CA2548993A1

CA2548993A1 - Artificial intervertebral disc

Info

Publication number: CA2548993A1
Application number: CA002548993A
Authority: CA
Inventors: Michael S. Williams; Jeffrey A. Smith; Kevin D. Holbrook
Original assignee: Synecor LLC
Current assignee: Synecor LLC
Priority date: 2003-11-19
Filing date: 2004-11-19
Publication date: 2005-06-09
Also published as: US20050119752A1; AU2004292997A1; EP1691731A2; WO2005051228A3; WO2005051228A2

Abstract

Devices and methods for manufacturing devices for treating degenerated and/or traumatized intervertebral discs are disclosed. Artificial discs and components of discs may include an artificial nucleus and/or an artificial annulus and may be comprised of shape memory materials synthesized to achiev e desired mechanical and physical properties. An artificial nucleus and/or annulus according to the invention may comprise a hollow body that may be filled with a curable material for deployment. A hollow body according to th e invention may comprise one or more partitions to define one or more chambers and may comprise means for directing the flow of material within said hollow body.

Description

,; , , ~RT~B'I~AI~ I~I~~
II~LAT~D APPLICATIOhIS
This application is related to and claims the benefit of the priority date of U.~.
Provisional Patent t~pplicatcan ~erfal! I~o. 60~~3e,g~~4 entitlef "Artificial Ireter~rer~ebral Disc", fled 3anuary L2, 2004y U:~. Patent ~.pplic~.~an entitled "Artificial Intervertebral I O Disc", filed November 16, 2004; U.S. Provisional Patent Application serial No.
60/523,578 entitled "Highly Convertible ~ndolumenal Prostheses and Methods of l~anufacte~re", fled hTovexnber 19', 2003 ~y and T~.~~. Patent Application entitled: "I~igh:Iy Canvertr'ble ~ndalumenal Prostheses and l~Ieflrods of l~.fanufactore", fcled November I~, 2004.
i S ~IEi.D tI~ THE INTION
"The invention liereirn reLates~ generally to medical devices and methods of treatment, and mare pat tieularly ta~ devices anti zn ethods used in tl~e treatrrrent of a degenerated intervertebral disc.
BACK~GROIINi) OF THE ~NTION
20' Intervertebr ~ ! di~G degeneration i a lea ~ !'! ~ ~g cause of pain and disability, occurring in a ,substantial nzaJarity afpeoph; at same paint during ad-althoad. TITe intervertebral disc, comprising primarily the nucleus pulposus and surrounding annulus fibrasus, constitutes a vital component of the functional spinal unit. The intervertebral disc maintains space betWeerr adj-acent vertebral bodies., absorbs impact betWeert and cushions 25 the vertebral bodies. The disc allows far ffu~ed movement between fhe vertebral bodies, bath subtle (for example, with each breath inhaled and exhaled) and dramatic (including' rotatiaual movement and bending movement in all planes.) Deterioration of the bialagical and mechanical integrity of an infer~ertebrai disc as a result of disease andlar aging may limit mobility and produce pain, either directly ar indirectly as a result of 30 disruption of the functioning of the spine. estimated health care costs of treating disc degeneration in the United States exceed $~60 billion annually.
loge-related disc changes are pragressivey and, once si.gnificanf, increase the risl~
afrelated disorders of the spzne. The degenerative process alters intradiscal pressures, causing a relative shift of axial Ioad-bearing to the peripheral regions of the endplates and facets ofthe vertebral bodies. Such a shift promotes abnornxal loading of adjacent inter~rertebral discs and vertebral bodies, altering spinal balance, shifting the axis of rotation of the vertebral bodies, and increasing risk of injury to these units of the spine.
Further, the transfer of biomechanical loads appears to be associated with the development of ofher disorderly including both facet andl 'ligament hypertrophy, osteophyte forrmation, lyphosis, spondylolisthesis, nerve damage, and pain.
In addition to age-related changes, numerous individuals suffer trauma induced damage to the spine including the intervertebral discs. Trauma induced damage may include ruptures, tears, prolapse, herr~iations~,, and other injuries. that cause pain and reduce I~ strength anti function.
Non-operative therapeutic options for individuals with neck and back pain include zest, analgesics physical therapy, heat, and manipulation. These treatments fail in a significant number of patients. Current surgical options for spinal disease include dISCeGtt3lny, discectomy combined with fusion, and fusion alone. Nucnnerous disceetomies are performed annually in the United Mates. The procedure. is effective in promptly relieving significant radicular pain, but, in general, the return of pain increases proportionally with the length oftime following surgery. h~ fact, the majorify ofpatien s experience sign~ifi~cant back pain by ten years. following Iumbar d~scecforrxy.
An attempt to overcome some of the possible reasons for failure of discectomy,

2~ fusion has the potential to maintain normal disc. space height, to eliminate spine segment instability, and elinzirtate pain by preventing motion across a destabiliaed or degenerated spinal segment.
However, although some positive results are possible, spinal fusion may have harmful consequences as well. Fusion involves joining portions of adjacent vertebrae to 2'S one another Beeause rxsotian is. el~nnzinated at the treated level, the biomechanies of adjacent levels are disrupted. Resulting pathological processes such as spinal stenosis, disc degeneration, osteophyte formation, and others may occur at levels adjacent to a fusion, and cause pain in many patients. In addition, depending upon the device or devices and techniques used,, surgery may be invasive and require a lengthy recovery 3f~ period.
Consequently, there is a need in the art to treat degenerative disc disease and/or traumatized intervertebral discs, while eliminating the shortcomings of the prior art.
There remains a need in the art to achieve the benefit ofremovxl of a non-functioning ir~tervex-~ebral' disc, to replace all or a portion of the disc with a device that will function as a healthy disc, eliminating pain, while preserving oration. There remains a need for an artificial disc or other device that maintains the proper intervertebral spacing, allows for motion, distributes axial load appropriately, and provides stability. In addition, an artificial disc requires secure long-terrrx fixation to bone.
Further, tkxere remains a need. for an artificiak nucleus that can be implanted within.
the annulus fibrosus, in order to restore normal disc functioning. Such a nucleus must comprise the characteristic lower durometer than the annulus fibrosus, and the annulus fibrosus must comprise the requisite stiffness as compared with the nucleus.
Further, there remains a need for an artificial disc that can withstand typical cyclic stresses and perform throughout the life a patient. An artificial disc that can be implanted using minimally invasive techniques is also needed. ~lnd finally, a device that is compatible with current imaging modalities, such as Magnetic I~.esanance Imaging (1~II~L~
is needed.
5~~~~Y (~F fiH~ INV'~I~TIQN
An endoprosthesis for partial or complete replacement of an intervertebral disc is ~' disclosed comprising one or more shape memory polymers , the shape memory polymers synthesized from a first and second monomer seleetaad to impart predetermined properties on said shape memory polymer. The ~crst and second monomers are combined in a ratio to impart predetermined properties on said shape memory polymer. The first and second monomers are selected for molecular weight, hard and soft segments, transition temperature of said hard and soft segments, and other characteristics. The predetermined proper~es comprise load bearing capability, compressive resistance, stiffness, crystaklinity, (ensile strength, mechanical strength, durometer, elasticity, strain recovery rate, strain fixity rate, melting temperature, crystallization temperature, cross-linking ~5 density, extent ofphysicak cross-Iin~ing, extent ofcovalent bond cross-linl~ir~g, extent of formation of interpenetrating networks, and heat of fusion, for example.
The artificial discs disclosed herein substantially replicate the functions of a natural, healthy nucleus pukposus, annulus fibrosis; or both. .An artificial disc according to the invention may, for example, comprise a disc-like structure that may have a convex ~0 portion, and may have one or more securing rims. An artificial disc disclosed herein may have varying durometers, with, for example, a lower durometer in the nucleus region and a higher durometer in the annular region.

3 artif cial disc may alternatively comprise a hallow membrane in its delivery eordguration and a filled membrane in its deployed configuration. The filling material may in addition be selectively cured to form a more rigid structure. The membrane may, after filling, define an artificial nucleus and/or an artificial annulus, may define a single unitary structure wiah sefarate internal cha~rn'bers, ar may define separate porf~ons that may be used separately or together. The infiernal chambers and/or par~iaxrs may comprise interbody connections, baffles, partitions, and/or internal seams. An artificial disc or nucleus may comprise a particular durometer selected for its suitability to the particular interv~ertebral disc undergoing treatment, incl~udimg the level afthe vertebra within the l~~ spine.
Methods for making an endoprosthesis disclosed herein comprise the steps selecting a first monomer comprising a first set of characteristics that serves as a first parameter in dete~g the properties of a shape memory polymer; selecting a sseeand monomer comprising a second set of charactexTStics that serves as a second parameter in 1 S determining the properties of a shape memory polymer; determining a desired ratio of said first monomer to said second monomer; synthesi~g a shape memory polymer from said first and said secar~d xnor~arner; manufaGt~zring an endoprasthesis far poi E.ial ar fatal replacement of an intervextebral disc from said shape memory polymers setting a permanent shape for said endoprosthesis; setting a temporary shape for said 2U endoprosthesis.
BRIR14 I~E~GR::~"TIO-N O~F' TIC D'It~V'~ING~
FIG.1~ is' a perspective view afaa embodiment according to the invention in its deployed configuration.
FiG.1B is a side view of the embodiment of FIG. I .
RIG. ~A represents a crass section Taken along line t~,-~ ofFIG. IB.
FIG. 2B represents the same Gross section of an alternative embodiment of the invenfiion.
RIG. ~ illustrates, a cross section afthe embodiment ofli'I~~.1 arid ~ after being 3a~ placed partially in. a delivery configuration.
RIG. 4 is a plan view of the embodiment of FIB. 1 in its delivery configuration.
FIG. 5 is a side view of two vertebrae and a cross secfion of the embodiment of FIB. Y deployed therebetween.

~G. fi is a side view of a -~wo~ vertebrae and a side view of a crass section of the embodiment af~IG. 2B in. its deployed configurafiion.
FIG. 7 is a perspective view of an embodiment according to the invention.
FIG. 8A-B is a perspecfiive view of an arfiificiai nucleus according to the invention befar . a and after deployxnrent.
FIG. 9~ is a plan view of yet another embodiment according to the invention.
L
FIG.10 is a plan view of yet. another embodiment according to the invention FIG.11 is a side view of the embodiment of FIG. 10.
FIG.1~ is a perspective view aftFre embodiment c~fFIts~. lfl ~d I I.
lfl FIG.1~A is a perspective view afyet another alternative errxbodimeot according to the invention.
FIG.13B is a perspective posterior view of the embodiment of FIG. 20A ih sity,~.
FIB I~ 4 i~s a perspective view of an alternative embad'~rrTent according to the invention in its delivery car~g~xrafian rr~aunted upon a delivery mandrel.
IS FIG.15A is a side view of an embodiment according to the invention in its deployed configuration isz sitz~
FIGb Lis a perspective "cut away" view o~ftne exmbadiment afplG: L~, taken along line B ~ of G. I 9.
20 FIG. I6 is an "exploded'T in situ view of an embodiment similar to that illustrated in FIGS. 15A and I SB.
FIG.1~ is a posterior perspective "exp~l!oded" ire .~atr~ view of an alterrtatvve embodirr~er~t according to the invention.
FIG.18 is a perspective view of an embodiment according to the invention in ifs 25 deployed configuration.
FIG.19A is a plan view cross section c~~f an embadinrent according to the invention.
FIGS.19B-I9D illustrate three examples of cross section profiles according to the invention.
3~~ FIG.19~ illustrates a p an view cross, section ofam ernbo ~ ~ ~ ent according to the invention.
FIG.19~' illustrates an exemplary profile cross section of the embodiment of pIG.
I9E.

FIG. 2tl is a perspective view of auembodiment according to the invention.
FIG. ~1' is an "exploded" in ~it~c view of an embodiment according to fine invention.
FIG. 22 is an anterior perspective view of the embodiment of FIG. i 9 i~ sits S FIG. 2~ is a perspective "see~fihrough" view of a membrane can~g~,wafion of an alternative embodiment according to the invention.
FIG. 24 is a pexspeetive view of an alternative membxane configuration according to the invention.
D~FZ' ~AIIIrF'II DPFS'C:~IE' i ~0~ ~ ~ (IF ~ ~, ~ ;~~~II~~iY
t~,n endoprostbesis known as an at-~i~cial disc andlor an artificial disc nucleus are designed to xeplace a degenerated interverfebral disc Such an artificial disc or disc nucleus may be expandable and/or self expanding.
~.n "expandable:" endoprostlxesis: cornprvses a reduced profile configuration and an expanded profile configuration. ~n expandable endopros~hesis according to the invention may undergo a transition from a reduced configuration to an expanded profile conf guration via any suitable means, or may be self expanding. Some embodiments according to~ the invention may comprise a subs ~ ~ ~ aal!ly ho~I'To~v interior that rnay be fi i !ed with: a suitable medium, examples ofwhich are set for~li below. Such embodiments may accordingly be introduced into the body in. a collapsed configuration, and, following introduction, may be filled to form a deployed configuration. Embodiments according to the invention may accordingly l7e implanted percutaneously or surgically. If iznplantef surgically, embodiments according to the invention may be implanted from either an u., anterior or a posterior approach, following the removal of some or all of the native disc, excepting the periphery of the native nucleus.
"Spinal fr~sion'y is a process by which one or more adjacent vertebral bodies are adjoined to on:~ another in order to eliminate motion across an unstable ar degenerated spinal segment.
"Preservafion of mobility" refers to the desired maintenance of normal motion between separate spinal segments.
3fl "Spinal' unit" refers to a set ofthe vital functional parts of the spine including a vertebral body? endplates, facets, and intervertebral disc.
The term "cable" refers to any generally elongate member fabricated from any suitable material, whether polymeric, metal ar metal alloy, natural or synthetic.

'Fhe term "fiber" refers to any generally elongate member fabricated from any suitable material, wHether polymeric, metal or metal alloy, natural or synthetic.
As used herein, the term "braid~T refers to any braid or mesh or similar wound or woven structure produced from between 1 and several hundred longitudinal and/or transverse elongate elements wound, woven, b~aaded, lifted, helically v~ound, or interC~uinerl by any manner, at angles between 0~ and 1 g0 degrees and usually between 45 and 105 degrees, depending upon the overall geometry and dimensions desired.
Unless specified, suitable means of attachment may include by thermal melt, chemical bond, adhes~ivey sinferirsg~ welding, or ~ ~ y means known in the art.
.t~s used herein, a device is "ixrtplanted5~ ifit is placed ~uitl~in the body to remain for any length of time following the conclusion of the procedure to place the device within the body.
The term "diffusio~v coeffic~cent" refers ~ ~ the rate by ~l~ch a s ~ bstance elutes, or is released either passiveYy or actively from a substrate.
Unless specified, suitable means of attachment may include by thermal melt, chemical bond, adhesive, sintering, welding, or any means known in the art.
"shape rnernory'~ refers to the ability of a material to~ undergo structural phase transformation such that the rmaterral may define a first configuration under particular physical and/or chemical conditions, and to revert to an alternate configuration upon a change in those conditions. Shape memory materials may be metal alloys including but not limited to nicl~el t~tani ~ ~ : , or may be poTynzeriG. A. poFym~r is a shape memory polymer if the original shape ofthe polymer is recovered by heating it above ,a shape recovering temperature (defined as the transition temperature of a soft segment) even if the original molded shape of the polymer is destroyed mechanically at a lower temperature than the shape recovering tempera ~ture, or ifthe memorized shape is recoverable by application of another stimulus. such other stimulus may include but is not limited to pH, salinity, hydration, radiation, including but not limited to radiation in the ultraviolet range, and others. Some embodiments according to the invention may comprise one or more polymers having a strut ~ ~ a that assumes a first configuration, a second. configuration, and a Hydrophilic polymer of suf -C~cient rigidity coated upon at Ieast a portion of the structure when the device is in the second configuration.
Upon placement of the device in an aqueous environment and consequent hydration of the hydrophilic polymer, the polymer structure reverfs to the first configuration.

Some embodiments according ~o the invention, while not technically co~tprising shape memory characteristics, may nonetheless readily convert from a consfxained configuration to a deployed configuration upon removal of constraints, as a result of a material's elasticity, super-elasticity, a particular method of "rolling down"
and constraining the device for delivery, or a combination ofthe foregoing. such embodiments may comprise one ar more elastomeric or rubber materials.
As used herein, the term "segment" refers to a block or sequence of polymer forming part of the shape memory polymer. The terms hard segment and soft segment are relative terms, relating to the transition temperature ofthe segments.
C~errerally speaking, 1 (1 hard segments have a higher glass transition temperature than. soft segments, but there are exceptions.
"Transition temperature" refers to the 'temperature above which a shape memory polymer reverts to its original Fnexnorized con~gurafian.
The term "strain ~xity rate" Rfis a cluanti~cation ofthe Viability of a shape 15 memory polymer's temporary form, and is determined using both strain and thermal programs. The strain fixity rate is determined by gathering data from heating a sample above its melting pointy expanding the sa~nphe to 2~ifl~~a a~fi~'~empo~rary size, cooling it in the expanded state, and drawing back the extension to U%, and employing the mathematical formula:
~f ~~ '' ~u~f~m where ~~ is tlxe extensic~z~ m the tenstor~ free staf~ while dxawing back the extension, and ~m is ~tl~°/a.
The "strain recovery rate"' R,. describes the extent to which the permanent shape is recovered:

~,y - ~
~'r ~ ° ~m - EP t~ r~
3a where ~~, is the extenstion at the tension free state.
A "switching segment" comprises a transition temperature and is responsible for the shape memory polymer's ability to fix atemporary shape.
g A "thermoplastic elastomer" is a shape memory polymer comprising crosslinks that are predominantly physical crosslinks.
A "thermoset'T is a shape memory polymer comprising a Large number of crosslinks that are covalent bonds.
Shape memory polymers are highly versatile, and many ofthe advantageous properties listed above are readily controlled anti modified through a variety of techniques. Several macroscopic properties such as transition temperature and mechanical properties can be varied in a wide range by only small changes in their chernieal structure and composition. More speci~c examples are set forth in Provisional 111 Il.~. P'atent Application ~eriat loo. 6ar~5~3,5?~ and are incorporated in their entirety as if fully set forth herein.
Shape memory polymers are characterized by two features, triggering segments having a tlxer~nal transition 'fwi'~thin the temperate range of interest, and crosslinks determining the permanent shape. Depending on the kind of crosslinks (physical versus 15 covalent bonds), shape memory polymers can be thermoplastic elastomers or thermosets.
By manipulating the types of crosslinks, the transition temperature, and other characteristics, shape ~ne~nory polymers can be tailored for specific clinical applications.
lVlore specilieally, according the invention herein, one can the control shape memory behavior and mechanical properties of a shape memory polymer through 211 selecfion of segments chosen for their transition temperature, and mechanical properties can be in~~zenced by the content ofrespec~ve segments. The extent of crosslinking eax~
be controlled depending on the type of~naterial desired through selection of materials where greater crosslinking makes for a tougher material than a polymer network, Tn addition, the molecular weight of a macromonomeric crosslinker is one parameter on the ~S molecular level to afg~xst crystall'ini~ and mechanical properties of the polymer networks.
An additional mano~ner may be introduced to represent a second parameter:
Further, the annealing process (comprising heating of the materials according to chosen parameters including but not limited to time and temperature) increases polymer chain crystallization, theret~y increasing the strength ofthe material.
~onsequentl~r, 30 according to the invention, the desired material properties can be achieved by using the appropriate ratio of materials and by annealing the materials.
Additionally, the properties of polymers can be enhanced and differenfiiated by controlling the degree to which the material crystallizes through straininduced crysleallization. deans far imparting strain-induced crystallization are enhanced during deployment of an endaprasthesis according to the invention. Upon expansion of an endoprosthesis according to the invention, focal regions of plastic deformation undergo strain-induced crystallization, further enhancing the desired mechanical properties of the device, such as further increasing radial strengtl'a. The steeng~ is optimized when the endoprasthesis is induced to bend preferentially at desired points.
Natural polymer segments or polymers include but are not limited to proteins such as casein, gelatins, gluten, zein, modified zero, serum albumin, and collagen, and polysaccharides such as alginate, cbit~, cellulases, dextrans, pullulane, and t0 polyhyaluronie acid; poly(3 ~ydraxyalkanoate)s, especially poly(.beta.
~ydraxybutyrate), poly(3-hydroxyoctanoate) and poly(3 hydroxyfatty acids).
Suitable synthetic polymer blocks include polyphosphazenes, polyvinyl alcohols), polyan~ides, polyester amides, paly(anaina acid~s> synthetic paly(amina acids), polycarbonates, palyaerylates, polyall~ylenes, polyacrylarr~des, palyalkylene glycols, polyalkylene oxides, polyalkylene terephthalates, polyvinyl ethers, polyvinyl esters, polyvinyl halides, poiyvinylpyrrolidone, polyesters, polyethylene terephthalate, polysilaxanes, polyurethanes, Il'uarapalyrners. (inel ! ~ ~g but not limited to polyfluarotetraethylene), and capalyrners thereof:
>;xamples of suitable polyacrylates include poly(methyl methacrylate), poly(ethyl ~0 methacryIate), poly(butyl methacrylate), poly(isobutyl methacrylate), poly(hexyl methacrylate), poly(isodecyl' rnethacrylate), paly(Iauryl methacryl'ate), poly(phenyl methacrylate), poly(methyl acrylafe), poly(isapropyl acrylate), poly(isabutyl acrylafe) and poly(octadecyl acrylate).
synthetically modified natural polymers include cellulose derivatives such as 2~ alkyl celluloses, liydroxyalkyT cellulases, cell ~'ose ethers, cel'lulase esters, nitracellulases, and chitasan. lxamples of suitable cellulose derivatives include methyl cellulose, ethyl cellulose, hydroxypropyl cellulose, hydroxypxopyl methyl cellulose, hydroxybutyl methyl cellulose, cellulose acetate, cellulose propionate, cellulose acetate butyrate, cellulose acetate phthalate, arboxymethyl' celluFose, cellulose triacetate and cellulose sulfate 30 sadiurn salt. These ate collectively referred to herein as "cellulases".
for those embodiments comprising a shape memory polymer, the degree of crystallinity of the polymer or polymeric blocks) is between 3 and 80%, more o$en between 3 ant ~S°/. The tensile modulus ofthe polymers below the transition IO

temperature is typically between 50 M~a and 2 C-f"a (gigapascals), whereas the tensile modulus ofthe polymers above the transition temperature is typically between I
and S00 ~l'a. Most often, the ratio of elastic modulus above and below the transition temperature is 20 or more.
S The melting point and glass transition temperature ofthe hard segment are generally at least I O degrees C., and preferably' 20 degrees C., higher than the transition temperature of the soft segment. The transition temperature of the hard segment is preferably between -60 and 270 degrees C., and more often between 30 and 150 degrees C. ~ he ratio by weight ofthe hard segment to sQi~ segments is between about ~:~5 and ~0 9~~:5, and most often between 20:80 and 80:20. The shape memory polymers contain at least one physical crosslink (physical interaction of the hard segment) or contain covalent crosslinks instead of a hard segment. The shape memory polymers can also be interpenetrating networks or semi-interpenetra ~ ~ g networks. t~ tylrical shape memory polymer is a block copolymer.
I S Examples of suitable hydrophilic polymers include but are not limited to poly(etl~ylene oxide), polyvinyl pyrrolidone, polyvinyl alcohol, polyethylene glycol), polyacrylan~ide poTy(hydroxy alkyl rnethacrylates), poly(hydr~rxy ethyl rnethacrylate), hydrophilic polytn'ethanes, I-1~P, oriented IP, poly(lxydroxy ethyl acrylate), hydroxy ethyl cellulose, hydroxy propyl cellulose, methoxylated pectin gels, agar, 20 starches, modified starches, alginates, hydroxy ethyl carbohydrates and mixtures and copolymers thereof.
Hydrogels can be formed from polyethylene glycol, polyethylene oxide, polyvinyl alcohol, polyvinyl pyrrolidone, polyacrylates, poly (ethylene terephthalate), polyvinyl acetate), and copolymers and blends thereof. Several polymeric segments, for example, 2~ acrylic acid, are elastorneric only- when the pa~lymer is hydrated and hydrogels are formed. ether polymeric segments, for example, methacryTic acid, are crystalline and capable of melting even when the polymers are not hydrated. dither type of polymeric black can be used, depending on the desired application and conditions of use.
l xamples o~fhighTy~ elastic materials in:clufing but not limited to vulcanized 30 rubber, polyurethanes, thex~raplastie elastamers, and others may be used according to the invention.
Curable materials include any material capable of being able to Transform from a ftuent or soft material to a harder material, by cross-linking, polymerization, or other suitable process. lVlaterials may be cured over time, thermally, chemically, or b~y exposure to radiation. por those materials that are cured by exposure to radiation, many types of radiation may be used, depending upon the material. Wavelengths in the spectral range of about 100-1300 nm may be used. The material should absorb light.
within a wavelength range that is not readily absorbedi by tissue, blood elements, physiological fluids, or water. Ultraviolet radiation having a wavelength ranging from about nm may be used, as well as visible, infrared and thermal radiation. The.
following materials are some examples of curable materials: urethanes, polyurethane oligomer yes, acrylate monomers, aliphatic urethane acxylate oligomers, aerylamides, If'~
I0 curable epoxies, photopoly~nerizable polyanhydrides and other curable monomers.
Alternatively, the curable material can be a material capable of being chemically cured, such as silicone based compounds which undergo room temperature vulcanization.
Though not limited thereto, some embo 'din7ents according to fhe i~ventior~
comprise one or more therapeutic substances that will elute from the surface.
suitable I S therapeutics include but are not limited to bone. growth accelerators, bone growth inducing factors; osteoinductive agents, immunosuppressive agents; steroids;
anti-infiammatory agents, pain management agenfs ~e.g, analgesics, tissue proliferative agents to enhance regrowth andPor strengthening ofnative disc materials, and others.
According to the invention, such surface treatment andlor incorporation of therapeutic 20 substances may be performed utilizing one or more of numerous processes That utilize carbon dioxide ~'uiel, e.g., carbon dioxide in a liduid or supercri~:cal state. A supercritical fluid is a substance above its critical temperature and critical pressure for "critical point".
The use of polymeric materials in the fabrication of endoprostheses confers the advantages of improved flexibility, compliance and conformability. ~abricaiion of an 2S endoprosthesis accorfing to~ the invention allows for the use of different materials in different regions of the prosthesis to aclfieve different physical properties as desired for a selected region. An endoprosthesis comprising polymeric materials has the additional advantage of compatibility with magnetic resonance imaging, potenfially a long-term clinical benefit.
30 As set ford. above, some embodiments according to the invention may comprise components that have a substantially hollow interior that may be filled after being delivered to a treatment site with a suitable material in order to place the device in a deployed configuration. Accordingly, such embodiments may comprise a fluid retention bag having a membrane layer comprising polyvinyl chloride (PVC), polyurethane, and or laminates of polyethylene terephthalate (PE'lI ~ or nylon fibers or films within layers of PVC, polyurethane or other suitable material. such a fluid retention bag or membrane layer alternatively may comprise Kevlar, polyimide, a suitable metal, or other suitable S material within layers ofPV~, polyurethane or other suitable material. Such laminates may be of solid core, braided, woven, wound, or other fiber mesh structure, and provide stability, strength, and a controlled degree of compliance. such a laminate membrane layer may be manufactured using radiofrequency or ultrasonic welding, adhesives including ultravviolet curable adhesives, or therm~ energy.
1~ ~. fluid retention bag as set forth above may be filled with any stuta~rle material including but not limited to saline, contrast media, hydogels, a polymeric foam, or any combination thereof. A polymeric foam may comprise a polyurethane intermediate comprising polyjneric diisocyanate, polyals, and a hydrocarbon, ar a carbon dioxide gas mixture. such a foam may be loaded with any ofnun~erous solid or liquid materiala 15 known in the art that confer radiopaciiy.
Such a fluid retention membrane and/or bag may be designed to replace an entire inte~vertebral' disc. ~l'terna~vely, it may replace only the nucleus pulposus or only the annulus fibroses. such a device may conxprise one or more filling ports, and include separate filling ports for the nucleus pulposus and annulus fibroses, to allow for varying 20 durometers, and possibly varied materials in order to mimic the properties of the native disc components.
Such a device rnay comprise a single unit, or may be two or more individual parts.
If the device comprises two or more component parts, the parts may fit together in a puzzle-like fashion. The device may further comprise alignment tabs for stable alignment ~S between the vertebral bodies.
Such a fluid: retention membrane andfor bag may comprise interbody connections and/or baffles and/or partitions or generally vertically oriented membranes in order to maintain structural integrity after filling, to increase the devices ability to withstand compressive, shear, and other loading forces',, andl or to direct filling material flow and ~fl positioning, anffor to partition porCions of the disc in order to separate infection of different types or amounts of filling materials. )-~urther, such a device may comprise a characteristic durometer selected for suitability to the level of the vertebra within the spine for which the intervertebral disc is being treated. P'or example, an artificial intervertebral disc nucleus within the cervical spine may comprise a lower durometer than a replacement nucleus in the lumbar region.
Following surgical or minimally invasive surgical access and removal of all or a portion of the native disc, a deflated fluid retention bag or membrane may be delivered to the intervertebral space surgically or through a catheter andlor cannula. 'f he membrane andfor bag is positioned within. the intervertebral space. The membrane inflation port or poz~s are then attached to the injection source. Filling material is then injected.
Following injection of the filling material, which may be curable by any suitable means or may be catalytically activated or may remainu ~ ~ fluid form, the injection source is detacfied and removed.
Details of the invention can be better understood from the following descriptions of specific embodiments according to the invention. FIG. lA illustrates a perspective view of artificial dice IO' aceordin,g to the ~vex~tion ~ its deployed configuration. FIG.
I~ illustrates a side view of artif vial disc I O' according to the invention in its deployed configuration. In its deployed configuration, cross sectional area of artificial disc 10 is most often between 800mm and 2000mm2, and between 5.0 mm and I5.0 mm high depending upon the di~rensions reduired of a particular clinical application.
A cross section of artif vial disc I 0 taken along fine A ~ is illustrated in FIG. ZA.
Artificial fist I O comprises annular rim I2, annular region 1 l and nucleus region 14.
Nucleus region I4 may comprise properties that differ significantly from annular region 11.
More specifically, nuclear region L 4 may comprise a lower durorneter, more compliant material, corresponding to the properties of a natural nucleus pulposus. Ire contrast, annular region 11 may comprise a tougher, stiffer, less compliant material with a higher durometer, in order to achieve the objectives of a natural annulus. Overall, the resulting device must be able to withstand load's ofbefween F SON, consisterft with a typical load at supine rest to between 4000N and greater than 6000N, consistent with typical loads experienced during lifting and jumping.
A cross section of an alternative embodiment taken along the same line is shown in FIG. ~&. Artificial disc 4Q similarly comprises annular ~ " ~ 28 and nucleus region 24.
I~owvever, nucleus region 24 also comprises convex portion 42 disposed generally about a center point of nucleus region 24.
Returning to the embodiment of FIGS. l and ZA, artificial disc 10 is illustrated in FIG. 3 following a step ofplacing artificial disc 10 in its delivery configuration. As shown in cross section in FIG. 3, annular rim I2 is folded down in a step in order to achieve a delivery configuration. l~ex~, artificial disc 10 is "rolled" in order to form an even more compact configuration for delivery, as illustrated in FIG. 4.
Alternatively, or in addition, artificial disc 10 may be folded in order to achieve a compact delivery configuration.
In its delivery conf guration, ar~if~.eial disc 10 is most often between 30.0 mm and 70.0 mm in length, 5.0 mm and 25.0 mm wide, and between 5.0 mm and 25.0 mm high, again depending upon the dimensions required of a particular clinical application.
Artifeeial disc 10 may be manufactGred from shape memory materials exhibiting properties selectively huparted into the materials, and may transition between its delivery configuration and deployed configuration following change in temperature, hydration, salinity, or the application of heat, radiation, or other initiator.
FIG. ~ depicts the e~ubodiment of~C~. IA, 2A, 3 and ~ wi ~ . ~ a a typical treatment site folloW~g a partial or complete discectomy. Accordingly, artificial disc 10 I S is shown in cross sectipn its deployed configuration placed between vertebral bodies 15 and 20. Annular rim 12 secures artificial disc 10 against displacement by surrounding and engag~g vertebral bodies 1~ and 20, while central region 14 se~wes to restore and mPaintaia a healthy lntervertebral space, absorb axial load, serve as a cushion between vertebral bodies 15 and 20, and otherwise serve the functions much of a healthy intervertebral disc.
FIG. f sets forth another embodinren~t accar ~' ~ ~g to the invex~tior~.
Artificial disc 3~, comprising securing rhr~ ~0, and convex portion 42 is shown in its deployed configuration in cross section, situated between vertebral bodies 36 and 37.
Convex portion 42 serves to restore the normal intervertebral space and to serve as a shock absorber while allaWir~g a normal ratzge ofmotion in all planes, including -~-f IO degrees flexion, +/ ~ degrees exterrsionilateral bending arid +f 2 degrees rotation.
Convex portion 42 further acts as an alignment and nucleus load bearing structure.
Convey portion 42 most often comprises materials having a hardness in the range of 20-70 Shore A durometer, most often around 3~ Shore A durorneter, consistent with the function of 30' convex portion ~2 as a substitute nucleus. In contrasts securing rim 40 and the exterior of artificial disc 35 most often comprises materials of a higher durometer of between 3S and 90 Shore A, consistent with the function of these portions as a replacement for the natural annulus fibroses. Alteniatively, the durometer ofartificial disc 3~ may be varied.

throughout the device, with a lov~est duroFneter at or near the most central interior portion of the device, with durameter gradually increasing from such point to a highest durometer at the outer annular portions of artificial disc 35.
Such varying durometer may be achieved, for example, according to a process whereby the outer annular region of the vial disc, comprising one or more curable materials, is cured following delivery of the device. ~ueh curing serves to modify the chemical structure of the material which toughens the portion of the artificial disc simulating the annulus region, thereby increasing the wear properfiies and increasing the materials' torsionat stuffiness and~or torsional ~no~nent. ~uclr.
characteristics can I O' alternatively be instilled via either a cross-1'Wing or a catalytieally activated process prior to delivery.
An alternative embodiment according to the invention is illustrated in a perspective viev~ in FIB 7'. ~ ' ~ ~ciat disc Sfl comprises annular ran S2 and central region 54. Artificial disc 50~ also co~uprises central void S6. Artificial nucleus ~5, 15 illustrated in its delivery configuration in FIG. 8A and in its deployed configuration in FIG. 8B, is designed for either insertion into central void 56 in a second step, or as a stand-alone implant wi ~ ~ a ~ ~ a native disc annulus where a ne~v nucleus only is required.
Artificial disc Sa can thereby accommodate a more ccr~npact delivery configuration to facilitate a minimally invasive procedure.
2~ Artificial disc 60 of FIG. ~ similarly comprises central void 66 within central region &4, in wlxich artificial nucleus 55 ofFIG~. 8A-8B can be inserted. t~-tificial disc 60 further co~np~ses engaging tabs 6~ for securing artificial disc 60 to a vertebral body (not pictured).
Yet another alternative embodiment is shown. in a plan view in. FiG. I0, in a side 25 view in FIG. II, and a perspective view in FIG. ~. ~rtif vial disc 47 coFnprises securing tabs 48. feeuring tabs 48 surround and engage a superior and an inferior vertebral body (not pictured) and affix artificial disc 47 thereto. The disc remains free-floating and the edge tabs keep the device in place by preventing lateral movement of the disc in relation to~ the superior and 'nnferior vertebral bodies.
3~ FIGS. I~t~ and I~B are three-dimensional illustrations of an embodiment similar to that illustrated in I*IG~. I O-12. Artificial disc 70, which comprises alignment tabs 75 and anterior alignment tab 76, for the secure alignment c~f artificial disc 70 within the intervertebral space. Gnce artificial disc 70 is deployed within the inte~wertebral space, alignment tabs 75 and anterior alignment tab 76 bear against the superior and inferior vertebral bodies 77 and 78, as illustrated in FIG.13B.
FIGS. 14-24 introduce alternative disc replacement devices according to the invention. FIG. I4 illustrates a perspeciave view of artificial annulus 80 in its collapsed, unffled delivery configuration. Artificial annul~zs 80 generally comprises a finable membrane that may alternatively be designed tc~ replace both the nucleus pulposus and annulus fibrosus, or the nucleus pulposus alone, as illustrated below.
In the delivery configuration, artificial annulus 80 may be delivered to the intervertebral space in auy of the suitable methods set forth above. Following delivery to I0 the treatment site, artificial annulus 80 may be filled with: a suitable material in order to achieve its deployed configuration, as illustrated in FIG. 1.5A. Artificial annulus 80, comprising fill port 85 is positioned between vertebral bodies 83 and 84. A
liquid or dry polymer may be irutroduced i~nta the interior of artificial! ~ ~ ~ulus 80~ via fill port 8S.
Following delivery, the polymer will undergo a reaction to change into a solid porous body or gel. Arigid polyurethane foam, for example, will then be in place within the interior of the membrane of artificial annulus 80.
In I~IG. Zy a "cut away~~ taT~en along 1!ine B ~ ofFIG. r~A, is shown to better illustrate the position and structure ofartificial annulus 80 irz situ. Also revealed in FIG.
15B, artificial annulus 80 can be utilized alone or in conjunction with a separate artificial nucleus (not pictured).
For fe~rther illustration a~f srzch an ert~bodi~uent~ a three-dinnensional "exploded"
view of acs artificial annulus 82 with fill port 87 is illustrated in »G. L~.
Turning now to FIG.17, artificial nucleus 90 is illustrated in an exploded view in situ in FIG. 17. As set forth above, an embodiment according to the invention may 2~~ cornpr ise a nucleus only replacement. ~uitablle filling material quay be introeluced into the interior of artificial nucleus 90 via frlling port 92. fuitable filling material may comprise liquid or dry polymer that changes into a solid porous structure or gel following introduction. For an artificiai nucleus, a lower modulus foam or hydrogel may be most suitable. Accordingly artificial nucleus 9a wfl~ more closely mimic the mechanical properties of a healthy native nucleus pulposus.
TIG.18 illustrates an opaque three dimensional perspective view of an embodiment according comprising both of the foregoing components discussed.
Artificial disc 8~ comprises artificial nucleus 86 and artificial annulus fitbrosus $7.
i7 ~cial disc 85 may be constr~zcted whereby artificial nucleus 86 and artificial annulus 87 are integral with. one another, or, alternatively, as two separate pieces that f t together.
For example, an artificial disc according to the invention may be comprise of a unitary membiane having internal channels leading to separate internal chambers.
lxa~nples ofthe configuration ofthe iz~ternal! channels and intern chambers are set forth iz~ ~G~. I9~ 19F. separate internal channels allow the introduction of varying materials into the separate chambers of the member in order to confer varying mechanical properties upon the respective portions of the device. Further, a membrane according to the invention may convprise inverted seams to reduce trauma to body tissues.
find as I0 illustrated in FI~~.19~~-19F, an embodiment according to the invention may farther comprise baffles to direct fluid flow and to impart stability upon the devise.
Turning now to FIG. 20, artificial disc 100, comprising component artificial nucleus 10~~ and artificial annulus 10'x. .t~rtificial annulus may further comprise superior component 10I anel inferior component 10~, and internal interbody nzernbrane I S connections 108 that serve to secure superior component 101 to inferior component 102, and vice versa. Further, nucleus 1 OS may comprise nucleus filling port 114, and artificial annulus 10'7 nay comprise annulus filling port li I2. separate port for the annulus and the nucleus enable the separate f fling of these components. ~.ccordingly, artificial nucleus 1 OS may be filled with a material that has a lower durometer than a material used to fill 20 artificial annulus 10'7, whereby artificial nucleus i OS and artificial annulus 107 will more closely replicate ~ ~ a physical arid mechanical properties of a l~ealtby native nucle~zs and annulus respectively.
FIG. 21 illustrates via an "exploded" view that separate component artificial annulus 115 and artificial nucleus 120, and illustrates the "mating" of the respective 25 components i~ s~t~. ~~ - ~ ~ 'ar to the embodiments set forth above, artificial annulus comprises annulus port I I?, and artificial nucleus comprises nucleus port I
18. In their delivery configuration, the combined device appears as illusfrated in FtG. 22, with artificial annulus i 15 encircling the now hidden artificial nucleus.
FxarnpTes of possible cortstre~ctions ofthe rneznbrane for a device according to the invention are illustrated in FIGS. 23 and 24. In FIG. 23, membrane I30 comprises a first layer 132 and a second layer 136 of suitable material such as, for example, polyurethane, or PVC. Disposed between first layer I30 and second layer I36 is middle layer 134 of any suitable material such as, for example, PhI'; nylon, I~evlar, polyimide, metal, or other suitable material. Diddle layer I34 may be a solid core, but membrane layer 13~ is a braided fiber stmcture. ~ccord~gly, wound or woven fibers 138 confer stability, strength and wear properties, and controlled compliance.
Membrane 145 of FIG. 24 similarly comprises a first layer 150 and a second layer S 152 of suitable materials. 1'l~.ddle layer F 53 co ~ prises a solid steczcture. Examples of suitable nxaterials used. in the constmctiorx ofmembrane 45 are set forth above in relation to FIG. 23.
While all of the foregoing embodiments can most advantageously be delivered in a minimally invasive, percutaneous manner, the foregoing embodiments may also be implanted surgically. Further, while particular forms of the invention bane beer illustrated and described above, the foregoing descriptions are intended as examples, and to one skilled in the art it will be apparent that various modifications can be made without departing from the spit and scope of the invention.

Claims

WE CLAIM:

1. ~An endoprosthesis for partial or complete replacement of an intervertebral disc comprising one or more shape memory polymers, wherein said one or more shape memory polymers is synthesized from a first monomer and a second monomer, said first and second. monomers selected to impart predetermined properties on said shape memory polymer.

2. ~The endoprosthesis according to claim 2 wherein said first monomer and said second monomer are combined in a ratio to impart predetermined properties on said shape memory polymer.

3. ~The endoprosthesis according to claim 2 wherein said first monomer comprises a first molecular weight wherein said first molecular weight is a first parameter in determining said predetermined properties of said shape memory polymer.

4.~The endoprosthesis according to claim 2. wherein said one or more shape memory polymers comprises one or more hard segments and one or more soft segments, said hard segments and soft segments formed from said first and second monomer and wherein said one or more hard segments comprises a first transition temperature, and said one or more soft segments comprises a second transition temperature.

5.~The endoprosthesis according to claim 4 wherein said one or more hard segments comprises a transition temperature between 37° C and 81 ° C, and said one or more soft segments comprises a transition temperature that is at least 10° C less than the transition temperature of said hard segment.

6. ~The endoprosthesis according to claim 2 wherein said properties comprise one or more properties comprises load bearing capability, compressive resistance, stiffness, crystallinity, tensile strength, mechanical strength, durometer, elasticity, strain recovery rate, strain fixity rate, melting temperature, crystallization temperature, cross-linking density, extent of physical cross-linking, extent of covalent bond cross-liking, extent of formation of interpenetrating networks, and heat of fusion.

7. ~The endoprosthesis according to claim 1 wherein said shape memory polymer comprises one or more segments. comprising polyurethanes, polyethylenes, fluoropolymers, thermoplastic elastomers, and composites thereof.

8. ~The endoprosthesis according to claim 1 wherein said endoprosthesis substantially replicates the functions of a naturally occurring, healthy intervertebral disc.

9. ~The endoprosthesis according to claim 1, said endoprosthesis further comprising a delivery configuration and a deployed configuration.

10. ~The endoprosthesis according to claim 9, said endoprosthesis further comprising a generally flat, elliptical structure, said generally flat, elliptical structure comprising a securing rim for engagement with one or more of a first and second vertebral body in a spine.

11. ~The endoprosthesis according to claim 10, wherein said first and second vertebral bodies each comprise a posterior region, and wherein said rim does not engage said first and second vertebral bodies at said posterior region.

12. ~The endoprosthesis according to claim 13, said generally flat, circular structure further comprising a top surface and a bottom surface, wherein one or more of said top and bottom surface comprises a convex portion.

13. ~The endoprosthesis according to claim 12, said endoprosthesis further comprising a generally disc-shaped structure, said generally disc-shaped structure comprising one or more securing tabs for engagement with one or more of a first and second vertebral body in a spine.

14. ~The endoprosthesis according to claim 1, wherein said endoprosthesis comprises an artificial disc nucleus for replacement of an intervertebral disc nucleus.

15. ~The artificial disc nucleus according to claim 14, wherein said disc nucleus comprises a durometer in the range of 20 to 70 Shore A,

16.~The endoprosthesis according to claim 1, wherein said endoprosthesis comprises the capability of withstanding a mechanical load of between 800N and or more.

17. ~The endoprosthesis according to claim 1, wherein said endoprosthesis comprises the capability of withstanding two million or more cycles of fatigue testing.

18. ~The endoprosthesis according to claim 1, wherein said endoprosthesis comprises the capability of allowing range of motion of a spine of 10 degrees or more in all directions.

19. ~The endoprosthesis according to claim 1 wherein said one or more shape memory polymers is hydrophobic.

20. ~The endoprosthesis according to claim 1 wherein said one or more shape memory polymers is a thermoplastic elastomer.

21. The endoprosthesis according to claim 1 wherein said one or more shape memory polymers is a thermoset.

22. The endoprosthesis according to claim 1 wherein said one endoprosthesis comprises a generally flat, circular structure, and wherein said generally flat, circular structure comprises a central region, said central region comprising a void for receiving an artificial disc nucleus.

23. The endoprosthesis according to claim 22 wherein said endoprosthesis comprises a durometer in the range of between 20 and 70 Shore A.

24. The endoprosthesis according to claim 1, where said endoprosthesis substantially completely replaces an intervertebral disc, wherein said endoprosthesis comprises a nucleus region and an annulus region, and wherein said nucleus region comprises a first durometer and said annulus region comprises a second durometer, wherein said first durometer is lower than said second durometer.

25. The endoprosthesis according to claim 24, wherein said nucleus region is generally central within said endoprosthesis, said nucleus region comprises a first durometer, and wherein said prosthesis comprises a range of gradually increasing durometers, wherein said first durometer is a lowest durometer, and said gradually increasing durometers increase incrementally from said nucleus region annularly, outward throughout said annulus region.

26. The endoprosthesis according to claim 25, wherein said endoprosthesis comprises a nucleus portion and an annular portion, wherein said nucleus portion and said annulus portion are combined to form an intervertebral disc assembly.

27. The endoprosthesis according to claim 26, wherein said nucleus portion comprises a first durometer and said annulus portion comprises a second durometer, wherein said first durometer is lower than said second durometer.

28. An artificial intervertebral disc for the complete or partial replacement of an intervertebral disc comprising a delivery configuration and a deployed configuration, wherein said deployed configuration comprises a generally disc-shaped structure and wherein said artificial intervertebral disc substantially replicates the functions of a naturally occurring, healthy intervertebral disc.

29. The endoprosthesis according to claim 28 wherein said endoprosthesis comprises a durometer in the range of between 20 and 70 Shore A.

30. The endoprosthesis according to claim 28, wherein said endoprosthesis substantially completely replaces an intervertebral disc, wherein said endoprosthesis comprises a nucleus region and an annulus region, and wherein said nucleus region comprises a first durometer and said annulus region comprises a second durometer, wherein said first durometer is lower than said second durometer.

31. The endoprosthesis according to claim 30, wherein said nucleus region is generally central within said endoprosthesis, said nucleus region comprises a first durometer, and wherein said prosthesis comprises a range of gradually increasing durometers, wherein said first durometer is a lowest durometer, and said gradually increasing durometers increase incrementally from said nucleus region annularly, outward throughout said annulus region.

32. The endoprosthesis according to claim 28, wherein said endoprosthesis comprises a nucleus portion and annular portion, wherein said nucleus portion and said annulus portion are combined to form an intervertebral disc assembly.

33. The endoprosthesis according to claim 32, wherein said nucleus portion comprises a first durometer and said annulus portion comprises a second durometer, wherein said first durometer is lower than said second durometer.

34. The artificial intervertebral disc according to claim 28, said generally flat, circular structure comprising a securing rim for engagement with one or more of a first and second vertebral body in a spine.

35. The artificial intervertebral disc according to claim 34, wherein said first and second vertebral bodies each comprise posterior portion, and wherein said securing rim does not engage said first and second vertebral bodies at said posterior portion.

36. The artificial intervertebral disc according to claim 28, said generally flat, circular structure further comprising a top surface and a bottom surface, wherein one or more of said top and bottom surface comprises a convex portion.

37. The artificial intervertebral disc according to claim 36, said generally disc-shaped structure comprising one or more securing tabs for engagement with ode or more of a first and second vertebral body in a spine.

38. The artificial intervertebral disc according to claim 36, wherein said artificial intervertebral disc comprises the capability of withstanding a mechanical load of between 800N and 6000N or more.

39. The artificial intervertebral disc according to claim 36, wherein said artificial intervertebral disc comprises the capability of withstanding two million or more cycles of fatigue testing.

40. A method of manufacturing an endoprosthesis for partial or total replacement of an intervertebral disc comprising:

selecting a fast monomer comprising a first set of characteristics that serves as a first parameter in determining the properties of a shape memory polymer;

selecting a second monomer comprising a second set of characteristics that serves as a second parameter in determining the properties of a shape memory polymer;

determining a desired ratio of said first monomer to said second monomer;

synthesising a shape memory polymer from said first and said second monomer;

manufacturing an endoprosthesis for partial or total replacement of an intervertebral disc from said shape memory polymer;

setting a permanent shape for said endoprosthesis;

setting a temporary shape for said endoprosthesis.

41. The method according to claim 40 wherein said first and second sets of characteristics comprise molecular weight, transition temperature, readiness to form physical crosslinks, readiness to form covalent bonds, or crystallinity.

42. The method according to claim 40 wherein said properties of a shape memory polymer comprise extent of physical crosslinking, extent of covalent bonds, extent of networking, tensile strength, transition temperature, melting temperature, strain recovery rate, strain fixity rate, modules of elasticity, degree of crystallization, or hydrophobicity.

43. The method according to claim 40 with the added step of:

curing said endoprosthesis according to a desired pattern.

44. The method according to claim 42 with the added step of:

increasing the degree of crystallization of said polymer according to a desired pattern.

45. The method according to claim 40 with the added step of:

cross-linking said endoprosthesis according to a desired pattern.

46. The method according to claim 40, wherein the step of setting a temporary shape includes folding the endoprosthesis into a temporary shape and constraining said endoprosthesis in said temporary shape.

47. A method of completely or partially replacing an intervertebral disc, said method comprising the steps of:

removing all or a portion of the native disc;

providing an endoprosthesis comprising one or more shape memory polymers synthesized from a fast monomer and a second monomer, said first and. second monomers selected to impart predetermined properties on sand shape memory polymer;

delivering said endoprosthesis;

deploying said endoprosthesis.

48. The method according to claim 47, wherein the step of removing all or a portion of the native disc does not include removing the periphery of the native annulus fibrosus.

49. The method according to claim 47, wherein the step of removing all or a portion of the native disc includes removal of the native nucleus only, and where tire step of delivering an endoprosthesis comprises delivering an artificial nucleus pulposus.

50. The method according to claim 47, wherein said step of delivering an endoprosthesis comprises delivering an artificial annulus fibrousus, followed by the delivery of an artificial nucleus pulposus.

5l. The method according to claim 47, wherein said step of removing all or a portion of said native intervertebral disc comprises removing substantially all of said native intervertebral disc, and said step of percutaneously delivering said endoprosthesis comprises delivering a complete replacement artificial disc.

52. The method according to claim 47, wherein said method is performed surgically.

53. The method according to claim 52, wherein said method is performed surgically from an anterior approach.

54. The method according to claim 47, wherein said method is performed percutaneously.

55. The method according to claim 54, wherein said method is performed percutaneously from a posterior approach.

56. The method according to claim 47, wherein said endoprosthesis comprises one or more constraints, and said step of deploying said endoprosthesis comprises removing said one or more constraints.

57. The method according to claim 47, wherein said step of deploying said endoprosthesis comprises exposing said endoprosthesis to one or more initiators.

58. A method of completely or partially replacing an intervertebral disc, said method comprising the steps of:

removing all or a portion of the native disc;

providing an endoprosthesis comprising one or more superelastic polymers synthesized from a first monomer and a second monomer, said first and second monomers selected to impart predetermined properties on said superelastic polymer;

percutaneously delivering said endoprosthesis;

deploying said endoprosthesis.

59. The method according to claim 58, wherein the step of removing all or a portion of the native disc does not include removing the periphery of the native annulus fibrosus.

60. The method according to claim 58, wherein the step of removing all or a portion of the native disc includes removal of the native nucleus only, and wherein the step of delivering an endoprosthesis comprises delivering an artificial nucleus pulposus.

61. The method according to claim 58, wherein skid step of delivering an endoprosthesis comprises delivering an artificial annulus fibrousus, followed by the delivery of an artificial nucleus pulposus.

62. The method according to claim 58, wherein said step of removing all or a portion of said native intervertebral disc comprises removing substantially all of said native intervertebral disc, and seed step of percutaneously delivering said endoprosthesis comprises delivering a complete replacement artificial disc.

63. The method according to claim 58, wherein said method is performed surgically.

64. The method according to claim 63, wherein said method is performed surgically from an anterior approach.

65. The method according to claim 58, wherein said method is performed percutaneously.

66. The method according to claim 65, wherein said method is performed percutaneously from a posterior approach.

67. The method according to claim 58, wherein said endoprosthesis comprises one or more constraints, and said step of deploying said endoprosthesis comprises removing said one or more constraints.

68. An artificial disc comprising one or more substantially hollow bodies, a delivery configuration and a deployed configuration, wherein said one or more substantially hollow bodies is placed in said deployed configuration upon the introduction of a material within said one or more substantially hollow bodies.

69. The artificial disc according to claim 68 wherein said artificial disc is place in its deployed configuration after it is delivered to a treatment site.

70. The artificial disc according to claim 68 wherein said artificial disc comprises an artificial annulus component and an artificial nucleus component.

71. The artificial disc according to claim 68 wherein said one or more substantially hollow bodies comprises a membrane comprising one or more layers.

72. The artificial disc according to claim 71 wherein said one or more layers comprises one or more material from the group consisting of polyurethane, polyethylene terephthalate, polyvinyl chloride, nylon, Kevlar, polyimide, and metal.

73. The artificial disc according to claim 68 wherein said artificial disc comprises a filling material when in its deployed configuration.

74. The artificial disc according to claim 73 wherein said filling material comprises one or more materials from the group consisting of saline, contrast medium, hydrogel, perfluoropolyethers and polymeric foam.

75. The artificial disc according to claim 74 wherein said polymeric foam composes a polymeric diisocyanate, polyol and hydrocarbon.

76. The artificial disc according to claim 74 wherein said polymeric foam comprises carbon dioxide.

77. The artificial disc according to claim 72 wherein one or more layers comprises a braided fiber structure.

78. The artificial disc according to claim 77 wherein said braided fiber structure is disposed between two or more solid layers.

79. The artificial disc according to claim 68 further comprising one or more injection ports,

80, The artificial disc according to claim 70 wherein said artificial nucleus comprises an injection port and said artificial annulus comprises an injection port.

81. The artificial disc according to claim 80 wherein said artificial disc, when in its deployed configuration, comprises a first filling medium within said artificial nucleus, and a second filling medium within said artificial annulus.

82. The artificial disc according to claim 81 wherein said first filling medium confers on said artificial. nucleus properties similar to a native nucleus pulposus, and said second filling medium confers properties on said artificial annulus similar to a native annulus fibrosus.

83. An artificial nucleus comprising one or more substantially hollow bodies, a delivery configuration and a deployed configuration, wherein said one or more substantially hollow bodies is placed in said deployed configuration upon the introduction of a material within said one or more substantially hollow bodies.

84. An artificial annulus comprising one or more substantially hollow bodies, a delivery configuration and a deployed configuration, wherein said one or more substantially hollow bodies is placed in said deployed configuration upon the introduction of a material within said one or more substantially hollow bodies.

85. The artificial disc according to claim 75 wherein said polymeric foam comprises one or more additional gases.

86. The artificial disc according to claim 68 wherein said one or more of said substantially hollow bodies comprises one or more means for directing flow of said material within said substantially hollow bodies.

87. The artificial disc according to claim 86 wherein one or more of said means for directing flow of said material comprises one or more inverted seams.

88. The artificial disc according to claim 68 wherein said one or more of said substantially hollow bodies comprises one or more interbody connections.

89. An artificial disc nucleus comprising one or more hollow bodies, one or more chambers within said one or more hollow bodies, and one or more materials within the interior of one or more of said hollow bodies, wherein said artificial disc nucleus further comprises one or more materials formed from a polymer synthesized from a first monomer and a second monomer to impart shape memory characteristics upon said material.

90. An artificial disc or disc nucleus for the treatment of a degenerated or traumatized intervertebral disc, said disc or nucleus comprising a durometer selected for the level within the spine of the disc undergoing treatment.