July 2019
Volume 60, Issue 9
Open Access
ARVO Annual Meeting Abstract  |   July 2019
Characterizing Mechanical Properties of Silk Films with Atomic Force Microscopy
Author Affiliations & Notes
  • Michael Sun
    Ophthalmology, University of Illinois at Chicago, Chicago, Illinois, United States
  • Tao Teng
    Bioengineering, University of Illinois at Chicago, Chicago, Illinois, United States
  • Yuncin Luo
    Ophthalmology, University of Illinois at Chicago, Chicago, Illinois, United States
  • Qiang Zhou
    Ophthalmology, University of Illinois at Chicago, Chicago, Illinois, United States
  • James Lee
    Bioengineering, University of Illinois at Chicago, Chicago, Illinois, United States
  • Mark Rosenblatt
    Ophthalmology, University of Illinois at Chicago, Chicago, Illinois, United States
  • Footnotes
    Commercial Relationships   Michael Sun, None; Tao Teng, None; Yuncin Luo, None; Qiang Zhou, None; James Lee, None; Mark Rosenblatt, None
  • Footnotes
    Support  R21EY019561, P30EY001792, Research to Prevent Blindness Career Development Award
Investigative Ophthalmology & Visual Science July 2019, Vol.60, 4095. doi:https://doi.org/
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    • Get Citation

      Michael Sun, Tao Teng, Yuncin Luo, Qiang Zhou, James Lee, Mark Rosenblatt; Characterizing Mechanical Properties of Silk Films with Atomic Force Microscopy. Invest. Ophthalmol. Vis. Sci. 2019;60(9):4095. doi: https://doi.org/.

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      © ARVO (1962-2015); The Authors (2016-present)

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Abstract

Purpose : The cornea neuro-epithelium is an actively remodeling layer that provides clarity and sensation to the eye. Stem cells derived from the limbus constantly replace epithelial cells in the normal cornea. To appropriately localize, these cells follow physical cues of the microenvironment by converting mechanical stimuli such as matrix stiffness and elasticity to biochemical signals in a process known as mechanotransduction. Here we developed a novel sample preparation technique to study silk film biomechanics, to understand how this biomaterial may influence corneal regeneration and wound repair.

Methods : Silk films were made from processing the cocoons of Bombyx mori silkworms. The films were adhered onto glass slides using a mounting solution made of 10% w/v gelatin, 0.1% w/v chrome alum in dH2O. Atomic force microscopy (AFM) nanoindentation was used to measure the stiffness (Young’s modulus) of the films once rehydrated in dH2O. Indentation parameters were fixed and three silk films were each measured in 16 separate areas to account for regional variation. The Young’s modulus was determined by fitting data with the Hertzian model for describing non-adhesive, elastic contact mechanics.

Results : Chrome alum-gelatin provided stable adhesion of silk films under dH2O immersion as evident from lack of sample drift seen under AFM. The 95% confidence intervals for the three films were 14.36 ± 1.13 MPa, 13.03 ± 0.94 MPa, and 13.25 ± 0.86 MPa. Statistical analysis showed no significant difference between the films. Little hysteresis was seen in force curves which justifies use of the Hertz model and indicates that hydrated silk films have almost purely elastic mechanical behavior.

Conclusions : Here we characterized the Young’s modulus of hydrated silk films using a chrome alum-gelatin mounting solution. Previously, AFM with thin, hydrated samples proved to be particularly challenging as most water resistant adhesives chemically alter the sample and therefore its stiffness. We believe this technique can be extended to biomaterials that have previously proven difficult to measure using AFM. Our next step is to determine how corneal cell behavior changes to silk films of different Young's modulus.

This abstract was presented at the 2019 ARVO Annual Meeting, held in Vancouver, Canada, April 28 - May 2, 2019.

 

Data of silk films presented as whisker plots subdivided into quartiles.

Data of silk films presented as whisker plots subdivided into quartiles.

 

An example force curve. The red and blue lines represent the indentation and retraction phases, respectively. The dotted black line is the fitted Hertz model.

An example force curve. The red and blue lines represent the indentation and retraction phases, respectively. The dotted black line is the fitted Hertz model.

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