Injectable hydrogels have become a key focus in tissue filling due to their minimal adverse effects, faster recovery, and good results. These hydrogels can be made through chemical, physical, or biological crosslinking, enabling reversible bonds or delayed gelatinization for minimally invasive tissue filling. Injectable hydrogels support tissue augmentation and regeneration by providing slow degradation, mechanical support, and modulation of host cell functions. This review summarizes recent advances in the synthesis of injectable hydrogels and their applications in tissue filling, discussing challenges and future directions. Injectable hydrogels are constructed through interactions between polymer chains, with different crosslinking methods offering distinct advantages and limitations. Chemical covalent crosslinking provides stability and adjustable mechanical properties, while physical crosslinking, such as hydrogen bonding, hydrophobic interactions, and host-guest interactions, offers reversible properties. Biological crosslinking, using enzymes, provides high efficiency and biosafety. These hydrogels are composed of natural or synthetic polymers, such as HA, SF, collagen, PVA, PEG, and PLGA, which are chosen for their biocompatibility, biodegradability, and mechanical properties. The mechanical strength of injectable hydrogels must match the target tissue to ensure effective filling. Degradation rates are crucial for long-term stability, with biodegradable hydrogels decomposing naturally without requiring surgical removal. Biological functions of injectable hydrogels include promoting cell proliferation, collagen deposition, and angiogenesis, which are essential for tissue regeneration. HA-based hydrogels are widely used in cosmetic and medical applications due to their viscoelasticity and biosafety, but their mechanical strength and stability can be improved through crosslinking or addition of other biomaterials. SF-based hydrogels offer excellent biosafety and biodegradability, making them suitable for tissue filling. These hydrogels can be fabricated into microparticles for enhanced injectability and controlled degradation. Injectable hydrogels are increasingly used in cosmetic procedures for tissue filling and regeneration, with ongoing research aimed at optimizing their therapeutic potential and addressing challenges such as mechanical strength, degradation rates, and biosafety.Injectable hydrogels have become a key focus in tissue filling due to their minimal adverse effects, faster recovery, and good results. These hydrogels can be made through chemical, physical, or biological crosslinking, enabling reversible bonds or delayed gelatinization for minimally invasive tissue filling. Injectable hydrogels support tissue augmentation and regeneration by providing slow degradation, mechanical support, and modulation of host cell functions. This review summarizes recent advances in the synthesis of injectable hydrogels and their applications in tissue filling, discussing challenges and future directions. Injectable hydrogels are constructed through interactions between polymer chains, with different crosslinking methods offering distinct advantages and limitations. Chemical covalent crosslinking provides stability and adjustable mechanical properties, while physical crosslinking, such as hydrogen bonding, hydrophobic interactions, and host-guest interactions, offers reversible properties. Biological crosslinking, using enzymes, provides high efficiency and biosafety. These hydrogels are composed of natural or synthetic polymers, such as HA, SF, collagen, PVA, PEG, and PLGA, which are chosen for their biocompatibility, biodegradability, and mechanical properties. The mechanical strength of injectable hydrogels must match the target tissue to ensure effective filling. Degradation rates are crucial for long-term stability, with biodegradable hydrogels decomposing naturally without requiring surgical removal. Biological functions of injectable hydrogels include promoting cell proliferation, collagen deposition, and angiogenesis, which are essential for tissue regeneration. HA-based hydrogels are widely used in cosmetic and medical applications due to their viscoelasticity and biosafety, but their mechanical strength and stability can be improved through crosslinking or addition of other biomaterials. SF-based hydrogels offer excellent biosafety and biodegradability, making them suitable for tissue filling. These hydrogels can be fabricated into microparticles for enhanced injectability and controlled degradation. Injectable hydrogels are increasingly used in cosmetic procedures for tissue filling and regeneration, with ongoing research aimed at optimizing their therapeutic potential and addressing challenges such as mechanical strength, degradation rates, and biosafety.