Constitutive Effects of Hydrolytic Degradation in Electro-Spun Polyester-Urethane Scaffolds for Soft Tissue Regeneration - Tissue Engineering: Computer Modeling, Biofabrication and Cell Behavior - page 51

The change of mechanical properties associated with degradation has been
studied for various biodegradable polymers. Raghunath et al. [ 25 ] characterised
solid sheets of biodegradable polyhedral oligomeric silsesquioxane modified
poly(caprolactone/carbonate) urethane/urea during accelerated in vitro degradation
of up to eight weeks. Kang et al. [ 26 ] studied the in vitro degradation of a porous
poly(l-lactic acid)/ β -tricalcium phosphate scaffold, fabricated by particulate leach-
ing, of up to six weeks and reported the effect on the compressive strength.
While the mechanics of electro-spun degradable scaffolds has been investigated
prior to degradation, the information on the effects of the degradation process on
the mechanical properties is limited. Lee et al. [ 23 ] studied the maintenance of ten-
sile properties of electro-spun poly( ε -caprolactone)/collagen scaffolds subjected to
a perfusion bioreactor environment for up to four weeks. Henry et al. [ 27 ] mechani-
cally characterised electro-spun meshes of a slow degrading polyester-urethane dur-
ing hydrolytic in vitro degradation of up to 346 days.
We investigated a highly porous, electro-spun structure made from a fast-
degrading polyester-urethane. The change of structural and mechanical properties
of the scaffold was studied during hydrolytic in vitro degradation of up to 34 days.
Based on these data, a constitutive model for the scaffold was developed that specif-
ically aims at representing the changes in scaffold mechanical properties due to
degradation. This is important as the tissue ingrowth and scaffold degradation oc-
curs simultaneously and scaffold contribution during healing must be tailored to
compliment that of the new tissue [ 28 ].
2 Effects of Degradation on Mechanical Scaffold Properties
2.1 Scaffold Material
DegraPol ® (ab medica S.p.A, Lainate, Italy) is a biodegradable polyester-urethane
that consists of poly(3-(R-hydroxybutyrate)-co-( ε -caprolactone))-diol (hard seg-
ment) and poly( ε -caprolactone-co-glycolide)-diol (soft segment). Both polymer
segments are biodegradable and their degradation products are non-toxic [ 29 ]. By
using different ratios of hard and soft segment the mechanical properties of the final
product can be modulated, whereas by changing the ratio of ε caprolactone to gly-
colide the degradation characteristics can be modulated. This versatility, combined
with the non-toxicity and haemocompatibility makes DegraPol ® a promising choice
for tissue engineering scaffolds. DegraPol ® DP30 has a ε -caprolactone-to-glycolide
ratio of 70:30 and a hard-to-soft segment ratio of 40:60 (unpublished data). The
electro-spinning solution was prepared by dissolving DegraPol ® DP30 in chloro-
form with a 20 % by weight concentration at room temperature and subsequently
sonicating in distilled water at 37 °C for 90 min.