Understanding how polymers such as PLLA degrade in vivo will enhance biodegradable stent design. This study examined the effect of static and dynamic loads on PLLA stent fibers in vitro. The stent fibers (generously provided by TissueGen, Inc.) were loaded axially with 0 N, 0.5 N, 1 N, or 0.125–0.25 N (dynamic group, 1 Hz) and degraded in PBS at 45 °C for an equivalent degradation time of 15 months. Degradation was quantified through changes in tensile mechanical properties. The mechanical behavior was characterized using the Knowles strain energy function and a degradation model. A nonsignificant increase in fiber stiffness was observed between 0 and 6 months followed by fiber softening thereafter. A marker of fiber softening, β, increased between 9 and 15 months in all groups. At 15 months, the β values in the dynamic group were significantly higher compared to the other groups. In addition, the model indicated that the degradation rate constant was smaller in the 1-N (0.257) and dynamic (0.283) groups compared to the 0.5-N (0.516) and 0-N (0.406) groups. While the shear modulus fluctuated throughout degradation, no significant differences were observed. Our results indicate that an increase in static load increased the degradation of mechanical properties and that the application of dynamic load further accelerated this degradation.

References

1.
Lanckohr
,
C.
,
Torsello
,
G.
,
Scheld
,
H.
,
Schieffer
,
B.
, and
Theilmeier
,
G.
,
2012
, “
Drug-Eluting Stents and Perioperative Risk—More Than Matters of the Heart?
,”
Vasa
,
41
(
6
), pp.
410
418
.10.1024/0301-1526/a000231
2.
Nishio
,
S.
,
Kosuga
,
K.
,
Igaki
,
K.
,
Okada
,
M.
,
Kyo
,
E.
,
Tsuji
,
T.
,
Takeuchi
,
E.
,
Inuzuka
,
Y.
,
Takeda
,
S.
,
Hata
,
T.
,
Takeuchi
,
Y.
,
Kawada
,
Y.
,
Harita
,
T.
,
Seki
,
J.
,
Akamatsu
,
S.
,
Hasegawa
,
S.
,
Bruining
,
N.
,
Brugaletta
,
S.
,
De Winter
,
S.
,
Muramatsu
,
T.
,
Onuma
,
Y.
,
Serruys
,
P. W.
, and
Ikeguchi
,
S.
,
2012
, “
Long-Term (>10 Years) Clinical Outcomes of First-in-Human Biodegradable Poly-L-Lactic Acid Coronary Stents: Igaki-Tamai Stents
,”
Circulation
,
125
(
19
), pp.
2343
2353
.10.1161/CIRCULATIONAHA.110.000901
3.
Tamai
,
H.
,
Igaki
,
K.
,
Kyo
,
E.
,
Kosuga
,
K.
,
Kawashima
,
A.
,
Matsui
,
S.
,
Komori
,
H.
,
Tsuji
,
T.
,
Motohara
,
S.
, and
Uehata
,
H.
,
2000
, “
Initial and 6-Month Results of Biodegradable Poly-L-Lactic Acid Coronary Stents in Humans
,”
Circulation
,
102
(
4
), pp.
399
404
.10.1161/01.CIR.102.4.399
4.
Okamura
,
T.
,
Garg
,
S.
,
Gutierrez-Chico
,
J. L.
,
Shin
,
E. S.
,
Onuma
,
Y.
,
Garcia-Garcia
,
H. M.
,
Rapoza
,
R. J.
,
Sudhir
,
K.
,
Regar
,
E.
, and
Serruys
,
P. W.
,
2010
, “
In vivo Evaluation of Stent Strut Distribution Patterns in the Bioabsorbable Everolimus-Eluting Device: An OCT Ad Hoc Analysis of the Revision 1.0 and Revision 1.1 Stent Design in the Absorb Clinical Trial
,”
EuroIntervention
,
5
(
8
), pp.
932
938
.10.4244/EIJV5I8A157
5.
Onuma
,
Y.
,
Serruys
,
P. W.
,
Gomez
,
J.
,
De Bruyne
,
B.
,
Dudek
,
D.
,
Thuesen
,
L.
,
Smits
,
P.
,
Chevalier
,
B.
,
Mcclean
,
D.
,
Koolen
,
J.
,
Windecker
,
S.
,
Whitbourn
,
R.
,
Meredith
,
I.
,
Garcia-Garcia
,
H.
, and
Ormiston
,
J. A.
,
2011
, “
Comparison of in vivo Acute Stent Recoil Between the Bioresorbable Everolimus-Eluting Coronary Scaffolds (Revision 1.0 and 1.1) and the Metallic Everolimus-Eluting Stent
,”
Cathet. Cardiovasc. Interv.
,
78
(
1
), pp.
3
12
.10.1002/ccd.22864
6.
Diletti
,
R.
,
Serruys
,
P. W.
,
Farooq
,
V.
,
Sudhir
,
K.
,
Dorange
,
C.
,
Miquel-Hebert
,
K.
,
Veldhof
,
S.
,
Rapoza
,
R.
,
Onuma
,
Y.
,
Garcia-Garcia
,
H. M.
, and
Chevalier
,
B.
,
2012
, “
Absorb II Randomized Controlled Trial: A Clinical Evaluation to Compare the Safety, Efficacy, and Performance of the Absorb Everolimus-Eluting Bioresorbable Vascular Scaffold System against the Xience Everolimus-Eluting Coronary Stent System in the Treatment of Subjects With Ischemic Heart Disease Caused by De Novo Native Coronary Artery Lesions: Rationale and Study Design
,”
Am. Heart J.
,
164
(
5
), pp.
654
663
.10.1016/j.ahj.2012.08.010
7.
Grabow
,
N.
,
BüNger
,
C. M.
,
Sternberg
,
K.
,
Mews
,
S.
,
Schmohl
,
K.
, and
Schmitz
,
K.-P.
,
2007
, “
Mechanical Properties of a Biodegradable Balloon-Expandable Stent From Poly(L-Lactide) for Peripheral Vascular Applications
,”
ASME J. Med. Devices
,
1
(
1
), pp.
84
88
.10.1115/1.2355683
8.
Venkatraman
,
S. S.
,
Tan
,
L. P.
,
Joso
,
J. F. D.
,
Boey
,
Y. C. F.
, and
Wang
,
X.
,
2006
, “
Biodegradable Stents With Elastic Memory
,”
Biomaterials
,
27
(
8
), pp.
1573
1578
.10.1016/j.biomaterials.2005.09.002
9.
Bunger
,
C. M.
,
Grabow
,
N.
,
Sternberg
,
K.
,
Goosmann
,
M.
,
Schmitz
,
K. P.
,
Kreutzer
,
H. J.
,
Ince
,
H.
,
Kische
,
S.
,
Nienaber
,
C. A.
,
Martin
,
D. P.
,
Williams
,
S. F.
,
Klar
,
E.
, and
Schareck
,
W.
,
2007
, “
A Biodegradable Stent Based on Poly(L-Lactide) and Poly(4-Hydroxybutyrate) for Peripheral Vascular Application: Preliminary Experience in the Pig
,”
J. Endovasc. Ther.
,
14
(
5
), pp.
725
733
.10.1583/1545-1550(2007)14[725:ABSBOP]2.0.CO;2
10.
Vogt
,
F.
,
Stein
,
A.
,
Rettemeier
,
G.
,
Krott
,
N.
,
Hoffmann
,
R.
,
Vom Dahl
,
J.
,
Bosserhoff
,
A. K.
,
Michaeli
,
W.
,
Hanrath
,
P.
,
Weber
,
C.
, and
Blindt
,
R.
,
2004
, “
Long-Term Assessment of a Novel Biodegradable Paclitaxel-Eluting Coronary Polylactide Stent
,”
Eur. Heart J.
,
25
(
15
), pp.
1330
1340
.10.1016/j.ehj.2004.06.010
11.
Su
,
S. H.
,
Chao
,
R. Y.
,
Landau
,
C. L.
,
Nelson
,
K. D.
,
Timmons
,
R. B.
,
Meidell
,
R. S.
, and
Eberhart
,
R. C.
,
2003
, “
Expandable Bioresorbable Endovascular Stent. I. Fabrication and Properties
,”
Ann. Biomed. Eng.
,
31
(
6
), pp.
667
677
.10.1114/1.1575756
12.
Wu
,
Y.
,
Shen
,
L.
,
Wang
,
Q.
,
Ge
,
L.
,
Xie
,
J.
,
Hu
,
X.
,
Sun
,
A.
,
Qian
,
J.
, and
Ge
,
J.
,
2012
, “
Comparison of Acute Recoil Between Bioabsorbable Poly-L-Lactic Acid Xinsorb Stent and Metallic Stent in Porcine Model
,”
ASME J. Biomed. Biotechnol.
,
2012
, p.
413956
.10.1155/2012/413956
13.
Li
,
S.
,
1999
, “
Hydrolytic Degradation Characteristics of Aliphatic Polyesters Derived From Lactic and Glycolic Acids
,”
J. Biomed. Mater. Res.
,
48
(
3
), pp.
342
353
.10.1002/(SICI)1097-4636(1999)48:3%3C342::AID-JBM20%3E3.0.CO;2-7
14.
Tsuji
,
H.
,
2008
,
Degradation of Poly(Lactide)-Based Biodegradable Materials
,
Nova Science Publishers, Inc.
, New York.
15.
Tsuji
,
H.
,
Akira
,
M.
, and
Ikada
,
Y.
,
2000
, “
Properties and Morphology of Poly(L-Lactide). III. Effects of Initial Crystallinity on Long-Term in vitro Hydrolysis of High Molecular Weight Poly(L-Lactide) Film in Phosphate-Buffered Solution
,”
J. Appl. Polym. Sci.
,
77
, pp.
1452
1464
.10.1002/1097-4628(20000815)77:7%3C1452::AID-APP7%3E3.0.CO;2-S
16.
Grizzi
,
I.
,
Garreau
,
H.
,
Li
,
S.
, and
Vert
,
M.
,
1995
, “
Hydrolytic Degradation of Devices Based on Poly(Dl-Lactic Acid) Size-Dependence
,”
Biomaterials
,
16
(
4
), pp.
305
311
.10.1016/0142-9612(95)93258-F
17.
Yuan
,
X.
,
Mak
,
A. F. T.
, and
Yao
,
K.
,
2002
, “
Comparative Observation of Accelerated Degradation of Poly(L-Lactic Acid) Fibres in Phosphate Buffered Saline and a Dilute Alkaline Solution
,”
Polym. Degrad. Stabil.
,
75
(
1
), pp.
45
53
.10.1016/S0141-3910(01)00203-8
18.
Yew
,
G. H.
,
Yusof
,
A. M. M.
,
Ishak
,
Z. a. M.
, and
Ishiaku
,
U. S.
,
2005
, “
Water Absorption and Enzymatic Degradation of Poly(Lactic Acid)/Rice Starch Composites
,”
Polym. Degrad. Stabil.
,
90
(
3
), pp.
488
500
.10.1016/j.polymdegradstab.2005.04.006
19.
Weir
,
N. A.
,
Buchanan
,
F. J.
,
Orr
,
J. F.
,
Farrar
,
D. F.
, and
Dickson
,
G. R.
,
2004
, “
Degradation of Poly-L-Lactide. Part 2: Increased Temperature Accelerated Degradation
,”
Proc. Inst. Mech. Eng., Part H
,
218
(
5
), pp.
321
330
.10.1243/0954411041932809
20.
Lyu
,
S.
,
Schley
,
J.
,
Loy
,
B.
,
Lind
,
D.
,
Hobot
,
C.
,
Sparer
,
R.
, and
Untereker
,
D.
,
2007
, “
Kinetics and Time−Temperature Equivalence of Polymer Degradation
,”
Biomacromolecules
,
8
(
7
), pp.
2301
2310
.10.1021/bm070313n
21.
Van Dijk
,
M.
,
Tunc
,
D. C.
,
Smit
,
T. H.
,
Higham
,
P.
,
Burger
,
E. H.
, and
Wuisman
,
P. I.
,
2002
, “
In vitro and in vivo Degradation of Bioabsorbable PLLA Spinal Fusion Cages
,”
J. Biomed. Mater. Res.
,
63
(
6
), pp.
752
759
.10.1002/jbm.10466
22.
Leenslag
,
J. W.
,
Pennings
,
A. J.
,
Bos
,
R. R.
,
Rozema
,
F. R.
, and
Boering
,
G.
,
1987
, “
Resorbable Materials of Poly(L-Lactide). VII. In vivo and in vitro Degradation
,”
Biomaterials
,
8
(
4
), pp.
311
314
.10.1016/0142-9612(87)90121-9
23.
Bedoya
,
J.
,
Meyer
,
C. A.
,
Timmins
,
L. H.
,
Moreno
,
M. R.
, and
Moore
,
J. E.
,
2006
, “
Effects of Stent Design Parameters on Normal Artery Wall Mechanics
,”
ASME J. Biomech. Eng.
,
128
(
5
), pp.
757
765
.10.1115/1.2246236
24.
Fan
,
Y.
,
Li
,
P.
, and
Yuan
,
X.
,
2010
, “
Influence of Mechanical Loads on Degradation of Scaffolds
,”
WCB 2010, IFMBE Proceedings
,
31
, pp.
549
552
.
25.
Wan
,
Y. Z.
,
Wang
,
Y. L.
,
Zheng
,
L. Y.
,
Zhou
,
F. G.
,
Zhao
,
Q.
, and
Cheng
,
G. X.
,
2001
, “
Influence of External Stress on the in vitro Degradation Behavior of C3d/Pla Composites
,”
J. Mater. Sci. Lett.
,
20
, pp.
1957
1959
.10.1023/A:1013138919801
26.
Thompson
,
D. E.
,
Agrawal
,
C. M.
, and
Athanasiou
,
K.
,
1996
, “
The Effects of Dynamic Compressive Loading on Biodegradable Implants of 50-50% Polylactic Acid-Polyglycolic Acid
,”
Tissue Eng.
,
2
(
1
), pp.
61
74
.10.1089/ten.1996.2.61
27.
Gopferich
,
A.
,
1996
, “
Mechanisms of Polymer Degradation and Erosion
,”
Biomaterials
,
17
(
2
), pp.
103
114
.10.1016/0142-9612(96)85755-3
28.
Deng
,
M.
,
Zhou
,
J.
,
Chen
,
G.
,
Burkley
,
D.
,
Xu
,
Y.
,
Jamiolkowski
,
D.
, and
Barbolt
,
T.
,
2005
, “
Effect of Load and Temperature on in vitro Degradation of Poly(Glycolide-Co-L-Lactide) Multifilament Braids
,”
Biomaterials
,
26
(
20
), pp.
4327
4336
.10.1016/j.biomaterials.2004.09.067
29.
Rajagopal
,
K. R.
,
Srinivasa
,
A. R.
, and
Wineman
,
A. S.
,
2007
, “
On the Shear and Bending of a Degrading Polymer Beam
,”
Int. J. Plasticity
,
23
(
9
), pp.
1618
1636
.10.1016/j.ijplas.2007.02.007
30.
Soares
,
J. S.
,
Moore
,
J. E.
, and
Rajagopal
,
K. R.
,
2010
, “
Modeling of Deformation-Accelerated Breakdown of Polylactic Acid Biodegradable Stents
,”
ASME J. Med. Devices
,
4
(
4
), p.
041007
.10.1115/1.4002759
31.
Soares
,
J. S.
,
Rajagopal
,
K. R.
, and
Moore
,
J. E.
,
2009
, “
Deformation-Induced Hydrolysis of a Degradable Polymeric Cylindrical Annulus
,”
Biomech. Model. Mechanobiol.
,
9
(
2
), pp.
177
186
.10.1007/s10237-009-0168-z
32.
Soares
,
J. S.
,
Moore
,
J. E.
, and
Rajagopal
,
K. R.
,
2008
, “
Constitutive Framework for Biodegradable Polymers With Applications to Biodegradable Stents
,”
ASAIO J.
,
54
(
3
), pp.
295
301
.10.1097/MAT.0b013e31816ba55a
33.
Soares
,
J. S.
,
2008
, “
Constitutive Modeling for Biodegradable Polymers for Application in Endovascular Stents
,” Ph.D. thesis, Texas A&M, College Station, TX.
34.
Humphrey
,
J. D.
,
2002
,
Cardiovascular Solid Mechanics: Cells, Tissues, and Organs
,
Springer
,
New York
.
35.
Agrawal
,
C. M.
,
Huang
,
D.
,
Schmitz
,
J. P.
, and
Athanasiou
,
K. A.
,
1997
, “
Elevated Temperature Degradation of a 50:50 Copolymer of PLA-PGA
,”
Tissue Eng.
,
3
(
4
), pp.
345
352
.10.1089/ten.1997.3.345
36.
Knowles
,
J. K.
,
1977
, “
The Finite Anti-Plane Shear Field Near the Tip of a Crack for a Class of Incompressible Elastic Solids
,”
Int. J. Fract.
,
13
(
5
), pp.
611
639
.10.1007/BF00017296
37.
Mano
,
J. F.
,
Ribelles
,
J. L. G.
,
Alves
,
N. M.
, and
Sanchez
,
M. S.
,
2005
, “
Glass Transition Dynamics and Structural Relaxation of PLLA Studied by DSC: Influence of Crystallinity
,”
Polymer
,
46
(
19
), pp.
8258
8265
.10.1016/j.polymer.2005.06.096
38.
Fan
,
Y.-B.
,
Li
,
P.
,
Zeng
,
L.
, and
Huang
,
X.-J.
,
2008
, “
Effects of Mechanical Load on the Degradation of Poly(D,L-Lactic Acid) Foam
,”
Polym. Degrad. Stabil.
,
93
(
3
), pp.
677
683
.10.1016/j.polymdegradstab.2007.12.015
39.
Kang
,
Y.
,
Yao
,
Y.
,
Yin
,
G.
,
Huang
,
Z.
,
Liao
,
X.
,
Xu
,
X.
, and
Zhao
,
G.
,
2009
, “
A Study on the in vitro Degradation Properties of Poly(L-Lactic Acid)/Beta-Tricalcuim Phosphate (PLLA/Beta-TCP) Scaffold Under Dynamic Loading
,”
Med. Eng. Phys.
,
31
(
5
), pp.
589
594
.10.1016/j.medengphy.2008.11.014
40.
Tsuji
,
H.
, and
Ikada
,
Y.
,
2000
, “
Properties and Morphology of Poly(L-Lactide) 4. Effects of Structural Parameters on Long-Term Hydrolysis of Poly(L-Lactide) in Phosphate Buffered Solution
,”
Polym. Degrad. Stabil.
,
67
(
1
), pp.
179
189
.10.1016/S0141-3910(99)00111-1
41.
Perego
,
G.
,
Cella
,
G. D.
, and
Bastioli
,
C.
,
1996
, “
Effect of Molecular Weight and Crystallinity on Poly(Lactic Acid) Mechanical Properties
,”
J. Appl. Polym. Sci.
,
59
(
1
), pp.
37
43
.10.1002/(SICI)1097-4628(19960103)59:1%3C37::AID-APP6%3E3.0.CO;2-N
42.
Onuma
,
Y.
, and
Serruys
,
P. W.
,
2011
, “
Bioresorbable Scaffold: The Advent of a New Era in Percutaneous Coronary and Peripheral Revascularization?
,”
Circulation
,
123
(
7
), pp.
779
797
.10.1161/CIRCULATIONAHA.110.971606
43.
Galwey
,
A. K.
, and
Brown
,
M. E.
,
2002
, “
Application of the Arrhenius Equation to Solid State Kinetics: Can This Be Justified?
,”
Thermochim. Acta
,
386
(
1
), pp.
91
98
.10.1016/S0040-6031(01)00769-9
44.
Muliana
,
A.
, and
Rajagopal
,
K. R.
,
2012
, “
Modeling the Response of Nonlinear Viscoelastic Biodegradable Polymeric Stents
,”
Int. J. Solids Struct.
,
49
, pp.
989
1000
.10.1016/j.ijsolstr.2011.12.007
You do not currently have access to this content.