Magnetic electrospun fibers for neural regeneration applications

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Funnell, Jessica, Lynn
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Electronic thesis
Biomedical engineering
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Nervous system damage caused by physical trauma or degenerative diseases can result in loss of sensory and motor function for patients. Biomaterial interventions have shown promise in animal studies, providing contact guidance for extending neurites or sustained release of various drugs and growth factors; however, these approaches often target only one aspect of the regeneration process. More recent studies investigate hybrid approaches, creating complex materials that can reduce inflammation or provide neuroprotection in addition to stimulating growth and regeneration. Magnetic materials have shown promise in this field, as they can be manipulated non-invasively, are easily functionalized, and can be used to mechanically stimulate cells. By combining different types of biomaterials (hydrogels, nanoparticles, electrospun fibers) and incorporating magnetic elements, magnetic materials can provide multiple physical and chemical cues to promote regeneration.Electrospun fibers are a promising approach for providing contact guidance for regenerating axons in the peripheral nervous system and providing sustained drug release in the central nervous system after injury. Aligned electrospun fibers used in synthetic nerve conduits improve axonal regeneration across large gap distances in preclinical peripheral nerve injury models but do not fully recover nerve function and do not address variability between patients. Magnetic materials can be non-invasively stimulated with a magnetic field, allowing for the therapeutic stimulation regimen to be easily modified depending on the patient. To further enhance fiber scaffolds, superparamagnetic iron oxide nanoparticles (SPIONs) can be incorporated to generate composite scaffolds that are actively manipulated by magnetic fields. This thesis focuses on developing magnetic electrospun fiber scaffolds designed to either mechanically stimulate neuronal outgrowth while also providing structural support and guidance cues, or to provide a means to release a bioactive growth factor on demand to alleviate a neurotoxic reactive astrocyte phenotype. First, I investigated the potential of magnetic field stimulation to enhance neurite outgrowth on aligned electrospun fibers, SPION-grafted fibers, and fibers with SPIONs dispersed in the culture media. The addition of SPIONs grafted to aligned fibers was hypothesized to create a means of actively stimulating regeneration using an external magnetic field. In this study, we fabricated and characterized the fiber diameter, density, and alignment of SPION-grafted aligned electrospun fibers. I then directly compared a static, alternating, and linearly moving magnetic field and showed that an alternating magnetic field increases neurite length from rat dorsal root ganglia (DRG) on aligned control and SPION-grafted fibers compared to a static magnetic field. Additionally, I showed that both neurite length and area coverage are increased on SPION-grafted fibers compared to cells cultured on control fibers with untethered, dispersed SPIONs added to the culture media. Next, I developed protein-loaded magnetic coaxial electrospun fibers to alleviate a neurotoxic reactive astrocyte phenotype. In the central nervous system after spinal cord injury, the inflammatory response varies depending on patient demographics and injury severity. Electrospun fibers can provide local release of therapeutics to limit adverse off-target effects; however, drug-releasing fibers do not address the variability of patient inflammation. To provide a means of tailoring the therapeutic delivery to a patient, I fabricated magnetic, growth factor-loaded coaxial electrospun fibers that can be stimulated non-invasively with a magnetic field to increase the rate of growth factor release from the fibers. I then tested the efficacy of these scaffolds by incubating them with activated astrocyte cultures and assessed their phenotype. We found that these magnetic coaxial scaffolds alleviate a neurotoxic reactive astrocyte phenotype in vitro, but that more work is needed to improve the magnetic field stimulation to provide an optimal dosing regimen for maintaining reduced astrocyte reactivity. The findings detailed in this thesis demonstrate the design and in vitro characterization of novel magnetic electrospun fiber scaffolds and their effect on primary nervous system cells. The knowledge gained from these works provides a basis for further optimization of these fibrous therapeutic platforms for future testing in preclinical animal models.
School of Engineering
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Rensselaer Polytechnic Institute, Troy, NY
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