Macromolecular-bottlebrush polymeric gels with tissue-mimetic swelling and mechanical properties

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NON-TECHNICAL SUMMARYLiving tissues are distinct in their ability to seamlessly span a range of mechanical properties from ultra-soft brain to super-tough cartilage at nearly constant water fraction. On the contrary, synthetic analogs of tissues (i.e. polymeric gels) are currently not capable to control the amount of water without affecting their mechanics. A new class of polymeric materials based on bottlebrush-macromolecular architectures is proposed here to enable independent and programmable control over gel composition and mechanical properties. In contrast to traditional linear polymers, the bottlebrush architecture introduces a myriad of side chains or “bristles” that afford additional molecular parameters to tune softness without changing the water fraction. Furthermore, tailoring the chemistry of side-chain ends will empower novel applications such as programmable and injectable materials for additive manufacturing of tissue-mimetic devices. The proposed novel class of polymeric gels will provide ample opportunities for interdisciplinary research through integration of cutting-edge polymer chemistry, soft-matter physics, and emerging technologies that may lead to breakthroughs in many applications such as biomedical devices, tissue-engineering scaffolds, and soft robotics. TECHNICAL SUMMARYThe project will address three fundamental challenges. First, the equilibrium swelling ratio and gel’s mechanical properties will be separately correlated with architectural parameters of brush-like networks such as the side chain length and grafting density. Triangulation of architecture-swelling-mechanics correlations will afford independent control over swelling, softness, and non-linear mechanical response. For example, this will create an unprecedented series of synthetic gels with the same solvent fraction, but widely different moduli varying within several orders of magnitude. The second goal is to design brush-like mesoblocks that enable solvent-free injection of tissue-mimetic elastomers. The challenge is to control curing time from seconds to days separate from mechanical properties of fully cured polymer networks. Lastly, successful implementation of goals 1 and 2 will enable a new class of bioink materials based on thermosensitive hydrogels that can inject and 3D-print objects with well-defined solvent fractions and mechanical properties. The main challenge here is to integrate controlled-temperature gelation of printed materials with the design-by-architecture objectives pursued in goals 1 and 2.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.