Tissue engineering: current state and prospects

Bioactive Hydrogels Inspired by Laminin: An Emerging Biomaterial for Tissue Engineering Applications

Tissue or organ damage due to severe injuries or chronic diseases can adversely affect the quality of life. Current treatments rely on organ or tissue transplantation which has limitations including unavailability of donors, ethical issues, or immune rejection after transplantations. These limitations can be addressed by tissue regeneration which involves the development of bioactive scaffolds closely mimicking the extracellular matrix (ECM). One of the major components of ECM is the laminin protein which supports several tissues associated with important organs. In this direction, peptide-based hydrogels can effectively mimic the essential characteristics of laminin. While several reports have discussed the structure of laminin, the potential of laminin-derived peptide hydrogels as effective biomaterial for tissue engineering applications is yet to be discussed. In this context, the current review focuses on the structure of laminin and its role as an essential ECM protein. Further, the potential of short peptide hydrogels in mimicking the crucial properties of laminin is proposed. The review further highlights the significance of bioactive hydrogels inspired by laminin - in addressing numerous tissue engineering applications including angiogenesis, neural, skeletal muscle, liver, and adipose tissue regeneration along with a brief outlook on the future applications of these laminin-based hydrogels.

Advancements in Tissue Engineering: A Review of Bioprinting Techniques, Scaffolds, and Bioinks

Tissue engineering is a multidisciplinary field that uses biomaterials to restore tissue function and assist with drug development. Over the last decade, the fabrication of three-dimensional (3D) multifunctional scaffolds has become commonplace in tissue engineering and regenerative medicine. Thanks to the development of 3D bioprinting technologies, these scaffolds more accurately recapitulate in vivo conditions and provide the support structure necessary for microenvironments conducive to cell growth and function. The purpose of this review is to provide a background on the leading 3D bioprinting methods and bioink selections for tissue engineering applications, with a specific focus on the growing field of developing multifunctional bioinks and possible future applications.

Tissue Regeneration on Rise: Dental Hard Tissue Regeneration and Challenges-A Narrative Review

Background

As people live longer, there is an increasing need for hard tissue regeneration and whole-tooth regeneration. Despite the advancements in the field of medicine, the field of regenerative dentistry is still challenging due to the complexity of dental hard tissues. Cross-disciplinary collaboration among material scientists, cellular biologists, and odontologists aimed at developing strategies and uncovering solutions related to dental tissue regeneration. Methodology. A search of the literature was done for pertinent research. Consistent with the Preferred Reporting Items for Systematic Review and Meta-Analysis (PRISMA) 2020 Statement, the electronic databases looked at were PubMed, Science Direct, Scopus, and Google Scholar, with the keyword search "hard dental tissue regeneration."

Results

Database analysis yielded a total of 476 articles. 222 duplicate articles have been removed in total. Articles that have no connection to the directed regeneration of hard dental tissue were disregarded. The review concluded with the inclusion of four studies that were relevant to our research objective.

Conclusion

Current molecular signaling network investigations and novel viewpoints on cellular heterogeneity have made advancements in understanding of the kinetics of dental hard tissue regeneration possible. Here, we outline the fundamentals of stem hard dental tissue maintenance, regeneration, and repair, as well as recent advancements in the field of hard tissue regeneration. These intriguing findings help establish a framework that will eventually enable basic research findings to be utilized towards oral health-improving medicines.

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Gelatin methacrylate (GelMA) hydrogels have gained significant traction in diverse tissue engineering applications through the utilization of 3D printing technology. As an artificial hydrogel possessing remarkable processability, GelMA has emerged as a pioneering material in the advancement of tissue engineering due to its exceptional biocompatibility and degradability. The integration of 3D printing technology facilitates the precise arrangement of cells and hydrogel materials, thereby enabling the creation of in vitro models that simulate artificial tissues suitable for transplantation. Consequently, the potential applications of GelMA in tissue engineering are further expanded. In tissue engineering applications, the mechanical properties of GelMA are often modified to overcome the hydrogel material's inherent mechanical strength limitations. This review provides a comprehensive overview of recent advancements in enhancing the mechanical properties of GelMA at the monomer, micron, and nano scales. Additionally, the diverse applications of GelMA in soft tissue engineering via 3D printing are emphasized. Furthermore, the potential opportunities and obstacles that GelMA may encounter in the field of tissue engineering are discussed. It is our contention that through ongoing technological progress, GelMA hydrogels with enhanced mechanical strength can be successfully fabricated, leading to the production of superior biological scaffolds with increased efficacy for tissue engineering purposes.

Proliferation of mammalian cells with Chlorococcum littorale algal compounds without serum support

In recent years, serum-free medium for mammalian cell cultivation has attracted a lot of attention, considering the high cost of production and environmental load involved in developing the conventional animal sera. The use of alternative growth-promoting products in mammalian cell cultivation such as extracts from microalgae has proven to be quite beneficial and environmental-friendly. This research aims to cultivate mammalian cells with growth-promoting factors derived from Chlorococcum littorale. We have established a simple extraction using the ultrasonication method and applied the extract in place of serum on mammalian C2C12 cell lines, 3T3 cell lines, and CHO cell lines to compare and analyze the effectiveness of the extract. Cell passage was conducted in a suspended culture condition with the addition of the extract. The results indicate that the extract from microalgae shows a high proliferation rate in all cell lines without fetal bovine serum. Moreover, it is eco-friendly and has huge potential to replace the traditional cell culture system. It could be applied in the fields of regenerative medicine, gene/cell therapies, as well as cultured meat production.

Design of Recombinant Spider Silk Proteins for Cell Type Specific Binding

Cytophilic (cell-adhesive) materials are very important for tissue engineering and regenerative medicine. However, for engineering hierarchically organized tissue structures comprising different cell types, cell-specific attachment and guidance are decisive. In this context, materials made of recombinant spider silk proteins are promising scaffolds, since they exhibit high biocompatibility, biodegradability, and the underlying proteins can be genetically functionalized. Here, previously established spider silk variants based on the engineered Araneus diadematus fibroin 4 (eADF4(C16)) are genetically modified with cell adhesive peptide sequences from extracellular matrix proteins, including IKVAV, YIGSR, QHREDGS, and KGD. Interestingly, eADF4(C16)-KGD as one of 18 tested variants is cell-selective for C2C12 mouse myoblasts, one out of 11 tested cell lines. Co-culturing with B50 rat neuronal cells confirms the cell-specificity of eADF4(C16)-KGD material surfaces for C2C12 mouse myoblast adhesion.

Tissue Engineering in Neuroscience: Applications and Perspectives

Neurological disorders have always been a threat to human physical and mental health nowadays, which are closely related to the nonregeneration of neurons in the nervous system (NS). The damage to the NS is currently difficult to repair using conventional therapies, such as surgery and medication. Therefore, repairing the damaged NS has always been a vast challenge in the area of neurology. Tissue engineering (TE), which integrates the cell biology and materials science to reconstruct or repair organs and tissues, has widespread applications in bone, periodontal tissue defects, skin repairs, and corneal transplantation. Recently, tremendous advances have been made in TE regarding neuroscience. In this review, we summarize TE's recent progress in neuroscience, including pathological mechanisms of various neurological disorders, the concepts and classification of TE, and the most recent development of TE in neuroscience. Lastly, we prospect the future directions and unresolved problems of TE in neuroscience.

A Comprehensive Review of Electrospun Fibers, 3D-Printed Scaffolds, and Hydrogels for Cancer Therapies

Anticancer therapies and regenerative medicine are being developed to destroy tumor cells, as well as remodel, replace, and support injured organs and tissues. Nowadays, a suitable three-dimensional structure of the scaffold and the type of cells used are crucial for creating bio-inspired organs and tissues. The materials used in medicine are made of non-degradable and degradable biomaterials and can serve as drug carriers. Developing flexible and properly targeted drug carrier systems is crucial for tissue engineering, regenerative medicine, and novel cancer treatment strategies. This review is focused on presenting innovative biomaterials, i.e., electrospun nanofibers, 3D-printed scaffolds, and hydrogels as a novel approach for anticancer treatments which are still under development and awaiting thorough optimization.

Evaluation of Angiogenesis in an Acellular Porous Biomaterial Based on Polyhydroxybutyrate and Chitosan Using the Chicken Ex Ovo Chorioallantoic Membrane Model

Simple Summary

The chorioallantoic membrane (CAM) is an avian extraembryonic membrane widely used as an experimental assay to study angiogenesis and its inhibition in response to tissues, cells, or soluble factors. In recent years, the CAM has become popular in scientific studies focused on the use of its potential for the study of biocompatibility of materials for regenerative strategies and tissue engineering applications. Great research efforts are being made to develop innovative biomaterials able to treat hard tissue defects, including diseases such as a bone cancer. In this article, we describe an approach to detect the formation of blood vessels inside the porous acellular biopolymer polyhydroxybutyrate/chitosan (PHB/CHIT) scaffold using the CAM assay as an in vivo alternative animal model, including macroscopic, histological, immunohistochemical, and molecular evaluation of the biocompatibility.

Abstract

The chorioallantoic membrane (CAM) is a highly vascularized avian extraembryonic membrane widely used as an in vivo model to study angiogenesis and its inhibition in response to tissues, cells, or soluble factors. In recent years, the use of CAM has become an integral part of the biocompatibility testing process for developing biomaterials intended for regenerative strategies and tissue engineering applications. In this study, we used the chicken ex ovo CAM assay to investigate the angiogenic potential of innovative acellular biopolymer polyhydroxybutyrate/chitosan (PHB/CHIT) scaffold, which is intended for the treatment of hard tissue defects, depending on treatment with pro- and anti-angiogenic substances. On embryonic day (ED) 7, the experimental biomaterials were placed on the CAM alone or soaked in vascular endothelial growth factor (VEGF-A), saline solution (PHY), or tyrosine kinase inhibitor (SU5402). After 72 h, the formation of vessels was analyzed in the surrounding area of the scaffold and inside the pores of the implants, using markers of embryonic endothelium (WGA, SNA), myofibroblasts (α-SMA), and macrophages (KUL-01). The morphological and histochemical analysis showed strong angiogenic potential of untreated scaffolds without additional effect of the angiogenic factor, VEGF-A. The lowest angiogenic potential was observed in scaffolds soaked with SU5402. Gene expression of pro-angiogenic growth factors, i.e., VEGF-A, ANG-2, and VE-CAD, was upregulated in untreated scaffolds after 72 h, indicating a pro-angiogenic environment. We concluded that the PHB/CHIT has a strong endogenous angiogenic potential and could be promising biomaterial for the treatment of hard tissue defects.

Surface Functionalized Polyaniline Nanofibers:Chitosan Nanocomposite for Promoting Neuronal-like Differentiation of Primary Adipose Derived Mesenchymal Stem Cells and Urease Activity

Bioscaffolds having electrically conducting polymers (CPs) have become increasingly relevant in tissue engineering (TE) because of their ability to regulate conductivity and promote biological function. With this in mind, the current study shows a conducting polyaniline nanofibers (PNFs) dispersed chitosan (Ch) nanocomposites scaffold with a simple one-step surface functionalization approach using glutaraldehyde for potential neural regeneration applications. According to the findings, 4 wt % PNFs dispersion in Ch matrix is an optimal concentration for achieving desirable biological functions while maintaining required physicochemical properties as evidenced by SEM, XRD, current-voltage (I-V) measurement, mechanical strength test, and in vitro biodegradability test. Surface chemical compositional analysis using XPS and ATR FT-IR confirms the incorporation of aldehyde functionality after functionalization, which is corroborated by surface energy calculations following the Van Oss-Chaudhury-Good method. Surface functionalization induced enhancement in surface hydrophilicity in terms of the polar component of surface energy (γ_i^AB) from 6.35 to 12.54 mN m^-1 along with an increase in surface polarity from 13.61 to 22.54%. Functionalized PNF:Ch scaffolds demonstrated improvement in enzyme activity from 67 to 94% and better enzyme kinetics with a reduction of Michaelis constants (K_m) from 21.55 to 13.81 mM, indicating favorable protein-biomaterial interactions and establishing them as biologically perceptible materials. Surface functionalization mediated improved cell-biomaterial interactions led to improved viability, adhesion, and spreading of primary adipose derived mesenchymal stem cells (ADMSCs) as well as improved immunocompatibility. Cytoskeletal architecture assessment under differentiating media containing 10 ng/mL of each basic fibroblast growth factor (bFGF) and epidermal growth factor (EGF) revealed significant actin remodeling with neurite-like projections on the functionalized scaffolds after 14 days. Immunocytochemistry results showed that more than 85% of cells expressed early neuron specific β III tubulin protein on the functionalized scaffolds, whereas glial fibrillary acidic protein (GFAP) expression was limited to approximately 40% of cells. The findings point to the functionalized nanocomposites' potential as a smart scaffold for electrically stimulated neural regeneration, as they are flexible enough to be designed into microchanneled or conduit-like structures that mimic the microstructures and mechanical properties of peripheral nerves.

Recombinant Proteins-Based Strategies in Bone Tissue Engineering

The increase in fracture rates and/or problems associated with missing bones due to accidents or various pathologies generates socio-health problems with a very high impact. Tissue engineering aims to offer some kind of strategy to promote the repair of damaged tissue or its restoration as close as possible to the original tissue. Among the alternatives proposed by this specialty, the development of scaffolds obtained from recombinant proteins is of special importance. Furthermore, science and technology have advanced to obtain recombinant chimera’s proteins. This review aims to offer a synthetic description of the latest and most outstanding advances made with these types of scaffolds, particularly emphasizing the main recombinant proteins that can be used to construct scaffolds in their own right, i.e., not only to impregnate them, but also to make scaffolds from their complex structure, with the purpose of being considered in bone regenerative medicine in the near future.

Avian Egg: A Multifaceted Biomaterial for Tissue Engineering

Most components in avian eggs, offering a natural and environmentally friendly source of raw materials, hold great potential in tissue engineering. An avian egg consists of several beneficial elements: the protective eggshell, the eggshell membrane, the egg white (albumen), and the egg yolk (vitellus). The eggshell is mostly composed of calcium carbonate and has intrinsic biological properties that stimulate bone repair. It is a suitable precursor for the synthesis of hydroxyapatite and calcium phosphate, which are particularly relevant for bone tissue engineering. The eggshell membrane is a thin protein-based layer with a fibrous structure and is constituted of several valuable biopolymers, such as collagen and hyaluronic acid, that are also found in the human extracellular matrix. As a result, the eggshell membrane has found several applications in skin tissue repair and regeneration. The egg white is a protein-rich material that is under investigation for the design of functional protein-based hydrogel scaffolds. The egg yolk, mostly composed of lipids but also diverse essential nutrients (e.g., proteins, minerals, vitamins), has potential applications in wound healing and bone tissue engineering. This review summarizes the advantages and status of each egg component in tissue engineering and regenerative medicine, but also covers their current limitations and future perspectives.

Proliferation of endothelial cells (HUVEC) on specific-modified collagen sponges loaded with different growth factors

In general, matrices for tissue engineering must maintain structural integrity during the process of tissue formation and promote vascularization of developing tissue. Therefore, collagen sponges, manufactured by an approach that offers the potential of unidirectional pore size, were seeded with human umbilical vein endothelial cells (HUVEC) to demonstrate a positive effect on cell proliferation. In addition, vascular endothelial growth factor (VEGF) and basic fibroblast growth factor (bFGF) have been used to promote proliferation of HUVEC on optimized collagen sponges. Growth and viability of the cells were evaluated. Potential unidirectional pore structure demonstrated an improvement of both, endothelial cell growth and viability. Supplementation of growth factors showed an additional increase of endothelial cell growth on collagen sponges, which confirmed the high potential of combining this biomaterial with growth factors. The results suggest that a collagen sponge with a potential specific pore size could be a suitable scaffold for endothelial cells and might be a promising implantable biomaterial with enhanced angiogenic capabilities for future clinical applications.

Fabrication of a novel 3D scaffold for cartilage tissue repair: In-vitro and in-vivo study

Self-repairing is not an advanced ability of articular cartilage. Tissue engineering has provided a novel way for reconstructing cartilage using natural polymers because of their biocompatibility and bio-functionality. The purpose of cartilage tissue engineering is to design a scaffold with proper pore structure and similar biological and mechanical properties to the native tissue. In this study, porous scaffolds prepared from gelatin, chitosan and silk fibroin were blended with varying ratios. Between the blends of chitosan (C), gelatin (G) and silk fibroin (S), the scaffold with the weight per volume ratio of 2:2:3 (w/v) showed the most favorable and higher certain properties than the other blends. The CGS 2:2:3 scaffold showed the best pore size that is between 100 μm and 300 μm. The water absorption and degradation rate of the CGS 2:2:3 scaffold were found suitable for cartilage tissue engineering. Cell culture study using human chondrocytes showed good cell adhesion and proliferation. To further study the effect of this scaffold on the living tissue, 36 rabbits were randomly assigned to CGS 2:2:3 scaffold with and without seeded chondrocytes and control groups. Hematoxylin and Eosin (H&E), Masson's trichrome (MT), and safranin O (SO) staining showed 65 ± 9.1% new cartilage tissue present in the defect filled with cell-seeded scaffold and most of the cartilaginous tissue was hyaline cartilage, while the control group showed no new cartilage tissue.

Bi-layer silk fibroin skeleton and bladder acellular matrix hydrogel encapsulating adipose-derived stem cells for bladder reconstruction

A scaffold, constructed from a bi-layer silk fibroin skeleton (BSFS) and a bladder acellular matrix hydrogel (BAMH) encapsulated with adipose-derived stem cells (ASCs), was developed for bladder augmentation in a rat model. The BSFS, prepared from silk fibroin (SF), had good mechanical properties that allowed it to maintain the scaffold shape and be used for stitching. The prepared BAM was digested by pepsin and the pH was adjusted to harvest the BAMH that provided an extracellular environment for the ASCs. The constructed BSFS-BAMH-ASCs and BSFS-BAMH scaffolds were wrapped in the omentum to promote neovascularization and then used for bladder augmentation; at the same time, a cystotomy was used as the condition for the control group. Histological staining and immunohistochemical analysis confirmed that the omentum incubation could promote scaffold vascularization. Hematoxylin and eosin and Masson's trichrome staining indicated that the BSFS-BAMH-ASCs scaffold regenerated the bladder wall structure. In addition, immunofluorescence analyses confirmed that the ASCs could promote the regeneration of smooth muscle, neurons and blood vessels and the restoration of physiological function. These results demonstrated that the BSFS-BAMH-ASCs may be a promising scaffold for promoting bladder wall regeneration and the restoration of physiological function of the bladder in a rat bladder augmentation model.

Bio-assembling and Bioprinting for Engineering Microvessels from the Bottom Up

Blood vessels are essential in transporting nutrients, oxygen, metabolic wastes, and maintaining the homeostasis of the whole human body. Mass of engineered microvessels is required to deliver nutrients to the cells included in the constructed large three-dimensional (3D) functional tissues by diffusion. It is a formidable challenge to regenerate microvessels and build a microvascular network, mimicking the cellular viabilities and activities in the engineered organs with traditional or existing manufacturing techniques. Modular tissue engineering adopting the "bottom-up" approach builds one-dimensional (1D) or two-dimensional (2D) modular tissues in micro scale first and then uses these modules as building blocks to generate large tissues and organs with complex but indispensable microstructural features. Building the microvascular network utilizing this approach could be appropriate and adequate. In this review, we introduced existing methods using the "bottom-up" concept developed to fabricate microvessels including bio-assembling powered by different micromanipulation techniques and bioprinting utilizing varied solidification mechanisms. We compared and discussed the features of the artificial microvessels engineered by these two strategies from multiple aspects. Regarding the future development of engineering the microvessels from the bottom up, potential directions were also concluded.

A Sandwich Structure of Human Dental Pulp Stem Cell Sheet, Treated Dentin Matrix, and Matrigel for Tooth Root Regeneration

Tooth loss can cause a lot of physiological and psychological suffering. And tooth root engineering is a promising way for tooth loss treatment. Two kinds of seed cells are usually adopted for tooth root regeneration. In this study, a practical sandwich structure for tooth root regeneration was developed, which was constituted by only one kind of seed cell: human dental pulp stem cells (hDPSCs) and three kinds of graft materials: Vitamin C (VC) induced hDPSC sheet, human treated dentin matrix (hTDM), and Matrigel. It was found that VC could induce hDPSCs to form a cell sheet with two or three cell layers and promote their collagen type I (COL1) mRNA expression obviously. hDPSCs could attach and grow on hTDM, and the mRNA expression of osteocalcin (OCN), dentin sialophosphoprotein (DSPP), vascular endothelial growth factor receptor 1 (VEGFR1), and Nestin in hDPSCs was obviously upregulated by hTDM leaching solution. hDPSCs could stretch and proliferate in Matrigel. And when cultured in Matrigel condition medium, they positively expressed CD31, β3-Tubulin, and Nestin proteins, as well as increased the mRNA expression of OCN, ALP, and Nestin. Furthermore, periodontium, dentin, and pulp-like tissues were successfully regenerated after the sandwich structure of hDPSC sheet/TDM/Matrigel was transplanted in nude mice subcutaneously for 3 months. Periodontium-like dense connective tissue was regenerated around the hTDM, and a great mass of predentin was formed on the cavity side of hTDM. Odontoblast-like cells and blood vessel-like structures, even nerve-like fibers, were observed in the pulp cavity. In summary, the above results showed that hDPSCs could be used as seed cells for the whole tooth root regeneration, and the sandwich structure constituted by hDPSC sheet, TDM/hDPSCs, and Matrigel/hDPSCs could be utilized for tooth root regeneration.

Rapid harvesting of stem cell sheets by thermoresponsive bulk poly(N-isopropylacrylamide) (PNIPAAm) nanotopography

To date, cell sheet engineering-based technologies have actualized diverse scaffold-free bio-products to revitalize unintentionally damaged tissues/organs, including cardiomyopathy, corneal defects, and periodontal damage. Although substantial interest is now centered on the practical utilization of these bio-products for patients, the long harvest period of stem cells- or other primary cell-sheets has become a huge hurdle. Here, we dramatically reduce the total harvest period of a cell sheet (from cell layer formation to cell sheet detachment) composed of human bone marrow mesenchymal stem cells (hBMSCs) down to 2 d with the help of bulk thermoresponsive poly(N-isopropylacrylamide) (PNIPAAm) substrate nanotopography, which is not achievable via the previous grafting methods using PNIPAAm. We directly replicated an isotropic 400 nm-nanopore-array pattern on a bulk PNIPAAm substrate through UV polymerization of highly concentrated NIPAAm monomers, which was achieved using a remarkably increased Young's modulus of bulk PNIPAAm that was 1500 times higher than conventional PNIPAAm. The rapid harvesting of the hBMSC sheet on the bulk PNIPAAm substrate nanotopography was not only based on the accelerated formation and maturation of the hBMSC layer, but also the easy detachment of the hBMSC sheet induced by the abrupt change in the surface roughness of the substrate below the lower critical solution temperature (LCST) owing to the enlarged surface area of the substrate. Our findings may contribute to reverse presumptions about the limitations regarding the grafting methods for the cell sheet harvest and could broaden the practical utilization of cell sheets for patients in the near future.

A Comparative Review of Natural and Synthetic Biopolymer Composite Scaffolds

Tissue engineering (TE) and regenerative medicine integrate information and technology from various fields to restore/replace tissues and damaged organs for medical treatments. To achieve this, scaffolds act as delivery vectors or as cellular systems for drugs and cells; thereby, cellular material is able to colonize host cells sufficiently to meet up the requirements of regeneration and repair. This process is multi-stage and requires the development of various components to create the desired neo-tissue or organ. In several current TE strategies, biomaterials are essential components. While several polymers are established for their use as biomaterials, careful consideration of the cellular environment and interactions needed is required in selecting a polymer for a given application. Depending on this, scaffold materials can be of natural or synthetic origin, degradable or nondegradable. In this review, an overview of various natural and synthetic polymers and their possible composite scaffolds with their physicochemical properties including biocompatibility, biodegradability, morphology, mechanical strength, pore size, and porosity are discussed. The scaffolds fabrication techniques and a few commercially available biopolymers are also tabulated.

Bone Matrix Non-Collagenous Proteins in Tissue Engineering: Creating New Bone by Mimicking the Extracellular Matrix

Engineering biomaterials that mimic the extracellular matrix (ECM) of bone is of significant importance since most of the outstanding properties of the bone are due to matrix constitution. Bone ECM is composed of a mineral part comprising hydroxyapatite and of an organic part of primarily collagen with the rest consisting on non-collagenous proteins. Collagen has already been described as critical for bone tissue regeneration; however, little is known about the potential effect of non-collagenous proteins on osteogenic differentiation, even though these proteins were identified some decades ago. Aiming to engineer new bone tissue, peptide-incorporated biomimetic materials have been developed, presenting improved biomaterial performance. These promising results led to ongoing research focused on incorporating non-collagenous proteins from bone matrix to enhance the properties of the scaffolds namely in what concerns cell migration, proliferation, and differentiation, with the ultimate goal of designing novel strategies that mimic the native bone ECM for bone tissue engineering applications. Overall, this review will provide an overview of the several non-collagenous proteins present in bone ECM, their functionality and their recent applications in the bone tissue (including dental) engineering field.

Liver bioengineering: Recent trends/advances in decellularization and cell sheet technologies towards translation into the clinic

Development of novel technologies provides the best tissue constructs engineering and maximizes their therapeutic effects in regenerative therapy, especially for liver dysfunctions. Among the currently investigated approaches of tissue engineering, scaffold-based and scaffold-free tissues are widely suggested for liver regeneration. Analogs of liver acellular extracellular matrix (ECM) are utilized in native scaffolds to increase the self-repair and healing ability of organs. Native ECM analog could improve liver repairing through providing the supportive framework for cells and signaling molecules, exerting normal biomechanical, biochemical, and physiological signal complexes. Recently, innovative cell sheet technology is introduced as an alternative for conventional tissue engineering with the advantage of fewer scaffold restrictions and cell culture on a Thermo-Responsive Polymer Surface. These sheets release the layered cells through a temperature-controlled procedure without enzymatic digestion, while preserving the cell-ECM contacts and adhesive molecules on cell-cell junctions. In addition, several novelties have been introduced into the cell sheet and decellularization technologies to aid cell growth, instruct differentiation/angiogenesis, and promote cell migration. In this review, recent trends, advancements, and issues linked to translation into clinical practice are dissected and compared regarding the decellularization and cell sheet technologies for liver tissue engineering.

Supercritical carbon dioxide decellularization of plant material to generate 3D biocompatible scaffolds

The use of plant-based biomaterials for tissue engineering has recently generated interest as plant decellularization produces biocompatible scaffolds which can be repopulated with human cells. The predominant approach for vegetal decellularization remains serial chemical processing. However, this technique is time-consuming and requires harsh compounds which damage the resulting scaffolds. The current study presents an alternative solution using supercritical carbon dioxide (scCO2). Protocols testing various solvents were assessed and results found that scCO2 in combination with 2% peracetic acid decellularized plant material in less than 4 h, while preserving plant microarchitecture and branching vascular network. The biophysical and biochemical cues of the scCO2 decellularized spinach leaf scaffolds were then compared to chemically generated scaffolds. Data showed that the scaffolds had a similar Young's modulus, suggesting identical stiffness, and revealed that they contained the same elements, yet displayed disparate biochemical signatures as assessed by Fourier-transform infrared spectroscopy (FTIR). Finally, human fibroblast cells seeded on the spinach leaf surface were attached and alive after 14 days, demonstrating the biocompatibility of the scCO2 decellularized scaffolds. Thus, scCO2 was found to be an efficient method for plant material decellularization, scaffold structure preservation and recellularization with human cells, while performed in less time (36 h) than the standard chemical approach (170 h).

Enhancement of Podocyte Attachment on Polyacrylamide Hydrogels with Gelatin-Based Polymers

Biological activities of cells such as survival and differentiation processes are mainly maintained by a specific extracellular matrix (ECM). Hydrogels have recently been employed successfully in tissue engineering applications. In particular, scaffolds made of gelatin methacrylate-based hydrogels (GelMA) showed great potential due to their biocompatibility, biofunctionality, and low mechanical strength. The development of a hydrogel having tunable and appropriate mechanical properties as well as chemical and biological cues was the aim of this work. A synthetic and biological hybrid hydrogel was developed to mimic the biological and mechanical properties of native ECM. A combination of gelatin methacrylate and acrylamide (GelMA-AAm)-based hydrogels was studied, and it showed tunable mechanical properties upon changing the polymer concentrations. Different GelMA-AAm samples were prepared and studied by varying the concentrations of GelMA and AAm (AAm_2.5% + GelMA_3%, AAm_5% + GelMA_3%, and AAm_5% + GelMA_5%). The swelling behavior, biodegradability, physicochemical and mechanical properties of GelMA-AAm were also characterized. The results showed a variation of swelling capability and a tunable elasticity ranging from 4.03 to 24.98 kPa depending on polymer concentrations. Moreover, the podocyte cell morphology, cytoskeleton reorganization and differentiation were evaluated as a function of GelMA-AAm mechanical properties. We concluded that the AAm_2.5% + GelMA_3% hydrogel sample having an elasticity of 4.03 kPa can mimic the native kidney glomerular basement membrane (GBM) elasticity and allow podocyte cell attachment without the functionalization of the gel surface with adhesion proteins compared to synthetic hydrogels (PAAm). This work will further enhance the knowledge of the behavior of podocyte cells to understand their biological properties in both healthy and diseased states.

Highly effective fibrin biopolymer scaffold for stem cells upgrading bone regeneration

Fibrin scaffold fits as a provisional platform promoting cell migration and proliferation, angiogenesis, connective tissue formation and growth factors stimulation. We evaluated a unique heterologous fibrin biopolymer as scaffold to mesenchymal stem cells (MSCs) to treat a critical-size bone defect. Femurs of 27 rats were treated with fibrin biopolymer (FBP); FBP + MSCs; and FBP + MSC differentiated in bone lineage (MSC-D). Bone repair was evaluated 03, 21 and 42 days later by radiographic, histological and scanning electron microscopy (SEM) imaging. The FBP + MSC-D association was the most effective treatment, since newly formed Bone was more abundant and early matured in just 21 days. We concluded that FBP is an excellent scaffold for MSCs and also use of differentiated cells should be encouraged in regenerative therapy researches. The FBP ability to maintain viable MSCs at Bone defect site has modified inflammatory environment and accelerating their regeneration.

Bacterial cellulose micro-nano fibres for wound healing applications

Bacterial cellulose (BC) is cellulose produced by a few limited species of bacteria in given conditions. BC has many remarkable properties such as its attractive mechanical properties, water uptake ability and biocompatibility which makes it a very desirable material to be used for wound healing. Inherently due to these important properties, the material is very resistant to easy processing and thus difficult to produce into useful entities. Additionally, being rate limited by the dependency on bacterial production, high yield is difficult to obtain and thus secondary material processing is sought after. In this review, BC is explained in terms of synthesis, structure and properties. These beneficial properties are directly related to the material's great potential in wound healing where it has also been trialled commercially but ultimately failed due to processing issues. However, more recently there has been increased frequency in scientific work relating to BC processing into hybrid polymeric fibres using common laboratory fibre forming techniques such as electrospinning and pressurised gyration. This paper summarises current progress in BC fibre manufacturing, its downfalls and also gives a future perspective on how the landscape should change to allow BC to be utilised in wound care in the current environment.

Tissue Engineering Approaches for Enamel, Dentin, and Pulp Regeneration: An Update

Stem/progenitor cells are undifferentiated cells characterized by their exclusive ability for self-renewal and multilineage differentiation potential. In recent years, researchers and investigations explored the prospect of employing stem/progenitor cell therapy in regenerative medicine, especially stem/progenitor cells originating from the oral tissues. In this context, the regeneration of the lost dental tissues including enamel, dentin, and the dental pulp are pivotal targets for stem/progenitor cell therapy. The present review elaborates on the different sources of stem/progenitor cells and their potential clinical applications to regenerate enamel, dentin, and the dental pulpal tissues.

Synthesis and Characterizations of a Collagen-Rich Biomembrane with Potential for Tissue-Guided Regeneration

Objectives  In this study, a collagen-rich biomembrane obtained from porcine ­intestinal submucosa for application in guided bone regeneration was developed and characterized. Then, its biological and mechanical properties were compared with that of commercial products ( GenDerm [Baumer], Lumina-Coat [Critéria], Surgitime PTFE [Bionnovation], and Surgidry Dental F [Technodry]).

Materials and Methods  The biomembrane was extracted from porcine intestinal submucosa. Scanning electron microscopy, spectroscopic dispersive energy, glycosaminoglycan quantification, and confocal microscopy by intrinsic fluorescence were used to evaluate the collagen structural patterns of the biomembrane. Mechanical tensile and deformation tests were also performed.

Statistical Analysis   The results of the methods used for experimental membrane characterizations were compared with that obtained by the commercial membranes and statistically analyzed (significance of 5%).

Results  The collagen-rich biomembrane developed also exhibited a more organized, less porous collagen fibril network, with the presence of glycosaminoglycans. The experimental biomembrane exhibited mechanical properties, tensile strength, and deformation behavior with improved average stress/strain when compared with other commercial membranes tested. Benefits also include a structured, flexible, and ­bioresorbable characteristics scaffold.

Conclusions  The experimental collagen-rich membrane developed presents physical–chemical, molecular, and mechanical characteristics similar to or better than that of the commercial products tested, possibly allowing it to actively participating in the process of bone neoformation.

Current Status of Stem Cell Therapies in Tissue Repair and Regeneration

Tissue engineering is a multi-disciplinary field such as material science, life science, and bioengineering that are necessary to make artificial tissue or rejuvenate damaged tissue. Numerous tissue repair techniques and substitute now exist even though it has several shortcomings; these shortcomings give a good reason for the continuous research for more acceptable tissue-engineered substitutes. The search for and use of a suitable stem cell in tissue engineering is a promising concept. Stem cells have a distinctive capability to differentiate and self-renew that make more suitable for cell-based therapies in tissue repair and regeneration. This review article focuses on stem cell for tissue engineering and their methods of manufacture with their application in nerve, bone, skin, cartilage, bladder, cardiac, liver tissue repair and regeneration.

Conductive electrospun scaffolds with electrical stimulation for neural differentiation of conjunctiva mesenchymal stem cells

An electrical stimulus is a new approach to neural differentiation of stem cells. In this work, the neural differentiation of conjunctiva mesenchymal stem cells (CJMSCs) on a new 3D conductive fibrous scaffold of silk fibroin (SF) and reduced graphene oxide (rGo) were examined. rGo (3.5% w/w) was dispersed in SF-acid formic solution (10% w/v) and conductive nanofibrous scaffold was fabricated using the electrospinning method. SEM and TEM microscopies were used for fibrous scaffold characterization. CJMSCs were cultured on the scaffold and 2 electrical impulse models (Current 1:115 V/m, 100-Hz frequency and current 2:115 v/m voltages, 0.1-Hz frequency) were applied for 7 days. Also, the effect of the fibrous scaffold and electrical impulses on cell viability and neural gene expression were examined using MTT assay and qPCR analysis. Fibrous scaffold with the 220 ± 20 nm diameter and good dispersion of graphene nanosheets at the surface of nanofibers were fabricated. The MTT result showed the viability of cells on the scaffold, with current 2 lower than current 1. qPCR analysis confirmed that the expression of β-tubulin (2.4-fold P ≤ 0.026), MAP-2 (1.48-fold; P ≤ 0.03), and nestin (1.5-fold; P ≤ 0.03) genes were higher in CJMSCs on conductive scaffold with 100-Hz frequency compared to 0.1-Hz frequency. Collectively, we proposed that SF-rGo fibrous scaffolds, as a new conductive fibrous scaffold with electrical stimulation are good strategies for neural differentiation of stem cells and the type of electrical pulses has an influence on neural differentiation and proliferation of CJMSCs.

Square prism micropillars on poly(methyl methacrylate) surfaces modulate the morphology and differentiation of human dental pulp mesenchymal stem cells

Use of soluble factors is the most common strategy to induce osteogenic differentiation of mesenchymal stem cells (MSCs) in vitro, but it may raise potential side effects in vivo. The topographies of the substrate surfaces affect cell behavior, and this could be a promising approach to guide stem cell differentiation. Micropillars have been reported to modulate cellular and subcellular shape, and it is particularly interesting to investigate whether these changes in cell morphology can modulate gene expression and lineage commitment without chemical induction. In this study, poly(methyl methacrylate) (PMMA) films were decorated with square prism micropillars with different lateral dimensions (4, 8 and 16 μm), and the surface wettability of the substrates was altered by oxygen plasma treatment. Both, pattern dimensions and hydrophilicity, were found to affect the attachment, proliferation, and most importantly, gene expression of human dental pulp mesenchymal stem cells (DPSCs). Decreasing the pillar width and interpillar spacing of the square prism pillars enhanced cell attachment, cell elongation, and deformation of nuclei, but reduced early proliferation rate. Surfaces with 4 or 8 μm wide pillars/gaps upregulated the expression of early bone-marker genes and mineralization over 28 days of culture. Exposure to oxygen plasma increased wettability and promoted cell attachment and proliferation but delayed osteogenesis. Our findings showed that surface topography and chemistry are very useful tools in controlling cell behavior on substrates and they can also help create better implants. The most important finding is that hydrophobic micropillars on polymeric substrate surfaces can be exploited in inducing osteogenic differentiation of MSCs without any differentiation supplements.

Dynamic observation and quantification of type I/II collagen in chondrogenesis of mesenchymal stem cells by second-order susceptibility microscopy

Second-order susceptibility (SOS) microscopy is used to image and characterize chondrogenesis in cultured human mesenchymal stem cells. SOS analysis shows that the SOS tensor ratios can be used to characterize type I and II collagens in living tissues and that both collagen types are produced at the onset of chondrogenesis. Time-lapse analysis shows a modulation of extracellular matrix results in a higher rate in increase of type II collagen, as compared to type I collagen. With time, type II collagen content stabilizes at the composition of 70% of total collagen content. SOS microscopy can be used to continuously and noninvasively monitor the production of collagens I and II. With additional development, this technique can be developed into an effective quality control tool for monitoring extracellular matrix production in engineered tissues.

Advancements in craniofacial prosthesis fabrication: A narrative review of holistic treatment

The treatment of craniofacial anomalies has been challenging as a result of technological shortcomings that could not provide a consistent protocol to perfectly restore patient-specific anatomy. In the past, wax-up and impression-based maneuvers were implemented to achieve this clinical end. However, with the advent of computer-aided design and computer-aided manufacturing (CAD/CAM) technology, a rapid and cost-effective workflow in prosthetic rehabilitation has taken the place of the outdated procedures. Because the use of implants is so profound in different facets of restorative dentistry, their placement for craniofacial prosthesis retention has also been widely popular and advantageous in a variety of clinical settings. This review aims to effectively describe the well-rounded and interdisciplinary practice of craniofacial prosthesis fabrication and retention by outlining fabrication, osseointegrated implant placement for prosthesis retention, a myriad of clinical examples in the craniofacial complex, and a glimpse of the future of bioengineering principles to restore bioactivity and physiology to the previously defected tissue.

In vitro artificial skin engineering by decellularized placental scaffold for secondary skin problems of meningomyelocele

BACKGROUND

Meningomyelocele (MMC) is a condition that is originated by the fusion defect of the neural tube. It is a congenital anomaly and can be characterized by spinal cord defects and impaired skin integrity. It is very important to close the skin openings via three-dimensional artificial skin like construction for preventing infection and maintaining the healthy skin structure. Therefore, we aim to generate artificial skin like structures formed by the own cells of donor for treating the MMC-related skin disorder.

METHODS

In this study, waste placental tissues were collected and decellularization process was applied. Decellularized and normal placental tissues were compared by immunohistochemistry (IHC). Donor's own placental stem cells were seeded onto biological scaffold and were differentiated into skin related cell types. Finally, gene expressions were evaluated, and the structural integrity were analyzed with IHC. Tube formation assay was also performed for examining the angiogenesis formation of the tissue in order to evaluate the possibility of a healthy organ development.

RESULTS

Characterization experiments proved that the decellularized skin preserved a normal skin 3D construction and vasculature along with significant ECM arrangements. The well-kept placental ECM scaffold was cytocompatible, supportive of mesenchymal cell types. Native organ related scaffold is expected to carry a huge influence in skin tissue engineering via delivering a niche for skin-based cells and even for stem/progenitor cells. Regarding to the data obtained from this study, in vivo investigation the skin-like structure in animal models is thought to be the next step as a future prospect.

CONCLUSION

This study is a reference investigation for skin engineering based on placental stem cells and biological scaffolds.

Synergistic effect of extracellularly supplemented osteopontin and osteocalcin on stem cell proliferation, osteogenic differentiation, and angiogenic properties

A high demand for functional bone grafts is being observed worldwide, especially due to the increased life expectancy. Osteoinductive components should be incorporated into functional bone grafts, accelerating cell recruitment, cell proliferation, angiogenesis, and new bone formation at a defect site. Noncollagenous bone matrix proteins, especially osteopontin (OPN) and osteocalcin (OC), have been reported to regulate some physiological process, such as cell migration and bone mineralization. However, the effects of OPN and OC on cell proliferation, osteogenic differentiation, mineralization, and angiogenesis are still undefined. Therefore, we assessed the exogenous effect of OPN and OC supplementation on human bone marrow mesenchymal stem/stromal cells (hBM MSC) proliferation and osteogenic differentiation. OPN dose-dependently increased the proliferation of hBM MSC, as well as improved the angiogenic properties of human umbilical vein endothelial cells (HUVEC) by increasing the capillary-like tube formation in vitro. On the other hand, OC enhanced the differentiation of hBM MSC into osteoblasts and demonstrated an increase in extracellular calcium levels and alkaline phosphatase activity, as well as higher messenger RNA levels of mature osteogenic markers osteopontin and osteocalcin. In vivo assessment of OC/OPN-enhanced scaffolds in a critical-sized defect rabbit long-bone model revealed no infection, while new bone was being formed. Taken together, these results suggest that OC and OPN stimulate bone regeneration by inducing stem cell proliferation, osteogenesis and by enhancing angiogenic properties. The synergistic effect of OC and OPN observed in this study can be applied as an attractive strategy for bone regeneration therapeutics by targeting different vital cellular processes.

Biomimetic matrices for rapidly forming mineralized bone tissue based on stem cell-mediated osteogenesis

Bone regeneration, following fracture, relies on autologous and allogenic bone grafts. However, majority of fracture population consists of older individuals with poor quality bone associated with loss and/or modification of matrix proteins critical for bone formation and mineralization. Allografts suffer from same limitations and carry the risk of delayed healing, infection, immune rejection and eventual fracture. In this work, we apply a synergistic biomimetic strategy to develop matrices that rapidly form bone tissue - a critical aspect of fracture healing of weight bearing bones. Collagen matrices, enhanced with two selected key matrix proteins, osteocalcin (OC) and/or osteopontin (OPN), increased the rate and quantity of synthesized bone matrix by increasing mesenchymal stem/stromal cell (MSC) proliferation, accelerating osteogenic differentiation, enhancing angiogenesis and showing a sustained bone formation response from MSC obtained from a variety of human tissue sources (marrow, fat and umbilical cord). In vivo assessment of OC/OPN mineralized scaffolds in a critical sized-defect rabbit long-bone model did not reveal any foreign body reaction while bone tissue was being formed. We demonstrate a new biomimetic strategy to rapidly form mineralized bone tissue and secure a sustained bone formation response by MSC from multiple sources, thus facilitating faster patient recovery and treatment of non-union fractures in aging and diseased population. Acellular biomimetic matrices elicit bone regeneration response from MSC, obtained from multiple tissue sources, and can be used in variety of scaffolds and made widely available.

β Cell Replacement Therapy: The Next 10 Years

β cell replacement with either pancreas or islet transplantation has progressed immensely over the last decades with current 1- and 5-year insulin independence rates of approximately 85% and 50%, respectively. Recent advances are largely attributed to improvements in immunosuppressive regimen, donor selection, and surgical technique. However, both strategies are compromised by a scarce donor source. Xenotransplantation offers a potential solution by providing a theoretically unlimited supply of islets, but clinical application has been limited by concerns for a potent immune response against xenogeneic tissue. β cell clusters derived from embryonic or induced pluripotent stem cells represent another promising unlimited source of insulin producing cells, but clinical application is pending further advances in the function of the β cell like clusters. Exciting developments and rapid progress in all areas of β cell replacement prompted a lively debate by members of the young investigator committee of the International Pancreas and Islet Transplant Association at the 15th International Pancreas and Islet Transplant Association Congress in Melbourne and at the 26th international congress of The Transplant Society in Hong Kong. This international group of young investigators debated which modality of β cell replacement would predominate the landscape in 10 years, and their arguments are summarized here.

In Vitro Human Tissues via Multi-material 3-D Bioprinting

This paper highlights the foundational research on multi-material 3-D bioprinting of human tissues, for which the Lewis Bioprinting team at Harvard University was awarded the 2017 Lush Science Prize. The team's bioprinting platform enables the rapid fabrication of 3-D human tissues that contain all of the essential components found in their in vivo counterparts: cells, vasculature (or other tubular features) and extracellular matrix. The printed 3-D tissues are housed within a customised perfusion system and are subjected to controlled microphysiological environments over long durations (days to months). As exemplars, the team created a thick, stem cell-laden vascularised tissue that was controllably differentiated toward an osteogenic lineage in situ, and a 3-D kidney tissue that recapitulated the proximal tubule, a sub-unit of the nephron responsible for solute reabsorption. This highly versatile platform for manufacturing 3D human tissue in vitro opens new avenues for replacing animal models used to develop next-generation therapies, test toxicity and study disease pathology.

Isolation and Culture of Embryonic Stem Cells, Mesenchymal Stem Cells, and Dendritic Cells from Humans and Mice

Stem cells are cells capable of proliferation, self-renewal, and differentiation into specific phenotypes. They are an essential part of tissue engineering, which is used in regenerative medicine in case of degenerative diseases. In this chapter, we describe the methods of isolating and culturing various types of stem cells, like human embryonic stem cells (hESCs), human umbilical cord derived mesenchymal stem cells (hUC-MSCs), murine bone marrow derived mesenchymal stem cells (mBM-MSCs), murine adipose tissue derived mesenchymal stem cells (mAD-MSCs), and murine bone marrow derived dendritic cells (mBMDCs). All these cell types can be used in tissue engineering techniques.