Stem cells and extra cellular matrices: Applications in tissue engineering

Natural and synthetic polymeric hydrogel: A bioink for 3D bioprinting of tissue models

Tissue engineering (TE) is a modern approach to improve or restore tissues that has been diseased or damaged by combining the factors in growth signaling and appropriate cells to form compatible biomaterial scaffold. Bone repair has been a major global health challenge in recent decades. Bone transplantation is widely used as an effective clinical treatment for this purpose. However, there are several serious issues with transplantation, including a shortage of autologous bone, immune rejection, the risk of virus transmission with allogeneic bone, and postoperative complications. In recent years, scaffolds for bone tissue engineering have emerged as a promising alternative for bone repair. These scaffolds have porous structures that mimic the extracellular matrix, which can enhance the migration, proliferation, and differentiation of osteoblasts. This process accelerates the repair of bone defects.The usage of bioactive materials has become important tool in tissue engineering and regenerative medicine application as they are to mimic tissues mechanically, chemically, and physically. Polymeric scaffold provides numerous advantageous for tissue engineering since the physicochemical properties such as porosity, pore size, solubility and biocompatibility can be controlled. Therefore, research works were carried out to explore the potential of various materials in producing bone scaffolds in tissue engineering technology. As for both newcomers and experts, this review paper will help them to find information on various types of biomaterials in imparting or enhancing their biological properties such as biocompatibility, bacterial inhibition, tissue regeneration and cell growth, bio inertness, bioactive and resorbability for bone scaffold tissue engineering application.

Objective To observe three-dimensional structure and biological features of rat acellular spinal cord scaffold prepared by sonic oscillation and chemical extraction in order to offer an ideal scaffold for spinal cord tissue engineering research.Methods Rat spinal cord underwent acellular treatment with sonic oscillation and chemical extraction (Triton X-100 at volume fracture of 2％ and sodium deoxycholate at volume fracture of 2％) (acellular spinal cord group).In contrast with spinal cord tissue of normal rats (control group),general morphology,histology and ultramicro three-dimensional structure of acellular spinal cord scaffold were observed and aperture size,factor of porosity,water ratio,enzymolysis ratio and stability in water solution of the scaffold were also detected.Results Acellular spinal cord group showed effective removal of original cell components with factor of porosity for (94.57 ±3.45) ％ and water content for (88.62 ± 1.0) ％,and satisfactory three-dimensional structure with average aperture of 46 μm.Scaffold showed gradual degradation in enzymolysis solution and enzymolysis rate reached (69.03 ± 2.19)％ at 20 hours.Besides,scaffold showed stepwise disintegration in double distilled water and hydrolysis rate was (62.55 ± 1.70) ％ at 8 days.While,normal spinal cord showed close structure,generous neurons and myelin sheath with factor of porosity for (0.04 ± 0.02) ％ and water content for (62.4 ± 1.5) ％,and unobvious pore structure under scanning electron microscope.Normal spinal cord were degraded gradually in enzymolysis solution and enzymolysis rate was (37.62 ± 0.9)％ at 20hours.In the meantime,normal spinal cord were disintegrated gradually in double distilled water and hydrolysis rate was (40.97 ± 0.81) ％ at 8 days.Conclusions Acellular spinal cord scaffold prepared by sonic oscillation plus chemical extraction achieves complete removal of cell components,intact extracellular matrix,and satisfactory results in three-dimensional network structures,factor of porosity and water content.Also,the scaffold meets theoretical demands of tissue-engineered spinal cord scaffold and is an ideal alterative for tissue-engineered spinal cord scaffold. Key words: Spinal cord injuries; Tissue engineering; Sonication; Acellular spinal cord scaffold

Matrikines for therapeutic and biomedical applications

ABSTRACTIntroduction: The applications of naturally obtained polymers are tremendously increased due to them being biocompatible, biodegradable, environmentally friendly and renewable in nature. Among them, polyhydroxyalkanoates are widely studied and they can be utilized in many areas of human life research such as drug delivery, tissue engineering, and other medical applications.Areas covered: This review provides an overview of the polyhydroxyalkanoates biosynthesis and their possible applications in drug delivery in the range of micro- and nano-size. Moreover, the possible applications in tissue engineering are covered considering macro- and microporous scaffolds and extracellular matrix analogs.Expert commentary: The majority of synthetic plastics are non-biodegradable so, in the last years, a renewed interest is growing to develop alternative processes to produce biologically derived polymers. Among them, PHAs present good properties such as high immunotolerance, low toxicity, biodegradability, so, they are promisingly using as biomaterials in biomedical applications.

To evaluate the potential use of decellularized porcine stromal matrix (PSM) for reconstruction of corneal stroma in a rabbit model. Ten chinchilla bastard rabbit corneas were exposed to a circular half-thickness keratotomy with a 3.0 mm diameter at the central cornea. Porcine corneas were decellularized using hypotonic tris buffer, ethylene diamine tetra-acetic acid (EDTA, 0.1%), aprotinin (10 K IU/ml) and 0.3% sodium dodecyl sulphate (SDS). The 3.0 mm in diameter decellularized corneal stromal xenograft was inserted into the pocket, and the incision was closed with four 10.0 nylon sutures. Clinical photographs were taken at day 1, day 7, day 30 and on a monthly basis for up to 6 months after transplantation. Six months after surgery, the rabbits were killed and eyes were enucleated. Haematoxylin-eosin (HE) and 4,6-diamidino-2-phenylindole (DAPI) staining were performed to confirm the complete removal of the corneal cells after decellularization of porcine corneas and repopulation with rabbit cells. Alcian blue staining was performed for analysing the structure of the extracellular matrix (ECM). Efficient elimination of porcine cells was achieved by our decellularization protocol and confirmed via HE and DAPI stainings. Moreover, the major histoarchitectural ECM structure had been maintained as visualized by the alcian blue stain. Finally, the PSM was biocompatible with the host's epithelium evidenced as a regrowth covering the exposed xenograft. This novel technique of tissue engineering may provide one of many solutions to addressing anterior corneal pathological conditions in the face of a shortage of human corneal material.

Tissue damage related to bone and cartilage is a common clinical disease. Cartilage tissue has no blood vessels and nerves. The limited cell migration ability results in low endogenous healing ability. Due to the complexity of the osteochondral interface, the clinical treatment of osteochondral injury is limited. Tissue engineering provides new ideas for solving this problem. The ideal tissue engineering scaffold must have appropriate porosity, biodegradability and specific functions related to tissue regeneration, especially bioactive polymer nanofiber composite materials with controllable biodegradation rate and appropriate mechanical properties have been getting more and more research. The nanofibers produced by electrospinning have high specific surface area and suitable mechanical properties, which can effectively simulate the natural extracellular matrix (ECM) of bone or cartilage tissue. The composition of materials can affect mechanical properties, plasticity, biocompatibility and degradability of the scaffold, thereby further affect the repair efficiency. This article reviews the characteristics of polymer materials and the application of its electrospun nanofibers in bone, cartilage and osteochondral tissue engineering.

Fabrication of the FGF1-functionalized sericin hydrogels with cell proliferation activity for biomedical application using genetically engineered Bombyx mori (B. mori) silk

Electrospinning is a promising and versatile technique that is used to fabricate polymeric nanofibrous scaffolds for bone tissue engineering. Ideal scaffolds should be biocompatible and bioactive with appropriate surface chemistry, good mechanical properties and should mimic the natural extracellular matrix (ECM) of bone. Selection of the most appropriate material to produce a scaffold is an important step towards the construction of a tissue engineered product. Bone tissue engineering is an interdisciplinary field, where the principles of engineering are applied on bone-related biochemical reactions. Scaffolds, cells, growth factors, and their interrelation in microenvironment are the major concerns in bone tissue engineering. This review covers the latest development of biomimetic electrospun polymeric biomaterials for bone tissue engineering. It includes the brief details to bone tissue engineering along with bone structure and ideal bone scaffolds requirements. Details about various engineered materials and methodologies used for bone scaffolds development were discussed. Description of electrospinning technique and its parameters relating their fabrication, advantages, and applications in bone tissue engineering were also presented. The use of synthetic and natural polymers based electrospun nanofibrous scaffolds for bone tissue engineering and their biomineralization processes were discussed and reviewed comprehensively. Finally, we give conclusion along with perspectives and challenges of biomimetic scaffolds for bone tissue engineering based on electrospun nanofibers.

Electrically conductive biomaterials based on natural polysaccharides: Challenges and applications in tissue engineering

As the cornerstone of tissue engineering and regeneration medicine research, developing a cost-effective and bionic extracellular matrix (ECM) that can precisely modulate cellular behavior and form functional tissue remains challenging. An artificial ECM combining polysaccharides and fibrillar proteins to mimic the structure and composition of natural ECM provides a promising solution for cardiac tissue regeneration. In this study, we developed a bionic hydrogel scaffold by combining a quaternized β-chitin derivative (QC) and fibrin-matrigel (FM) in different ratios to mimic a natural ECM. We evaluated the stiffness of those composite hydrogels with different mixing ratios and their effects on the growth of human umbilical vein endothelial cells (HUVECs). The optimal hydrogels, QCFM1 hydrogels were further applied to load HUVECs into nude mice for in vivo angiogenesis. Besides, we encapsulated human pluripotent stem cell-derived cardiomyocytes (hPSC-CMs) into QCFM hydrogels and employed 3D bioprinting to achieve batch fabrication of human-engineered heart tissue (hEHT). Finally, the myocardial structure and electrophysiological function of hEHT were evaluated by immunofluorescence and optical mapping. Designed artificial ECM has a tunable modulus (220-1380 Pa), which determines the different cellular behavior of HUVECs when encapsulated in these. QCFM1 composite hydrogels with optimal stiffness (800 Pa) and porous architecture were finally identified, which could adapt for in vitro cell spreading and in vivo angiogenesis of HUVECs. Moreover, QCFM1 hydrogels were applied in 3D bioprinting successfully to achieve batch fabrication of both ring-shaped and patch-shaped hEHT. These QCFM1 hydrogels-based hEHTs possess organized sarcomeres and advanced function characteristics comparable to reported hEHTs. The chitin-derived hydrogels are first used for cardiac tissue engineering and achieve the batch fabrication of functionalized artificial myocardium. Specifically, these novel QCFM1 hydrogels provided a reliable and economical choice serving as ideal ECM for application in tissue engineering and regeneration medicine.

The main task of tissue engineering (TE) is to reproduce, replicate, and mimic all kinds of tissues in the human body. Nowadays, it has been proven useful in TE to mimic the natural extracellular matrix (ECM) by an artificial ECM (scaffold) based on synthetic or natural biomaterials to regenerate the physiological tissue/organ architecture and function. Hydrogels have gained interest in the TE community because of their ability to absorb water similar to physiological tissues, thus mechanically simulating the ECM. In this work, we present a novel hydrogel platform based on poly(2-ethyl-2-oxazoline)s, which can be processed to 3D microstructures via two-photon polymerization (2PP) with tunable mechanical properties using monomers and crosslinker with different degrees of polymerization (DP) for future applications in TE. The ideal parameters (laser power and writing speed) for optimal polymerization via 2PP were obtained using a specially developed evaluation method in which the obtained structures were binarized and compared to the computer-aided design (CAD) model. This evaluation was performed for each composition. We found that it was possible to tune the mechanical properties not only by application of different laser parameters but also by mixing poly(2-ethyl-2-oxazoline)s with different chain lengths and variation of the crosslink density. In addition, the swelling behavior of different fabricated hydrogels were investigated. To gain more insight into the viscoelastic behavior of different fabricated materials, stress relaxation tests via nanoindentation experiments were performed. These new hydrogels can be processed to 3D microstructures with high structural integrity using optimal laser parameter settings, opening a wide range of application properties in TE for this material platform.

Tissue engineering is simply defined as the replacement or regeneration of an injured or damaged cell through the fabrication of new tissue at any segment of the human body. It may be orthopaedic, cardiovascular, spinal, gastro, urological, dermal, etc. Generally, tissue-engineering materials are classified into two categories, synthetic and natural polymers. Due to some side effects caused by synthetic polymers, natural biopolymers are most preferable for use in a biological system. Biomaterial along with nanoparticles, drug incorporation of scaffold or hydrogel may speed up the tissue regenerative process. Bionanomaterials have ideal characteristics such as being biodegradable, biocompatible, nontoxic, useful in drug delivery, antimicrobial, antioxidant, etc. These properties of bionanomaterials improve or promote mechanical, biochemical, electrical properties and are also capable of differentiation, cell adhesion, proliferation and cultivating cell growth. This chapter introduces tissue engineering and biomaterials, then continues with a deeper discussion of bionanomaterial tissue engineering regeneration for cardiovascular, urological and dermal use.

Synthetic polymers have been an integral part of modern society since the early 1960s. Besides their most well-known applications to the public, such as packaging, construction, textiles and electronics, synthetic polymers have also revolutionized the field of medicine. Starting with the first plastic syringe developed in 1955 to the complex polymeric materials used in the regeneration of tissues, their contributions have never been more prominent. Decades of research on polymeric materials, stem cells, and three-dimensional printing contributed to the rapid progress of tissue engineering and regenerative medicine that envisages the potential future of organ transplantations. This perspective discusses the role of synthetic polymers in tissue engineering, their design and properties in relation to each type of application. Additionally, selected recent achievements of tissue engineering using synthetic polymers are outlined to provide insight into how they will contribute to the advancement of the field in the near future. In this way, we aim to provide a guide that will help scientists with synthetic polymer design and selection for different tissue engineering applications.

Tissue engineering involves materials science, bioengineering, and regenerative medicine and many other disciplines. In the early stage, it aims to develop functional biological alternatives that improve, or maintain the function of lost or damaged tissue by combining the scaffold, cells, and biological molecules (such as growth factors). In addition, the ultimate goal of tissue engineering is to regenerate or repair damaged tissues with the help of the biological substitutes. Therefore, the tissue engineering scaffold should mimic the property, structure of the damaged tissue and mimic the extracellular matrix to support cell survival and growth to improve the tissue function. Moreover, the scaffold should also enhance cell proliferation and guide differentiation to regenerate or repair damaged tissues. Over the years, numerous studies have demonstrated that electrical signals can influence cellular behavior and function and conductive materials can enhance cell proliferation and guide differentiation of stem cells through promoting intercellular signaling. Traditional polymers have good process property, biodegradability, and good biocompatibility. So they are most widely used in tissue engineering, but traditional polymers are insulators, which cannot respond to signal transmission between cells to further control cellular activities, such as cell proliferation, migration and differentiation. However, researchers have discovered a variety of electrically conducting polymers in recent decades, such as polyaniline (PANi), polypyrrole (PPy), polythiophene, and their derivatives (mainly aniline oligomers and poly(3,4-ethylenedioxythiophene)) which have good biocompatibility and excellent electrical conductivity. They have been widely used in biomedical fields including drug delivery systems, biosensors, neural implants, and biological actuator, mostly used in the field of tissue engineering scaffolds. Moreover, their excellent electrical conductivity can promote cell adhesion and proliferation at the interface between the polymer and tissue by electrical stimulation, thereby promoting tissue growth. Therefore, the field of tissue engineering by conductive polymeric biomaterials has received more and more attention. However, the pure conductive polymers are brittle and their poor processability limits their applications in tissue engineering. Therefore, composite conductive polymeric biomaterials have been developed based on the above-mentioned conductive polymers and biocompatible degradable polymers, which have excellent biocompatibility, electrical conductivity, and processability. This review will summarize a variety of composite conductive polymeric biomaterials used in tissue engineering, such as pure conducting polymers, conducting blends or composite films, conducting copolymer films, conducting nanofibers, conducting hydrogels, and conducting composite three-dimensional (3D) scaffolds. In addition, recent research in tissue engineering has found that these conductive polymeric biomaterials can be used in various electrical signal sensitive tissues engineering including bone, muscle, nerve and cardiac tissue engineering. The above aspects will be discussed in detail in this paper.