Hydrogels for orthopedic repair

Abstract

Hydrogels intended for orthopedic applications, including repair and regeneration of cartilage, bone, joint surfaces and related tissues, must possess greater strength and toughness than hydrogels used in soft tissue repair. A hydrogel formulation is provided which has high strength, toughness, a suitable mechanical modulus and low equilibrium hydration. It may also have controlled porosity or degradation time. It can be made to polymerize in situ with high (“good” to “excellent”) adherence to target tissue or surfaces. A preferred formulation for forming such gels comprises 40 to 80% by weight of a low-molecular weight polar monomer and 30 to 10% of a hydrophilic macromeric crosslinker.

Description

[0001] This application claims priority to U.S. Ser. No. 60 / 153,190, filed Sep. 10, 1999.FIELD OF THE INVENTION [0002] This invention is generally in the field of treatments of disease, particularly disease of skeletal or orthopedic tissues such as cartilage and bone, using polymeric materials having high adherence to tissue, low degree of swelling, toughness and biocompatibility. BACKGROUND OF THE INVENTION [0003] Hydrogel materials are useful in coating, sealing and adhesion of soft tissues, for example as described in U.S. Pat. No. 5,410,016 to Hubbell et al., U.S. Pat. No. 5,800,373 to Melanson et al., and U.S. Pat. Nos. 5,844,016, and 5,900,245 to Sawhney et al. Important properties of these hydrogels are their biocompatibility, their ability to adhere strongly to tissue, and good mechanical compliance, which is appropriately matched to that of the tissue. Biocompatibility is achieved by the use of materials that are especially compatible with tissue, such as polyalkylene oxide...

AI Technical Summary

Benefits of technology

[0010] Polymeric materials have been developed which can be effective in treatment of orthopedic tissues, such as cartilage, bone and accessory structures, and implants. In one embodiment, the material includes a mixture of two components which copolymerize to form a hydrogel that contains hydrophilic and hydrophobic regions. The first component is covalently-crosslinkable, hydrophilic, polymeric, of high biocompatibility, and optionally spontaneously hydrolyzing (“biodegradable”). It is preferably sufficiently hydrophilic to be water-soluble at a temperature between about 0 and 70° C. The second component is more hydrophobic (although it is preferably water-soluble under the same conditions), is covalently polymerizable, provides structural strength and limits the water absorption capacity of the formed gel. Upon reaction in situ in the presence of polymerization initiators bound to or adhered to the tissue (“priming systems”), the resulting polymerized hydrogel adheres tightly to the tissues, and has suitable mechanical properties, including toughness, strength and resiliency to facilitate repair or regeneration of the tissue. It also remains as a hydrogel, retaining the advantages of biocompatibility and lubricity. The hydrogel is optionally biodegradable.

[0013] The polymerized materials have a controlled, low degree of swelling on continued exposure to water, combined with a tensile modulus which may be in excess of 1 MPa and also having a significant elongation to break (e.g., 10% or more). This combination of properties makes the materials tough, resilient, and able to withstand cyclic mechanical stress for extended periods. The material can also be made porous, and thereby permissive of cell or tissue ingrowth in the process of tissue repair. Porosity formation may be intrinsic to the materials or may be provided by pore-forming excipients or processes.

Problems solved by technology

However, these gels are less useful in situations in which the gels are subject to high mechanical stress.

Repair of injuries, disease or defects of orthopedic tissues can be difficult because the gel needs to offer protection to the structures under mechanical stress.

Repair of articular cartilage is especially difficult.

Traditional hydrogels are not strong enough to withstand the applied stresses, particularly over the length of time required, especially for long periods of time such as those required for regeneration of bone or connective tissue.

Such gels also tend to swell extensively in aqueous environments, which can interfere with mechanical properties of the injured joint or other site.

On the other hand, traditional solid implants (which typically are formed of hydrophobic materials) can be too rigid and brittle, thereby impeding or preventing tissue repair or regeneration.

They may also lack lubricity, which can compromise performance in joints as well as pose a risk of abrasion of the opposing surface.

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