---

Aims: In bone tissue engineering, the scaffold as a supportive structure, plays a vital role. Putting the scaffold in dynamic cell culture, such as perfusion bioreactor, makes the role of mechanical parameters such as shear stress and hydrodynamic pressure more important. On the other hand, these mechanical parameters are influenced by scaffold architecture. In this study, the effects of bone scaffold architecture on mechanical stimuli have been analyzed and their effects on the mesenchymal stem cell fate have been predicted.
Material & Methods: Using the tools of computer simulation, five bone scaffolds (Gyroid, high porous Gyroid, Diamond, IWP, and gradient architecture Gyroid) based on mathematical functions of minimal surfaces were designed and exposed in a simulated dynamic cell culture under the inlet velocities of 1, 10, 25, 50, and 100μm/s. Cell accumulation on the inner part of the scaffold was considered as an 8.5-micron layer. This layer was designed for Gyroid and IWP scaffolds.
Findings: Based on the results, Diamond scaffold showed the most efficient performance from the homogeneity of stresses point of view. In the presence of the cell layer, the von Mises stress was reported as 60 and 50 mPa on the Gyroid and IWP scaffolds, respectively which eases osteogenic differentiation.
Conclusion: In gradient architecture scaffolds under dynamic conditions, there is a gradient in shear stress that causes various signaling in different positions of theses scaffold and facilitates multi-differentiation of the cells on the same scaffold.

---

---

Since one of the main problems in bone tissue repair is the bacterial infections, recently the development of drug-eluting nanocomposite scaffolds for bone regenerative medicine applications has attracted significant attention. In this study Polycaprolactone (PCL)-based composite scaffolds containing 10vol% of titanium dioxide nanoparticles (~21nm), and bioactive glass particles (~6µm), were prepared without drug and also loaded by Tetracycline hydrochloride (TCH) antibiotic (0.57, 1.15 mg/mL) through solvent casting method for bone tissue engineering applications. Structural characterizations based on Scanning Electron Microscopy (SEM), and FTIR analysis were utilized to study the chemical bonds of glass/ceramic particles, and antibiotic crystals on the surface. In addition, in vitro cytotoxicity, and antibacterial analysis were performed by MTT, and Agar well-diffusion assays, respectively. In this study polymeric and composite scaffolds were fabricated with TCH clusters decorated on the surface. It was shown that the bioactive glass/PCL scaffolds loaded by 0.57 mg/mL of TCH revealed significant antibacterial effect, despite the acceptable cell viability. These scaffolds seem to be of interest as a potential candidate in drug-eluting scaffolds for bone tissue engineering applications.

 

---

Fibrinogen is a major component of the coagulation cascade following tissue damage and rapidly forms an insoluble fibrin scaffold. Fibrin is a filamentous biopolymer that naturally forms from fibrinogen polymerization during blood clotting. After tissue damage and coagulation cascade initiation, soluble fibrinogen polymerization by thrombin enzymebegins and forms an insoluble fibrin network and blood clots with platelets. This fibrin network is crucial for the development of homeostasis after tissue damage. This biopolymer also plays a key role in the wound healing as a temporary scaffoldand due to its unique structural properties and physiological function; it is used in reconstructive medicine. Fibrin is able to absorb extracellular matrix proteins (ECM) such as fibronectin and growth factors. The main types of fibrin scaffolds like platelet-rich fibrin (PRF) and platelet-rich plasma (PRP) are being used as autologous biomaterials in reconstructive medicine, wound healing, orthopedics and skin reconstruction and cosmetic sciences. Fibrin derivatives and degradation products also play an important role in the process of wound healing by stimulating cell infiltration and tissue regeneration and they are being widely used in developing new products as a biological material for over a century.

---

Objective: Tissue engineering is an (interdisciplinary field that applies polymeric scaffolds to control tissue formation in three-dinemtion (3D). The scaffold provides the microenvironment (synthetic temporary extracellular matrix) for regenerative cells, supporting cell attachment, proliferation, differentiation, and neo tissue genesis due to their suitable chemical, physical and biological structures. In this study, chitosan/poly (vinyl alcohol) (CS/PVA) was exploited as scaffold for nerve regeneration. Materials and Methods: Electrospinning was used to fabricate CS/PVA nanocomposites for U373 cells seeding and proliferation. Electrospinning is a versatile and simple method to fabricate non-woven thin layer fibers from polymeric solutions. Consequently, the biocompatibility of CS/PVA nanocomposite was evaluated using biological assays and cell attachment study. Results: Results indicated that CS/PVA nanocomposites with 15/85 proportion shown an almost homogenous network of the electrospun fibers and confirmed that they can be knitted in meshes and improve U373 cells proliferation and cell attachment. Conclusion: The nano-sized CS/PVA scaffolds are nontoxic and biocompatible which can promote proliferation of U373 cells and their appropriate adhesion to nanocomposite for improved peripheral nerve regeneration.

---

Objective: Nowadays, as the field of neural tissue engineering advances, the fabrication and application of combined structures open a new window of research for the regeneration of nervous system injuries. In this study, chitosan/poly(vinyl alcohol)-carbon nanotube nanocomposites has been exploited as scaffolds. Materials and Methods: Electrospinning was used to fabricate chitosan/poly(vinyl alcohol)-carbon nanotube scaffolds. Raman spectroscopy and scanning electron microscopy (SEM) was used to evaluate the chemical and physical structure of the electrospun scaffolds. Then, the biocompatibility of the scaffolds was evaluated using MTT assay and Neutral red assay. Results: The results showed that the chitosan/poly(vinyl alcohol)-carbon nanotube nanocomposites have suitable structural and morphological aspects for human brain-derived cells growth and proliferation. Therefore, the cells could maintain their usual morphology while adhering to the surface of the nanocomposites due to an appropriate biocompatibility of the scaffolds. Conclusion: Chitosan/poly(vinyl alcohol)-carbon nanotube nanocomposites could enhance the proliferation of human brain-derived cells due to their proper structure and biocompatibility.

---

---

Objective: Cell vital function has correlation with mechanical loadings that cell experiences. Here, effects of in-vitro combined cyclic-static stretch on proliferation of human mesenchymal stem cell (HMSC) were evaluated. Materials and Methods: HMSCs were cultured on gelatin coated elastic membranes, and exposed to stretch loading. Four different regimes of cyclic, static, combined cyclic-static, and cyclic with a period of unloading were exerted on the elastic membrane. Duration of cyclic loading and static loading was 5 and 12 hours respectively. Results: The results illustrate that 10% cyclic stretch causes cell alignment but there were no significant proliferation differences between control and test group. Combined cyclic-static stretch reduced proliferation significantly while cyclic stretch with an unloading period increased cell proliferation significantly. At last, static stretch did not affect cell proliferation significantly. Conclusion: Cell stretching regimes and post-loading duration are effective factors on cell proliferation.

---

Stem cells are characterized by their capacity for self-renewal and their ability to differentiate into specific cell types under the influence of their microenvironment. It is known that matrix chemistry controls stem cell differentiation. Single cell encapsulations of the Mesenchymal stem cells into a semi-permeable microgel, allows a greater control of the stem cell fate. In this study, a chip for single-cell encapsulation was designed and fabricated using microfluidic technology. By using microfluidic chip, human bone marrow mesenchymal stem cells (hBMSCs) are encapsulated inside alginate and alginate-poly-l lysine (PLL) microgels. The results of long-term viability of MSCs inside alginate-PLL microgels, shows a significant increase compared to alginate microgels. Mesenchymal stem cell proliferation in alginate-PLL microgels also increased significantly on days 14 and 21. It seems that PLL improves cell adhesion and function by creating a positively charged matrix. Microscopic studies indicate that the morphology of the cells inside the microgels is spherical. However, the average diameter and volume of cells in microgels containing PLL are smaller than others, which indicates more proliferation and space limitation inside the microgels. Therefore, single cell alginate-PLL microgels provide a suitable substrate in clinical studies for tissue engineering, organ transplantation and cell therapy.

---

Objective: Biodegradable polycaprolactone/starch composites can be used for bone tissue engineering applications. The effect of the ratio of components on composite properties is of tremendous importance. Methods: Polycaprolactone/starch composite of 80/20 and 70/30 ratios were fabricated by dissolving them in chloroform followed by evaporation of the solvent. Results: The composites were characterized by fourier transform infrared spectroscopy. Their bioactivity was evaluated by studying the apatite formation ability after immersing the specimens in simulated body fluid. The results of compressive test on samples showed that the composite’s modulus and strength approximated that of human trabecular bone. Mass loss in distilled water and starch degradation rate in PBS was evaluated, which showed that the starch ratio was effective in composite degradation. MTT analysis and alkaline phosphatase levels showed that this composite had no toxicity and could increase G-299 cell line osteoblastic activities. Conclusion: The increase in cellular osteoblastic activities and the ability for apatite formation on the composite surface, in addition to the polycaprolactone/starch samples' mechanical properties shows their capability to be used as substitutes for bone. Because this composite degradation rate is controlled by changing the starch ratio, it has the potential for use in bone tissue engineering applications. Samples that have a 70/30 ratio are considered optimal due to their enhanced cellular response and better mechanical properties.

---

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.

---

Objective: Human retinal pigment epithelium (hRPE) is a cell monolayer located in the outer part of the retina that is in contact with photoreceptors. In many diseases RPE cells damage. One way for treating this disease is the implantation of intact instead of damaged cells. For this reason different types of substrates have been used for cell cultivation. This study has used alginate and a blend of alginate/gelatin (A/G) to study RPE cell growth. Methods: We prepared alginate solutions in concentrations of 1% and 2% (w/v) in water and DMEM/F12. The solutions were infused into each well of 6-well micro plates until a uniform culture substrate that had a 1 mm thickness was generated. Passage-4 hRPE cells were cultivated on the substrate and the cell characteristics studied. hRPE cells did not adhere to alginate in DMEM/F12 and did not exhibit interaction with alginate substrate. For this reason A/G solutions at concentrations of 1% and 2% (w/v) in water were prepared. We prepared A/G blends at weight ratios of: 20:80, 30:70, 40:60, 50:50, 60:40, 70:30, and 80:20. These blends were infused into each well of 6-well plates until the appropriate 1 mm thickness of A/G was achieved. Isolated hRPE cells were cultured on synthetic substrate after which we studied the cells' characteristics.   Result: hRPE cell generated adhesive colonies on the A/G substrate. In all studied combinations of A/G, the diffused hRPE cells formed a monolayer under the substrate sheets. However the A/G 20:80 ratio had cell growth in the upper face of the substrate. hRPE survived indefinitely on A/G substrate. After the cells were re-cultured on polystyrene, they showed general morphological features of normal hRPE cells. Conclusion: The A/G blend at a 20:80 ratio was chosen to be used for future studies.

---

Tissue engineering is a rapidly growing field of research for several decades, which is driven by the human urgent need for tissue substitutes and transplantable organs. Considering the advancements, the clinical applications in the field of tissue engineering have been limited until now. The major reason toward this limitation is the lack of sufficient blood supply for the tissue in the earliest phase after implantation. Time-consuming process of angiogenesis leads to inadequate vascularization and finally, death of cells and destruction of tissue. During recent years, by implementing a strategy called Inosculation, it has been tried to facilitate tissue vascularization by a preformed vasculature network within tissue structure. In the current research considering cellular nature of angiogenesis process, relying on a cell-based mathematical model, the effect of inosculation strategy is investigated through the dynamics of angiogenesis process with respect to extracellular, cellular and intracellular spatio-temporal scales. The results show the advantages of inosculation strategy over angiogenesis strategy in vascularization of tissue constructs. The model demonstrates the capability of inosculation strategy to improve the anastomosis probability, which is providing the crucial requisite for the blood to flow through capillary network. Furthermore, the cellular model was developed in a way that illustrates the effects of extracellular matrix on morphogenesis through branching phenomenon.

---

The use of porous scaffolds for repairing the damaged bone tissues has been increased in recent years. As exploration of the mechanical properties of the scaffolds on the basis of experiments is time consuming and uneconomic, mathematical models are increasingly being introduced into the field, but most of them rely on finite element method and theoretical studies are rarely found in the literature. In this paper, different micromechanical models are presented for obtaining the effective elastic properties of bone scaffolds. Using these models, the mechanical properties of different scaffolds, including ceramic and composite bone scaffolds, are investigated. Single scale and multi-scale modeling approaches are used to simulate the ceramic and composite scaffolds, respectively. Furthermore, because of the wide application of hydroxyapatite in fabrication of bone scaffolds, the mechanical properties of hydroxyapatite scaffolds in different porosities are obtained in the current study by means of the presented methods. Results show that Dewey, self-consistent and differential schemes are the best methods in calculation of the value of Young’s modulus of these scaffolds in porosity ranges of less than 30 %, 30 to 60 % and more than 60 %, respectively. Moreover, self-consistent scheme gives good estimation of the value of Poisson’s ratio of hydroxyapatite scaffolds in different porosities. By obtaining the values of the mechanical properties of the scaffolds in different porosities by these models and using the statistical analysis, the mathematical relationship between the porosity and the mechanical properties of this kind of scaffolds (Young’s modulus and Poisson’s ratio) is obtained.

---

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.

---

Objective: Tissue engineering, as an interdisciplinary field, assists cell therapy by using scaffolds, cells, and growth factors since 30 years ago. Cells isolated from the body should be supported by a scaffold which could mimic the function and structure of natural extracellular matrix (ECM). To accomplish this goal, we have fabricated and characterized synthetic wet electrospun poly(lactic) acid (PLA) scaffolds.
Methods: ThePLA polymer was used at various concentrations (10%, 13%, 15%, 17%, 20% w/v) with a novel architecture produced by a wet-electrospinning process for tissue engineering applications. In the wet electrospinning method, we used an aqueous solution of sodium hydroxide (NaOH) as the coagulation bath. Then, we characterized the biocompatibility and morphology of these scaffolds by the MTT assay and SEM, respectively.
Results: The data collected from the characterization of scaffolds and in vitro human Wharton’s jelly-derived stem cells/scaffold culture showed that the 15% w/v of PLA with high porosity was the best polymer concentration in terms of cell attachment and proliferation.
Conclusion:Electrospinning PLA at the 10% or 20% w/v concentrations was difficult. Additionally, they could not provide a favorable matrix for cell proliferation and attachment. However, the results have suggested that the novel nanofiber fabrication system would be very useful for the structure control of 3D nanofiber fabrics.

---

Synthetic biomaterials are currently used as bone graft substitutes to treat bone disorders. Based on biomechanical properties, these biomaterials are selected to engineer bioactive and bioresorbable scaffolds that increase tissue ingrowth. These porous scaffolds play an important role in new bone formation and vascularization with the ability to incorporate genes, drugs, growth factors, and stem cells. This review focuses on recent advances on bioactive glass materials for bone regeneration. Despite inherent brittleness, bioactive glasses have many promising characteristics for bone engineering scaffolds. Compared to silicate bioactive glasses, borate and borosilicate have the ability to enhance new bone formation .These materials have controllable degradation rates that closely match new bone formation. Interestingly, bioactive glasses can be doped with elements such as Cu, Zn, and Sr, which are advantageous for healthy bone growth. Although bioactive glasses have been examined in detail for bone repair, few investigations have been performed on their applications for repair of soft tissues. A recent work has shown bioactive glass has the ability to promote angiogenesis for healing of soft tissue wounds.
In this review, we highlight current advances in the use of bioactive glass materials and their conversion into scaffolds with the essential anatomical shape. Methods used to manipulate the materials’ structures in bone tissue engineering applications and growth factors involved in bone regeneration will be briefly discussed.

---

Introduction: Cartilage is a tissue without vessel and lymph in body. If it has a massive defect, it cannot regenerate and reconstruct itself. In this society, cartilage diseases such as osteoarthritis and cartilage defects have increased. Its defects can disrupt the daily function of the patient and can be accompanied by pain due to bone wear. Common methods used to treat cartilage defects, which are considered invasive with low efficacy, include autologous chondrocytes, microfracture, bone marrow stimulation, and debridement. Current treatments are not definitive methods, which is why the use of stem cells and cartilage tissue engineering has been turned on. In the current review, the types of stem cells used in cartilage therapy and cartilage tissue engineering were investigated. Then, cellular signaling factors such as growth factors, mechanical and environmental factors were mentioned and referred to scaffolds based on the biomaterials used to engineer high-efficiency stem cells for the reconstruction of cartilage tissue. Therefore, the aim of this study was to review the use of stem cells in cartilage tissue regeneration and engineering.
Conclusion: The role of stem cells in regeneration of cartilage has been properly proven, but the mechanism and method of creating this regeneration has not yet been determined. Mesenchymal cells have the highest safety in cell therapy in cartilage, and these types of cells have the most clinical usage. In Iran, cell therapy is performed clinically for patients, but cartilage tissue engineering has not yet reached the clinical stage.

---

Functional disorder in different tissues is a consequence of cell damage in a part of a tissue that can occur because of diseases, traumas, or accidents. Organ transplantation has so far been the only treatment approach for these damages; however, transplantation therapies have been greatly limited by the serious shortage of donors or immune rejection. One of the alternative approaches is tissue engineering that recently has attracted the tremendous attentions of many researchers. Cell sheet engineering is a technology that can construct bioengineered sheet-like tissues without the need of using scaffolds and it is called “scaffold-free tissue engineering”. Cells are cultured at 37℃ on the surfaces grafted with the temperature responsive polymer “poly (N-isopropylacrylamide)”. Then, the cell sheet is harvested with a simple reduced-temperature treatment up to 20℃ and transplanted directly onto the injured surface without sutures or glues. In the present article, researches and experiments in the field of cell sheet engineering have been paid attention. Moreover, the advantages and challenges of this method have been discussed.

---