Presentation Title

Constitutive Model of PLG 10-90 for Anterior Cruciate Ligament Reconstruction

Faculty Mentor

Mehrdad Haghi

Start Date

17-11-2018 8:30 AM

End Date

17-11-2018 10:30 AM

Location

HARBESON 25

Session

POSTER 1

Type of Presentation

Poster

Subject Area

engineering_computer_science

Abstract

Keywords: absorbable, synthetic, polymer, biopolymer, mechanics, constitutive model, ACL, reconstruction

There are an estimated 100,000 cases of torn Anterior Cruciate Ligaments (ACL) in the United States each year [1]. Although autografts and allografts are approved treatments, they are expensive, labor intensive, cause donor site morbidity, and require a lengthy patient recovery process [2]. Despite decellularization treatments, DNA left in allografts can increase the risk of disease transmission and an immunogenic response [3]. Synthetic implants eliminate the harvesting procedure and have great biocompatibility. Understanding the full scope of mechanical properties of a synthetic material that closely matches those of native ligaments is imperative for ACL reconstruction innovation.

PLG 10-90 (L-lactide -co-glycolide) monofilament is an absorbable biopolymer utilized as suture in orthopedic surgery. The biopolymer sufficiently matches average native ACL tensile strength, percent elongation to fracture, and the dissolution time is approximately that of ACL growth time. These factors make PLG 10-90 a strong candidate for ACL reconstructive procedures. This research will determine a constitutive model of PLG 10-90 whose variables are expressed as evolutionary equations to adapt the model to the dissolution of the material. Data from stress relaxation tests at varying degrees of dissolution induced by PBS (1X pH 7.4) to emulate in-vivo conditions will be used to construct a Standard Linear Solid model. The model will provide insight into the viscoelastic properties of PLG 10-90 and may be constructed in ANSYS, an advanced simulation software. Monotonic tensile tests at increasing strain rates will determine the strain rate sensitivity of the material and thus the validity of the model. When the model has been validated, ANSYS may simulate life cycle fatigue under conditions which are not feasible to conduct experimentally. These extrapolated mechanical responses of degrading PLG 10-90 will help determine the viability of the biopolymer for ACL reconstruction.

Summary of research results to be presented

Current progress on this project has been the construction of test clamps, a proven statistical approach to determining the actual diameter of the monofilaments, and initial tensile test data. The test clamps were designed to reduce stress concentrations during monotonic tensile loading on an Instron 3360. The yield strength and percent elongation to fracture, obtained from testing, have fallen within the acceptable ranges specified by the manufacturer of the material. The progress and results have shown that a constitutive model, specifically a Standard Linear Solid Model using a stress relaxation test, of PLG 10-90 may be created. The model can provide insight into the viscous and elastic components of PLG 10-90. Ultimately, the material may be constructed in ANSYS to simulate life cycle fatigue under a variety of loading conditions and extrapolated mechanical responses for further analysis.

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Nov 17th, 8:30 AM Nov 17th, 10:30 AM

Constitutive Model of PLG 10-90 for Anterior Cruciate Ligament Reconstruction

HARBESON 25

Keywords: absorbable, synthetic, polymer, biopolymer, mechanics, constitutive model, ACL, reconstruction

There are an estimated 100,000 cases of torn Anterior Cruciate Ligaments (ACL) in the United States each year [1]. Although autografts and allografts are approved treatments, they are expensive, labor intensive, cause donor site morbidity, and require a lengthy patient recovery process [2]. Despite decellularization treatments, DNA left in allografts can increase the risk of disease transmission and an immunogenic response [3]. Synthetic implants eliminate the harvesting procedure and have great biocompatibility. Understanding the full scope of mechanical properties of a synthetic material that closely matches those of native ligaments is imperative for ACL reconstruction innovation.

PLG 10-90 (L-lactide -co-glycolide) monofilament is an absorbable biopolymer utilized as suture in orthopedic surgery. The biopolymer sufficiently matches average native ACL tensile strength, percent elongation to fracture, and the dissolution time is approximately that of ACL growth time. These factors make PLG 10-90 a strong candidate for ACL reconstructive procedures. This research will determine a constitutive model of PLG 10-90 whose variables are expressed as evolutionary equations to adapt the model to the dissolution of the material. Data from stress relaxation tests at varying degrees of dissolution induced by PBS (1X pH 7.4) to emulate in-vivo conditions will be used to construct a Standard Linear Solid model. The model will provide insight into the viscoelastic properties of PLG 10-90 and may be constructed in ANSYS, an advanced simulation software. Monotonic tensile tests at increasing strain rates will determine the strain rate sensitivity of the material and thus the validity of the model. When the model has been validated, ANSYS may simulate life cycle fatigue under conditions which are not feasible to conduct experimentally. These extrapolated mechanical responses of degrading PLG 10-90 will help determine the viability of the biopolymer for ACL reconstruction.