Associate Professor Arizona State University, United States
Introduction:
Introduction: Approximately 14 million fibrous connective tissue injuries occur each year in the United States.1 These ligaments, tendons, and joint capsules are comprised of highly organized tissues.1 During healing, disorganized tissue is typically formed with inferior mechanical properties.1,2 New treatment options that are capable of regenerating these highly organized fibrous structures are needed. Tissue engineering is a promising approach that uses cells, signaling cues, and scaffolds to regenerate functional tissue. For connective tissues, fibers serve as a critical physical signaling cue to direct cell behavior. Electrospinning is a well-established technique to produce fibrous biomaterials that mimic the extracellular matrix of many tissues. Research has shown that cell morphology and gene expression are highly dependent on electrospun fiber alignment.2,3 Further research is needed to better understand the temporal role of these physical cues on cell behavior and new tissue formation.
To address this, we designed a magneto-responsive fiber-hydrogel composite with temporal control over fiber alignment. Magnetic nanoparticles were incorporated into short, electrospun fibers to enable alignment in the presence of a magnetic field. Fibers were embedded within guest-host hydrogels, which are crosslinked using reversible hydrophobic interactions. These non-covalent crosslinks enable fiber alignment to be continuously modified at user-controlled timepoints. We characterized fiber alignment as a function of fiber length, magnetic field strength, and magnetic field exposure time.
Materials and
Methods:
Methods: Polycaprolactone was dissolved in 1:1 chloroform:acetic acid containing superparamagnetic iron oxide nanoparticles (SPIONs) and Nile Red for visualization, then electrospun. The resultant fibrous mat was cut into short fibers.3 Dynamic hydrogels were synthesized using guest-host chemistry by combining adamantane-modified HA with β-cyclodextrin-modified HA.4 Short fibers (0.5 wt%) were mixed into PBS, which was then used to dissolve each component of the dynamic hydrogel. The dissolved components were mixed in equal parts to form the fiber-hydrogel composites. Rheology was performed to determine the composite’s mechanical properties. Fiber alignment within the hydrogels was visualized using microscopy and quantified using FiberFit5 as a function of: magnetic field strength (300-760 mT), fiber length (20 and 40 µm), and magnetic field exposure time (0-120 mins).
Results, Conclusions, and Discussions:
Results: Short, magneto-responsive, fibers with encapsulated SPIONs were embedded within dynamically crosslinked hydrogels. Fibers aligned within the hydrogels in the extended presence of a strong magnetic field (620, 760 mT), demonstrating the ability of the magnetic field to generate sufficient shear stresses to break the dynamic crosslinks and enable fiber movement (Fig 1). Fiber alignment was visible after 30 minutes of exposure and continued to increase until reaching a plateau at 120 minutes of magnetic field exposure. Fiber alignment was not significantly affected by fiber length. Higher magnetic field strengths resulted in slightly higher fiber alignment after 120 minutes of exposure. To demonstrate temporal control over fiber alignment (Fig 2), fibers were first aligned horizontally and then, at a user-defined timepoint, fibers were aligned vertically by changing the direction of the magnetic field.
Discussion: A magnetic field stronger than 300 mT was needed to align fibers. Fibers did not affect the hydrogel’s shear-thinning or self-healing properties. Critically, dynamic fiber-hydrogel composites with magneto-responsive fibers enable in situ control over fiber alignment at any user-defined timepoint via the application of a magnetic field. This system will allow us to investigate the temporal role of fiber alignment on cell behavior. Ongoing work is evaluating cell behavior as a function of dynamic fiber alignment within these fiber-hydrogel composites.
References: 1Yang G. Birth Defects Res. C Embryo Today. 2013;99:203-222. 2Petre DG. Tissue Eng. Part B Rev. 2022;28:141-159. 3Omidinia‐Anarkoli A. Small. 2017;13:1702207. 4Loebel C. Nat Protoc. 2017;12:1521-1541. 5Morrill EE. Biomech Model Mechanobiol. 2016;15(6):1467-1478.
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