BIOMATERIALS AND MANUFACTURING METHODS FOR SCAFFOLD IN REGENERATIVE MEDICINE - Intelligent Scaffolds for Tissue Engineering and Regenerative Medicine - page 39

1.3.3 Sterilization Method for Scaffolds
Sterilizability of polymeric scaffold biomaterials is an important
aspect of the properties because, especially, polymers have lower
thermal and chemical stability than other materials such as ceram-
ics and metals, and consequently, they are more di cult to sterilize
using conventional techniques. Commonly used sterilization tech-
niques are dry heat sterilization, autoclaving, radiation, and ethyl-
ene oxide gas (EOG) sterilization. Also, plasma glow discharge and
electronbeamsterilizationhavebeenrecentlyproposedduetotheir
conveniences 5 .
In dry heat sterilization, the temperature varies between 160 ◦ C
and 190 ◦ C. This is above the melting and softening temperatures of
many linear polymers like PLGA, resulting in shrinking of the scaf-
fold dimension. PLA scaffolds were sterilized by 129 ◦ Cfor60sec-
onds, resulting in minimal change in tensile properties. One of the
significant problems was the decrease of molecular weight, which
mightaffectthedegradationkineticsofthepolymers.Theonlypoly-
mers that can safely be dry-sterilized are polytetrafluoroethylene
(PTFE) and silicone rubber. However, ceramic and metallic scaf-
folds were safe in the range of this temperature. Steam steriliza-
tion (autoclaving) is performed under high steam pressure at rela-
tively low temperature (125 ◦ C-130 ◦ C). In the case of the family of
poly( α -hydroxy ester)s, the trace of water can deteriorate the PLGA
backbone.
ChemicalagentssuchasEOGandpropyleneoxidegasesandphe-
nolic and hypochloride solutions are widely used for sterilizing all
biomaterials since they can be used at relatively low temperatures.
Chemicalagentssometimescausepolymerdeteriorationevenwhen
sterilization takes place at room temperature. However, the time of
exposure is relatively short (overnight), and almost all of the scaf-
folds can be sterilized with this method. Especially, the cold EOG
sterilization method is the most widely method in the condition of
35 ◦ Cand95%humidity.WhilethehotEOGmethodof60 ◦ Cand95%
humidity can cause shrinkage of PLGA scaffolds. One of the signifi-
cant problems is the residual EOG caused harm on the surface and
withinthepolymer.So,itisimportantthatthescaffoldsbesubjected
to adequate degassing or aeration subsequent to EOG sterilization