Compressive failure of hydrogel spheres
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Compressive failure of hydrogel spheres Jeremiah D. James1, Jacob M. Ludwick1, Mackenzie L. Wheeler1, Michelle L. Oyen1,a) 1
Department of Engineering, East Carolina University, Greenville, North Carolina 27858, USA Address all correspondence to this author. e-mail: [email protected] This paper has been selected as an Invited Feature Paper. a)
Received: 14 February 2020; accepted: 20 April 2020
Hydrogels have gained recent attention for biomedical applications because of their large water content, which imparts biocompatibility. However, their mechanical properties can be limiting. There has been significant recent interest in the strength and fracture toughness of hydrogel materials in addition to their stiffness and timedependent behavior. Hydrogels can fail in a brittle manner, although they are extremely compliant. In this work, the failure and fracture of hydrogels are examined using a compression test of spherical hydrogel particles. Spheres of commercially available polyacrylamide–potassium polyacrylate were hydrated and tested to failure in compression as a function of loading rate. The spheres exhibited little relaxation when compressed to small fixed displacements. The distributions of strength values obtained were examined in a particle fracture framework previously used for brittle ceramics. There was loading rate dependence apparent in the measured peak force and calculated peak strength values, but the data fell on a single empirical distribution function of strength for the hydrogels regardless of loading rate. Strength values for these hydrogels were mostly in the range of 0.05–0.3 MPa, illustrating the challenges using hydrogels for mechanically demanding applications such as tissue engineering.
Introduction There has been considerable recent interest in hydrogel materials— hydrated polymer networks with very large water contents—for biomedical applications including tissue engineering [1, 2] and drug delivery [3, 4]. The large water contents of these materials allow for excellent biocompatibility, and the polymer networks can be constructed from a range of natural and synthetic polymeric base chemistries [5]. Furthermore, the polymer networks can be chemically or physically cross-linked [6], and composite gels with double independent networks [7, 8], nanoparticles [9], or nanofibers [10, 11] can be easily constructed. Overall, this very large parameter space of chemistries gives rise to an interesting class of materials with fascinating structure–property relationships. Because of the large water contents inherent to these hydrogel materials, the mechanical properties have been one key limitation in their biomedical use [6], especially for physically demanding tissue engineering applications, such as articular cartilage [12, 13] or cornea [14]. There has been particular recent interest in failure and fracture properties of single network hydrogels [15], double network hydrogels [7], and nanofiberreinforced hydrogel composites [16]. Comparisons of physical properties of soft biological tissues have s
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