Paper Number
GN10 

Session
Gels and Networks

Title
How viscoelastic are tissues? Insights into tissue rheology and on gels that can mimic the same

Presentation Date and Time
October 14, 2024 (Monday) 2:30

Track / Room
Track 1 / Waterloo 3

Authors (Click on name to view author profile)

1. Srivastava, Mahima (University of Maryland College Park, Chemical and Biomolecular Engineering)
2. Raghavan, Srinivasa R. (University of Maryland)

Author and Affiliation Lines (in printed abstract book)
Mahima Srivastava and Srinivasa R. Raghavan
Chemical and Biomolecular Engineering, University of Maryland College Park, College Park, MD 20740

Speaker / Presenter 
Srivastava, Mahima

Keywords
experimental methods; biological systems; gels

Text of Abstract
Tissues like articular cartilage, muscles, and tendons can withstand high impact and considerable deformation. What exactly is the rheology of these tissues? Are they elastic or viscoelastic? How does tissue rheology relate to function, especially to their protective ability? Can we create synthetic materials, i.e., hydrogels, with rheology comparable to those of tissues? Motivated by these questions, we have embarked on a systematic study on tissue rheology and on the design of tissue-mimetic gels. Our focus for this talk will be on cartilage, which is a stiff tissue known for its ‘cushioning’ or ‘shock absorbing’ ability. We find that bovine cartilage shows the expected gel-like response in dynamic rheology in the linear regime (i.e., its moduli are independent of frequency). Cartilage has a high elastic modulus (G’ > 10⁵ Pa), but curiously its viscous modulus G” is also high (in turn, its loss tangent tan δ = G”/G’ is ~ 0.4). Thus, cartilage is indeed viscoelastic and its tan δ exceeds those of typical hydrogels. Turning to non-linear rheology, cartilage exhibits a large ‘hysteresis loop’ in cyclic compression. The area enclosed by this loop correlates with energy dissipation. For gels to mimic the rheology of cartilage, they have to be rendered more viscoelastic. We have explored several strategies towards this end. Gels of gelatin and acrylamide have been prepared with different additives that can enhance their viscous dissipation, notably starch granules. We have been able to design a class of gels that exhibit the combination of rheological properties seen in cartilage, i.e., (1) high stiffness (G’); (2) high viscoelasticity (tan δ and (3) high ability to dissipate energy at large deformations. The unique properties of these cartilage-mimicking gels will be revealed through a series of demonstrations.