Barbieri Thesis - BioMedical Materials program (BMM)

Chapter 6 – Fluid uptake as instructive factor
rel = tpol / tChlor
sp = rel – 1
inh = ln(rel) / ĉ
= [sqrt(2 · (sp – ln(rel) ))] / ĉ
ln(inh) = ln(K) + ā · ln(Mw) from which Mw = exp[ (ln(inh) – ln(K)) / ā ]
where tpol and tChlor are the measured time for the solution of polymer in chloroform
and pure chloroform to flow in the viscometer respectively, ĉ is the polymer
concentration in chloroform, K and ā are the Mark–Houwink constants related to
inherent viscosity (Table 2). The effective content by weight (%wt.) of apatite and
polymer in the extruded composites was determined by burning the polymer out from
the composites in a sinter oven (C19, Nabertherm, Lilienthal, Germany) at 900±5°C
for two hours. The bulk and surface chemistry of the composites were analysed with
XRD and FTIR as described in §6.2.1. Scanning electron microscopy (SEM) in
secondary electron modality was performed on loose granules to evaluate their
surface topography and apatite exposure.
Table 2. Mark–Houwink constants for the three polymers. They are constants valid when the
measurements are done in chloroform at the initial concentration of 0.1 g dL –1 and temperature 25°C and
can be used to calculate the weight average molecular weight with inherent viscosity inh. These values
are provided by the polymer supplier. [337] Please note that, as also confirmed by the supplier, since PLD
has a content of L–lactide monomer near 100%, its constants can be approximated to those typically
used for poly(L–lactide).
K
[dL g –1 ]
ā
PLD 4.7 · 10 –4 0.67
PLDL 2.0 · 10 –4 0.73
PDL 1.8 · 10 –4 0.72
6.2.4. Protein adsorption and fluid uptake from 0.1%FBS
Sterile granules (0.2 cc) of the composites and cylinders of the two tricalcium
phosphate ceramics were weighed before use (m0) and placed respectively in 2 and
3.8 mL of 0.1% foetal bovine serum (FBS, Invitrogen, Darmstadt, Germany)
containing 0.0025%v. sodium azide to prevent bacterial infection (in triplicate). They
were incubated at 37±0.5°C and 5% CO2 for one week. Proteins adsorbed from
FBS were measured after seven days using micro BCA assay kit (Pierce
Biotechnology Inc., Rockford, IL, USA) and spectrophotometer (Anthos) with
absorbance filter of 595 nm. The serum protein adsorbed by the samples (expressed
in g per cc) was estimated through a calibration serum proteins curve using FBS
after determining the total proteins content in FBS (i.e. 33.78±0.64 mg mL –1 ). The
granules and cylinders were then used to determine the uptake of serum. Excess fluid
was carefully wiped away from the analyzed samples and their wet weight was
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