Mathematical Modeling and Experimental Evaluation for the predication of single nanofiber modulus

A Study on the Effect of Doping Metallic Nanoparticles on Fracture Properties of Polylactic Acid Nanofibres via Molecular Dynamics Simulation

All-atom molecular dynamics simulations are conducted to elucidate the fracture mechanism of polylactic acid nanofibres doped with metallic nanoparticles. Extensional deformation is applied on polymer nanofibres decorated with spherical silver nanoparticles on the surface layer. In the obtained stress-strain curve, the elastic, yield, strain softening and fracture regions are recognized, where mechanical parameters are evaluated by tracking the stress, strain energy and geometrical evolutions. The energy release rate during crack propagation, which is a crucial factor in fracture mechanics, is calculated. The results show that the presence of doping nanoparticles improves the fracture properties of the polymer nanofibre consistently with experimental observation. The nanoparticles bind together polymer chains on the surface layer, which hinders crack initiation and propagation. The effect of the distribution of nanoparticles is studied through different doping decorations. Additionally, a discussion on the variation of internal energy components during uniaxial tensile loading is provided to unravel the deformation mechanism of nanoparticle-doped nanofibres.

Method for production of aligned nanofibers and fiber elasticity measurement

A novel method for collection of electrospun polymer nanofibers is proposed. This method can be applied to extrusion of various polymers and deposition on various types of substrates or without use of a substrate at all. The fiber is forced to alternate in its deposit in between two different segments of a collector electrode by a pair of square electric potential functions in anti-phase applied to these two electrode segments. As the fiber oscillation frequency is equal to the potential function frequency, the fiber deposition rate in between these two collector segments can be controlled. If an electrically non-conductive material is placed in between the two segments of the collector electrode, aligned fibers are simply deposited on the surface of this material. The method is used to perform stiffness measurements of the fibers demonstrating Young's modulus of 200.1 MPa with a standard deviation of 30.7 MPa. The stiffness measurement does not require any specialized equipment and requires minimal sample preparation. A sample consists of known amount of aligned fibers collected between a pair of thin coaxial rods leading to a cylindrical bundle with known number of fibers. A tensile test is then performed to obtain stress-strain curve and to find the Young's modulus of the fiber material.

Incorporation of F-MWCNTs into electrospun nanofibers regulates osteogenesis through stiffness and nanotopography

Nanotopography and stiffness are major physical cues affecting cell fate. However, the current nanofiber modifications techniques are limited by their ability to control these two physical cues irrespective of each other without changing the materials' surface chemistry. For this reason, the isolated effects of topography and stiffness on osteogenic regulation in electrospun nanofibers have been studied incompletely. Here, we investigated 1. how functionalized multiwall carbon nanotubes (F-MWCNTs) loaded in Polycaprolactone (PCL) nanofibers control their physical properties and 2. whether the resulting unique structures lead to distinctive phenotypes in bone progenitor cells. Changes in material properties were measured by high-resolution electron microscopes, protein adsorption and tensile tests. The effect of the developed structures on human mesenchymal stem cell (MSC) osteogenic differentiation was determined by extensive quantification of early and late osteogenic marker genes. It was found that F-MWCNT loading was an effective method to independently control the PCL nanofiber surface nanoroughness or stiffness, depending on the applied F-MWCNT concentration. Collectively, this suggests that stiffness and topography activate distinct osteogenic signaling pathway. The current strategy can help our further understanding of the mechano-biological responses in osteoprogenitor cells, which could ultimately lead to improved design of bone substitute biomaterials.