Hydrogel arthroplasty device

Inventors

Myung, DavidKourtis, LamprosHartmann, LauraFrank, Curtis W.Goodman, Stuart B.Carter, Dennis R.

Assignees

US Department of Veterans AffairsOffice of General Counsel of VALeland Stanford Junior University

Publication Number

US-8679190-B2

Publication Date

2014-03-25

Expiration Date

2025-10-04

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Abstract

An arthroplasty device is provided having an interpenetrating polymer network (IPN) hydrogel that is strain-hardened by swelling and adapted to be held in place in a joint by conforming to a bone geometry. The strain-hardened IPN hydrogel is based on two different networks: (1) a non-silicone network of preformed hydrophilic non-ionic telechelic macromonomers chemically cross-linked by polymerization of its end-groups, and (2) a non-silicone network of ionizable monomers. The second network was polymerized and chemically cross-linked in the presence of the first network and has formed physical cross-links with the first network. Within the IPN, the degree of chemical cross-linking in the second network is less than in the first network. An aqueous salt solution (neutral pH) is used to ionize and swell the second network. The swelling of the second network is constrained by the first network resulting in an increase in effective physical cross-links within the IPN.

Core Innovation

The present invention provides a bone-sparing arthroplasty device comprising an interpenetrating polymer network (IPN) hydrogel that is strain-hardened by swelling and adapted to be held in place in a mammalian joint by conforming to a naturally or artificially prepared geometry of a bone in that joint. The IPN hydrogel includes two different networks: a first network of non-silicone preformed hydrophilic non-ionic telechelic macromonomers chemically cross-linked by polymerization of their end-groups, and a second network of non-silicone ionizable monomers polymerized and chemically cross-linked in the presence of the first network forming physical cross-links with it. Within the IPN, the second network has a lesser degree of chemical cross-linking than the first network.

The device features a bone-interfacing region adapted to bind to calcium-containing and phosphate-containing bone matrix constituents and a bearing region with a lubricious surface adapted to articulate with another bearing surface. The bone-interfacing region may have porosity or surface roughness to accommodate bone formation and may be pre-coated with calcium-containing or phosphate-containing constituents or chemically or physically bonded biomolecules to promote bone integration. The device can be tailored to either a convex or concave three-dimensional bone-receiving surface by adjusting its size and swelling capacity to create either an elastic contraction fit or an expansion fit, respectively.

The IPN hydrogel is strain-hardened by swelling the second ionizable network in an aqueous salt solution of neutral pH, with swelling constrained by the first network, resulting in an increase in effective physical cross-links and a raised initial Young's modulus greater than either network alone or the IPN swollen in pure water. The invention also provides methods of fabrication involving UV-initiated polymerization of telechelic macromonomers and polymerization of ionizable monomers within the swollen first network. The resulting device mimics the molecular structure, elastic modulus, fracture strength, and lubricious surface of natural cartilage, enabling a novel, bone-sparing, biomimetic resurfacing arthroplasty procedure that can be applied to various joints.

Claims Coverage

The patent presents one independent claim focusing on a multi-network arthroplasty device integrating an IPN hydrogel bearing region and a distinct bone-interfacing polymer region to form a triple network.

Hydrogel bearing region with a double interpenetrating polymer network

The bearing region comprises a hydrogel having a first interpenetrating polymer network formed by a first and second network that interpenetrate each other.

Bone-interfacing region forming a triple interpenetrating network

The bone-interfacing region comprises another polymer partially interpenetrated within the hydrogel's first and second networks, forming a triple network in the bone-interfacing region.

Use of non-ionic telechelic macromonomers in the IPN

The interpenetrating polymer network includes preformed non-ionic telechelic macromonomers as part of the hydrogel's first network.

Defined end groups on telechelic macromonomers

The macromonomers have at least one end group selected from diacrylates, dimethacrylates, diallyl ethers, divinyls, diacrylamides, dimethacrylamides.

Use of ionic polymers with specific functional groups

The interpenetrating polymer network hydrogel comprises an ionic polymer with carboxylic acid groups, sulfonic acid groups, or both, including poly(acrylic acid).

Physical entanglement between networks

The first network of preformed non-ionic telechelic macromonomers is physically entangled with the ionic polymer network in the hydrogel.

Bone-interfacing region composition

The bone-interfacing region comprises polymers selected from polyurethane, silicone rubber, or their derivatives or combinations.

The claims cover an arthroplasty device that integrates a strain-hardened interpenetrating polymer network hydrogel bearing region with a distinct bone-interfacing polymer region that forms a triple network, utilizing specific macromonomers and ionic polymers for improved mechanical and biological integration with bone.

Stated Advantages

The device mimics the molecular structure, elastic modulus, fracture strength, and lubricious surface of natural cartilage.

It is bone-sparing, reducing the amount of bone excised during arthroplasty procedures.

The hydrogel exhibits high tensile and compressive strength with low friction and high water content similar to natural cartilage.

Anchoring strategies provide mechanical, biological, and chemical fixation to bone, including osteointegration through interactions with calcium and phosphate.

The device can conform and self-adjust to bone geometries via stimulus-responsive swelling or shrinking.

It offers wear resistance and low wear rates suitable for long-term joint replacement applications.

Documented Applications

Replacement or resurfacing of cartilage in hip joints, including femoral head and acetabulum components.

Application to the knee joint including distal femur components and tibial plateau resurfacing.

Use in shoulder, hands, fingers (e.g., carpometacarpal joint), feet, ankle, toes, and intervertebral discs or facet joints.

Replacement of menisci, bursae, and labral structures in mammalian joints.

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