Acoustic and Rheological Characterization of Hydrogel Viscoelasticity
Open Access DepositedHydrogels mimic soft tissues which has made them popular for a range of biomedical applications. Gelatin methacrylate (GelMA) has been identified as an especially promising candidate, particularly within the field of tissue engineering. To optimize GelMA hydrogels for particular applications, systematic characterization of their mechanical properties is needed. In this work, GelMA hydrogels were made with a range of material properties by varying both GelMA concentration and ultraviolet light curing time. The samples were evaluated using pulse-echo ultrasound, a non-invasive and non-destructive characterization technique, obtaining acoustic parameters such as the speed of sound, acoustic impedance, and attenuation coefficient. Each hydrogel’s bulk modulus and Poisson’s ratio was also calculated. Additionally, compression testing was performed to obtain the Young’s moduli. The results show that an increase in GelMA concentration corresponds to a faster speed of sound, and both an increase in GelMA concentration and an increase in ultraviolet light curing time corresponds to a higher elastic modulus. The mechanical properties were found to be similar to those of soft tissue. By comparing the acoustic and mechanical properties of the GelMA hydrogels to the acoustic and mechanical properties of human tissues, these results can inform the selection of GelMA synthesis and fabrication parameters for a variety of tissue engineering applications.Given that human tissues are complex viscoelastic materials, viscoelastic characterization of hydrogels is another important consideration for targeting specific needs. Traditional characterization methods utilize mechanical and rheological tests, requiring specific sample sizes, extensive sample preparation, and destructive measurements. Acoustic characterization techniques offer an alternative, but they rarely include insight into viscosity and often require complicated equipment or materials that behave as liquids. In the second part of this work we show how a simple pulse echo ultrasound setup can be used to obtain both the viscosity and elasticity of a hydrogel, resulting in a non-invasive viscoelastic characterization. We performed our characterization on polymeric hydrogels of various concentrations, types, and curing times to gain insight on how viscoelasticity is affected by different parameters. The results closely align with results from traditional testing, demonstrating the effectiveness of this acoustic method which could greatly enhance quality control in the field of tissue engineering. In the third part of this work, oscillatory shear rheology and atomic force microscopy (AFM) were performed on GelMA samples of various concentrations and curing times. The results of rheology frequency and amplitude sweeps revealed shear thinning behavior, irreversible chemical crosslinking, and a mostly elastic response in all of the hydrogels. Shear moduli were found to increase with GelMA concentration, and a calculation of the flow transition index revealed a low tendency to brittle fracturing in all of the hydrogels. The results from AFM tests revealed no significant differences in elasticity or viscosity of the hydrogels, indicating that differences in GelMA hydrogel mechanical properties emerge at longer length scales. More generally, all of the moduli at 1 Hz (measured from both testing methods) were shown to follow the viscoelastic curve expected for human tissues. Finally, the structure of GelMA hydrogels was explored using a constitutive model by Dobrynin et al. which offers insight into crosslinked hydrogel networks using compression data. No differences were found between the hydrogels on a monomer level. This work connects hydrogel processing parameters to mechanical properties found via ultrasound, compression, steady shear rheology, oscillatory shear rheology, and AFM. The results inform the selection of GelMA for biomedical applications and reveal the effects of deformation type, measurement length scale, and measurement frequency on hydrogel properties.
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Jariwala_gwu_0075A_17006.pdf | 2025-04-11 | Open Access |
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