Characterisation and biocompatibility of crosslinked hyaluronic acid with BDDE and PEGDE for clinical applications

Hyaluronic acid (HA) is a versatile biomaterial frequently utilized in regenerative medicine due to its gel-like properties, making it well-suited for clinical applications. However, its linear form is susceptible to rapid enzymatic degradation, limiting its longevity within the body. To address this challenge, extensive research has focused on crosslinking mechanisms to enhance the durability of HA gels. One early approach involved crosslinking HA with 1,4-butanediol diglycidyl ether (BDDE) to create HA-BDDE, a clinically used product since the 1990s. However, the manufacturing process for HA-BDDE, primarily used in industry, lacks comprehensive documentation in the literature. More recently, poly(propylene glycol) diglycidyl ether (PEGDE) has emerged as an alternative to BDDE for crosslinking, offering improved gel elasticity and reduced cytotoxicity. In this study, we present the manufacturing process for producing both crosslinked gels, HA-BDDE and HA-PEGDE, with negligible residual crosslinkers, as confirmed by FTIR and NMR analysis. We characterize the crosslinking kinetics and the resulting formulations, revealing that HA-PEGDE gel exhibits comparable stiffness (G' = 60 Pa vs. 75 Pa) to HA-BDDE, despite a lower effective crosslinking ratio (CrR = 0.12 vs. 0.24). Intriguingly, our cytotoxicity testing demonstrates significantly greater cell viability for HA-PEGDE compared to HA-BDDE (151% versus 108%). Overall, both gels can be readily manufactured using a similar process and demonstrate excellent in vitro biocompatibility. This study elucidates why HA-BDDE is widely utilized in clinical settings and underscores the potential promise of HA-PEGDE as an emerging variant for clinical applications.