Conditioned medium produced by fibroblasts cultured in low oxygen pressure allows the formation of highly structured capillary-like networks in fibrin gels

Physiological skin oxygen levels: An important criterion for skin cell functionality and therapeutic approaches

The skin is made up of different layers with various gradients, which maintain a complex microenvironment, particularly in terms of oxygen levels. However, all types of skin cells are cultured in conventional incubators that do not reproduce physiological oxygen levels. Instead, they are cultured at atmospheric oxygen levels, a condition that is far removed from physiology and may lead to the generation of free radicals known to induce skin ageing. This review aims to summarize the current literature on the effect of physiological oxygen levels on skin cells, highlight the shortcomings of current in vitro models, and demonstrate the importance of respecting skin oxygen levels. We begin by clarifying the terminology used about oxygen levels and describe the specific distribution of oxygen in the skin. We review and discuss how skin cells adapt their oxygen consumption and metabolism to oxygen levels environment, as well as the changes that are induced, particularly, their redox state, life cycle and functions. We examine the effects of oxygen on both simple culture models and more complex reconstructed skin models. Finally, we present the implications of oxygen modulation for a more therapeutic approach.

Tissue Engineering for Penile Reconstruction

The penis is a complex organ with a development cycle from the fetal stage to puberty. In addition, it may suffer from either congenital or acquired anomalies. Penile surgical reconstruction has been the center of interest for many researchers but is still challenging due to the complexity of its anatomy and functionality. In this review, penile anatomy, pathologies, and current treatments are described, including surgical techniques and tissue engineering approaches. The self-assembly technique currently applied is emphasized since it is considered promising for an adequate tissue-engineered penile reconstructed substitute.

The Immunomodulatory Role of Cell-Free Approaches in SARS-CoV-2-Induced Cytokine Storm-A Powerful Therapeutic Tool for COVID-19 Patients

Currently, there is still no effective and definitive cure for the coronavirus disease 2019 (COVID-19) caused by the infection of the novel highly contagious severe acute respiratory syndrome virus (SARS-CoV-2), whose sudden outbreak was recorded for the first time in China in late December 2019. Soon after, COVID-19 affected not only the vast majority of China's population but the whole world and caused a global health public crisis as a new pandemic. It is well known that viral infection can cause acute respiratory distress syndrome (ARDS) and, in severe cases, can even be lethal. Behind the inflammatory process lies the so-called cytokine storm (CS), which activates various inflammatory cytokines that damage numerous organ tissues. Since the first outbreak of SARS-CoV-2, various research groups have been intensively trying to investigate the best treatment options; however, only limited outcomes have been achieved. One of the most promising strategies represents using either stem cells, such as mesenchymal stem cells (MSCs)/induced pluripotent stem cells (iPSCs), or, more recently, using cell-free approaches involving conditioned media (CMs) and their content, such as extracellular vesicles (EVs) (e.g., exosomes or miRNAs) derived from stem cells. As key mediators of intracellular communication, exosomes carry a cocktail of different molecules with anti-inflammatory effects and immunomodulatory capacity. Our comprehensive review outlines the complex inflammatory process responsible for the CS, summarizes the present results of cell-free-based pre-clinical and clinical studies for COVID-19 treatment, and discusses their future perspectives for therapeutic applications.

Three-dimensional culture conditioned bone marrow MSC secretome accelerates wound healing in a burn injury mouse model

Mesenchymal stem cell (MSC)-based therapy has emerged as a promising regenerative therapeutic approach for wound healing. To determine the effects of cultured MSCs as a 2D monolayer (2D-MSCs) and 3D spheroids (3D-MSCs) on their secretomes, and to examine the effect of 3D-MSC secretomes on endothelial cells (ECs) and MSCs in a burn injury mouse model. MSCs were cultured as 2D monolayers (2D-MSCs) and 3D spheroids (3D-MSCs) and their cellular characteristics were evaluated by western blotting. 2D-MSC and 3D-MSC secretomes (condition medium: CM) were analyzed using an angiogenic array. The activation of ECs by 2D-MSC and 3D-MSC CMs was examined in cellular proliferation, migration, and tube formation assays. The wound healing effects of 2D-MSCs and 3D-MSCs were determined in vivo using a burn injury mouse model. 3D culture conditions altered the markers of components that regulate cell survival, cytoskeletal, adhesion, and proliferation. Interleukin-6 (IL-6), vascular endothelial growth factor A (VEGFA), IL-8, and chemokine (CXC motif) ligand 1 (CXCL1) were present at high levels in the CM of 3D-MSCs compared with 2D-MCs. 3D-MSC-CMs promoted the proliferation, migration, and tube formation of ECs. Furthermore, 3D-MSC treatment enhanced wound healing in a burn injury mouse model. 3D culture improves proangiogenic factors in the MSC secretome and 3D-MSCs represent a new cell-based treatment strategy for wound healing.

Biocompatible Glycol Chitosan Microgels as Effective Drug Carriers

Glycol chitosan (GC) is a chitosan (CH) derivative with improved water solubility with regards to CH which affords significant solubility advantages. In this study, microgels of GC as p(GC) were synthesized by a microemulsion technique at various crosslinking ratios e.g., 5%, 10%, 50%, 75%, and 150% based on the repeating unit of GC using divinyl sulfone (DVS) as a crosslinker. The prepared p(GC) microgels were tested for blood compatibility and it was found that p(GC) microgels at 1.0 mg/mL concentration possessed a 1.15 ± 0.1% hemolysis ratio and 89 ± 5% blood clotting index value confirming their hemocompatibility. In addition, p(GC) microgels were found biocompatible with 75.5 ± 5% cell viability against L929 fibroblasts even at a 2.0 mg/mL concentration. By loading and releasing tannic acid (TA) (a polyphenolic compound with high antioxidant activity) as an active agent, p(GC) microgels' possible drug delivery device application was examined. The TA loading amount of p(GC) microgels was determined as 323.89 mg/g, and TA releases from TA loaded microgels (TA@p(GC)) were found to be linear within 9 h and a total amount of TA released was determined as 42.56 ± 2 mg/g within 57 h. According to the Trolox equivalent antioxidant capacity (TEAC) test, 400 µL of the sample added to the ABTS+ solution inhibited 68.5 ± 1.7% of the radicals. On the other hand, the total phenol content (FC) test revealed that 2000 μg/mL of TA@p(GC) microgels resulted in 27.5 ± 9.5 mg/mL GA eq antioxidant properties.

Comparative analysis of the potential of the secretomes of cardiac resident stromal cells and fibroblasts

The secretome of different cell types has been applied on in vitro and in vivo assays, indicating considerable therapeutic potential. However, the choice of the ideal cell type and culture conditions for obtaining the best set of soluble factors, as well as the assays to assess specific effects, remain subjects of vigorous debate. In this study, we used mass spectrometry to characterize the secretomes of ventricle derived-cardiac resident stromal cells (vCRSC) and human dermal fibroblasts (HDFs) and evaluate them in an effort to understand the niche specificity of biological responses toward different cellular behaviors, such as cell proliferation, adhesion, migration, and differentiation. It was interesting to note that the HDF and vCRSC secretomes were both able to induce proliferation and cardiac differentiation of H9c2 cells, as well as to increase the adhesion activity of H9c2 cells and human umbilical vein endothelial cells. Analysis of the secretome composition showed that the vCRSCs derived from different donors secreted a similar set of proteins. Despite the differences, almost half of the proteins identified in conditioned medium were common to both HDF and vCRSC. Consequently, a high number of common biological processes were identified in the secretomes of the two cell types, which could help to explain the similar results observed in the in vitro assays. We show that soluble factors secreted by both HDF and vCRSC are able to promote proliferation and differentiation of cardiomyoblasts in vitro. Our study indicates the possible use of vCRSC or HDF secretomes in acellular therapies for regenerative medicine.

Tissue Engineering for Gastrointestinal and Genitourinary Tracts

The gastrointestinal and genitourinary tracts share several similarities. Primarily, these tissues are composed of hollow structures lined by an epithelium through which materials need to flow with the help of peristalsis brought by muscle contraction. In the case of the gastrointestinal tract, solid or liquid food must circulate to be digested and absorbed and the waste products eliminated. In the case of the urinary tract, the urine produced by the kidneys must flow to the bladder, where it is stored until its elimination from the body. Finally, in the case of the vagina, it must allow the evacuation of blood during menstruation, accommodate the male sexual organ during coitus, and is the natural way to birth a child. The present review describes the anatomy, pathologies, and treatments of such organs, emphasizing tissue engineering strategies.

Tissue Engineering in Gynecology

Female gynecological organ dysfunction can cause infertility and psychological distress, decreasing the quality of life of affected women. Incidence is constantly increasing due to growing rates of cancer and increase of childbearing age in the developed world. Current treatments are often unable to restore organ function, and occasionally are the cause of female infertility. Alternative treatment options are currently being developed in order to face the inadequacy of current practices. In this review, pathologies and current treatments of gynecological organs (ovaries, uterus, and vagina) are described. State-of-the-art of tissue engineering alternatives to common practices are evaluated with a focus on in vivo models. Tissue engineering is an ever-expanding field, integrating various domains of modern science to create sophisticated tissue substitutes in the hope of repairing or replacing dysfunctional organs using autologous cells. Its application to gynecology has the potential of restoring female fertility and sexual wellbeing.

Evaluation of a Serum-Free Medium for Human Epithelial and Stromal Cell Culture

Over the past decade, growing demand from many domains (research, cosmetics, pharmaceutical industries, etc.) has given rise to significant expansion of the number of in vitro cell cultures. Despite the widespread use of fetal bovine serum, many issues remain. Among them, the whole constitution of most serums remains unknown and is subject to significant variations. Furthermore, the presence of potential contamination and xenogeny elements is challenging for clinical applications, while limited production is an obstacle to the growing demand. To circumvent these issues, a Serum-Free Medium (SFM) has been developed to culture dermal and vesical fibroblasts and their corresponding epithelial cells, namely, keratinocytes and urothelial cells. To assess the impact of SFM on these cells, proliferation, clonogenic and metabolic assays have been compared over three passages to conditions associated with the use of a classic Fetal Bovine Serum-Containing Medium (FBSCM). The results showed that the SFM enabled fibroblast and epithelial cell proliferation while maintaining a morphology, cell size and metabolism similar to those of FBSCM. SFM has repeatedly been found to be better suited for epithelial cell proliferation and clonogenicity. Fibroblasts and epithelial cells also showed more significant mitochondrial metabolism in the SFM compared to the FBSCM condition. However, the SFM may need further optimization to improve fibroblast proliferation.

Biological activity of a vascular endothelial cell-hydroxyapatite orbital implant complex: An experimental study

The reduction in postoperative complications is a considerable concern after orbital reparation and reconstruction. Selecting the appropriate scaffold materials to improve the survival rates of the seeded cells is a challenge in tissue engineering. The aim of the present study was to evaluate the biological activity of a vascular endothelial cell-hydroxyapatite orbital complex, which was constructed with tissue engineering and used as an implant after enucleation of the eyeNew Zealand white rabbits were randomly divided into two groups that underwent hydroxyapatite orbital implant surgery in the right eye. The primary orbital microvascular endothelial cells were collected from the microvascular tissue and subsequently cultured. Then, hydroxyapatite ocular implants were cultured with vascular endothelial cells in the endothelial cell (EC) group, and implants were cultured without vascular endothelial cells in the blank group. Characterization of the cells was performed with immunofluorescence staining and a Transwell migration and cell tube formation assay. The levels of interleukin-8 (IL-8) and vascular endothelial growth factor (VEGF) in the rabbit conjunctiva were measured with an ELISA. The results showed that the levels of IL-8 were decreased in the EC group and increased in the blank group. The levels of VEGF were increased in the EC group when compared to the blank group with statistical significance. The average depth of the fibrovascular tissue was obviously thicker in the EC group compared with that found in the blank group. These findings suggest that the vascular endothelial cell-hydroxyapatite orbital implant complex may be an effective strategy with which to accelerate vascularization and reduce complications of infection with satisfactory biological activity.

Oxygenation therapies for improved wound healing: Current trends and technologies

Degree of oxygenation is one of the important parameters governing various processes, including cell proliferation, angiogenesis, extracellular matrix production, and even combating the microbial burden at the wound site, all...

Cell secretomes for wound healing and tissue regeneration: Next generation acellular based tissue engineered products

Wound represents a significant socioeconomic burden for both affected individuals and as a whole healthcare system. Accordingly, stem cells have garnered attention due to their differentiation capacity and ability to aid tissue regeneration by releasing biologically active molecules, found in the cells’ cultivated medium which known as conditioned medium (CM) or secretomes. This acellular approach provides a huge advantage over conventional treatment options, which are mainly used cellular treatment at wound closure. Interestingly, the secretomes contained the cell-secreted proteins such as growth factors, cytokines, chemokines, extracellular matrix (ECM), and small molecules including metabolites, microvesicles, and exosomes. This review aims to provide a general view on secretomes and how it is proven to have great potential in accelerating wound healing. Utilizing the use of secretomes with its secreted proteins and suitable biomaterials for fabrications of acellular skin substitutes can be promising in treating skin loss and accelerate the healing process.

Vascularization in skin wound healing: where do we stand and where do we go?

Cutaneous healing is a highly complex process that, if altered due to, for example, impaired vascularization, results in chronic wounds or repaired neotissue of poor quality. Significant progress has been achieved in promoting neotissue vascularization during tissue repair/regeneration. In this review, we discuss the strategies that have been explored and how each one of them contributes to regulate vascularization in the context of cutaneous wound healing from two different perspectives - biomaterial-based and a cell-based approaches. Finally, we discuss the implications of these findings on the development of the 'next generation' approaches to target vascularization in wound healing highlighting the importance of going beyond its contribution to regulate vascularization and take into consideration the temporal features of the healing process and of different types of wounds.

Oxygen releasing materials: Towards addressing the hypoxia-related issues in tissue engineering

Manufacturing macroscale cell-laden architectures is one of the biggest challenges faced nowadays in the domain of tissue engineering. Such living constructs, in fact, pose strict requirements for nutrients and oxygen supply that can hardly be addressed through simple diffusion in vitro or without a functional vasculature in vivo. In this context, in the last two decades, a substantial amount of work has been carried out to develop smart materials that could actively provide oxygen-release to contrast local hypoxia in large-size constructs. This review provides an overview of the currently available oxygen-releasing materials and their synthesis and mechanism of action, highlighting their capacities under in vitro tissue cultures and in vivo contexts. Additionally, we also showcase an emerging concept, herein termed as "living materials as releasing systems", which relies on the combination of biomaterials with photosynthetic microorganisms, namely algae, in an "unconventional" attempt to supply the damaged or re-growing tissue with the necessary supply of oxygen. We envision that future advances focusing on tissue microenvironment regulated oxygen-supplying materials would unlock an untapped potential for generating a repertoire of anatomic scale, living constructs with improved cell survival, guided differentiation, and tissue-specific biofunctionality.

Recent Advances in Functional Polymers Containing Coumarin Chromophores

Natural and synthetic coumarin derivatives have gained increased attention in the design of functional polymers and polymer networks due to their unique optical, biological, and photochemical properties. This review provides a comprehensive overview over recent developments in macromolecular architecture and mainly covers examples from the literature published from 2004 to 2020. Along with a discussion on coumarin and its photochemical properties, we focus on polymers containing coumarin as a nonreactive moiety as well as polymer systems exploiting the dimerization and/or reversible nature of the [2πs + 2πs] cycloaddition reaction. Coumarin moieties undergo a reversible [2πs + 2πs] cycloaddition reaction upon irradiation with specific wavelengths in the UV region, which is applied to impart intrinsic healability, shape-memory, and reversible properties into polymers. In addition, coumarin chromophores are able to dimerize under the exposure to direct sunlight, which is a promising route for the synthesis and cross-linking of polymer systems under "green" and environment-friendly conditions. Along with the chemistry and design of coumarin functional polymers, we highlight various future application fields of coumarin containing polymers involving tissue engineering, drug delivery systems, soft robotics, or 4D printing applications.