A nanofibrous electrospun patch to maintain human mesenchymal cell stemness

Regulation Mechanisms and Maintenance Strategies of Stemness in Mesenchymal Stem Cells

Stemness pertains to the intrinsic ability of mesenchymal stem cells (MSCs) to undergo self-renewal and differentiate into multiple lineages, while simultaneously impeding their differentiation and preserving crucial differentiating genes in a state of quiescence and equilibrium. Owing to their favorable attributes, including uncomplicated isolation protocols, ethical compliance, and ease of procurement, MSCs have become a focal point of inquiry in the domains of regenerative medicine and tissue engineering. As age increases or ex vivo cultivation is prolonged, the functionality of MSCs decreases and their stemness gradually diminishes, thereby limiting their potential therapeutic applications. Despite the existence of several uncertainties surrounding the comprehension of MSC stemness, considerable advancements have been achieved in the clarification of the potential mechanisms that lead to stemness loss, as well as the associated strategies for stemness maintenance. This comprehensive review provides a systematic overview of the factors influencing the preservation of MSC stemness, the molecular mechanisms governing it, the strategies for its maintenance, and the therapeutic potential associated with stemness. Finally, we underscore the obstacles and prospective avenues in present investigations, providing innovative perspectives and opportunities for the preservation and therapeutic utilization of MSC stemness.

Electrospun electroconductive constructs of aligned fibers for cardiac tissue engineering

Myocardial infarction remains the leading cause of death in the western world. Since the heart has limited regenerative capabilities, several cardiac tissue engineering (CTE) strategies have been proposed to repair the damaged myocardium. A novel electrospun construct with aligned and electroconductive fibers combining gelatin, poly(lactic-co-glycolic) acid and polypyrrole that may serve as a cardiac patch is presented. Constructs were characterized for fiber alignment, surface wettability, shrinkage and swelling behavior, porosity, degradation rate, mechanical properties, and electrical properties. Cell-biomaterial interactions were studied using three different types of cells, Neonatal Rat Ventricular Myocytes (NRVM), human lung fibroblasts (MRC-5) and induced pluripotent stem cells (iPSCs). All cell types showed good viability and unique organization on construct surfaces depending on their phenotype. Finally, we assessed the maturation status of NRVMs after 14 days by confocal images and qRT-PCR. Overall evidence supports a proof-of-concept that this novel biomaterial construct could be a good candidate patch for CTE applications.

Bioactive engineered scaffolds based on PCL-PEG-PCL and tumor cell-derived exosomes to minimize the foreign body reaction

Long-term presence of M1 macrophages causes serious foreign body reaction (FBR), which is the main reason for the failure of biological scaffold integration. Inducing M2 polarization of macrophages near scaffolds to reduce foreign body response has been widely researched. In this work, inspired by the special capability of tumor exosomes in macrophages M2 polarization, we integrate tumor-derived exosomes into biological scaffolds to minimize the FBR. In brief, breast cancer cell-derived exosomes are loaded into polycaprolactone-b-polyethylene glycol-b-polycaprolactone (PCL-PEG-PCL) fiber scaffold through physical adsorption and entrapment to constructed bioactive engineered scaffold. In cellular experiments, we demonstrate bioactive engineered scaffold based on PCL-PEG-PCL and exosomes can promote the transformation of macrophages from M1 to M2 through the PI3K/Akt signaling pathway. In addition, the exosomes release gradually from scaffolds and act on the macrophages around the scaffolds to reduce FBR in a subcutaneous implant mouse model. Compared with PCL-PEG-PCL scaffolds without exosomes, bioactive engineered scaffolds reduce significantly inflammation and fibrosis of tissues around the scaffolds. Therefore, cancer cell-derived exosomes show the potential for constructing engineered scaffolds in inhibiting the excessive inflammation and facilitating tissue formation.

Vascular Graft Infections: An Overview of Novel Treatments Using Nanoparticles and Nanofibers

Vascular disease in elderly patients is a growing health concern, with an estimated prevalence of 15–20% in patients above 70 years old. Current treatment for vascular diseases requires the use of a vascular graft (VG) to revascularize lower or upper extremities, create dialysis access, treat aortic aneurysms, and repair dissection. However, postoperative infection is a major complication associated with the use of these VG, often necessitating several operations to achieve complete or partial graft excision, vascular coverage, and extra-anatomical revascularization. There is also a high risk of morbidity, mortality, and limb loss. Therefore, it is important to develop a method to prevent or reduce the incidence of these infections. Numerous studies have investigated the efficacy of antibiotic- and antiseptic-impregnated grafts. In comparison to these traditional methods of creating antimicrobial grafts, nanotechnology enables researchers to design more efficient VG. Nanofibers and nanoparticles have a greater surface area compared to bulk materials, allowing for more efficient encapsulation of antibiotics and better control over their temporo-spatial release. The disruptive potential of nanofibers and nanoparticles is exceptional, and they could pave the way for a new generation of prosthetic VG. This review aims to discuss how nanotechnology is shaping the future of cardiovascular-related infection management.

Three-Dimensional Modeling of the Structural Microenvironment in Post-Traumatic War Wounds

BACKGROUND:

The development of post-traumatic heterotopic ossification (HO) is a common, undesirable sequela in patients with high-energy (war-related) extremity injuries. While inflammatory and osteoinductive signaling pathways are known to be involved in the development and progression of post-traumatic HO, features of the structural microenvironment within which the ectopic bone begins to form remain poorly understood. Thus, increasing our knowledge of molecular and structural changes within the healing wound may help elucidate the pathogenesis of post-traumatic HO and aid in the development of specific treatment and/or prevention strategies.

METHODS:

In this study, we performed high-resolution microscopy and biochemical analysis of tissues obtained from traumatic war wounds to characterize changes in the structural microenvironment. In addition, using an electrospinning approach, we modeled this microenvironment to reconstitute a three-dimensional type I collagen scaffold with non-woven, randomly oriented nanofibers where we evaluated the performance of primary mesenchymal progenitor cells.

RESULTS:

We found that traumatic war wounds are characterized by a disorganized, densely fibrotic collagen I matrix that influences progenitor cells adhesion, proliferation and osteogenic differentiation potential.

CONCLUSION:

Altogether, these results suggest that the structural microenvironment present in traumatic war wounds has the potential to contribute to the development of post-traumatic HO. Our findings may support novel treatment strategies directed towards modifying the structural microenvironment after traumatic injury.

Supplementary Information

The online version contains supplementary material available at 10.1007/s13770-021-00355-y.

Comparison of percentage of CD90-positive cells and osteogenic differentiation potential between mesenchymal stem cells grown on dish and nonwoven fabric

Although nonwoven fabric (NWF) has been reported to be a candidate scaffold for the large-scale expansion of mesenchymal stem cells (MSCs), the quality of cells grown in NWF has not been well clarified. In this report, MSCs grown in an NWF disc for 3 weeks showed higher osteogenic differentiation potential and percentage of CD90 (+) cells than MSCs grown on the bottom surface of dish. The amount of the extracellular matrix (ECM) per unit surface area of fibers was larger than that on the bottom surface of the dish in the first 2 weeks of culture. The osteogenic differentiation potential of MSCs inoculated onto cell-free ECM increased with increasing amount of ECM. The higher percentage of CD90 (+) cells and osteogenic differentiation potential of cells grown in an NWF disc than of cells grown on a dish might, at least in part, be due to the higher amount of ECM.

Engineering and Functionalization of Gelatin Biomaterials: From Cell Culture to Medical Applications

Health care and medicine were revolutionized in recent years by the development of biomaterials, such as stents, implants, personalized drug delivery systems, engineered grafts, cell sheets, and other transplantable materials. These materials not only support the growth of cells before transplantation but also serve as replacements for damaged tissues in vivo. Among the various biomaterials available, those made from natural biological sources such as extracellular proteins (collagen, fibronectin, laminin) have shown significant benefits, and thus are widely used. However, routine biomaterial-based research requires copious quantities of proteins and the use of pure and intact extracellular proteins could be highly cost ineffective. Gelatin is a molecular derivative of collagen obtained through the irreversible denaturation of collagen proteins. Gelatin shares a very close molecular structure and function with collagen and thus is often used in cell and tissue culture to replace collagen for biomaterial purposes. Recent technological advancements such as additive manufacturing, rapid prototyping, and three-dimensional printing, in general, have resulted in great strides toward the generation of functional gelatin-based materials for medical purposes. In this review, the structural and molecular similarities of gelatin to other extracellular matrix proteins are compared and analyzed. Current strategies for gelatin crosslinking and production are described and recent applications of gelatin-based biomaterials in cell culture and tissue regeneration are discussed. Finally, recent improvements in gelatin-based biomaterials for medical applications and future directions are elaborated. Impact statement In this study, we described gelatin's biochemical properties and compared its advantages and drawbacks over other extracellular matrix proteins and polymers used for biomaterial application. We also described how gelatin can be used with other polymers in creating gelatin composite materials that have enhanced mechanical properties, increased biocompatibility, and boosted bioactivity, maximizing its benefits for biomedical purposes. The article is relevant, as it discussed not only the chemistry of gelatin, but also listed the current techniques in gelatin/biomaterial manufacturing and described the most recent trends in gelatin-based biomaterials for biomedical applications.

Hydrogel Nanospike Patch as a Flexible Anti-Pathogenic Scaffold for Regulating Stem Cell Behavior

Vertically aligned nanomaterials, such as nanowires and nanoneedles, hold strong potential as efficient platforms onto which living cells or tissues can be interfaced for use in advanced biomedical applications. However, their rigid mechanical properties and complex fabrication processes hinder their integration onto flexible, tissue-adaptable, and large-area patch-type scaffolds, limiting their practical applications. In this study, we present a highly flexible patch that possesses a spiky hydrogel nanostructure array as a transplantable platform for enhancing the growth and differentiation of stem cells and efficiently suppressing biofilm formation. In vitro studies show that the hydrogel nanospike patch imposes a strong physical stimulus to the membranes of stem cells and enhances their osteogenic, chondrogenic, and adipogenic differentiation and the secretion of crucial soluble factors without altering cell viability. At the same time, the array exhibits effective bactericidal properties against Gram-positive and Gram-negative bacteria. In vivo studies further demonstrate that the flexible hydrogel patch with its spiky vertical nanostructures significantly promotes the regeneration of damaged cranial bone tissues while suppressing pathogenic bacterial infections in mouse models.

Electrospun Patch Functionalized with Nanoparticles Allows for Spatiotemporal Release of VEGF and PDGF-BB Promoting In Vivo Neovascularization

The use of nanomaterials as carriers for the delivery of growth factors has been applied to a multitude of applications in tissue engineering. However, issues of toxicity, stability, and systemic effects of these platforms have yet to be fully understood, especially for cardiovascular applications. Here, we proposed a delivery system composed of poly(dl-lactide- co-glycolide) acid (PLGA) and porous silica nanoparticles (pSi) to deliver vascular endothelial growth factor (VEGF) and platelet-derived growth factor (PDGF). The tight spatiotemporal release of these two proteins has been proven to promote neovascularization. In order to minimize tissue toxicity, localize the release, and maintain a stable platform, we conjugated two formulations of PLGA-pSi to electrospun (ES) gelatin to create a combined ES patch releasing both PDGF and VEGF. When compared to freely dispersed particles, the ES patch cultured in vitro with neonatal cardiac cells had significantly less particle internalization (2.0 ± 1.3%) compared to free PLGA-pSi (21.5 ± 6.1) or pSi (28.7 ± 2.5) groups. Internalization was positively correlated to late-stage apoptosis with PLGA-pSi and pSi groups having increased apoptosis compared to the untreated group. When implanted subcutaneously, the ES patch was shown to have greater neovascularization than controls evidenced by increased expression of α-SMA and CD31 after 21 days. Quantitative reverse transcription-polymerase chain reaction results support increased angiogenesis by the upregulation of VEGFA, VEGFR2, vWF, and COL3A1, exhibiting a synergistic effect with the release of VEGF-A164 and PDGF-BB after 21 days in vivo. The results of this study proved that the ES patch reduced cellular toxicity and may be tailored to have a dual release of growth factors promoting localized neovascularization.

Substrate-independent immunomodulatory characteristics of mesenchymal stem cells in three-dimensional culture

Mesenchymal stem cells (MSCs) play important roles in tissue regeneration, and multi-lineage differentiation and immunomodulation are two major characteristics of MSCs that are utilized in stem cell therapy. MSCs in vivo have a markedly different three-dimensional (3D) niche compared to the traditional two-dimensional (2D) culture in vitro. A 3D scaffold is predicted to provide an artificial 3D environment similar to the in vivo environment. Significant changes in MSC differentiation are shown to be occurred when under 3D culture. However, the immunomodulatory characteristics of MSCs under 3D culture remain unknown. In this study, 3D culture systems were constructed using different substrates to evaluate the common immunomodulatory characteristics of MSCs. Compared to the MSCs under 2D culture, the MSCs under 3D culture, which had higher stemness and maintained cell phenotype, showed altered immunophenotypic pattern. Gene expression profile analysis at mRNA and protein level detected by gene chip and protein chip, respectively, further revealed the difference between 3D cultured MSCs and 2D cultured MSCs, which was mainly concentrated in the immunoregulation related aspects. Moreover, the immunoregulatory role of 3D culture was confirmed by our immunosuppressive experiments. These findings demonstrated that the immunomodulatory capacities of MSCs were enhanced by the 3D geometry of substrates.

Biomimetic Tissue Engineering: Tuning the Immune and Inflammatory Response to Implantable Biomaterials

Regenerative medicine technologies rely heavily on the use of well-designed biomaterials for therapeutic applications. The success of implantable biomaterials hinges upon the ability of the chosen biomaterial to negotiate with the biological barriers in vivo. The most significant of these barriers is the immune system, which is composed of a highly coordinated organization of cells that induce an inflammatory response to the implanted biomaterial. Biomimetic platforms have emerged as novel strategies that aim to use the principle of biomimicry as a means of immunomodulation. This principle has manifested itself in the form of biomimetic scaffolds that imitate the composition and structure of biological cells and tissues. Recent work in this area has demonstrated the promising potential these technologies hold in overcoming the barrier of the immune system and, thereby, improve their overall therapeutic efficacy. In this review, a broad overview of the use of these strategies across several diseases and future avenues of research utilizing these platforms is provided.

Direct Control of Stem Cell Behavior Using Biomaterials and Genetic Factors

Stem cells have recently emerged as an important candidate for cell therapy. However, some major limitations still exist such as a small quantity of cell supply, senescence, and insufficient differentiation efficiency. Therefore, there is an unmet need to control stem cell behavior for better clinical performance. Since native microenvironment factors including stem cell niche, genetic factors, and growth factors direct stem cell fate cooperatively, user-specified in vitro settings are required to understand the regulatory roles and effects of each factor, thereby applying the factors for improved cell therapy. Among others, various types of biomaterials and transfection method have been employed as key tools for development of the in vitro settings. This review focuses on the current strategies to improve stemness maintenance, direct differentiation, and reprogramming using biomaterials and genetic factors without any aids from additional biochemicals and growth factors.

Biomimetic nanoparticles with enhanced affinity towards activated endothelium as versatile tools for theranostic drug delivery

Activation of the vascular endothelium is characterized by increased expression of vascular adhesion molecules and chemokines. This activation occurs early in the progression of several diseases and triggers the recruitment of leukocytes. Inspired by the tropism of leukocytes, we investigated leukocyte-based biomimetic nanoparticles (i.e., leukosomes) as a novel theranostic platform for inflammatory diseases.

Methods: Leukosomes were assembled by combining phospholipids and membrane proteins from leukocytes. For imaging applications, phospholipids modified with rhodamine and gadolinium were used. Leukosomes incubated with antibodies blocking lymphocyte function-associated antigen 1 (LFA-1) and CD45 were administered to explore their roles in targeting inflammation. In addition, relaxometric assessment of NPs was evaluated.

Results: Liposomes and leukosomes were both spherical in shape with sizes ranging from 140-170 nm. Both NPs successfully integrated 8 and 13 µg of rhodamine and gadolinium, respectively, and demonstrated less than 4% variation in physicochemical features. Leukosomes demonstrated a 16-fold increase in breast tumor accumulation relative to liposomes. Furthermore, quantification of leukosomes in tumor vessels demonstrated a 4.5-fold increase in vessel lumens and a 14-fold increase in vessel walls. Investigating the targeting mechanism of action revealed that blockage of LFA-1 on leukosomes resulted in a 95% decrease in tumor accumulation. Whereas blockage of CD45 yielded a 60% decrease in targeting and significant increases in liver and spleen accumulation. In addition, when administered in mice with atherosclerotic plaques, leukosomes exhibited a 4-fold increase in the targeting of inflammatory vascular lesions. Lastly, relaxometric assessment of NPs demonstrated that the incorporation of membrane proteins into leukosomes did not impact the r₁ and r₂ relaxivities of the NPs, demonstrating 6 and 30 mM^-1s^-1, respectively.

Conclusion: Our study demonstrates the ability of leukosomes to target activated vasculature and exhibit superior accumulation in tumors and vascular lesions. The versatility of the phospholipid backbone within leukosomes permits the incorporation of various contrast agents. Furthermore, leukosomes can potentially be loaded with therapeutics possessing diverse physical properties and thus warrant further investigation toward the development of powerful theranostic agents.

Heparan Sulfate: A Potential Candidate for the Development of Biomimetic Immunomodulatory Membranes

Clinical trials have demonstrated that heparan sulfate (HS) could be used as a therapeutic agent for the treatment of inflammatory diseases. Its anti-inflammatory effect makes it suitable for the development of biomimetic innovative strategies aiming at modulating stem cells behavior toward a pro-regenerative phenotype in case of injury or inflammation. Here, we propose collagen type I meshes fabricated by solvent casting and further crosslinked with HS (HS-Col) to create a biomimetic environment resembling the extracellular matrix of soft tissue. HS-Col meshes were tested for their capability to provide physical support to stem cells’ growth, maintain their phenotypes and immunosuppressive potential following inflammation. HS-Col effect on stem cells was investigated in standard conditions as well as in an inflammatory environment recapitulated in vitro through a mix of pro-inflammatory cytokines (tumor necrosis factor-α and interferon-gamma; 20 ng/ml). A significant increase in the production of molecules associated with immunosuppression was demonstrated in response to the material and when cells were grown in presence of pro-inflammatory stimuli, compared to bare collagen membranes (Col), leading to a greater inhibitory potential when mesenchymal stem cells were exposed to stimulated peripheral blood mononuclear cells. Our data suggest that the presence of HS is able to activate the molecular machinery responsible for the release of anti-inflammatory cytokines, potentially leading to a faster resolution of inflammation.