Fabrication Techniques and Properties of Scaffolds - Biodegradable Polymer-Based Scaffolds for Bone Tissue Engineering - page 26

engineering or medical application, the surfaces can be modified and tailored
depending on the selected method.
It is often necessary to modify the surface properties without changing the bulk
attributes as a biomaterial rarely possess good surface characteristics suitable for
bone tissue engineering. It has been described that biological tissues interact with
mainly the outermost atomic layers of an implant and the primary interactions
scope is about 0.1-1 nm (Ong and Lucas 1998 ; Zhao et al. 1999 ; Chen 2006 ). In
order to achieve the desired biological responses, it is often necessary to modify
the biomaterial surface and hence surface modification of biomaterials is one of
the key issues in the development of tissue engineering.
In order to modulate tissue responses to biomaterials, biochemical surface
modification has received increasing consideration. Collagen is one of the two
primary components of extracellular bone matrix. It contains specific amino acid
receptors that allow them to bind directly to cell-surface receptors. It was reported
that surface properties of PDLLA could be modified by combining plasma treat-
ment and collagen modification (Yang et al. 2002 ) and the roughness as well as
hydrophilicity was improved. Cell affinity of PDLLA was greatly improved.
Collagen immobilization was carried out on the surface of ultra thin PCL films
and it was found that the hydrophilicity was improved significantly after the sur-
face modification (Cheng and Teoh 2004 ). The films also showed excellent cell
attachment and proliferation rate.
2.3 Protein Adsorption
Within seconds of implantation, protein adsorption onto the foreign surface occurs
when biomaterials are implanted into animals or humans. By rapid protein adsorp-
tion it is meant that the arriving cells at the biomaterial surface interact with the
adsorbed protein layer in stead of the material itself (Balasubramanian et al. 1999 ).
The response between implanted biomaterial and the body depends on the initial
protein adsorption onto a biomaterial surface. Thus adsorption of protein plays
a key role. The three primary plasma proteins are albumin, immunoglobulin and
fibrinogen (Tang and Eaton 1995 ). Among these three proteins, albumin is the pre-
dominant plasma protein which makes up 60-70 % of plasma. It was reported that
albumin could “passivate” the surface of biomaterial and reduced the acute inflam-
matory response to the biomaterial (Tang and Eaton 1995 ). Comprising about
20 % of the plasma, immunoglobulins is the second most abundant class of plasma
protein and is reported not to appear for initiation of inflammatory responses to
biomaterial implants (Tang et al. 1993 ). Being the third primary plasma protein,
fibrinogen, in contrast to albumin and immunoglobulin, plays the major role in the
inflammatory response to the implant (Tang and Eaton 1995 ).
It was reported that osteoblast adhesion was significantly greater on nano-
phase alumina, titania and HA which was due to enhanced adsorption of protein
vibronectin by the bioceramics (Webster et al. 2000 ). Protein adsorption of cerium