Reprogrammable and Light-Adaptive Mechanical Gradients in Waterborne High-Performance Nanocellulose Materials

机械梯度在自然界中普遍存在（韧带与骨骼的连接），有助于应力离域并优化韧性、刚度和耐磨性方面的机械性能。它们对未来的合成材料在结构和功能应用中具有启发性，它们可以在刚性和弹性材料之间提供更坚固的连接，允许在结构化，响应性水凝胶中进行变形程序，或指导细胞命运和迁移。从概念上讲，梯度材料可以分为（i）横向和夹层型梯度，（ii）2D与3D图案化材料，以及（iii）从一次性不可逆写入梯度到可重新编程/可编程梯度再到自适应梯度的复杂性。该提案的中心目的是实施、理解和利用单向和可逆的光化学缀合，以在机械性能中构建永久的、可重新编程的和光适应性横向梯度，从而设计由高度限定的互补纤维素纳米纤丝和聚合物组成的机械上级和透明的混合纳米纸。我们专注于三代CNF/聚合物混合纳米纸，其复杂性和性能水平不断变化：（i）具有自报告和不可逆光共轭的单向梯度，（ii）使用可逆光共轭的可重写梯度，（iii）利用可逆光共轭动力学的光适应机械梯度。为了解决这些跨学科和多尺度的挑战，我们建立了两个互补的研究小组的一致联盟，将高效光化学，精密大分子合成和表面工程（Barner-Kowollik，KIT）所需的专业知识与纳米纤维素，胶体科学，仿生纳米复合材料和先进的机械测试（Walther，DWI）合并。我们的共同目标是从光化学反应的基本动力学通过纳米/介观/自上而下的结构分子控制的复杂宏观力学性能的整体理解。

Mechanical gradients are ubiquitous in nature (attachment of ligaments to bones) and serve stress delocalization and optimize mechanical properties with regard to toughness, stiffness and abrasion resistance. They are inspiring for future synthetic materials in both structural as well as functional applications, where they can provide tougher joints between stiff and elastic materials, allow morphing procedures in structured, responsive hydrogels, or instruct cell fate and migration. Conceptually, gradient materials can be divided into (i) lateral and sandwich type gradients, (ii) 2D versus 3D patterned materials, and (iii) in terms of complexity from a one-time, irreversibly written gradient to a reprogrammable/rewritable gradient to an adaptive gradient. The central aim of this proposal is to implement, understand and exploit one-way and reversible photochemical conjugations to structure permanent, reprogrammable and light adaptive lateral gradients in mechanical properties to engineer mechanically superior and transparent hybrid nanopapers composed of highly defined complementary cellulose nanofibrils and polymers. We focus on three generations of CNF/polymer hybrid nanopapers with evolving complexity and property levels: (i) One-way gradients with self-reporting and irreversible photo-conjugations, (ii) Rewritable gradients using reversible photo-conjugations, (iii) Light-adaptive mechanical gradients exploiting the dynamics of reversible photo-conjugations. To address these interdisciplinar and multiscale challenges, we forge a coherent consortium of two complementary research groups to merge the required expertise in highly efficient photochemistry, precision macromolecular synthesis and surface engineering (Barner-Kowollik, KIT) with nanocellulose, colloid science, biomimetic nanocomposites and advanced mechanical testing (Walther, DWI). Jointly we aim at an integral understanding from the fundamental kinetics of the photochemical reactions via nano-/meso-/top-down structuring to molecularly controlled complex macroscale mechanical properties.