Fabrication and Characterization of Nanopillar-Like HA Coating on Porous Ti6Al4V Scaffold by a Combination of Alkali-Acid-Heat and Hydrothermal Treatments

doi:10.1007/s40195-019-00920-4

Abstract

Abstract:

Porous titanium scaffold with suitable porous architecture exhibits enormous potentials for bone defect repairs. However, insufficient osteointegration and osteoinduction still remain to open as one of the major problems to achieve satisfactory therapeutic effect. To solve this problem, many studies have been carried out to improve the bioactivity of porous titanium scaffold by surface modifications. In this study, porous Ti6Al4V scaffolds were fabricated using additive manufacturing technique. Porous architectures were built up based on a diamond pore structure unit. Alkali-acid-heat (AH) treatment was applied to create a TiO₂ layer on the porous Ti6Al4V scaffold (AH-porous Ti6Al4V). Subsequently, a hydrothermal treatment was employed to enable the formation of HA coating with nanopillar-like morphology on the alkali-acid-heat-treated surface (HT/AH-porous Ti6Al4V). The effects of surface modifications on apatite-forming ability, protein adsorption, cell attachment, cell proliferation and osteogenic gene expression were studied using apatite-forming ability test, protein adsorption assay and in vitro cell culture assay. It was found that the HT/AH-porous Ti6Al4V exhibited the highest apatite formation ability and best affinity to fibronectin and vitronectin. In vitro studies indicated that the mesenchymal stem cells (MSCs) cultured on the HT/AH-porous Ti6Al4V presented improved adhesion and differentiation compared with the porous Ti6Al4V and AH-porous Ti6Al4V.

Key words: Additive manufacturing, Biomaterials, Porous titanium scaffold, HA coating

Li Jun-Lei, Wang Shuai, Cao Fang, Lin Xiao, Wei Xiao-Wei, Zhao Zhen-Hua, Dou Xiao-Jie, Yu Wei-Ting, Yang Ke, Zhao De-Wei. Fabrication and Characterization of Nanopillar-Like HA Coating on Porous Ti6Al4V Scaffold by a Combination of Alkali-Acid-Heat and Hydrothermal Treatments[J]. Acta Metallurgica Sinica (English Letters), 2019, 32(9): 1075-1088.

Figures/Tables 13

Fig. 1 a 3D digital model of the diamond unit cell, b 3D digital model of the cylindrical porous Ti6Al4V, c macrophotograph of the cylindrical porous Ti6Al4V fabricated by AM, dSEM image of the porous Ti6Al4V fabricated by AM

Table 1 Structural and mechanical properties of the porous Ti6Al4V

Properties	Values
Strut diameter (μm)	408.3?±?8.8
Porosity (%)	67.9?±?1.1
Max pore size (μm)	691?±?11.2
Compressive strength (MPa)	82.1?±?3.7
Elastic modulus (GPa)	4.2?±?0.1

Fig. 2 a Pictures of the porous Ti6Al4V, AH-porous Ti6Al4V and HT/AH-porous Ti6Al4V; b surface morphology of HT/AH-porous Ti6Al4V; c cross section of coating on HT/AH-porous Ti6Al4V; d EDS analysis of the elements found on the surface of HT/AH-porous Ti6Al4V

Fig. 3 XRD patterns of porous Ti6Al4V, AH-porous Ti6Al4V and HT/AH-porous Ti6Al4V

Fig. 4 Ultrapure water and glycerol contact angle measurement on the porous Ti6Al4V substrate (a, d), AH-porous Ti6Al4V coating (b, e), HT/AH-porous Ti6Al4V coating (c, f)

Table 2 Mean contact angle (CA) values (±?standard deviation) and mean values (±?standard deviation) of the total surface-free energy (SFE) of the porous Ti6Al4V, AH-porous Ti6Al4V and HT/AH-porous Ti6Al4V

Samples	Mean CA (°)		Mean SFE (mJ/m²)
Samples	Ultrapure water	Glycerol	Mean SFE (mJ/m²)
Porous Ti6Al4V	91.7?±?1.7	72.6?±?0.5	52.2?±?3.1
AH-porous Ti6Al4V	48.6?±?0.6	36.2?±?1.1	61.7?±?2.3
HT/AH-porous Ti6Al4V	22.1?±?1.2	2.5?±?0.2	65.3?±?1.5

Fig. 5 Force-Displacement curve of the HT/AH-treated Ti6Al4V during the bonding strength test

Fig. 6 SEM photographs and EDS analysis of surfaces of porous Ti6Al4V (a-c), AH-porous Ti6Al4V (d-f), HT/AH-porous Ti6Al4V (g-i) immersed in SBF for 7 days

Fig. 7 A Concentrations of Ca2+ (a) phosphate (b) ions measured by ICP, which were released from porous Ti6Al4V, AH-porous Ti6Al4V and HT/AH-porous Ti6Al4V as a function of soaking time in deionized water; B influence of surface treatment on fibronectin (a) vitronectin (b) adsorption, n?=?3, asterisks (*) indicate statistical significance, p?<?0.05

Fig. 8 a Measurement of MSCs proliferation by CCK-8 assay after 1, 4 and 7 days incubation. For each group, n?=?3; asterisks (*) indicate statistical significance, p?<?0.05; bmorphology of MSCs adhesions on porous Ti6Al4V, AH-porous Ti6Al4V and HT/AH-porous Ti6Al4V surfaces after 24 h of cell culture; c live/dead staining of MSCs on surfaces of porous Ti6Al4V, AH-porous Ti6Al4V and HT/AH-porous Ti6Al4V after 7 and 14 days of cell cultures

Fig. 9 a ALP activities of MSCs incubated for 7, 14 and 21 days on surfaces of porous Ti6Al4V, AH-porous Ti6Al4V and HT/AH-porous Ti6Al4V; b relative mRNA expressions of ALP, Col-1, OCN, Runx2 and OPN after 7, 14 and 21 days of cell cultures, n?=?3, asterisks (*) indicate statistical significance, p?<?0.05

Table 3 Ratio of OD values between different groups after cultures for 1, 4 and 7 days

The ratio of OD value	porous Ti6Al4V	AH-porous Ti6Al4V	HT/AH-porous Ti6Al4V
Day 4/Day 1	2.214	1.854	1.909
Day 7/Day 4	1.309	1.308	1.472

Fig. 10 Mechanism of enhanced MSCs adhesion and differentiation on porous Ti6Al4V scaffold with nanopillar-like HA coating

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