ECM-based macroporous sponges release essential factors to support the growth of hematopoietic cells

Biomedical polymer scaffolds mimicking bone marrow niches to advance in vitro expansion of hematopoietic stem cells

Hematopoietic stem cell (HSC) transplantation provides an effective platform for the treatment of hematological disorders. However, the donor shortage of HSCs and immune responses severely restrict the clinical applications of HSCs. Compared to allogeneic transplantation, autogenous transplantation poses less risk to the immune system, but the problem associated with insufficient HSCs remains a substantial challenge. A significant strategy for obtaining sufficient HSCs is to promote the expansion of HSCs. In vivo, a bone marrow microenvironment supports the survival and hematopoiesis of HSCs. Therefore, it is crucial to establish a platform that mimics the features of a bone marrow microenvironment for the in vitro expansion of HSCs. Three-dimensional (3D) scaffolds have emerged as the most powerful tools to mimic cellular microenvironments for the growth and proliferation of stem cells. Biomedical polymers have been widely utilized as cell scaffolds due to their advantageous features including favorable biocompatibility, biodegradability, as well as adjustable physical and chemical properties. This review focuses on recent advances in the study of biomedical polymer scaffolds that mimic bone marrow microenvironments for the in vitro expansion of HSCs. Bone marrow transplantation and microenvironments are first introduced. Then, biomedical polymer scaffolds for the expansion of HSCs and future prospects are summarized and discussed.

Preparation and Use of Decellularized Extracellular Matrix for Tissue Engineering

The multidisciplinary fields of tissue engineering and regenerative medicine have the potential to revolutionize the practise of medicine through the abilities to repair, regenerate, or replace tissues and organs with functional engineered constructs. To this end, tissue engineering combines scaffolding materials with cells and biologically active molecules into constructs with the appropriate structures and properties for tissue/organ regeneration, where scaffolding materials and biomolecules are the keys to mimic the native extracellular matrix (ECM). For this, one emerging way is to decellularize the native ECM into the materials suitable for, directly or in combination with other materials, creating functional constructs. Over the past decade, decellularized ECM (or dECM) has greatly facilitated the advance of tissue engineering and regenerative medicine, while being challenged in many ways. This article reviews the recent development of dECM for tissue engineering and regenerative medicine, with a focus on the preparation of dECM along with its influence on cell culture, the modification of dECM for use as a scaffolding material, and the novel techniques and emerging trends in processing dECM into functional constructs. We highlight the success of dECM and constructs in the in vitro, in vivo, and clinical applications and further identify the key issues and challenges involved, along with a discussion of future research directions.

Human Protein-Based Porous Scaffolds as Platforms for Xeno-Free 3D Cell Culture

Extracellular matrix and protein-based biomaterials emerge as attractive sources to produce scaffolds due to their great properties regarding biocompatibility and bioactivity. In addition, there are concerns regarding the use of animal-derived supplements in cell culture not only due to the risk of transmission of xenogeneic contaminants and antigens but also due to ethical issues associated with collection methods. Herein, a novel human protein-derived porous scaffold produced from platelet lysates (PL) as platform for xeno-free 3D cell culture has been proposed. Human PL are chemically modified with methacryloyl groups (PLMA) to make them photocrosslinkable and used as precursor material to produce PLMA-based sponges. The herein reported human-based sponges have highly tunable morphology and mechanical properties, with an internal porous structure and Young's modulus dependent on the concentration of the polymer. Human adipose-derived stem cells (hASCs) are cultured on top of PLMA sponges to validate their use for 3D cell culture in xeno-free conditions. After 14 days hASCs remained viable, and results show that cells are able to proliferate during time even in the absence of animal-derived supplementation. This study reveals for the first time that such scaffolds can be promising platforms for culture of human cells avoiding the use of any animal-derived supplement.

Engineering strategies to achieve efficient in vitro expansion of haematopoietic stem cells: development and improvement

Haematopoietic stem cells are the basis for building and maintaining lifelong haematopoietic mechanisms and important resources for the treatment of blood disorders. Haematopoietic niches are microenvironment in the body where...

A Novel Bionic Extracellular Matrix Polymer Scaffold Enhanced by Calcium Silicate for Bone Tissue Engineering

A novel porous calcium silicate (CS)-enhanced small intestinal submucosa (SIS) scaffold was prepared by freeze-drying to mimic the natural extracellular matrix environment for bone tissue engineering. The micro-morphology, physicochemical properties, biological characteristics, and effects on osteogenic differentiation in vitro were explored; the effects on promoting bone formation in vivo were evaluated. The composite scaffold had an ideal three-dimensional porous structure. The amount of calcium silicate played a significant role in improving mechanical properties and promoting osteogenic differentiation. The SIS/2CS scaffold promoted proliferation and osteogenic differentiation in human bone marrow mesenchymal stem cells; it also significantly increased osteogenesis in vivo. This novel composite polymer scaffold has potential applications in bone tissue engineering.

Harnessing organs-on-a-chip to model tissue regeneration

Tissue engineering has markedly matured since its early beginnings in the 1980s. In addition to the original goal to regenerate damaged organs, the field has started to explore modeling of human physiology "in a dish." Induced pluripotent stem cell (iPSC) technologies now enable studies of organ regeneration and disease modeling in a patient-specific context. We discuss the potential of "organ-on-a-chip" systems to study regenerative therapies with focus on three distinct organ systems: cardiac, respiratory, and hematopoietic. We propose that the combinatorial studies of human tissues at these two scales would help realize the translational potential of tissue engineering.

Sustained delivery of 17β-estradiol by human amniotic extracellular matrix (HAECM) scaffold integrated with PLGA microspheres for endometrium regeneration

The endometrial injury usually results in intrauterine adhesions (IUAs). However, there is no effective treatment to promote the regeneration of the endometrium currently. The decellularized amnion membrane (AM) is a promising material in human tissue repair and regeneration due to its biocompatibility, biodegradability, as well as the preservation of abundant bioactive components. Here, an innovative drug-delivering system based on human amniotic extracellular matrix (HAECM) scaffolds were developed to facilitate endometrium regeneration. The 17β-estradiol (E2) loaded PLGA microspheres (E2-MS) were well dispersed in the scaffolds without altering their high porosity. E2 released from E2-MS-HAECM scaffolds in vitro showed a decreased initial burst release followed with a sustained release for 21 days, which coincided with the female menstrual cycle. Results of cell proliferation suggested E2-MS-HAECM scaffolds had good biocompatibility and provided more biologic guidance of endometrial cell proliferation except for mechanical supports. Additionally, the mRNA expression of growth factors in endometrial cells indicated that HAECM scaffolds could upregulate the expression of EGF and IGF-1 to achieve endometrium regeneration. Therefore, these advantages provide the drug-loaded bioactive scaffolds with new choices for the treatments of IUAs.

The combined effects of hierarchical scaffolds and mechanical stimuli on ex vivo expansion of haematopoietic stem/progenitor cells

We describe the ex vivo expansion of haematopoietic stem/progenitor cells (HSPCs) with consideration of their eventual in-vivo niche. We firstly fabricated hierarchically structured scaffolds (lattices derived via three-dimensional plotting combined with electrospun submicron fibers coated with vitronectin to increase cell affinity). We also applied intermittent hydrostatic pressure (IHP) to mimic the physical environment of the in vivo niche. In the absence of mechanical stimuli, the cell phenotype (CD34⁺, CD34⁺CD38^-) remained excellent in the vitronectin-treated group. Two IHP regimens were tested; optimally, cells were pressurized (20 kPa) for 2 min and then rested for 13 min. On day 7 of culture, the total cell number had increased 21.2-fold and that of CD34⁺ cells 10.94-fold. CD34⁺ and CD34⁺CD38^- cells constituted 44.50 and 44.07% of total cells, respectively. Colony-forming counts and the long-term culture-initiating cell assay showed that clonogenic potential was greatly improved under our experimental conditions. Scaffolds with hierarchical structures were valuable in this context. Furthermore, ex vivo expansion of HSPCs was improved by physical stimulation.

Personalized Hydrogels for Engineering Diverse Fully Autologous Tissue Implants

Despite incremental improvements in the field of tissue engineering, no technology is currently available for producing completely autologous implants where both the cells and the scaffolding material are generated from the patient, and thus do not provoke an immune response that may lead to implant rejection. Here, a new approach is introduced to efficiently engineer any tissue type, which its differentiation cues are known, from one small tissue biopsy. Pieces of omental tissues are extracted from patients and, while the cells are reprogrammed to become induced pluripotent stem cells, the extracellular matrix is processed into an immunologically matching, thermoresponsive hydrogel. Efficient cell differentiation within a large 3D hydrogel is reported, and, as a proof of concept, the generation of functional cardiac, cortical, spinal cord, and adipogenic tissue implants is demonstrated. This versatile bioengineering approach may assist to regenerate any tissue and organ with a minimal risk for immune rejection.

Off-the-Shelf Biomimetic Graphene Oxide-Collagen Hybrid Scaffolds Wrapped with Osteoinductive Extracellular Matrix for the Repair of Cranial Defects in Rats

Hydrogels such as type I collagen (COL) have been widely studied in bone tissue repair, whereas their weak mechanical strength has limited their clinical application. By adding graphene oxide (GO) nanosheets, researchers have successfully improved the mechanical properties and biocompatibility of the hydrogels. However, for large bone defects, the osteoinductive and cell adhesion ability of the GO hybrid hydrogels need to be improved. Mesenchymal stem cell (MSC) secreted extracellular matrix (ECM), which is an intricate network, could provide a biomimetic microenvironment and functional molecules that enhance the cell proliferation and survival rate. To synergize the advantages of MSC-ECM with GO-COL hybrid implants, we developed a novel ECM scaffold construction method. First, an osteoinductive extracellular matrix (OiECM) was created by culturing osteodifferentiated bone marrow mesenchymal stem cells (BMSCs) for 21 days. Then, the GO-COL scaffold was fully wrapped with the OiECM to construct the OiECM-GO-COL composite for implantation. The morphology, physical properties, biocompatibility, and osteogenic performance of the OiECM-GO-COL implants were assessed in vitro and in vivo (5 mm rat cranial defect model). Both gene expression and cell level assessments suggested that the BMSCs cultured on OiECM-GO-COL implants had a higher proliferation rate and osteogenic ability compared to the COL or GO-COL groups. In vivo results showed that the OiECM-GO-COL implants achieved better repair effects in a rat critical cranial defect model, whereas bone formation in other groups was limited. This study provides a promising strategy, which greatly improves the osteogenic ability and biocompatibility of the GO hydrogels without the procedure of seeding and culturing MSCs on scaffolds in vitro, demonstrating its potential as an off-the-shelf method for bone tissue engineering.

Rebuilding a better home for transplanted islets

Diabetes can be treated with β cell replacement therapy, where a patient is transplanted with cadaveric human islets to restore glycemic control. Despite this being an effective treatment, the process of isolating islets from the pancreas requires collagenase digestion which disrupts the islet extracellular matrix (ECM) and activates anoikis-mediated apoptosis. To improve islet survival in culture and after transplantation, the islet microenvironment may be enhanced with the addition of ECM components which are lost during isolation. Furthermore, novel β cell replacement strategies, such as stem cell-derived beta cell (SCβC) treatments or alternative transplant sites and devices, could benefit from a better understanding of how β cells interact with ECM. In this mini-review, we discuss the current understanding of the pancreas and islet ECM composition and review decellularization approaches to generate a native pancreatic ECM scaffold for use in both islet and SCβC culture and transplantation.

A microfluidic chip containing multiple 3D nanofibrous scaffolds for culturing human pluripotent stem cells

In microfluidics-based lab-on-a-chip systems, which are used for investigating the effect of drugs and growth factors on cells, the latter are usually cultured within the device's channels in two-dimensional, and not in their optimal three-dimensional (3D) microenvironment. Herein, we address this shortfall by designing a microfluidic system, comprised of two layers. The upper layer of the system consists of multiple channels generating a gradient of soluble factors. The lower layer is comprised of multiple wells, each deposited with 3D, nanofibrous scaffold. We first used a mathematical model to characterize the fluid flow within the system. We then show that induced pluripotent stem cells can be seeded within the 3D scaffolds and be exposed to a well-mixed gradient of soluble factors. We believe that utilizing such system may enable in the future to identify new differentiation factors, investigate drug toxicity, and eventually allow to perform analyses on patient-specific tissues, in order to fit the appropriate combination and concentration of drugs.

Stem cell therapy for abrogating stroke-induced neuroinflammation and relevant secondary cell death mechanisms

Ischemic stroke is a leading cause of death worldwide. A key secondary cell death mechanism mediating neurological damage following the initial episode of ischemic stroke is the upregulation of endogenous neuroinflammatory processes to levels that destroy hypoxic tissue local to the area of insult, induce apoptosis, and initiate a feedback loop of inflammatory cascades that can expand the region of damage. Stem cell therapy has emerged as an experimental treatment for stroke, and accumulating evidence supports the therapeutic efficacy of stem cells to abrogate stroke-induced inflammation. In this review, we investigate clinically relevant stem cell types, such as hematopoietic stem cells (HSCs), mesenchymal stem cells (MSCs), endothelial progenitor cells (EPCs), very small embryonic-like stem cells (VSELs), neural stem cells (NSCs), extraembryonic stem cells, adipose tissue-derived stem cells, breast milk-derived stem cells, menstrual blood-derived stem cells, dental tissue-derived stem cells, induced pluripotent stem cells (iPSCs), teratocarcinoma-derived Ntera2/D1 neuron-like cells (NT2N), c-mycER(TAM) modified NSCs (CTX0E03), and notch-transfected mesenchymal stromal cells (SB623), comparing their potential efficacy to sequester stroke-induced neuroinflammation and their feasibility as translational clinical cell sources. To this end, we highlight that MSCs, with a proven track record of safety and efficacy as a transplantable cell for hematologic diseases, stand as an attractive cell type that confers superior anti-inflammatory effects in stroke both in vitro and in vivo. That stem cells can mount a robust anti-inflammatory action against stroke complements the regenerative processes of cell replacement and neurotrophic factor secretion conventionally ascribed to cell-based therapy in neurological disorders.

Cardiac tissue engineering: from matrix design to the engineering of bionic hearts

The field of cardiac tissue engineering aims at replacing the scar tissue created after a patient has suffered from a myocardial infarction. Various technologies have been developed toward fabricating a functional engineered tissue that closely resembles that of the native heart. While the field continues to grow and techniques for better tissue fabrication continue to emerge, several hurdles still remain to be overcome. In this review we will focus on several key advances and recent technologies developed in the field, including biomimicking the natural extracellular matrix structure and enhancing the transfer of the electrical signal. We will also discuss recent developments in the engineering of bionic cardiac tissues which integrate the fields of tissue engineering and electronics to monitor and control tissue performance.