Biodegradable polymeric nanofibrous scaffold comprises individual nanofibers where their stiffnesses can promote or undermine the various cellular functions as well as structural integrity of the scaffold. As such, there is a need to investigate the nanomechanical properties of these individual nanofibers. However, conducting mechanical tests of individual fibers at the nanometer scale can pose great challenges and difficulties. Here, we present novel techniques to perform nanomechanical testing of individual polymeric nanofibers. For demonstration of the nano tensile tests, polycaprolactone (PCL) nanofibers were produced via electrospinning. These fibers were deposited across two parallel edges of a cardboard frame so that a single nanofiber can be isolated for tensile test using a nano tensile tester. For nanoscale three-point bend test, a Poly (L-lactic acid) (PLLA) nanofiber was suspended across a microsized groove etched on a silicon wafer. An atomic force microscope (AFM) tip was then used to apply a point load on the mid-span of the suspended fiber. Beam bending theory was then used to calculate the elastic modulus of the nanofiber. For nanoindentation test, a PLLA nanofiber was deposited on a mica substrate and an AFM tip used to indent the nanofiber. Modified Hertz theory for normal contact was then used to evaluate the elastic modulus of the nanofiber.
Micropipette aspiration is one of the most widely used techniques for measuring the mechanical properties of single cells. The homogeneous linear elastic half-space model has been frequently applied to characterize the micropipette aspiration of chondrocytes and endothelial cells. However, the linear elastic model is limited to small deformation and the half-space assumption is frequently invalidated when moderately large micropipettes are used. In this work, the linear elastic constitutive model is extended to the neo-Hookean constitutive model and the geometry is simulated more realistically by considering the cell as a sphere. The large-deformation contact mechanics problem is solved using dimensionless axisymmetric finite element analysis. The effects of pipette diameter and fillet radius on the cellular rheological behaviour are also systematically studied. Based on the finite element simulation, empirical relationships have been derived for the direct interpretation of the elastic mechanical parameters from the micropipette aspiration experiments. Micropipette aspiration of late-stage malaria-infected red blood cells (schizonts) is conducted. The infected cells are found to exhibit elastic solid behavior in contrast to the liquid drop behavior of healthy red blood cells. The apparent shear modulus of the schizonts, interpreted from the elastic solid model, is found to be 119±62 Pa.
The tensile mechanical behavior of a short carbon fiber filled liquid crystalline polymer (LCP) composite, Vectra A230, was examined under static extension and dynamic loading at three temperatures. Dynamic tension was applied using a pendulum-type tensile spilt Hopkinson bar device. Specimens fabricated according to both the mould flow and transverse directions were tested. The stress-strain curves at various strain rates and temperatures were determined and found to be sensitive to strain rate as well as temperature for both types of specimens. With reference to the properties of pure LCP, mechanical anisotropy and fiber reinforcement effects were characterized and are discussed. Failed specimens were observed suing an optical microscope. Deformation and failure mechanisms in the microstructure of the LCP composite were studied to understand the effects of strain rate and temperature on material strength and failure strain.
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