[ review on different approaches for improving cell infiltration in electrospun nanofibrous scaffolds]

In recent years, electrospinning that has the capability to form polymeric nano-microfibers has gained substantial attention for fabrication of tissue engineering scaffolds. The morphological resemblance to native extracellular matrix [ECM], high surface to volume ratio, high porosity, and pore interconnectivity are amongst the brilliant features of electrospun structures. The high surface area to volume ratio and interconnected pores of these fibrous meshes confer desirable cell attachment and growth. However, due to small pore sizes and high packing density of electrospun nanofibers, cell penetration into a conventional electrospun mat is completely restrained. Scarce cell infiltration in turn prohibit cell migration into internal parts of the scaffold, cause inhomogeneous cell distribution throughout the structure, limit vascularization, and impede tissue ingrowth. In fact, traditional electrospun nanofibrous scaffolds in practice act as two-dimensional [2D] surfaces rather than three-dimensional [3D] microenvironments. Thus far, a number of approaches have been employed to solve this problem, which range from simple variations in electrospinning parameters to intricate post-processing modifications. Some efforts directly manipulate the electrospun mat characteristics to enhance cell penetration, while others combine cells with scaffolds or encourage cells to migrate into internal parts with different stimuli. In the present study, we have attempted to provide an overview of different approaches offered for improving cell infiltration in electrospun scaffolds

[Effect of mechanical stimulations on the fate of stem cells - a review]

The provision of an adequate quantity of cells with proper function and purity is one of the main challenges of tissue engineering studies. Stem cells, with their self-renewal and differentiation capacity, are considered one of the main cell sources in the field of tissue engineering. Previously, the use of chemical factors seemed to be the only possible way for stem cell differentiation. However, scientists have recently realized that physiological processes of the human body are composed of chemical, mechanical and electrical signals. Mechanical stimulation is one of the current methods that produce cells with proper morphology and alignment in the scaffold. Specific differentiation, a higher rate of cell growth, proliferation and differentiation, and lower experiment costs can be achieved using mechanical stimulation. Different parameters such as the chemical environment, physical environment that surrounds the cell [including geometry, stiffness and topology of scaffold surface], amplitude, frequency, and duration of mechanical stimulation can affect the stem cell fate. In this study we have investigated the impact of all types of mechanical stimulations under different loading regimes on the fate of stem cells with respect to the target tissue. The result has been reflected in the design of a proper bioreactor

Study of Collagen Immobilization on a Novel Nanocomposite to Enhance Cell Adhesion and Growth

Surface properties of a biomaterial could be critical in determining biomaterial's biocompatibility due to the fact that the first interactions between the biological environment and artificial materials are most likely occurred at material's surface. In this study, the surface properties of a new nanocomposite [NC] polymeric material were modified by combining plasma treatment and collagen immobilization in order to enhance cell adhesion and growth. Methods: NC films were plasma treated in reactive O[2] plasma at 60 W for 120 s. Afterward, type I collagen was immobilized on the activated NC by a safe, easy, and effective one-step process. The modified surfaces of NC were characterized by water contact angle measurement, water uptake, scanning electron microscopy [SEM], and Fourier transformed infrared spectroscopy in attenuated total reflection mode [ATR-FTIR]. Furthermore, the cellular behaviors of human umbilical vascular endothelial cells [HUVEC] such as attachment, growth and proliferation on the surface of the NC were also evaluated in vitro by optical microscopy and 3-[4,5-dimethylthiazol-2-yl]-2,5-diphenyltetrazolium bromide test. Results: The outcomes indicated that plasma treatment and collagen immobilization could improve hydrophilicity of NC. SEM micrograph of the grafted film showed a confluent layer of collagen with about 3-5 jum thicknesses. In vitro tests showed that collagen-grafted and plasma-treated surfaces both resulted in higher cell adhesion and growth state compared with untreated ones. Conclusion: Plasma surface modification and collagen immobilization could enhance the attachment and proliferation of HUVEC onto NC, and the method would be usefully applied to enhance its biocompatibility