Antioxidant Ascorbic Acid Influences Cell-mediated Alterations in Localized Hydrogel Crosslinking and Affects...

Photopolymerizable and degradable poly(ethylene glycol) (PEG) hydrogels are a promising platform to deliver chondrocytes for cartilage tissue engineering. Previous studies reported that cells are exposed to and react with free-radicals produced during encapsulation, creating a pericellular region of reduced crosslink density measured by the distance R_d. This study tests the hypothesis that increasing R_d improves spatial elaboration of deposited extracellular matrix (ECM) (i.e., micro-tissue) in a degrading hydrogel. Chondrocytes pre-treated or not with the antioxidant ascorbic acid atlow (1 nM) and high (1000 nM) concentrations prior to encapsulation resulted in increasingly larger R_d's: 3.3 (0 nM), 6.7 (1 nM), and 10 (1000 nM) µm. Encapsulated chondrocytes when cultured up to ten weeks, produced micro-tissues within the hydrogels. The median micro-tissue area increased by 29% (1 nM) and 570% (1000 nM) compared to 0 nM condition. This work shows that bolstering antioxidant defense mechanisms enhances chondrocyte inhibition of the polymerization immediately around the cell, resulting in larger regions of reduced crosslinking. This local variation in network structure, which degrades more quickly, led to improved neotissue assembly and larger micro-tissues, comprised primarily of sulfated glycosaminoglycans and collagen type II. This approach offers a novel way to improve ECM elaboration and interconnectivity in free-radical polymerized hydrogels for tissue engineering.