Electrospinning is a widely established polymer-processing technology that allows generation of fibers (in nanometer to micrometer size) that can be collected to form nonwoven structures. By choosing suitable process parameters and appropriate solvent systems, fiber size can be controlled. Since the technology allows the possibility of tailoring the mechanical properties and biological properties, there has been a significant effort to adapt the technology in tissue regeneration and drug delivery. This review focuses on recent developments in adapting this technology for tissue regeneration applications. In particular, different configurations of nozzles and collector plates are summarized from the view of cell seeding and distribution. Further developments in obtaining thick layers of tissues and thin layered membranes are discussed. Recent advances in porous structure spatial architecture parameters such as pore size, fiber size, fiber stiffness, and matrix turnover are summarized. In addition, possibility of developing simple three-dimensional models using electrosprayed fibers that can be utilized in routine cell culture studies is described. Tissue EngineeringT issue engineering or regeneration is a multidisciplinary study to restore, maintain, and enhance tissue and organ function. 1 In tissue engineering, biodegradable scaffolds are used to support and guide cells to proliferate, organize, and produce their own extracellular matrix (ECM). Scaffolding material eventually disappears leaving only the necessary healthy tissue in a topologically required form. 2,3 Assembly and maturation of ECM elements is important in determining the biomechanics and the quality of the tissue. For example, collagen provides tensile strength to the tissue, elastic fibers contribute to the elasticity of the tissue, while proteoglycans fills the extracellular space, creating a space for the tissue regulation of growth factors and other interactions. 4 Delicate balance between different matrix elements is necessary to generate healthy tissue. The size and shape of collagen fibers in ECM relies on tissues and organs even in the same species. The shape is cord or tape with a width of 1-20 mm and the collagen fibrils (unit can be observed by electron microscopy) are cylindrical with a diameter ranging from 10 to over 500 nm where cell is attaching and hugging. 5 Obtaining a biodegradable matrix conducive for cell colonization is a fundamental requirement for tissue regeneration. Like ECM, biomimic scaffold should allow cell attachment and migration, enables diffusion of vital cell nutrients, and retains cells. Further, chemical and mechanical properties of scaffold influence cell viability and proliferation. 6 Appropriate pore size and porosity are essential to modulate cell seeding and diffusion. Biodegradability is essential because scaffolds are absorbed and distributed to the nearby tissue, which allows no surgical removal from body. The surface of scaffold is suitable for cell attachment and migration. The mechanical properties...

Regeneration of tissues using biodegradable porous scaffolds has been an intensely investigated area. Since electrospinning can produce scaffolds mimicking nanofibrous architecture found in the body, it recently has gained widespread attention. However, a major problem is the lack of pore size necessary for infiltration of cells into the layers below the surface, restricting cell colonization to the surfaces only. This study describes a novel twist to the traditional electrospinning technology. In particular, collector plates are designed which allows forming very thin layers with pore sizes suitable for cell infiltration. Thin samples can be handled without mechanically damaging the structure and can be transferred into cell culture. These thin layers were stacked by layer-by-layer assembly to develop thick structures. Thirty day cultures of fibroblasts show attachment and spreading of cells in every layer. This concept is useful in regenerating thick tissues with uniformly distributed cells and others in vitro cell culture.

Although the technique of coronary stenting has remarkably improved long-term results in recent years, (sub)acute thrombosis and late restenosis still remain problems to be solved. Metallic surfaces were regarded as thrombogenic, due to their positive surface charges, and stenosis resulted from the activation and proliferation of vascular smooth muscle cells (VSMCs). In this study, a unique surface modification method for metallic surfaces was studied using a self-assembled monolayer (SAM) technique. The method included the deposition of thin gold layers, the chemisorption of disulfides containing functional groups, and the subsequent coupling of PEG derivatives or heparin utilizing the functional groups of the disulfides. All the reactions were confirmed by ATR-FTIR and XPS. The surface modified with sulfonated PEG (Au-S-PEG-SO3) or heparinized PEG (Au-S-PEG-Hep) exhibited decreased static contact angles and therefore increased hydrophilicity to a great extent, which resulted from the coupling of PEG and the ionic groups attached. In vitro fibrinogen adsorption and platelet adhesion onto the Au-S-PEG-SO3 or Au-S-PEG-Hep surfaces decreased to a great extent, indicating enhanced blood compatibility. This decreased interaction of the modified surfaces should be attributed to the non-adhesive property of PEG and the synergistic effect of sulfonated PEG. The effect of the surface modification on the adhesion and proliferation of VSMCs was also investigated. The modified Au-S-PEG-SO3 or Au-S-PEG-Hep surfaces also exhibited decreased adhesion of VSMCs, while the deposited gold layer itself was effective. The enhanced blood compatibility and the decreased adhesion of VSMCs on the modified metallic surfaces may help to decrease thrombus formation and suppress restenosis. It would therefore be very useful to apply these modified surfaces to stents for improved functions. A long-term in vivo study using animal models is currently under way.

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Many variations in the electrospinning process have emerged to control pore size needed in tissue scaffolds including introducing voids in the collector plate. However, the effect of different shapes and sizes of voids on fiber and pore sizes is not well understood. In this study, we evaluated the effect of void size and shapes in the collector plate on polycaprolactone (PCL) fiber size and pore size. First, we performed experiments using three different sizes of circular voids (0.9, 1.4, and 1.9 cm). Also, we evaluated the effect of triangular and rectangular voids. Further, changes in the electrical field within the voids were evaluated using computational fluid dynamic software COMSOL. Fibers using mixtures of PCL (high, medium, and low molecular weight) formed using void collector plate and performed degradation characteristics for 30 days in physiological conditions (37 C and 7.4 pH). These results showed that the size and the morphology of fibers are not affected by the geometrical patterns of the voids. However, fiber alignment is affected by the void shape due to favorable rearrangement in the electrical field. Fibers can be formed by mixing PCL of different molecular weight, and degradation of PCL fiber was accelerated by the mixture with low molecular weight. V C 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 128: 1583-1591, 2013