Introduction
Tissue engineering is the science of creating suitable substitutes for body organs and tissues.1,2 The three main bases of tissue engineering are scaffolds, cells, and growth factors to overcome limitation in organ transplant.3,4 Scaffolds can form an integral part of tissue engineering as an extra cellular matrix for cell growth and proliferation. Decellularized biological scaffolds have advantages over synthetic scaffolds, including being natural, being easily available, and economical.5-7 They can be extracted from various tissues including the bladder,8 small intestine,9 liver10 and tracheal tissues.11 Stem cells are also highly differentiable cells widely used in tissue engineering. They can be extracted from different sources such as bone marrow, adipose tissue,
and derma.12 Adipose derived stem cells (ADSCs) have shown to possess considerable proliferation potential as well as secretion of cytokines, growth factors, and angiogenic factors.13,14 In addition, ADSCs are able to interact with acellular scaffolds.15 However, researchers have made no coordinating efforts to improve the growth and proliferation of these cells on acellular scaffolds. Therefore, natural materials such as mineral pitch, plants, and their derivatives could be examined for this purpose. Mineral pitch is a natural substance, which is generally found at heights with a color ranging from Brown to black. This substance is formed on some certain plant species due to the activity of microorganisms.16,17 Also, it contains sulphur, magnesium, nitrogen, polysaccharide, and oxygen.
Mineral pitch can be found in two forms as water-soluble and fat-soluble. For topical application, it is dissolved in sweltering water and then massaged on to the affected place such as a wound or a swollen joint.18 In traditional medicine, mineral pitch was used to treat bone fracture and wounds.19 High mobility group box 1 (HMGB1) is a gene associated with cell damage, which is involved in intracellular homeostasis. Accordingly, it induces inflammatory responses by exciting the cytokines and chemokines. This gene was released by macrophages as a result of necrosis. Also, as Recent research suggested, this type of gene remains in acellular scaffolds and stimulate the immune system.20,21 However, the expression of this gene in acellular scaffolds caused by loading stem cells or other substances, has not been investigated yet. Stromal derived factor1 (SDF1) is an important regulatory factor contributing to wound healing through angiogenesis.22 A higher expression of SDF1 gene has been shown during healing process of human wounds.23 According to a recent study, the transmission and concentration of stem cells in target tissues are resulted from the combination of this factor with biologic scaffolds.24 Also, another study proved the effect of this factor on angiogenesis. This gene was originally extracted from the stromal cells on mice bone marrow, while it is expressed in the stromal cells of some tissues including the small intestine tissue.25 However, no study has explored the expression of this gene in acellular scaffolds under the effect of cells or other materials. Acellular scaffolds provide a proper environment for cell growth; however, the use of materials promoting cell growth can be effective. The substance that we used in this study was mineral pitch; therefore, we examined its effect by adding an effective dose to the acellular scaffold. Furthermore, analyzing the expression of HMGB1 and SDF1 genes in acellular scaffolds under the effect of mineral pitch were evaluated.
