Graphene-Based Scaffolds: Fundamentals and Applications for Cardiovascular Tissue Engineering

Cardiac tissue engineering requires materials that can faithfully recapitulate and support the native in vivo microenvironment while providing a seamless bioelectronic interface. Current limitations of cell scaffolds include the lack of electrical conductivity and suboptimal mechanical properties. Here we discuss how the incorporation of graphene into cellular scaffolds, either alone or in combination with other materials, can affect morphology, function, and maturation of cardiac cells. We conclude that graphene-based scaffolds hold great promise for cardiac tissue engineering.

The Healing of Bone Defects by Cell-Free and Stem Cell-Seeded 3D Printed PLA Tissue Engineered Scaffolds

One of the main issues in bone tissue engineering is to realize the response of the host to the engineered scaffolds. In this paper, the in-vivo healing of critical-sized bony defects by cell-free and stem cell-seeded 3D printed PLA scaffolds was studied in rat calvaria bone. First, the scaffolds were 3D printed based on a designed computer model and half of them were seeded by with bone marrow-derived mesenchymal stem cells (BMSCs). The SEM images of the surfaces of PLA and PLA+Cell scaffolds were taken for morphological analysis. All the scaffolds were implanted in the defect sites of rat calvaria bones and histological analysis was conducted after 8 and 12 weeks. The results showed that both cell-free and stem cell-seeded scaffolds exhibited superb healing compared with the empty defect controls. The histological observation revealed the formation of both new bone and connective tissues in the healing site after 8 and 12 weeks, postoperatively. The bone cells including osteoblasts and osteocytes with lacuna were also observed. The higher filled area and the higher bone formation and bone maturation were observed after 12 weeks and in particular for PLA+Cell scaffolds. Furthermore, the systemic toxicity evaluation of the scaffolds using ALT and AST tests reject any toxicity for both cell-free and stem cell-seeded scaffolds. It can be concluded that the 3D printed PLA scaffold with BMSCs seeding has well osteogenic potential to be used for bone defect healing.

Biofabrication of controllable alginate hydrogel cell scaffolds based on bipolar electrochemistry

Bipolar electrochemistry successfully realized the electrodeposition of calcium alginate hydrogels in specific target areas in tissue engineering. However, the shape and quantity of three-dimensional cannot be accurately controlled. We presented a novel growth model for fabricating hydrogels based on bipolar electrochemical by patterned bipolar electrodes using photolithography. This work highlights pattern customization and quantitative control of hydrogels in cell culture platforms. Furthermore, alginate hydrogels with different heights can be controlled by adjusting the key parameters of the growth model. This strategy exhibits promising potential for cell-oriented scaffolds in tissue engineering.

Hydroxyapatite Particles from Simulated Body Fluids with Different pH and Their Effects on Mesenchymal Stem Cells

Bone-like hydroxyapatite (HAp) has been prepared by biomimetic synthesis using simulated body fluid (SBF), mimicking inorganic ion concentrations in human plasma, or 1.5SBF that has 1.5-times higher ion concentrations than SBF. In this study, the controllable preparations of HAp particles from 1.5SBF with different pH values were examined. The particles obtained as precipitates from 1.5SBF showed different morphologies and crystallinities depending on the pH of 1.5SBF. Micro-sized particles at pH 7.4 of 1.5SBF had a higher Ca/P ratio and crystallinity as compared with nano-sized particles at pH 8.0 and pH 8.4 of 1.5SBF. However, a mixture of micro-sized and nano-sized particles was obtained from pH 7.7 of 1.5SBF. When Ca2+ concentrations in 1.5SBF during mineralization were monitored, the concentration at pH 7.4 drastically decreased from 12 to 24 h. At higher pH, such as 8.0 and 8.4, the Ca2+ concentrations decreased during pH adjustment and slightly decreased even after 48 h. In this investigation at pH 7.7, the Ca2+ concentrations were higher than pH 8.0 and 8.4. Additionally, cytotoxicity of the obtained precipitates to mesenchymal stem cells was lower than that of synthetic HAp. Controllable preparation HAp particles from SBF has potential applications in the construction of building components of cell scaffolds.

Biomimetic scaffolds based on chitosan in bone regeneration. A review.

The article focuses on a polysaccharide of natural origin – chitosan and its application in tissue engineering. The preparation process and physicochemical properties of the saccharide are described. The degradation of chitosan and the properties influencing the process both outside and in living organism were examined. Four applications in bone tissue engineering can be distinguished: preparation of cell scaffolds exclusively from chitosan, from a chitosan composite or from a chitosan polyelectrolyte complex. The fourth way is to modify the surface of scaffolds made of other materials by covering them with a layer of chitosan. At the end of the article, the processes taking place after placing the implant inside the body are described, how the structure of chitosan affects the behaviour of bone cells in the adhesion process and life processes.

Single-Macromolecular Level Imaging of a Hydrogel Structure

Hydrogels are promising materials for several applications, including cell scaffolds and artificial load-bearing substitutes (cartilages, ligaments, tendons, etc.). Direct observation of the nanoscale polymer network of hydrogels is essential in understanding its properties. However, imaging of individual network strands at the molecular level is not achieved yet due to the lack of suitable methods. Herein, for the first time, we developed a novel mineral-staining method and network fixation method for transmission electron microscopy observation to visualize the hydrogel network in its unperturbed conformation with nanometer resolution. Surface network observation indicates that the length of surface dangling chains, which play a major role in friction and wetting, can be estimated from the gel mesh size. Moreover, bulk observations reveals a hierarchical formation mechanism of gel heterogeneity. These observations have the great potential to advance gel science by providing comprehensive perspective that link bulk gel properties with nanoscale.

Collagen Bioinks for Bioprinting: A Systematic Review of Hydrogel Properties, Bioprinting Parameters, Protocols, and Bioprinted Structure Characteristics

Bioprinting is a modern tool suitable for creating cell scaffolds and tissue or organ carriers from polymers that mimic tissue properties and create a natural environment for cell development. A wide range of polymers, both natural and synthetic, are used, including extracellular matrix and collagen-based polymers. Bioprinting technologies, based on syringe deposition or laser technologies, are optimal tools for creating precise constructs precisely from the combination of collagen hydrogel and cells. This review describes the different stages of bioprinting, from the extraction of collagen hydrogels and bioink preparation, over the parameters of the printing itself, to the final testing of the constructs. This study mainly focuses on the use of physically crosslinked high-concentrated collagen hydrogels, which represents the optimal way to create a biocompatible 3D construct with sufficient stiffness. The cell viability in these gels is mainly influenced by the composition of the bioink and the parameters of the bioprinting process itself (temperature, pressure, cell density, etc.). In addition, a detailed table is included that lists the bioprinting parameters and composition of custom bioinks from current studies focusing on printing collagen gels without the addition of other polymers. Last but not least, our work also tries to refute the often-mentioned fact that highly concentrated collagen hydrogel is not suitable for 3D bioprinting and cell growth and development.