Barbieri Thesis - BioMedical Materials program (BMM)

Chapter 5 – Alkali surface treatment effects
a=9.41±0.03 Å and c=6.88±0.02 Å, which are similar to those reported in literature for
human cortical bone apatite (a=9.38 Å, c=6.87 Å) on the same reflection planes. [315]
Using CR (Figure 1b) we observed that the spectrum of the synthesized apatite
contained all the characteristic vibrational bands for a calcium phosphate apatite, and
chemical similarity with bone mineral was seen (see also Table 3 in Chapter 4).
Needle–like apatite particles having 200–350 nm length and 20–30 nm width were
seen with TEM (Figure 1c), and such size is similar to that of needle–like apatite
observed in human cortical bone. [23] Interplanar spacing (i.e. the d–value) in the
synthesized apatite has been estimated with FFT–HRTEM as 7.85±0.39 Å (Figure
1d) that is close to the typical values recorded for synthetic hydroxyapatite. [365]
5.3.2. Characterization of composites
5.3.2.1. Physicochemical (granules and discs)
The composite was prepared by extruding high molecular weight 96%mol. L–
lactide/4%mol. D–lactide copolymer with calcium phosphate apatite particles.
Measurements with Ubbelohde viscometer showed significant post–extrusion
decreases in intrinsic viscosity for the copolymer contained in the composites.
However, the final three composites had comparable polymer phase intrinsic viscosity
(Table 2). Chemical characterization demonstrated that, after alkali treatment, the
chemistry was similar for the three composites. In particular, XRD showed that the
diffraction peaks of apatite and copolymer were present in the patterns of all the
composites indicating their compositional similarity (Figure 1a). These observations
are strengthened by the presence of all vibrational bands of copolymer and apatite in
CR patterns of the composites (Figure 1b). Further to this, CR indicated that surface
treatment had no effects on the surface chemistry since no additional phase than
apatite and polymer were detected (Figure 1b). For more in–depth results about CR
analysis on composites containing this copolymer, see also Table 3 in Chapter 4.
After burning the polymer out, the CaP content was similar for M1 and M2 but M0
had slightly less apatite content (ANOVA, p>0.09; Table 3), which is probably due to
the fact that alkali surface treatment removed the polymer from the surface. SEM
observations confirmed that alkali treatment exposed apatite particles that were
previously covered by the polymer, generating fairly uniform nano–structured surfaces
(Figure 2). BSEM of the cross–sectioned granules showed (significant different)
increases in the thickness of the exposed apatite layers with increasing treatment
strength (ANOVA, p