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Supramolecular polymers can be random and entangled coils with the mechanical properties of plastics and elastomers, but with great capacity for processability, recycling, and self-healing due to their reversible monomer-to-polymer transitions. At the other extreme, supramolecular polymers can be formed by self-assembly among designed subunits to yield shape-persistent and highly ordered filaments. The use of strong and directional interactions among molecular subunits can achieve not only rich dynamic behavior but also high degrees of internal order that are not known in ordinary polymers. They can resemble, for example, the ordered and dynamic one-dimensional supramolecular assemblies of the cell cytoskeleton, and possess useful biological and electronic functions.

I. Introduction 4071 II. The Term Supramolecular Polymers 4071 III. General Aspects of Supramolecular Polymers 4073 IV. Supramolecular Polymers Based on Hydrogen Bonding 4073 A. Strength of Hydrogen Bonds 4073 B. Hydrogen Bonding Enforced by Liquid Crystallinity 4075 C. Hydrogen Bonding Enforced by Phase Separation 4076 D. Strong Dimerization of Multiple Hydrogen-Bonding Units 4077 E. Ureidopyrimidinone-Based Polymers 4079 V. Supramolecular Polymers Based on Discotic Molecules 4081 A. Arene−Arene Interactions 4082 1. Triphenylenes 4082 2. Phthalocyanines and Porphyrins 4083 3. Helicenes 4084 4. m-Phenylene Ethynylene Oligomers 4084 5. Other Systems 4085 6. Chromonics 4086 B. Hydrogen Bonding 4086 C. Arene−Arene Interactions and Hydrogen Bonding 4087 1. Guanine and Pterine Derivatives 4087 2. Hydrogen-Bonded Pairs 4089 3. Complexation of Tetrazoles with 1,3,5-Tris (4,5-dihydroimidazol-2-yl)benzene 4089 4. C 3 -Symmetrical Discotic Molecules 4090 VI. Supramolecular Coordination Polymers and Miscellaneous Systems 4091 VII. Conclusions and Outlook 4094 VIII. Acknowledgments 4094 IX. References and Notes 4094

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Units of 2-ureido-4-pyrimidone that dimerize strongly in a self-complementary array of four cooperative hydrogen bonds were used as the associating end group in reversible self-assembling polymer systems. The unidirectional design of the binding sites prevents uncontrolled multidirectional association or gelation. Linear polymers and reversible networks were formed from monomers with two and three binding sites, respectively. The thermal and environmental control over lifetime and bond strength makes many properties, such as viscosity, chain length, and composition, tunable in a way not accessible to traditional polymers. Hence, polymer networks with thermodynamically controlled architectures can be formed, for use in, for example, coatings and hot melts, where a reversible, strongly temperature-dependent rheology is highly advantageous.

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Polymers, ceramics and metals have historically dominated the application of materials in medicine. Yet rationally designed materials that exploit specific, directional, tunable and reversible non-covalent interactions offer unprecedented advantages: they enable modular and generalizable platforms with tunable mechanical, chemical and biological properties. Indeed, the reversible nature of supramolecular interactions gives rise to biomaterials that can sense and respond to physiological cues, or that mimic the structural and functional aspects of biological signalling. In this Review, we discuss the properties of several supramolecular biomaterials, as well as their applications in drug delivery, tissue engineering, regenerative medicine and immunology. We envision that supramolecular biomaterials will contribute to the development of new therapies that combine highly functional materials with unmatched patient- and application-specific tailoring of both material and biological properties.