Fabrication Techniques and Properties of Scaffolds - Biodegradable Polymer-Based Scaffolds for Bone Tissue Engineering - page 25

and Healy 2002 ). The mixture was then homogenized, poured into a copper
mold, and quenched in liquid nitrogen. After quenching, the polymer scaffold
was freeze-dried to remove the water and solvent. Scaffolds with porosity of
up to 90 % and median pore sizes in the range of 15-35 μ m could be fabri-
cated with an interconnected pore structure. In comparison to solvent cast-
ing/particulate leaching, the scaffolds produced with this method offer much
higher specific pore surface area as well as the ability to make thick poly-
mer scaffolds. But the overall pore size was smaller. These parameters were
very much dependent on the extrinsic parameters such as the ratio of polymer
solution to water and viscosity of the emulsion as these values influenced the
stability of the emulsion prior to quenching. With further adjustment, it was
possible to increase pore sizes.
2.2 Surface Modification for Bone Tissue Engineering
Scaffolds
Surface properties of any tissue engineering scaffolds are extremely important as
the surface interacts with the host tissue. Tissue engineering scaffolds should be
not only biocompatible and biodegradable, the surface should also be conducive to
cell attachment and subsequent tissue growth. Without altering other properties, it
is desired to adjust surface properties of the scaffolds to suit the intended applica-
tion. It is often required or desired to modify the surface to improve or maximize
cellular attachment or to provide a selection for the desired cell type or types. The
aim of the modification is to improve and optimize cellular attachment which can
be done by attaching or coating the surface with a bioactive compound or peptide
which promotes cellular attachment. Depending on the requirements, the coating
or bioactive compound may be attached to the surface either covalently or non-
covalently (Williams et al. 1999 ).
In order to alter the surface properties, one of the procedures involves the use
of gas plasma. This technique can introduce new functional groups by modify-
ing polymer surface covalently. Subsequently, the polymer surfaces can be further
modified by attachment of biologically active compounds. Growth factors can
stimulate cell and tissue growth, cellular attachment factors to promote cell and
tissue attachment, labeling agents to assist in locating and monitoring the implant,
drug molecules to aid in tissue repair, as well as agents to improve biocompat-
ibility, such as anti-coagulants to prevent thrombogenesis are the common com-
pounds that can be used in this procedure. In order to modify surface, it is also
possible to expose the surface of the polymer to other reactive reagents, including
acids, bases, and neocleophiles in addition to gas plasma. As for example, modifi-
cation can be done on the surface of the polymer in order to liberate acid groups
or charged species by pH treatments which can promote subsequent cellular
attachment and cell proliferation. In order to suit the particular needs of a tissue