Electrospinning nanofiber scaffolds with alignment gradient and three-dimensional structure
Nowlin, John William
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An important part of creating artificial tissues is recreating the structure of the extracellular matrix. Some tissues have randomly oriented cellular structures, some aligned, and some transitioning between the two states. The tendon-to-bone interface is one such transition state, with the tendon consisting of aligned fibroblast cells and the bone consisting of randomly oriented osteoblast cells, with a thin gradient between these two regions. Electrospinning is a method to create polymer nano and microfibers that can be used as artificial cellular scaffolding. A target consisting of two parallel bars was electrospun with polycaprolactone (PCL) to recreate this structure of the tendon-to-bone interface. Fibroblast cells were seeded on the aligned fibers bridging between the parallel bars and osteosarcoma cells were seeded on the randomly oriented structure. These cells grew with the alignment of the fiber structure when incubated, with some cellular mixing in the transition region between the two orientations. A rotating cone was electrospun upon with a mixture of PCL and collagen type I to attempt to create a controllable gradient structure. Changing the rotational velocity and electrospinning distance resulted in significant effects on the fiber orientation relative to its position on the cone. Recreating the 3D structure of native tissue is crucial for the viability of an artificial tissue scaffold. Four different targets were tested with PCL to create a 3D fiber volume. Three of these, the four-sided bevel, cone, and square target, only produced thin bridging between the surfaces with a random orientation to the fibers forming the bridge. The two-sided bevel target reliably produced a 3D fiber volume consisting of relatively aligned fibers. This was then expanded to electrospinning with different mixtures of sodium alginate, polyethylene oxide, and triton X-100, a surfactant. These solutions created a 2D bridge spanning between the walls of the target, the height of which was determined to be related to the viscosity of the solution. The orientation of the fibers on the walls of the target was inversely related to the conductivity of the solution, which itself was related to the sodium alginate concentration. Testing with parallel bar targets of different sizes was used in an attempt to connect 2D and 3D electrospinning.