The development of a biomimetic patch for annulus fibrosus repair (2016)

Thirty-one million Americans experience low-back pain (LBP) at any given time in their lives.1 LBP is the single leading cause of disability worldwide and its prevalence in the US is approximately 80%.2 The intervertebral disc (IVD) is composed of the nucleus pulposus (NP), a gelatinous core that resists compressive loading through the generation of intradiscal pressure (IDP), and the annulus fibrosus (AF), which has concentric sheets (lamellae) of aligned Type I collagen which alternate the fiber-preferred direction with each subsequent layer allowing for resistance to IDP, and tensile and torsional loads. Although, IVD degeneration (IVDD) and herniation (IVDH) represent two independent pathological mechanisms; they both contribute significantly to LBP. Potential clinical treatments for herniation and degeneration include discectomy (removal of the herniated IVD fragments) and NP arthroplasty, respectively. However, both treatment options are insufficient by themselves; especially when the defect in the outer AF is >6mm.3 We hypothesized that an ideal AF patch to be used for repairing the AF and promoting its regeneration can be developed from adjoined sheets of decellularized porcine pericardium due to its aligned type I collage fiber architecture resembling the native AF structure. The objective of the research presented herein was to illustrate the feasibility of developing a biomimetic patch to biologically augment AF repair. Porcine pericardium was harvested at a local abattoir and decellularized in order to minimize potential immunological reactions.4 Decellularization was confirmed via, Hematoxylin & Eosin (H&E), agarose gel electrophoresis, nanodrop quantification and immunohistochemistry for the removal of the porcine antigenic epitope, alpha-gal. Tensile mechanical testing was performed on single-ply AF sheets and fresh pericardium in the fiber preferred and cross-fiber orientation to determine tensile mechanical properties and to compare values reported in literature for a single AF lamellae, and to ensure the modified decellularization procedure did not alter the mechanical strength of the tissue. Ball burst test of multi-laminate AF patches composed of decellularized pericardial layers was performed to assess the maximum burst strength the pericardium could withstand and the necessary number of layers needed to resist the IDP generated by the NP exerted as hoop stresses within the AF. Production of ply-angle-ply multi-laminate AF patches were constructed via the use of decellularized pericardium sheets were sewn in conjunction with a backing material, surgical suture and a sewing machine in order to develop a scalable manufacture methodology. Cytocompatibility of the AF patches was verified through a 15 day in vitro pilot cell study to assess bovine AF cell viability and proliferation when seeded on the patch. Results to be presented illustrate a repeatable method for developing a multi-laminate ply-angle-ply AF patch. The AF patch demonstrates comparable tensile elastic modulus to native AF, adequate burst strength and cytocompatibility to be considered a potential option for AF tissue engineering. Taken together, results suggest that the multi-laminate ply-angle-ply AF patches may be suitable for use as an adjunct to nucleus arthroplasty implantation as an early-stage treatment for patients demonstrating the onset of IVDD or as a sequestration device in patients undergoing discectomy following large IVDHs to help mitigate the risk for re-herniation.