KEYWORDS: Atomic force microscopy, Modeling, Polystyrene, Mechanics, Equipment, Composites, Beam analyzers, Analog electronics, 3D modeling, 3D metrology
This study explores Atomic Force Microscopy's (AFM) applicability for 3D analysis by determining its "mechanical focal plane" in soft composites. The investigators determined the AFM's ability to measure mechanics from a distance when target components are immersed in a secondary medium. Using the Kelvin-Voigt model under quasi-static and dynamic conditions, a sample material with polystyrene beads embedded in agarose gel is analyzed at varying scanning parameters. The results include a model of the effective depth and the effect that a secondary medium has on the ability to measure an embedded component's properties.
Maintaining the heart's health is one of the largest challenges in medicine due to the proclivity of life-threatening cardiovascular diseases, such as myocardial infarctions. When the heart experiences an infarction, a scar begins forming within an hour of the event, which will continue to grow and weaken the heart’s ability to contract. The myocardium after an infarction will increase in stiffness as the tissue becomes fibrotic; the influx of collagen dampens the flexion of the ventricles and reduces the cardiac output. The nature of the tissue stiffness is vital to understand not only at the tissue level but also at the mesoscopic domain. It is necessary to specify how the primary structural tissue components at the subcellular level contribute to the mechanical behavior of the muscle. To investigate this, we produced a procedure for mapping the mechanical nature of fresh myocardium: using atomic force microscopy to measure the mechanical properties of each structural component imaging determined by our second harmonic generation (SHG) microscopy. To coregistered AFM and SHG image, which has not been accomplished previously, we developed a convenient means of marking PDMS to be visible in SHG at 830 nm. Our research draws the line between the macroscopic mechanical behavior of the tissue to the nanoscopic structures.
Mechanical signaling in vascular tissue can have major effects on remodeling outcomes and the viability of bypass grafts. When a vein is placed into an environment matching that of an artery, the vein begins to remodel to act like an artery. This change is dependent on mechanotransduction pathways that sense stress from the blood flow. To properly study these pathways, vessels need to be studied ex vivo to control the stress patterns vessels will experience within a patient. The mechanical properties of the vessel will then need to be analyzed at a cellular level to correlate the strain of the environment to the cell response. Optical coherence tomography (OCT) is able to capture b-scans of the entire vessel wall to observe changes at different lateral and axial positions. Multiple b-scans can be captured as the vessel experiences a pressure waveform mimicking physiological pressures and digital image correlation (DIC) can be performed to quantify the mechanical response of the tissue at each spot in the b-scan. A custom-built optical coherence tomography system was used to record images of a porcine carotid artery undergoing pressure changes to observe movements inside the vessel wall. DIC was performed to correlate the strain of the tissue to the experienced stress as a means of testing the system. This imaging method will provide valuable mechanical information as a vein is remodeled in a perfusion bioreactor.
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