Abstract
Biomaterials based on electrospun nanofibers are increasingly used in biomedical applications. Polycaprolactone (PCL) is a biocompatible, biodegradable, FDA-approved, synthetic polymer suitable for such applications. In this study, we used a nanomanipulation technique based on a combined atomic force/optical microscope to investigate key mechanical properties of electrospun PCL nanofibers as a function of PCL molecular weight (150 kDa, 114 kDa, and 74 kDa) and fiber diameter (20–250 nm). Mechanical properties extracted from different types of stress-strain curves included maximum stress and strain, elasticity, Young’s modulus, strain-dependent energy loss/storage, and stress relaxation time. We found that PCL molecular weight had a marginal effect on mechanical properties. In contrast, fiber diameter had a strong effect on fiber modulus. Specifically, extensibility, elastic limit, and stress relaxation time ranged from 123% to 133%, 16–44%, and 21–14 s, respectively. Energy loss/cycle was 35% for low strains (strain, 10–20%) and 65% for high strains (strain > 80%). The Young’s modulus decreased from 3000 MPa to 500 MPa as the diameter increased from 40 nm to 100 nm; above 100 nm, the diameter-dependence waned, and the fiber modulus approached the PCL bulk modulus of about 300 MPa. The diameter-dependence of the modulus opens the intriguing possibility of producing electrospun PCL nanofibers with very different stiffnesses simply by adjusting the fiber diameter.
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