title: Static and dynamic fatigue behavior of topology designed and conventional 3D printed bioresorbable PCL cervical interbody fusion devices.
abstract: Recently, as an alternative to metal spinal fusion cages, 3D printed bioresorbable materials have been explored; however, the static and fatigue properties of these novel cages are not well known. Unfortunately, current ASTM testing standards used to determine these properties were designed prior to the advent of bioresorbable materials for cages. Therefore, the applicability of these standards for bioresorbable materials is unknown. In this study, an image-based topology and a conventional 3D printed bioresorbable poly(ε)-caprolactone (PCL) cervical cage design were tested in compression, compression-shear, and torsion, to establish their static and fatigue properties. Difficulties were in fact identified in establishing failure criteria and in particular determining compressive failure load. Given these limitations, under static loads, both designs withstood loads of over 650 N in compression, 395 N in compression-shear, and 0.25 Nm in torsion, prior to yielding. Under dynamic testing, both designs withstood 5 million (5M) cycles of compression at 125% of their respective yield forces. Geometry significantly affected both the static and fatigue properties of the cages. The measured compressive yield loads fall within the reported physiological ranges; consequently, these PCL bioresorbable cages would likely require supplemental fixation. Most importantly, supplemental testing methods may be necessary beyond the current ASTM standards, to provide more accurate and reliable results, ultimately improving preclinical evaluation of these devices.
authors.affiliation: J. Vernon Luck, Sr., M.D. Orthopaedic Research Center at Orthopaedic Institute for Children, 403 W. Adams Blvd., Los Angeles, CA 90007, USA; Department of Biomedical Engineering, University of California, 420 Westwood Plaza, 5121 Engineering V, Los Angeles, CA 90095, USA.
authors.forename: Ashleen R
authors.initials: AR
authors.lastname: Knutsen
authors.affiliation: J. Vernon Luck, Sr., M.D. Orthopaedic Research Center at Orthopaedic Institute for Children, 403 W. Adams Blvd., Los Angeles, CA 90007, USA; Department of Biomedical Engineering, University of California, 420 Westwood Plaza, 5121 Engineering V, Los Angeles, CA 90095, USA.
authors.forename: Sean L
authors.initials: SL
authors.lastname: Borkowski
authors.affiliation: J. Vernon Luck, Sr., M.D. Orthopaedic Research Center at Orthopaedic Institute for Children, 403 W. Adams Blvd., Los Angeles, CA 90007, USA; Department of Orthopedic Surgery, University of California, Orthopaedic Center, 100 UCLA Medical Plaza Suite 755, Los Angeles, CA 90095, USA. Electronic address: Edward.Ebramzadeh@ucla.edu.
authors.forename: Edward
authors.initials: E
authors.lastname: Ebramzadeh
authors.affiliation: Department of Biomedical Engineering, University of Michigan, 1107 Carl A. Gerstacker Building, 2200 Bonisteel Blvd., Ann Arbor, MI 48109, USA.
authors.forename: Colleen L
authors.initials: CL
authors.lastname: Flanagan
authors.affiliation: Department of Biomedical Engineering, University of Michigan, 1107 Carl A. Gerstacker Building, 2200 Bonisteel Blvd., Ann Arbor, MI 48109, USA; Department of Mechanical Engineering, University of Michigan, 2350 Hayward St., Room 2206 GG Brown, Ann Arbor, MI 48109, USA; Department of Surgery, University of Michigan, 1500 E. Medical Center Dr., Ann Arbor, MI 48109, USA.
authors.forename: Scott J
authors.initials: SJ
authors.lastname: Hollister
authors.affiliation: J. Vernon Luck, Sr., M.D. Orthopaedic Research Center at Orthopaedic Institute for Children, 403 W. Adams Blvd., Los Angeles, CA 90007, USA; Department of Orthopedic Surgery, University of California, Orthopaedic Center, 100 UCLA Medical Plaza Suite 755, Los Angeles, CA 90095, USA.
authors.forename: Sophia N
authors.initials: SN
authors.lastname: Sangiorgio
mesh_terms: D020341:Absorbable Implants; D002574:Cervical Vertebrae / Q000601:surgery*; D008422:Materials Testing / Q000295:instrumentation / Q000379:methods*; D055595:Mechanical Phenomena; D011091:Polyesters; D066330:Printing, Three-Dimensional; D011474:Prosthesis Design; D013123:Spinal Fusion / Q000295:instrumentation*; D016474:Weight-Bearing
chemical_list: D011091:Polyesters; C016240:polycaprolactone
keywords: ASTM testing; Bioresorbable cages; Fatigue properties; Interbody fusion; Spine fusion; Structural properties