Recent Advances in Layered Double Hydroxides and Their Derivatives for Biomedical Applications

With the awareness of human and public health increasing, biomedical research has been paid more and more attention. 2D intercalation materials with versatile physicochemical advantages have attracted extensive interest in biomedical applications. Layered double hydroxides (LDHs), as a class of typical 2D materials, have been widely utilized as various multi-function materials and exhibited great promise in biomedical applications. The general chemical formula of LDHs can be described as [M1-x2+Mx3+ (OH)(2)](q+)(A(n-))(q/n)center dot yH(2)O, where M2+ and M3+ refer to divalent and trivalent mental cations, respectively, and An- is an exchangeable anion, including inorganic, organic, biological compound, and even gene. LDHs have attracted a great attention in the field of biomaterials due to their good biocompatibility, pH sensitivity, biodegradability, high intracellular delivery efficacy and low cost, etc. In this review, we summarize the development of LDHs and related nanocomposites for biomedical applications including sterilization, cancer therapy, bioimaging, etc. In general, the LDH-based sterilization materials can be divided into four categories. The first type is the pristine LDHs and their derivatives named mixed mental oxides (MMO). The second type is organo-modified LDHs nanostructures, including surface modified LDHs and interlayer assembled biomaterials, which embed antibacterial agents or other biomolecules in the interlayer spaces. The last two are enzyme immobilized LDHs and Ag NPs deposited LDHs, respectively. In addition to sterilization, LDHs have also been applied to cancer diagnosis and therapy. We mainly introduce three types of cancer monotherapy, including photodynamic, photothermal and chemodynamic therapy. Moreover, cancer combination therapy and bioimaging for cancer diagnosis are also discussed. Furthermore, the large-scale synthesis of LDH-based materials plays a fundamental role in the potential biomedical applications in the future. Therefore, we summarize the feasible methods of large-scale production of LDHs reported in recent years. Among them, the SNAS (separate nucleation and aging steps) method with a simple and quick operation, and has realized the industrial scale-up production of LDHs. Finally, we also discussed the future challenges and opportunities of LDH-based biomaterials.