Biodegradable PHBV Polymer-Based Scaffolds for Bone Tissue Engineering - Biodegradable Polymer-Based Scaffolds for Bone Tissue Engineering - page 57

It was established that the strength and stiffness of the materials reduced on
in vitro environment exposure in PBS at 37 °C for periods up to 4 months
(Fig. 3.13 ). The degradation rate was a function of composition and process-
ing conditions and the materials did not show any conclusive evidence of exten-
sive structural breakdown in vitro during the study period. Major morphological
changes were observed in composite scaffolds after the study period (Fig. 3.14 ).
Fabrication, characterization, and in vitro degradation of composite scaffolds
based on PHBV and bioactive glass (BG) were performed by another research
group (Li et al. 2005 ). These results suggested that incorporation of BG into
PHBV could improve the hydrophilicity of the composites and the enhancement
was dependent on the BG content.
The degradation assessment of the scaffolds was performed in PBS at 37 °C
and the measurement of molecular weight loss of the PHBV scaffolds showed that
the degradation rate is slow. The weight loss, crystallinity, compressive mechan-
ical properties of PHBV scaffolds were also monitored and compared with that
of 10 % nHA/PHBV composite scaffolds. The nano-sized HA particles in the
composite scaffolds accelerated the weight loss of the composite scaffolds due
to dissolution of nHA particles and capillary water uptake through the interfaces
of nHA particles. This process can increase the hydrolytic attack of the polymer
matrix. The increasing trend of crystallinity of PHBV scaffolds, nHA/PHBV scaf-
folds was due to the degradation of the amorphous part of the polymers. This
degradation was a result of hydrolytic scission of polymer chains in the more sus-
ceptible amorphous part of the scaffold matrix. The decrease in compressive prop-
erties can emphasize the fact that degradation proceeded with random cleavage of
polymer chain backbone (Sultana and Khan 2012c ).
3.4 Surface Modification and In Vitro Biological Evaluation
of the Scaffolds
In order to modify surface properties, rat tail collagen type 1, BDB Falcon (BD
Bioscience, USA) was used as a thin coating. The collagen solution of concentration
4.46 mg/ml was diluted with phosphate buffered saline (PBS) and used as a concentra-
tion of 0.446 mg/ml for the coating purpose. The scaffold specimens were immersed
in the collagen solution and incubated at room temperature for 1 h. The scaffolds spec-
imens were washed with PBS and then air dried (Sultana and Wang 2012b ).
It was observed that collagen was simply adsorbed onto the surface. It can be
stated that the surface modifying collagen solution spread well on the scaffold
substrate in order to ensure coating efficiency. The wettability of PHBV-based
scaffolds with or without coating was measured by measuring the contact angles
that showed variation between the scaffolds surfaces. It was found that the con-
tact angle of PHBV scaffolds, and nHA/PHBV scaffolds decreased after coating
(Sultana and Wang 2012b ).