Enzyme-Directed Biomineralization Coating on TiO₂ Nanotubes and its Positive Effect on Osteogenesis

Abstract

Hydroxyapatite (HA)-coated TiO2 nanotubes (TNTs) have been reported to enhance osteogenesis. However, the nanoscale topography of TNTs usually vanishes due to the uncontrollable mineralization on the surface. In this study, TNTs with different diameters­(small, 25 nm; medium, 55 nm; and large, 85 nm) were fabricated by anodization in 3 different voltages. Enzyme-directed biomineralization was adopted to deposit calcium phosphate on the above TNTs. The surface structures and properties of the coatings were characterized by scanning electron microscopy, dispersive X-ray spectrometry, X-ray diffraction, and Fourier-transform infrared spectroscopy. The osteogenesis effect of the hybrid TNT/HA and the original TNTs were evaluated. The results showed that hydroxyapatite deposited homogeneously along the TiO2 nanotubes while preserving the intrinsic nanotopography. Mechanically, alkaline phosphatase­(ALP) played a critical role in the mineralization and large nanotube size is more favorable for the mineralizing process because of more ALP absorption. Besides, the hybrid nanosurface TNT/HA coating was found to improve the adhesion, proliferation, and osteogenic differentiation of MC3T3-E1 cells compared to pure TNTs. Our study suggests that the hybrid TNT/HA coating constructed by enzyme-directed biomineralization on TiO2 nanotubes is a promising modification strategy for titanium implants.

<p>TiO₂ Nanotubes Alleviate Diabetes-Induced Osteogenetic Inhibition</p>

“…To evaluate the osteogenetic ability of MC3T3-E1 on different modified Ti surfaces under high-glucose states, we conducted immunofluorescent staining assays of ALP and osteopontin (OPN), as previously described. 18 Briefly, cells were seeded on the substrates and cultured in mineralizing medium (complete medium supplemented with 0.1 μM dexamethasone, 50 μg/mL ascorbic acid, and 10 mM β-glycerophosphate) at glucose concentrations of 5.5 or 22 mM on the different modified Ti surfaces. After culture for 7 (ALP) or 14 (OPN) days, cells were fixed with 4% paraformaldehyde, treated with 0.1% Triton for 20 min, and sealed with 5% bovine serum albumin (BSA) for 1 h. Thereafter, the cells were incubated with anti-ALP (1:100, Abcam, UK) or anti-OPN (1:200, Abcam, UK) at 4°C for 16 h. Then, the cells were incubated with the green fluorescent second antibody (1:200, Abcam, UK) in the darkroom for 1 h, and cell nuclei was stained with DAPI in the darkroom for 15 min.…”

Biomimetic Hydroxyapatite on Graphene Supports for Biomedical Applications: A Review

“…However, it is difficult to apply the pure HA for bone tissue engineering and biomedical implant due to its relative weak toughness and tensile strength. To solve this problem, the combination of HA with other kinds of bioactive tough materials, such as Ti alloys [14], polymer matrix [15], self-assembled peptide/protein nanofibers [16,17], carbon materials (carbon nanotubes and graphene) [18,19], and others [20,21], have been performed to improve the mechanical properties of HA-based materials. It is obvious that the introduction of these reinforcing materials to HA extended the potential applications of HA in biomedical fields.…”

Enzyme-Mediated Mineralization of TiO2 Nanotubes Subjected to Different Heat Treatments

“…The cellular and tissue responses to the surface characteristics of an implant, especially its topography, hydrophilicity, and roughness, and the bioactive chemical components it contains, − determine its clinical success. Since the human bone has unique structures at the nano level where bone cells operate, biomaterials with nanostructures mimicking those of bone promise to be ideal biomedical materials for bone repair.…”

“…TNT have diameters ranging from 10 to 250 nm, tube lengths from 100 nm to several hundred micrometers, and wall thicknesses from 11 to 27 nm . It has been extensively shown that TNT, with their nanoscale features, are able to increase the surface bioactivity of implants , and consequently the formation of surrounding bone tissue . Our previous research also showed that TNT on titanium implants greatly improved platelet and bovine serum albumin (BSA) adhesion, while inhibiting adhesion of microorganisms. , As-grown TNT prepared by anodic oxidation are amorphous.…”

“…This biomimetic mineralization method allowed the slow release of phosphate ions from the hydrolysis of β-glycerophosphate by ALP in the fetal bovine serum to regulate mineralization, thus avoiding rapid nucleation in solution. Our previous study successfully used this enzyme-mediated mineralization method to deposit calcium phosphate on the surface of TNT with different diameters (25, 55, 85 nm) while still preserving their nanotopography . However, the question as to which crystalline phase of TiO 2 would better promote the formation of a topography-preserving calcium phosphate coating needs further study.…”