Bioinspired Articular Cartilage Mimetic Adhesive Hydrogels

Adhesive triple network (TN) hydrogels were developed as articular cartilage mimetic building blocks to repair chondral defects. Chondral defects occur due to arthritis, age, and wear of the joint, where the articular cartilage has a low capacity to heal. To replace the damaged tissue typical treatments, rely on grafting, hard implants, and often need biological factors. These treatments often have adverse effects such as donor site morbidity, wear debris generation and fibrocartilage formation leading to the need for a bioinspired tissue mimetic approach. Hydrogels are an excellent candidate for cartilage tissue due to the structure and high hydration akin to native cartilage (60-90%). While, they have been used for tissue engineering, hydrogels remain limited due to weak mechanical properties. Articular cartilage has discrete depth-dependent mechanical properties to allow for articulating and load bearing requiring a robust biomimetic replacement. To recapitulate the depth-dependent properties, these electrostatic TN hydrogels were developed to incorporate a polyampholyte (i.e., dual-charged [±]) 3^rd network to allow for articular cartilage mimetic mechanical properties and adhesion. The inclusion of the polyampholyte 3^rd network demonstrated a double in compressive strength (σ_C~13 MPa) compared to the previously developed anionic [-] TN hydrogel (σ_C ~5 MPa). The doubled mechanical strength was attributed to the increased internetwork electrostatic interactions, providing dynamic bonds to improve stress dissipation. The charge [+, -, or ±] presence in the 3^rd network of these hydrogels promoted robust electrostatic adhesion characterized by shear strengths of ~100 kPa. These hydrogels are mechanically robust, adhesive, and hydrated presenting a strategy for creating biphasic articular cartilage mimetic implant achieving the necessary criteria.