Integrated Zr‐MOF/NH₄TiOF₃Bilayer Coating on Magnesium for Controllable Corrosion, Cytocompatibility, and Drug Delivery Multifunctionalities

Abstract

replacement implants, magnesium possesses closer elasticity modulus to bones than other metals for effectively avoiding stress shielding effects, which can also avoid the damage and cost associated with secondary surgery. [4,5] However, the major bottleneck inhibiting large-scale clinical utilizations of Mg matrix is the high corrosion rate, which would cause premature loss of mechanical integrity, aggregation of hydrogen, alkalinization of body fluid, and low cytocompatibility, resulting in the implant failure. [6][7][8][9] Coating technology onto Mg-matrix surface is an effective strategy to break the bottleneck. Various coatings, including fluoride coatings, hydroxyapatite coatings, β-tricalcium phosphate coating, and micro-arc oxidation coatings, etc., have been developed to extend the service term of Mg matrix for matching the healing time of bones, and to improve the surface cytocompatibility for accelerating the formation of new bones. [10][11][12] These coatings have greatly improved the corrosion resistance and biocompatibility of Mg matrix. However, in the face of increasing complex clinical requirements of diagnosis, therapy, antibiosis, and anti-inflammatory, it is challenging for the current coatings to achieve effective integration of multiple functionalities, such as the loading/releasing or modification of functional molecules including drugs, antibiotics, contrast agents, and biomacromolecules. [13][14][15] Therefore, the exploration of novel coatings to realize the construction of multifunctional platform is the key to promote the large-scale clinical applications of Mg matrix.Alternatively, ammonium trifluorotitanate (NH 4 TiOF 3 ) is a mesocrystalline intermediate of anatase TiO 2 with favorable cytocompatibility and blood compatibility. [16][17][18][19][20] The conversion degree of NH 4 TiOF 3 to TiO 2 can be regulated to achieve the adjustable crystal structure through changing the temperature and time in solvothermal synthesis. The NH 4 TiOF 3 layer fabricated onto Mg-matrix surface could availably resist the invasion of corrosive media; while its alterable structures correspond to different anticorrosion effects, [20,21] expecting to realize the controllable corrosion of Mg matrix. At present, few researches have been reported on the NH 4 TiOF 3 coatings on Mg-matrix surfaces. Meanwhile, metal-organic frameworks (MOFs), the organic-inorganic hybrid materials with intramolecular pores formed by self-assembly of organic ligands and metal ions or Magnesium (Mg) and its alloys biodegrade safely in human body for implant applications. The major bottleneck inhibiting their clinical utilizations is the high corrosion rate. Modification with anticorrosive and bioactive coatings is an ideal strategy to break the bottleneck. In this study, a multifunctional coating constructed by Zr-based metal-organic framework UiO-66-NH 2 (UiO) and ammonium trifluorotitanate NH 4 TiOF 3 (NTiF) bilayers (UiO/NTiF) is fabricated onto Mg matrix through facile solvothermal method. The inner NTiF layer can be designed ...

Integrated MOF-74 Coatings on Magnesium for Corrosion Control, Cytocompatibility, and Antibacterial Properties

“…The accumulated hydrogen volume for the NTiF layer-coated Mg (17.4 mL cm –2 ) is obviously lower than that of bare Mg (49.9 mL cm –2 ), indicating the anticorrosive protection of the NTiF layer. The fabrication of MOF-74 membranes on NTiF surfaces further controls the corrosion of the Mg matrix, owing to the characteristics of well-intergrown crystals, compact structure, and effective rejection of corrosion ions of MOF membranes as physical barrier layers, , which show the low corrosion rates of less than 1 mm y –1 calculated based on hydrogen volumes (Figure b). The total volumes of hydrogen evolution for MOF-74/NTiF-coated Mg in descending order are as follows: MOF-74(1)/NTiF (16.1 mL cm –2 ), MOF-74(5)/NTiF (14.5 mL cm –2 ), and MOF-74(3)/NTiF (8.9 mL cm –2 ), displaying the different protective effects of these MOF-74/NTiF coatings.…”

“…Immersing for 30 days, the XRD characteristic peaks of MOF-74(1) disappear basically. Until 60 days of immersion, the XRD pattern shows almost no characteristic peaks of NH 4 TiOF 3 , suggesting the gradual degradation of NH 4 TiOF 3 crystals; however, the NTiF layer still maintains the structural integrity, continuing to protect the Mg matrix . The FT-IR characteristic peaks of DHTA and the O–Metal–O vibrational peak at 582 cm –1 are weakened gradually and disappear finally with the increasing immersion time, indicating the decomposition of the MOF-74(1) membrane.…”

“…The cell densities on the NTiF layer and all of the MOF-74/NTiF coatings significantly increase as the culture time increases, in which the cells exhibit distinct filamentous pseudopods and diffuse morphology of flattened cell membranes for favorable adhesion and proliferation. However, the live cells on bare Mg reveal a severe decrease in number in 5 days of culture, due to the locally high pH value and accumulated hydrogen resulting from rapid corrosion of the Mg surface . The main reasons for the satisfactory cytocompatibility of MOF-74/NTiF coatings could be conjectured as follows: (a) The coatings can effectively control the corrosion of Mg matrixes, creating a relatively stable interface microenvironment for cell adhesion and proliferation.…”

“…A universal method based on a polydopamine- or 3-aminopropyltriethoxysilane (APTES)-modified layer can be applied to prepare various MOF membranes on different metal surfaces as protective coatings. − Another difficulty to construct MOF membranes on a Mg matrix is active Mg surfaces, which could be corroded during the deposition of MOF membranes, impairing the membrane–substrate bonding strength. Our previous studies have designed and fabricated an interlayer composed of NH 4 TiOF 3 (NTiF) crystals, which are the key precursors for TiO 2 mesocrystals, serving as the primary protection layer for the Mg matrix and a stable surface for the growth of MOF membranes . The NTiF layer, which shows favorable cytocompatibility, can be adjusted with different crystal structures to regulate its protective effects for controlling the degradation rates of Mg matrixes to match the clinical demand.…”

pH-Responsive Fluorescent Metal–Organic Framework as a Functional Nanofiller for Smart Coatings

“…Metal–organic frameworks (MOFs), composed of metal ions connected by organic linkers, have received considerable attention in various fields owing to their large specific surface areas, rich active sites, designable frameworks, and great chemical stability. − MOFs can be used as nanofillers to improve the anticorrosion performance of the coatings. − Alipanah et al synthesized MIL-88A­(Fe) particles as corrosion-inhibiting fillers to enhance the protective property of the epoxy/polyamide coating . On the other hand, MOFs are attempted to be nanocontainers to load corrosion inhibitors for the self-repairing coatings. − Li et al selected a ZIF-8 nanocontainer with 2-mercaptobenzimidazole loading to prepare the self-repairing epoxy coating .…”