Preparation and characterization of polyoxymethylene‐copolymer/hydroxyapatite nanocomposites for long‐term bone implants

Abstract

In this work, new polyoxymethylene (POM)/hydroxyapatite (HAp) nanocomposites for long‐term bone implants have been obtained via extrusion and injection molding processes and characterized by differential scanning calorimetry (DSC), temperature‐modulated DSC (TMDSC), scanning electron microscopy (SEM), transmission electron microscopy (TEM), wide‐angle X‐ray diffraction (WAXD), Fourier transform infrared spectroscopy (FTIR), thermogravimetry (TG), and tensile mechanical and in vitro stability tests. Based on the DSC results, it was found that the degree of crystallinity increases for POM/0.5% HAp sample and decreases for POM/1.0% HAp and POM/2.5% HAp. SEM and TEM observations for POM/HAp nanocomposites indicated that the dispersion of HAp in the polymer matrix was uniform and the diameter of the HAp particles was less than 100 nm for most of them. Young's modulus increases with increasing HAp concentration, whereby elongation at break decreases. On the contrary, HAp concentration does not have a significant influence on the tensile strength. TG results show that for POM/0.5% HAp, POM/1.0% HAp, and POM/2.5% HAp, thermal stability slightly increases in comparison to pure POM, whereas for POM/5.0 HAp and POM/10.0% HAp, lower thermal stability was observed. In vitro data reveal that with an increase of HAp content, bioactivity of nanocomposites increases; a good in vitro chemical stability of POM and POM nanocomposites was confirmed. Copyright © 2011 John Wiley & Sons, Ltd.

The Influence of Nanohydroxyapatite on the Thermal, Mechanical, and Tribological Properties of Polyoxymethylene Nanocomposites

“…while for POM HAp nanocomposites the highest degree of crystallinity was determined for T2H5, next one was for UH5, and the lowest one was for DH5 (52.94%, 46.98%, and 41.18%, resp.) [15][16][17]. The same trend was observed for the hardness results that confirm our previous results.…”

“…The same trend was observed for the hardness results that confirm our previous results. Different hardness values ( Figure 6) can be probably attributed to crystalline and amorphous regions as shown in SEM microphotographs [15][16][17]. This dependence was well documented in the literature for different macromolecular systems, and, generally, microhardness increases with increasing degree of crystallinity of polymer [33].…”

“…On the other hand, incorporation of nanoparticles into POM matrix causes the effect of heterogeneous nucleation leading to thinner spherulites and lower degree of crystallinity, which can help to improve impact strength. The decrease of the crystallinity degree reduced the tensile strength [8,15,16]. We found in an in vitro evaluation that addition of HAp nanoparticles to POM matrix enhances bioactivity of the nanocomposites, and an excellent stability of POM/HAp nanomaterials under these conditions was confirmed [16].…”

“…This effect can be attributed to the higher degree of crystallinity of DH and T2H as well as their nanocomposites when comparing to the degree of crystallinity of UH copolymer and its nanocomposites [15][16][17]. The reason is that ordered crystalline fractions produce stronger intermolecular interactions, leading to increased mechanical properties and, consequently, to an increase of ultrasonic wave velocity [35].…”

“…Please note that in our previous papers we investigated only tensile behaviour of POM/HAp nanocomposites [15][16][17]. In this study three POM types (homopolymer and two copolymers) with similar melt flow index and processability but with different mass-average molar mass have been used to find the best formulation for long-term orthopaedic implants.…”