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Hydrogel materials - soft contact lenses

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Posts: 3
Topic starter
(@jonak)
New Member
Joined: 15 years ago

Hi,

I am modelling soft contact lenses and am currently using an isotropic linear elastic material model in Marc-Mentat. When modelling the inside out turning (flipping) of a soft contact lens I get very good agreement of shapes with laboratory measurements. However, the material model is unable to capture effects of material modulus on the inverted lens shape, i.e. whichever modulus I am using the inverted lens shape doesnt change at all. Does someone know why and has anyone got some experience with modelling hydrogel or silicone hydrogel materials?

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Posts: 3998
(@jorgen)
Member
Joined: 4 years ago

Since hydrogels typically have a very high water content their response can be more challenging than traditional engineering rubbers. The complexity of the model that is required will depend on how much of the micromechanical diffusion etc that you want to capture. A set of carefully obtained experimental data is also very useful.

I dont quite follow your description about the lense deformation, but I am not suprised that a simple linear elastic model does not work that well.

-Jorgen

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Posts: 3
Topic starter
(@jonak)
New Member
Joined: 15 years ago

thanks Jorgen,

actually, a linear elastic material doesnt perform too bad for my current modelling. The model I am currently working on is for lens inversion, i.e. flipping a soft contact lens inside out, say people dont recognise the proper direction and insert their contact lenses the wrong way around, I am simulating the inverted geometry in order to evaluate the optical and mechanical on eye performance. I dont really have much instrumentation available to measure viscoelastic and other properties but am still looking for a better material model for some other modelling I am doing, namely on eye behaviour of soft contact lenses. Are you, or is anyone else aware of any published model for hydrogels or silicone hydrogels?

Also, the fact that the inverted (flipped) geometry is always exactly the same, totally independent from elastic modulus, is that normal? sorry, but talking to an optometrist here 🙂

thanks

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Posts: 3998
(@jorgen)
Member
Joined: 4 years ago

There are plenty of publications about hydrogels. I think I have also read some publications about soft contact lenses. I dont recall the exact references though 🙁

I would think that the inverted shape should be slightly different, I dont know why you dont see that.

-Jorgen

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