Smart Materials Solve Contradictions - Systematic Innovation

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situation where we have a mechanical stimulus and are looking to trigger a mechanical response. The reason for thinking about the world in this kind of stimulus-response manner is that it allows us to make a very simple and effective way to classify smart material solutions. Table 1 presents the results of arranging known smart materials in this way. Across the top of the table is a range of different kinds of response that a designer might wish to achieve. This is usually the place to start when looking at the table since it focuses on the outcome we are looking to achieve, and therefore the type of problem we are trying to solve. The ‘stimulus’ column down the left hand side of the table then prompts the user to think about what is changing (or what could be changed) in the system in order to trigger the desired response. The range of different classes of stimulus is intended to remind users that there are a number of possible options. In the wrist replacement problem, as in any situation where we are trying to create an ‘ideal’ solution, the idea is to make use of a stimulus that is already present in the system. What the list reminds us, is that if there is no existing stimulus, there may be things we could add to the system. Table 1:List of known ‘intelligent’ or ‘smart’ resources: response→ electrical magnetic optical thermal mechanical chemical ↓stimulus electrical magnetoelectronics, spinelectronics, spintronics electrochromic, electroluminescent, electro-optic, piezo-chromic, Kerr Effect, thermoelectric (Peltier) piezo-electric, electrostrictive electrorheological electro-kinetic electrolysis, electro-chemical, bio-electric, electro-migration magnetic optical thermal mechanical chemical magnetoelectronics, spin-electronics, spintronics Hall Effect photoconductive thermo-electric, superconductivity, Radiometer Effect pyro-electric piezo-electric, electrostrictive opto-magnetic Curie point rheopexic, auxetic, shearthinning, dilatants, non- Newtonian, pseudoplastic magnetochemical Pockel Effect magneto-optic, piezo-chromic thermochromic, thermoluminescent magnetostrictive mechanochromic, rheo-chromic colour-change, litmus, luminescence exo-thermic endothermic optical bistability photothermic optomechanical photoacoustic shapememory magnetothermal magnetostrictive, magnetorheological nuclear-magneticresonance, magneto-chemical photo-chemical, photosynthesis, photo-catalyst catalysis The best way to think of the table is as a list of keywords that can be used to instigate and guide a more detailed Internet or patent database search to find actual solutions. In the wrist replacement case, the box at the intersection between desired mechanical response and input mechanical stimulus indicates that auxetic materials are already an established solution in some applications. All of the entries in the Table – which we don’t claim to be comprehensive at this point in time, merely ‘a hopefully ‘useful start’ – comprise materials or materials systems where the kind of non-linear ‘phasechange’ behaviour illustrated in Figure 4 has been achieved. 4.0 Another Example Figure 5 illustrates an example of a rather more simple use of one of the smart materials identified in the table. The picture illustrates a ‘self-timing’ egg. The incorporated smart material solves a common problem with boiled eggs that we all like our eggs cooked a certain way, but we often get a result we weren’t expecting. The reason we get our eggs cooked incorrectly more often than not is that we all cook our eggs using an ‘optimization’ rather than ‘ideal’ mindset. That you probably don’t recognise this fact is a good indication of how difficult and insidious the optimizationversus-ideal shift can be.
Applying a bit of thermochromic ink to an egg-shell on the other hand merely needs the connection between the solution and a real problem to be made. If the designer gets the self-timing egg solution wrong, the consequence for the customer is an over-cooked egg. The joint designer, on the other hand put simply has the responsibility for the quality of a patient’s life sitting on his or her shoulders. Figure 5: ‘Self-Timing’ Egg We have all of us thought about the egg problem as an optimization problem because we all know how long we like our eggs cooked for. Alas, we have all remembered one (optimized) number (‘a four minute egg’), when of course, no two eggs are the same. What the self-timing egg solution does is effectively says, wouldn’t it be nice if my specific egg in my specific pan ‘tells me’ how cooked it is. The desired response, thinking to Table 1 is ‘tells me’. The table presents a number of possibilities here. Most likely the simplest of those possibilities, and certainly the choice made by the owners of the Figure 5 solution, is optical’. The next question, then, is what are the available stimuli that might trigger the desired response. Again, as with the wrist replacement problem, we need to look at what is changing in the system. Again as far as the owners of the solution were concerned, the simplest and most obvious change is in the temperature of the egg. There is a rather splendid quotation in John Naisbitt’s latest book (Reference 5), ‘don’t get so far ahead of the parade that no-one knows you’re in the parade anymore’. This quote gets right to the heart of the scientist’s dilemma in the world of smart materials. If the basic patent on a platform material technology protect your IP for 17 years (there are various tricks and strategies that can be applied to extend this period, but, for argument’s sake we will stay with this number since it doesn’t significantly alter the form or extent of the dilemma). The moment patents are filed, the clock is ticking in terms of commercialising and achieving a return on the investment that created the basic material. This means that unless applications that can be brought to market well inside the 17 year window, the basic material technology has limited if any value. Thermochromic inks are fundamentally simple and inexpensive, so their transition to market for a host of applications has been relatively simple. Despite many years of effort on auxetic materials, looking at the other end of the spectrum, there are still virtually no commercialised applications. Despite the often profound benefits they present to designers in a host of situations. Perhaps a good example of an organisation ‘getting it right’ is Dow Corning and the ‘Active Protection System’ (APS) material solution spun out of research at Imperial College in London – Figure 6. Look up optical response from thermal stimulus in Table 1, and the first answer in the list of possibilities is thermochromic. Which is precisely the solution adopted by the self-timing egg inventors. Or rather, almost (as ever, there is always a ‘yes, but’) because what makes the solution especially powerful is that it contains two subtly different thermochromic inks, each with a slightly different colour change trigger temperature. Hence, the word ‘soft’ (as shown in the Figure) is triggered at one temperature, and the word ‘hard’ is triggered at another, slightly higher temperature. 5.0 From The Material Scientist’s Perspective In many ways the self-timing egg and the wrist replacement joint cases provide two ends of a spectrum as far as the materials scientist is concerned. In the wrist replacement case, the medical devices industry may well be guilty of defining the wrong problem, but one of the reasons they have been thinking in optimization rather than contradiction-solving terms is that they know how difficult it is to prove to the regulatory authorities that the solutions they are proposing are safe. Tweaking the shape of a titanium pin is a far easier thing to prove is safe than some new form or structure of titanium. Proving a new material is safe can involve several years of expensive validation testing. Figure 6: Dow-Corning Active Protection System APS is a material system that is flexible under low loading conditions (top-left part of the figure), but which becomes very stiff when subjected to a high impulse load (top right). In terms of Table 1, APS is, like the afore-mentioned auxetics, a material that achieves a mechanical response to a mechanical stimulus. The material is in fact a very elegant example of a shearthickening dilatant silicone coating. The material has a potential role to play in any situation where the ‘flexible and stiff’ contradiction is present. Having patented the basic platform technology the race is now on to find appropriate applications for the technology. Being aware of the contradiction being
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