Development of a Flow Evolution Network Model for the Stress-Strain Behavior of Poly(L-lactide).

Computational modeling is critical to medical device development and has grown in its utility for predicting device performance. Additionally, there is an increasing trend to use absorbable polymers for the manufacturing of medical devices. However, computational modeling of absorbable devices is hampered by a lack of appropriate constitutive models that capture their viscoelasticity and postyield behavior. The objective of this study was to develop a constitutive model that incorporated viscoplasticity for a common medical absorbable polymer. Microtensile bars of poly(L-lactide) (PLLA) were studied experimentally to evaluate their monotonic, cyclic, unloading, and relaxation behavior as well as rate dependencies under physiological conditions. The data were then fit to a viscoplastic flow evolution network (FEN) constitutive model. PLLA exhibited rate-dependent stress-strain behavior with significant postyield softening and stress relaxation. The FEN model was able to capture these relevant mechanical behaviors well with high accuracy. In addition, the suitability of the FEN model for predicting the stress-strain behavior of PLLA medical devices was investigated using finite element (FE) simulations of nonstandard geometries. The nonstandard geometries chosen were representative of generic PLLA cardiovascular stent subunits. These finite element simulations demonstrated that modeling PLLA using the FEN constitutive relationship accurately reproduced the specimen's force-displacement curve, and therefore, is a suitable relationship to use when simulating stress distribution in PLLA medical devices. This study demonstrates the utility of an advanced constitutive model that incorporates viscoplasticity for simulating PLLA mechanical behavior.

[1]  M. Boyce,et al.  A constitutive model for the nonlinear viscoelastic viscoplastic behavior of glassy polymers , 1995 .

[2]  M. Cima,et al.  Mechanical properties of dense polylactic acid structures fabricated by three dimensional printing. , 1996, Journal of biomaterials science. Polymer edition.

[3]  Mary C. Boyce,et al.  Constitutive modeling of the large strain time-dependent behavior of elastomers , 1998 .

[4]  G. Vendroux,et al.  Submicron deformation field measurements: Part 2. Improved digital image correlation , 1998 .

[5]  J C Middleton,et al.  Synthetic biodegradable polymers as orthopedic devices. , 2000, Biomaterials.

[6]  H. Lu,et al.  Deformation measurements by digital image correlation: Implementation of a second-order displacement gradient , 2000 .

[7]  Geoffrey J. Frank,et al.  A viscoelastic–viscoplastic constitutive model for glassy polymers , 2001 .

[8]  C. Chen,et al.  Preparation and characterization of biodegradable PLA polymeric blends. , 2003, Biomaterials.

[9]  J F Orr,et al.  Processing, annealing and sterilisation of poly-L-lactide. , 2004, Biomaterials.

[10]  Jessie Q. Xia,et al.  High-resolution determination of soft tissue deformations using MRI and first-order texture correlation , 2004, IEEE Transactions on Medical Imaging.

[11]  John Rose,et al.  The effect of crystallinity on the deformation mechanism and bulk mechanical properties of PLLA. , 2005, Biomaterials.

[12]  Mary C. Boyce,et al.  Mechanics of the rate-dependent elastic¿plastic deformation of glassy polymers from low to high strain rates , 2006 .

[13]  A. Drozdov,et al.  Cyclic viscoplasticity of thermoplastic elastomers , 2007 .

[14]  Farshid Guilak,et al.  Measurement of intracellular strain on deformable substrates with texture correlation. , 2007, Journal of biomechanics.

[15]  S. W. Robertson,et al.  Fatigue and durability of Nitinol stents. , 2008, Journal of the mechanical behavior of biomedical materials.

[16]  João S. Soares,et al.  Constitutive Framework for Biodegradable Polymers with Applications to Biodegradable Stents , 2008, ASAIO journal.

[17]  T. Smit,et al.  Time-Dependent Mechanical Strength of 70/30 Poly(l,dl-lactide): Shedding Light on the Premature Failure of Degradable Spinal Cages , 2008, Spine.

[18]  F. Guilak,et al.  Transfer of macroscale tissue strain to microscale cell regions in the deformed meniscus. , 2008, Biophysical journal.

[19]  D. Untereker,et al.  Degradability of Polymers for Implantable Biomedical Devices , 2009, International journal of molecular sciences.

[20]  Satoshi Kobayashi,et al.  Effects of strain rate on the mechanical properties of tricalcium phosphate/poly(l-lactide) composites , 2009, Journal of materials science. Materials in medicine.

[21]  R. Rapoza,et al.  Design principles and performance of bioresorbable polymeric vascular scaffolds. , 2009, EuroIntervention : journal of EuroPCR in collaboration with the Working Group on Interventional Cardiology of the European Society of Cardiology.

[22]  João S Soares,et al.  Deformation-induced hydrolysis of a degradable polymeric cylindrical annulus , 2010, Biomechanics and modeling in mechanobiology.

[23]  J. Bergström,et al.  An Advanced Thermomechanical Constitutive Model for UHMWPE , 2010 .

[24]  T. Smit,et al.  Time-dependent failure in load-bearing polymers: a potential hazard in structural applications of polylactides , 2009, Journal of materials science. Materials in medicine.

[25]  Lambèrt C.A. van Breemen,et al.  Rate- and Temperature-Dependent Strain Softening in Solid Polymers , 2012 .

[26]  Adnan H Siddiqui,et al.  Computer modeling of deployment and mechanical expansion of neurovascular flow diverter in patient-specific intracranial aneurysms. , 2012, Journal of biomechanics.

[27]  Theo H Smit,et al.  Time-dependent failure of amorphous poly-D,L-lactide: influence of molecular weight. , 2012, Journal of the mechanical behavior of biomedical materials.

[28]  Romuald Będziński,et al.  Mechanical, rheological, fatigue, and degradation behavior of PLLA, PGLA and PDGLA as materials for vascular implants , 2013 .

[29]  P. Zavattieri,et al.  Tips and tricks for characterizing shape memory wire part 5: Full-field strain measurement by digital image correlation , 2013, Experimental Techniques.

[30]  Kamran A. Khan,et al.  A phenomenological constitutive model for the nonlinear viscoelastic responses of biodegradable polymers , 2013 .

[31]  Mary C. Boyce,et al.  Constitutive modeling of the rate-dependent resilient and dissipative large deformation behavior of a segmented copolymer polyurea , 2013 .

[32]  M. Dreher,et al.  Characterization of load dependent creep behavior in medically relevant absorbable polymers. , 2014, Journal of the mechanical behavior of biomedical materials.

[33]  Nishant M. Tikekar,et al.  Modeling polyethylene wear acceleration due to femoral head dislocation damage. , 2014, The Journal of arthroplasty.

[34]  S. Miller,et al.  The effect of static and dynamic loading on degradation of PLLA stent fibers. , 2014, Journal of biomechanical engineering.

[35]  Danika M. Hayman,et al.  An Overview of Mechanical Properties and Material Modeling of Polylactide (PLA) for Medical Applications , 2015, Annals of Biomedical Engineering.

[36]  J. Fitoussi,et al.  Implicit implementation and consistent tangent modulus of a viscoplastic model for polymers , 2015 .

[37]  J. S. Bergström,et al.  Mechanics of Solid Polymers: Theory and Computational Modeling , 2015 .

[38]  Patrick Segers,et al.  A finite element strategy to investigate the free expansion behaviour of a biodegradable polymeric stent. , 2015, Journal of biomechanics.

[39]  B. Reddy,et al.  Computational analysis of the radial mechanical performance of PLLA coronary artery stents. , 2015, Medical engineering & physics.

[40]  Development of a flow evolution network model for predicting the viscoplastic behavior of poly(L-lactide) , 2016 .

[41]  G. V. Savrasov,et al.  Modeling of transcatheter aortic valve replacement: Patient specific vs general approaches based on finite element analysis , 2016, Comput. Biol. Medicine.

[42]  Stefan Lohfeld,et al.  Experimental mechanical testing of Poly (l-Lactide) (PLLA) to facilitate pre-degradation characteristics for application in cardiovascular stenting , 2016 .

[43]  Srinidhi Nagaraja,et al.  Effects of fatigue on the chemical and mechanical degradation of model stent sub-units. , 2016, Journal of the mechanical behavior of biomedical materials.