Elsevier

Materials Letters

Volume 58, Issues 3–4, January 2004, Pages 357-360
Materials Letters

Compressibility of porous magnesium foam: dependency on porosity and pore size

https://doi.org/10.1016/S0167-577X(03)00500-7Get rights and content

Abstract

Mechanical properties of porous magnesium with the porosity of 35–55% and the pore size of about 70–400 μm are investigated by compressive tests focusing on the effects of the porosity and pore size on the Young's modulus and strength. Results indicated that the Young's modulus and peak stress increase with decreasing porosity and pore size. The mechanical properties of the porous magnesium were in a range of those of cancellous bone. Therefore, it is suggested that the porous magnesium is one of promising scaffold materials for hard tissue regeneration.

Introduction

There has been an increasing interest in porous scaffold substitutes for bone tissue engineering applications because osteoblasts obtained from the patient's hard tissues can be expanded in culture and seeded onto the scaffold that will be gradually integrated with new bone tissues [1], [2], [3], [4]. Several types of scaffold materials, for example, hydroxyapatite (HA), poly(-hydroxyesters) and natural polymers such as collagen and chitin [5], [6], [7], [8] have been developed for tissue engineering bone and cartilage. In particular, calcium apatite scaffolds for bone substitutes are currently commercially available. The porous bioactive ceramic and polymeric scaffolds promote bone or tissue ingrowth into open pores, thereby allowing a rapid return to the physiologically acceptable state of function. However, the porous bioactive ceramic and polymeric scaffold materials show poor mechanical properties. For example, the porous bioactive ceramics are very brittle. Also, the strength and Young's modulus of the porous polymers are often lower than those of human bones. Thus, they are hardly applicable in load-bearing applications. Therefore, it is crucial to develop new scaffold implant materials with both excellent mechanical properties and a porous structure similar to natural bones. Furthermore, it is desirable for the scaffold materials to be biodegraded and bioresorbed completely after an appropriate period in a human body.

Magnesium has been recently recognized as a promising biomaterial for bone substitute materials due to its excellent properties, e.g. relatively low Young's modulus and proper strength [9], excellent biocompatibility [10], [11], biodegradability and bioresorbability [12], [13]. These unique features make porous magnesium an ideal scaffold for bone tissue regeneration. The purpose of the present study is to develop porous magnesium with Young's modulus and strength close to those of nature bone. Mechanical properties of porous magnesium materials with the porosity of 35–55% and with the pore size of about 70–400 μm are investigated by compressive tests focusing on the effects of the porosity and pore size on the Young's modulus and strength.

Section snippets

Experimental procedures

Pure magnesium powder (purity≧99.9%, powder size≦180 μm) was used as a starting material. Carbamide (CO(NH2)2) particles were chosen as space holder particles. Carbamide particles with four kinds of particle sizes, i.e. 45–100; 100–200; 200–300; 300–500 μm, were prepared. The fabrication method of porous magnesium materials was the same as that in the previous study [14]. Briefly, the magnesium powder and the space holder particles were thoroughly mixed in an agate mortar. The mixed powder was

Results and discussion

The SEM micrograph of a porous magnesium specimen is shown in Fig. 1, where the porosity of the specimen is 45% and the average pore size is 168 μm. Some pores were interconnected and the porous magnesium had an open-cell structure. However, there were isolated pores, which were not interconnected. The number of isolated pores increased with decreasing porosity. The pore size distribution for porous magnesium is not as large as that for porous aluminum produced by liquid-state process [15].

Conclusions

Mechanical properties of porous magnesium with the porosity of 35–55% and with the pore size of approximately 70–400 μm were investigated by compressive tests focusing on the effects of the porosity and pore size on the Young's modulus and strength. Results indicated that the Young's modulus and peak stress increases with a decrease in porosity and pore size. In particular, the specimen with the low porosity of 35% (average pore size of 250 μm) showed the high Young's modulus of 1.8 GPa and the

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