Sharif Digital Repository

Hybrid perovskite solar cells (PSCs) have gained significant attention owing to their excellent physicochemical and photovoltaic properties. PSCs typically consist of a perovskite light absorber sandwiched between two carrier selective layers optimized with respect to optimal band alignment and low interfacial recombination. The quality of the perovskite layer and interfaces play major roles in the fabrication of high-performance PSCs. In the present work, we systematically investigate the planar structure PSCs based on TiO2 and TiO2/ZnO electron transport layers (ETLs), which provide deeper insight into the charge recombination and accumulation mechanisms. We show that the double-layer... 

Although graphene/stem cell-based tissue engineering has recently emerged and has promisingly and progressively been utilized for developing one of the most effective regenerative nanomedicines, it suffers from low differentiation efficiency, low hybridization after transplantation and lack of appropriate scaffolds required in implantations without any degrading in functionality of the cells. In fact, recent studies have demonstrated that the unique properties of graphene can successfully resolve all of these challenges. Among various stem cells, neural stem cells (NSCs) and their neural differentiation on graphene have attracted a lot of interest, because graphene-based neuronal tissue... 

Interface engineering of solar cell device is a prominent strategy to improve the device performance. Herein, we synthesize reduced-graphene scaffold (rGS) by using a new and simple chemical approach. In this regard, we synthesize a hollow structure of graphene and then fabricate a three-dimensional scaffold of graphene with a superior surface area using electrophoretic process. We employ this scaffold as an interface layer between the electron transfer and absorber layers in perovskite solar cell. The characterization tests and photovoltaic results show that rGS improves the carrier transportation, yielding a 27% improvement in device performance as compared to conventional device. Finally,... 

Applying engineering approaches to non-engineering systems such as biological systems has brought a new research filed to the surface. The sole purpose of this research is mathematical modeling the cell cycle control system in the fissionyeast cell using Ordinary Differential Equations (ODE).This paper, in fact, introduces the capabilities of engineering knowledge and engineering of control, in particular, in this field. ©2009 IEEE  

Despite the promise of hydrogel-based stem cell therapies in orthopedics, a significant need still exists for the development of injectable microenvironments capable of utilizing the regenerative potential of donor cells. Indeed, the quest for biomaterials that can direct stem cells into bone without the need of external factors has been the "Holy Grail" in orthopedic stem cell therapy for decades. To address this challenge, we have utilized a combinatorial approach to screen over 63 nanoengineered hydrogels made from alginate, hyaluronic acid, and two-dimensional nanoclays. Out of these combinations, we have identified a biomaterial that can promote osteogenesis in the absence of... 

A cell spheroid is a three-dimensional (3D) aggregation of cells. Synthetic, in-vitro spheroids provide similar metabolism, proliferation, and species concentration gradients to those found in-vivo. For instance, cancer cell spheroids have been demonstrated to mimic in-vivo tumor microenvironments, and are thus suitable for in-vitro drug screening. The first part of this paper discusses the latest microfluidic designs for spheroid formation and culture, comparing their strategies and efficacy. The most recent microfluidic techniques for spheroid formation utilize emulsion, microwells, U-shaped microstructures, or digital microfluidics. The engineering aspects underpinning spheroid formation... 

Interfacial engineering between the perovskite and hole transport layers has emerged as an effective way to improve perovskite solar cell (PSC) performance. A variety of organic halide salts are developed to passivate the traps and enhance the charge carrier transport. Here, the use of guanidinium iodide (GuaI) for interfacial modification of mixed-cation (Cs)x(FA)1−xPbI3 perovskite films, which results in the formation of a low-dimensional δ-FAPbI3-like phase on the 3D perovskite surface, is reported. The presence of this thin layer facilitates charge transfer at interfaces and reduces charge carrier recombination pathways as evidenced by enhanced carrier lifetimes and favorable interfacial... 

For bone tissue engineering, stem cell‐based therapy has become a promising option. Re-cently, cell transplantation supported by polymeric carriers has been increasingly evaluated. Herein, we encapsulated human olfactory ectomesenchymal stem cells (OE‐MSC) in the collagen hydrogel system, and their osteogenic potential was assessed in vitro and in vivo conditions. Col-lagen type I was composed of four different concentrations of (4 mg/mL, 5 mg/mL, 6 mg/mL, 7 mg/mL). SDS‐Page, FTIR, rheologic test, resazurin assay, live/dead assay, and SEM were used to characterize collagen hydrogels. OE‐MSCs encapsulated in the optimum concentration of collagen hydrogel and transplanted in rat calvarial... 

Myocardial infarction (MI) causes a high mortality rate in the world every year. Myocardial tissue engineering using extracellular matrix-derived substrate and cytocompatible biopolymers is a promising approach for treating MI. Besides, injectable porous microspheres are developing engineer constructs to use as dual-purpose microcarriers for cell culture and injectable scaffolds in trivial invasiveness for tissue implantation. This study aimed to fabricate porous microcarriers composed of myocardial extracellular matrix and chitosan using an electrospraying technique. The effect of electrospraying parameters, including extracellular matrix/chitosan ratio and voltage, on MCs diameter was... 

Microfluidic experiments have found wide applications in medical sciences and engineering, such as cell separation and focusing. In the present study, focusing and separation of particles with different sizes and densities were investigated by designing inertial microfluidic devices. The microfluidic channel is designed by analyzing the induced forces on the particles. In the designing process, the objective was to focus and separate the particles in the shortest length of the channel with the lowest possible cycles and high efficiency. The simulation is then used for analyzing the two proposed geometries to evaluate their particle separation and focusing ability, named convergent and... 

Besides the conventional fiber production methods, microfluidics has emerged as a promising approach for the engineered spinning of fibrous materials and offers excellent potential for fiber manufacturing in a controlled and straightforward manner. This method facilitates low-speed prototype synthesis of fibers for diverse applications while providing superior control over reaction conditions, efficient use of precursor solutions, reagent mixing, and process parameters. This article reviews recent advances in microfluidic technology for the fabrication of fibrous materials with different morphologies and a variety of properties aimed at various applications. First, the basic principles, as... 

Conducting polymer-based devices and scaffolds has become remarkably popular due to their properties such as conductivity, tunable electrochemical properties, and straightforward fabrication procedures. Hence, they have versatile applications and can be used as implants, biosensors, cell capture/release devices, and regenerative medicine scaffolds. This review addresses the effect of conductive polymers on cell behavior since their conductive features can be applied to simulate a cellular response. Moreover, the impact of polymer chemical and physical properties on cellular response has been discussed. Recent biomedical engineering approaches used for cell capture and release were reviewed... 

Microfluidic devices have received wide attention and shown great potential in the field of tissue engineering and regenerative medicine. Investigating cell response to various stimulations is much more accurate and comprehensive with the aid of microfluidic devices. In this study, we introduced a microfluidic device by which the matrix density as a mechanical property and the concentration profile of a biochemical factor as a chemical property could be altered. Our microfluidic device has a cell tank and a cell culture chamber to mimic both 2D to 3D and 3D to 3D migration of three types of cells. Fluid shear stress is negligible on the cells and a stable concentration gradient can be... 

The performance of the tower based concentrated solar thermal (CST-tower) plant is very sensitive to the operation strategy of the plant and the incident heat flux on the receiver. To date, most studies have been examined only the design mode characteristics of the cavity receivers, but this paper significantly expands the literature by considering non-design operating conditions of this important sub-component of the CST-tower plants. A feasible non-design operating conditions of the cavity receivers that was considered in this study is the storage mode of operation. Two practical dynamic control strategies were examined then to find the most efficient approach: fixed solar field mass... 

In this study, we reported the preparation of self cross-linked oxidized alginate-gelatin hydrogels for muscle tissue engineering. The effect of oxidation degree (OD) and oxidized alginate/gelatin (OA/GEL) weight ratio were examined and the results showed that in the constant OA/GEL weight ratio, both cross-linking density and Young's modulus enhanced by increasing OD due to increment of aldehyde groups. Furthermore, the degradation rate was increased with increasing OD probably due to decrement in alginate molecular weight during oxidation reaction facilitated degradation of alginate chains. MTT cytotoxicity assays performed on Wharton's Jelly-derived umbilical cord mesenchymal stem cells... 

Modern techniques for expanding stem cells play a substantial role in tissue engineering: the raw material that facilitates regeneration of damaged tissues and treats diseases. The environmental conditions and bioprocessing methods are the primary determinants of the rate of cultured stem cell proliferation. Bioceramic scaffolds made of calcium phosphate are effective substrates for optimal cell proliferation. The present study investigates the effects of two bioceramic scaffolds on proliferating cells in culture media. One scaffold was made of hydroxyapatite and the other was a mixture of hydroxyapatite and ferromagnetic material (Fe3O4 nanoparticles). Disk-shaped (10 mm × 2 mm) samples of... 

Nanofibrous structures that mimic the native extracellular matrix and promote cell adhesion have attracted considerable interest for biomedical applications. In this study, GO-modified nanofibrous biopolymers (GO) were prepared by electrospinning blended solutions of chitosan (80 vol%), polyvinyl pyrrolidone (15 vol%), polyethylene oxide (5 vol%) containing GO nanosheets (0–2 wt%). It is shown that GO nanosheets significantly change the conductivity and viscosity of highly concentrated chitosan solutions, so that ultrafine and uniform fibers with an average diameter of 60 nm are spinnable. The GO-reinforced nanofibers with controlled pore structure exhibit enhanced elastic modulus and... 

Interfacial studies and band alignment engineering on the electron transport layer (ETL) play a key role for fabrication of high-performance perovskite solar cells (PSCs). Here, an amorphous layer of SnO2 (a-SnO2) between the TiO2 ETL and the perovskite absorber is inserted and the charge transport properties of the device are studied. The double-layer structure of TiO2 compact layer (c-TiO2) and a-SnO2 ETL leads to modification of interface energetics, resulting in improved charge collection and decreased carrier recombination in PSCs. The optimized device based on a-SnO2/c-TiO2 ETL shows a maximum power conversion efficiency (PCE) of 21.4% as compared to 19.33% for c-TiO2 based device.... 

A stereolithography-based bioprinting platform for multimaterial fabrication of heterogeneous hydrogel constructs is presented. Dynamic patterning by a digital micromirror device, synchronized by a moving stage and a microfluidic device containing four on/off pneumatic valves, is used to create 3D constructs. The novel microfluidic device is capable of fast switching between different (cell-loaded) hydrogel bioinks, to achieve layer-by-layer multimaterial bioprinting. Compared to conventional stereolithography-based bioprinters, the system provides the unique advantage of multimaterial fabrication capability at high spatial resolution. To demonstrate the multimaterial capacity of this... 

Producing mature and functional cardiomyocytes (CMs) by in vitro differentiation of induced pluripotent stem cells (iPSCs) using only biochemical cues is challenging. To mimic the biophysical and biomechanical complexity of the native in vivo environment during the differentiation and maturation process, polydimethylsiloxane substrates with 3D topography at the micrometer and sub-micrometer levels are developed and used as cell-culture substrates. The results show that while cylindrical patterns on the substrates resembling mature CMs enhance the maturation of iPSC-derived CMs, sub-micrometer-level topographical features derived by imprinting primary human CMs further accelerate both the...