Collagen-based scaffolds are gaining more prominence in the field of tissue engineering. However, readily available collagen scaffolds either lack the rigid structure (hydrogels) and/or the organization (biopapers) seen in many organ tissues, such as the cornea and meniscus. Direct-write electrospinning is a promising potential additive manufacturing technique for constructing highly ordered fibrous scaffolds for tissue engineering and foundational studies in cellular behavior, but requires specific process parameters (voltage, relative humidity, solvent) in order to produce organized structures depending on the polymer chosen. To date, no work has been done to optimize direct-write electrospinning parameters for use with pure collagen. In this work, a custom electrospinning 3D printer was constructed to derive optimal direct write electrospinning parameters (voltage, relative humidity and acetic acid concentrations) for pure collagen. A LabVIEW program was built to automate control of the print stage. Relative humidity and electrospinning current were monitored in real-time to determine the impact on fiber morphology. Fiber orientation was analyzed via a newly defined parameter (spin quality ratio (SQR)). Finally, tensile tests were performed on electrospun fibrous mats as a proof of concept.

When as-received or sensitized AA5083 are immersed in an electrolyte, a growing crack creates a galvanic couple with the external surfaces according to the differential aeration hypothesis. Monitoring the resulting “coupling current” yields information about the mechanisms of crack advance. The purpose of this study is to determine if the scanning vibrating electrode technique (SVET) can be used to monitor the coupling current flowing through the solution from the crack to the external surfaces. If successful, this method, which maps potential as a function of probe position via a scanning vibrating probe (SVP), can be used to visualize and quantify the coupling current emanating from a growing stress corrosion crack in sensitized and unsensitized aluminum alloy samples to yield more localized information about the crack growth process. Preliminary feasibility studies were performed to map the current/potential in larger galvanic couples designed to simulate Cu-rich intermetallics dispersed in an aluminum matrix (as in the Cu-rich particles in AA2024 and Mg-rich intermetallics in AA5083). A fracture mechanics apparatus, designed to apply a known stress intensity, was employed to reveal the onset of subcritical crack growth. The final goal is to combine the typical fracture mechanics testing with the SVET and acoustic emissions. We report on the progress that has been made in designing a customized four-point bend, fracture mechanics device that allows for simultaneous loading and electrochemical mapping. Future work will report data gathered from in-situ electrochemical and acoustic emissions testing on pre-cracked AA5083 specimens.

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When as-received or sensitized AA5083 are immersed in an electrolyte, a growing crack creates a galvanic couple with the external surfaces according to the differential aeration hypothesis. Monitoring the resulting “coupling current” yielded “real-time” information about the status of a stress corrosion crack. As a result of this study, we have determined that the scanning vibrating electrode technique (SVET) can be used to monitor the coupling current flowing through the solution from the crack to the external surfaces. Preliminary feasibility studies were performed to map the current/potential in larger galvanic couples designed to simulate Cu-rich intermetallics dispersed in an aluminum matrix. A novel horizontal fracture mechanics apparatus, designed to apply a known stress intensity, was employed to reveal the onset of subcritical crack growth. In addition to the preliminary studies, we successfully designed a setup to allow the typical fracture mechanics testing to occur with the SVET. We report on the progress that was made in designing a customized four-point bend, fracture mechanics device that allows for simultaneous loading and electrochemical mapping. Spatially resolved coupling current/potential maps indicate that both the notch and the crack-tip become and remain anodic for a considerable duration of the crack growth process. Furthermore, there are peaks in the coupling current associated with the onset of subcritical crack growth.