Introduction

Hydrogels are an excellent scaffold structure for numerous applications in tissue engineering and regenerative medicine. In particular, they can be used as cell and drug carriers to deliver such therapeutic components directly and locally [1]. Hydrogels can be injected and crosslinked in situ, reducing the need for risky invasive surgeries [2]. In addition, hydrogels can mimic the natural extracellular matrix (ECM) environment, and allow one to control cellular and tissue functions as well as the transport of nutrients and bioactive molecules [3, 4].

Fumarate-based hydrogels are synthetic polymers, allowing flexible control of physical, mechanical, and degradative properties for a desired application [4]. Fumaric acid, the fundamental component of these hydrogel scaffolds, is an unsaturated organic acid that is commonly found in the human body and can be metabolized through the Krebs cycle [5–7]. Polymer chains that contain fumarate units crosslink easily via the unsaturated double bonds and degrade through hydrolysis of the ester bonds in the fumarate group [6–9]. Furthermore, the biodegradable nature of these hydrogels allows neotissue ingrowth and eliminates the need for further surgery to remove the implanted scaffold [5, 10].