Synergistic protein secretion by mesenchymal stromal cells seeded in 3D scaffolds and circulating leukocytes in physiological flow

Development of an iPSC-derived tissue-resident macrophage-based platform for the in vitro immunocompatibility assessment of human tissue engineered matrices

Upon implanting tissue-engineered heart valves (TEHVs), blood-derived macrophages are believed to orchestrate the remodeling process. They initiate the immune response and mediate the remodeling of the TEHV, essential for the valve's functionality. The exact role of another macrophage type, the tissue-resident macrophages (TRMs), has not been yet elucidated even though they maintain the homeostasis of native tissues. Here, we characterized the response of hTRM-like cells in contact with a human tissue engineered matrix (hTEM). HTEMs comprised intracellular peptides with potentially immunogenic properties in their ECM proteome. Human iPSC-derived macrophages (iMφs) could represent hTRM-like cells in vitro and circumvent the scarcity of human donor material. iMφs were derived and after stimulation they demonstrated polarization towards non-/inflammatory states. Next, they responded with increased IL-6/IL-1β secretion in separate 3/7-day cultures with longer production-time-hTEMs. We demonstrated that iMφs are a potential model for TRM-like cells for the assessment of hTEM immunocompatibility. They adopt distinct pro- and anti-inflammatory phenotypes, and both IL-6 and IL-1β secretion depends on hTEM composition. IL-6 provided the highest sensitivity to measure iMφs pro-inflammatory response. This platform could facilitate the in vitro immunocompatibility assessment of hTEMs and thereby showcase a potential way to achieve safer clinical translation of TEHVs.

Functional regeneration at the blood-biomaterial interface

The use of cardiovascular implants is commonplace in clinical practice. However, reproducing the key bioactive and adaptive properties of native cardiovascular tissues with an artificial replacement is highly challenging. Exciting new treatment strategies are under development to regenerate (parts of) cardiovascular tissues directly in situ using immunomodulatory biomaterials. Direct exposure to the bloodstream and hemodynamic loads is a particular challenge, given the risk of thrombosis and adverse remodeling that it brings. However, the blood is also a source of (immune) cells and proteins that dominantly contribute to functional tissue regeneration. This review explores the potential of the blood as a source for the complete or partial in situ regeneration of cardiovascular tissues, with a particular focus on the endothelium, being the natural blood-tissue barrier. We pinpoint the current scientific challenges to enable rational engineering and testing of blood-contacting implants to leverage the regenerative potential of the blood.

Macrophage-extracellular matrix interactions: Perspectives for tissue engineered heart valve remodeling

In situ heart valve tissue engineering approaches have been proposed as promising strategies to overcome the limitations of current heart valve replacements. Tissue engineered heart valves (TEHVs) generated from in vitro grown tissue engineered matrices (TEMs) aim at mimicking the microenvironmental cues from the extracellular matrix (ECM) to favor integration and remodeling of the implant. A key role of the ECM is to provide mechanical support to and attract host cells into the construct. Additionally, each ECM component plays a critical role in regulating cell adhesion, growth, migration, and differentiation potential. Importantly, the immune response to the implanted TEHV is also modulated biophysically via macrophage-ECM protein interactions. Therefore, the aim of this review is to summarize what is currently known about the interactions and signaling networks occurring between ECM proteins and macrophages, and how these interactions may impact the long-term in situ remodeling outcomes of TEMs. First, we provide an overview of in situ tissue engineering approaches and their clinical relevance, followed by a discussion on the fundamentals of the remodeling cascades. We then focus on the role of circulation-derived and resident tissue macrophages, with particular emphasis on the ramifications that ECM proteins and peptides may have in regulating the host immune response. Finally, the relevance of these findings for heart valve tissue engineering applications is discussed.

Black pepper and vegetable oil-based emulsion synergistically enhance carotenoid bioavailability of raw vegetables in humans

This study demonstrated the combination of black pepper and a canola oil-based emulsion synergistically enhanced carotenoid bioavailability of raw vegetables in humans. In a randomized crossover design, healthy young adults consumed (1) vegetable salad (control), (2) salad with canola oil emulsion (COE), (3) salad with black pepper (BP), and (4) salad with canola oil emulsion and black pepper (COE + BP). COE + BP led to a higher AUC_0-10h of total plasma carotenoids (p < 0.0005) than the control (6.1-fold), BP (2.1-fold), and COE (3.0-fold). COE + BP increased AUC_0-10h of plasma lutein, α-carotene, β-carotene, and lycopene by 4.8, 9.7, 7.6, and 5.5-fold than the control, respectively (p < 0.0001). COE + BP produced a significant synergy in increasing both C_max and AUC_0-10h of total carotenoids, α-carotene, β-carotene, and lycopene. Moreover, COE + BP produced a stronger enhancement on AUC_0-10h of total carotenoids, α-carotene, β-carotene, and lycopene in females than in males.

Scaffold-Mediated Immunoengineering as Innovative Strategy for Tendon Regeneration

Tendon injuries are at the frontier of innovative approaches to public health concerns and sectoral policy objectives. Indeed, these injuries remain difficult to manage due to tendon’s poor healing ability ascribable to a hypo-cellularity and low vascularity, leading to the formation of a fibrotic tissue affecting its functionality. Tissue engineering represents a promising solution for the regeneration of damaged tendons with the aim to stimulate tissue regeneration or to produce functional implantable biomaterials. However, any technological advancement must take into consideration the role of the immune system in tissue regeneration and the potential of biomaterial scaffolds to control the immune signaling, creating a pro-regenerative environment. In this context, immunoengineering has emerged as a new discipline, developing innovative strategies for tendon injuries. It aims at designing scaffolds, in combination with engineered bioactive molecules and/or stem cells, able to modulate the interaction between the transplanted biomaterial-scaffold and the host tissue allowing a pro-regenerative immune response, therefore hindering fibrosis occurrence at the injury site and guiding tendon regeneration. Thus, this review is aimed at giving an overview on the role exerted from different tissue engineering actors in leading immunoregeneration by crosstalking with stem and immune cells to generate new paradigms in designing regenerative medicine approaches for tendon injuries.

Immuno-regenerative biomaterials for in situ cardiovascular tissue engineering - Do patient characteristics warrant precision engineering?

In situ tissue engineering using bioresorbable material implants - or scaffolds - that harness the patient's immune response while guiding neotissue formation at the site of implantation is emerging as a novel therapy to regenerate human tissues. For the cardiovascular system, the use of such implants, like blood vessels and heart valves, is gradually entering the stage of clinical translation. This opens up the question if and to what extent patient characteristics influence tissue outcomes, necessitating the precision engineering of scaffolds to guide patient-specific neo-tissue formation. Because of the current scarcity of human in vivo data, herein we review and evaluate in vitro and preclinical investigations to predict the potential role of patient-specific parameters like sex, age, ethnicity, hemodynamics, and a multifactorial disease profile, with special emphasis on their contribution to the inflammation-driven processes of in situ tissue engineering. We conclude that patient-specific conditions have a strong impact on key aspects of in situ cardiovascular tissue engineering, including inflammation, hemodynamic conditions, scaffold resorption, and tissue remodeling capacity, suggesting that a tailored approach may be required to engineer immuno-regenerative biomaterials for safe and predictive clinical applicability.

Extracellular Matrix-Based Biomaterials for Cardiovascular Tissue Engineering

Regenerative medicine and tissue engineering strategies have made remarkable progress in remodeling, replacing, and regenerating damaged cardiovascular tissues. The design of three-dimensional (3D) scaffolds with appropriate biochemical and mechanical characteristics is critical for engineering tissue-engineered replacements. The extracellular matrix (ECM) is a dynamic scaffolding structure characterized by tissue-specific biochemical, biophysical, and mechanical properties that modulates cellular behavior and activates highly regulated signaling pathways. In light of technological advancements, biomaterial-based scaffolds have been developed that better mimic physiological ECM properties, provide signaling cues that modulate cellular behavior, and form functional tissues and organs. In this review, we summarize the in vitro, pre-clinical, and clinical research models that have been employed in the design of ECM-based biomaterials for cardiovascular regenerative medicine. We highlight the research advancements in the incorporation of ECM components into biomaterial-based scaffolds, the engineering of increasingly complex structures using biofabrication and spatial patterning techniques, the regulation of ECMs on vascular differentiation and function, and the translation of ECM-based scaffolds for vascular graft applications. Finally, we discuss the challenges, future perspectives, and directions in the design of next-generation ECM-based biomaterials for cardiovascular tissue engineering and clinical translation.

Chemokine-Induced PBMC and Subsequent MSC Migration Toward Decellularized Heart Valve Tissue

PURPOSE

Enhancing the recellularization of a decellularized heart valve in situ may lead to an improved or ideal heart valve replacement. A promising approach is leveraging the immune response for inflammation-mediated recellularization. However, this mechanism has not been previously demonstrated in vitro.

METHODS

This study investigated loading the chemokine MCP-1 into decellularized porcine heart valve tissue and measured the migration of human peripheral blood mononuclear cells (PBMCs) and mesenchymal stem cells (MSCs) toward the chemokine loaded valve tissue.

RESULTS

The results of this study demonstrate that MCP-1-loaded tissues increase PBMC migration compared to non-loaded tissues. Additionally, we demonstrate MCP-1-loaded tissues that have recruited PBMCs lead to increased migration of MSCs compared to decellularized tissue alone.

CONCLUSION

The results of this study provide evidence for the inflammation-mediated recellularization mechanism. Furthermore, the results support the use of such an approach for enhancing the recellularization of a decellularized heart valve.

Improving the immunosuppressive potential of articular chondroprogenitors in a three-dimensional culture setting

Cartilage repair in osteoarthritic patients remains a challenge. Identifying resident or donor stem/progenitor cell populations is crucial for augmenting the low intrinsic repair potential of hyaline cartilage. Furthermore, mediating the interaction between these cells and the local immunogenic environment is thought to be critical for long term repair and regeneration. In this study we propose articular cartilage progenitor/stem cells (CPSC) as a valid alternative to bone marrow-derived mesenchymal stem cells (BMMSC) for cartilage repair strategies after trauma. Similar to BMMSC, CPSC isolated from osteoarthritic patients express stem cell markers and have chondrogenic, osteogenic, and adipogenic differentiation ability. In an in vitro 2D setting, CPSC show higher expression of SPP1 and LEP, markers of osteogenic and adipogenic differentiation, respectively. CPSC also display a higher commitment toward chondrogenesis as demonstrated by a higher expression of ACAN. BMMSC and CPSC were cultured in vitro using a previously established collagen-chondroitin sulfate 3D scaffold. The scaffold mimics the cartilage niche, allowing both cell populations to maintain their stem cell features and improve their immunosuppressive potential, demonstrated by the inhibition of activated PBMC proliferation in a co-culture setting. As a result, this study suggests articular cartilage derived-CPSC can be used as a novel tool for cellular and acellular regenerative medicine approaches for osteoarthritis (OA). In addition, the benefit of utilizing a biomimetic acellular scaffold as an advanced 3D culture system to more accurately mimic the physiological environment is demonstrated.

Differential Leaflet Remodeling of Bone Marrow Cell Pre-Seeded Versus Nonseeded Bioresorbable Transcatheter Pulmonary Valve Replacements

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Bone marrow mononuclear cell pre-seeding of polycarbonate bisurea–based tissue-engineered heart valves has detrimental effects on long-term performance and in situ remodeling and, therefore, should be avoided.

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Leaflet-specific analysis revealed pronounced remodeling differences with regard to cell infiltration, scaffold resorption, and extracellular matrix deposition within the same valve explant.

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The heterogeneity in remodeling of polycarbonate bisurea–based tissue-engineered heart valves may have important safety implications in terms of clinical translation.

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An in-depth understanding of the mechanobiological mechanisms involved in the in situ remodeling is required to limit the risk of unpredictable (maladaptive) remodeling.

This study showed that bone marrow mononuclear cell pre-seeding had detrimental effects on functionality and in situ remodeling of bioresorbable bisurea-modified polycarbonate (PC-BU)-based tissue-engineered heart valves (TEHVs) used as transcatheter pulmonary valve replacement in sheep. We also showed heterogeneous valve and leaflet remodeling, which affects PC-BU TEHV safety, challenging their potential for clinical translation. We suggest that bone marrow mononuclear cell pre-seeding should not be used in combination with PC-BU TEHVs. A better understanding of cell–scaffold interaction and in situ remodeling processes is needed to improve transcatheter valve design and polymer absorption rates for a safe and clinically relevant translation of this approach.

Non-physiologic Bioreactor Processing Conditions for Heart Valve Tissue Engineering

PURPOSE

Conventional methods of seeding decellularized heart valves for heart valve tissue engineering have led to inconsistent results in interstitial cellular repopulation, particularly of the distal valve leaflet, and notably distinct from documented re-endothelialization. The use of bioreactor conditioning mimicking physiologic parameters has been well explored but cellular infiltration remains challenging. Non-characteristic, non-physiologic conditioning parameters within a bioreactor, such as hypoxia and cyclic chamber pressure, may be used to increase the cellular infiltration leading to increased recellularization.

METHODS

To investigate the effects of novel and perhaps non-intuitive bioreactor conditioning parameters, ovine aortic heart valves were seeded with mesenchymal stem cells and cultured in one of four environments: hypoxia and high cyclic pressures (120 mmHg), normoxia and high cyclic pressures, hypoxia and negative cyclic pressures (- 20 mmHg), and normoxia and negative cyclic pressures. Analysis included measurements of cellular density, cell phenotype, and biochemical concentrations.

RESULTS

The results revealed that the bioreactor conditioning parameters influenced the degree of recellularization. Groups that implemented hypoxic conditioning exhibited increased cellular infiltration into the valve leaflet tissue compared to normoxic conditioning, while pressure conditioning did not have a significant effect of recellularization. Protein expression across all groups was similar, exhibiting a stem cell and valve interstitial cell phenotype. Biochemical analysis of the extracellular matrix was similar between all groups.

CONCLUSION

These results suggest the use of non-physiologic bioreactor conditioning parameters can increase in vitro recellularization of tissue engineered heart valve leaflets. Particularly, hypoxic culture was found to increase the cellular infiltration. Therefore, bioreactor conditioning of tissue engineered constructs need not always mimic physiologic conditions, and it is worth investigating novel or uncharacteristic culture conditions as they may benefit aspects of tissue culture.

Can We Grow Valves Inside the Heart? Perspective on Material-based In Situ Heart Valve Tissue Engineering

In situ heart valve tissue engineering using cell-free synthetic, biodegradable scaffolds is under development as a clinically attractive approach to create living valves right inside the heart of a patient. In this approach, a valve-shaped porous scaffold "implant" is rapidly populated by endogenous cells that initiate neo-tissue formation in pace with scaffold degradation. While this may constitute a cost-effective procedure, compatible with regulatory and clinical standards worldwide, the new technology heavily relies on the development of advanced biomaterials, the processing thereof into (minimally invasive deliverable) scaffolds, and the interaction of such materials with endogenous cells and neo-tissue under hemodynamic conditions. Despite the first positive preclinical results and the initiation of a small-scale clinical trial by commercial parties, in situ tissue formation is not well understood. In addition, it remains to be determined whether the resulting neo-tissue can grow with the body and preserves functional homeostasis throughout life. More important yet, it is still unknown if and how in situ tissue formation can be controlled under conditions of genetic or acquired disease. Here, we discuss the recent advances of material-based in situ heart valve tissue engineering and highlight the most critical issues that remain before clinical application can be expected. We argue that a combination of basic science - unveiling the mechanisms of the human body to respond to the implanted biomaterial under (patho)physiological conditions - and technological advancements - relating to the development of next generation materials and the prediction of in situ tissue growth and adaptation - is essential to take the next step towards a realistic and rewarding translation of in situ heart valve tissue engineering.

Clot-entrapped blood cells in synergy with human mesenchymal stem cells create a pro-angiogenic healing response

Blood clots stop bleeding and provide cell-instructive microenvironments. Still, in vitro models used to study implant performance typically neglect any possible interactions of recruited cells with surface-adhering blood clots. Here we study the interaction and synergies of bone marrow derived human mesenchymal stem cells (hMSCs) with surface-induced blood clots in an in vitro model by fluorescence microscopy, scanning and correlative light and electron microscopy, ELISA assays and zymography. The clinically used alkali-treated rough titanium (Ti) surfaces investigated here are known to enhance blood clotting compared to native Ti and to improve the healing response, but the underlying mechanisms remain elusive. Here we show that the presence of blood clots synergistically increased hMSC proliferation, extracellular matrix (ECM) remodelling and the release of matrix fragments and angiogenic VEGF, but did not increase the osteogenic differentiation of hMSCs. While many biomaterials are nowadays engineered to release pro-angiogenic factors, we show here that clot-entrapped blood cells on conventional materials in synergy with hMSCs are potent producers of pro-angiogenic factors. Our data might thus not only explain why alkali-treatment is beneficial for Ti implant integration, but they suggest that the physiological importance of blood clots to create pro-angiogenic environments on implants has been greatly underestimated. The importance of blood clots might have been missed because the pro-angiogenic functions get activated only upon stimulation by synergistic interactions with the invading cells.

Puncturing of lyophilized tissue engineered vascular matrices enhances the efficiency of their recellularization

Data on in vitro engineered "off the shelf" matrices support the concept of endogenous cellular repopulation driving the graft's remodeling via immune-mediated response. This seems important to further accelerate the cell reconstitution and may play a crucial role when mononuclear cells are used. Nevertheless, studies on decellularized xenogeneic grafts showed only limited host cell repopulation post-implantation. This study aims at a systematic comparison of reseeding methods (dripping, injection, bathing in a cell suspension and combined puncturing-dripping method) to define the most efficient technique enhancing recellularization of tissue engineered vascular matrices (patches, vessels, small diameter and standard size valves) prior implantation. The constructs were analyzed histologically, biochemically and biomechanically. Various preconditioning treatments (wet, lyophilized and air-dried) combined with reseeding methods demonstrated the highest cell loading efficiency, despite applied crimping and flow stress, of lyophilization followed by puncturing-dripping technique. This novel seeding method allows for an efficient, time-saving graft reseeding that can be used within a one-step cardiovascular clinical intervention.

STATEMENT OF SIGNIFICANCE

The concept of living tissue engineered, self-repairing, autologous cardiovascular replacements, was proposed alternatively to existing synthetic/xenogeneic prostheses. Recent studies in animal models demonstrate faster in vivo recellularization after grafts pre-seeding with cells prior implantation. Pre-seeded cells hold either, the ability to differentiate directionally or attract host cells, crucial for graft integration and remodeling. It is unclear, however, how efficient the pre-loading is and how well cells withstand the flow. The study presents a systematic overview of cell loading techniques of different cardiovascular constructs, tested under static and dynamic conditions. Comparison illustrates a significantly higher efficiency of cells loading in lyophilized tissues punctured before their standard seeding. This technique may beneficially accelerate remodeling of cardiovascular grafts in further in vivo studies.

Extended bioreactor conditioning of mononuclear cell-seeded heart valve scaffolds

The tissue-engineered heart valve may be the ideal valve replacement option but still must overcome challenges in leaflet recellularization. This study sought to investigate the potential for leaflet matrix restoration and repopulation following mononuclear cell seeding and extended periods of bioreactor conditioning. Human aortic heart valves were seeded with mononuclear cells and conditioned in a pulsatile bioreactor for 3 days, 3 weeks, or 6 weeks. The results of this study determined that a mononuclear cell population can be readily localized within the leaflet tissue in as little as 3 days. Furthermore, as extended bioreactor condition continued to the 3- and 6-week time points, the mesenchymal stem cell subfraction proliferated and appeared to become the predominant cell phenotype. This was evident through positive expression of mesenchymal stem cell markers and no expression of mononuclear cell markers observed by immunohistochemistry in the 3- and 6-week groups. In addition, cells in the 3- and 6-week groups exhibited an up-regulation of mesenchymal stem cell–associated genes (THY1, NT5E, and ITGB1) and a down-regulation of mononuclear cell–associated genes (CD14, ICAM1, and PECAM1) compared to the initial seeded cell population. However, repopulation of the leaflet interstitium was less extensive than anticipated. Valves in the 6-week time point also exhibited retracted leaflets. Thus, while the 3-week bioreactor-conditioning period used in this study may hold some promise, a bioreactor-conditioning period of 6 weeks is not a viable option for clinical translation due to the negative impact on valve performance.

The Host Response in Tissue Engineering: Crosstalk Between Immune cells and Cell-laden Scaffolds

Implantation of cell-laden scaffolds is a promising strategy for regenerating tissue that has been damaged due to injury or disease. However, the act of implantation initiates an acute inflammatory response. If the scaffold is non-biologic (i.e., a modified biologic scaffold or synthetic-based scaffold), inflammation will be prolonged through the foreign body response (FBR), which eventually forms a fibrous capsule and walls off the implant from the surrounding host tissue. This host response, from a cellular perspective, can create a harsh environment leading to long-lasting effects on the tissue engineering outcome. At the same time, cells embedded within the scaffold can respond to this environment and influence the interrogating immune cells (e.g., macrophages). This crosstalk, depending on the type of cell, can dramatically influence the host response. This review provides an overview of the FBR and highlights important and recent advancements in the host response to cell-laden scaffolds with a focus on the impact of the communication between immune cells and cells embedded within a scaffold. Understanding this complex interplay between the immune cells, notably macrophages, and the tissue engineering cells is a critically important component to a successful in vivo tissue engineering therapy.

Cardiovascular tissue engineering: From basic science to clinical application

Valvular heart disease is an increasing population health problem and, especially in the elderly, a significant cause of morbidity and mortality. The current treatment options, such as mechanical and bioprosthetic heart valve replacements, have significant restrictions and limitations. Considering the increased life expectancy of our aging population, there is an urgent need for novel heart valve concepts that remain functional throughout life to prevent the need for reoperation. Heart valve tissue engineering aims to overcome these constraints by creating regenerative, self-repairing valve substitutes with life-long durability. In this review, we give an overview of advances in the development of tissue engineered heart valves, and describe the steps required to design and validate a novel valve prosthesis before reaching first-in-men clinical trials. In-silico and in-vitro models are proposed as tools for the assessment of valve design, functionality and compatibility, while in-vivo preclinical models are required to confirm the remodeling and growth potential of the tissue engineered heart valves. An overview of the tissue engineered heart valve studies that have reached clinical translation is also presented. Final remarks highlight the possibilities as well as the obstacles to overcome in translating heart valve prostheses into clinical application.

Preparation of Protein Molecular-Imprinted Polysiloxane Membrane Using Calcium Alginate Film as Matrix and Its Application for Cell Culture

Bovine serum albumin (BSA) molecular-imprinted polysiloxane (MIP) membrane was prepared by sol-gel technology, using silanes as the functional monomers, BSA as the template and CaAlg hydrogel film as the matrix. The stress-strain curves of wet CaAlg membrane and molecular-imprinted polysiloxane membrane were investigated. We evaluate the adsorption and recognition properties of MIP membrane. Results showed that the adsorption capacity of BSA-imprinted polysiloxane for BSA reached 28.83 mg/g, which was 2.18 times the non-imprinted polysiloxane (NIP) membrane. The adsorption rate was higher than that of the protein-imprinted hydrogel. BSA-imprinted polysiloxane membrane could identify the protein template from competitive proteins such as bovine hemoglobin, ovalbumin and bovine γ-globulin. In order to obtain the biomaterial that can promote cell adhesion and proliferation, fibronectin (FN)-imprinted polysiloxane (FN-MIP) membrane was obtained by using fibronectin as the template, silanes as functional monomers, and CaAlg hydrogel membrane as the substrate or matrix. The FN-MIP adsorbed more FN than NIP. The FN-imprinted polysiloxane membrane was applied to culture mouse fibroblast cells (L929) and the results proved that the FN-MIP had a better effect on cell adhesion than NIP.

3D-cultured adipose tissue-derived stem cells inhibit liver cancer cell migration and invasion through suppressing epithelial-mesenchymal transition

Adipose tissue-derived stem cells (ADSCs) are considered promising candidates for stem cell therapy; however, the tumorigenicity of ADSCs remains controversial. The present study aimed to investigate the association between ADSCs and liver cancer cells, and to determine whether culture methods could influence the effects of ADSCs on liver cancer cell growth in vitro. Liver cancer cells were treated with ADSCs-conditioned medium (CM) that was collected using the two-dimensional (2D) culture method, sphere culture method, or three-dimensional (3D) culture method. After that, cell viability and apoptosis were measured using CCK-8 and Annexin V-FITC assay, respectively; the cell motility and adhesive capacity were analyzed by scratch wound healing and cell adhesion assay, respectively; the cell migration and invasion were examined by Transwell units; and the molecular mechanisms of ADSCs on effecting epithelial mesenchymal transition signaling pathway were further analyzed. The results demonstrated that ADSCs-CM was able to inhibit the growth of liver cancer cells by inhibiting cell proliferation and promoting cell apoptosis, as well as by suppressing cell motility, adhesive capacity, migration and invasion. In addition, ADSCs-CM was able to suppress cell growth via the downregulation of epithelial-mesenchymal transition signaling. Notably, the enhanced inhibitory effects of ADSCs on liver cancer cell growth could be achieved after cultu ring using a 3D approach. These findings suggested that ADSCs may provide a novel promising therapeutic approach for the treatment of patients with liver cancer, and the 3D culture method may provide a novel approach to explore the association between ADSCs and cancer.

Biomaterial-driven in situ cardiovascular tissue engineering-a multi-disciplinary perspective

There is a persistent and growing clinical need for readily-available substitutes for heart valves and small-diameter blood vessels. In situ tissue engineering is emerging as a disruptive new technology, providing ready-to-use biodegradable, cell-free constructs which are designed to induce regeneration upon implantation, directly in the functional site. The induced regenerative process hinges around the host response to the implanted biomaterial and the interplay between immune cells, stem/progenitor cell and tissue cells in the microenvironment provided by the scaffold in the hemodynamic environment. Recapitulating the complex tissue microstructure and function of cardiovascular tissues is a highly challenging target. Therein the scaffold plays an instructive role, providing the microenvironment that attracts and harbors host cells, modulating the inflammatory response, and acting as a temporal roadmap for new tissue to be formed. Moreover, the biomechanical loads imposed by the hemodynamic environment play a pivotal role. Here, we provide a multidisciplinary view on in situ cardiovascular tissue engineering using synthetic scaffolds; starting from the state-of-the art, the principles of the biomaterial-driven host response and wound healing and the cellular players involved, toward the impact of the biomechanical, physical, and biochemical microenvironmental cues that are given by the scaffold design. To conclude, we pinpoint and further address the main current challenges for in situ cardiovascular regeneration, namely the achievement of tissue homeostasis, the development of predictive models for long-term performances of the implanted grafts, and the necessity for stratification for successful clinical translation.

Heterogeneity of proangiogenic features in mesenchymal stem cells derived from bone marrow, adipose tissue, umbilical cord, and placenta

Background

Mesenchymal stem cells (MSCs) have been widely proven effective for therapeutic angiogenesis in ischemia animal models as well as clinical vascular diseases. Because of the invasive method, limited resources, and aging problems of adult tissue-derived MSCs, more perinatal tissue-derived MSCs have been isolated and studied as promising substitutable MSCs for cell transplantation. However, fewer studies have comparatively studied the angiogenic efficacy of MSCs derived from different tissues sources. Here, we evaluated whether the in-situ environment would affect the angiogenic potential of MSCs.

Methods

We harvested MSCs from adult bone marrow (BMSCs), adipose tissue (AMSCs), perinatal umbilical cord (UMSCs), and placental chorionic villi (PMSCs), and studied their “MSC identity” by flow cytometry and in-vitro trilineage differentiation assay. Then we comparatively studied their endothelial differentiation capabilities and paracrine actions side by side in vitro.

Results

Our data showed that UMSCs and PMSCs fitted well with the minimum standard of MSCs as well as BMSCs and AMSCs. Interestingly, we found that MSCs regardless of their tissue origins could develop similar endothelial-relevant functions in vitro, including producing eNOS and uptaking ac-LDL during endothelial differentiation in spite of their feeble expression of endothelial-related genes and proteins. Additionally, we surprisingly found that BMSCs and PMSCs could directly form tubular structures in vitro on Matrigel and their conditioned medium showed significant proangiogenic bioactivities on endothelial cells in vitro compared with those of AMSCs and UMSCs. Besides, several angiogenic genes were upregulated in BMSCs and PMSCs in comparison with AMSCs and UMSCs. Moreover, enzyme-linked immunosorbent assay further confirmed that BMSCs secreted much more VEGF, and PMSCs secreted much more HGF and PGE2.

Conclusions

Our study demonstrated the heterogeneous proangiogenic properties of MSCs derived from different tissue origins, and the in vivo isolated environment might contribute to these differences. Our study suggested that MSCs derived from bone marrow and placental chorionic villi might be preferred in clinical application for therapeutic angiogenesis.

Electronic supplementary material

The online version of this article (doi:10.1186/s13287-016-0418-9) contains supplementary material, which is available to authorized users.

Knitting for heart valve tissue engineering

Knitting is a versatile technology which offers a large portfolio of products and solutions of interest in heart valve (HV) tissue engineering (TE). One of the main advantages of knitting is its ability to construct complex shapes and structures by precisely assembling the yarns in the desired position. With this in mind, knitting could be employed to construct a HV scaffold that closely resembles the authentic valve. This has the potential to reproduce the anisotropic structure that is characteristic of the heart valve with the yarns, in particular the 3-layered architecture of the leaflets. These yarns can provide oriented growth of cells lengthwise and consequently enable the deposition of extracellular matrix (ECM) proteins in an oriented manner. This technique, therefore, has a potential to provide a functional knitted scaffold, but to achieve that textile engineers need to gain a basic understanding of structural and mechanical aspects of the heart valve and in addition, tissue engineers must acquire the knowledge of tools and capacities that are essential in knitting technology. The aim of this review is to provide a platform to consolidate these two fields as well as to enable an efficient communication and cooperation among these two research areas.

Bioengineered living cardiac and venous valve replacements: current status and future prospects

Valvular heart disease remains to be a major cause of death worldwide with increasing prevalence, mortality, and morbidity. Current heart valve replacements are associated with several limitations due to their nonviable nature. In this regard, heart valve tissue engineering has shown to represent a promising concept in order to overcome these limitations and replace diseased cardiac valves with living, autologous constructs. These bioengineered valves hold potential for in situ remodeling, growth, and repair throughout the patient's lifetime without the risk of thromboembolic complications and adverse immune responses. For the fabrication of tissue-engineered heart valves, several concepts have been established, the "classical" in vitro tissue engineering approach, the in situ tissue engineering approach, and alternative approaches including three-dimensional printing and electrospinning. Besides first attempts have been conducted in order to produce a tissue-engineered venous valve for the treatment of deep venous valve insufficiency. Here we review basic principals and current scientific status of valvular tissue engineering, including a critical discussion and outlook for the future.

Synergistic interactions of blood-borne immune cells, fibroblasts and extracellular matrix drive repair in an in vitro peri-implant wound healing model

Low correlations of cell culture data with clinical outcomes pose major medical challenges with costly consequences. While the majority of biomaterials are tested using in vitro cell monocultures, the importance of synergistic interactions between different cell types on paracrine signalling has recently been highlighted. In this proof-of-concept study, we asked whether the first contact of surfaces with whole human blood could steer the tissue healing response. This hypothesis was tested using alkali-treatment of rough titanium (Ti) surfaces since they have clinically been shown to improve early implant integration and stability, yet blood-free in vitro cell cultures poorly correlated with in vivo tissue healing. We show that alkali-treatment, compared to native Ti surfaces, increased blood clot thickness, including platelet adhesion. Strikingly, blood clots with entrapped blood cells in synergistic interactions with fibroblasts, but not fibroblasts alone, upregulated the secretion of major factors associated with fast healing. This includes matrix metalloproteinases (MMPs) to break down extracellular matrix and the growth factor VEGF, known for its angiogenic potential. Consequently, in vitro test platforms, which consider whole blood-implant interactions, might be superior in predicting wound healing in response to biomaterial properties.

Mesenchymal stromal cell implantation for stimulation of long bone healing aggravates Staphylococcus aureus induced osteomyelitis

Large bone defects requiring long-term osteosynthetic stabilization or repeated surgeries show a considerable rate of infection. Mesenchymal stromal cells (MSCs) have been successfully used to enhance bone regeneration, but their powerful immunomodulatory effects may impose an enhanced risk for osteomyelitis development. In order to unravel whether implantation of MSCs aggravates a simultaneous bone infection, a hydrogel-supported osteomyelitis ostectomy model was developed in which rats received a femoral bone defect with rigid plate-fixation. After fibrin-assisted transfer of Staphylococcus aureus (SA), effects of MSC implantation on osteomyelitis development were quantified over 3-4 weeks. All SA-infected animals developed an acute local osteomyelitis with significantly increased blood neutrophil count, abscess formation and bone destruction. MSC-treatment of infected defects aggravated osteomyelitis according to a significantly elevated osteomyelitis score and enhanced distal bone loss with spongy alteration of cortical bone architecture. Increased attraction of macrophages, osteoclasts and regulation of pro- and anti-inflammatory mediators were potential MSC actions. Overall trophic actions of MSCs implanted into non-sterile bone defects may enhance an infection and/or exacerbate osteomyelitis. Studies on antibiotic carrier augmentation or antibiotic treatment are warranted to decide whether MSC implantation is a safe and promising therapy for orthopedic implant-stabilized bone defects at high risk for development of infection.

Three-dimensional spheroid cell culture of umbilical cord tissue-derived mesenchymal stromal cells leads to enhanced paracrine induction of wound healing

Introduction

The secretion of trophic factors by mesenchymal stromal cells has gained increased interest given the benefits it may bring to the treatment of a variety of traumatic injuries such as skin wounds. Herein, we report on a three-dimensional culture-based method to improve the paracrine activity of a specific population of umbilical cord tissue-derived mesenchymal stromal cells (UCX®) towards the application of conditioned medium for the treatment of cutaneous wounds.

Methods

A UCX® three-dimensional culture model was developed and characterized with respect to spheroid formation, cell phenotype and cell viability. The secretion by UCX® spheroids of extracellular matrix proteins and trophic factors involved in the wound-healing process was analysed. The skin regenerative potential of UCX® three-dimensional culture-derived conditioned medium (CM3D) was also assessed in vitro and in vivo against UCX® two-dimensional culture-derived conditioned medium (CM2D) using scratch and tubulogenesis assays and a rat wound splinting model, respectively.

Results

UCX® spheroids kept in our three-dimensional system remained viable and multipotent and secreted considerable amounts of vascular endothelial growth factor A, which was undetected in two-dimensional cultures, and higher amounts of matrix metalloproteinase-2, matrix metalloproteinase-9, hepatocyte growth factor, transforming growth factor β1, granulocyte-colony stimulating factor, fibroblast growth factor 2 and interleukin-6, when compared to CM2D. Furthermore, CM3D significantly enhanced elastin production and migration of keratinocytes and fibroblasts in vitro. In turn, tubulogenesis assays revealed increased capillary maturation in the presence of CM3D, as seen by a significant increase in capillary thickness and length when compared to CM2D, and increased branching points and capillary number when compared to basal medium. Finally, CM3D-treated wounds presented signs of faster and better resolution when compared to untreated and CM2D-treated wounds in vivo. Although CM2D proved to be beneficial, CM3D-treated wounds revealed a completely regenerated tissue by day 14 after excisions, with a more mature vascular system already showing glands and hair follicles.

Conclusions

This work unravels an important alternative to the use of cells in the final formulation of advanced therapy medicinal products by providing a proof of concept that a reproducible system for the production of UCX®-conditioned medium can be used to prime a secretome for eventual clinical applications.

Electronic supplementary material

The online version of this article (doi:10.1186/s13287-015-0082-5) contains supplementary material, which is available to authorized users.