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Abstract
We introduce laser cavitation rheology (LCR) as a minimally-invasive optical method to characterize mechanical properties within the interior of biological and synthetic aqueous soft materials at high strain-rates. We utilized time-resolved photography to measure cavitation bubble dynamics generated by the delivery of focused 500 ps duration laser radiation at λ = 532 nm within fibrin hydrogels at pulse energies of Ep = 12, 18 µJ and within polyethylene glycol (600) diacrylate (PEG (600) DA) hydrogels at Ep = 2, 5, 12 µJ. Elastic moduli and failure strains of fibrin and PEG (600) DA hydrogels were calculated from these measurements by determining parameter values which provide the best fit of the measured data to a theoretical model of cavitation bubble dynamics in a Neo-Hookean viscoelastic medium subject to material failure. We demonstrate the use of this method to retrieve the local, interior elastic modulus of these hydrogels and both the radial and circumferential failure strains.
Highlights
We introduce laser cavitation rheology (LCR) as a minimally-invasive optical method to characterize mechanical properties within the interior of biological and synthetic aqueous soft materials at high strain-rates
Visualization of the cavitation bubble dynamics obtained from time-resolved photography when formed within fibrin and polyethylene glycol (600) diacrylate (PEG (600) DA) hydrogels is depicted in Fig. 3a,b, respectively
As a point of comparison, identical bubble sizes formed in water, which represents a material with similar density but no elasticity, would have cavitation cycle times of 22.9 and 28.8 μs for the bubble sizes formed in the 2.5 mg mL−1 fibrin hydrogel at Ep = 12 μJ and 18 μJ, respectively, and 20.7 and 26.0 μs for the bubble sizes formed in the 10.0 mg mL−1 fibrin hydrogel at Ep = 12 μJ and 18 μJ, respectively
Summary
We introduce laser cavitation rheology (LCR) as a minimally-invasive optical method to characterize mechanical properties within the interior of biological and synthetic aqueous soft materials at high strain-rates. 3D culture systems have emerged wherein cells are typically enclosed in viscoelastic hydrogels fabricated from ECM-derived materials in an attempt to mimic the cellular microenvironment in vivo[10,11,12,13,14,15] In this context, investigation of the m echanoreciprocity[16,17] i.e., the interplay between local ECM s tiffness[18,19] and cellular mechanotransduction would benefit from a minimally-invasive method that can mechanically stimulate and measure the local viscoelastic response of soft biological m aterials[20]. The analysis used for LCR considers the bubble dynamics occurring within a viscoelastic material capable of undergoing material deformation with potential failure at high strains and strain rates
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