Mal-amido-PEG9-acid is widely used in bioconjugation and drug delivery systems due to its polyethylene glycol (PEG) spacer, which enhances solubility and reduces immunogenicity. It serves as a linker in the development of antibody-drug conjugates (ADCs), enabling targeted delivery of therapeutic agents to specific cells. Additionally, it is utilized in the modification of proteins and peptides to improve their stability and prolong their circulation time in the body. The compound is also employed in the synthesis of hydrogels and biomaterials for tissue engineering and regenerative medicine applications. Its reactive groups allow for efficient coupling with various biomolecules, making it a versatile tool in pharmaceutical and biomedical research.