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Updated: 5 hours 28 min ago

Pig skin protein as stitching polymer

Sat, 2018-12-08 21:09

In reply to Topological adhesion for wood

Dear Shengqiao,

Thank you for raising up such interesting glue! I have two small question. 1, Is the pig skin glue you mentioned a gelatin? Because I remember when I cook pig feet, the soup becomes jelly when it is cold, but when I put it on hot rice, it quickly melt. 2, You say it is topological adhesion for wood, does it mean the pig skin proten can interpenetrate with the cellulose of the wood?

I am very interested on

Sat, 2018-12-08 21:03

In reply to Dynamic covalent bonds vs. noncovalent bonds

I am very interested on dynamic covalent bond, and I realize that more and more such dynamic bonds are used in hydrogel. In your opinion, is design and synthesis of dynamic bonds in hydrogel more challenging in practice compared to noncovalent bonds? 

If we want huge bulk dissipation, is dynamic bonds better than noncovalent bonds?

For the last comment, my

Sat, 2018-12-08 20:51

In reply to Hi Zhijian,

For the last comment, my topological adhesion paper has one data shows that the measured adhesion energy is even higher than the fracture energy of the hydrogel.

Very nice and deep work! I am

Sat, 2018-12-08 20:47

In reply to Mechanics in designing soft and tough adhesion

Very nice and deep work! I am wondering how two figures interact with each other if you stretch the material really large.

This is interesting thought.

Sat, 2018-12-08 20:40

In reply to Hi Hyunwoo,

This is interesting thought. But the equation itself does not tell you how strong the weak bonds are that can elicit the bulk hysteresis. It is intriguing to study how the strength of interfacial bonds influence the bulk dissiaption.

Hi Qihan,

Sat, 2018-12-08 20:30

In reply to Hi Jiawei,

Hi Qihan,

Yes. The topological adhesion can be applicable for any polymer network, so long as the chain can go into both networks and make stitch.

Molecular stitching is one version, we also have another version, called molecular staple. Can you think anything macroscopic version of fastening two objects that can be created in the molecular level?

The last comment is quite interesting, currently I am also exploring some properties.

Dynamic covalent bonds vs. noncovalent bonds

Sat, 2018-12-08 17:14

In reply to Dynamic covalent bonds vs. noncovalent bonds

Thanks, Zhigang. Yes. The roles of dynamic covalent bonds and noncovalent bonds are very similar, breaking and reforming. In my opinion, the difference may be bond strength. The covalent bonds are stronger than the non-covalent bonds, which seems important for the tough adhesion in bulk and surface treatment approach. For the topological design, I am not sure whether strong bond strength is critically important or not. Some understanding in these approaches can help the design of tough adhesives.

The disadvantage of dynamic covalent bond may be the side reaction. Sometimes they can not be totally reversible. 

Dynamic covalent bonds vs. noncovalent bonds

Sat, 2018-12-08 16:23

In reply to Dear Zhigang,

Thank you Zhijian.  So far as the mechanical behavior of hydrogels is concerned, dynamic covalent bonds and noncovalent bonds serve the same attributes:  they can break and reform. These attributes lead to, respectively, toughness and heal.

The similarity between dynamic covalent bonds and noncovalent bonds is clearly articulated in a review of self-healing hydrogels.  The devil is in details.  Table 1 of the review lists the condition of heal.  In our Ca-alginate-polyacrylamide hydrogel, heal happens at elevated temperatures (e.g., 80C).  People are cooked by then. Many other gels now can heal at room temperature, in minutes or faster.

From your perspective, do dynamic covalent bonds bring any advantage over noncovalent bonds?  Perhaps they are just different chemistries, and have different attributes unrelated to mechanical behavior.  I’d love to hear your view.

Thermoreversible adhesion, thermodetachable topological adhesion

Sat, 2018-12-08 16:00

In reply to Topological adhesion for wood

Excellent point.  We've playing with animal glues.  

Topological adhesion for wood

Sat, 2018-12-08 15:51

In reply to Topological adhesion

In ancient China (in particular Ming and Qing Dynasty), people made wood furniture by using glue. The glue is a bio-protein (from for example skin of pigs), which is a liquid at high temperature and gelled at low temperature. The wood furniture can be very study at room temperature. Nowadays, when an experienced craftsman tries to repair those anique, they simply spray boiled water onto the furniture and then can easily dissemble them (the bio-gel turns to liquid state)- (on-demand detachment). 


Topological adhesion

Sat, 2018-12-08 15:02

In reply to Stimuli-responsive adhesion

Hi Jiawei and Zhigang,

I am very interested in the topological ahesion done by you. In the lab, we actually often use the mechaism implicitly. When we try to glue two elastomer, one way we often adopt is to partially cure both elastomers, put them in contact with each other and let the curring process finish to enable the bonding. For this case, reversible bonding and detachment cannot be achieved, as demonstrated in your work.   


An exciting field

Sat, 2018-12-08 14:55

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

Dear Qihan, 

Thanks for the timely review and insightful elaborations. Most of us have witnessed the rapid advancement in the field of chemo-mechanics of adhesion in recent years. Though I have noticed most of work cited here, your summary and the incurred discussions indeed make the development of the field much clearer to me. 

In chemistry field, recently, there have also been some signficant progress in the adhesion field. For example, the work done by Messersmith group on Mussel inpired adhesion, which must be known to many of you.  

I imagine deeper interactions between mechanics and chemistry may lead to new opportunities in the field. 



Dear Zhigang,

Sat, 2018-12-08 13:15

In reply to Stimuli-responsive adhesion

Dear Zhigang,

Thanks for your comments. The topological adhesion is really a nice design without the need for treatment of raw materials. This strategy can also be easily combined with reversible polymer networks. 

The dynamic covalent bond is a newly emerging field. Up to now, most of the dynamic covalent bonds are triggered by high temperature in the presence of catalysts, which limits their applications in certain fields. Only those which can be triggered by light, including the disulfide bonds and reversible addition fragmentation transfer reagents, have been reported in designing self-healing hydrogels. 

More and more dynamic covalent bonds, which can be triggered in mild conditions, may be developed in the future and applied in tough adhesion.

Stimuli-responsive adhesion

Sat, 2018-12-08 08:03

In reply to Dear Qihan,

Dear Zhijian,

Thank you very much to bringing your enormous expertise in chemistry to this discussion.  This discussion reminds me of a previous iMechanica discussion hosted by you and Shengqiang, where you discussed extensively on dynamic covalent bonds.  These reversible covalent bonds, along with so many noncovalent bonds, have transformed the development of polymers and polymer gels.  A particularly lively field is self-healing materials.  

It is conceivable that the same dynamic bonds will transform the development of adhesion.  Here we can use dynamic bonds to add functions to adhesion. An example is topological adhesion.  Here a trigger (a change in pH) can cause both strong adhesion and on-demand detachment.  The strong adhesion requires no functional groups in the two adherends. A third species of polymers stitches the preexisting networks of the two adherends.  That is, the stitching polymers act like a molecular suture. As noted in the paper, one can imagine other triggers (ions, molecules, temperature, light). The possibilities are wide open.    

May the new development of adhesion adhere mechanics and chemistry in new ways.


Fri, 2018-12-07 04:02

In reply to Congratulations

Dear Zhigang,

Thank you! You are absolutely right. Moreover, mechanics is a must when soft materials are considered in any application: large deformation is what makes materials "soft". For hard materials, deformation and, consequently, mechanics might be a secondary issue.


Thu, 2018-12-06 18:54

In reply to Mechanics of Soft Materials: Editorial

Congratulations on the launch of the new journal.  May the new journal become a place where mechanics meets chemistry, biology, and life itself.

An interesting corollary

Thu, 2018-12-06 16:32

In reply to Stress of a spatially uniform dislocation density field

It is classically known in continuum mechanics, stated first by the brothers Cosserat [Shield, 1973], that if a second order tensor field on a simply connected domain is at most a curl-free field of rotations, then the field is necessarily constant on the domain. A corollary of the work above is that, at least in dimension 2, this classical result is in fact a special case of a more general situation where the curl of the given rotation field is only known to be at most a constant.

The classical result can be directly read off from the Rigidity Estimate of Friesecke, James, and Muller (and of course the Generalized Rigidity estimate of Muller, Scardia, Zeppieri (MSZ)). Reading off the present corollary from the Generalized Rigidity Estimate of MSZ would seem to require a little work (Irene Fonseca has shown me such a proof provided the constant in the MSZ Generalized Rigidity Estimate can be shown not to depend on the domain).

another example

Wed, 2018-12-05 14:03

In reply to Stress-life vs strain life approaches in ?

Smooth specimen, no surface finish, no notch factor

Stress life

Nf = 683000

Strain life

Nf = 670851 cycles

This is fine.


But when I add surface finish effect alone, there is a dramatic effect in stress-life, life drops by a factor 185, while strain life by a factor 5.6 only.


Stress life

Ksf=.5, Kt = 1

Analysis Results

Nf = 3700


  • Smax or emax = 300 MPa
  • Smin or emin = -300 MPa
  • Material Type = steel
  • Material Name = Steel 1045, Annealed, BHN=225
  • Su = 752 MPa
  • E = 207000 MPa
  • Sf′ = 867 MPa
  • b = -0.079
  • kSF = .5
  • Surface Finish Type = none
  • kL = 1
  • Loading Factor Type = none
  • ksize = 1
  • Kt = 1
  • Use Fatigue Notch Factor = No
  • Mean Stress Definition = None


Strain life

Ksf=.5, Kt = 1

Analysis Results

Nf = 120962 cycles


  • Smax or emax = 300 MPa
  • Smin or emin = -300 MPa
  • Material Type = steel
  • Material Name = Steel 1045, Annealed, BHN=225
  • σf′ = 916 MPa
  • b = -0.079
  • εf′ = 0.486
  • c = -0.52
  • E = 207000 MPa
  • K′ = 1022 MPa
  • n′ = 0.152
  • Su = 752 MPa
  • kSF = .5
  • Surface Finish Type = none
  • Kt = 1
  • Use Fatigue Notch Factor = No


Excellent perspective on the mechanics of adhesion

Wed, 2018-12-05 08:01

In reply to Multiscale mechanics of tough adhesion of soft materials

Teng:  Thank you for these valuable comments.  The papers cited are very helpful.  Rong Long's August 2017 iMech jClub discussion gave additional discussion of fracture mechanics of soft materials.  The development of new methods of adhesion goes hand in hand with the development of deeper understanding of mechanics.  Soft materials bring hard problems.  Life in mechanics and materials has not been dull.  

ratchetting vs other approaches

Wed, 2018-12-05 06:00

In reply to Ratcheting

Ajay Kapoor did a lot of work along these lines with with Johnson, following Allan Bower who did his phd with Johnson.  The papers I have written are mostly comparing with other approaches to the problem, which may not include detailed investigations of ratchetting.  I also shown that the Dang Van criterion, widely used in France also by railways people, is not remotely useful for the case of RCF where there is very high hydrostatic compression.

A comparison of multiaxial fatigue criteria as applied to rolling contact fatigue


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