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Collagen Nanoyarns: Hierarchical 3-D Biomaterial Constructs for Tendon Fiber Reconstruction

Friday, December 16, 2022

2:00 PM-4:00 PM

BIOMED PhD Thesis Defense

Collagen Nanoyarns: Hierarchical Three-Dimensional Biomaterial Constructs for Tendon Fiber Reconstruction
Chukwuemeka Chikelu, PhD Candidate
School of Biomedical Engineering, Science and Health Systems
Drexel University
Lin Han, PhD
Associate Professor
School of Biomedical Engineering, Science and Health Systems
Drexel University

Caroline Schauer, PhD
Margaret C. Burns Chair in Engineering
Associate Dean for Research
Materials Science and Engineering
College of Engineering
Drexel University

Rotator cuff tendon (RCT)  disorders, among musculoskeletal problems, are noteworthy because of their preponderance in the elderly, and the high surgical failure rates in cases presenting with massive tears. Surgical strategies include the augmentation of the repair site mechanically by various graft materials, with autografts and allografts being the main options for the restoration and repair of damaged tendons. However, challenges such as immune rejection and donor site morbidity among others still exist. Synthetic grafts, on the other hand, are limited by poor cell adhesion, induced chronic inflammation and foreign body giant cell reaction.

Hierarchical fibrous scaffolds consist of nanoscale fibers arranged in larger macroscale structures, much in the same pattern as in native tissue such as tendon and bone. Creation of continuous macroscale nanofiber yarns has been made possible using modified electrospinning set-ups that combine electrospinning with techniques such as twisting, drawing, and winding. Collagen, the main protein and load-bearing structure of connective tissues, is considered the ideal scaffold biomaterial because of its inherent biocompatibility and non-inflammatory properties. However, the use of cytotoxic solvents and the typical 2D, mat-based geometry of electrospun collagen scaffolds render them inadequate for 3D tissue reconstruction and augmentation. Also, low porosity of electrospun nanofibrous scaffolds hampers cell infiltration and restricts tissue formation to the scaffold surface. The central hypothesis of this work was that Type I collagen nanoyarns used as biomimetic scaffolds can replicate the topography of the tendon ECM, thus regulating native cell response. We tested this hypothesis within 3 specific aims: fabricating collagen nanofiber yarns (CNY) by the nanoyarn-electrospinning of collagen solution; tuning CNY porosity by the inclusion, and subsequent removal, of sacrificial poly(ethylene oxide) (PEO) nanofibers; and enhancing the mechanical integrity of CNY scaffolds by crosslinking and twisting while observing the response of cells cultured on the scaffolds in vitro.

Continuous type I CNYs were successfully created by using a nanoyarn electrospinning set-up to spin acid-soluble type I collagen solution prepared in acetic acid. Structural denaturation assessment of native collagen using circular dichroism (CD) spectroscopy showed that 60% of the triple-helical collagen content in CNYs was preserved. Glutaraldehyde vapor-crosslinking of CNY samples significantly improved their tensile strength and stiffness, as well as stability in aqueous media as they show little signs of degradation until after 14 days. To tune the porosity of CNY scaffolds, a sacrificial nanofiber removal process was executed by spinning and crosslinking of PEO-CNY composites, suspension of crosslinked composites in DI H2O to dissolve out the PEO nanofiber component, and lyophilization of samples. Porosity-tuned CNYs (PT-CNY) had an average pore diameter of 12 ± 5.0 µm and showed a 5-fold increase in porosity and a 2-fold decrease in density when compared to regular CNYs, although this came with a 2-fold and 4-fold decrease in tensile strength and stiffness, respectively. PT-CNYs showed improved cell adhesion, infiltration, and viability, with cells displaying the characteristic spindle-shaped morphology of cells grown on surfaces with aligned topography.

Collectively, the results demonstrate the promising potential of collagen nanoyarns as a new class of shapable biomaterial scaffold and building block for generating macroscale fiber-based tissues.

Contact Information

Natalia Broz

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