The Study Of Nanosized Hydroxyapatite-g-poly(ε-caprolactone) Composite Biomaterals

The preparations of needle-like nanohydroxyapatite crystals (HA) were hydrothermalsynthesized at normal atmospheric pressure by orthogonal experiments. Fourier transform infraredspectroscopy (FTIR), X-ray diffraction(XRD) and transmission electron microscopy (TEM) wereused to characterize the structure and morphology of hydroxyapatite crystals. The influence ofconcentration of materials, stirring velocity, pH (pH＞10) and dispersant concentration on theshape and size of hydroxyapatite was studied. The change of preparation conditions affected themorphology of HA slightly. The needle-like nanohydroxyapatite crystals with high purity andgood dispersion could be obtained. Those HA were similar to the natural bone apatite incomposition, morphology, crystallinity and shape. The more important influencing factors of thepreparation of needle-like nanohydroxyapatite crystals (HA) studied by orthogonal method wereas follows: the concentration of dispersant and materials had obvious influence on the length ofHA crystals. Stirring velocity and pH were in favor of the ratio of length and diameter of HAcrystals. By the discussion of the influence factor on HA's preparation, we got the best condition-C_Ca(NO3)2=0.60mol/l, pH=12.0, V_DMF=28% and stirring velocity=300rm/min.The needle-like nanohydroxyapatite crystals (HA) were surface-grafted withpoly(ε-caprolactone) (PCL) by the ring-opening polymerization of e-caprolactones. Theeffects of HA on the crystallization behavior of PCL were investigated by FTIR, XRD,DSC and PLM. From the analyses about FTIR, XRD and DSC of HA-PCL compositebiomaterials, it was known that the degrees of PCL crystallinity in the HA-PCLcomposite biomaterials were lower than the degree of the pure PCL crystallinity. Such aphenomenon indicated that the degrees of PCL crystallinity in the HA-PCL compositebiomaterials were confined by HA. However, increases of HA content had no influenceto the degrees of PCL crystallinity and the crystalline structures. The crystallizationtemperatures and melting temperatures of PCL showed that the effects of HA promoting nucleation of PCL were increased with increasing the content of HA until up to 5wt%;PLM results showed that the crystallization sizes of PCL became smaller with increasingHA content, but they became larger when HA content was over 5wt%. Moreover, theHA-PCL composite biomaterials could produce distinct ring-banded spherulites withregular Maltese cross only when the HA content was low 1wt% and the temperature wasup to 45℃. From the analyses about TEM, SEM and molecular weight of HA-PCLcomposite biomaterials, it was known that the viscosity of melted PCL makes HAagglomerate in HA-PCL composite biomaterials, especially in HA-PCL compositebiomaterials in which HA content was high. The general mechanical properties ofHA-PCL composite biomaterials were enhanced very much, especially in HA-PCLcomposite biomaterials' toughness. Elongation break of HA-PCL composite biomaterialscould reach 700% when the synthesized time was enough and HA-PCL compositebiomaterials' molecular weight was above 40000. But Elongation break of HA-PCLcomposite biomaterials in which content was high declined because HA wasagglomerated. What's more, HA could make HA-PCL composite biomaterials' compressstrength enhanced, and HA-PCL composite biomaterials' compress strength achieveddemand of the natural bone.In conclusion, the degrees of PCL crystallinity declined by the addition of HA, but thedepression of the degrees of PCL crystallinity was helpful for improving HA-PCLcomposite biomaterials' toughness. However, HA-PCL composite biomaterials'toughness declined somewhat by reason of HA agglomerating. So HA-PCL compositebiomaterials in which HA content was 1wt%-7wt% had good thermal and mechanicalproperties when the synthesized time was enough and HA dispersed well. It implied thatHA-PCL composite biomaterials could apply to restoring and substituting dendriticbone.