Hydroxyapatite-Mediated Mechanical Modulation of GelMA Hydrogels Influences Osteogenic Differentiation of 3D Spheroids

TL;DR

This study shows that adding hydroxyapatite to hydrogels affects their stiffness and how well they support bone cell development in 3D cultures.

Contribution

The study reveals a non-linear relationship between hydrogel stiffness and osteogenic differentiation, suggesting optimal rather than maximal stiffness is best.

Findings

GelMA+HAp10 showed the highest alkaline phosphatase activity despite lower stiffness than GelMA+HAp5.

Higher hydroxyapatite concentrations reduced crosslinking efficiency in GelMA hydrogels.

Optimizing mechanical properties, not maximizing them, is more effective for bone tissue engineering.

Abstract

Substrate stiffness critically regulates osteogenic differentiation, yet systematic identification of optimal mechanical conditions in three-dimensional culture remains limited. This study investigated how hydroxyapatite (HAp)-mediated mechanical modulation of gelatin methacryloyl (GelMA) hydrogels influences osteogenic differentiation of encapsulated SAOS-2 spheroids. GelMA hydrogels with HAp at 5, 10, and 15 μg/mL were characterized for mechanical properties and used to encapsulate pre-formed spheroids under osteogenic conditions. GelMA+HAp5 achieved the highest compressive modulus, while higher HAp concentrations reduced crosslinking efficiency. All formulations maintained comparable viability and metabolic activity. Notably, GelMA+HAp10 produced the highest alkaline phosphatase activity at Days 7 and 14, despite lower stiffness than GelMA+HAp5, demonstrating a non-linear relationship between substrate mechanics and osteogenic response. These results establish that optimizing rather than maximizing mechanical properties represents a more effective scaffold design strategy for bone tissue engineering.

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