Chitosan is a naturally occurring compound that can be obtained from deacetylated chitin, which is obtained from various sources such as fungi, crustaceans, and insects. Commercially, chitosan is produced from crustaceans. Based on the range of its molecular weight, chitosan can be classified into three different types, namely, high molecular weight chitosan (HMWC, >700 kDa), medium molecular weight chitosan (MMWC, 150–700 kDa), and low molecular weight chitosan (LMWC, less than 150 kDa). Chitosan shows several properties that can be applied in horticultural crops, such as plant root growth enhancer, antimicrobial, antifungal, and antiviral activities. Nevertheless, these properties depend on its molecular weight (MW) and acetylation degree (DD). Therefore, this article seeks to extensively review the properties of chitosan applied in the agricultural sector, classifying them in relation to chitosan’s MW, and its use as a material for sustainable agriculture.

Organ failure constitutes a significant global concern requiring urgent attention. While organ transplantation offers prospective treatment, it remains suboptimal. The scarcity of donor organs and the need for lifelong immunosuppressive treatments highlight the necessity for innovative approaches in regenerative medicine. In response, tissue engineering has emerged as a promising alternative, particularly through advancements in three-dimensional (3D) and four-dimensional (4D) printing technologies. These approaches enable the fabrication of complex, patient-specific constructs for regenerating tissues such as skin, bone, cartilage, and vascularized organs. This review systematically examines 3D printing techniques, commonly used biomaterials (e.g., hydrogels, bio-inks, and polymers), and their applications in dermal, cardiovascular, bone, and neural regeneration. In addition to discussing 3D technology, an introduction to 4D bioprinting is provided, enabling advanced biomedical applications and establishing itself as an innovative tool that enhances the classic approach to 3D bioprinting in the context of regenerative medicine. Finally, key challenges and ethical considerations are discussed to provide a comprehensive perspective on the current state and future of printed scaffolds in regenerative medicine.