High-Strength Hydrogel Attachment through Nanofibrous Reinforcement.

The repair of a cartilage lesion with a hydrogel requires a method for long-term fixation of the hydrogel in the defect site. Attachment of a hydrogel to a base that allows for integration with bone can enable long-term fixation of the hydrogel, but current methods of forming bonds to hydrogels have less than a tenth of the shear strength of the osteochondral junction. This communication describes a new method, nanofiber-enhanced sticking (NEST), for bonding a hydrogel to a base with an adhesive shear strength three times larger than the state-of-the-art. An example of NEST is described in which a nanofibrous bacterial cellulose sheet is bonded to a porous base with a hydroxyapatite-forming cement followed by infiltration of the nanofibrous sheet with hydrogel-forming polymeric materials. This approach creates a mineralized nanofiber bond that mimics the structure of the osteochondral junction, in which collagen nanofibers extend from cartilage into a mineralized region that anchors cartilage to bone.

3D Printing of a Double Network Hydrogel with a Compression Strength and Elastic Modulus Greater than those of Cartilage.

This article demonstrates a two-step method to 3D print double network hydrogels at room temperature with a low-cost ($300) 3D printer. A first network precursor solution was made 3D printable via extrusion from a nozzle by adding a layered silicate to make it shear-thinning. After printing and UV-curing, objects were soaked in a second network precursor solution and UV-cured again to create interpenetrating networks of poly(2-acrylamido-2-methylpropanesulfonate) and polyacrylamide. By varying the ratio of polyacrylamide to cross-linker, the trade-off between stiffness and maximum elongation of the gel can be tuned to yield a compression strength and elastic modulus of 61.9 and 0.44 MPa, respectively, values that are greater than those reported for bovine cartilage. The maximum compressive (93.5 MPa) and tensile (1.4 MPa) strengths of the gel are twice that of previous 3D printed gels, and the gel does not deform after it is soaked in water. By 3D printing a synthetic meniscus from an X-ray computed tomography image of an anatomical model, we demonstrate the potential to customize hydrogel implants based on 3D images of a patient's anatomy.