Design of a 3D potentially auxetic polymer for biomedical applications Cardona M.A. 1 , Volpi S. 2 , Grima, J.N. 1,3 , Casnati A. 2 , Gatt, R. 1 1 Metamaterials Unit, Faculty of Science, University of Malta, Malta, 2 Dipartimento di Scienze Chimiche, della Vita e della Sostenibiltà Ambientale, Università degli Studi di Parma, Italy, 3 Department of Chemistry, Faculty of Science, University of Malta, Malta The development of intrinsically auxetic synthetic material has been a longstanding goal of the auxetics community. 1 It attempts to introduce chemical tuneability and widen the spectrum of applications for such materials. 2 To date, only one liquid crystalline elastomer has been synthesized and shown to exhibit a negative Poisson’s ratio. 3 A number of other molecular structures have been predicted to exhibit auxetic behaviour, including a polymeric network built from calix 4 arenes which mimics an “egg-rack” structure. 4 This structure was, however, deemed too difficult to synthesize. In this study, a different related design was explored. This design uses calix 4 tubes which in turn consist of two calix 4 arenes connected through the lower rim. 5 The upper rims of the calix 4 arenes were connected through rigid linkers kept apart using supramolecular interactions. The overall chemical structure forms a 3D molecular network. The auxetic potential of this system was confirmed using force-field based simulations and a synthetic strategy was devised for the synthesis of this molecular material. If synthesized, this material would have a great potential for applications in the biomedical field, such as in the production of more comfortable catheters. References 1. Evans, K. E. Auxetic polymers: a new range of materials. Endeavour 15 , 170–174 (1991). 2. Mir, M., Ali, M. N., Sami, J. & Ansari, U. Review of Mechanics and Applications of Auxetic Structures. Advances in Materials Science and Engineering 2014 , 753496 (2014). 3. Mistry, D. et al. Coincident molecular auxeticity and negative order parameter in a liquid crystal elastomer. Nat Commun 9 , 5095 (2018). 4. Grima, J. N., Williams, J. J., Gatt, R. & Evans, K. E. Modelling of auxetic networked polymers built from calix 4 arene building blocks. Mol Simul 31 , 907–913 (2005). 5. Matthews, S. E., Schmitt, P., Felix, V., Drew, M. G. B. & Beer, P. D. Calix 4 tubes: A New Class of Potassium-Selective Ionophore. J Am Chem Soc 124 , 1341–1353 (2002).
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