Indentation mapping revealed poroelastic, but not viscoelastic, properties spanning native zonal articular cartilage

Abstract

Osteoarthrosis is a debilitating disease affecting millions, yet engineering materials for cartilage regeneration has proven difficult because of the complex microstructure of this tissue. Articular cartilage, like many biological tissues, produces a time-dependent response to mechanical load that is critical to cell’s physiological function in part due to solid and fluid phase interactions and property variations across multiple length scales. Recreating the time-dependent strain and fluid flow may be critical for successfully engineering replacement tissues but thus far has largely been neglected. Here, microindentation is used to accomplish three objectives: (1) quantify a materials time-dependent mechanical response, (2) map material properties at a cellular relevant length scale throughout zonal articular cartilage, (3) and elucidate the underlying viscoelastic, poroelastic, and nonlinear poroelastic causes of deformation in articular cartilage. Untreated and trypsin-treated cartilage were sectioned perpendicular to the articular surface and indentation was used to evaluate properties throughout zonal cartilage on the cut surface. The experimental results demonstrated that within all cartilage zones, the mechanical response was well represented by a model assuming nonlinear biphasic behavior and did not follow conventional viscoelastic or linear poroelastic models. Additionally, 10% (w/w) agarose was tested and, as anticipated, behaved as a linear poroelastic material. The approach outlined here provides a method, applicable to many tissues and biomaterials, which reveals and quantifies the underlying causes of time-dependent deformation, elucidates key aspects of material structure and function, and that can be used to provide important inputs for computational models and targets for tissue engineering.

A 3D, Dynamically Loaded Hydrogel Model of the Osteochondral Unit to Study Osteocyte Mechanobiology

“…A representative image of a histological section of human osteochondral tissue ( Figure 1A) illustrates articular cartilage overlaying a thin interfacial calcified cartilage layer, underlying cortical subchondral bone plate, and subchondral trabecular bone. [10,47,48] The osteochondral unit possesses a large mismatch in the compressive moduli between articular cartilage, ranging from 1 to 10 MPa, [49,50] and the subchondral bone, ranging from 1 to 10 GPa. [51,52] These disparate properties influence strain transfer from cartilage to bone during normal joint movement.…”

Nanoindentation of Soft Biological Materials

“…Other applications involved in indentation to soft tissue include, but are not limited to, poroelastic properties of articular cartilage [154], viscoelastic properties of liver tissues [155], remineralization of demineralized dentin [156], and in vivo tests of skin [157].…”

Direct AFM-based nanoscale mapping and tomography of open-circuit voltages for photovoltaics

“…8.5 min (for 256 × 256 pixel resolution), compared to 4.3 h if based on pcAFMs (with 30 voltage steps and, hence, image frames), or 18.2 h for traditional point-by-point studies (based on a duration of 1 s to acquire each spectrum, move to the next location, and settle the probe). Of course, high-speed data acquisition can in principle accelerate such measurements of thousands of discrete spectra, as implemented for “peak force” [ 16 ] or “fast force” mapping [ 17 – 18 ] where arrays of force–distance curves are acquired during continuous scanning. However, current detection is generally slower than force transduction due to LRC time constants, and in any case tracing full I – V curves over a constant range of biases at every location may damage specimens due to occasional high current flow (i.e., heat) or even breakdown.…”