Page 27 - Tailoring Electrospinning Techniques for Regenerative Medicine - Marc Simonet

led to an e ort in understanding these influences and in constructing environmentally controlled electrospinning equipmentl.
The influence of relative humidity on the pore formation at the fiber surface was the first reported ambient parameter e ect.36 As also confirmed by follow-up studies, an increase in humidity directly results in more and larger pores.66–69 Electrospinning at a lower humidity or a higher temperature increases the solvent evaporation, allowing to adjust the amount of fused fibers.70 A higher temperature also reduces the solution viscosity and hence fiber diameter.71,72 Oğulata et al. reported a diameter decrease of 50% with a temperature increase of 25 K. The influence of relative humidity on the fiber diameter depends on the used polymer/solvent combination, the rate of solvent evaporation and sensitivity to humidity. See Table 1.3 for an overview of how relative humidity a ects electrospun fibers.
A few studies describe the formation of smooth, beaded or broken fibers in relation to the relative humidity.48,69,73–75 With water soluble polymers there is an increase in bead formation at elevated humidity reported. This has been attributed to water absorption and hence reduced polymer concentrations.48,74 The opposite e ect has been reported for polystyrene fiber, where it was hypothesized that higher humidity delayed the jet solidification and hence, the jet instabilities
overcame the bead formation.69 Changes in relative 1 humidity can also cause breakage of the jet and
result in spinning short fibers, caused by excessive
charges on the jet. Due to the low humidity, the
charges dissipate much slower into the surrounding atmosphere and the repulsive force breaks the jet.75 The di erence in charge dissipation due to the relative humidity has also been considered to be the reason that self-assembled 3D electrospun structures might occur or not.48,74
In summary, one needs to be aware that an optimized set of solution and process parameters is o en very specific to a certain set of ambient parameters. This is also reflected by the fact that in recent studies, the ambient electrospinning parameters are more frequently mentioned in the materials and method section as electrospinning parameters.
1.6 Fiber assemblies to match ECM blueprint
1.6.1 Match the ECM structural build up
When comparing the SEM images of the electrospun sca olds in Figure 1.2 with SEM images of ECM, it can be seen why electrospinning is o en referred to as a promising method to create ECM analogues. Electrospinning creates sca olds which directly assemble some of the structural features of ECM.
GENERAL INTRODUCTION
l The first commercial climate controlled electrospinning was on the market in 2011, by IME Technologies, NL
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