503  and curing heads  1504 . 
     In operation, a computer  1201  can convert a CAD model to build instructions for both woven substrate fabrication and 3D scaffold track fabrication, which can be transmitted (e.g., via connection  1202 ) to the 3D printing system  1501  and a 3D weaving system  1506 . The 3D weaving system  1506  can attach the fabricated woven substrate to the mandrel  1505  of the 3D printing system  1501 , where the jetting heads  1503  can jet polyisoprene or other materials onto the mandrel  1505  and the curing heads  1504  can cure the freshly jetted polyisoprene or other materials as the mandrel rotates underneath the printing apparatus. Each rotation can lay down a single layer of polyisoprene or other material, and the printing apparatus can be raised  1507  with each full rotation. After the 3D printing is completed, the completed 3D printed part  1508 , which can include the printed tracks and the woven substrate  1502  to which they are attached, can be removed  1509 . The part  1508  can contract as it is removed from tension around the mandrel  1505 . 
       FIGS. 16A-E  illustrate an example process for manufacturing an expanding cage device.  FIGS. 16A-E  show a 3D printing system  1601  for use in a meta-material extrusion process  1600  that is designed to work with existing 3D weaving systems for fabricating a woven substrate  1502 . The 3D printing system  1601  can include a mandrel  1505  holding the woven substrate  1502  (e.g., a polyester substrate in some embodiments) and a printing apparatus including an extrusion head  1602  that can travel on an extrusion head gantry  1605  and contain the 3D printing material  1602 . 
     In operation, a computer  1201  can convert a CAD model to build instructions for both woven substrate fabrication and 3D scaffold track fabrication, which can be transmitted (e.g., via connection  1202 ) to the 3D printing system  1601  and a 3D weaving system  1506 . The 3D weaving system  1506  can attach the fabricated woven substrate to the mandrel  1505  of the 3D printing system  1601 , where the extrusion head  1602  can print the tracks  1606  onto the woven substrate  1502  by moving  1607  along the gantry  1605 , and being indexed away from the mandrel  1505  after each layer is printed. After the 3D printing is completed, the completed 3D printed part  1608 , which includes the woven substrate  1502  and the printed tracks  1606 , can be removed  1609 . The part  1608  can contract as it is removed from tension around the mandrel  1505 . 
     Other Alternatives 
     In addition to the above-described materials that can be utilized to create the expanding cage devices described herein, other materials can be utilized in some embodiments. For example, in some embodiments certain metallic materials can be utilized with the above-described processes. Examples of such materials can include stainless steel, cobalt-chromium, titanium, tantalum, and nitinol, among others. 
     Moreover, in some embodiments additional features can be integrated with the 3D printed components described herein. For example, additively manufactured components can be individually tracked using unique identifiers, such as geometric keys or tags printed into the product. In the case of a tag, for example, a unique serial number, QR (quick response) code, or other identifier can be automatically printed on a tag incorporated into the structure, or on any surface of the structure. Still further, parts can be printed with reliefs to accommodate RFID (radio frequency identification) tags or other types of tracking components. 
     In some embodiments, the filler materials can comprise multiple materials so that elastic properties of the filler material can be adjusted as well. For instance, creating an emulsion of bone cement and either a liquid or a fluid can alter the modulus of the final cured state of the cement. In addition, some embodiments include incorporating elastomeric or ceramic beads in the mix, which can achieve similar results by altering the modulus of the final cured state of the cement. 
     In addition to being directed to the specific combinations of features claimed below, the present disclosure is also directed to embodiments having other combinations of the dependent features claimed below and other combinations of the features described above. 
     One skilled in the art will appreciate further features and advantages of the disclosure based on the above-described embodiments. Accordingly, the disclosure is not to be limited by what has been particularly shown and described, except as indicated by the appended claims. This description will suggest many variations and alternatives to one of ordinary skill in this art. All these alternatives and variations are intended to be included within the scope of the claims. Those familiar with the art may recognize other equivalents to the specific embodiments described herein and such equivalents are also intended to be encompassed by the claims. All publications and references cited herein are expressly incorporated herein by reference in their entirety.