Mechano-responsiveness

To date, heat-triggered shape memory polymers have had the greatest share of research and application adaptation. However, trigger mechanisms could also be chemo-responsive, e.g., water, ethanol, and pH change photo-responsive, e.g., UV or IR, including radio waves and/or mechano-responsive, e.g., stretching, impact, etc. 

Fan, J. et ah. Tunable mechano-responsive organogels by ring-opening copolymerizations of N-carboxyanhydrides. Chemical Science, 2014. 5 141-150. 

In this chapter, we will discuss the design, synthesis, and the properties of mechano-responsive polymeric materials with foeus on meehanoehromie systems. Initially, natural meehanoehromie events will be deseribed in order to show how these mechanisms can serve as inspiration in the design of artificial devices. Following, meehanieal responsiveness in the eontext of mechanochromic materials will be reviewed. The effeet of meehanieal forces on the molecular, supramolecular, microscopic and macroscopic levels will be taken into consideration, as well as the use of meehanieally responsive biological macromolecules for the preparation of self-reporting polymer-protein hybrid materials. 

Mechanical transduction in these systems can be at the molecular, supramolecular or the micro/macro levels. For instance, chemical and structural changes caused by mechanical stimuli, such as flow- and ultrasound-induced chain scission, are interesting phenomena that can be taken into account in the development of mechano-responsive materials. In the following section, we will look closely at the types of response to mechanical stimuli and the underlying mechanisms involved either in mechano-chemical or physical transformations. 

Therefore, it has become feasible to prepare mechano-responsive materials that rely on mechanobiochemical effects. 

Another interesting field of application of the self-reporting approach would be biomedical materials. However, to the best of our knowledge, mechanochromic polymer-based materials have not yet been designed for such applications. For example, the synthesis of mechano-responsive nanoparticles, which would exert their biomedical function in response to a mechanical stimulus and simultaneously generate a change in colour, would permit to develop new theranostics tools. Such systems could lead to a better... 

Mechano-responsive organogels are reported by Beck and Rowan [96]. A solution of bis(methylbenzimidazolyl)pyridine-dimer 63 in chloroform/aceto-nitrile formed an organogel by coordination with either Co/La, Co/Eu, Zn/La, or Zn/Eu, in which either Co(ll) or Zn(ll) ions act as linear chain extension binding units, whereas either La(lll) or Eu(lll) ions act as cross-linking components (Fig. 35). These materials are mechano-responsive, exhibiting a thixotropic (shear-thinning) behavior. The reversible sol-gel formation by the mechanical shaking occurs for a short time of ca. 20 sec. Thus,... 

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