Innovations in 3D bioprinting and biomaterials for liver tissue engineering: Paving the way for tissue-engineered liver

The liver is a pivotal organ that maintains internal homeostasis and actively participates in multiple physiological processes. Liver tissue engineering (LTE), by which in vitro biomimetic liver models are constructed, serves as a platform for disease research, drug screening, and cell replacement therapies. 3D bioprinting is used in tissue engineering to create microenvironments that closely mimic authentic tissues with carefully selected functional biomaterials. Ideal functional biomaterials exhibit characteristics such as high biocompatibility, mechanical strength, flexibility, processability, and tunable degradability. Biomaterials can be categorized into natural and synthetic biomaterials, each with its own advantages and limitations, and their combinations serve as a primary source of 3D bioprinting materials. It is noteworthy that the liver decellularized extracellular matrix (dECM), obtained by removing cellular components from tissues, possesses traits such as bioactivity, biocompatibility, and non-immunogenicity, making it a common choice among functional biomaterials. Furthermore, crosslinking of biomaterials significantly impacts the mechanical strength, physicochemical properties, and cellular behavior of the printed structures. This review covers the current utilization of biomaterials in LTE, focusing on natural and synthetic biomaterials as well as the selection and application of crosslinking methods. The aim is to enhance the fidelity of in vitro liver tissue models by providing a comprehensive coverage of functional biomaterials, thereby establishing a versatile platform for tissue-engineered livers.