| dc.description.abstract | Clinical treatments for intervertebral disc (IVD) degeneration aim to relieve pain and stabilize the spine. However, recovery is limited by a lack of adequate replication of joint mechanics, donor site morbidity, and a low healing capability of the avascular tissue. Studies have shown that hydrogels are promising alternatives to typical metal or ceramic implants based on their hydration and unique mechanical properties, as well as biocompatibility. Electrostatic double network (DN) hydrogels, such as those based on negatively charged poly(2-acrylamido-2-methylpropane sulfonic acid) (PAMPS), have a distinct ability to achieve high strength through the energy dissipation in the second network. Recently, the reversible, hydrophobic interactions of poly(N-isopropylacrylamide) (PNIPAAm) were leveraged by the Grunlan Lab in a DN design consisting of a PAMPS first network and PNIPAAm-co-acrylamide (AAm) second network. A PAMPS/P(NIPAAm-co-AAm) (90:10 wt% ratio NIPAAm:AAm) DN yielded a unique combination of articular cartilage-like high modulus (~1 MPa), high strength (~25 MPa), and high water content (~80%). More recently, the modulus of this hydrogel was further increased to ~3 MPa – within the range of annulus fibrosus (AF) tissue - without compromising the high strength or water content by incorporation of a cationic third network poly(acrylamidopropyl trimethyl-ammonium chloride) (PAPTAC). The IVD has two major regions with different mechanical properties, the AF and the nucleus pulposus (NP). Thus, this present study sought to create a single hydrogel that exhibits such regional differences. This was accomplished with a triple network hydrogel for one region, and fabrication of a gelatinous interpenetrating polymer network (IPN) hydrogel for the second region. Connection of the two regions was accomplished with charged induced adhesion. Key material properties were evaluated (e.g. water content, modulus, and strength) and compared to the previously studied PAMPS/P(NIPAAm-co-AAm) hydrogel and mechanical properties of a healthy IVD. Results showed the creation of a hydrogel with two mechanical properties. | |
