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Updated: 22 hours 58 min ago

Thanks for the comment. Here,

Sun, 2018-12-16 07:58

In reply to in the figure you report G, but I guess this is really Delta_G

Thanks for the comment. Here, we applied cyclic loading with Gmax= G and Gmin=0, therefore the G in this figure is delta G as you mentioned. People usually used G instead of K in highly stretchable materials such as elastomers [1-3] and hydrogels [4]. I attached one representative curve of crack extension versus tearing energy for elastomers as below for reference [1]. In this work, we kept Gmin=0 and didn’t vary the load ratio of R=Gmax/Gmin. People did show effect of Gmin in rubbers that exhibit strain-crystallization [5]. It would be interesting to investigate the effect of load ratio on anti-fatigue-fracture properties of nano-crystalline hydrogels in future works. Thanks for the suggestion!

 

[1] A. Gent, P. Lindley, A. J. J. o. A. P. S. Thomas, Cut growth and fatigue of rubbers. I. The relationship between cut growth and fatigue. 8, 455-466 (1964).

[2] G. Lake, P. J. J. o. A. P. S. Lindley, The mechanical fatigue limit for rubber. 9, 1233-1251 (1965).

[3] G. Lake, P. J. J. o. A. P. S. Lindley, Cut growth and fatigue of rubbers. II. Experiments on a noncrystallizing rubber. 8, 707-721 (1964).

[4] R. Bai, Q. Yang, J. Tang, X. P. Morelle, J. Vlassak, Z. J. E. M. L. Suo, Fatigue fracture of tough hydrogels. 15, 91-96 (2017).

[5] W. Mars, A. J. R. C. Fatemi, Technology, Factors that affect the fatigue life of rubber: a literature survey. 77, 391-412 (2004).

in the figure you report G, but I guess this is really Delta_G

Sun, 2018-12-16 06:46

In reply to Anti-fatigue-fracture hydrogels

In any case, this is not the same as Delta_K.   Obviously G==K^2, so when you make delta_G=Gmax-Gmin this is not the same as delta_K^2.   The troubles start when you want to examine the effect of mean values.  Have you tried different load ratios R?

Hi Roy,

Sat, 2018-12-15 22:00

In reply to fracture toughness is defined on a sharp crack

Hi Roy,

Thanks for your comment. In our experiment, a pre-crack was cut using a razor blade with tip radius of around 200 um, simulating the sharp crack tip at undeformed state. The image shown here is at deformed state. I attached the schematic as below showing for the single-notch test specimen with a sharp pre-cut at undeformed state [1]. 

[1] A. Gent, et al. Cut growth and fatigue of rubbers. I. The relationship between cut growth and fatigue. 8, 455-466 (1964)

Hi Ruobing,

Sat, 2018-12-15 21:20

In reply to Very nice work

Hi Ruobing,

Thanks! Also congratulations on your nice review on fatigue of hydrogels! The set of papers on fatigue-fracture in your group truly inspire people and motivate people to develop anti-fatigue-fracture hydrogels for applications which require long-term robustness.

Best,

Shaoting

fracture toughness is defined on a sharp crack

Sat, 2018-12-15 17:59

In reply to Anti-fatigue-fracture hydrogels

Nice work but I find your photos showed a notch, not a sharp tip. 

Very nice work

Sat, 2018-12-15 15:20

In reply to Anti-fatigue-fracture hydrogels

Dear Shaoting,

Congratulations on this very nice work. Look forward to more development in the field of fatigue of hydrogels!

 

Sincerely,

Ruobing

Photodetachable adhesion

Fri, 2018-12-14 10:12

In reply to Journal Club for December 2018: Bonding hydrophilic and hydrophobic soft materials for functional soft devices

 

 

Dear Qihan,

 

Thank you very much for initiating the discussion on this appealing topic. I really learned a lot from your review and the comments posted by all the people. Here, I would like to share our newly published work and learn from your feedback.

 

Derived from Jiawei’s topological adhesion [1], we proposed an approach to achieve both strong adhesion and easy detachment between hydrogels and other kinds of substrates (e.g. tissue, elastomer, inorganic solid) [2]. The stitching network was functionalized to undergo a gel-sol transition under UV radiation. Therefore, the strong adhesion can be easily removed by exposure to UV light.  

 

We found the adhesion performance was strongly affected by the gelling and dissolving behavior (by rheology study) of the stitching polymer.

 

The stimuli responsive bonds would enable stimuli responsive adhesion. We are wondering the application of these stimuli responsive adhesions? And what kinds of chemistries are suitable for functionalizing the stitching polymer (it need to be sample, work under mild condition, and provide proper gelation time and dissolution time)?

 

[1] J. W. Yang, R. B. Bai, Z. G. Suo, "Topological adhesion of wet materials", Advanced Materials. 2018, 30, 1800671.

 

[2] Y. Gao, K. Wu, Z. G. Suo, “Photodetachable adhesion”, Advanced Materials. 2018, 1806948

 

Adhesion method applied for coating

Fri, 2018-12-14 03:23

In reply to Journal Club for December 2018: Bonding hydrophilic and hydrophobic soft materials for functional soft devices

Dear Qihan,

There're solutions for hydrogels to get a strong adhesion with hydrophobic materials[1-2], and effective coatings were realized[3]. And topological adhesion without modification has also achieved[4]. Based on these adhesion methods, hydrogel coating for medical steel, ceramic, catheter have developed. One problem may get attention. The silane method and benzophenone method all need a special group to get the combination for hydrophilic and hydrophobic coating. However, there is no vinyl for some hydrogel or hydrophilic materials. Is it possible to get a hydrophobic coating for hydrogel bulk without modification?

[1] Hyunwoo Yuk, Teng Zhang, German Alberto Parada, Xinyue Liu, Xuanhe Zhao*, Skin-inspired hydrogel-elastomer hybrids with robust interfaces and functional microstructures, Nature Communications 7, 12028 (2016)

[2] Liu, Q., et al., Bonding dissimilar polymer networks in various manufacturing processes. Nature communications, 2018. 9(1): p. 846.

[3]Paul Le Floch, Xi Yao, Qihan Liu, Zhengjing Wang, Guodong Nian, Yu Sun, Li Jia, and Zhigang Suo. 2017. “Wearable and Washable Conductors for Active Textiles.” ACS Applied Materials and Interfaces.

 

[4] Yang, Jiawei, Ruobing Bai, and Zhigang Suo. "Topological adhesion of wet materials." Advanced Materials 30.25 (2018): 1800671.

Hydrophilic-hydrophobic materials

Thu, 2018-12-13 22:38

In reply to Journal Club for December 2018: Bonding hydrophilic and hydrophobic soft materials for functional soft devices

Though the hydrogel is most used at present, the strategy for the combination of hydrophilic and hydrophobic structures can also be applied for other materials like ionogel. 

[1]Hang Yang, Chenghai Li, Jingda Tang and Zhigang Suo. Soft coating for ionogel. Unpublished.

If we target existing

Wed, 2018-12-12 15:01

In reply to Hi Qihan,

If we target existing functional group on the tissue surface then we don't need to modify the tissue.

Hi Qihan,

Wed, 2018-12-12 01:15

In reply to Journal Club for December 2018: Bonding hydrophilic and hydrophobic soft materials for functional soft devices

Hi Qihan,

Thank you for your quick response. The explanation for the poor adhesion of swollen hydrogels is quite reasonable.  Bulk modification is a good suggestion for the bonding of hydrogels and elastomers. But for hydrogels and tissues, is it still applicable, considering tissue can hardly be modified? 

Hi Jingda,

Tue, 2018-12-11 23:24

In reply to Hydrogel adhesive for medical use

Hi Jingda,

Nice questions. For your questions (2) swelling is a problem because you are changing the surface chemistry by diluting the polymer chain density to an extremely low level. There's not much to grab on the surface to form a bonding anymore. In theory, the bulk modification strategy should be insensitive to swelling because the diffusion of the coupling agent is unaffected by the swelling. For the current version with silane coupling agent, you have to swell the hydrogel in controled pH buffer to control the kinetics. I would look for other bulk modification chemistry if fully swollen hydrogel is concerned.

For your questions (3), Chenghai was asking the same question. We can ask Zhijian see if he has some insight in Chemistry.

About delicious glues

Tue, 2018-12-11 23:09

In reply to Hi Jiawei

Actually I have played with this kind of glue a lot. We use dankey skin gelatin (阿胶) to glue reed membrane (笛膜) on bamboo flute to get the unique Chinese flute sound. We will use the humidity of our breath to soften the glue and adjust the tension of the membrane before we start playing. And Chinese people certainly have talent with delicious glues. As another example, Chinese caligraphy and painting are framed (装裱) by starch solution(浆糊). I have a vague memory that the Great Wall is built by sticky-rice based glue since we didn't have cement. These glues function in a similar fashion to the modern resin glues e.g. epoxy or acrylic glue. Essentialy, the surface must be porous for the polymer to penetrate. As the glue solidifies, it forms interlocking structure that locks to parts together. However, such macroscopic interlocking mechanism won't work for soft materials, as I mentioned in the main post, because the interlocking structure can readily detach by deformation. For interlocking mechanism to work for soft materials, we need to go down to the mesh level. And that is topological adhesion.

Hydrogel adhesive for medical use

Tue, 2018-12-11 21:24

In reply to Journal Club for December 2018: Bonding hydrophilic and hydrophobic soft materials for functional soft devices

Dear Qihan,

Thank you for your clear classification of the adhesion between hydrophilic and hydrophobic soft materials. When we introduced the progress in this field to the hospital doctors in Xi'an, they were impressed and very interested in using it for hemostasis. We notice that there are several issues not solved in this area:

(1) Biodegradability. Once the hydrogel adhesive is applied, it is better to be dissovlved in vivo to prevent the second surgery. To solve this problem, we proposed a strategy to bond tough biodegradable hydrogels to tissues. The adhesion energy can reach the order of 1000J/m2 and the degradation speed of the hydrogel can be tuned on demand [1].

(2) Poor adhesion of fully swollen hydrogels. It is a common practice to fully swell the as-prepared hydrogel to remove the unreacted chemicals. However, we surprisely found that the fully swollen hydrogels cannot be bonded to other materials, such as the two-step synthesized alginate/PAAm. Not only gels, even fully swollen VHB (in acetone) is not sticky any more. What are the possible reasons? Will the surface properties of hydrogels influence their adhesion properties?

(3) Instant bonding. For the surgical hemostasis, the time window for doctor's operation is only several minutes. It is important to realize good adhesion in this short time. Jianyu and Jiawei showed a succesful strategy for bonding between gels and tissues based on topological adhesion. Is there any other approach to achieve this?  

New questions call for new solutions. I wish to hear your opinion. 

[1] Hang Yang, Chenghai Li, Jingda Tang and Zhigang Suo. Biodegradable adhesive hydrogel. Unpublished.

 Hi, Zhijian. Considering the

Tue, 2018-12-11 20:30

In reply to That is really interesting!

 Hi, Zhijian. Considering the cyanoacrylate glue, it do not need special chemical group neither and can combine two bulks together. Especially for hydrogel, we can directly see the infiltration and entanglement when the cyanoacrylate work. That’s similar with Jiawei’s method. I think it’s a general method to realize adhesion (reversible or not) for hydrogels by choosing proper bridge polymers. And there are many kinds of reversible or dynamic bond you have mentioned. 

ok, but I don't see where the error comes from

Tue, 2018-12-11 04:32

In reply to Is Tribology Approaching Its Golden Age? Grand Challenges in Engineering Education and Tribological Research

In your equality, there is d(mu)/dV, and the rest is certainly positive.  So where is the error coming from? It sounds you should rewrite the entire paragraph (if not more....)

 

thanks, m

Dear Mike,

Mon, 2018-12-10 17:32

In reply to Is Tribology Approaching Its Golden Age? Grand Challenges in Engineering Education and Tribological Research

Dear Mike,

Thank you for your interest in our book!... It looks like you discovered a mistake (thank you), when the stability criterion is satisfied, the system is STABLE, not unstable. When d mu / d V > 0 (friction increases with velocity), it is stable!

I don't think we reviewed Soviet-time ideas on entropy. As far as non-equilibrium thermodynamics, some are from Nobel prize winning Lars Onsager and Ilya Prigogine (who lived far away from the USSR!) :) , others may be from the last two decades. I hope they will lead somewhere.

Thanks,

Michael 

 

 

Self-healing mechanics

Mon, 2018-12-10 14:51

In reply to Stimuli-responsive adhesion

Dear Zhigang, 

I would like to echo your comments regarding self-healing materials with dynamic bonds. Though MD simulations for self-healing materials have been carried out by some researchers, surprisingly, mechanics models to explain the interfacial self-healing remain largely unexplored. In recent years, my group makes several attempts. Hope they can be some references for this journal club: 

1. General dynamic bonds: 

Kunhao Yu, An Xin, Qiming Wang, Mechanics of self-healing polymer networks crosslinked by dynamic bonds, Journal of the Mechanics and Physics of Solids, 121, 409-431, 2018. 

2. Nanoparticle crosslinkers:

Qiming Wang, Zheming Gao, Kunhao Yu, Interfacial Self-healing of Nanocomposite Hydrogels: Theory and Experiment, Journal of the Mechanics and Physics of Solids, 109, 288-306, 2017.

3. Light-induced self-healing:

Kunhao Yu, An Xin, Qiming Wang, Mechanics of Light-Activated Self-Healing Polymer Networks, Journal of the Mechanics and Physics of Solids, 124, 643-662, 2019. 

4. Electrically-induced bonding:

An Xin, Runrun Zhang, Kunhao Yu, Qiming Wang, Mechanics of Electrophoresis-Induced Reversible Hydrogel Adhesion, Journal of the Mechanics and Physics of Solids, accepted, 2018.

Best regards,

Qiming

Jiawei, thanks. For

Mon, 2018-12-10 12:12

In reply to Very nice and deep work! I am

Jiawei, thanks. For neohookean solid, the neighboring fingers suppress with each other and eventually stabilize when the stretch is large. If you further stretch the material, hierachical instabilities initiate and develop in the original fingers. I attached one image showing hierachical instabilities under extremely large deformation. For stiffening materials, the fingerings tend to more stabilize.

You will see a very smooth

Sun, 2018-12-09 22:50

In reply to That is really interesting!

You will see a very smooth crack goes through the entire hydrogel sample.

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