Bioinspired Materials Science and Engineering

15Tuning Mechanical Properties of Protein Hydrogels: Inspirations from Nature and Lessons from Synthetic Polymers

Xiao‐Wei Wang, Dong Liu, Guang‐Zhong Yin, and Wen‐Bin Zhang*

College of Chemistry and Molecular Engineering, Peking University, Beijing, China

15.1 Introduction

Hydrogels are three‐dimensional polymeric networks containing large amounts of water [1]. While gelatins have been around in human life for thousands of years, they were not well understood until the emergence of the macromolecular hypothesis [2] introduced the idea of network formation in terms of “infinite molecular weight” and “percolation” [1]. It took several more decades for gels to evolve from simple viscoelastic solids into contact lenses, to superabsorbent materials, and further into “smart” hydrogels with phase transitions [3]. Since their compositions and physical states are similar to most biological tissues, hydrogels have been intensively studied as an excellent platform and matrix for engineered functions in the biological context [4]. For example, in living tissues, cells reside in a 3D extracellular matrix with heterogeneous compositions but well‐defined spatiotemporal distribution of mechanical properties and biological cues [4]. Such highly sophisticated hierarchical structures enable the control of cell fate. Mimicking natural materials is being actively pursued [5]. With the development of the hydrogel theories and the increasingly powerful polymer chemistry, it is no longer uncommon ...