Biodegradable PHBV Polymer-Based Scaffolds for Bone Tissue Engineering - Biodegradable Polymer-Based Scaffolds for Bone Tissue Engineering - page 52

with further strain compressing the solid itself, giving the final region of rapidly
increasing stress. The reinforcing effect of HA nanoparticles and the compres-
sive deformation behavior of PHBV and HA/PHBV scaffolds were similarly
observed in the HA-containing PHBV/PLLA scaffolds system (Sultana and
Wang 2008a , b ).

3.3 In Vitro Degradation of PHBV and HA/PHBV Scaffolds

In order to study the aqueous degradation of PHBV and 10 wt % nHA/PHBV
scaffolds, selected samples fabricated from 10 % (w/v) polymer solution were cut
to the correct height (1.5 mm) and diameter (10 mm) with a sharp razor blade and
weighed. Phosphate buffered saline (PBS) was prepared by dissolving tablets of
PBS (supplied by Zymed laboratories; USA) with distilled water. The specimens
were placed in sealable vials in 10 ml of PBS solution (pH 7.4). The samples were
pressed under PBS by applying vacuum. Air trapped in pores was removed by
venting with the aid of a vacuum oven. PBS solution was replaced with new solu-
tion each week. At regular intervals, samples from buffer were removed, exten-
sively rinsed with distilled water and dried under vacuum at 37 °C and weighed.
The experiment was performed for a period of 11 months and according to ASTM
F 1,635-04a standard test method (ASTM 2004 ). The test method is intended to
help assess the biodegradation rates (that is, the mass loss rate) and changes in
material or structural properties.
Molecular weight was measured using a Zetasizer Nano series (Malvern
Instruments Ltd., U.K.) which can perform molecular (Tsuji 2008 ) weight
measurements using a process called Static Light Scattering (SLS) which is a
non-invasive technique used to characterise the molecules in a solution. Static
light scattering technique makes use of the time-averaged intensity of scattered
light after the particles in a sample being illuminated by a light source such as
laser. The initial molecular weight of the sample was measured. Samples were
removed at each specified time period throughout the duration of the test, dried
and tested for the molecular weight as above. The autocatalysis rate equation is
given by:

(3.1)

LN M nt =− kt + LN M no

where;

M nt is the molecular weight after in vitro degradation at time t,

M no is the initial molecular weight,

K is the rate constant.

Three test samples were weighed prior to placement in the physiological solu-
tion. Upon completion of the specified time period, each sample was removed,
gently rinsed with distilled water and dried to a constant weight and the weight
loss were recorded. Weight loss during investigation was determined as: