Biomimetics, Micro-design, Arctium minus et al Hook and Velcro – A PhD and a Virtual Textbook on Biological Attachment Mechanisms and their Mimicking

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Paper 3 Background



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It is a strange to think that one can find a Biomimetic principle on demand.  This study, however, has found at least one in the consideration of its objective, to take all known studies of hooks and to compare them and others in order to define a new hook that is advantageous to design for a purpose that precludes all known uses so far, i.e. that is intended for a use that has not so far been defined.  However it is such that it can be assumed that all the new designs are going to be on the purpose/possibility frontier, namely in this case, micro design and the design of micron-ranged size-structures that do not altogether behave in a “normal” way under use.  Such as the tarsal hooks of an insect and their manner of sticking or adhering to a surface. It  is somewhat of a mystery yet but which can be considered and mimicked to find its own properties that reflect their sizes (the hooks).

It is through the design of these autonomous structures and their variants that microdesign such as those parts used by computer-aided medical devices are possible.  But it is a mystery yet in the scientific literature, how these marvels are designed such that it can be studied.  There are new ways of doing things that need chronicling so that their progress can be chartered and modified according to new discovery.

The title of the thesis proposal was “The Functional Ecology and Mechanical Properties of Hooks in Nature”.  This tells us that each hook must be studied as a part of a system, hence the mechanical properties will only be revealed once the hook has been brought into interaction with a substrate of some properties of its own. Attention is now drawn to the publication of a paper that is significant to this study, namely [1] that is recently published where in it is described how a process of electro-chemical deposition is used to draw the bead of the new substance, namely copper, to draw in the “cubic pixels” or voxels, that then make up the shape required or drawn, or in this case, scanned on a confocal microscope as executed in paper 2 of this research. [2]  This enables the process to continue, of evaluating the progress such that it can be concluded how to best design a hook made of copper at the size of 100 micron span say, manufacturing it in a macro fashion and predicting its behaviour in an absolute fashion.

Being considered here is a necessarily obscure manner of approaching the issue, to predict who or what will be the manner of making these structures and how the design will process the data of the new part such that it will behave in a fashion that will be predictable or not depending on the way it is fashioned or the material itself and its issues with solidarity and maintaining shape.  How to draw a free-body diagram of such a structure, for instance, would be quite specific and yet very different from predicted Newtonian behaviour.  There is a way to get all of the parts of the design into one sphere and that is to generate a curve that shows their behaviours under different variants, according to different criteria.  It is not going to be easy to explain the use of Dimensionless Groups to produce performance curves but these make the use of criteria that may come into the design such as Brownian motion or molarity of particles in self-assembly or electro-chemistry.  Each will affect the solution of the entropy of the system but will also preclude the discovery of any new criteria unless they are included in the symmetry of the equation that makes all the forces equal at any one state or stage.  Otherwise we will have movement and this is what we are trying to arrest with a probabilistic fastener.  In short, all forces must be balanced.

[3] describes the discovery of a shape/size-scaling effect while completing a study of long-shafted cellulose hooks started by Gorb [4].  The A. minus hook was found to be exceptionally strong, an affect answered by calculation as being an illustration of the hook’s propensity to be strong through either composition or shape and therefore span and fibre content.  This is of little importance since we are simply warned that there are these effects present in Nature.

There is however a consequence of our study which is that we have a selection of six long-shafted hooks of cellulose from which to choose and the most frequent and strongest, namely A. minus .was chosen, as per George de Mestral and his Velcro. It is then that we undertook to scan the hook under the confocal microscope together with two other samples noted for their frequent occurrence in British wildlife, namely the tarsi of the British common wasp and grasshopper  (Apis mellifera and Omocestus viridulus).  This led to the conclusion that we had the route to three evolutionary pathways plotted on our confocal microscope and preserved for further analysis or manipulation in the form of .tiff files. [2] Each is a permanent reusable fastener and yet each does equip its owner without the need for a sample to identify it and make it from i.e. they are without a pattern, possessing only a genetic code for growth and form.

Functional Ecology

When considering the system of the hook-shaped structure, going back to the Cambrian Era, one is struck by the fact that there is no apparent control system.  Natural Laws prevail.  The first hooks shapes appearing on the fossil record were of primitive cellulose and chitin.

When studying a biological specimen the prescribed ethos is to study it’s interaction within its system since it is the system that is of interest to a biologist and to a designer.  The entire system needs to be considered, of a frictional fastener such as the probabilistic (i.e. non-random) fastener which the hooks A.minus form, and how the fastener shall be designed is based upon the performance of these hooks and their substrates. In the case of the growth and formation of hook-shapes in Nature, their biochemistry will be of equal importance and must have been fundamental to the very first organisms that appeared with shapes of biomaterial.

It is possible to break up a system into discrete segments or sections and this enables the identification of bio-design indicators such as scaling effects that predict the alignment of microfibrils for instance or the percentage volume required of a matrix cavity in a gel.

A free-body diagram is such an example and is selected and constructed along subjective lines for the purposes of force analysis.  A free body diagram can enclose an entire system or can be used to analyse part thereof.

Botanical hook structures and bio-design indicators for a reusable, silent, probabilistic attachment mechanism

What we need to consider is that we have passed step one, the choice of a cellulose representative of a single hook fastener-type, exposed on the end of a shaft where behavior is more isolated from the base or surface from which it originates.  This led us to a discussion above.  There is then the choice of three, which has been presented [ ].  Now it must be established which of the three is most suitable for pre-production analysis and study and a cellulose single-hook has been chosen.  This is because

  1. It is a non-assembly.
  2. It is long and therefore accessible to the head of a 3-D printer for its overhang if necessary.

For this work there are special qualities that may be included in the design which may or may not increase the quality of the attachment such as the inclusion of setae-like protrusions from the shaft or hook itself.  These might ease adhesion.

So it is a conclusion of the previous research that we must produce a sample hook in .stl data file format that can be used as a basis or datum structure and that can morph into variations according to need and application.  It is then understood that all the variations will be available to research, as would be those of the other two samples which have yet to be deciphered onto Solidworks but it may not be deemed necessary in the light of [1] where direct control of the data transfer is allowed and thus the treatment of the structures under testing will be available in copper only which is a very conducive, malleable substance. From a point of view of application, what needs be considered is the requirements of application of the attachment and what bio-principle we can derive from this structural mimicry and that includes the obvious – a tactile manner of carrying a load up a direct incline of 90 degrees.  It also includes the obvious use of copper’s varying impedance under stress which is used in strain gauges and can now be used in the biomedical sensor field.

It is with this in mind that all thought of concluding with a 3-D representation of all three when they are quite readily available through the microscope’s own image-ware is not economical.  Instead, a single sample is included that is to scale and leads to the following development of the design for the purposes of manufacture and testing.  It is noted here that all the sundry tests have been carried out through the Solidworks software itself such as FEA but we do not know the true directions from which forces are applied when considering analysis of the hook.  A point load seems inappropriate as does a limited forcing being applied through the length of the shaft in sheer.  It should be under pressure throughout, not as it seems here, as the cross-stresses are prevalent throughout the real-life loading of the hook.

The point of using Solidworks, in spite of its problems with an analogous material is that it converses with a rapid prototyping device and produces a file in .stl format,  not it’s FEA capabilities which are vastly insufficient.



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