Significance: The spatial organization of collagen fibers has been used as a biomarker for assessing injury and disease progression. However, quantifying this organization for complex structures is challenging.
Aim: To quantify and classify complex collagen fiber organizations.
Approach: Using quantitative second-harmonic generation (SHG) microscopy, we show that collagen-fiber orientation can be viewed as pseudovector fields. Subsequently, we analyze them using fluid mechanic metrics, such as energy U, enstrophy E, and tortuosity τ.
Results: We show that metrics used in fluid mechanics for analyzing fluid flow can be adapted to analyze complex collagen fiber organization. As examples, we consider SHG images of collagenous tissue for straight, wavy, and circular fiber structures.
Conclusions: The results of this study show the utility of the chosen metrics to distinguish diverse and complex collagen organizations. We find that the distribution of values for E and U increases with collagen fiber disorganization, where they divide between low and high values corresponding to uniformly aligned fibers and disorganized collagen fibers, respectively. We also confirm that the values of τ cluster around 1 when the fibers are straight, and the range increases up to 1.5 when wavier fibers are present.
The motion and growth of plants is the inspiration for a new biomimetic actuator that uses fluid transport across a bilayer lipid membrane (BLM) to create internal pressure and cause displacement in the actuator. In order for the actuator to be viable the BLM must be able to withstand this internal pressure without failing. In this study BLMs are formed over a porous polycarbonate substrate and a hydrostatic pressure is applied to the BLM and gradually increased until it fails. This test is performed over different pore sizes to measure the failure pressure of the BLM as a function of pore radius. A similar test is used for polymer films to compare the failure pressure trends of a BLM to conventional engineering materials. The polymer films and BLMs are modeled as a simply supported circular plate under uniform load, first with the assumption of small deflections and then with the assumption of large deflections. It was found that the large deflection model better represents the trend of failure pressure versus pore radius than the small deflection model.
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