## 8 Relevant Applications of Melt Electrospinning
### Biomedical Applications and Tissue Engineering
The melt electrowritten rectangular pattern approximated to the broad mechanical properties of native cardiac tissue. This scaffold promoted the seeded cardiac progenitor cell (CPC) alignment along the fiber main direction of the construct. Moreover, after 7 days of culture, the survival rate was estimated to be 99.9%. However, the pores in the structure were not uniform and so this issue should be addressed in further works as well as improving conductivity of pHMGCL, which has been proved to positively influence CPC behaviour. In another work, [PERSON] et al. [237] designed a PCL scaffold with hexagonal microstructures to repair cardiac tissue as a treatment for ischemic heart disease and heart failure. To evaluate its performance, human induced pluripotent stem cells-derived cardiomyocytes (iPSC-CM) were encapsulated in a collagen-based hydrogel and were then seeded on this scaffold. Compared to fiber scaffolds that had been produced up until then, this one appeared to deliver 40 times more elastic energy, showed a 1.5-fold beating rate, an enhanced iPSC-CM maturation and cell alignment, and sarcomere content and organisation. Moreover, an in vivo test using a porcine model was performed to demonstrate the potential of minimally invasive application by creating a functional myocardial patch and injecting it via catheter-like tubing into a beating porcine heart. Even though spontaneous contractions were observed 30 min after the injection, the beating decreased after 2 days. Similar results were observed in vitro after 2 and 5 days (Figure 15). In another cardiac tissue engineering application, [PERSON] et al. [238] fabricated a bi-layered scaffold to promote tissue growth at the interface between a suture-less inflow cannula to be implanted without bypass and in the left ventricle of the myocardium. The first layer of the scaffold was a silicone based layer to mimic the seal, and the other layer was a melt electrospun PCL scaffold with the function of integrating tissue as human foreskin fibroblasts were seeded onto it. At day 1 of culture, the scaffold showed a >95% cell viability and the percentage of dead cells did not significantly increase over the time course, which indicated no cytotoxic effects. Yet in another heart tissue engineering study, a scaffold mimicking a heart valve was developed by [PERSON] et al. [239]. The importance of heart valve tissue engineering lies on the more than 5 million people affected in the US and the 3% sudden deaths in the European Union, annually [240; 241]. With respect to the clinically available heart valve prostheses, this scaffold overcomes a few problems, such as supporting tissue remodeling and growth. One of the main components in the tissue is collagen; thus, the microarchitecture of the fiber scaffolds was controlled by melt electrowriting to mimic the crimped structure of natural collagen. Results after cell seeding and culture of human umbilical cord vein smooth muscle cells in the scaffold showed its capability to promote the cells growth, proliferation, and creation of their own ECM [239]. As mentioned early in this section, vascularization is a current challenge in tissue engineering that needs to be overcome or circumvented. A possible solution could be the development of scaffolds that stimulate vascularization by their structure. [PERSON] et al. [211] synthesized a highly structured PCL scaffold by melt electrowriting. Human umbilical vein endothelial cells (HUVEC) were seeded onto the scaffold and cultured for one day before adding normal human dermal fibroblasts (NHDF) that had been previously coated with a fibronectin and gelatine nanofilm, both ECM-derived components [26]. After a 3-day incubation period, capillary-like structures were found to be oriented along the fibers. Additionally, secretion of the angiogenic factor (VEGF) from NHDF and the consumption of VEGF by HUVEC were demonstrated. Moreover, VEGF secretion from the tissues was higher on the scaffolds than on the controls, which implies the generation of neovascular tissue [211].