Functional arrays of human pluripotent stem cell-derived cardiac microtissues.

To accelerate the cardiac drug discovery pipeline, we set out to develop a platform that would be capable of quantifying tissue-level functions such as contractile force and be amenable to standard multiwell-plate manipulations. We report a 96-well-based array of 3D human pluripotent stem cell (hPSC)-derived cardiac microtissues - termed Cardiac MicroRings (CaMiRi) - in custom 3D-print-molded multiwell plates capable of contractile force measurement. Within each well, two elastomeric microcantilevers are situated above a circumferential ramp. The wells are seeded with cell-laden collagen, which, in response to the gradual slope of the circumferential ramp, self-organizes around tip-gated microcantilevers to form contracting CaMiRi. The contractile force exerted by the CaMiRi is measured and calculated using the deflection of the cantilevers. Platform responses were robust and comparable across wells, and we used it to determine an optimal tissue formulation. We validated the contractile force response of CaMiRi using selected cardiotropic compounds with known effects. Additionally, we developed automated protocols for CaMiRi seeding, image acquisition, and analysis to enable the measurement of contractile force with increased throughput. The unique tissue fabrication properties of the platform, and the consequent effects on tissue function, were demonstrated upon adding hPSC-derived epicardial cells to the system. This platform represents an open-source contractile force screening system useful for drug screening and tissue engineering applications.

Human Wharton's jelly mesenchymal stem cells promote skin wound healing through paracrine signaling.

INTRODUCTION: The prevalence of nonhealing wounds is predicted to increase due to the growing aging population. Despite the use of novel skin substitutes and wound dressings, poorly vascularized wound niches impair wound repair. Mesenchymal stem cells (MSCs) have been reported to provide paracrine signals to promote wound healing, but the effect of human Wharton's jelly-derived MSCs (WJ-MSCs) has not yet been described in human normal skin. METHODS: Human WJ-MSCs and normal skin fibroblasts were isolated from donated umbilical cords and normal adult human skin. Fibroblasts were treated with WJ-MSC-conditioned medium (WJ-MSC-CM) or nonconditioned medium. RESULTS: Expression of genes involved in re-epithelialization (transforming growth factor-ß2), neovascularization (hypoxia-inducible factor-1α) and fibroproliferation (plasminogen activator inhibitor-1) was upregulated in WJ-MSC-CM-treated fibroblasts (P≤0.05). WJ-MSC-CM enhanced normal skin fibroblast proliferation (P≤0.001) and migration (P≤0.05), and promoted wound healing in an excisional full-thickness skin murine model. CONCLUSIONS: Under our experimental conditions, WJ-MSCs enhanced skin wound healing in an in vivo mouse model.

Effect of human Wharton's jelly mesenchymal stem cell paracrine signaling on keloid fibroblasts.

Keloid scars are abnormal benign fibroproliferative tumors with high recurrence rates and no current efficacious treatment. Accumulating evidence suggests that human umbilical cord Wharton's jelly-derived mesenchymal stem cells (WJ-MSCs) have antifibrotic properties. Paracrine signaling is considered one of the main underlying mechanisms behind the therapeutic effects of mesenchymal stem cells. However, the paracrine signaling effects of WJ-MSCs on keloids have not yet been reported. The aim of this study is to investigate paracrine signaling effects of human WJ-MSCs on keloid fibroblasts in vitro. Human umbilical cords and keloid skin samples were obtained, and WJ-MSCs and keloid fibroblasts were isolated and cultured. One-way and two-way paracrine culture systems between both cell types were investigated. Plasminogen activator inhibitor-I and transforming growth factor-ß2 (TGF-ß2) transcripts were upregulated in keloid fibroblasts cultured with WJ-MSC-conditioned medium (WJ-MSC-CM) and cocultured with inserts, while showing lower TGF-ß3 gene expression. Interleukin (IL)-6, IL-8, TGF-ß1, and TGF-ß2 protein expression was also enhanced. The WJ-MSC-CM-treated keloid fibroblasts showed higher proliferation rates than their control keloid fibroblasts with no significant change in apoptosis rate or migration ability. In our culture conditions, the indirect application of WJ-MSCs on keloid fibroblasts may enhance their profibrotic phenotype.

Electrospun elastin-like polypeptide enriched polyurethanes and their interactions with vascular smooth muscle cells.

In vascular tissue, elastin is an essential extracellular matrix protein that plays an important biomechanical and biological signalling role. Native elastin is insoluble and is difficult to extract from tissues, which results in its relatively rare use for the fabrication of vascular tissue engineering scaffolds. Recombinant elastin-like polypeptide-4 (ELP4), which mimics the structure and function of native tropoelastin, represents a practical alternative to the native elastic fibre for vascular applications. In this study, electrospinning was utilized to fabricate fibrous scaffolds which were subsequently surface modified with ELP4 and used as substrates for smooth muscle cell culture. ELP4 surface modified materials demonstrated enhanced smooth muscle cell (SMC) adhesion and maintenance of cell numbers over a 1-week period relative to controls. SMCs seeded on the ELP4 surface modified materials were also shown to exhibit the cell morphology and biological markers of a contractile phenotype including a spindle-like morphology, actin filament organization and smooth muscle myosin heavy chain expression. Competitive inhibition experiments demonstrated that the elastin-laminin cell surface receptor and its affinity for the VGVAPG peptide sequence on ELP4 molecules are likely involved in the initial SMC contact with the ELP4 modified materials. Elastin-like polypeptides show promise as surface modifiers for candidate scaffolds for engineering contractile vascular tissues.

Platelet inhibition and endothelial cell adhesion on elastin-like polypeptide surface modified materials.

Platelet adhesion and activation are important early markers of biomaterial blood compatibility, while surfaces that promote enhanced endothelial cell adhesion and eNOS expression are strategic targets for long term vascular graft applications. Materials surface modified with fluorinated surface modifiers, containing peptides inspired from elastin cross-linking domains, have been used for the cross-linking of elastin-like polypeptide 4 (ELP4) macromolecules onto polyurethane surfaces. In the present study, ELP4 modified polyurethanes were evaluated in vitro to assess platelet adhesion, microparticle formation and bulk platelet activation following blood-material interactions. Reduced platelet adhesion and bulk platelet activation were observed following contact between reconstituted human blood and the ELP4 materials, relative to the uncoated base polyurethane controls. ELP4 modified materials also promoted endothelial cell adhesion and retention over a period of one week and showed that the endothelial cells exhibited an organized actin cytoskeleton and enhanced endothelial nitric oxide synthase (eNOS) expression relative to the control surfaces. These results indicate that polyurethane elastomers modified with ELP4 covalently bound to fluorinated surface modifiers provide a promising approach for endowing synthetic elastomers with both reduced blood platelet activation properties and enhanced endothelial cell adhesion for potential use in vascular graft applications.

Surface immobilization of elastin-like polypeptides using fluorinated surface modifying additives.

Elastin-like polypeptide (ELP) surface modification represents a valuable approach for the development of biomaterials in a wide range of medical applications. In this study, ELP surface modification has been achieved through the use of elastin cross-linking peptide (ECP) bioactive fluorinated surface modifiers (ECP-BFSMs). The synthesis of low molecular weight fluorinated additives was described and their subsequent blending with a base polycarbonate urethane (PCNU) was shown to successfully enrich the surface to allow for ELP surface cross-linking via lysine moieties on the peptide segments of the ECP-BFSMs. The kinetics for the surface migration of fluorescent ECP-BFSMs was studied over a 2-week period by two-photon confocal microscopy. A decrease in advancing contact angle from 87.9° to 75.3° was observed for ECP-BFSM modified PCNU and was associated with the presence of ECP peptides on the surface. X-ray photoelectron spectroscopy demonstrated an increase in surface atomic percent of fluorine (from 0.2 to 7.2%) and nitrogen (from 1.0 to 3.0%) associated with the surface localization of fluoro groups and amide groups associated with the peptides in the ECP-BFSMs. A further increase in surface atomic percent of nitrogen (from 3.0 to 8.3%) was observed after ELP surface cross-linking. These ELP-modified surfaces were shown to promote increased smooth muscle cell adhesion, spreading and retention over a 7-day culture period relative to their non-ELP4 analogs. This novel surface modifying additive approach may be used for various biomimetic applications since it generates a stable ECM-like surface retained onto a relatively inert fluorinated background.

Stem Cell Therapy: A New Treatment for Burns?

Stem cell therapy has emerged as a promising new approach in almost every medicine specialty. This vast, heterogeneous family of cells are now both naturally (embryonic and adult stem cells) or artificially obtained (induced pluripotent stem cells or iPSCs) and their fates have become increasingly controllable, thanks to ongoing research in this passionate new field. We are at the beginning of a new era in medicine, with multiple applications for stem cell therapy, not only as a monotherapy, but also as an adjunct to other strategies, such as organ transplantation or standard drug treatment. Regrettably, serious preclinical concerns remain and differentiation, cell fusion, senescence and signalling crosstalk with growth factors and biomaterials are still challenges for this promising multidisciplinary therapeutic modality. Severe burns have several indications for stem cell therapy, including enhancement of wound healing, replacement of damaged skin and perfect skin regeneration - incorporating skin appendages and reduced fibrosis -, as well as systemic effects, such as inflammation, hypermetabolism and immunosuppression. The aim of this review is to describe well established characteristics of stem cells and to delineate new advances in the stem cell field, in the context of burn injury and wound healing.

Bioactivation of porous polyurethane scaffolds using fluorinated RGD surface modifiers.

Biomaterial scaffolds for tissue engineering require appropriate cell adhesion, proliferation, and infiltration into their three-dimensional (3D) porous structures. Surface modification techniques have the potential to enhance cell infiltration into synthetic scaffolds while retaining bulk material properties intact. The objective of this work was to assess the potential of achieving a uniform surface modification in 3D porous constructs through the blending of surface-modifying additives known as bioactive fluorinated surface modifiers (BFSMs) with a base polyurethane material. By coupling RGD peptides to the fluorinated surface modifiers to form RGD-BFSMs, the BFSMs can act as a vehicle for the delivery of RGD moieties to the surface without direct covalent attachment to the polymer substrate. Fluorescent RGD-BFSMs were shown to migrate to the polymer-air interfaces within the porous scaffolds by two-photon confocal microscopy. A-10 rat aortic smooth muscle cells were cultured for 4 weeks on nonmodified and RGD-BFSM-modified porous scaffolds, and cell adhesion, proliferation, and viability were quantified at different depths. RGD-BFSM-modified scaffolds showed significantly greater cell numbers within deeper regions of the scaffolds, and this difference became more pronounced over time. This study demonstrates an effective approach to promote cell adhesion and infiltration within thick (approximately 0.5 cm) porous synthetic scaffolds by providing a uniform distribution of adhesive peptide throughout the scaffolds without the use of covalent surface reaction chemistry.

Mechanical heart valve prostheses: identification and evaluation (erratum).

Mechanical heart value prostheses have been in use since the 1950s. Many prostheses have been used for a while and then discontinued. Today, there are a large number and variety of prostheses in use and an even larger variety that are in place in patients. These may be explanted at any time for a number of reasons. It is essential for the practicing pathologist to be able to identify the prosthesis and be aware of some of its reported complications and modes of failure. This article, and a second one on bioprosthetic heart valves, is designed as a ready reference guide to heart valve prostheses, their important identifying features, their common complications, and modes of failure. It should help in the accurate identification of explanted prosthetic valves and more definitive reports. This accuracy of identification as well as tracking of abnormalities noted will, we hope, permit the identification of new failure modes and the recording of causes of failure of new (or even modified) prosthetic heart valves.