Fabrication Techniques and Properties of Scaffolds - Biodegradable Polymer-Based Scaffolds for Bone Tissue Engineering - page 37

hand, xenogeneic cells obtained from non-human donors could provide enough
cell numbers. These cells have also the limitations due to immunogenicity and the
possibilities of the transmission of infectious agents. The mesenchymal stem cells
(MSC) located in the bone marrow, have also gained much interest in the bone tis-
sue engineering field. These cells have been used in clinical trials for applications
in bone tissue engineering (Pittenger 2001 ).
Polymer or composite scaffolds can either be seeded with cells prior to
use or simply implanted directly. In the former case, biocompatibility can be
enhanced by cell seeding, the growth of the desired tissue can be promoted
and the lost function can be provided and restored. The cells to be used to seed
the scaffolds, should be carefully chosen from the appropriate type of tissue
and are preferably harvested from the patient to minimize the tissue rejection
and reduce the probability of disease transmission. Cells may also be obtained
from a cell bank or derived by genetic engineering techniques. The polymers
may be coated with bioactive compounds such as cell attachment protein prior
to seeding which can help to assist cell attachment and tissue growth. After
seeding, the cells can be grown in vitro until the desired viability for a desired
application in obtained and the seeded scaffolds are ready for implantation
(Williams et al. 1999 ).
It has been demonstrated in the literature that polymeric biomaterials have the
potential to support osteoblast growth and development for bone tissue repair.
The attachment characteristics, self-renewal capacity, and osteogenic potentials
of osteoblast like cells (MC3T3-E1S14) were cultured on PHBV films compared
with tissue culture polystyrene (Kumarasuriyar et al. 2005 ). Cells were assayed
over 2 weeks and morphology, attachment, number and proliferation status etc.
were studied and it was reported that time dependent cell attachments acceler-
ated on PHBV substrate. The PHBV substrate was rougher and more hydrophobic
and it was concluded that PHBV polymer is a suitable candidate for the continued
development as a biomaterial for bone tissue engineering. Differentiation pattern
of Vero cells cultured on PLLA/PHBV blends were conducted and the study con-
cluded that the blends were efficient in maintaining cell growth and produced an
extracellualar matrix on them (Santos et al. 2004 ). Investigation of in vitro bio-
compatibility of poly(hydroxybutyrate-co-hydroxyhexanoate) (PHBHHx) which
is another member of polyhydroxyalkanoate biopolyesters, with bone marrow
stromal cells was conducted and their differentiation and proliferation was investi-
gated by histochemical assay and MTT (Yang et al. 2004 ). The results showed that
bone marrow stromal cells could attach, proliferate and differentiate into osteo-
blasts on PHBHHx films. It was also demonstrated that the main component of
PHBHHx is DL- β -hydroxybutyric acid (HB), a ketone body which is produced
in vivo and hence the effects of HB treatment on murine fibroblast L929 cells,
human umbilical vein endothelial cells, and rabbit articular cartilages were studied
(Cheng et al. 2005 ). The results collectively indicated that HB had a stimulatory
effect on cell cycle progression that was mediated by a signalling pathway depend-
ent upon increase in [Ca 2 + ] i and the study concluded that this trophic effect may
underlie the good biocompatibility observed for PHBHHx. It was also found that