Stick-slip instability for viscous fingering in a gel

The growth dynamics of an air finger injected in a visco-elastic gel (a PVA/borax aqueous solution) is studied in a linear Hele-Shaw cell. Besides the standard Saffmann-Taylor instability, we observe - with increasing finger velocities - the existence of two new regimes: (a) a stick-slip regime for which the finger tip velocity oscillates between 2 different values, producing local pinching of the finger at regular intervals, (b) a ``tadpole'' regime where a fracture-type propagation is observed. A scaling argument is proposed to interpret the dependence of the stick-slip frequency with the measured rheological properties of the gel.Comment: 7 pages, 4 figures. Submitted to Europhysics Letter

MicroRNA-Mediated Direct Reprogramming of Human Adult Fibroblasts Toward Cardiac Phenotype

open6Modulation of microRNA expression holds the promise to achieve direct reprogramming of fibroblasts into cardiomyocyte-like cells as a new strategy for myocardial regeneration after ischemic heart disease. Previous reports have shown that murine fibroblasts can be directly reprogrammed into induced cardiomyocytes (iCMs) by transient transfection with four microRNA mimics (miR-1, 133, 208, and 499, termed "miRcombo"). Hence, study on the effect of miRcombo transfection on adult human cardiac fibroblasts (AHCFs) deserves attention in the perspective of a future clinical translation of the approach. In this brief report, we studied for the first time whether miRcombo transient transfection of AHCFs by non-viral vectors might trigger direct reprogramming of AHCFs into cardiomyocyte-like cells. Initially, efficient miRNA delivery to cells was demonstrated through the use of a commercially available transfection agent (DharmaFECT1). Transient transfection of AHCFs with miRcombo was found to upregulate early cardiac transcription factors after 7 days post-transfection and cardiomyocyte specific marker cTnT after 15 days post-transfection, and to downregulate the expression of fibroblast markers at 15 days post-transfection. The percentage of cTnT-positive cells after 15 days from miRcombo transfection was ∼11%, as evaluated by flow cytometry. Furthermore, a relevant percentage of miRcombo-transfected AHCFs (∼38%) displayed spontaneous calcium transients at 30 days post-transfection. Results evidenced the role of miRcombo transfection on triggering the trans differentiation of AHCFs into iCMs. Although further investigations are needed to achieve iCM maturation, early findings from this study pave the way toward new advanced therapies for human cardiac regeneration.openPaoletti C; Divieto C; Tarricone G; Di Meglio F; Nurzynska D; Chiono VPaoletti, C; Divieto, C; Tarricone, G; Di Meglio, F; Nurzynska, D; Chiono,

The IkB kinase inhibitor nuclear factor-kB essential modulator–binding domain peptide for inhibition of balloon injury-induced neointimal formation

Objective—The activation of nuclear factor-kB (NF-kB) is a crucial step in the arterial wall’s response to injury. The identification and characterization of the NF-kB essential modulator– binding domain (NBD) peptide, which can block the activation of the IkB kinase complex, have provided an opportunity to selectively abrogate the inflammation-induced activation of NF-kB. The aim of the present study was to evaluate the effect of the NBD peptide on neointimal formation.<br></br> Methods and Results—In the rat carotid artery balloon angioplasty model, local treatment with the NBD peptide (300 microg/site) significantly reduced the number of proliferating cells at day 7 (by 40%; P<0.01) and reduced injury-induced neointimal formation (by 50%; P<0.001) at day 14. These effects were associated with a significant reduction of NF-kB activation and monocyte chemotactic protein-1 expression in the carotid arteries of rats treated with the peptide. In addition, the NBD peptide (0.01 to 1 micromol/L) reduced rat smooth muscle cell proliferation, migration, and invasion in vitro. Similar results were observed in apolipoprotein E-/-, mice in which the NBD peptide (150 microg/site) reduced wire-induced neointimal formation at day 28 (by 47%; P<0.01).<br></br> Conclusion—The NBD peptide reduces neointimal formation and smooth muscle cell proliferation/migration, both effects associated with the inhibition of NF-kB activation

Diversity of dermal fibroblasts as major determinant of variability in cell reprogramming

Induced pluripotent stem cells (iPSCs) are adult somatic cells genetically reprogrammed to an embryonic stem cell-like state. Notwithstanding their autologous origin and their potential to differentiate towards cells of all three germ layers, iPSC reprogramming is still affected by low efficiency. As dermal fibroblast is the most used human cell for reprogramming, we hypothesize that the variability in reprogramming is, at least partially, because of the skin fibroblasts used. Human dermal fibroblasts harvested from five different anatomical sites (neck, breast, arm, abdomen and thigh) were cultured and their morphology, proliferation, apoptotic rate, ability to migrate, expression of mesenchymal or epithelial markers, differentiation potential and production of growth factors were evaluated in vitro. Additionally, gene expression analysis was performed by real-time PCR including genes typically expressed by mesenchymal cells. Finally, fibroblasts isolated from different anatomic sites were reprogrammed to iPSCs by integration-free method. Intriguingly, while the morphology of fibroblasts derived from different anatomic sites differed only slightly, other features, known to affect cell reprogramming, varied greatly and in accordance with anatomic site of origin. Accordingly, difference also emerged in fibroblasts readiness to respond to reprogramming and ability to form colonies. Therefore, as fibroblasts derived from different anatomic sites preserve positional memory, it is of great importance to accurately evaluate and select dermal fibroblast population prior to induce reprogramming

Compact and tunable stretch bioreactor advancing tissue engineering implementation. Application to engineered cardiac constructs

Physical stimuli are crucial for the structural and functional maturation of tissues both in vivo and in vitro. In tissue engineering applications, bioreactors have become fundamental and effective tools for providing biomimetic culture conditions that recapitulate the native physical stimuli. In addition, bioreactors play a key role in assuring strict control, automation, and standardization in the production process of cell-based products for future clinical application. In this study, a compact, easy-to-use, tunable stretch bioreactor is proposed. Based on customizable and low-cost technological solutions, the bioreactor was designed for providing tunable mechanical stretch for biomimetic dynamic culture of different engineered tissues. In-house validation tests demonstrated the accuracy and repeatability of the imposed mechanical stimulation. Proof of concepts biological tests performed on engineered cardiac constructs, based on decellularized human skin scaffolds seeded with human cardiac progenitor cells, confirmed the bioreactor Good Laboratory Practice compliance and ease of use, and the effectiveness of the delivered cyclic stretch stimulation on the cardiac construct maturation

Cardiac shock wave therapy: Assessment of safety and new insights into mechanisms of tissue regeneration

Although low-energy extracorporeal cardiac shock wave (ECSW) therapy represents an attractive non-invasive treatment option for ischaemic heart disease, the precise mechanisms of its action and influence on the cardiac tissue remain obscure. The goal of this study was to evaluate the effects of SW application on cardiac function and structure. Four-month-old Fisher 344 rats were subjected to ECSW therapy. Echocardiographic measurements of cardiac function were performed at baseline and at 1 and 3 months after treatment. Signs of inflammation, apoptosis and fibrosis were evaluated by immunohistochemistry in the control and treated hearts. ECSW applicationdid not provoke arrhythmia or increase the troponin-I level. At all time points, the left ventricular ejection fraction and fractional shortening remained stable. Histological analysis revealed neither differences in the extracellular matrix collagen content nor the presence of fibrosis; similarly, there were no signs of inflammation. Moreover, a population of cardiac cells that responded eagerly to ECSW application in the adult heart was identified; c-kit–positive, Ki67-positive, orthochromatic cells, corresponding to cardiac primitive cells, were 2.65-fold more numerous in the treated myocardium. In conclusion, non-invasive ECSW therapy is a safe and effective way of activating cardiac stem cells and myocardial regeneration. Because many factors influence cellular turnover in the ischaemic myocardium during the course of ischaemic heart disease, cardiac remodelling, and heart failure progression, studies to identify the optimal treatment time are warranted

The Long and Winding Road to Cardiac Regeneration

Cardiac regeneration is a critical endeavor in the treatment of heart diseases, aimed at repairing and enhancing the structure and function of damaged myocardium. This review offers a comprehensive overview of current advancements and strategies in cardiac regeneration, with a specific focus on regenerative medicine and tissue engineering-based approaches. Stem cell-based therapies, which involve the utilization of adult stem cells and pluripotent stem cells hold immense potential for replenishing lost cardiomyocytes and facilitating cardiac tissue repair and regeneration. Tissue engineering also plays a prominent role employing synthetic or natural biomaterials, engineering cardiac patches and grafts with suitable properties, and fabricating upscale bioreactors to create functional constructs for cardiac recovery. These constructs can be transplanted into the heart to provide mechanical support and facilitate tissue healing. Additionally, the production of organoids and chips that accurately replicate the structure and function of the whole organ is an area of extensive research. Despite significant progress, several challenges persist in the field of cardiac regeneration. These include enhancing cell survival and engraftment, achieving proper vascularization, and ensuring the long-term functionality of engineered constructs. Overcoming these obstacles and offering effective therapies to restore cardiac function could improve the quality of life for individuals with heart diseases

A low-cost scalable 3D-printed sample-holder for agitation-based decellularization of biological tissues

Decellularized extracellular matrix is one of the most promising biological scaffold supporting in vitro tissue growth and in vivo tissue regeneration in both preclinical research and clinical practice. In case of thick tissues or even organs, conventional static decellularization methods based on chemical or enzymatic treatments are not effective in removing the native cellular material without affecting the extracellular matrix. To overcome this limitation, dynamic decellularization methods, mostly based on perfusion and agitation, have been proposed. In this study, we developed a low-cost scalable 3D-printed sample-holder for agitation-based decellularization purposes, designed for treating multiple specimens simultaneously and for improving efficiency, homogeneity and reproducibility of the decellularization treatment with respect to conventional agitation-based approaches. In detail, the proposed sample-holder is able to house up to four specimens and, immersed in the decellularizing solution within a beaker placed on a magnetic stirrer, to expose them to convective flow, enhancing the solution transport through the specimens while protecting them. Computational fluid dynamics analyses were performed to investigate the fluid phenomena establishing within the beaker and to support the sample-holder design. Exploratory biological tests performed on human skin specimens demonstrated that the sample-holder reduces process duration and increases treatment homogeneity and reproducibility

Image resampling and discretization effect on the estimate of myocardial radiomic features from T1 and T2 mapping in hypertrophic cardiomyopathy

Radiomics is emerging as a promising and useful tool in cardiac magnetic resonance (CMR) imaging applications. Accordingly, the purpose of this study was to investigate, for the first time, the effect of image resampling/discretization and filtering on radiomic features estimation from quantitative CMR T1 and T2 mapping. Specifically, T1 and T2 maps of 26 patients with hypertrophic cardiomyopathy (HCM) were used to estimate 98 radiomic features for 7 different resampling voxel sizes (at fixed bin width), 9 different bin widths (at fixed resampling voxel size), and 7 different spatial filters (at fixed resampling voxel size/bin width). While we found a remarkable dependence of myocardial radiomic features from T1 and T2 mapping on image filters, many radiomic features showed a limited sensitivity to resampling voxel size/bin width, in terms of intraclass correlation coefficient (> 0.75) and coefficient of variation (< 30%). The estimate of most textural radiomic features showed a linear significant (p < 0.05) correlation with resampling voxel size/bin width. Overall, radiomic features from T2 maps have proven to be less sensitive to image preprocessing than those from T1 maps, especially when varying bin width. Our results might corroborate the potential of radiomics from T1/T2 mapping in HCM and hopefully in other myocardial diseases