Highly porous titanium (Ti) scaffolds with bioactive microporous hydroxyapatite/TiO2 hybrid coating layer

doi:10.1016/j.matlet.2009.06.023

Materials Letters

Volume 63, Issue 23, 30 September 2009, Pages 1995-1998

https://doi.org/10.1016/j.matlet.2009.06.023 Get rights and content

Abstract

Highly porous Ti scaffolds with a bioactive microporous hydroxyapatite (HA)/TiO₂ hybrid coating layer were fabricated using the sponge replication process and micro-arc oxidation (MAO) treatment to produce the porous Ti scaffold and hybrid coating layer, respectively. In particular, the morphology and chemical composition of the hybrid coating layer were controlled by carrying out the MAO treatment in electrolyte solutions containing various concentrations of HA, ranging from 0 to 30 wt.%. The fabricated sample showed high porosity of approximately 70 vol.% with interconnected pores and reasonably high compressive strength of 18 ± 0.3 MPa. Furthermore, the surfaces could be coated successfully with a bioactive microporous HA/TiO₂ hybrid layer. The amount of HA particles in the hybrid coating layer increased with increasing HA content in the electrolyte solution, while preserving the microporous morphology. This hybrid coating improved the osteoblastic activity of the porous Ti scaffolds significantly.

Introduction

Titanium (Ti) and its alloys are well recognized as one of the most attractive biomaterials that have been extensively used for dental and orthopedic implants over the past few decades, owing to their excellent mechanical properties (e.g., high strength and toughness), biocompatibility, and chemical stability [1]. Recently, considerable effort has been made to produce porous Ti scaffolds to match their mechanical properties (particularly, elastic modulus and stiffness) to those of the surrounding bone and provide a favorable environment for bone ingrowth [2], [3].

Currently, there are a variety of manufacturing methods available for producing porous Ti scaffolds, including the sintering of metal powders [4], space holder method [5], rapid prototyping method [6], and freeze casting method [7,8]. Recently, the sponge replication method has also been proven to be a very useful method, since it can produce porous Ti scaffolds with high porosity and good interconnections between the pores [9], [10], [11]. These characteristics are believed to be quite beneficial to the bone ingrowth and vascularization of newly formed tissue [12]. In addition, the biocompatibility of the porous Ti scaffolds can be improved significantly by coating their surfaces with bioactive materials [10], [11], [13], [14], [15].

Therefore, in this study, we fabricated highly porous Ti scaffolds using the polymeric sponge replication method and coated their surfaces with a bioactive, microporous HA/TiO₂ hybrid coating layer using the micro-arc oxidation (MAO) treatment. In particular, the MAO treatment was carried out in an electrolyte solution containing HA particles to incorporate them into the coating layer in an in-situ manner [16]. In order to the control morphology and chemical composition of the hybrid coating layer, HA was added to the electrolyte solution at various concentrations (0, 10, 20, and 30 wt.%). The porous Ti scaffolds prepared were characterized in terms of their pore structures, crystalline phases, chemical compositions, and compressive strengths. The preliminary osteoblastic activity of the samples was also evaluated using in vitro tests.

Section snippets

Experimental procedure

Highly porous Ti scaffolds were produced by coating a ~ 15 × 15 × 20 mm polyurethane sponge (25 pores per inch, Jeil Urethane Co., Korea) with a titanium hydride (TiH₂) slurry that was prepared by dispersing 60 g TiH₂ powders (Alfa Aesar, Ward Hill, MA, USA) in 200 ml of ethanol containing 3 g of triethyl phosphate (TEP; (C₂H₅)₃PO₄, Sigma-Aldrich, USA) as a dispersant, and 3 g of polyvinylbutyl (PVB, Sigma-Aldrich, USA) as a binder. The TiH₂-coated sponges were then heat-treated at 800 °C for 3 h to

Results and discussion

The sponge replication method allowed the production of highly porous Ti scaffolds with good interconnections between pores, as shown in Fig. 1 (A). In addition, it was observed that Ti walls could be densified well without noticeable defects, such as pores and cracks, as shown in Fig. 1 (B). These results suggest that the sponge replication method using a TiH₂ slurry is quite useful for producing highly porous Ti scaffolds. The sample had a reasonably high compressive strength of 18 ± 0.2 MPa at

Conclusions

Highly porous Ti scaffolds with a bioactive, microporous HA/TiO₂ hybrid coating layer were fabricated. The porous Ti scaffolds produced using the polymeric sponge replication method had a highly porous structure with interconnected pores and a reasonably high compressive strength of 18 ± 0.3 MPa at a porosity of approximately 70 vol.%. In addition, the surfaces of the Ti struts were coated successfully with the microporous HA/TiO₂ hybrid layer using the MAO treatment in the electrolyte solution

Acknowledgments

This research was supported by a grant from the Fundamental R&D Program for Core Technology of Materials funded by the Ministry of Knowledge Economy, Republic of Korea.

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Highly porous titanium (Ti) scaffolds with bioactive microporous hydroxyapatite/TiO2 hybrid coating layer

Abstract

Introduction

Section snippets

Experimental procedure

Results and discussion

Conclusions

Acknowledgments

Biomaterials

Mater Sci Eng A

Scripta Mater

Biomaterials

Acta Mater

Mater Lett

Powder Technol

Mater Lett

Highly porous titanium (Ti) scaffolds with bioactive microporous hydroxyapatite/TiO₂ hybrid coating layer