Prosthesis (i.e. – artificial body members) – parts thereof – or ai – Implantable prosthesis – Bone
Reexamination Certificate
2001-11-08
2004-02-17
Philogene, Pedro (Department: 3732)
Prosthesis (i.e., artificial body members), parts thereof, or ai
Implantable prosthesis
Bone
C623S017160, C623S023580
Reexamination Certificate
active
06692528
ABSTRACT:
FIELD OF THE INVENTION
The present invention provides articles formed from dense polymer membranes and films, which articles spontaneously inflate/expand (or deflate/contract) under the effects of osmotic pressure. By varying the initial volume, molecular weight, solubility, concentration, and temperature of solutions contained within formed articles, the volume of the formed articles and the pressure within the formed articles can be precisely controlled. This invention is therefore useful for many medical, industrial, and consumer applications.
BACKGROUND OF THE INVENTION
U.S. Pat. No. 4,157,085 discloses a surgically implantable device for expanding skin and mucous tissue. The device comprises a partially collapsed sealed envelope formed from a material that is permeable to extracellular body fluids, and a material which establishes an osmotic potential across the envelope wall. As bodily fluid crosses the membrane to fill the envelope, the envelope expands, thereby expanding the adjacent tissue. The envelope material, which ranges from 0.001 to 0.020 inches in thickness, can be formed from such polymers as cellulose acetate, crosslinked polyvinyl alcohol, polyurethane, nylon, ethylene vinyl acetate copolymer, polyolefin, polyvinyl chloride, and silicone rubber. The material used to establish the osmotic potential can be, for instance, sodium chloride, calcium chloride, potassium sulphate, sodium acetate, ammonium phosphate, magnesium succinate, glucose, alanine, vinyl pyrrolidone, carboxymethylcellulose, urea, “blood by-products”, proteins, and/or dextran. The amount of expansion material used is selected depending on the desired speed of expansion of the envelope and the desired final volume thereof.
U.S. Pat. No. 5,005,591 points out that the device described in U.S. Pat. No. 4,157,085 has problems. One problem is in the use of silicone as the envelope material. In thicknesses that are adequate for product safety, silicone is relatively impermeable to extracellular water. In order to compensate for the required silicone thickness and allow for timely inflation of the tissue, the implant must contain an inordinately high amount of solute. Another, related problem is that rupture of the implanted envelope results in dispersion of highly concentrated solute into the surrounding tissues.
EP 0 784 987 discloses an inflatable prosthesis that contains a dehydrated substance which forms a gel when mixed with an aqueous solution. The dehydrated substance is a polyacrylamide, polyvinylpyrrolidone, hydroxypropyl methyl-cellulose, polyvinyl alcohol, polyethylene oxide, polypropylene oxide, polyethylene glycol, polylactic acid polyglycolic acid, hydrogel polyurethane, chrondotoin sulfate, hyaluronic acid, alginate, etc. The dehydrated substance is placed within an outer shell constructed from a polydimethyl siloxane, a polyurethane, a polyurethane/polyester copolymer, or another similar viscoelastic material. As shown in
FIG. 3
of the publication, after the prosthesis is implanted into the body, an aqueous solution is added to the inner cavity thereof by a syringe. The addition of the aqueous solution combines with the dehydrated substance in the cavity to form a gel within the implant.
U.S. Pat. No. 5,756,632 claims an article comprising a hydrophilic gel with a water content of at least about 35% substantially enclosed within a membrane comprising a biocompatible, hydrophilic, segmented block polyurethane copolymer. The block copolymer comprises about 5 to 45 weight-% of at least one hard segment and about 95 to 55 weight-% of at least one soft segment. The soft segment of the block copolymer comprises at least one hydrophilic, hydrophobic, or amphipathic oligomer selected from the group consisting of aliphatic polyols, aliphatic polyamines, aromatic polyamines, and mixtures thereof. This patent also claims a method of permeating molecules—such as glucose, angiotensin I, glucagon, insulin, aprotinin, albumin, IgG, and oxygen—while substantially preventing the passage of cells and particulate matter between two fluids, using a biocompatible, hydrophilic, segmented block polyurethane copolymer.
U.S. Pat. No. 6,264,695 discloses a spinal nucleus implant for replacement of a portion of nucleus pulposus tissue removed from a spinal disc. The implant is an anisotropically swellable, biomimetic xerogel plastic, having a negatively charged lubricious surface and having a two phase structure with a hydrophobic phase having high crystallinity and low water content and a hydrophilic phase having low crystallinity and high water content. The xerogel plastic is capable of rehydration and of osmotic movement of liquid therethrough in response to osmotic pressure change to thereby increase and decrease liquid content in its hydrated state. Example 1 of the patent molds an acrylonitrile/acrylic acid block copolymer into the shape of a nucleus pulposus, and indicates that when the molded article is implanted into a vertebrate spine, it will be partially hydrated by body fluids, swelling to the shape and tension required for its long-term function. The patent also discloses surgical implant procedures utilizing the disclosed spinal nucleus implant.
SUMMARY OF THE INVENTION
The present invention provides devices that are implantable in animal bodies. In one embodiment, the devices of the present invention include a solute that is encapsulated by a water-permeable polymer membrane. The membrane polymer will ideally be biocompatible, strong and flexible, abrasion resistant, biostable, and highly permeable to water while providing an effective barrier to the solute. The membrane should also be sterile and processable by thermoplastic or solution methods suitable for device fabrication. The solute should be water soluble, non-toxic, and biostable within the internal cavity of the device.
One specific application of the present invention is a self-inflating/shape-memory prosthetic nucleus for percutaneous insertion in a minimally invasive treatment of human spinal disc degeneration. Another embodiment of this invention is a method for treating a spine of a vertebrate which comprises inserting such a device into an area of the spine that contains a degenerated, damage, or missing disc and allowing the device to expand by permeation of aqueous fluid into a cavity containing the solute.
This invention includes the use of a water-permeable polymer (preferably biostable) in the form of a dense membrane with moderate to low water absorption (less than 50 weight-%, preferably less than 15 weight-%, of the combined weight of the polymer and the absorbed water) containing a dispersed polymeric or monomeric solute to fabricate a device or formed article. This invention provides a high strength, dense osmotic membrane containing a low molecular weight solute to produce high osmotic pressure.
In summary, this invention provides a device implantable in an animal (including human) body. The device comprises a water-absorbing solute encapsulated by a non-porous, water-permeable polymer membrane. The membrane has a moisture vapor transmission rate (MVTR) by ASTM Method E96BW greater than 100 g/square meter/day at 1 mil thickness, a dry tensile strength of greater than 500 psi, and a permeability to said solute of less than 10
−3
cm
2
/sec. In preferred embodiments of this invention, the MVTR minimum may be >1000, >2000, >5000, or >10,000 g/square meter/day at 1 mil thickness, the tensile strength may be >1000, >2000, or >5000 psi, and the permeability may be <10
−4,
<10
−5
, or <10
−6
cm
2
/sec. The solute is capable of providing said device with a pressure of approximately 0.1 psi or more for a period of at least 24 hours. In preferred embodiments of this invention, the osmotic pressure that can be held may be >1, >10, or >100 psi and the osmotic pressure can be held at those levels for >1 week, >6 weeks, or >1 year.
In accordance with this invention, each of these parameters may be varied independently. In a particularly preferred device of t
Coviello Sallie K.
Ward Robert S.
Philogene Pedro
The Polymer Technology Group Incorporated
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