# Chitosan- and Gelatin-Based Composite Granular Hydrogels for Cartilage Tissue Regeneration

## TL;DR

This paper introduces a new type of injectable hydrogel made from chitosan and gelatin that improves cartilage tissue regeneration by supporting cell growth and differentiation.

## Contribution

The novel contribution is the development of composite granular hydrogels with enhanced mechanical properties and chondrogenic potential for cartilage regeneration.

## Key findings

- Composite hydrogels showed increased storage modulus compared to traditional ALMA hydrogels.
- 50:50 CHIMA:GelMA hydrogels supported a 6.6-fold increase in cell number over 28 days.
- The hydrogels promoted chondrogenic differentiation with significant glycosaminoglycan deposition and marker expression.

## Abstract

Cartilage regeneration remains an unmet clinical challenge. Despite the great advances in the production of hydrogels as support matrices for cartilage regeneration, the resulting mechanical properties remain low. Granular composite hydrogels appear as ideal candidates due to their injectability and modularity in design. Here, we report on the fabrication and characterization of heterogeneous composite granular hydrogels based on methacrylated chitosan (CHIMA) and gelatin (GelMA) microparticles supported by an interstitial methacrylated alginate (ALMA) matrix. Microparticles were prepared by an oil-emulsion method and their size and morphology optimized, resulting in CHIMA and GelMA microparticles of 10.8 µm (95% CI 9.2, 13.1) and 115.8 µm (95% CI 107.5, 137.6) in diameter, respectively. The microparticles were mixed with ALMA and crosslinked to form granular hydrogels that demonstrated reduced swelling and weight loss. The storage modulus increased from 33 to 66.4 kPa for CHIMA/ALMA hydrogels and from 11.5 to 19.5 kPa for GelMA/ALMA hydrogels when the particle concentration increased from 10 to 50%, and was higher than traditional ALMA hydrogels. Hydrogels of 50:50 CHIMA:GelMA permitted a 6.6-fold increase in cell number after 28 days of culture, and promoted the chondrogenic differentiation of embedded mouse mesenchymal stem cells with a glycosaminoglycan deposition of over 15 µg and the expression of chondrogenic markers.