A novel empirical and rheometric assessment of viscoelastic hydrogel implant cohesiveness
Pritha Sarkar, Danny J. Soares, Alec McCarthy, Alina Lee, Cavan Cohoes, Thomas J. Kean, Kausik Mukhopadhyay
Abstract
• The Modulus of Cohesion (MOC) is a novel rheometric measurement of gel cohesion, solving a longstanding problem in biomaterials research. • The MOC captures the energy storage/dissipation balance of a hydrogel through strain sweep rheometry, from zero strain to crossover point. • This measure offers an integrated metric of gel strength and ductility as the energy necessary to induce solid-to-fluid phase transition. • Testing of 11 products confirms the validity and reliability of the MOC relative to other empirical and qualitative measurements of cohesion. Therapeutic implantable hydrogels are increasingly utilized in medicine due to their versatile viscoelastic properties. Nonetheless, the clinical efficacy and longevity of these products is predicated on their ability to retain structural integrity post-implantation. Gel cohesion, defined as the capacity to resist fragmentation, has lacked empirical standardization, especially in high shear environments, with present methods often conflating this mechanical parameter with gel ductility or qualitative perceptions of tackiness. In this study, we introduce a novel quantitative method of cohesion analysis termed the Modulus of Cohesion (MOC). The MOC is derived from rheometric strain sweep testing by calculating the difference between the elastic and viscous moduli from 0% strain to the crossover point. This novel parameter provides a direct measure of mechanical energy storage and dissipation balance, accounting for linear and nonlinear deformation in shear strain. Eleven commercially available hyaluronic acid gels are evaluated using this method, alongside uniaxial tension and drop weight methods to establish correlations between MOC and existing cohesion metrics. Additionally, haptic sensory analysis and aqueous dispersion methods from previous reports are correlated with rheometric and mechanical tests. Our results demonstrate that MOC provides a reliable, reproducible measure of gel cohesiveness, correlating strongly with other quantitative methods with augmented precision.