Constitutive Effects of Hydrolytic Degradation in Electro-Spun Polyester-Urethane Scaffolds for Soft Tissue Regeneration - Tissue Engineering: Computer Modeling, Biofabrication and Cell Behavior - page 65

the load cycles may be considered to prevent excessive plastic deformation during
cycling and to determine the change of the elastic limit of the scaffold with pro-
gressing degradation. When evaluating the increasing lack of structural stability of
the degrading scaffold, the potential mechanical effect of tissue regenerating in the
scaffold needs to be considered. For the design of a tissue regenerating implant, the
structural degradation of the scaffold needs to be adjusted to the rate of tissue re-
generation so as to prevent structural failure of the implant. If this is not feasible,
alternative designs need to ensure structural integrity of the implant, for example
composite structures comprising two or more components.
The normalised stress difference ψ indicated a good model accuracy and suc-
cessful representation of the constitutive scaffold properties including the effects of
degradation. The material coefficient c 1 followed the same trend with degradation
time as the tensile stress at 20 % strain, σ 20 % , exp , with an overall decrease of c 1 and
stress with increasing degradation time (see Table 2 ). This observation was, how-
ever, not true on a time-point to time-point basis. The latter was ascribed to incon-
sistencies possibly in the manufacture and testing procedures that need addressing
in future work.
This study was a first step to extend the research in mechanics and constitu-
tive modelling of degrading tissue regenerative scaffolds. Future studies with exten-
sions of the work presented, e.g. use of physiological degradation solution such as
phosphate buffered saline, characterisation of molecular weight of the scaffold, and
changes thereof during degradation, will provide important additional data. With
the aim of developing more comprehensive constitutive models for scaffold-based
soft tissue regeneration, further research will also address important aspects such
as strain rate sensitivity of the scaffold material, effect of tissue incorporation and
application-specific mechanics.
Acknowledgements The authors thank ab medica S.p.A for donating the DegraPol ® material
for this study. ETH Zurich and University of Zurich are owners and ab medica S.p.A is exclusive
licensee of all IP Rights of DegraPol ® .
Funding Sources This study was supported financially by the National Research Foundation
(NRF) of South Africa. Any opinion, findings and conclusions or recommendations expressed
in this publication are those of the authors and therefore the NRF does not accept any liability
in regard thereto. HK received a Matching Dissertation Grant from the International Society of
Biomechanics.
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