Elsevier

Scripta Materialia

Volume 45, Issue 10, 19 November 2001, Pages 1147-1153
Scripta Materialia

Processing of biocompatible porous Ti and Mg

https://doi.org/10.1016/S1359-6462(01)01132-0Get rights and content

Abstract

A new powder manufacturing process for Ti and Mg metallic foams designs porosity, pore size and morphology. These open-cellular foams (pores: 200–500 μm) have exceptional characteristics (e.g., Ti foam porosity 78%, compressive strength 35 MPa, Young's modulus 5.3 GPa). Anticipated applications include biocompatible implant materials.

Introduction

Metallic foams are a new class of materials with extremely low densities and unique combination of excellent mechanical, thermal, electrical and acoustic properties [1]. They offer opportunities for a wide range of applications, such as shock and impact energy absorbers, dust and fluid filters, engine exhaust mufflers, porous electrodes, high-temperature gaskets, silencers, flame arresters, heaters, heat exchangers, catalyst supporters, construction materials [2], [3], [4], [5], [6], and most importantly, biocompatible implants, because their open-cellular structure permits the ingrowths of the new-bone tissues and the transport of the body fluids [7], [8]. It is especially attractive that the strength and the Young's modulus of the cellular materials can be adjusted through the adjustments of the porosity to match the strength and the Young's modulus of the nature bone. Considerable progress has been made recently in the production of metallic foams. However, methods for production biocompatible metal foams are far from perfect because the requirements on the porous implant are the designed pore morphology, pore size, porosity and high purity to guarantee the biomechanical properties and the biocompatibility. Investigations indicated that in porous bone substitutes, the optimal pore size for attachment, differentiation and growth of osteoblasts and vascularization is approximately 300–400 μm [9] or 200–500 μm [8]. The aim pore-size of the present study is 200–500 μm for flexibility.

The ideal bone substitute material should be osteoconductive in order to allow as rapid as possible integration with host bone, biodegradable and bioresorbable at a preferred rate in order to eventually be replaced by newly formed natural bone, and strong enough to fulfill required load bearing functions during the implantation period. It should preferably exhibit osteoinductive characteristics in order to encourage rapid new bone formation although this may require the incorporation of biological factors with synthetic materials. Studies on the use of biodegradable organic based porous scaffolds for some of these applications have been suggested. These have usually involved polylactide, polyglycolide, or copolymers formed from these materials [10]. A major limitation of these porous polyester based materials is their relatively low moduli and strength properties making them unsuitable for load bearing bone substitute applications [11]. Hence it is indispensable to develop new bone-substitute materials with high strength and appropriate Young's modulus to ensure the biomechanical properties of nature bones.

It is well known that Ti and some Ti alloys are nowadays the most attractive metallic biomaterials due to their excellent mechanical properties, wonderful biocompatibility, and the good corrosion resistance [12], [13]. Mg has been recently recognized as a very promising biomaterial for bone implants because of its characteristics of biodegradable and bioresorbable [14]. In the present study, porous Ti and Mg foams were fabricated by powder metallurgical process for bone substitute applications. The fabricating processes, the mechanical properties, and the potential applications of these metallic foams are described.

Section snippets

Experimental procedures

Starting materials are commercially available Ti powders (purity: 99.9%, powder size ≦45 μm) and Mg powders (purity: 99.9%, powder size ≦180 μm). Ammonium hydrogen carbonate particles and carbamide particles were used as spacer materials. Spacer particles are of spherical shapes and have a size in the range of 200–600 μm and purity of 99.0%. The selection of the size of the spacer particles was determined according to empirical investigations. The choosing of the spacer material was based on

Results and discussions

The optical micrographs of the porous Ti foam and the Mg foam are shown in Fig. 2. The porosity of the Ti foam is 78% and the Mg foam 50%. The scanning electron micrographs of the porous Ti and Mg are shown in Fig. 3. It can be seen that in these porous metals there are two types of pores, i.e. small isolated micropores distributed in the wall of the open interpenetrated macropores. The former is of several micrometers, and the latter is in the range of 200–500 μm. These micropores are

Summary

Biocompatible porous metals, including Ti and Mg, are successfully fabricated by an innovative powder metallurgical process. The porous morphology, pore size, and the porosity of the metals can be controlled exactly in this powder metallurgical process. In the present study, Ti foams and Mg foams have been produced with an open-cellular structure; and their pore size distribution is in a range of 200–500 μm, which is specially managed for their appropriateness for porous bone substitutes. The

Acknowledgements

The present work has been supported by the NEDO (New Energy and Industrial Technology Development Organization, Japan) Project of “Preparation of Biocompatible Porous Ti Implant Materials with High Strength and Ultra-Low Density”.

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