Hydrogel arthroplasty device
Inventors
Myung, David • Kourtis, Lampros • Hartmann, Laura • Frank, Curtis W. • Goodman, Stuart B. • Carter, Dennis R.
Assignees
US Department of Veterans Affairs • Leland Stanford Junior University
Publication Number
US-9387082-B2
Publication Date
2016-07-12
Expiration Date
2025-10-04
Interested in licensing this patent?
MTEC can help explore whether this patent might be available for licensing for your application.
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 invention provides a bone-sparing arthroplasty device utilizing an interpenetrating polymer network (IPN) hydrogel that is strain-hardened by swelling, designed to mimic the molecular structure, elastic modulus, fracture strength, and lubricious surface of natural cartilage. This hydrogel forms the basis of a biomimetic resurfacing procedure that replaces only cartilage, fabricated as flexible implantable devices with lubricious articular surfaces and osteointegrable bone-interfaces. The hydrogel conforms to bone geometries in mammalian joints, enabling fixation through conforming to naturally or artificially prepared bone surfaces, and can be adapted for various joints including hips, knees, shoulders, hands, and intervertebral facets.
The strain-hardened IPN hydrogel comprises two distinct, non-silicone polymer networks: a first chemical network formed from preformed hydrophilic non-ionic telechelic macromonomers cross-linked via polymerization of end-groups, and a second network composed of ionizable monomers polymerized and chemically cross-linked in the presence of the first network. The second network forms physical cross-links with the first and has a lower degree of chemical cross-linking. An aqueous salt solution with neutral pH ionizes and swells the second network, constrained by the first, resulting in increased effective physical cross-links and an enhanced Young's modulus beyond that of individual networks or their combination swollen in pure water.
The device features a bearing region opposite to a bone-interfacing region; the latter conforms and fixates to bone geometry and can be porous or coated with calcium- and phosphate-containing substances to promote bone ingrowth and osteointegration. The hydrophilic first network often consists of derivatives of poly(ethylene glycol), while the second network comprises acrylic acid monomers. The device may include stimulus-responsive polymers enabling volume changes in response to environmental factors such as pH, salt concentration, temperature, or electric field, facilitating secure conformal fit to convex or concave bone surfaces after implantation.
Claims Coverage
The patent includes one independent claim focused on the composition and structural gradient of a cartilage replacement prosthesis.
Composition gradient of polyacrylic acid within a polyurethane network
The prosthesis comprises a covalently cross-linked polyacrylic acid network interpenetrating a polyurethane network with a composition gradient such that polyacrylic acid content is maximal at the lubricious second surface and decreases towards the first surface, while polyurethane is present throughout.
Hydration gradient within the prosthesis
The prosthesis contains water forming a continuous hydration gradient within both the polyacrylic acid network and the polyurethane network.
Surface shape and bone interfacing adaptations
The first surface of the prosthesis can have a primarily concave or convex shape adapted to mate with joint bone structures (e.g. femoral head or acetabular cavity). The first surface is adapted for anchoring to bone and may include a bonding agent for attachment.
Lubricious second surface adapted for articulation
The lubricious second surface is adapted to articulate with another surface different from the first surface, facilitating joint movement.
The claims cover a cartilage replacement prosthesis structurally composed of a polyurethane matrix with a polyacrylic acid gradient, featuring hydration and compositional gradients, surface shapes tailored for bone interfacing and articulation, and adaptations for secure bone attachment and lubricious articulation.
Stated Advantages
The hydrogel material mimics natural cartilage by providing a combination of cartilage-like stiffness, high water content, and low surface friction.
The device is bone-sparing, avoiding the highly invasive bone removal of traditional joint replacements.
Anchoring strategies promote osteointegration, enabling the device to integrate with bone tissue over time for secure fixation.
The device's lubricious bearing surfaces and high mechanical strength provide smooth sliding motion and load distribution comparable to natural cartilage.
Stimulus-responsive polymers allow the device to conform securely to bone surfaces through shrinking or swelling post-implantation.
The strain-hardened IPN hydrogels have improved tensile strength and elastic modulus beyond previous hydrogels, enhancing durability and function in joint loading.
The hydrogel's permeability and surface properties support low friction and reduced wear, potentially extending implant lifetime.
Documented Applications
Total or partial replacement or resurfacing of the hip joint, including femoral head and acetabulum components for cap-on-cap or cap-on-cartilage articulation.
Knee joint applications including distal femur and tibial plateau components, with designs that accommodate ligament insertions and press-fit fixation in prepared bone depressions.
Applications to other joints such as shoulder, hands, fingers, feet, ankle, toes, and intervertebral discs or facets.
Replacement or repair of intervertebral discs, bursae, menisci, and labral structures in the body.
Interested in licensing this patent?