| 其他摘要 | ABSTRACT
Artificial bone materials are those used to substitute broken human bone in bone repair surgery. They include metallic materials, ceramics and polymer based composites．The metallic materials are easy to cause stress shielding effect due to their much higher modulus compared to human bone. As well their biological properties are poor compared to the other two kinds of materials．The bioceramics materials, which can’t be used in load-bearing parts due to the low strength and bad ductility, are always added into other two kinds of materials as fillers to enhance their biological activity. The polymer based composites can be adjusted to achieve good mechanical properties as well be modified to have good biocompatibility by filling with bioceramics (hydroxyapatite(HA), for example). However, its strength and modulus is too low to match the requirements of the mechanical properties of bone substitutes. Therefore, the main research purpose of polymer based bone substitute materials is to increase the strength and modulus to meet the human load-bearing bone’s requirements.
Polyetheretherketone (PEEK) is one thermal plastic which has good mechanical properties. It was shown that the biological material of Polyetheretherketone/Hydroxyapatite （PEEK/HA） composites can approach the lower-limit of the mechanical requirements of bone substitutes. However, its mechanical properties were far from catching up with the requirements for load bearing human bone. Carbon fibre (CF) has good mechanical properties and chemical resistance, and is always used as a common reinforcement to reinforce other materials. For these reasons, Polyetheretherketone/Hydroxyapatite/Carbon fibre （PEEK/HA/CF ）composites, which is made by adding short CF to reinforce the PEEK/HA composites, might be one material that can well meet the mechanical requirements of load-bearing bone substitutes.
In this paper， PEEK/HA and PEEK/HA/CF composites were made by injection molding after blending in rheometer. The tensile, flexural and Izod impact properties of the two kinds of composites were investigated. The reinforcement and fracture mechanisms were discussed by analyzing the scanning electronic microscope (SEM) photomicrograph of the composites fracture surfaces. PEEK/HA and PEEK/HA/CF composites had been soaked in three simulated body fluid (SBF)(each SBF has a different prepared process) for studying the in vitro bioactivity, and the mechanisms of the product growth during soaking were discussed.
Rheometer was used to blend HA with PEEK (PEEK/CF) to make homogeneous distribution of the fillers. Back-scattered electronic microscope (BEM) photos showed that HA and CF were well dispersed in PEEK matrix. The CF stayed on surface of the molded samples had a random orientation distribution. In contrast, the CF situated in interior part of the samples had a favorite orientation along the melt flow direction. These orientation features were determined by the fluid mechanics during injection molding process.
It was revealed that the tensile and flexural modulus increased with the increase of HA content in PEEK/HA composites. On the other hand, the tensile and flexural strength decreased. Furthermore, the increase of HA content would also cause the PEEK/HA composites more brittle. This was evidenced by SEM photos of fracture surfaces which showed that increase of HA content inhibited the plastic deformation of PEEK matrix and thus induced the decrease of strain at break. This was evidenced by photos of fracture surfaces. The trend of impact strength of PEEK/HA composites with HA content was complicated due to the complex toughening mechanisms from both of the plastic deformation of PEEK resin matrix and the pull-out and debonding of HA particles from the matrix. However, the mechanical properties of PEEK/HA composites is far away from the requirements of human bone substitutes, therefore, it couldn’t be used as one bone substitute material.
PEEK/HA/CF composites have much better mechanical properties than PEEK/HA composites. It was shown that with the same HA content the tensile strength and modulus, as well as the flexural strength and modulus, increased with the increase of CF content in PEEK/HA/CF composites. However, when the CF content was fixed, the tensile and flexural modulus increased with the increase of HA content in PEEK/HA/CF composites, while the tensile and flexural strength showed less change. The contribution from the pull-out and debonding of HA particles from PEEK matrix on the impact work absorption is far less than its negative effect of restraining the plastic deformation of PEEK resin matrix. Therefore, for PEEK/HA/CF composites with the same HA content, the impact strength increased with the increase of CF content. On the other hand, for PEEK/HA/CF composites with the same CF content, the impact strength decreased with the increase of HA content. In one word, the CF has dominant influence on the mechanical properties of PEEK/HA/CF composites.
There are three SBF, each SBF has its own PH value before the final PH value adjusting process. When soaking these samples of PEEK/HA and PEEK/HA/CF composites into these SBF, we found that there was a close relationship between the PH value during the SBF preparing process and the product growth conditions. It was evidenced that the samples soaked in SBF that had a neutral PH value before and after PH value adjusting process generated more products on their surface than those samples soaked in the other two kinds of SBF. It was also observed that the quantity of the grown product was also determined by the HA content in the original samples. The higher the HA content in the samples, the more product generated on their surfaces. It was further showed that the nucleation stage and growth process of HA product had a close relationship with the enriched process of calcium ions in SBF by observing the BEM photos of cross-section of samples soaked in SBF for a given period.
In conclusion, the PEEK/HA/CF composites performed good bioactivity and wonderful mechanical properties, such as high tensile modulus and high tensile strength, which had a good match to the requirements of load-bearing human bone substitutes. Therefore, the PEEK/HA/CF composite is expected to be used as a candidate for human bone substitute materials.
Key Words: PEEK/HA，PEEK/HA/CF，mechanical properties，bioactivity。 |
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