Date of Award
Doctor of Philosophy (PhD)
Annually, over 5.7 million Americans are diagnosed with two IVD-associated pathologies: IVD herniation (IVDH- a mechanical disruption of the concentric fibrous layers of the annulus fibrosus (AF)) and/or degeneration (IVDD- a multifactorial process which initiates within the inner gelatinous core (NP), and results in a biochemical degradation of NP tissue), with over 2.7 million requiring surgical interventions. Although both underlying pathologies are different, quite often they both lead to a decrease in IVD height, impaired mechanical function, and increased pain and disability. These pain symptoms affect approximately 80% of the adult population during their lifetime with estimated expenditures exceeding $85.9 billion.
Current surgical procedures for IVDH and IVDD are palliative and suffer from drawbacks. While they are performed to address patient symptoms, they fail to address the underlying pathology of a focal defect remaining within the subsequent outer layers of the AF. It is hypothesized that an effective AF closure/repair device in conjunction with a less aggressive discectomy for IVDH and/or NP arthroplasty for IVDD may result in improved patient outcomes, decreased pain, and provide fewer revision surgeries via lower re-herniation and expulsion rates. Therefore, an intact AF must be re-established to prevent implant expulsion or re-herniation, thus addressing the two major spinal pathologies directly associated with an IVD.
Currently, within the medical device market, no tissue engineering biomaterials are available for AF closure/repair. Current market AF closure devices (Intrinsic Barricaid®, Anulex X-Close® Tissue Repair System, and Anulex Inclose® Surgical Mesh System) are synthetic materials focused solely on preserving and reinforcing the native tissue and lack effective strategies for implantation, fixation, and regeneration. Therefore, there has been an increase in tissue engineering and regenerative therapeutic approaches aiming for structural and biological AF repair investigated over the last decade using in vitro and in vivo experimentation. It is proposed that the optimum AF tissue engineering scaffold should reproduce the native AF microarchitecture and native mechanical properties. Recent articles illustrate several novel sutures, sealants, and barrier techniques currently under development, resulting in an increasing attention at scientific workshops and conferences.
To develop a tissue engineering biomaterial that is suitable for AF closure we propose it must first meet the following criteria: (1) mimic the structural angle-ply architecture of the native AF, (2) fundamentally demonstrate mechanical properties mimicking the native functional characteristics, and (3) demonstrate cytocompatibility while promoting tissue regeneration. Current biomaterials gaining attention in the tissue engineering academic field, electrospinning, polymers, glue, silk scaffolds, and honeycomb-scaffolds, require complex manufacturing procedures and typically work to address two of the three criteria (mimicking the biological or structural characteristics). Therefore, the use of a decellularized tissue from a xenogeneic source may be ideal due to its advantage of maintaining native extracellular matrix (ECM) while also removing all potential harmful xenogeneic factors. Although, the mechanical advantage of closing annular focal defects to retain NP material seems intuitive, only recently have AF closure devices begun to examined in human cadaveric or animal tissues for their ability to withstand in situ IDP or flexibility testing.
We propose to address all three criteria with the development of a biomimetic, collagen-based angle-ply annulus fibrosus repair patch (AFRP) comprised of the decellularized porcine pericardium. The porcine pericardium was chosen due to its innate type I collagen content, mechanical strength, and cytocompatibility. The objectives of this research were to investigate the development of this biomimetic AFRP to biologically augment AF repair by (1) mimicking and characterizing the micro-architecture of the multi-laminate angle-ply AFRP, (2) mechanically evaluating the AFRP’s mechanical properties and attachment strength in situ, (3) evaluating the ability of the AFRPs to support AF tissue regeneration in the context of a healthy and inflammatory environment, and (4) evaluating the in vivo mechanical strength, biocompatibility, and tissue regeneration capacity of the AFRP in a large animal model for intervertebral disc degeneration/herniation.
Borem, Ryan, "Development of a Biomimetic, Collagen-Based Scaffold for the Repair and Regeneration of the Annulus Fibrosus" (2018). All Dissertations. 2562.