Barbieri Thesis - BioMedical Materials program (BMM)

Chapter 6 – Fluid uptake as instructive factor
microscopy (SEM) in secondary electron modality. The porosity, along with specific
surface area and pore distribution, was studied outsource with mercury intrusion
(Micromeritics Instr. Corp., Norcross, GA, USA). The dissolution rate of the ceramics
has been evaluated in a simulated physiological solution (SPS) prepared by
dissolving NaCl (Merck, Darmstadt, Germany; concentration 8 g L –1 ) and 4–(2–
hydroxyethyl)–1–piperazineethane–sulfonic acid (HEPES) (Sigma–Aldrich, Steinheim,
Germany; concentration 11.92 g L –1 ) in distilled water. The pH of the solution was
adjusted to 7.3 with 2M NaOH (Sigma–Aldrich). Calcium ion release was evaluated
by soaking the ceramic cylinders in 100 mL of SPS at 37±1°C for eight hours. While
carefully stirring at 150±5 rpm with stirring bar (L=24 mm; ∅=6 mm) avoiding the
contact between bar and cylinders, the calcium ion concentration in SPS was
continuously recorded every minute using a calcium electrode (Metrohm 692 ISE
meter, Ag/AgCl reference electrode, Metrohm, Herisau, Switzerland).
6.2.2. Apatite preparation and characterization
Nano–apatite powder was synthesized by adding (NH4)2HPO4 (Fluka, Steinheim,
Germany) aqueous solution (c=63.1 g L –1 ) to Ca(NO3)2·4H2O (Fluka) aqueous
solution (c=117.5 g L –1 ) at the controlled speed of 12.5 mL min –1 and 80±5ºC, with the
reaction pH kept above 10 by using ammonia (Fluka). After precipitation, the resulting
powder was aged overnight, washed with distilled water to remove ammonia,
dehydrated in acetone (Fluka) and finally dried at 60±1°C. Its chemistry was then
investigated with X–ray diffractometry (XRD, MiniFlex II, Rigaku, Japan) using Cu K
radiation (=1.54056 Å) operating at 30 kV and 15 mA. Spectra were collected at
0.083 deg sec –1 in the 2 range 5–60 deg and later analysed with the software Jade
(v6.5.26, Materials Data Inc., Livermore, CA, USA). FTIR was run according a typical
KBr pellet protocol and spectra were collected in the range 400–4000 cm –1 and
analysed with the software OriginPro (v8.0773, OriginLab Corporation, Northampton,
MA, USA) without any pattern elaboration. The apatite particle size and morphology
were characterized using transmission electron microscopy (TEM, Tecnai–200FEG,
FEI Europe, Eindhoven, the Netherlands).
6.2.3. Composites preparation and characterization
The precipitated powder was extruded with three different polymers in a ratio
50/50%wt. apatite/polymer to make three composites. The polymers used were
96%mol. L–lactide/4%mol. D–lactide copolymer (PLD, declared inherent viscosity
5.67dL g –1 with residual monomer