Page 148 - Tailoring Electrospinning Techniques for Regenerative Medicine - Marc Simonet

CHAPTER 7
clear. Using a fast rotating disk is still the most frequently applied method to obtain aligned thick sca olds. However, it is hypothesized that retained charges on the deposited fibers influence the fibers to be deposited.4,5 Additionally, increasing wind and electric field turbulences with growing sca old thickness will have a, for thinner fibers more pronounced, negative e ect on the desired alignment.6,7
An example of the challenges of combining di erent demands is illustrated in Figure 7.1. Here, the ECM structures from Figure 1.2 in chapter 1 are compared with electrospun analogue structures developed in this thesis. Structurally, there are many obvious similarities. Due to the advances made in increasing porosity, the electrospun sca olds look much more similar to the native counterparts, especially when considering the sca old cross section (Figure 7.1 a to d). In addition to the enhanced structural similarity to ECM, these examples have an increased porosity and hence larger pore size to enhance cell infiltration. However, in the sca old with aligned fibrous stacks as well as in the LTE spun sca old, this increased porosity was achieved at the cost of mechanical strength. Due to the high alignment, the stacked sca olds tear easily perpendicular to the fiber direction, and the mechanics of LTE spun meshes are best described as cotton wool like. While these mechanics are a perfect
fit for applications like the bone cotton wool,8–10 it might pose some handling challenges for in-vivo studies and it will exclude them from mechanical demanding in-situ applications.
The di erent fiber diameters between the ECM structures and electrospun analogues in the shown examples should of course also not be neglected. The focus of the LTE related studies was on maintaining the same spinning settings, to directly compare the di erent sca olds rather than creating submicrometer fiber diameters. However, switching to a more suited polymer-solvent mixture for submicrometer fibers should allow to converge the fiber diameters.
7.2.2 Additional consideration on the LTE spinning
The problems with respect to the structural integrity of LTE spun meshes limits the possible applications of such highly porous sca olds. Nevertheless, this cotton wool like structural integrity can be overcome with time, since the large voids in these meshes enable in-vitro as well as in-vivo a fast cell ingrowth and neo-tissue formation. For example in a pilot test, the LTE spun PLA sca olds a er 7 days of culturing with human vena saphena cells (HVSC) were stronger than the conventionally spun PLA (Figure 7.2).
As demonstrated in studies, this might render them as a promising sca old type for applications without imminent mechanical loading.9,10,14,15 Alternatively,
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