Advanced cell therapies with and without scaffolds

Engineering a 3-dimensional tissue construct with adipose-derived stem cells for healing bone defect: An ex vivo study with femur head

The compatibility of bone graft substitutes (BGS) with mesenchymal stem cells (MSCs) is an important parameter to consider for their use in repairing bone defects as it eventually affects the clinical outcome. In the present study, a few commercially available BGS - β-tricalcium phosphate (β-TCP), calcium sulfate, gelatin sponge, and different forms of hydroxyapatite (HAP) were screened for their interactions with MSCs from adipose tissue (ADSCs). It was demonstrated that HAP block favorably supported ADSC viability, morphology, migration, and differentiation compared to other scaffolds. The results strongly suggest the importance of preclinical evaluation of bone scaffolds for their cellular compatibility. Furthermore, the bone regenerative potential of HAP block with ADSCs was evaluated in an ex vivo bone defect model developed using patient derived trabecular bone explants. The explants were cultured for 45 days in vitro and bone formation was assessed by expression of osteogenic genes, ALP secretion, and high resolution computed tomography. Our findings confirmed active bone repair process in ex vivo settings. Addition of ADSCs significantly accelerated the repair process and improved bone microarchitecture. This ex vivo bone defect model can emerge as a viable alternative to animal experimentation and also as a potent tool to evaluate patient specific bone therapeutics under controlled conditions.

Biofunctionalized Electrospun Vascular Scaffolds for Enhanced Antithrombotic Properties and In Situ Endothelialization

The development of innovative vascular substitutes has become increasingly significant due to the prevalence of vascular diseases. In this study, we designed a biofunctionalized electrospun vascular scaffold by chemically conjugating heparin molecules as an antithrombotic agent with an endothelial cell (EC)-specific antibody to promote in situ endothelialization. To optimize this biofunctionalized electrospun vascular scaffolding system, we examined various parameters, including material compositions, cross-linker concentrations, and cross-linking and conjugation processes. The findings revealed that a higher degree of heparin conjugation onto the vascular scaffold resulted in improved antithrombotic properties, as confirmed by the platelet adhesion test. Additionally, the flow chamber study demonstrated that the EC-specific antibody immobilization enhanced the scaffold's EC-capturing capability compared to a nonconjugated vascular scaffold. The optimized biofunctionalized vascular scaffolds also displayed exceptional mechanical properties, such as suture retention strength and tensile properties. Our research demonstrated that the biofunctionalized vascular scaffolds and the directed immobilization of bioactive molecules could provide the necessary elements for successful acellular vascular tissue engineering applications.

The Osteogenic Role of Biomaterials Combined with Human-Derived Dental Stem Cells in Bone Tissue Regeneration

The use of stem cells in regenerative medicine had great potential for clinical applications. However, cell delivery strategies have critical importance in stimulating the differentiation of stem cells and enhancing their potential to regenerate damaged tissues. Different strategies have been used to investigate the osteogenic potential of dental stem cells in conjunction with biomaterials through in vitro and in vivo studies. Osteogenesis has a broad implication in regenerative medicine, particularly for maxillofacial defects. This review summarizes some of the most recent developments in the field of tissue engineering using dental stem cells.

Acellular Tissue-Engineered Vascular Grafts from Polymers: Methods, Achievements, Characterization, and Challenges

Extensive and permanent damage to the vasculature leading to different pathogenesis calls for developing innovative therapeutics, including drugs, medical devices, and cell therapies. Innovative strategies to engineer bioartificial/biomimetic vessels have been extensively exploited as an effective replacement for vessels that have seriously malfunctioned. However, further studies in polymer chemistry, additive manufacturing, and rapid prototyping are required to generate highly engineered vascular segments that can be effectively integrated into the existing vasculature of patients. One recently developed approach involves designing and fabricating acellular vessel equivalents from novel polymeric materials. This review aims to assess the design criteria, engineering factors, and innovative approaches for the fabrication and characterization of biomimetic macro- and micro-scale vessels. At the same time, the engineering correlation between the physical properties of the polymer and biological functionalities of multiscale acellular vascular segments are thoroughly elucidated. Moreover, several emerging characterization techniques for probing the mechanical properties of tissue-engineered vascular grafts are revealed. Finally, significant challenges to the clinical transformation of the highly promising engineered vessels derived from polymers are identified, and unique perspectives on future research directions are presented.

In Vivo Comparison of Synthetic Macroporous Filamentous and Sponge-like Skin Substitute Matrices Reveals Morphometric Features of the Foreign Body Reaction According to 3D Biomaterial Designs

Synthetic macroporous biomaterials are widely used in the field of skin tissue engineering to mimic membrane functions of the native dermis. Biomaterial designs can be subclassified with respect to their shape in fibrous designs, namely fibers, meshes or fleeces, respectively, and porous designs, such as sponges and foams. However, synthetic matrices often have limitations regarding unfavorable foreign body responses (FBRs). Severe FBRs can result in unfavorable disintegration and rejection of an implant, whereas mild FBRs can lead to an acceptable integration of a biomaterial. In this context, comparative in vivo studies of different three-dimensional (3D) matrix designs are rare. Especially, the differences regarding FBRs between synthetically derived filamentous fleeces and sponge-like constructs are unknown. In the present study, the FBRs on two 3D matrix designs were explored after 25 days of subcutaneous implantation in a porcine model. Cellular reactions were quantified histopathologically to investigate in which way the FBR is influenced by the biomaterial architecture. Our results show that FBR metrics (polymorph-nucleated cells and fibrotic reactions) were significantly affected according to the matrix designs. Our findings contribute to a better understanding of the 3D matrix tissue interactions and can be useful for future developments of synthetically derived skin substitute biomaterials.

3D Bioprinted cancer models: Revolutionizing personalized cancer therapy

After cardiovascular disease, cancer is the leading cause of death worldwide with devastating health and economic consequences, particularly in developing countries. Inter-patient variations in anti-cancer drug responses further limit the success of therapeutic interventions. Therefore, personalized medicines approach is key for this patient group involving molecular and genetic screening and appropriate stratification of patients to treatment regimen that they will respond to. However, the knowledge related to adequate risk stratification methods identifying patients who will respond to specific anti-cancer agents is still lacking in many cancer types. Recent advancements in three-dimensional (3D) bioprinting technology, have been extensively used to generate representative bioengineered tumor in vitro models, which recapitulate the human tumor tissues and microenvironment for high-throughput drug screening. Bioprinting process involves the precise deposition of multiple layers of different cell types in combination with biomaterials capable of generating 3D bioengineered tissues based on a computer-aided design. Bioprinted cancer models containing patient-derived cancer and stromal cells together with genetic material, extracellular matrix proteins and growth factors, represent a promising approach for personalized cancer therapy screening. Both natural and synthetic biopolymers have been utilized to support the proliferation of cells and biological material within the personalized tumor models/implants. These models can provide a physiologically pertinent cell-cell and cell-matrix interactions by mimicking the 3D heterogeneity of real tumors. Here, we reviewed the potential applications of 3D bioprinted tumor constructs as personalized in vitro models in anticancer drug screening and in the establishment of precision treatment regimens.

Construction of tissue-engineered bone with differentiated osteoblasts from adipose-derived stem cell and coral scaffolds at an ectopic site

Cell sheets from bone marrow mesenchymal stem cells (BMSC) have been widely used in the field of bone tissue engineering, although their source remains a challenging issue. In this study, adipose-derived stem cells (ADSC) were induced to differentiate into osteoblasts, and the incorporation of coral scaffolds with ADSC sheets for bone formation at an ectopic site was also investigated. First, ADSC isolated from inguinal adipose tissue of New Zealand rabbits were cultured for two weeks without passaging under osteogenic induction, and the microstructures of cell sheets were analysed by histological and scanning electron microscope (EM) observation. In addition, the activity of alkaline phosphatase (ALP) and alizarin red staining was also measured to detect their osteogenic ability. Subsequently, ADSC were proved to be able to proliferate well when seeded on the coral scaffolds. Next, coral scaffolds were wrapped in cell sheets to prepare sheet-coral complexes, which were implanted into subcutaneous pockets in nude mice. At eight weeks after implantation, gross examination, microcomputed tomography (MicroCT), and histological analysis were investigated to assess new bone formation. MicroCT scanning and histological analysis showed that there was more highly dense tissue formed in the complex group than control group (p=0.0004). These results indicated that osteoblastic ADSC sheets could be used to construct engineered bone and the incorporation of coral scaffolds with ADSC sheets significantly improved bone formation, providing a newly approach for bone tissue engineering.

Stem cells and new intervention measures as emerging therapy in cardiac surgery

Cardiovascular disease (CVD) presents a great burden for elderly patients, their caregivers, and health systems. Structural and functional alterations of vessels accumulate throughout life, culminating in increased risk of developing CVD. Several inflammatory pathway are involved in vascular ageing. The growing elderly population worldwide highlights the need to understand how aging promotes CVD in order to develop new strategies to confront this challenge. In this review we analyzed the role of stem cells and new intervention measures as emerging drugs for vascular aging.

Intra-Articular Injection of Stromal Cell-Derived Factor 1α Promotes Meniscal Healing via Macrophage and Mesenchymal Stem Cell Accumulation in a Rat Meniscal Defect Model

The stromal-cell-derived factor-1α (SDF-1) is well-known for playing important roles in the regeneration of tissue by enhancing cell migration. However, the effect of SDF-1 in meniscal healing remains unknown. The purpose of this study is to investigate the effects of intra-articular injection of SDF-1 on meniscus healing in a rat meniscal defect model. The intra-articular SDF-1 injection was performed at meniscectomy and one week later. Macroscopic and histological assessments of the reparative meniscus were conducted at one, two and six weeks after meniscectomy in rats. In the macroscopic evaluation, the SDF-1 group showed an increase in the size of the reparative meniscus at six weeks after meniscectomy compared to the phosphate-buffered saline (PBS) injection (no-treatment) group. Histological findings showed that intra-articular injection of SDF-1 enhanced the migration of macrophages to the site of the regenerative meniscus at one and two weeks after meniscectomy. CD68- and CD163-positive cells in the SDF-1 group at one week after meniscectomy were significantly higher than in the no-treatment group. CD163-positive cells in the SDF-1 group at two weeks were significantly higher than in the no-treatment group. At one week after meniscectomy, there were cells expressing mesenchymal-stem-cell-related markers in the SDF-1 group. These results indicate the potential of regenerative healing of the meniscus by SDF-1 injection via macrophage and mesenchymal stem cell accumulation. In the present study, intra-articular administration of SDF-1 contributed to meniscal healing via macrophage, CD90-positive cell and CD105-positive cell accumulation in a rat meniscal defect model. The SDF-1–CXCR4 pathway plays an important role in the meniscal healing process. For potential clinical translation, SDF-1 injection therapy seems to be a promising approach for the biological augmentation in meniscal injury areas to enhance healing capacity.

Tissue engineering in female pelvic floor reconstruction

Pelvic organ prolapse is a common and frequently occurring disease in middle-aged and elderly women. Mesh implantation is an ideal surgical treatment. The polypropylene mesh commonly used in clinical practice has good mechanical properties, but there are long-term complications. The application of tissue engineering technology in the treatment of pelvic organ prolapse disease can not only meet the mechanical requirements of pelvic floor support, but also be more biocompatible than traditional polypropylene mesh, and can promote tissue repair to a certain extent. In this paper, the progress of tissue engineering was summarized to understand the application of tissue engineering in the treatment of pelvic organ prolapse disease and will help in research.

Preparation and effect of lyophilized platelet-rich fibrin on the osteogenic potential of bone marrow mesenchymal stem cells in vitro and in vivo

Objectives

The goal of this study was to prepare lyophilized platelet-rich fibrin (L-PRF) and analyze the combined use of L-PRF and osteogenic bone marrow mesenchymal stem cell (BMSC) sheet fragments for bone tissue engineering via in vivo injection.

Methods

First, fresh PRF (F-PRF) was lyophilized to prepare L-PRF, the characteristics of which were examined through gross morphological, and histological and microstructural observations. In addition, the kinetics of growth factor release from L-PRF and F-PRF were also determined by enzyme-linked immunosorbent assay (ELISA). Subsequently, after assessing the proliferation and osteogenic differentiation of BMSCs exposed to L-PRF or F-PRF in vitro, we subcutaneously injected BMSC sheet fragments with L-PRF or F-PRF into nude mice and assessed bone formation through microcomputed tomography and histological analyses.

Results

We observed that L-PRF released growth factors that favored BMSC proliferation and osteogenic differentiation in vitro. The combined use of L-PRF and osteogenic BMSC sheet fragments enabled bone tissue regeneration in vivo, and no significant difference between the F-PRF and L-PRF groups was observed (P = 0.24).

Conclusions

The results of this study demonstrate that the combined use of L-PRF and osteogenic BMSC sheets may have potential in the fabrication of engineered bone.

The Efficacy of a Scaffold-free Bio 3D Conduit Developed from Autologous Dermal Fibroblasts on Peripheral Nerve Regeneration in a Canine Ulnar Nerve Injury Model: A Preclinical Proof-of-Concept Study

Autologous nerve grafting is widely accepted as the gold standard treatment for segmental nerve defects. To overcome the inevitable disadvantages of the original method, alternative methods such as the tubulization technique have been developed. Several studies have investigated the characteristics of an ideal nerve conduit in terms of supportive cells, scaffolds, growth factors, and vascularity. Previously, we confirmed that biological scaffold-free conduits fabricated from human dermal fibroblasts promote nerve regeneration in a rat sciatic nerve injury model. The purpose of this study is to evaluate the feasibility of biological scaffold-free conduits composed of autologous dermal fibroblasts using a large-animal model. Six male beagle dogs were used in this study. Eight weeks before surgery, dermal fibroblasts were harvested from their groin skin and grown in culture. Bio 3D conduits were assembled from proliferating dermal fibroblasts using a Bio 3D printer. The ulnar nerve in each dog’s forelimb was exposed under general anesthesia and sharply cut to create a 5 mm interstump gap, which was bridged by the prepared 8 mm Bio 3D conduit. Ten weeks after surgery, nerve regeneration was investigated. Electrophysiological studies detected compound muscle action potentials (CMAPs) of the hypothenar muscles and motor nerve conduction velocity (MNCV) in all animals. Macroscopic observation showed regenerated ulnar nerves. Low-level hypothenar muscle atrophy was confirmed. Immunohistochemical, histological, and morphometric studies confirmed the existence of many myelinated axons through the Bio 3D conduit. No severe adverse event was reported. Hypothenar muscles were re-innervated by regenerated nerve fibers through the Bio 3D conduit. The scaffold-free Bio 3D conduit fabricated from autologous dermal fibroblasts is effective for nerve regeneration in a canine ulnar nerve injury model. This technology was feasible as a treatment for peripheral nerve injury and segmental nerve defects in a preclinical setting.

Macroporous hydrogels derived from aqueous dynamic phase separation

A method to generate injectable macroporous hydrogels based on partitioning of polyethylene glycol (PEG) and high viscous polysaccharides is presented. Step growth polymerization of PEG was used to initiate a phase separation and the formation of a connected macroporous network with tunable dimensions. The possibilities and physical properties of this new category of materials were examined, and then applied to address some challenges in neural engineering. First, non-degradable macroporous gels were shown to support rapid neurite extension from encapsulated dorsal root ganglia (DRGs) with unprecedented long-term stability. Then, dissociated primary rat cortical neurons could be encapsulated with >95% viability, and extended neurites at the fast rate of ≈100 μm/day and formed synapses, resulting in functional, highly viable and long-term stable 3D neural networks in the synthetic extracellular matrix (ECM). Adhesion cues were found unnecessary provided the gels have optimal physical properties. Normal electrophysiological properties were confirmed on 3D cultured mouse hippocampal neurons. Finally, the macroporous gels supported axonal growth in a rat sciatic nerve injury model when used as a conduit filling. The combination of injectability, tunable pore size, stability, connectivity, transparency, cytocompatibility and biocompatibility, makes this new class of materials attractive for a wide range of applications.

The multiple functions of melatonin in regenerative medicine

Melatonin research has been experiencing hyper growth in the last two decades; this relates to its numerous physiological functions including anti-inflammation, oncostasis, circadian and endocrine rhythm regulation, and its potent antioxidant activity. Recently, a large number of studies have focused on the role of melatonin in the regeneration of cells or tissues after their partial loss. In this review, we discuss the recent findings on the molecular involvement of melatonin in the regeneration of various tissues including the nervous system, liver, bone, kidney, bladder, skin, and muscle, among others.

Trans-differentiation of human adipose-derived mesenchymal stem cells into cardiomyocyte-like cells on decellularized bovine myocardial extracellular matrix-based films

In this study, we aimed at fabricating decellularized bovine myocardial extracellular matrix-based films (dMEbF) for cardiac tissue engineering (CTE). The decellularization process was carried out utilizing four consecutive stages including hypotonic treatment, detergent treatment, enzymatic digestion and decontamination, respectively. In order to fabricate the dMEbF, dBM were digested with pepsin and gelation process was conducted. dMEbF were then crosslinked with N-hydroxysuccinimide/1-Ethyl-3-(3-dimethylaminopropyl)-carbodiimide (NHS/EDC) to increase their durability. Nuclear contents of native BM and decellularized BM (dBM) tissues were determined with DNA content analysis and agarose-gel electrophoresis. Cell viability on dMEbF for 3rd, 7th, and 14th days was assessed by MTT assay. Cell attachment on dMEbF was also studied by scanning electron microscopy. Trans-differentiation capacity of human adipose-derived mesenchymal stem cells (hAMSCs) into cardiomyocyte-like cells on dMEbF were also evaluated by histochemical and immunohistochemical analyses. DNA contents for native and dBM were, respectively, found as 886.11 ± 164.85 and 47.66 ± 0.09 ng/mg dry weight, indicating a successful decellularization process. The results of glycosaminoglycan and hydroxyproline assay, and sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE), performed in order to characterize the extracellular matrix (ECM) composition of native and dBM tissue, showed that the BM matrix was not damaged during the proposed method. Lastly, regarding the histological study, dMEbF not only mimics native ECM, but also induces the stem cells into cardiomyocyte-like cells phenotype which brings it the potential of use in CTE.

Cell-Free Strategies for Repair and Regeneration of Meniscus Injuries through the Recruitment of Endogenous Stem/Progenitor Cells

The meniscus plays a vital role in protecting the articular cartilage of the knee joint. The inner two-thirds of the meniscus are avascular, and injuries to this region often fail to heal without intervention. The use of tissue engineering and regenerative medicine techniques may offer novel and effective approaches to repairing meniscal injuries. Meniscal tissue engineering and regenerative medicine typically use one of two techniques, cell-based or cell-free. While numerous cell-based strategies have been applied to repair and regenerate meniscal defects, these techniques possess certain limitations including cellular contamination and an increased risk of disease transmission. Cell-free strategies attempt to repair and regenerate the injured tissues by recruiting endogenous stem/progenitor cells. Cell-free strategies avoid several of the disadvantages of cell-based techniques and, therefore, may have a wider clinical application. This review first compares cell-based to cell-free techniques. Next, it summarizes potential sources for endogenous stem/progenitor cells. Finally, it discusses important recruitment factors for meniscal repair and regeneration. In conclusion, cell-free techniques, which focus on the recruitment of endogenous stem and progenitor cells, are growing in efficacy and may play a critical role in the future of meniscal repair and regeneration.

Creating a 3D microenvironment for monocyte cultivation: ECM-mimicking hydrogels based on gelatine and hyaluronic acid derivatives

Macrophages play a critical role in the initial response to foreign materials in the body. As most biomaterial-based implantable devices would be treated as a foreign body by the immune system, there is a need for systems that can establish a favourable interaction between the implanted biomaterial and the host. Herein, we describe such a system that can be used as an ECM-like microenvironment for macrophage polarization. The hydrogel system was designed to provide a co-crosslinkable microenvironment containing both protein and glycosaminoglycan components, a hydroxyphenyl derivative of gelatine (GTN-HPA) and tyraminated hyaluronic acid (HA-TA). Both polymers can undergo a crosslinking reaction between polymer chains via the same polymerisation initiation system where the polymer network is formed by crosslinks between phenols in GTN-HPA and HA-TA. The mechanical properties and swelling of the hydrogel can be easily controlled as a function of the crosslinking mode and by the ratio of GTN-HPA and HA-TA compounds used. THP-1 monocytes were successfully encapsulated in the gels and cultured for up to 28 days. Cells exhibited higher metabolic activity when encapsulated in softer hydrogels (E ≈ 10 kPa) compared to stiffer (E ≈ 20 kPa) material in which monocytes tended to form large clusters. Encapsulation of monocytes in the material with HA-TA content enhanced the expression of macrophage-related genes. We demonstrated a co-crosslinkable GTN-HPA and HA-TA matrix microenvironment that is suitable for in vitro micro tissue model applications.

Human platelet lysate supports the formation of robust human periodontal ligament cell sheets

The use of stem cell-derived sheets has become increasingly common in a wide variety of biomedical applications. Although substantial evidence has demonstrated that human platelet lysate (PL) can be used for therapeutic cell expansion, either as a substitute for or as a supplement to xenogeneic fetal bovine serum (FBS), its impact on cell sheet production remains largely unexplored. In this study, we manufactured periodontal ligament stem cell (PDLSC) sheets in vitro by incubating PDLSCs in sheet-induction media supplemented with various ratios of PL and FBS, i.e. 10% PL without FBS, 7.5% PL + 2.5% FBS, 5% PL + 5% FBS, 2.5% PL + 7.5% FBS or 10% FBS without PL. Cultures with the addition of all the designed supplements led to successful cell sheet production. In addition, all the resultant cellular materials exhibited similar expression profiles of matrix-related genes and proteins, such as collagen I, fibronectin and integrin β1. Interestingly, the cell components within sheets generated by media containing both PL and FBS exhibited improved osteogenic potential. Following in vivo transplantation, all sheets supported significant new bone formation. Our data suggest that robust PDLSC sheets can be produced by applying PL as either an alternative or an adjuvant to FBS. Further examination of the relevant influences of human PL that benefit cell behaviour and matrix production will pave the way towards optimized and standardized conditions for cell sheet production.

The combination of stem cells and tissue engineering: an advanced strategy for blood vessels regeneration and vascular disease treatment

Over the past years, vascular diseases have continued to threaten human health and increase financial burdens worldwide. Transplantation of allogeneic and autologous blood vessels is the most convenient treatment. However, it could not be applied generally due to the scarcity of donors and the patient’s condition. Developments in tissue engineering are contributing greatly with regard to this urgent need for blood vessels. Tissue engineering-derived blood vessels are promising alternatives for patients with aortic dissection/aneurysm. The aim of this review is to show the importance of advances in biomaterials development for the treatment of vascular disease. We also provide a comprehensive overview of the current status of tissue reconstruction from stem cells and transplantable cellular scaffold constructs, focusing on the combination of stem cells and tissue engineering for blood vessel regeneration and vascular disease treatment.

Tension stimulation drives tissue formation in scaffold-free systems

Scaffold-free systems have emerged as viable approaches for engineering load-bearing tissues. However, the tensile properties of engineered tissues have remained far below the values for native tissue. Here, by using self-assembled articular cartilage as a model to examine the effects of intermittent and continuous tension stimulation on tissue formation, we show that the application of tension alone, or in combination with matrix remodelling and synthesis agents, leads to neocartilage with tensile properties approaching those of native tissue. Implantation of tension-stimulated tissues results in neotissues that are morphologically reminiscent of native cartilage. We also show that tension stimulation can be translated to a human cell source to generate anisotropic human neocartilage with enhanced tensile properties. Tension stimulation, which results in nearly sixfold improvements in tensile properties over unstimulated controls, may allow the engineering of mechanically robust biological replacements of native tissue.

Anisotropic Materials for Skeletal-Muscle-Tissue Engineering

Repair of damaged skeletal-muscle tissue is limited by the regenerative capacity of the native tissue. Current clinical approaches are not optimal for the treatment of large volumetric skeletal-muscle loss. As an alternative, tissue engineering represents a promising approach for the functional restoration of damaged muscle tissue. A typical tissue-engineering process involves the design and fabrication of a scaffold that closely mimics the native skeletal-muscle extracellular matrix (ECM), allowing organization of cells into a physiologically relevant 3D architecture. In particular, anisotropic materials that mimic the morphology of the native skeletal-muscle ECM, can be fabricated using various biocompatible materials to guide cell alignment, elongation, proliferation, and differentiation into myotubes. Here, an overview of fundamental concepts associated with muscle-tissue engineering and the current status of muscle-tissue-engineering approaches is provided. Recent advances in the development of anisotropic scaffolds with micro- or nanoscale features are reviewed, and how scaffold topographical, mechanical, and biochemical cues correlate to observed cellular function and phenotype development is examined. Finally, some recent developments in both the design and utility of anisotropic materials in skeletal-muscle-tissue engineering are highlighted, along with their potential impact on future research and clinical applications.

Cell-Based Strategies for Meniscus Tissue Engineering

Meniscus injuries remain a significant challenge due to the poor healing potential of the inner avascular zone. Following a series of studies and clinical trials, tissue engineering is considered a promising prospect for meniscus repair and regeneration. As one of the key factors in tissue engineering, cells are believed to be highly beneficial in generating bionic meniscus structures to replace injured ones in patients. Therefore, cell-based strategies for meniscus tissue engineering play a fundamental role in meniscal regeneration. According to current studies, the main cell-based strategies for meniscus tissue engineering are single cell type strategies; cell coculture strategies also were applied to meniscus tissue engineering. Likewise, on the one side, the zonal recapitulation strategies based on mimicking meniscal differing cells and internal architectures have received wide attentions. On the other side, cell self-assembling strategies without any scaffolds may be a better way to build a bionic meniscus. In this review, we primarily discuss cell seeds for meniscus tissue engineering and their application strategies. We also discuss recent advances and achievements in meniscus repair experiments that further improve our understanding of meniscus tissue engineering.

Microtissues in Cardiovascular Medicine: Regenerative Potential Based on a 3D Microenvironment

More people die annually from cardiovascular diseases than from any other cause. In particular, patients who suffer from myocardial infarction may be affected by ongoing adverse remodeling processes of the heart that may ultimately lead to heart failure. The introduction of stem and progenitor cell-based applications has raised substantial hope for reversing these processes and inducing cardiac regeneration. However, current stem cell therapies using single-cell suspensions have failed to demonstrate long-lasting efficacy due to the overall low retention rate after cell delivery to the myocardium. To overcome this obstacle, the concept of 3D cell culture techniques has been proposed to enhance therapeutic efficacy and cell engraftment based on the simulation of an in vivo-like microenvironment. Of great interest is the use of so-called microtissues or spheroids, which have evolved from their traditional role as in vitro models to their novel role as therapeutic agents. This review will provide an overview of the therapeutic potential of microtissues by addressing primarily cardiovascular regeneration. It will accentuate their advantages compared to other regenerative approaches and summarize the methods for generating clinically applicable microtissues. In addition, this review will illustrate the unique properties of the microenvironment within microtissues that makes them a promising next-generation therapeutic approach.

Addition of Adipose-Derived Stem Cells to Mesenchymal Stem Cell Sheets Improves Bone Formation at an Ectopic Site

To determine the effect of adipose-derived stem cells (ADSCs) added to bone marrow-derived mesenchymal stem cell (MSC) sheets on bone formation at an ectopic site. We isolated MSCs and ADSCs from the same rabbits. We then prepared MSC sheets for implantation with or without ADSCs subcutaneously in the backs of severe combined immunodeficiency (SCID) mice. We assessed bone formation at eight weeks after implantation by micro-computed tomography and histological analysis. In osteogenic medium, MSCs grew to form multilayer sheets containing many calcium nodules. MSC sheets without ADSCs formed bone-like tissue; although neo-bone and cartilage-like tissues were sparse and unevenly distributed by eight weeks after implantation. In comparison, MSC sheets with ADSCs promoted better bone regeneration as evidenced by the greater density of bone, increased mineral deposition, obvious formation of blood vessels, large number of interconnected ossified trabeculae and woven bone structures, and greater bone volume/total volume within the composite constructs. Our results indicate that although sheets of only MSCs have the potential to form tissue engineered bone at an ectopic site, the addition of ADSCs can significantly increase the osteogenic potential of MSC sheets. Thus, the combination of MSC sheets with ADSCs may be regarded as a promising therapeutic strategy to stimulate bone regeneration.

Advancing biomaterials of human origin for tissue engineering

Biomaterials have played an increasingly prominent role in the success of biomedical devices and in the development of tissue engineering, which seeks to unlock the regenerative potential innate to human tissues/organs in a state of deterioration and to restore or reestablish normal bodily function. Advances in our understanding of regenerative biomaterials and their roles in new tissue formation can potentially open a new frontier in the fast-growing field of regenerative medicine. Taking inspiration from the role and multi-component construction of native extracellular matrices (ECMs) for cell accommodation, the synthetic biomaterials produced today routinely incorporate biologically active components to define an artificial in vivo milieu with complex and dynamic interactions that foster and regulate stem cells, similar to the events occurring in a natural cellular microenvironment. The range and degree of biomaterial sophistication have also dramatically increased as more knowledge has accumulated through materials science, matrix biology and tissue engineering. However, achieving clinical translation and commercial success requires regenerative biomaterials to be not only efficacious and safe but also cost-effective and convenient for use and production. Utilizing biomaterials of human origin as building blocks for therapeutic purposes has provided a facilitated approach that closely mimics the critical aspects of natural tissue with regard to its physical and chemical properties for the orchestration of wound healing and tissue regeneration. In addition to directly using tissue transfers and transplants for repair, new applications of human-derived biomaterials are now focusing on the use of naturally occurring biomacromolecules, decellularized ECM scaffolds and autologous preparations rich in growth factors/non-expanded stem cells to either target acceleration/magnification of the body's own repair capacity or use nature's paradigms to create new tissues for restoration. In particular, there is increasing interest in separating ECMs into simplified functional domains and/or biopolymeric assemblies so that these components/constituents can be discretely exploited and manipulated for the production of bioscaffolds and new biomimetic biomaterials. Here, following an overview of tissue auto-/allo-transplantation, we discuss the recent trends and advances as well as the challenges and future directions in the evolution and application of human-derived biomaterials for reconstructive surgery and tissue engineering. In particular, we focus on an exploration of the structural, mechanical, biochemical and biological information present in native human tissue for bioengineering applications and to provide inspiration for the design of future biomaterials.

Two novel amino acid-coated super paramagnetic nanoparticles at low concentrations label and promote the proliferation of mesenchymal stem cells

We identified two amino acid-coated magnetic nanoparticles that promoted mesenchymal stem cell growth without the need for transfection agents by increasing the proportion of cells in the S phase.

Bioprinting for cancer research

Bioprinting offers the ability to create highly complex 3D architectures with living cells. This cutting-edge technique has significantly gained popularity and applicability in several fields. Bioprinting methods have been developed to effectively and rapidly pattern living cells, biological macromolecules, and biomaterials. These technologies hold great potential for applications in cancer research. Bioprinted cancer models represent a significant improvement over previous 2D models by mimicking 3D complexity and facilitating physiologically relevant cell-cell and cell-matrix interactions. Here we review bioprinting methods based on inkjet, microextrusion, and laser technologies and compare 3D cancer models with 2D cancer models. We discuss bioprinted models that mimic the tumor microenvironment, providing a platform for deeper understanding of cancer pathology, anticancer drug screening, and cancer treatment development.

Water-soluble photopolymerizable chitosan hydrogels for biofabrication via two-photon polymerization

Fabrication of three-dimensional (3D) hydrogel microenvironments with predefined geometry and porosity can facilitate important requirements in tissue engineering and regenerative medicine. Chitosan (CH) is well known as a biocompatible hydrogel with prospective biological properties for biomedical aims. So far, microstructuring of this soft material presents a great limitation for its application as functional supporting material for guided tissue formation. Enabling photopolymerization, chemically modified CH can be applied for the biofabrication of reproducible 3D scaffolds using rapid prototyping techniques like two-photon polymerization (2PP) or others. The application of this technique allows precise serial fabrication of computer-designed microstructure geometries by scanning a femtosecond laser beam within a photosensitive material. This work explores a new synthesis of water-soluble photosensitive chitosan and the fabrication of well-defined microstructures from the generated materials. To modulate the mechanical and biochemical properties of the material, CH was combined and cross-linked with synthetic poly(ethylene glycol) diacrylate. For a biological adaption to the in vivo situation, CH was covalently crosslinked with a photosensitive modified vascular endothelial growth factor (VEGF). Performed in vitro studies reveal that modified CH is biocompatible. VEGF enhances CH bioactivity. Furthermore, a 3D CH scaffold can be successfully seeded with cells. Therefore, the established CH holds great promise for future applications in tissue engineering.

The powerful functions of peptide-based bioactive matrices for regenerative medicine

In an effort to develop bioactive matrices for regenerative medicine, peptides have been used widely to promote interactions with cells and elicit desired behaviors in vivo. This paper describes strategies that utilize peptide-based molecules as building blocks to create supramolecular nanostructures that emulate not only the architecture but also the chemistry of the extracellular matrix in mammalian biology. After initiating a desired regenerative response in vivo, the innate biodegradability of these systems allow for the natural biological processes to take over in order to promote formation of a new tissue without leaving a trace of the nonnatural components. These bioactive matrices can either bind or mimic growth factors or other protein ligands to elicit a cellular response, promote specific mechano-biological responses, and also guide the migration of cells with programmed directionality. In vivo applications discussed in this review using peptide-based matrices include the regeneration of axons after spinal cord injury, regeneration of bone, and the formation of blood vessels in ischemic muscle as a therapy in peripheral arterial disease and cardiovascular diseases.

Concise review: workshop review: understanding and assessing the risks of stem cell-based therapies

The field of stem cell therapeutics is moving ever closer to widespread application in the clinic. However, despite the undoubted potential held by these therapies, the balance between risk and benefit remains difficult to predict. As in any new field, a lack of previous application in man and gaps in the underlying science mean that regulators and investigators continue to look for a balance between minimizing potential risk and ensuring therapies are not needlessly kept from patients. Here, we attempt to identify the important safety issues, assessing the current advances in scientific knowledge and how they may translate to clinical therapeutic strategies in the identification and management of these risks. We also investigate the tools and techniques currently available to researchers during preclinical and clinical development of stem cell products, their utility and limitations, and how these tools may be strategically used in the development of these therapies. We conclude that ensuring safety through cutting-edge science and robust assays, coupled with regular and open discussions between regulators and academic/industrial investigators, is likely to prove the most fruitful route to ensuring the safest possible development of new products.

Thermoforming techniques for manufacturing porous scaffolds for application in 3D cell cultivation

Within the scientific community, there is an increasing demand to apply advanced cell cultivation substrates with increased physiological functionalities for studying spatially defined cellular interactions. Porous polymeric scaffolds are utilized for mimicking an organ-like structure or engineering complex tissues and have become a key element for three-dimensional (3D) cell cultivation in the meantime. As a consequence, efficient 3D scaffold fabrication methods play an important role in modern biotechnology. Here, we present a novel thermoforming procedure for manufacturing porous 3D scaffolds from permeable materials. We address the issue of precise thermoforming of porous polymer foils by using multilayer polymer thermoforming technology. This technology offers a new method for structuring porous polymer foils that are otherwise available for non-porous polymers only. We successfully manufactured 3D scaffolds from solvent casted and phase separated polylactic acid (PLA) foils and investigated their biocompatibility and basic cellular performance. The HepG2 cell culture in PLA scaffold has shown enhanced albumin secretion rate in comparison to a previously reported polycarbonate based scaffold with similar geometry.

Digital microfluidics for automated hanging drop cell spheroid culture

Cell spheroids are multicellular aggregates, grown in vitro, that mimic the three-dimensional morphology of physiological tissues. Although there are numerous benefits to using spheroids in cell-based assays, the adoption of spheroids in routine biomedical research has been limited, in part, by the tedious workflow associated with spheroid formation and analysis. Here we describe a digital microfluidic platform that has been developed to automate liquid-handling protocols for the formation, maintenance, and analysis of multicellular spheroids in hanging drop culture. We show that droplets of liquid can be added to and extracted from through-holes, or "wells," and fabricated in the bottom plate of a digital microfluidic device, enabling the formation and assaying of hanging drops. Using this digital microfluidic platform, spheroids of mouse mesenchymal stem cells were formed and maintained in situ for 72 h, exhibiting good viability (>90%) and size uniformity (% coefficient of variation <10% intraexperiment, <20% interexperiment). A proof-of-principle drug screen was performed on human colorectal adenocarcinoma spheroids to demonstrate the ability to recapitulate physiologically relevant phenomena such as insulin-induced drug resistance. With automatable and flexible liquid handling, and a wide range of in situ sample preparation and analysis capabilities, the digital microfluidic platform provides a viable tool for automating cell spheroid culture and analysis.

Osteoblastic mesenchymal stem cell sheet combined with Choukroun platelet-rich fibrin induces bone formation at an ectopic site

AIMS

To analyze the effects of platelet-rich fibrin (PRF) on mesenchymal stem cells (MSCs) in vitro and investigate in vivo bone formation by MSC sheets with PRF.

MATERIALS AND METHODS

Cell proliferation and expression of osteogenesis-related genes within MSC sheets were assessed upon exposure to PRF from the same donors. We then injected MSC sheet fragments with or without PRF subcutaneously in nude mice and assessed bone formation by micro-computed tomography and histological analyses.

RESULTS

PRF significantly stimulated MSC proliferation and osteogenesis in vitro. MSC sheets injected with or without PRF formed new bone, but those with PRF produced significantly more and denser bone.

CONCLUSIONS

MSC sheets can be used to generate tissue engineered bone upon injection, and PRF increases the osteogenic capacity of MSC sheets in vitro and in vivo.

Tissue engineering: construction of a multicellular 3D scaffold for the delivery of layered cell sheets

Many tissues, such as the adult human hearts, are unable to adequately regenerate after damage.(2,3) Strategies in tissue engineering propose innovations to assist the body in recovery and repair. For example, TE approaches may be able to attenuate heart remodeling after myocardial infarction (MI) and possibly increase total heart function to a near normal pre-MI level.(4) As with any functional tissue, successful regeneration of cardiac tissue involves the proper delivery of multiple cell types with environmental cues favoring integration and survival of the implanted cell/tissue graft. Engineered tissues should address multiple parameters including: soluble signals, cell-to-cell interactions, and matrix materials evaluated as delivery vehicles, their effects on cell survival, material strength, and facilitation of cell-to-tissue organization. Studies employing the direct injection of graft cells only ignore these essential elements.(2,5,6) A tissue design combining these ingredients has yet to be developed. Here, we present an example of integrated designs using layering of patterned cell sheets with two distinct types of biological-derived materials containing the target organ cell type and endothelial cells for enhancing new vessels formation in the "tissue". Although these studies focus on the generation of heart-like tissue, this tissue design can be applied to many organs other than heart with minimal design and material changes, and is meant to be an off-the-shelf product for regenerative therapies. The protocol contains five detailed steps. A temperature sensitive Poly(N-isopropylacrylamide) (pNIPAAM) is used to coat tissue culture dishes. Then, tissue specific cells are cultured on the surface of the coated plates/micropattern surfaces to form cell sheets with strong lateral adhesions. Thirdly, a base matrix is created for the tissue by combining porous matrix with neovascular permissive hydrogels and endothelial cells. Finally, the cell sheets are lifted from the pNIPAAM coated dishes and transferred to the base element, making the complete construct.

Synthesis, Characterization, and Osteoblastic Cell Culture of Poly(L-co-D,L-lactide-co-trimethylene carbonate) Scaffolds

Lactide-based polymers have been widely investigated as materials for tissue engineering. However, characteristics such as low flexibility and elongation tend to limit particular applications, although these can be enhanced by adding plasticizers such as trimethylene carbonate (TMC) to the polymer chain of the copolymer poly(L-lactide-co-D,L-lactide) (PLDLA). The aim of this work was to synthesize and characterize a terpolymer of L-lactide, D,L-lactide, and TMC. The polymers were synthesized from 30% TMC by bulk polymerization and resulted in an average molar mass >10⁵ g/mol. Thermal investigation of PLDLA-TMC showed a decrease in the glass transition and onset temperatures compared to PLDLA. PLDLA-TMC scaffolds stimulated the proliferation and normal phenotypic manifestations of cultured osteoblasts. These results show that it was possible to produce a terpolymer from L-lactide, D,L-lactide, and TMC. Scaffolds of this terpolymer had important characteristics that could be useful for applications in bone tissue engineering.

Short Term Culture of Human Mesenchymal Stem Cells with Commercial Osteoconductive Carriers Provides Unique Insights into Biocompatibility

For spinal fusions and the treatment of non-union fractures, biological substrates, scaffolds, or carriers often are applied as a graft to support regeneration of bone. The selection of an appropriate material critically influences cellular function and, ultimately, patient outcomes. Human bone marrow mesenchymal stem cells (BMSCs) are regarded as a critical component of bone healing. However, the interactions of BMSCs and commercial bone matrices are poorly reported. BMSCs were cultured with several commercially available bone substrates (allograft, demineralized bone matrix (DBM), collagen, and various forms of calcium phosphates) for 48 h to understand their response to graft materials during surgical preparation and the first days following implantation (cell retention, gene expression, pH). At 30 and 60 min, bone chips and inorganic substrates supported significantly more cell retention than other materials, while collagen-containing materials became soluble and lost their structure. At 48 h, cells bound to β-tricalcium phosphate-hydroxyapatite (βTCP-HA) and porous hydroxyapatite (HA) granules exhibited osteogenic gene expression statistically similar to bone chips. Through 24 h, the DBM strip and βTCP-collagen became mildly acidic (pH 7.1–7.3), while the DBM poloxamer-putties demonstrated acidity (pH < 5) and the bioglass-containing carrier became basic (pH > 10). The dissolution of DBM and collagen led to a loss of cells, while excessive pH changes potentially diminish cell viability and metabolism. Extracts from DBM-poloxamers induced osteogenic gene expression at 48 h. This study highlights the role that biochemical and structural properties of biomaterials play in cellular function, potentially enhancing or diminishing the efficacy of the overall therapy.

Thermoresponsive hydrogels for cellular delivery

The delivery of living cells into a host body has emerged as a promising approach to treating a variety of different diseases and for tissue repair. However, one of the major obstacles for clinical success is to deliver the cells to the target tissue without losing control of cell fate and function after transplantation. Temperature-responsive biomaterials represent a promising vehicle to deliver cells noninvasively by injection of a liquid precursor, which undergoes a reversible phase transition at body temperature, thus, forming temperature-induced hydrogels in situ. The final material provides transplanted cells with a synthetic extracellular matrix, which retains the cells at the injection site, supports cell growth and mitigates migration. This mini review is intended to cover the fundamental physicochemical characteristics of these thermoresponsive biomaterials, and to examine the applications, with a focus on the recently developed cell-delivery systems for tissue engineering and cell therapy, including advantages, limitations and future challenges.

Trends in tissue engineering for blood vessels

Over the years, cardiovascular diseases continue to increase and affect not only human health but also the economic stability worldwide. The advancement in tissue engineering is contributing a lot in dealing with this immediate need of alleviating human health. Blood vessel diseases are considered as major cardiovascular health problems. Although blood vessel transplantation is the most convenient treatment, it has been delimited due to scarcity of donors and the patient's conditions. However, tissue-engineered blood vessels are promising alternatives as mode of treatment for blood vessel defects. The purpose of this paper is to show the importance of the advancement on biofabrication technology for treatment of soft tissue defects particularly for vascular tissues. This will also provide an overview and update on the current status of tissue reconstruction especially from autologous stem cells, scaffolds, and scaffold-free cellular transplantable constructs. The discussion of this paper will be focused on the historical view of cardiovascular tissue engineering and stem cell biology. The representative studies featured in this paper are limited within the last decade in order to trace the trend and evolution of techniques for blood vessel tissue engineering.

Tissue engineering as a potential alternative or adjunct to surgical reconstruction in treating pelvic organ prolapse

INTRODUCTION AND HYPOTHESIS

Cell-based tissue engineering strategies could potentially provide attractive alternatives to surgical reconstruction of native tissue or the use of surgical implants in treating pelvic organ prolapse (POP).

METHODS

Based on a search in PubMed, this review focuses on candidate cell types, scaffolds, and trophic factors used in studies examining cell-based tissue engineering strategies to treat POP, stress urinary incontinence (SUI), and the closely related field of hernias.

RESULTS

In contrast to the field of SUI, the use of cell-based tissue engineering strategies to treat POP are very sparsely explored, and only preclinical studies exist.

CONCLUSION

The available evidence suggests that the use of autologous muscle-derived cells, fibroblasts, or mesenchymal stem cells seeded on biocompatible, degradable, and potentially growth-promoting scaffolds could be an alternative to surgical reconstruction of native tissue or the use of conventional implants in treating POP. However, the vagina is a complex organ with great demands of functionality, and the perfect match of scaffold, cell, and trophic factor has yet to be found and tested in preclinical studies. Important issues such as safety and economy must also be addressed before this approach is ready for clinical studies.

Tissue engineering as a potential alternative or adjunct to surgical reconstruction in treating pelvic organ prolapse

INTRODUCTION AND HYPOTHESIS

Cell-based tissue engineering strategies could potentially provide attractive alternatives to surgical reconstruction of native tissue or the use of surgical implants in treating pelvic organ prolapse (POP).

METHODS

Based on a search in PubMed, this review focuses on candidate cell types, scaffolds, and trophic factors used in studies examining cell-based tissue engineering strategies to treat POP, stress urinary incontinence (SUI), and the closely related field of hernias.

RESULTS

In contrast to the field of SUI, the use of cell-based tissue engineering strategies to treat POP are very sparsely explored, and only preclinical studies exist.

CONCLUSION

The available evidence suggests that the use of autologous muscle-derived cells, fibroblasts, or mesenchymal stem cells seeded on biocompatible, degradable, and potentially growth-promoting scaffolds could be an alternative to surgical reconstruction of native tissue or the use of conventional implants in treating POP. However, the vagina is a complex organ with great demands of functionality, and the perfect match of scaffold, cell, and trophic factor has yet to be found and tested in preclinical studies. Important issues such as safety and economy must also be addressed before this approach is ready for clinical studies.

Stem cell-delivery therapeutics for periodontal tissue regeneration

Periodontitis, an inflammatory disease, is the most common cause of tooth loss in adults. Attempts to regenerate the complex system of tooth-supporting apparatus (i.e., the periodontal ligament, alveolar bone and root cementum) after loss/damage due to periodontitis have made some progress recently and provide a useful experimental model for the evaluation of future regenerative therapies. Concentrated efforts have now moved from the use of guided tissue/bone regeneration technology, a variety of growth factors and various bone grafts/substitutes toward the design and practice of endogenous regenerative technology by recruitment of host cells (cell homing) or stem cell-based therapeutics by transplantation of outside cells to enhance periodontal tissue regeneration and its biomechanical integration. This shift is driven by the general inability of conventional therapies to deliver satisfactory outcomes, particularly in cases where the disease has caused large tissue defects in the periodontium. Cell homing and cell transplantation are both scientifically meritorious approaches that show promise to completely and reliably reconstitute all tissue and connections damaged through periodontal disease, and hence research into both directions should continue. In view of periodontal regeneration by paradigms that unlock the body's innate regenerative potential has been reviewed elsewhere, this paper specifically explores and analyses the stem cell types and cell delivery strategies that have been or have the potential to be used as therapeutics in periodontal regenerative medicine, with particular emphasis placed on the efficacy and safety concerns of current stem cell-based periodontal therapies that may eventually enter into the clinic.