Cartilage has an intrinsically low
healing capacity, thereby requiring
surgical intervention. However, limitations of biological grafting
and existing synthetic replacements have prompted the need to produce
cartilage-mimetic substitutes. Cartilage tissues perform critical
functions that include load bearing and weight distribution, as well
as articulation. These are characterized by a range of high moduli
(≥1 MPa) as well as high hydration (60–80%). Additionally,
cartilage tissues display spatial heterogeneity, resulting in regional
differences in stiffness that are paramount to biomechanical performance.
Thus, cartilage substitutes would ideally recapitulate both local
and regional properties. Toward this goal, triple network (TN) hydrogels
were prepared with cartilage-like hydration and moduli as well as
adhesivity to one another. TNs were formed with either an anionic
or cationic 3rd network, resulting in adhesion upon contact
due to electrostatic attractive forces. With the increased concentration
of the 3rd network, robust adhesivity was achieved as characterized
by shear strengths of ∼80 kPa. The utility of TN hydrogels
to form cartilage-like constructs was exemplified in the case of an
intervertebral disc (IVD) having two discrete but connected zones.
Overall, these adhesive TN hydrogels represent a potential strategy
to prepare cartilage substitutes with native-like regional properties.