title: Laser Speckle Rheology for evaluating the viscoelastic properties of hydrogel scaffolds.
abstract: Natural and synthetic hydrogel scaffolds exhibit distinct viscoelastic properties at various length scales and deformation rates. Laser Speckle Rheology (LSR) offers a novel, non-contact optical approach for evaluating the frequency-dependent viscoelastic properties of hydrogels. In LSR, a coherent laser beam illuminates the specimen and a high-speed camera acquires the time-varying speckle images. Cross-correlation analysis of frames returns the speckle intensity autocorrelation function, g2(t), from which the frequency-dependent viscoelastic modulus, G*(ω), is deduced. Here, we establish the capability of LSR for evaluating the viscoelastic properties of hydrogels over a large range of moduli, using conventional mechanical rheometry and atomic force microscopy (AFM)-based indentation as reference-standards. Results demonstrate a strong correlation between |G*(ω)| values measured by LSR and mechanical rheometry (r = 0.95, p < 10-9), and z-test analysis reports that moduli values measured by the two methods are identical (p > 0.08) over a large range (47 Pa - 36 kPa). In addition, |G*(ω)| values measured by LSR correlate well with indentation moduli, E, reported by AFM (r = 0.92, p < 10-7). Further, spatially-resolved moduli measurements in micro-patterned substrates demonstrate that LSR combines the strengths of conventional rheology and micro-indentation in assessing hydrogel viscoelastic properties at multiple frequencies and small length-scales.
authors.affiliation: Wellman Center for Photomedicine, Massachusetts General Hospital, Harvard Medical School, Boston, MA, USA.
authors.forename: Zeinab
authors.initials: Z
authors.lastname: Hajjarian
authors.affiliation: Edwin Steele Laboratory for Tumor Biology, Massachusetts General Hospital, Harvard Medical School, Boston, MA, USA.
authors.forename: Hadi Tavakoli
authors.initials: HT
authors.lastname: Nia
authors.affiliation: Department of Electrical and Computer Engineering, University of Illinois at Urbana-Champaign, Urbana, IL, USA.
authors.forename: Shawn
authors.initials: S
authors.lastname: Ahn
authors.affiliation: Department of Mechanical Engineering, Massachusetts Institute of Technology, Cambridge, MA, USA.|Department of Biological Engineering, Massachusetts Institute of Technology, Cambridge, MA, USA.|Department of Electrical Engineering, Massachusetts Institute of Technology, Cambridge, MA, USA.
authors.forename: Alan J
authors.initials: AJ
authors.lastname: Grodzinsky
authors.affiliation: Edwin Steele Laboratory for Tumor Biology, Massachusetts General Hospital, Harvard Medical School, Boston, MA, USA.
authors.forename: Rakesh K
authors.initials: RK
authors.lastname: Jain
authors.affiliation: Wellman Center for Photomedicine, Massachusetts General Hospital, Harvard Medical School, Boston, MA, USA.
authors.forename: Seemantini K
authors.initials: SK
authors.lastname: Nadkarni
mesh_terms: D055119:Elastic Modulus; D004548:Elasticity; D020100:Hydrogels / Q000737:chemistry*; D007834:Lasers; D018625:Microscopy, Atomic Force; D012212:Rheology / Q000295:instrumentation*; D014783:Viscosity
chemical_list: D020100:Hydrogels