Mechanical properties of murine and porcine ocular tissues in compression

Abstract

Sub-retinal implantation of foreign materials is becoming an increasingly common feature of novel therapies for retinal dysfunction. The ultimate compatibility of implants depends not only on their in vitro chemical compatibility, but also on how well the mechanical properties of the material match those of the native tissue. In order to optimize the mechanical properties of retinal implants, the mechanical properties of the mammalian retina itself must be carefully characterized. In this study, the compressive moduli of eye tissues, especially the retina, were probed using a dynamic mechanical analysis instrument in static mode. The retinal compressive modulus was lower than that of the sclera or cornea, but higher than that of the RPE and choroid. Compressive modulus remained relatively stable with age. Conversely, apparent retinal softening occurred at an early age in mice with inherited retinal degeneration. Compressive modulus is an important consideration for the design of retinal implants. Polymer scaffolds with moduli that are substantially different than that of the native tissue in which they will ultimately reside will be less likely to aid in the differentiation and development of the appropriate cell types in vitro and will have reduced biocompatibility in vivo.

Photochemically crosslinked cell‐laden methacrylated collagen hydrogels with high cell viability and functionality

“…The compressive modulus of the collagen hydrogels was determined by taking the steepest slope between the 0 and 10% strain to ensure that the modulus is calculated within the elastic region of the stress–strain curve . Results from the current study showed that at high concentration of photoinitiator (0.1%), changing the photoinitiator type (i.e., I2959 vs. VA086) had no effect on the compressive modulus of CMA hydrogels (Fig.…”

“…Briefly, CMA hydrogels in a hydrated state (8 mm diameter, 2.5 mm thick) were mounted on the DMA system and a preload of 0.0001 N was applied to engage the compression clamp onto the surface of the sample. Following this, the hydrogels were subjected to uniaxial compression at a static loading rate of 0.01 N/min until the compression clamp reached the end position . Stress and strain were computed from the load and displacement data.…”

“…Stress and strain were computed from the load and displacement data. Compressive modulus was determined by taking the slope of the linear region of the stress–strain curve between the 0 and 10% strain …”

Fine-resolution maps of acoustic properties at 250 MHz of unstained fixed murine retinal layers

“…In retinitis pigmentosa and other inherited retinopathies, the photoreceptors and retinal pigment epithelium undergo progressive damage. Therefore, most retinal diseases are expected to occur concomitantly with changes in the local mechanical properties of the retina, as demonstrated in recent studies (Friedman et al, 1989;Worthington et al, 2014). Specifically, Worthington et al (2014) found a significant change in the compressive modulus associated with rapid degeneration of mouse retinas.…”

Biomechanical relationships between the corneal endothelium and Descemet's membrane

“…Our lab has extensively used AFM to characterize the stiffness of the distinct layers of the human and rabbit cornea 45–47 (detailed in Table 1), as well as the normal human trabecular meshwork (4.0 ± 2.2 kPa 48 ). The properties of the ECM can vary considerably between species 47,49,50 , and each layer in the rabbit eye is consistently softer than the corresponding structure in the human eye 47 . For further information, we direct the reader to these reviews on the nuances of stiffness measurements in ocular tissues 42,44 and comprehensive summaries of biomechanical measurements of ocular tissue 51–55 .…”