## 6 Summary and Future Perspective  
The ability to utilize a large number of polymers and their blends has led to an increasing number of studies that are related to MEW in recent years. Computer-controlled nature of the melt electrospinning writing process facilitates design and fabrication of the structures with great control over mechanical properties and, subsequently, cellular responses. Owing to the elimination of solvent in comparison with the solution electrospinning, this method reduces the cost of the process, with respect to the solvent removal and recycling, toxicity and miscibility, and ventilation system. The feasibility of inclusion of several types of nanoparticles and active biomaterials, such as bioactive glasses, carbon nanotubes, drugs, and antibiotics within the polymers has resulted in further expansion of the application of MEW in tissue engineering. Despite the highlighted advantages of MEW, progressive development in material libraries, and establishment of innovative hardware, some requirements are yet to be addressed. Figure 8: Hybrid setup of melt electrospinning writing-solution electrospinning (MEW-SE) for manufacturing of composite PCL/collagen structure. Reprinted from [125] Copyright (2008) with permission from Elsevier. For instance, the fiber diameter could not be obtained as low as natural ECM diameter. In addition, most of the polymers that were processed by this method possess hydrophobic surfaces with low control over cell attachment and protein adsorption. Although mechanical properties can be tuned by controlling the structure's architecture and porosity, high stiffness values, and low elasticities as compared to human tissues are major concerns in further applications. Moreover, the thermoplastic polymers which could be utilized at elevated temperatures are also limited. To address these challenges, the integration of MEW with other techniques as a hybrid process could indeed offer a promising strategy. This integration would, in turn, provide the possibility to include cell-laden hydrogels, heat-sensitive drugs, or bioactive molecules, and to functionalize the polymers with other AM techniques combined with MEW. The reinforcement of hydrogels by well-ordered melt electrospun structures is one of the most common hybrid approaches presented in the literature, which is mainly used for soft tissue regeneration applications. The implementation of rigid polymer meshes within less stiff hydrogels showed significant improvements in composite stiffness. This improvement is explained with the synergistic reinforcement effects with several hypotheses. In general, the residual tensile stress in the fibers due to the expansion of the hydrogel in the compressive loading, enhanced load transfer within the fiber network, and the role of hydrogels in the prevention of buckling have been emphasized. It should be noted that most of the mechanical tests were conducted under compressive loading conditions. However, no investigation on the reinforcement mechanism under other loading conditions (i.e., tensile and shear loading) has been conducted, although they significantly contribute to the mechanical behavior of native tissues. This approach holds high potential in the case of several areas of research, including cartilage, cardiac, neural, skin and bone tissue engineering, and wound healing applications, not only for improving the mechanical properties, but also maintaining a hydrated environment at the same time for cells to attach, migrate, and differentiate. By further development of materials and architectures, we foresee extensive progress in hybrid systems to utilize a wide variety of polymers and hydrogels with several biomolecules, cells, and nanoparticles. Hybrid approaches are not limited to fiber-reinforced composites. Other approaches, like functionalization or coating of the melt electrospun structures with calcium phosphate, sodium hydroxide, and plasma treatment, were also employed.