Page 29 - Tailoring Electrospinning Techniques for Regenerative Medicine - Marc Simonet

Electrospun sca olds are fully interconnected porous fibrous 3D structures and the technique enables to obtain the 3D shape of the targeted tissue by spinning onto a target resembling this structure.
Selecting specific solution and process parameters allows to adjust the fiber diameter towards the desired ranges. One set of parameters may lead to a narrow as well as a broad fiber diameter range,91,92 while spinning from di erent nozzles enables the production of a sca old with distinct di erent fiber diameter ranges.93,94 Surface features such as pores and grooves (see Figure 1.4) to visually mimic structured ECM fibers can be induced with the interplay of solvent, polymer and ambient conditions or alternatively by electrospinning a polymer blend.95,96
By means of electrospinning di erent fiber alignments, as found in tissues and in the di erent layers of tissues, can be achieved. When spinning on a rotating target, changing the target rpm to match the electrospinning jet speed is a simple way to obtain aligned fibers.99,100 This method has its limitations for small diameter tubular sca olds where it becomes troublesome to match the jet speed of up to 15 m/s by only increasing the target rpms.101 Alignment for these sca olds can be assisted by influencing the electrospinning jet with additional electrodes. These additional electrodes can be placed around the target (guiding electrodes, Figure 1.5a) or in-between the nozzle and target
(stirring or focusing electrodes, Figure 1.5b). Guiding 1 electrodes direct the fiber collection, in Figure 1.5a
collecting them highly aligned in-between the two
electrodes, whereas stirring electrodes force the jet
to oscillate in one main direction and thereby induce fiber alignment into the sca olds.102–105
Both methods enable the production of sca olds with radially or axially aligned fibers, or layers of each, for instance to be used for blood vessel or nerve guiding tissue engineering sca olds. As an alternative to additional electrodes, direct writing by melt electrospinning or with a stable jet recently gained a lot of attention to build sca olds with a high degree of control over the fiber deposition and hence fiber alignment.106–111 With both methods there is no jet instability. This allows to control the deposition of the fiber jet, but in general also results in thicker fiber diameters in the range of 0.5 to 100 mm vs. 4 nm to 20 mm for solution electrospinning.28,108
1.6.2 Matching the ECM functionality
Whereas ECM-look-alike electrospun sca olds can already be utilized for many research questions in two-dimensional and in-vitro experiments, thefunctionality of the electrospun sca old is crucial for the success of any in-vivo application. Especially for in-situ applications, degradable sca olds need to be mechanically robust for a prolonged period of time, until su icient tissue is formed by the cells.
GENERAL INTRODUCTION
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