Developing an accurate mechanical model of the behaviour of a biological system

requires understanding of both the geometry and the material properties of its

components. Gaining structural information about the incudostapedial joint (ISJ)

will be valuable for developing more realistic models of middle-ear mechanics.

There have been a number of anatomical and modelling studies of human, cat and

gerbil ISJ’s (e.g., Funnell et al., 2005, Karmody et al., 2009, Buytaert et al., 2011, Decraemer et al., 2015,

Soleimani et al., 2018a,b). Simplified geometries have been used for modelling and we

have found that the responses of models of the joint are very sensitive to its

geometry. We are doing a post-mortem study of the anatomy of the joint in gerbils

within three hours after sacrifice, using different imaging modalities: stereoscopic

microscope, X-ray nanoCT, and light-sheet microscope.

Adhesive

ISJ

IMJ• We used different imaging modalities to obtain detailed information about

diverse tissues in the ISJ

• The joint may be damaged after repeated pressurization cycles in post-

mortem animals

Imaging of the gerbil incudostapedial joint

Sajjad Feizollah1, Majid Soleimani1, W. Robert J. Funnell1, 2

1Department of BioMedical Engineering, McGill University, QC, Canada, 2Department of Otolaryngology - Head & Neck Surgery, McGill University, QC, Canada

E-mail: sajjad.feizollah@mail.mcgill.ca, majid.soleimani@mail.mcgill.ca, robert.funnell@mcgill.ca

Stapes

➢ Introduction

• The joint is very small and delicate, which makes

extraction and sample preparation very difficult.

➢ Methods: Pressurization

➢ Methods: Auditory bulla dissection

➢ Results: Examples of different imaging modalities

➢ Methods: Sample preparation and imaging

X-ray nano-CT

Fixation with paraformaldehyde

(PFA) in 10X phosphate-buffered

saline (PBS)

Phosphotungstic acid (PTA) staining

Tissue clearing

Hydrogel stabilization

Decalcification with ethylene

diamine triacetic acid (EDTA)

Refractive index matching

• Different sample preparation

methods are used to image various

tissue types for each sample

• Zeiss Xradia 520 Versa X-ray

nanoCT microscope and Zeiss Z.1

light-sheet microscope are used

• Process starts with preparing the

dissected sample for nanoCT

imaging, followed by tissue

clearing for light-sheet microscopy

This study made use of the facilities of McGill’s Advanced BioImaging Facility (for light-

sheet microscopy) and Integrated Quantitative Biology Initiative (for nanoCT). Support from

the Canadian Institutes of Health Research (CIHR) is gratefully acknowledged.

➢ Acknowledgements

➢ Conclusion

• Input pressures applied to ear canal

(multiple cycles)

• Pressure steps of 500 Pa for duration

of 5 seconds per step

➢ Results: Effect of pressurization

Extract bulla

Remove ear-canal pressure

Immobilize stapes using adhesive

Immobilize malleus and incus using adhesive

Seal and pressurize ear canal

Make hole in bulla for incudomallear joint (IMJ)

Make hole in bulla for ISJ

• We developed a dissection method which

preserves the geometry of the joint under

different static pressures while preparing the

sample for imaging

• Stapes, incus and malleus are attached

to the walls of the bulla using All-

Purpose Instant Krazy Glue.

• Changes of the joint are captured

using a stereoscopic microscope

while ear canal is being pressurized.

Stereo microscope X-ray nanoCT Light-sheet microscope

• X-ray nanoCT of a broken

ISJ

• Light-sheet scan of ISJ gap

• 3-D viewing of broken ISJ using different imaging modalities

• After a few full pressure cycles, a sudden change in the ISJ gap was observed in

three animals at high negative pressures (−2000 Pa and −2500 Pa) in which the

gap length had a very high elongation.

• After the sudden change, behaviour of the joint was significantly altered in

subsequent cycles.

• Continuing the pressurization after the sudden change caused the appearance of an

air bubble in the ISJ gap when changing the pressure from −2000 Pa to −2500 Pa.

Comparison of effects

of geometry and

material properties

−2000 Pa −2500 Pa

➢ References

Funnell, W. R. J., Siah, T. H., McKee, M. D., Daniel, S. J., & Decraemer, W. F. (2005): On the coupling between the incus and the

stapes in the cat. Journal of the Association for Research in Otolaryngology, 6(1), 9-18.

Karmody, C. S., Northrop, C. C., & Levine, S. R. (2009): The incudostapedial articulation: new concepts. Otology &

Neurotology, 30(7), 990-997.

Buytaert, J. A., Salih, W. H., Dierick, M., Jacobs, P., & Dirckx, J. J. (2011): Realistic 3D computer model of the gerbil middle ear,

featuring accurate morphology of bone and soft tissue structures. Journal of the Association for Research in Otolaryngology, 12(6),

681-696.

Decraemer, W. F., Maas, S. A., & Funnell, W. R. J. (2015): Finite-element modelling of the synovial fluid and contact in the

incudostapedial joint. 7th International Symposium on Middle-Ear Mechanics in Research and Otology, Aalborg (Denmark).

Soleimani, M., & Funnell, W. R. J. (2018a). Mechanical behaviour of short membranous liquid-filled cylinders under axial

loadings. International Journal of Mechanical Sciences, 145, 138-144.

Soleimani, M., Funnell, W. R. J., & Decraemer, W. F. (2018b): A new finite-element model of the incudostapedial joint. AIP Conf.

Proc. 1965: 110003

Capsule curvature

Capsule Veronda-Westmann

elastic constant C2

Human ISJ model of Soleimani

et al. (ms. in preparation)

−2000 Pa

1st to 4th cycle

−2000 Pa

4th cycle

Sudden elongation at change of

−1.5 kPa to −2 kPa

Right ear of gerbil 3

−2500 Pa

1st to 3rd cycle

−2500 Pa

3rd cycle

Sudden elongation at change of

−2 kPa to −2.5 kPa

Right ear of gerbil 2