iMechanica - Micro-scale compression testing for hydrogel microspheres between two rigid plates - Comments

alginate beads

Aaron Goh — Tue, 20 May 2008 13:49:10 -0400

I would have guessed that a simple hyperelastic + viscoelastic model would be ok?

By the way, I am rather curious. Have you tried to eat these beads? Do you know how they behave in the mouth? Are they 'sticky'?

Three more questions

Xuanhe Zhao — Fri, 09 May 2008 15:50:00 -0400

Dear Keekyoung

I would like to ask three more questions:

1. How long does the gel ball take to recover the initial state?

2. What type of covalent crosslink are you using(eg AAD, PEG et al)?

3. Would the mechanical behavior of the gel ball be a lot of difference if you did not use chitosan coating?

thank you.

Our constitutive model

Wei Hong — Mon, 28 Apr 2008 15:11:18 -0400

Hi Keekyoung,

The material model we used to build the FEM code is described in our recent JMPS paper. Lack of experimental data, we basically extends the Flory-Huggins Model to an arbitrary deformation state. If you are interested, I am happy to run a FEM simulation of the compression of a gel sphere and show you the result. But again, the current code is only for static response. In your experiments, the Force-displacement relation is rate dependent, the result I can give you corresponds to the slowest limit of your experiments. Let me know if you are interested. And also, do you know the relative water concentration at the begining?

Wei

FEM code

Keekyoung Kim — Mon, 28 Apr 2008 11:36:04 -0400

Hi Wei and Xuanhe,

Wei:

Currently I have force-deformation data but I could not find an appropriate constitutive equation-the relationship between force and deformation to descrive the exprimental configuration such as a hydrogel sphere compressed by two rigid plate-to extract Young' modulus from the experimental data. Could you tell me there is any force-deformation euqation you derived to build FEM code?

Xuanhe:

The time-dependently means the microsphere did not recover its initial shap immediately when I unload the compressive force. The shape was recovered slowly due to viscoelastic hysteresis.

Keekyoung

Hi Keekyoung, What do you

Xuanhe Zhao — Sat, 26 Apr 2008 20:13:13 -0400

Hi Keekyoung,

What do you mean by "the microspheres recovered its initial shape time-dependently"? Can you explain this point in more details? Thank you.

Our finite-element code

Wei Hong — Sat, 26 Apr 2008 12:43:56 -0400

Hi Keekyoung,

The FEM code we have now is for hydrogel is for the equilibrium or quasi-static deformation of a gel. It might be able to tell you the final deformation of your gel spheres, but not the time-dependent process, at least for now.

Wei

Alginate-Chitosan Microspheres

Keekyoung Kim — Fri, 25 Apr 2008 21:00:14 -0400

Hi Prof. Suo,

Thank you for your interest about my experiment. The hydrogel microspheres which I am using are alginate microspheres with chitosan coating to reduce pore sizes and encapsulate drugs. Yes, it is covalently cross-linked natural polymeric hydrogels. When I unloaded the force sensor, the microspheres recovered its initial shape time-dependently. The size is about 20 um in diameter. I would like to discuss about your methods a little bit more detail.

Large deformation of hydrogels

Zhigang Suo — Fri, 25 Apr 2008 13:36:45 -0400

My group is developing methods to compute large deformation due to swelling and mechanical loads. It might be interesting for us to apply our methods to your experiment. What hydrogles are you working with? Are the polymers covalently cross-linked? When you unload, does the gel recover its initial shape after some time?

hydrogel models

MichelleLOyen — Fri, 25 Apr 2008 04:33:30 -0400

I'd suggest having a look at a few other pages here on iMechanica concerning mechanics of hydrogels and also concerning poroelasticity , which might be a better approach to consider than a standard viscoelastic response. Good luck! It's a very exciting research area.

Micro-scale compression testing for hydrogel microspheres between two rigid plates

Keekyoung Kim — Thu, 24 Apr 2008 18:57:15 -0400

I am a last year Ph.D student at University of Toronto. During my study, I developed MEMS force sensor-based micro-scale compression testing for micrometer-sized spherical biomaterials. I applied this system for mechanical properties characterization of polymeric hydrogel microsphere for drug delivery.

I almost finished exprimental data acquisition and am trying to calculate mechanical properties such as Young's modulus and viscoelastic parameters using elastic and viscoelastic mechanics model. But I don't know which is the most appropriate mechanics model for describing this experimental situation. Could anybody please help me to find any elastic and viscoelastic mechanics model for the polymeric hydrogel microsphere in wet state compressed by two rigid plates. And I would like to verify this experiment with FEM analysis using ANSYS. Does anybody know how to analysis this problem using FEM?

Thank you for your kind help in advance.