Nanoindentation of soft hydrated materials for application to vascular tissues

Abstract

Soft hydrated materials, such as vascular tissues and other biomaterials, provide a number of challenges in the field of nanoindentation. However, the ability of nanoindentation to probe local, nanoscale mechanical properties of heterogeneous materials makes it desirable to adapt this technique for application to biologic tissues. To develop the field of nanoindentation for the analysis of soft hydrated materials, the goals of this study were fourfold: develop a sample hydration system, select an appropriate tip for soft material indentation, identify a substrate to be used for blunt tip alignment, and determine an appropriate control material for the development of future indentation protocols. A hydration system was developed that maintained sample hydration for over 8 h without completely submerging the sample. Further, a 100-microm radius of curvature conospherical tip was shown to be a suitable tip for indenting a variety of soft hydrated materials and back-illuminated agarose gel was found to be an effective material for use in tip alignment. Finally, agarose gel demonstrated similar qualitative and quantitative nanomechanical behavior to vascular tissue, suggesting that it will be an appropriate control material for the development of future indentation protocols for soft biologic tissues.

Time-dependent mechanical characterization of poly(2-hydroxyethyl methacrylate) hydrogels using nanoindentation and unconfined compression

“…The data suggest that the foam hydration method may not be ideal for pHEMA hydrogels, although it has previously been shown to be useful for other materials. 24 The hydrogels used in these experiments were continuously submerged after synthesis to ensure that dehydration and rehydration did not change the mechanical properties.…”

Mechanical characterization of deep vein thrombosis in a murine model using nanoindentation

“…Care was taken to ensure that the primary directions of physiological loading (circumferential, longitudinal, and luminal) were "tracked" through all processing procedures for each piece of tissue. Prior to nanoindentation testing, the samples were mounted using previously reported techniques [4][5][6], which have been shown to maintain sample hydration for up to eight hours and provide adequate mechanical substrate support for testing [4]. To insure complete equilibrium hydration testing, samples were submerged in saline at forty-five minute intervals for a minimum of twenty minutes.…”

“…A 100µm, 90º cone angle fluid cell nonporous diamond tip was used for all experiments. Ebenstein et al showed a conospherical diamond probe, with a 100µm radius of curvature was found to be suitable for testing a variety of soft hydrated materials [4]. Their work demonstrated repeatable measurement on all of the materials they tested, exhibited minimal approach problems, and had reasonable projected contact area to measure local tissue properties rather than individual cells or globally averaged tissue properties [4].…”

“…Biomechanical properties of vascular tissue on the cellular scale are difficult to evaluate through traditional mechanical testing techniques [4]. Nanoindentation has recently gained popularity for testing soft (elastic modulus ≈ 1MPa) biologic materials on the micrometer length scale [4][5][6][7].…”

“…Nanoindentation has recently gained popularity for testing soft (elastic modulus ≈ 1MPa) biologic materials on the micrometer length scale [4][5][6][7]. This technique utilizes small-diameter spherical tips (approximate 100µm) and micro-scale loads (approximate 100μN) and displacements (1000nm) to obtain accurate measurements in small tissue regions [6].…”