Scaffolds for Tissue Engineering - Biodegradable Polymer-Based Scaffolds for Bone Tissue Engineering - page 7

osteoprogenitor cells and osteoblasts to occupy the entire matrix after the implan-
tation (Liu et al. 2006 ). It was also mentioned that not only porosity, the pore sizes
must be of suitable diameter to allow osteoblasts and osteoblast-like cells in order
to migrate into the center of the matrix allowing complete healing. Thus the neces-
sity of a pore structure tends to acquire critical design decisions in order to con-
sider the structural integrity of the matrix (Liu et al. 2006 ).
1.3.3 Mechanical Properties
In fact, bone responds to the presence or absence of physical load. The resorp-
tion or formation of bones by body occurs in response to these loads. It has been
mentioned that it is important to design a matrix that possess mechanical proper-
ties that are similar to the tissue in the immediate surrounding area of the defect
(Liu et al. 2006 ). Around the implant site, an overdesigned matrix can induce bone
resorption while an underdesigned matrix may fail as a mechanical support to the
skeleton. By material selection, formation of composite structures, the overall
porosity of the matrix, the mechanical properties can be varied.
1.3.4 Degradation Properties
In order to match cell/tissue growth in vitro or in vivo, scaffolds should be bio-
degradable and should possess appropriate degradation rate (Hutmacher 2000 ;
Ma 2004 ). According to ASTM F1635-04a (ASTM 2004 ), if a material's degrada-
tion is primarily hydrolytic in nature, physiological conditions may be modeled at
37 °C under controlled pH conditions. Throughout the degradation period, various
properties can be monitored.
1.3.5 Sterilizability
In order to prevent infection, scaffold materials must be sterilizable (Zhou 2007 ).
The scaffolds should possess minimum residues if chemicals such as ethylene
oxide are used to sterilize the samples. Gamma radiation is an accepted alternative
to ethylene oxide sterilization. Sterilization methods should be carefully selected
so that it can have little effect on the properties of scaffolds. The effects of γ -ray
irradiation on PHB and PHBV had been reported by several researchers. It was
reported that PHB and PHBV could be sterilized by γ -ray irradiation (Holmes
1982 ). Some reduction in molecular weight was reported from this sterilization
technique. It was reported that PHBV membranes were sterilized by UV irradia-
tion for 30 min which showed satisfactory cell attachment, spreading and growth