Impacts of cross-linker chain length on the physical properties of polyampholyte hydrogels

Polymeric tissue engineering scaffolds have shown promise to aid in regeneration and repair of damaged tissue. In particular, nonfouling polymers have been proposed for eliminating biomaterial-induced concerns such as infection, scarring, and rejection by the immune system. Polyampholyte polymers are one class of nonfouling polymers that are composed of an equimolar mixture of positively and negatively charged monomer subunits. They possess nonfouling properties, bioactive molecule conjugation capabilities, and tunable mechanical properties. In this study, the influence of the cross-linker species on the degradation behavior, mechanical strength, and nonfouling properties of polyampholytes composed of a 1:1 molar ratio of [2-(acryloyloxy)ethyl] trimethylammonium chloride (positively charged) and 2-carboxyethyl acrylate (negatively charged) monomers was investigated. Specifically, the impact of ethylene glycol repeat units on the overall material performance was evaluated by synthesizing and characterizing hydrogels containing di-, tri-, and tetra-ethylene glycol dimethacrylate cross-linker species. The degradation studies were conducted for over 100 days in Sorenson's buffer with pH values of 4.5, 7.4, and 9.0 by tracking the swelling behavior and weight change over time. The mechanical properties were assessed using compression and tensile testing to failure. The retention of the nonfouling and protein conjugation capabilities was demonstrated using fluorescently labeled bovine serum albumin. The results demonstrate the tunability of both degradation behavior and mechanical properties through the cross-linker selection, without impacting the underlying nonfouling and biomolecule delivery capabilities. Therefore, it is concluded that polyampholyte hydrogels represent a promising platform for tissue engineering.