Three-dimensional spheroids of adipose-derived mesenchymal stem cells are potent initiators of blood vessel formation in porous polyurethane scaffolds

Breathing new life into tissue engineering: exploring cutting-edge vascularization strategies for skin substitutes

Tissue-engineered skin substitutes (TESS) emerged as a new therapeutic option to improve skin transplantation. However, establishing an adequate and rapid vascularization in TESS is a critical factor for their clinical application and successful engraftment in patients. Therefore, several methods have been applied to improve the vascularization of skin substitutes including (i) modifying the structural and physicochemical properties of dermal scaffolds; (ii) activating biological scaffolds with growth factor-releasing systems or gene vectors; and (iii) developing prevascularized skin substitutes by loading scaffolds with capillary-forming cells. This review provides a detailed overview of the most recent and important developments in the vascularization strategies for skin substitutes. On the one hand, we present cell-based approaches using stem cells, microvascular fragments, adipose tissue derived stromal vascular fraction, endothelial cells derived from blood and skin as well as other pro-angiogenic stimulation methods. On the other hand, we discuss how distinct 3D bioprinting techniques and microfluidics, miRNA manipulation, cell sheet engineering and photosynthetic scaffolds like GelMA, can enhance skin vascularization for clinical applications. Finally, we summarize and discuss the challenges and prospects of the currently available vascularization techniques that may serve as a steppingstone to a mainstream application of skin tissue engineering.

High hydrostatic pressure treatment for advanced tissue grafts in reconstructive head and neck surgery

The increasing importance of regenerative medicine has resulted in a growing need for advanced tissue replacement materials in head and neck surgery. Allo- and xenogenic graft processing is often time-consuming and can deteriorate the extracellular matrix (ECM). High hydrostatic pressure (HHP)-treatment could allow specific devitalization while retaining the essential properties of the ECM. Porcine connective tissue and cartilage were HHP-treated at 100-400 MPa for 10 min. Structural modifications following HHP-exposure were examined using electron microscopy, while devitalization was assessed through metabolism and cell death analyses. Furthermore, ECM alterations and decellularization were evaluated by histology, biomechanical testing, and DNA content analysis. Additionally, the inflammatory potential of HHP-treated tissue was evaluated in vivo using a dorsal skinfold chamber in a mouse model. The devitalization effects of HHP were dose-dependent, with a threshold identified at 200 MPa for fibroblasts and chondrocytes. At this pressure level, HHP induced structural alterations in cells, with a shift toward late-stage apoptosis. HHP-treatment preserved ECM structure and biomechanical properties, but did not remove cell debris from the tissue. This study observed a pressure-dependent increase of markers suggesting the occurrence of immunogenic cell death. In vivo investigations revealed an absence of inflammatory responses to HHP-treated tissue, indicating a favorable biological response to HHP. In conclusion, application of HHP devitalizes fibroblasts and chondrocytes at 200 MPa while retaining the essential properties of the ECM. Prospectively, HHP may simplify the preparation of allo- and xenogenic tissue replacement materials and increase the availability of grafts in head and neck surgery.

Mesenchymal Stem Cell Spheroids: A Promising Tool for Vascularized Tissue Regeneration

BACKGROUND

Mesenchymal stem cells (MSCs) are undifferentiated cells that can differentiate into specific cell lineages when exposed to the right conditions. The ability of MSCs to differentiate into particular cells is considered very important in biological research and clinical applications. MSC spheroids are clusters of MSCs cultured in three dimensions, which play an important role in enhancing the proliferation and differentiation of MSCs. MSCs can also participate in vascular formation by differentiating into endothelial cells and secreting paracrine factors. Vascularization ability is essential in impaired tissue repair and function recovery. Therefore, the vascularization ability of MSCs, which enhances angiogenesis and accelerates tissue healing has made MSCs a promising tool for tissue regeneration. However, MSC spheroids are a relatively new research field, and more research is needed to understand their full potential.

METHODS

In this review, we highlight the importance of MSC spheroids' vascularization ability in tissue engineering and regenerative medicine while providing the current status of studies on the MSC spheroids' vascularization and suggesting potential future research directions for MSC spheroids.

RESULTS

Studies both in vivo and in vitro have demonstrated MSC spheroids' capacity to develop into endothelial cells and stimulate vasculogenesis.

CONCLUSION

MSC spheroids show potential to enhance vascularization ability in tissue regeneration. Yet, further research is required to comprehensively understand the relationship between MSC spheroids and vascularization mechanisms.

A review of the therapeutic potential of dental stem cells as scaffold-free models for tissue engineering application

In the realm of regenerative medicine, tissue engineering has introduced innovative approaches to facilitate tissue regeneration. Specifically, in pulp tissue engineering, both scaffold-based and scaffold-free techniques have been applied. Relevant articles were meticulously chosen from PubMed, Scopus, and Google Scholar databases through a comprehensive search spanning from October 2022 to December 2022. Despite the inherent limitations of scaffolding, including inadequate mechanical strength for hard tissues, insufficient vents for vessel penetration, immunogenicity, and suboptimal reproducibility-especially with natural polymeric scaffolds-scaffold-free tissue engineering has garnered significant attention. This methodology employs three-dimensional (3D) cell aggregates such as spheroids and cell sheets with extracellular matrix, facilitating precise regeneration of target tissues. The choice of technique aside, stem cells play a pivotal role in tissue engineering, with dental stem cells emerging as particularly promising resources. Their pluripotent nature, non-invasive extraction process, and unique properties render them highly suitable for scaffold-free tissue engineering. This study delves into the latest advancements in leveraging dental stem cells and scaffold-free techniques for the regeneration of various tissues. This paper offers a comprehensive summary of recent developments in the utilization of dental stem cells and scaffold-free methods for tissue generation. It explores the potential of these approaches to advance tissue engineering and their effectiveness in therapies aimed at tissue regeneration.

Brain Homogenate of a Rat Model of Alzheimer's Disease Modifies the Secretome of 3D Cultured Periodontal Ligament Stem Cells: A Potential Neuroregenerative Therapy

Background

Alzheimer's disease (AD) is a progressive neurodegenerative disease leading to neuronal cell death and manifested by cognitive disorders and behavioral impairment. Mesenchymal stem cells (MSCs) are one of the most promising candidates to stimulate neuroregeneration and prevent disease progression. Optimization of MSC culturing protocols is a key strategy to increase the therapeutic potential of the secretome.

Objectives

Here, we investigated the effect of brain homogenate of a rat model of AD (BH-AD) on the enhancement of protein secretion in the secretome of periodontal ligament stem cells (PDLSCs) when cultured in a 3D environment. Moreover, the effect of this modified secretome was examined on neural cells to study the impact of the conditioned medium (CM) on stimulation of regeneration or immunomodulation in AD.

Methods

PDLSCs were isolated and characterized. Then, the spheroids of PDLSCs were generated in a modified 3D culture plate. PDLSCs-derived CM was prepared in the presence of BH-AD (PDLSCs-HCM) and the absence of it (PDLSCs-CM). The viability of C6 glioma cells was assessed after exposure to different concentrations of both CMs. Then, a proteomic analysis was performed on the CMs.

Results

Differentiation into adipocytes and high expression of MSCs markers verified the precise isolation of PDLSCs. The PDLSC spheroids were formed after 7 days of 3D culturing, and their viability was confirmed. The effect of CMs on C6 glioma cell viability showed that both CMs at low concentrations (> 20 mg/mL) had no cytotoxic effect on C6 neural cells. The results showed that PDLSCs-HCM contains higher concentrations of proteins compared to PDLSCs-CM, including Src-homology 2 domain (SH2)-containing PTPs (SHP-1) and muscle glycogen phosphorylase (PYGM) proteins. SHP-1 has a role in nerve regeneration, and PYGM is involved in glycogen metabolism.

Conclusions

The modified secretome derived from 3D cultured spheroids of PDLSCs treated by BH-AD as a reservoir of regenerating neural factors can serve as a potential source for AD treatment.

Biomimetic Surface Topography from the Rubus fruticosus Leaf as a Guidance of Angiogenesis in Tissue Engineering Applications

The promotion of angiogenesis is a fundamental step for efficient organ/tissue reconstitution and replacement. Thus, several strategies to promote vascularization of scaffolds were studied to satisfy this unsolved clinical need. The interface between cells and substrates is a determinant for the success of tissue engineering (TE) strategies. Substrate's topography is reported to play a key role in influencing endothelial cell behavior, namely, on its proliferation, metabolic activity, morphology, migration, and secretion of cytokines and chemokines. Therefore, surface topography of the biomaterial-based grafts is a crucial property that is considered in the development of a new TE approach. Herein, we hypothesize that the surface of Rubus fruticosus leaf plays a crucial role in driving angiogenesis since its architecture resembles the vascular structures at a biologically relevant size scale. For this, we produced biomimetic polycaprolactone (PCL) membranes (BpMs) replicating the surface topography of a R. fruticosus leaf by replica molding and nanoimprint lithography. Our results showed an enhanced performance in terms of proliferation of the human endothelial cell line on top of the BpM. Moreover, an asymmetric cellular spatial distribution among the surface of the BpM was observed. These cells seem to have higher density for longer time periods in the region that replicates the leaf veins. Finally, we assess the angiogenic capacity through a chick chorioallantoic membrane assay, revealing that BpMs are more prone to support angiogenesis than flat PCL membranes. We strongly believe that this strategy can bring new insights into developing TE strategies with an enhanced performance in terms of the vascular integration between the host and the scaffolds implanted.

The Dorsal Skinfold Chamber as a New Tympanic Membrane Wound Healing Model: Intravital Insights into the Pathophysiology of Epithelialized Wounds

BACKGROUND

Tympanic membrane perforations (TMPs) are a common complication of trauma and infection. Persisting perforations result from the unique location of the tympanic membrane. The wound is surrounded by air of the middle ear and the external auditory canal. The inadequate wound bed, growth factor, and blood supply lead to circular epithelialization of the perforation's edge and premature interruption of defect closure. Orthotopic animal models use mechanical or chemical tympanic membrane laceration to identify bioactive wound dressings and overcome premature epithelialization. However, all orthotopic models essentially lack repetitive visualization of the biomaterial-wound interface. Therefore, recent progress in 3D printing of customized wound dressings has not yet been transferred to the unique wound setup of the TMP. Here, we present a novel application for the mice dorsal skinfold chamber (DSC) with an epithelialized full-thickness defect as TMP model.

METHODS

A circular 2-mm defect was cut into the extended dorsal skinfold using a biopsy punch. The skinfold was either perforated through both skin layers without prior preparation or perforated on 1 side, following resection of the opposing skin layer. In both groups, the wound was sealed with a coverslip or left unclosed (n = 4). All animals were examined for epithelialization of the edge (histology), size of the perforation (planimetry), neovascularization (repetitive intravital fluorescence microscopy), and inflammation (immunohistology).

RESULTS

The edge of the perforation was overgrown by the cornified squamous epithelium in all pre-parations. Reduction in the perforation's size was enhanced by application of a coverslip. Microsurgical preparation before biopsy punch perforation and sealing with a coverslip enabled repetitive high-quality intravital fluorescence microscopy. However, spontaneous reduction of the perforation occurred frequently. Therefore, the direct biopsy punch perforation without microsurgical preparation was favorable: spontaneous reduction did not occur throughout 21 days. Moreover, the visualization of the neovascularization was sufficient in intravital microscopy.

CONCLUSIONS

The DSC full-thickness defect is a valuable supplement to orthotopic TMP models. Repetitive intravital microscopy of the epithelialized edge enables investigation of the underlying pathophysiology during the transition from the inflammation to the proliferation phase of wound healing. Using established analysis procedures, the present model provides an effective platform for the screening of bioactive materials and transferring progress in tissue engineering to the special conditions of tympanic membrane wound healing.

In Vitro Strategies to Vascularize 3D Physiologically Relevant Models

Vascularization of 3D models represents a major challenge of tissue engineering and a key prerequisite for their clinical and industrial application. The use of prevascularized models built from dedicated materials could solve some of the actual limitations, such as suboptimal integration of the bioconstructs within the host tissue, and would provide more in vivo-like perfusable tissue and organ-specific platforms. In the last decade, the fabrication of vascularized physiologically relevant 3D constructs has been attempted by numerous tissue engineering strategies, which are classified here in microfluidic technology, 3D coculture models, namely, spheroids and organoids, and biofabrication. In this review, the recent advancements in prevascularization techniques and the increasing use of natural and synthetic materials to build physiological organ-specific models are discussed. Current drawbacks of each technology, future perspectives, and translation of vascularized tissue constructs toward clinics, pharmaceutical field, and industry are also presented. By combining complementary strategies, these models are envisioned to be successfully used for regenerative medicine and drug development in a near future.

Diversity Models and Applications of 3D Breast Tumor-on-a-Chip

Breast disease is one of the critical diseases that plague females, as is known, breast cancer has high mortality, despite significant pathophysiological progress during the past few years. Novel diagnostic and therapeutic approaches are needed to break the stalemate. An organ-on-chip approach is considered due to its ability to repeat the real conditions found in the body on microfluidic chips, offsetting the shortcomings of traditional 2D culture and animal tests. In recent years, the organ-on-chip approach has shown diversity, recreating the structure and functional units of the real organs/tissues. The applications were also developed rapidly from the laboratory to the industrialized market. This review focuses on breast tumor-on-a-chip approaches concerning the diversity models and applications. The models are summarized and categorized by typical biological reconstitution, considering the design and fabrication of the various breast models. The breast tumor-on-a-chip approach is a typical representative of organ chips, which are one of the precedents in the market. The applications are roughly divided into two categories: fundamental mechanism research and biological medicine. Finally, we discuss the prospect and deficiencies of the emerging technology. It has excellent prospects in all of the application fields, however there exist some deficiencies for promotion, such as the stability of the structure and function, and uniformity for quantity production.

Flow cytometric quantification of apoptotic and proliferating cells applying an improved method for dissociation of spheroids

Spheroids are a promising tool for many cell culture applications, but their microscopic analysis is limited. Flow cytometry on a single cell basis, which requires a gentle but also efficient dissociation of spheroids, could be an alternative analysis. Mono-culture and coculture spheroids consisting of human fibroblasts and human endothelial cells were generated by the liquid overlay technique and were dissociated using AccuMax as a dissociation agent combined with gentle mechanical forces. This study aimed to quantify the number of apoptotic and proliferative cells. We were able to dissociate spheroids of differing size, age, and cellular composition in a single-step dissociation protocol within 10 min. The number of single cells was higher than 95% and in most cases, the viability of the cells after dissociation was higher than 85%. Coculture spheroids exhibited a higher sensitivity as shown by lower viability, higher amount of cellular debris, and a higher amount of apoptotic cells. Considerable expression of the proliferation marker Ki67 could only be seen in 1-day-old spheroids but was already downregulated on Day 3. In summary, our dissociation protocol enabled a fast and gentle dissociation of spheroids for the subsequent flow cytometric analysis. The chosen cell type had a strong influence on cell viability and apoptosis. Initially high rates of proliferative cells decreased rapidly and reached values of healthy tissue 3 days after generation of the spheroids. In conclusion, the flow cytometry of dissociated spheroids could be a promising analytical tool, which could be ideally combined with microscopic techniques.

Biofabrication and bioprinting using cellular aggregates, microtissues and organoids for the engineering of musculoskeletal tissues

The modest clinical impact of musculoskeletal tissue engineering (TE) can be attributed, at least in part, to a failure to recapitulate the structure, composition and functional properties of the target tissue. This has motivated increased interest in developmentally inspired TE strategies, which seek to recapitulate key events that occur during embryonic and post-natal development, as a means of generating truly biomimetic grafts to replace or regenerate damaged tissues and organs. Such TE strategies can be substantially enabled by emerging biofabrication and bioprinting strategies, and in particular the use of cellular aggregates, microtissues and organoids as 'building blocks' for the development of larger tissues and/or organ precursors. Here, the application of such biological building blocks for the engineering of musculoskeletal tissues, from vascularised bone to zonally organised articular cartilage, will be reviewed. The importance of first scaling-down to later scale-up will be discussed, as this is viewed as a key component of engineering functional grafts using cellular aggregates or microtissues. In the context of engineering anatomically accurate tissues of scale suitable for tissue engineering and regenerative medicine applications, novel bioprinting modalities and their application in controlling the process by which cellular aggregates or microtissues fuse and self-organise will be reviewed. Throughout the paper, we will highlight some of the key challenges facing this emerging field. STATEMENT OF SIGNIFICANCE: The field of bioprinting has grown substantially in recent years, but despite the hype and excitement it has generated, there are relatively few examples of bioprinting strategies producing implants with superior regenerative potential to that achievable with more traditional tissue engineering approaches. This paper provides an up-to-date review of emerging biofabrication and bioprinting strategies which use cellular aggregates and microtissues as 'building blocks' for the development of larger musculoskeletal tissues and/or organ precursors - a field of research that can potentially enable functional regeneration of damaged and diseased tissues. The application of cellular aggregates and microtissues for the engineering of musculoskeletal tissues, from vascularised bone to zonally organised articular cartilage, will be reviewed. In the context of engineering anatomically accurate tissues of scale, novel bioprinting modalities and their application in controlling the process by which cellular aggregates or microtissues self-organise is addressed, as well as key challenges facing this emerging field.

Comparison of 2- and 3-Dimensional Cultured Periodontal Ligament Stem Cells; a Pilot Study

This study compared the characteristics of periodontal ligament stem cells (PDLSCs) cultured using 3-dimensional (3D) versus conventional 2-dimensional (2D) methods. PDLSCs were cultured in either a 3D culture with a non-adhesive culture plate (Stemfit 3D®) or a conventional 2D culture using a 6-well plate. Morphology, viability, proliferation ability, and osteogenic differentiation were analyzed to characterize the differences induced in identical PDLSCs by 3D and 2D culture environments. In addition, gene expression was analyzed using RNA sequencing to further characterize the functional differences. The diameter and the viability of the 3D-cultured PDLSCs decreased over time, but the shape of the spheroid was maintained for 20 days. Although osteogenic differentiation occurred in both the 2D- and 3D-cultured PDLSCs, compared to the control group it was 20.8 and 1.6 higher in the 3D- and 2D-cultured cells, respectively. RNA sequencing revealed that PDLSCs cultured using 2D and 3D methods have different gene expression profiles. The viability of the 3D-cultured cells was decreased, but they showed superior osteogenic differentiation compared to 2D-cultured cells. Within the limitations of this study, the results demonstrate that the structure and function of PDLSCs are influenced by the cell culture method.

Overexpressing of caveolin-1 in mesenchymal stem cells promotes deep second-degree burn wound healing

Burn injury is one of the most common physical injuries in clinic. It is a big challenge to find an ideal treatment for burn injury. Mesenchymal stem cells (MSCs) have been suggested as a promising candidate for wound healing. However, it is critical to improve the therapeutic efficiency of MSCs for treatment of burn injury. Here, we demonstrated that overexpression of caveolin-1, the main component of the caveolae plasma membranes, promoted the proliferation of MSCs both in vitro and in vivo. Moreover, transplantation of MSCs overexpressing caveolin-1 facilitated the expression of various growth factors and immunoregulatory cytokines and accelerated deep second-degree burn wound healing in a rat model of burn injury. Our results suggest that overexpression of caveolin-1 can improve the therapeutic efficiency of MSCs, which may be a promising strategy for the treatment of deep second-degree burn injury in clinic.

[Preliminary exploration on the application of hydrogel from acellular porcine adipose tissue to assist lipofilling]

OBJECTIVE

To investigate the effect of hydrogel from acellular porcine adipose tissue (HAPA) on the survival of transplanted adipose tissue.

METHODS

For in vitro study, adipose tissue and HAPA-adipose tissue complex were cultured in normoxia and hypoxia atmospheres for 24 and 72 hours. TUNEL and Perilipin immunofluorescence staining were performed to observe the effect of HAPA on apoptosis and survival of adipocities. For in vivo study, 42 healthy male nude mice (4-6 weeks old) weighing 15-18 g were randomly divided into adipose group (group A), 10%HAPA group (group B), 20%HAPA group (group C), 30%HAPA group (group D), 40%HAPA group (group E), and 50%HAPA group (group F) according to different HAPA/adipose tissue volume ratio ( n=7). For each group, 1 mL adipose tissue or HAPA-adipose tissue complex was injected subcutaneously into the dorsum of the nude mice. At 4 weeks after transplantation, 7 nude mice in each group were sacrificed and grafts were harvested, gross observation, volume measurement, ultrasound examination, and histologic staining (HE staining, CD31 and Perilipin immunofluorescence stainings) were applied.

RESULTS

Hypoxia showed a tendency of promoting adipose tissue necrosis and apoptosis, while HAPA exhibited an obvious effect of inhibiting cell apoptosis in vitro study ( P<0.05). For in vivo study, grafts of all groups had intact fibrocapsule. No obvious signs of infection and necrosis were observed at 4 weeks. Volume shrinkage was observed in all groups, however, the groups A-D had significantly higher volume retention rate than groups E and F ( P<0.05). Ultrasound examination showed that there were no significant difference in the number and volume of liquify area of the grafts in each group ( P>0.05). With the increase of HAPA's volume ratio, HE staining proved an improved fat integrity while a gradually decreased vacuoles and fibrosis. CD31 immunohistochemical staining showed that the number of neo-vascularisation in groups E and F were significantly higher than those in groups A-D ( P<0.05). Perilipin immunofluorescence staining showed that with the increase of HAPA volume ratio, the number of living adipocytes increased gradually, and more new adipocytes could be seen in the field of vision.

CONCLUSION

As the volume ratio of HAPA gradually increased, the survival of transplanted adipose tissue also increased, but the volume retention rate decreased gradually. 30%HAPA was considered the relative optimal volume ratio for its superior adipose tissue survival and volume retation rate.

Comparison of the formation, adipogenic maturation, and retention of human adipose-derived stem cell spheroids in scaffold-free culture techniques

While three-dimensional spheroids outperform traditional two-dimensional monolayer culture for human adipose-derived stem cells (hASCs), there is not a consensus on the most successful method for enhancing their adipogenic differentiation and minimizing the loss of physiologically relevant, fatty spheroids during culture. To this end, we compared three culture methods, namely, elastin-like polypeptide-polyethyleneimine (ELP-PEI) coated surfaces, ultra-low attachment static culture, and suspension culture for their ability to form and retain productive hASC spheroids. The ELP-PEI coatings used the ELP conjugated to two molecular weights of PEI (800 or 25,000 g/mol). FTIR spectroscopy, atomic force microscopy, and contact angle goniometry revealed that the ELP-PEI coatings had similar chemical structures, surface topography, and hydrophobicity. Time-lapse microscopy showed that increasing the PEI molecular weight resulted in smaller spheroids. Measurement of triglyceride content showed that the three methods induced comparable differentiation of hASCs toward the adipogenic lineage. DNA content and morphometric analysis revealed merging of spheroids to form larger spheroids in the ultra-low attachment static culture and suspension culture methods. In contrast, the retention of hASC spheroid sizes and numbers with a regular spheroid size (~100 μm) were best atop the ELP-PEI800 coatings. Overall, this research shows that the spheroid culture atop the ELP-PEI coatings is a suitable cell culture model for future studies involving long-term, three-dimensional culture of mature adipocytes derived from hASCs.

Dual functional construct containing kartogenin releasing microtissues and curcumin for cartilage regeneration

BACKGROUND

Regeneration of articular cartilage poses a tremendous challenge due to its limited self-repair capability and inflammation at the damaged site. To generate the desired structures that mimic the structure of native tissue, microtissues with repeated functional units such as cell aggregates have been developed. Multicellular aggregates of mesenchymal stem cells (MSCs) can be used as microscale building blocks of cartilage due to their potential for cell-cell contact, cell proliferation, and differentiation.

METHODS

Chondrogenic microtissues were developed through incorporation of kartogenin-releasing poly (lactic-co-glycolic acid) (PLGA) microparticles (KGN-MP) within the MSC aggregates. The chondrogenic potential of KGN-MP treated MSC aggregates was proven in vitro by studying the chondrogenic markers at the RNA level and histological analysis. In order to address the inflammatory responses at the defect site, the microtissues were delivered in vivo via an injectable, anti-inflammatory hydrogel that contained gelatin methacryloyl (GelMA) loaded with curcumin (Cur).

RESULTS

The KGN-MPs were fabricated to support MSCs during cartilage differentiation. According to real-time RT-PCR analysis, the presence of KGN in the aggregates led to the expression of cartilage markers by the MSCs. Both toluidine blue (TB) and safranin O (SO) staining demonstrated homogeneous glycosaminoglycan production throughout the KGN-MP incorporated MSC aggregates. The curcumin treatment efficiently reduced the expressions of hypertrophy markers by MSCs in vitro. The in vivo results showed that implantation of chondrogenic microtissues (KGN-MP incorporated MSC aggregates) using the curcumin loaded GelMA hydrogel resulted in cartilage tissue regeneration that had characteristic features close to the natural hyaline cartilage according to observational and histological results.

CONCLUSIONS

The use of this novel construct that contained chondrogenic cell blocks and curcumin is highly desired for cartilage regeneration.

Vascularization Strategies in the Prevention of Nonunion Formation

Delayed healing and nonunion formation are major challenges in orthopedic surgery, which require the development of novel treatment strategies. Vascularization is considered one of the major prerequisites for successful bone healing, providing an adequate nutrient supply and allowing the infiltration of progenitor cells to the fracture site. Hence, during the last decade, a considerable number of studies have focused on the evaluation of vascularization strategies to prevent or to treat nonunion formation. These involve (1) biophysical applications, (2) systemic pharmacological interventions, and (3) tissue engineering, including sophisticated scaffold materials, local growth factor delivery systems, cell-based techniques, and surgical vascularization approaches. Accumulating evidence indicates that in nonunions, these strategies are indeed capable of improving the process of bone healing. The major challenge for the future will now be the translation of these strategies into clinical practice to make them accessible for the majority of patients. If this succeeds, these vascularization strategies may markedly reduce the incidence of nonunion formation. Impact statement Delayed healing and nonunion formation are a major clinical problem in orthopedic surgery. This review provides an overview of vascularization strategies for the prevention and treatment of nonunions. The successful translation of these strategies in clinical practice is of major importance to achieve adequate bone healing.

Composite Hydrogels in Three-Dimensional in vitro Models

3-dimensional (3D) in vitro models were developed in order to mimic the complexity of real organ/tissue in a dish. They offer new possibilities to model biological processes in more physiologically relevant ways which can be applied to a myriad of applications including drug development, toxicity screening and regenerative medicine. Hydrogels are the most relevant tissue-like matrices to support the development of 3D in vitro models since they are in many ways akin to the native extracellular matrix (ECM). For the purpose of further improving matrix relevance or to impart specific functionalities, composite hydrogels have attracted increasing attention. These could incorporate drugs to control cell fates, additional ECM elements to improve mechanical properties, biomolecules to improve biological activities or any combinations of the above. In this Review, recent developments in using composite hydrogels laden with cells as biomimetic tissue- or organ-like constructs, and as matrices for multi-cell type organoid cultures are highlighted. The latest composite hydrogel systems that contain nanomaterials, biological factors, and combinations of biopolymers (e.g., proteins and polysaccharide), such as Interpenetrating Networks (IPNs) and Soft Network Composites (SNCs) are also presented. While promising, challenges remain. These will be discussed in light of future perspectives toward encompassing diverse composite hydrogel platforms for an improved organ environment in vitro.

Extracellular matrix mimicking polycaprolactone-chitosan nanofibers promote stemness maintenance of mesenchymal stem cells via spheroid formation

The development of clinical applications has led to a perpetual increase in the demand for mesenchymal stem cells (MSCs). However, the ex vivo expansion of MSCs while maintaining their stemness and differentiation potential remains an immense challenge. MSCs require high cell density for their intercellular communication and specific physico-chemical cues from the surrounding environment for spheroid formation in order to maintain their stemness. Inadequacy of the traditional in vitro cell culture method (tissue culture plastic surface) to fulfill any of these special requirements is responsible for inducing the loss of stem cell properties of the MSCs over time. In this study, we propose that glucosaminoglycan (GAG) mimicking ultrafine nanofibers could support the spheroid culture for in vitro human MSC expansion. The geometrical and biochemical properties of nanofibers provide biomimicking cues to MSCs, as well as enhance cell-cell interactions and stimulate spheroid formation in MSCs, which subsequently result in increased cell proliferation, enhanced expression of stem cell markers and maintenance of their multilineage differentiation potential. Furthermore, close monitoring of the behavior of MSCs on nanofibers serves as the key to understand their mode of action in niche formation. Interestingly, GAG mimicking substrate stimulated MSCs for long-distance intercellular communication via 'tunneling tubes', their subsequent migration and niche formation. These kinds of cellular interactions over long distances have rarely been observed in MSCs to provide better insight for future studies on MSC niche. Furthermore, PCL-CHT nanofibers were observed to be as conducive to use as tissue culture polystyrene for stem cell expansion. Overall, these polymeric nanofibers provide a more relevant, convenient and more suitable substrate than the conventional monolayer culture for in vitro MSC expansion.

Immunomodulation in Vascularized Composite Allotransplantation: What Is the Role for Adipose-Derived Stem Cells?

Hand and face transplants are becoming increasingly common, recording progressively more penile, uterus, abdominal wall, and allotransplantation cases reported worldwide. Despite current protocols allow long-term survival of the allografts, the ultimate goal of donor-specific tolerance has not been achieved yet. In fact, the harmful adverse effects related to the lifelong administration of immunosuppressive agents are the main drawbacks for vascularized composite allotransplantations. Research is very active in investigating alternative methods to induce greater tolerance while minimizing toxicity. Adipose-derived stem cells (ASCs) represent promising cell therapies for immunomodulation in preclinical and clinical settings. Their clinical appeal is due to their easy harvest in large quantities through a noninvasive and well-accepted approach; they may well promote donor-specific tolerance and potentially reduce immunosuppression. Several experimental studies exist, but lacking review articles reporting current evidence. This work proposes a literature review on the immunomodulatory role of ASCs in vascularized composite allotransplantations. In vitro and in vivo evidence will be summarized. The role that cell passaging and upstream progenitors-the so-called spheroid ASCs-may play in modulating the immune response will also be discussed. Finally, this article will summarize current knowledge on biodistribution, migration, and homing of injected stem cells. This review may well provide useful information for preclinical and clinical studies, aiming at a breakthrough for donor-specific tolerance.

Microfluidic technologies to engineer mesenchymal stem cell aggregates-applications and benefits

Three-dimensional cell culture and the forming multicellular aggregates are superior over traditional monolayer approaches due to better mimicking of in vivo conditions and hence functions of a tissue. A considerable amount of attention has been devoted to devising efficient methods for the rapid formation of uniform-sized multicellular aggregates. Microfluidic technology describes a platform of techniques comprising microchannels to manipulate the small number of reagents with unique properties and capabilities suitable for biological studies. The focus of this review is to highlight recent studies of using microfluidics, especially droplet-based types for the formation, culture, and harvesting of mesenchymal stem cell aggregates and their subsequent application in stem cell biology, tissue engineering, and drug screening. Droplet-based microfluidics can be used to form microgels as carriers for delivering cells and to provide biological cues to the target tissue so as to be minimally invasive. Stem cell-laden microgels with a shape-forming property can be used as smart building blocks by injecting them into the injured tissue thereby constituting the cornerstone of tissue regeneration.

Vascularization strategies for skin tissue engineering

Lack of proper vascularization after skin trauma causes delayed wound healing. This has sparked the development of various tissue engineering strategies to improve vascularization.

3D microtissue-derived human stem cells seeded on electrospun nanocomposites under shear stress: Modulation of gene expression

OBJECTIVE

Different microenvironments trigger distinct differentiation of stem cells. Even without chemical supplementation, mechanical stimulation by shear stress may help to induce the desired differentiation. The cell format, such as three-dimensional (3D) microtissues (MTs), MT-derived cells or single cells (SCs), may have a pivotal impact as well. Here, we studied modulation of gene expression in human adipose-derived stem cells (ASCs) exposed to shear stress and/or after MT formation.

MATERIALS AND METHODS

Electrospun meshes of poly-lactic-co-glycolic acid and amorphous calcium phosphate nanoparticles (PLGA/aCaP) at a weight ratio of 60:40 were seeded with human ASCs as MTs or as SCs and cultured in Dulbecco's modified Eagle's medium without chemical supplementation. After 2 weeks of static culture, the scaffolds were cultured statically for another 2 weeks or placed in a Bose® bioreactor with a flow rate per area of 0.16 mL cm^-2 min^-1. Stiffness of the scaffolds was assessed as a function of time. After 4 weeks, minimum stem cell criteria markers and selected markers of osteogenesis, endothelial cell differentiation, adipogenesis and chondrogenesis were analysed by quantitative real-time polymerase chain reaction. Additionally, cell distribution within the scaffolds and the allocation of the yes-associated protein (YAP) in the cells were assessed by immunohistochemistry.

RESULTS

MTs decayed completely within 2 weeks after seeding on PLGA/aCaP. The osteogenic marker gene alkaline phosphatase and the endothelial cell marker gene CD31 were upregulated in MT-derived ASCs compared with SCs. Shear stress realised by fluid flow perfusion upregulated peroxisome proliferator-activated receptor gamma 2 expression in MT-derived ASCs and in SCs. The nuclear-to-cytoplasmic ratio of YAP expression was doubled under perfusion compared with that under static culture for MT-derived ASCs and SCs.

CONCLUSIONS

Osteogenic and angiogenic commitments were more pronounced in MT-derived ASCs seeded on bone biomimetic electrospun nanocomposite PLGA/aCaP than in SCs seeded without induction medium. Furthermore, the static culture was superior to the perfusion regimen used here, as shear stress resulted in adipogenic commitment for MT-derived ASCs and SCs, although the YAP nuclear-to-cytoplasmic ratio indicated higher cell tensions under perfusion, usually associated with preferred osteogenic differentiation.

Regulation of endothelial cell arrangements within hMSC - HUVEC co-cultured aggregates

Background

Micro-mass culturing or cellular aggregation is an effective method used to form mineralised bone tissue. Poor core cell viability, however, is often an impeding characteristic of large micro-mass cultures, and equally for large tissue-engineered bone grafts. Because of this, efforts are being made to enhance large graft perfusion, often through pre-vascularisation, which involves the co-culture of endothelial cells and bone cells or stem cells.

Methods

This study investigated the effects of different aggregation techniques and culture conditions on endothelial cell arrangements in mesenchymal stem cell and human umbilical vein endothelial cell co-cultured aggregates when endothelial cells constituted just 5%. Two different cellular aggregation techniques, i.e. suspension culture aggregation and pellet culture aggregation, were applied alongside two subsequent culturing techniques, i.e. hydrostatic loading and static culturing. Endothelial cell arrangements were assessed under such conditions to indicate potential pre-vascularisation.

Results

Our study found that the suspension culture aggregates cultured under hydrostatic loading offered the best environment for enhanced endothelial cell regional arrangements, closely followed by the pellet culture aggregates cultured under hydrostatic loading, the suspension culture aggregates cultured under static conditions, and the pellet culture aggregates cultured under static conditions.

Conclusions

The combination of particular aggregation techniques with dynamic culturing conditions appeared to have a synergistic effect on the cellular arrangements within the co-cultured aggregates.

Advanced drug delivery systems and artificial skin grafts for skin wound healing

Cutaneous injuries, especially chronic wounds, burns, and skin wound infection, require painstakingly long-term treatment with an immense financial burden to healthcare systems worldwide. However, clinical management of chronic wounds remains unsatisfactory in many cases. Various strategies including growth factor and gene delivery as well as cell therapy have been used to enhance the healing of non-healing wounds. Drug delivery systems across the nano, micro, and macroscales can extend half-life, improve bioavailability, optimize pharmacokinetics, and decrease dosing frequency of drugs and genes. Replacement of the damaged skin tissue with substitutes comprising cell-laden scaffold can also restore the barrier and regulatory functions of skin at the wound site. This review covers comprehensively the advanced treatment strategies to improve the quality of wound healing.

Cell membrane engineering with synthetic materials: Applications in cell spheroids, cellular glues and microtissue formation

Biologically inspired materials with tunable bio- and physicochemical properties provide an essential framework to actively control and support cellular behavior. Cell membrane remodeling approaches benefit from the advances in polymer science and bioconjugation methods, which allow for the installation of un-/natural molecules and particles on the cells' surface. Synthetically remodeled cells have superior properties and are under intense investigation in various therapeutic scenarios as cell delivery systems, bio-sensing platforms, injectable biomaterials and bioinks for 3D bioprinting applications. In this review article, recent advances in the field of cell surface remodeling via bio-chemical means and the potential biomedical applications of these emerging cell hybrids are discussed. STATEMENT OF SIGNIFICANCE: Recent advances in bioconjugation methods, controlled/living polymerizations, microfabrication techniques and 3D printing technologies have enabled researchers to probe specific cellular functions and cues for therapeutic and research purposes through the formation of cell spheroids and polymer-cell chimeras. This review article highlights recent non-genetic cell membrane engineering strategies towards the fabrication of cellular ensembles and microtissues with interest in 3D in vitro modeling, cell therapeutics and tissue engineering. From a wider perspective, these approaches may provide a roadmap for future advances in cell therapies which will expedite the clinical use of cells, thereby improving the quality and accessibility of disease treatments.

Dextran-based hydrogel with enhanced mechanical performance via covalent and non-covalent cross-linking units carrying adipose-derived stem cells toward vascularized bone tissue engineering

Hydrogels for biomedical applications were limited toward bone tissue engineering due to the poor mechanical performance. Tough hydrogels with strong and elastic features have received extensive attention, the application of which, however, was limited by their degradation. The present study introduced an approach to enhance mechanical properties of hydrogel while ensuring its degradation. Carboxyl dextran (Dex) was grafting modified by poly (ε-caprolactone) (PCL), sequentially followed by being cross-linked through polyethyleneglycol 400 (PEG400) to yield a gel with covalent cross-linking units in DMSO. The gel was underwent solvent displacement in H₂ O to induce hydrophobic association of PCL to form non-covalent cross-linking units. The tough Dex-g-PCL hydrogel showed maximum strain of Dex-g-PCL hydrogel was 90% ± 6%, with the corresponding stress of 2.7 ± 0.2 MPa, which was significantly enhanced when comparing to dextran hydrogel (maximum strain 65% ± 5%, with the corresponding stress of 0.225 ± 0.06 MPa). Most hydrogel degraded after 12 w in vivo with only a little residues. Adipose-derived stem cells (ASCs) proliferated well after being seeded in hydrogel to form micro-mass at 14 days post-seeding. In vitro and in vivo angiogenesis, as well as in vitro osteogenesis illustrated the potential of the Dex-g-PCL hydrogel carrying ASCs toward vascularized bone tissue engineering. © 2019 Wiley Periodicals, Inc. J Biomed Mater Res Part A: 107A: 1120-1131, 2019.

Prevascularization of collagen-glycosaminoglycan scaffolds: stromal vascular fraction versus adipose tissue-derived microvascular fragments

Background

The seeding of scaffolds with the stromal vascular fraction (SVF) of adipose tissue is a common prevascularization strategy in tissue engineering. Alternatively, adipose tissue-derived microvascular fragments (ad-MVF) may serve as vascularization units. In contrast to SVF single cells, they represent a mixture of intact arteriolar, capillary and venular vessel segments. Therefore, we herein hypothesized that the ad-MVF-based prevascularization of scaffolds is superior to the conventional SVF single cells-based approach.

Results

SVF single cells and ad-MVF were enzymatically isolated from epididymal fat pads of green fluorescent protein (GFP)⁺ donor mice to assess their viability and cellular composition using fluorescence microscopy and flow cytometry. Moreover, collagen-glycosaminoglycan matrices (Integra®) were seeded with identical amounts of the isolates and implanted into full-thickness skin defects within dorsal skinfold chambers of GFP⁻ recipient mice for the intravital fluorescent microscopic, histological and immunohistochemical analysis of implant vascularization and incorporation throughout an observation period of 2 weeks. Non-seeded matrices served as controls. While both isolates contained a comparable fraction of endothelial cells, perivascular cells, adipocytes and stem cells, ad-MVF exhibited a significantly higher viability. After in vivo implantation, the vascularization of ad-MVF-seeded scaffolds was improved when compared to SVF-seeded ones, as indicated by a significantly higher functional microvessel density. This was associated with an enhanced cellular infiltration, collagen content and density of CD31⁺/GFP⁺ microvessels particularly in the center of the implants, demonstrating a better incorporation into the surrounding host tissue. In contrast, non-seeded matrices exhibited a poor vascularization, incorporation and epithelialization over time.

Conclusions

The present study demonstrates that ad-MVF are highly potent vascularization units that markedly accelerate and improve scaffold vascularization when compared to the SVF.

Electronic supplementary material

The online version of this article (10.1186/s13036-018-0118-3) contains supplementary material, which is available to authorized users.

Stem Cell-Mediated Angiogenesis in Tissue Engineering Constructs

Angiogenesis has always been a concern in the field of tissue engineering. Poor vascularization of engineered constructs is a problem for the clinical success of these structures. Among the various methods employed to induce angiogenesis, stem cells provide a promising tool for the future. The present review aims to present the application of stem cells in the induction of angiogenesis. Additionally, it summarizes recent advancements in stem cell-mediated angiogenesis of different tissue engineering constructs.

The micromass formation potential of human adipose-derived stromal cells isolated from different various origins

BACKGROUND

Adult stem cells appear to be a promising subject for tissue engineering, representing an individual material for regeneration of aged and damaged cells. Especially adipose derived stromal cells (ADSC), which are easily to achieve, allow an encouraging perspective due to their capability of differentiating into miscellaneous cell types. Here we describe the in vitro formation of human subcutaneous, visceral and omental ADSC micromasses and compare their histological attributes while being cultivated on collagen membranes.

METHODS

Subcutaneous, visceral and omental fat tissue derived cells were isolated and processed according to standard protocols. Positively stained cells for CD13, CD44 and CD90 were cultivated on agarose in order to study micromass formation using a special method of cell tracking. Stained paraffin-embedded micromasses were analysed morphologically before and after being plated on collagen membranes.

RESULTS

The micromass formation process was similar in all three tissue types. Subcutaneous fat tissue derived micromasses turned out to develop a more homogeneous and compact shape than visceral and omental tissue. Nevertheless all micromasses adhered to collagen membranes with visible spreading of cells. The immune histochemical (IHC) staining of subcutaneous, visceral and omental ADSC micromasses shows a constant expression of CD13 and a decrease of CD44 and CD 90 expression within 28 days. After that period, omental fat cells don't show any expression of CD44.

CONCLUSION

In conclusion micromass formation and cultivation of all analysed fat tissues can be achieved, subcutaneous cells appearing to be the best material for regenerative concepts.

The therapeutic potential of the mesenchymal stem cell secretome in ischaemic stroke

Mesenchymal stem cells (MSCs) hold great potential as a regenerative therapy for stroke, leading to increased repair and functional recovery in animal models of cerebral ischaemia. While it was initially hypothesised that cell replacement was an important mechanism of action of MSCs, focus has shifted to their paracrine actions or the so called "bystander" effect. MSCs secrete a wide array of growth factors, chemokines, cytokines and extracellular vesicles, commonly referred to as the MSC secretome. There is evidence suggesting the MSC secretome can promote repair through a number of mechanisms including preventing cell apoptosis, modulating the inflammatory response and promoting endogenous repair mechanisms such as angiogenesis and neurogenesis. In this review, we will discuss the in vitro approaches currently being employed to drive the MSC secretome towards a more anti-inflammatory and regenerative phenotype. We will then examine the role of the secretome in promoting repair and improving recovery in preclinical models of cerebral ischaemia.

Cellular self-assembly into 3D microtissues enhances the angiogenic activity and functional neovascularization capacity of human cardiopoietic stem cells

While cell therapy has been proposed as next-generation therapy to treat the diseased heart, current strategies display only limited clinical efficacy. Besides the ongoing quest for the ideal cell type, in particular the very low retention rate of single-cell (SC) suspensions after delivery remains a major problem. To improve cellular retention, cellular self-assembly into 3D microtissues (MTs) prior to transplantation has emerged as an encouraging alternative. Importantly, 3D-MTs have also been reported to enhance the angiogenic activity and neovascularization potential of stem cells. Therefore, here using the chorioallantoic membrane (CAM) assay we comprehensively evaluate the impact of cell format (SCs versus 3D-MTs) on the angiogenic potential of human cardiopoietic stem cells, a promising second-generation cell type for cardiac repair. Biodegradable collagen scaffolds were seeded with human cardiopoietic stem cells, either as SCs or as 3D-MTs generated by using a modified hanging drop method. Thereafter, seeded scaffolds were placed on the CAM of living chicken embryos and analyzed for their perfusion capacity in vivo using magnetic resonance imaging assessment which was then linked to a longitudinal histomorphometric ex vivo analysis comprising blood vessel density and characteristics such as shape and size. Cellular self-assembly into 3D-MTs led to a significant increase of vessel density mainly driven by a higher number of neo-capillary formation. In contrast, SC-seeded scaffolds displayed a higher frequency of larger neo-vessels resulting in an overall 1.76-fold higher total vessel area (TVA). Importantly, despite that larger TVA in SC-seeded group, the mean perfusion capacity (MPC) was comparable between groups, therefore suggesting functional superiority together with an enhanced perfusion efficacy of the neo-vessels in 3D-MT-seeded scaffolds. This was further underlined by a 1.64-fold higher perfusion ratio when relating MPC to TVA. Our study shows that cellular self-assembly of human cardiopoietic stem cells into 3D-MTs substantially enhances their overall angiogenic potential and their functional neovascularization capacity. Hence, the concept of 3D-MTs may be considered to increase the therapeutic efficacy of future cell therapy concepts.

High-throughput fabrication of vascularized spheroids for bioprinting

Overcoming the problem of vascularization remains the main challenge in the field of tissue engineering. As three-dimensional (3D) bioprinting is the rising technique for the fabrication of large tissue constructs, small prevascularized building blocks were generated that can be incorporated throughout a printed construct, answering the need for a microvasculature within the small micron range (<10 μm). Uniform spheroids with an ideal geometry and diameter for bioprinting were formed, using a high-throughput non-adhesive agarose microwell system. Since monoculture spheroids of endothelial cells were unable to remain stable, coculture spheroids combining endothelial cells with fibroblasts and/or adipose tissue derived mesenchymal stem cells (ADSC) as supporting cells, were created. When applying the favorable coculture ratio, viable spheroids were obtained and endothelial cells spontaneously formed a capillary-like network and lumina, as shown by immunohistochemistry and transmission electron microscopy. Especially the presence of ADSC led to a higher vascularization and extracellular matrix production of the microtissue. Moreover, spheroids were able to assemble at random in suspension and in a hydrogel, creating a macrotissue. During at random assembly, cells reorganized, creating a branched capillary-network throughout the entire fused construct by inoculating with capillaries of adjacent spheroids. Combining the advantage of this natural capacity of microtissues to self-assemble and the controlled organization by bioprinting technologies, these prevascularized spheroids can be useful as building blocks for the engineering of large vascularized 3D tissues.

Adult Stem Cells Spheroids to Optimize Cell Colonization in Scaffolds for Cartilage and Bone Tissue Engineering

Top-down tissue engineering aims to produce functional tissues using biomaterials as scaffolds, thus providing cues for cell proliferation and differentiation. Conversely, the bottom-up approach aims to precondition cells to form modular tissues units (building-blocks) represented by spheroids. In spheroid culture, adult stem cells are responsible for their extracellular matrix synthesis, re-creating structures at the tissue level. Spheroids from adult stem cells can be considered as organoids, since stem cells recapitulate differentiation pathways and also represent a promising approach for identifying new molecular targets (biomarkers) for diagnosis and therapy. Currently, spheroids can be used for scaffold-free (developmental engineering) or scaffold-based approaches. The scaffold promotes better spatial organization of individual spheroids and provides a defined geometry for their 3D assembly in larger and complex tissues. Furthermore, spheroids exhibit potent angiogenic and vasculogenic capacity and serve as efficient vascularization units in porous scaffolds for bone tissue engineering. An automated combinatorial approach that integrates spheroids into scaffolds is starting to be investigated for macro-scale tissue biofabrication.

Hydrogel scaffolds for differentiation of adipose-derived stem cells

Natural extracellular matrices (ECMs) have been widely used as a support for the adhesion, migration, differentiation, and proliferation of adipose-derived stem cells (ADSCs). However, poor mechanical behavior and unpredictable biodegradation properties of natural ECMs considerably limit their potential for bioapplications and raise the need for different, synthetic scaffolds. Hydrogels are regarded as the most promising alternative materials as a consequence of their excellent swelling properties and their resemblance to soft tissues. A variety of strategies have been applied to create synthetic biomimetic hydrogels, and their biophysical and biochemical properties have been modulated to be suitable for cell differentiation. In this review, we first give an overview of common methods for hydrogel preparation with a focus on those strategies that provide potential advantages for ADSC encapsulation, before summarizing the physical properties of hydrogel scaffolds that can act as biological cues. Finally, the challenges in the preparation and application of hydrogels with ADSCs are explored and the perspectives are proposed for the next generation of scaffolds.

Changes in the secretome of tri-dimensional spheroid-cultured human mesenchymal stem cells in vitro by interleukin-1 priming

Background

Mesenchymal stem cells (MSCs) are one of the most promising candidates for the treatment of major neurological disorders. Desirable therapeutic properties of MSCs include reparative and regenerative potential but, despite their proven safety, the efficacy of MSCs remains controversial. Therefore, it is essential to optimise culture protocols to enhance the therapeutic potential of the MSC secretome. Here we aimed to: assess the increase in secretion of cytokines that may induce repair, regeneration, or immunomodulation when cultured in three dimensions; study the effect of interleukin (IL)-1 priming on two- (2D) and three-dimensional (3D) cultures of MSC; and evaluate the potential use of the modified secretome using microglial-MSC co-cultures.

Methods

We established a 3D spheroid culture of human MSCs, and compared the secretome in 2D and 3D cultures under primed (IL-1) and unprimed conditions. BV2 microglial cells were stimulated with lipopolysaccharide (LPS) and treated with spheroid conditioned media (CM) or were co-cultured with whole spheroids. Concentrations of secreted cytokines were determined by enzyme-linked immunosorbent assay (ELISA). Protein arrays were used to further evaluate the effect of IL-1 priming in 2D and 3D cultures.

Results

3D culture of MSCs significantly increased secretion of the IL-1 receptor antagonist (IL-1Ra), vascular endothelial growth factor (VEGF), and granulocyte-colony stimulating factor (G-CSF) compared with 2D culture, despite priming treatments with IL-1 being more effective in 2D than in 3D. The addition of CM of 3D-MSCs reduced LPS-induced tumour necrosis factor (TNF)-α secretion from BV2 cells, while the 3D spheroid co-cultured with the BV2 cells induced an increase in IL-6, but had no effect on TNF-α release. Protein arrays indicated that priming treatments trigger a more potent immune profile which is necessary to orchestrate an effective tissue repair. This effect was lost in 3D, partly because of the overexpression of IL-6.

Conclusions

Increased secretion of anti-inflammatory markers occurs when MSCs are cultured in 3D, but this specific secretome did not translate into anti-inflammatory effects on LPS-treated BV2 cells in co-culture. These data highlight the importance of optimising priming treatments and culture conditions to maximise the therapeutic potential of MSC spheroids.

Generation of Human Mesenchymal Stem Cell 3D Spheroids Using Low-binding Plates

The 3D culture of human mesenchymal stem cells (hMSCs) represents a more physiological environment than classical 2D culture and has been used to enhance the MSC secretome or extend cell survival after transplantation. Here we describe a simple and affordable method to generate 3D spheroids of hMSCs by seeding them at high density in a low-binding 96-well plate. Spheroids of hMSCs cultured in low-binding 96-well plates can be used to study the basic biology of the cells and to generate conditioned media or spheroids to be used in transplantation therapeutic approaches. These MSCs or their secretome can be used as a regenerative therapy and for tissue repair across multiple disease areas, including neurodegeneration. In comparison to other methods (hanging drop, use of gels or biomaterials, magnetic levitation, etc.), the method described here is simple and affordable with no need to use specialized equipment, expensive materials or complex reagents.

αvβ3 and α5β1 integrin-specific ligands: From tumor angiogenesis inhibitors to vascularization promoters in regenerative medicine?

Integrins are cell adhesion receptors predominantly important during normal and tumor angiogenesis. A sequence present on several extracellular matrix proteins composed of Arg-Gly-Asp (RGD) has attracted attention due to its role in cell adhesion mediated by integrins. The development of ligands that can bind to integrins involved in tumor angiogenesis and brake disease progression has resulted in new investigational drug entities reaching the clinical trial phase in humans. The use of integrin-specific ligands can be useful for the vascularization of regenerative medicine constructs, which remains a major limitation for translation into clinical practice. In order to enhance vascularization, immobilization of integrin-specific RGD peptidomimetics within constructs is a recommended approach, due to their high specificity and selectivity towards certain desired integrins. This review endeavours to address the potential of peptidomimetic-coated biomaterials as vascular network promoters for regenerative medicine purposes. Clinical studies involving molecules tracking active integrins in cancer angiogenesis and reasons for their failure are also addressed.

Prevascularization of 3D printed bone scaffolds by bioactive hydrogels and cell co-culture

Vascularization is a fundamental prerequisite for large bone construct development and remains one of the main challenges of bone tissue engineering. Our current study presents the combination of 3D printing technique with a hydrogel-based prevascularization strategy to generate prevascularized bone constructs. Human adipose derived mesenchymal stem cells (ADMSC) and human umbilical vein endothelial cells (HUVEC) were encapsulated within our bioactive hydrogels, and the effects of culture conditions on in vitro vascularization were determined. We further generated composite constructs by forming 3D printed polycaprolactone/hydroxyapatite scaffolds coated with cell-laden hydrogels and determined how the co-culture affected vascularization and osteogenesis. It was demonstrated that 3D co-cultured ADMSC-HUVEC generated capillary-like networks within the porous 3D printed scaffold. The co-culture systems promoted in vitro vascularization, but had no significant effects on osteogenesis. The prevascularized constructs were subcutaneously implanted into nude mice to evaluate the in vivo vascularization capacity and the functionality of engineered vessels. The hydrogel systems facilitated microvessel and lumen formation and promoted anastomosis of vascular networks of human origin with host murine vasculature. These findings demonstrate the potential of prevascularized 3D printed scaffolds with anatomical shape for the healing of larger bone defects. © 2017 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 106B: 1788-1798, 2018.

Human adipose-derived mesenchymal stem cells seeded into a collagen-hydroxyapatite scaffold promote bone augmentation after implantation in the mouse

Traumatic injury or surgical excision of diseased bone tissue usually require the reconstruction of large bone defects unable to heal spontaneously, especially in older individuals. This is a big challenge requiring the development of biomaterials mimicking the bone structure and capable of inducing the right commitment of cells seeded within the scaffold. In particular, given their properties and large availability, the human adipose-derived stem cells are considered as the better candidate for autologous cell transplantation. In order to evaluate the regenerative potential of these cells along with an osteoinductive biomaterial, we have used collagen/hydroxyapatite scaffolds to test ectopic bone formation after subcutaneous implantation in mice. The process was analysed both in vivo, by Fluorescent Molecular Tomography (FMT), and ex vivo, to evaluate the formation of bone and vascular structures. The results have shown that the biomaterial could itself be able of promoting differentiation of host cells and bone formation, probably by means of its intrinsic chemical and structural properties, namely the microenvironment. However, when charged with human mesenchymal stem cells, the ectopic bone formation within the scaffold was increased. We believe that these results represent an important advancement in the field of bone physiology, as well as in regenerative medicine.

Dorsal skinfold chamber models in mice

Background/purpose: The use of dorsal skinfold chamber models has substantially improved the understanding of micro-vascularisation in pathophysiology over the last eight decades. It allows in vivo pathophysiological studies of vascularisation over a continuous period of time. The dorsal skinfold chamber is an attractive technique for monitoring the vascularisation of autologous or allogenic transplants, wound healing, tumorigenesis and compatibility of biomaterial implants. To further reduce the animals’ discomfort while carrying the dorsal skinfold chamber, we developed a smaller chamber (the Leipzig Dorsal Skinfold Chamber) and summarized the commercial available chamber models. In addition we compared our model to the common chamber.

Methods: The Leipzig Dorsal Skinfold Chamber was applied to 66 C57Bl/6 female mice with a mean weight of 22 g. Angiogenesis within the dorsal skinfold chamber was evaluated after injection of fluorescein isothiocyanate dextran with an Axio Scope microscope. The mean vessel density within the dorsal skinfold chamber was assessed over a period of 21 days at five different time points. The gained data were compared to previous results using a bigger and heavier dorsal skinfold model in mice. A PubMed and a patent search were performed and all papers related to “dorsal skinfold chamber” from 1^st of January 2006 to 31^st of December 2015 were evaluated regarding the dorsal skinfold chamber models and their technical improvements. The main models are described and compared to our titanium Leipzig Dorsal Skinfold Chamber model.

Results: The Leipzig Dorsal Skinfold Chamber fulfils all requirements of continuous in vivo models known from previous chamber models while reducing irritation to the mice. Five different chamber models have been identified showing substantial regional diversity. The newly elaborated titanium dorsal skinfold chamber may replace the pre-existing titanium chamber model used in Germany so far, as it is smaller and lighter than the former ones. However, the new chamber does not reach the advantages of already existing chamber models used in Asia and the US, which are smaller and lighter.

Conclusion: Elaborating a smaller and lighter dorsal skinfold chamber allows research studies on smaller animals and reduces the animals’ discomfort while carrying the chamber. Greater research exchange should be done to spread the use of smaller and lighter chamber models.