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Table 1. Key parameters used in assessing degradation behaviour of polymer scaffolds
References Gong et al. [19] Liu et al. [20] Rodrigues et al. [21] Zamiri et al. [22] Grabow et al. [12]
(2007) (2014) (2016) (2010) (2007)
Materials PLLA scaffold PLLA scaffold Porous PLA scaffold PLLA scaffold/ PLLA scaffold
PLGA scaffold
Media PBS PBS PBS PBS PBS
Degradation times 39 weeks 200 days 8 weeks 25 weeks 24 weeks
Mass loss 30% 8% Remain relatively 5%/64% -
constant
Molecular weight From 177,000 to 80,000 From 179,000 to No significant change - 28%
loss 146,000 (120,000~150,000)
Water uptake Decreased dramatically with 900% - - -
degradation time, and lowest
value appeared between
week 9 and 12
Morphology Microcracks at week 9; more Some little holes on - - -
change cracks and big holes after the surface of the
week 23 porous walls
PLLA: poly-L-lactic acid; PBS: poly-butylene-succinate; PLA: poly lactic acid; PLGA: poly-lactic-co-glycolic acid

include mass loss, molecular weight change, water uptake and morphology change. Gong et al. carried
[19]
out in vitro degradation study of porous PLLA scaffolds over 39 weeks, and the scaffolds degraded at a
slow rate due to its highly porous structure in terms of weight water uptake and structure change. As
reported by Liu et al. , PLLA porous scaffolds exhibited a reduction in mass and molecular weight during
[20]
an in vitro degradation time of 200 days. Rodrigues et al. studied degradation process of porous PLA
[21]
scaffold immersed in phosphate-buffered-saline solution, and revealed that there was no significant change
in molecular weight over 8 weeks. Zamiri et al. compared the in vitro degradation behaviour of PLLA and
[22]
PLLA/PLGA braided scaffolds over 25 weeks, and the mass loss was found very limited for PLLA braided
scaffolds whereas PLLA/PLGA braided scaffolds experienced a mass loss of 64%. Grabow et al. reported a
[12]
gradual and steady reduction in molecular weight for a PLLA scaffold prototype during 24 weeks of in vitro
degradation. Table 1 gives a summary of these key parameters used in assessing degradation behaviour of
polymer scaffolds.

Mechanical properties (i.e., ductility, toughness and strength) of biodegradable polymers change significantly
during degradation due to hydrolytic chain scission at molecule level. It is of importance to understand the
mechanical behaviour of bioresorbable polymeric scaffolds during degradation period. The earliest assessment
of the mechanical performance of biodegradable stents was conducted by Agrawal et al. , who tested in vitro
[23]
the pressure-diameter behaviour of the Duke biodegradable stents made of PLLA fibres. They reported that
with a careful balance between fibre mechanical properties (varied with draw ratio and thermal treatments) and
stent designs, it was possible to achieve a successful biodegradable stent. Zilberman et al. reported a loss in
[24]
radial compression strength for their PLLA stent designs with degradation time, which is also associated with
reductions in elastic modulus and yield strain of the PLLA fibres. Nuutinen et al. carried out in vitro tests of a
[25]
woven fibre polymeric braided stent subjected to radial compression in a pressurized chamber. The stent design
did not perform well enough when made of biodegradable polymer, and the collapse pressure was still lower
than its metal counterpart even with thicker fibres. Specifically, the stent lost structural integrity after 36
weeks of degradation (immersed in saline at 37 °C) and the collapse pressure decreased by half at 30 weeks.
The in vitro degradation study by Liu et al. showed that PLLA porous scaffolds exhibited a reduction in
[26]
compressive modulus and strength during a degradation time of 200 days. Recently, Rodrigues et al.
[21]
carried out an in vitro degradation study of porous PLA scaffold immersed in phosphate-buffered-saline
solution for 8 weeks. The study revealed that compressive properties (i.e., compressive modulus and stress at
yield) of the scaffolds maintained constant during the initial 6 weeks and increased significantly at week 8.
Similarly, Grabow et al. conducted in vitro degradation study for a PLLA scaffold prototype in a deployed
[12]