# Inclusion of Chondroitin Sulfate Into a Gelatin Hydrogel Shifts Local and Global Mechanical Behavior and Fibrochondrogenic Phenotype for Applications in Insertional Tissue Engineering

## TL;DR

Adding chondroitin sulfate to a gelatin hydrogel changes its mechanical properties and cell behavior, making it better for tissue engineering applications like tendon-to-bone repair.

## Contribution

The study introduces a new method of incorporating chondroitin sulfate into hydrogels to enhance both mechanical and biological performance for tissue engineering.

## Key findings

- Incorporating chondroitin sulfate increases mesenchymal stem cell metabolic activity and osteo-tendinous differentiation.
- CS inclusion alters stress–strain behavior in hydrogel zones linking tendon and bone collagen scaffolds.
- Free CS incorporation versus covalent tethering of oxidized CS leads to different biological and mechanical outcomes.

## Abstract

Glycosaminoglycans (GAGs) like chondroitin sulfate (CS) influence both mechanical properties and biological signals within the tissue microenvironment. CS modifications have been prevalent in a range of biomaterial design strategies, particularly those with a focus on wound healing. Here, we investigate the impact of CS incorporation within a thiolated gelatin (Gel-SH) hydrogel previously established as a promising biomaterial for tendon-to-bone entheseal repair, reporting a dual biological and mechanical effect. We show that CS inclusion increases mesenchymal stem cell metabolic activity and osteo-tendinous differentiation patterns in the Gel-SH biomaterial. Additionally, we demonstrate that inclusion of CS into a Gel-SH hydrogel insertional zone used to link dissimilar tendon and bone specific collagen scaffolds induces favorable local changes in stress–strain behavior. We further show that the mode of incorporation, free incorporation of CS versus covalent tethering of oxidized CS (CSO), clearly impacts these observed effects. Overall, these results highlight promising new motifs to modulate Gel-SH hydrogels for greater promotion of enthesis-associated behavior in resident hMSCs; further, they offer broad insight into design strategies and key considerations for modification of multicompartment materials, namely in consideration of incorporation methods and on the interplay of mechanical and biological properties.