Expression of NaPi-IIb in rodent and human kidney and upregulation in a model of chronic kidney disease.

Na+-coupled phosphate cotransporters from the SLC34 and SLC20 families of solute carriers mediate transepithelial transport of inorganic phosphate (Pi). NaPi-IIa/Slc34a1, NaPi-IIc/Slc34a3, and Pit-2/Slc20a2 are all expressed at the apical membrane of renal proximal tubules and therefore contribute to renal Pi reabsorption. Unlike NaPi-IIa and NaPi-IIc, which are rather kidney-specific, NaPi-IIb/Slc34a2 is expressed in several epithelial tissues, including the intestine, lung, testis, and mammary glands. Recently, the expression of NaPi-IIb was also reported in kidneys from rats fed on high Pi. Here, we systematically quantified the mRNA expression of SLC34 and SLC20 cotransporters in kidneys from mice, rats, and humans. In all three species, NaPi-IIa mRNA was by far the most abundant renal transcript. Low and comparable mRNA levels of the other four transporters, including NaPi-IIb, were detected in kidneys from rodents and humans. In mice, the renal expression of NaPi-IIa transcripts was restricted to the cortex, whereas NaPi-IIb mRNA was observed in medullary segments. Consistently, NaPi-IIb protein colocalized with uromodulin at the luminal membrane of thick ascending limbs of the loop of Henle segments. The abundance of NaPi-IIb transcripts in kidneys from mice was neither affected by dietary Pi, the absence of renal NaPi-IIc, nor the depletion of intestinal NaPi-IIb. In contrast, it was highly upregulated in a model of oxalate-induced kidney disease where all other SLC34 phosphate transporters were downregulated. Thus, NaPi-IIb may contribute to renal phosphate reabsorption, and its upregulation in kidney disease might promote hyperphosphatemia.

Tailoring crystallinity for hemocompatible and durable PEEK cardiovascular implants.

Polymers have the potential to replace metallic or bioprosthetic heart valve components due to superior durability and inertness while allowing for native tissue-like flexibility. Despite these appealing properties, certain polymers such as polyetheretherketone (PEEK) have issues with hemocompatibility, which have previously been addressed through assorted complex processes. In this paper, we explore the enhancement of PEEK hemocompatibility with polymer crystallinity. Amorphous, semi-crystalline and crystalline PEEK are investigated in addition to a highly crystalline carbon fiber (CF)/PEEK composite material (CFPEEK). The functional group density of the PEEK samples is determined, showing that higher crystallinity results in increased amount of surface carbonyl functional groups. The increase of crystallinity (and negatively charged groups) appears to cause significant reductions in platelet adhesion (33 vs. 1.5 % surface coverage), hemolysis (1.55 vs. 0.75 %∙cm-2), and thrombin generation rate (4840 vs. 1585 mU/mL/min/cm2). In combination with the hemocompatibility study, mechanical characterization demonstrates that tailoring crystallinity is a simple and effective method to control both hemocompatibility and mechanical performance of PEEK. Furthermore, the results display that CFPEEK composite performed very well in all categories due to its enhanced crystallinity and complete carbon encapsulation, allowing the unique properties of CFPEEK to empower new concepts in cardiovascular device design.

Combining Cell Technologies With Biomimetic Tissue Engineering Applications: A New Paradigm for Translational Cardiovascular Therapies.

Cardiovascular disease is a major cause of morbidity and mortality worldwide and, to date, the clinically available prostheses still present several limitations. The design of next-generation regenerative replacements either based on cellular or extracellular matrix technologies can address these shortcomings. Therefore, tissue engineered constructs could potentially become a promising alterative to the current therapeutic options for patients with cardiovascular diseases. In this review, we selectively present an overview of the current tissue engineering tools such as induced pluripotent stem cells, biomimetic materials, computational modeling, and additive manufacturing technologies, with a focus on their application to translational cardiovascular therapies. We discuss how these advanced technologies can help the development of biomimetic tissue engineered constructs and we finally summarize the latest clinical evidence for their use, and their potential therapeutic outcome.

Endothelial Progenitor Cell-Based in vitro Pre-Endothelialization of Human Cell-Derived Biomimetic Regenerative Matrices for Next-Generation Transcatheter Heart Valves Applications.

Hemocompatibility of cardiovascular implants represents a major clinical challenge and, to date, optimal antithrombotic properties are lacking. Next-generation tissue-engineered heart valves (TEHVs) made from human-cell-derived tissue-engineered extracellular matrices (hTEMs) demonstrated their recellularization capacity in vivo and may represent promising candidates to avoid antithrombotic therapy. To further enhance their hemocompatibility, we tested hTEMs pre-endothelialization potential using human-blood-derived endothelial-colony-forming cells (ECFCs) and umbilical vein cells (control), cultured under static and dynamic orbital conditions, with either FBS or hPL. ECFCs performance was assessed via scratch assay, thereby recapitulating the surface damages occurring in transcatheter valves during crimping procedures. Our study demonstrated: feasibility to form a confluent and functional endothelium on hTEMs with expression of endothelium-specific markers; ECFCs migration and confluency restoration after crimping tests; hPL-induced formation of neo-microvessel-like structures; feasibility to pre-endothelialize hTEMs-based TEHVs and ECFCs retention on their surface after crimping. Our findings may stimulate new avenues towards next-generation pre-endothelialized implants with enhanced hemocompatibility, being beneficial for selected high-risk patients.

The path to a hemocompatible cardiovascular implant: Advances and challenges of current endothelialization strategies.

Cardiovascular (CV) implants are still associated with thrombogenicity due to insufficient hemocompatibility. Endothelialization of their luminal surface is a promising strategy to increase their hemocompatibility. In this review, we provide a collection of research studies and review articles aiming to summarize the recent efforts on surface modifications of CV implants, including stents, grafts, valves, and ventricular assist devises. We focus in particular on the implementation of micrometer or nanoscale surface modifications, physical characteristics of known biomaterials (such as wetness and stiffness), and surface morphological features (such as gratings, fibers, pores, and pits). We also review how biomechanical signals originating from the endothelial cell for surface interaction can be directed by topography engineering approaches toward the survival of the endothelium and its long-term adaptation. Finally, we summarize the regulatory and economic challenges that may prevent clinical implementation of endothelialized CV implants.

Recreating the heart's helical structure-function relationship with focused rotary jet spinning.

Helical alignments within the heart's musculature have been speculated to be important in achieving physiological pumping efficiencies. Testing this possibility is difficult, however, because it is challenging to reproduce the fine spatial features and complex structures of the heart's musculature using current techniques. Here we report focused rotary jet spinning (FRJS), an additive manufacturing approach that enables rapid fabrication of micro/nanofiber scaffolds with programmable alignments in three-dimensional geometries. Seeding these scaffolds with cardiomyocytes enabled the biofabrication of tissue-engineered ventricles, with helically aligned models displaying more uniform deformations, greater apical shortening, and increased ejection fractions compared with circumferential alignments. The ability of FRJS to control fiber arrangements in three dimensions offers a streamlined approach to fabricating tissues and organs, with this work demonstrating how helical architectures contribute to cardiac performance.

Human iPSCs and Genome Editing Technologies for Precision Cardiovascular Tissue Engineering.

Induced pluripotent stem cells (iPSCs) originate from the reprogramming of adult somatic cells using four Yamanaka transcription factors. Since their discovery, the stem cell (SC) field achieved significant milestones and opened several gateways in the area of disease modeling, drug discovery, and regenerative medicine. In parallel, the emergence of clustered regularly interspaced short palindromic repeats (CRISPR)-associated protein 9 (CRISPR-Cas9) revolutionized the field of genome engineering, allowing the generation of genetically modified cell lines and achieving a precise genome recombination or random insertions/deletions, usefully translated for wider applications. Cardiovascular diseases represent a constantly increasing societal concern, with limited understanding of the underlying cellular and molecular mechanisms. The ability of iPSCs to differentiate into multiple cell types combined with CRISPR-Cas9 technology could enable the systematic investigation of pathophysiological mechanisms or drug screening for potential therapeutics. Furthermore, these technologies can provide a cellular platform for cardiovascular tissue engineering (TE) approaches by modulating the expression or inhibition of targeted proteins, thereby creating the possibility to engineer new cell lines and/or fine-tune biomimetic scaffolds. This review will focus on the application of iPSCs, CRISPR-Cas9, and a combination thereof to the field of cardiovascular TE. In particular, the clinical translatability of such technologies will be discussed ranging from disease modeling to drug screening and TE applications.

Next-generation tissue-engineered heart valves with repair, remodelling and regeneration capacity.

Valvular heart disease is a major cause of morbidity and mortality worldwide. Surgical valve repair or replacement has been the standard of care for patients with valvular heart disease for many decades, but transcatheter heart valve therapy has revolutionized the field in the past 15 years. However, despite the tremendous technical evolution of transcatheter heart valves, to date, the clinically available heart valve prostheses for surgical and transcatheter replacement have considerable limitations. The design of next-generation tissue-engineered heart valves (TEHVs) with repair, remodelling and regenerative capacity can address these limitations, and TEHVs could become a promising therapeutic alternative for patients with valvular disease. In this Review, we present a comprehensive overview of current clinically adopted heart valve replacement options, with a focus on transcatheter prostheses. We discuss the various concepts of heart valve tissue engineering underlying the design of next-generation TEHVs, focusing on off-the-shelf technologies. We also summarize the latest preclinical and clinical evidence for the use of these TEHVs and describe the current scientific, regulatory and clinical challenges associated with the safe and broad clinical translation of this technology.

Tissue engineered heart valves for transcatheter aortic valve implantation: current state, challenges, and future developments.

INTRODUCTION: The establishment of transcatheter aortic valve implantation (TAVI) has revolutionized the treatment of severe aortic stenosis. However, with TAVI being approved for low-risk patients, valve durability is becoming of central importance. Here, we summarize how tissue engineered heart valves (TEHVs) may provide a clinically-relevant durable valve replacement compatible with TAVI. AREAS COVERED: Since its introduction, TAVI prostheses have advanced in design and development. However, TAVI bioprostheses are based on fixed xenogeneic materials prone to progressive degeneration. Transcatheter TEHVs may have the potential to overcome the drawbacks of current TAVI bioprostheses, with their remodeling, self-repair, and growth capacities. So far, performance and remodeling of transcatheter TEHV with in-situ regenerative potential were demonstrated in the low-pressure system, with acute performance proved in the systemic circulation. However, several challenges remain to be solved to ensure a safe clinical translation of TEHVs for TAVI approaches. EXPERT OPINION: With TAVI rapidly evolving, the establishment of long-term valve durability represents the top priority to reduce the rate of patient re-interventions, remove the associated risks and adverse events, and improve patients' life quality worldwide. With long-term performance and remodeling proved, TEHVs may represent the next-generation technology for a life-long TAVI prosthesis.

Geometry influences inflammatory host cell response and remodeling in tissue-engineered heart valves in-vivo.

Regenerative tissue-engineered matrix-based heart valves (TEM-based TEHVs) may become an alternative to currently-used bioprostheses for transcatheter valve replacement. We recently identified TEM-based TEHVs-geometry as one key-factor guiding their remodeling towards successful long-term performance or failure. While our first-generation TEHVs, with a simple, non-physiological valve-geometry, failed over time due to leaflet-wall fusion phenomena, our second-generation TEHVs, with a computational modeling-inspired design, showed native-like remodeling resulting in long-term performance. However, a thorough understanding on how TEHV-geometry impacts the underlying host cell response, which in return determines tissue remodeling, is not yet fully understood. To assess that, we here present a comparative samples evaluation derived from our first- and second-generation TEHVs. We performed an in-depth qualitative and quantitative (immuno-)histological analysis focusing on key-players of the inflammatory and remodeling cascades (M1/M2 macrophages, α-SMA+- and endothelial cells). First-generation TEHVs were prone to chronic inflammation, showing a high presence of macrophages and α-SMA+-cells, hinge-area thickening, and delayed endothelialization. Second-generation TEHVs presented with negligible amounts of macrophages and α-SMA+-cells, absence of hinge-area thickening, and early endothelialization. Our results suggest that TEHV-geometry can significantly influence the host cell response by determining the infiltration and presence of macrophages and α-SMA+-cells, which play a crucial role in orchestrating TEHV remodeling.

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

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.

Human cell-derived tissue-engineered heart valve with integrated Valsalva sinuses: towards native-like transcatheter pulmonary valve replacements.

Transcatheter valve replacement indication is currently being extended to younger and lower-risk patients. However, transcatheter prostheses are still based on glutaraldehyde-fixed xenogeneic materials. Hence, they are prone to calcification and long-term structural degeneration, which are particularly accelerated in younger patients. Tissue-engineered heart valves based on decellularized in vitro grown tissue-engineered matrices (TEM) have been suggested as a valid alternative to currently used bioprostheses, showing good performance and remodeling capacity as transcatheter pulmonary valve replacement (TPVR) in sheep. Here, we first describe the in vitro development of human cell-derived TEM (hTEM) and their application as tissue-engineered sinus valves (hTESVs), endowed with Valsalva sinuses for TPVR. The hTEM and hTESVs were systematically characterized in vitro by histology, immunofluorescence, and biochemical analyses, before they were evaluated in a pulse duplicator system under physiological pulmonary pressure conditions. Thereafter, transapical delivery of hTESVs was tested for feasibility and safety in a translational sheep model, achieving good valve performance and early cellular infiltration. This study demonstrates the principal feasibility of clinically relevant hTEM to manufacture hTESVs for TPVR.

Muscle tissue engineering in fibrous gelatin: implications for meat analogs.

Bioprocessing applications that derive meat products from animal cell cultures require food-safe culture substrates that support volumetric expansion and maturation of adherent muscle cells. Here we demonstrate scalable production of microfibrous gelatin that supports cultured adherent muscle cells derived from cow and rabbit. As gelatin is a natural component of meat, resulting from collagen denaturation during processing and cooking, our extruded gelatin microfibers recapitulated structural and biochemical features of natural muscle tissues. Using immersion rotary jet spinning, a dry-jet wet-spinning process, we produced gelatin fibers at high rates (~ 100 g/h, dry weight) and, depending on process conditions, we tuned fiber diameters between ~ 1.3 ± 0.1 µm (mean ± SEM) and 8.7 ± 1.4 µm (mean ± SEM), which are comparable to natural collagen fibers. To inhibit fiber degradation during cell culture, we crosslinked them either chemically or by co-spinning gelatin with a microbial crosslinking enzyme. To produce meat analogs, we cultured bovine aortic smooth muscle cells and rabbit skeletal muscle myoblasts in gelatin fiber scaffolds, then used immunohistochemical staining to verify that both cell types attached to gelatin fibers and proliferated in scaffold volumes. Short-length gelatin fibers promoted cell aggregation, whereas long fibers promoted aligned muscle tissue formation. Histology, scanning electron microscopy, and mechanical testing demonstrated that cultured muscle lacked the mature contractile architecture observed in natural muscle but recapitulated some of the structural and mechanical features measured in meat products.

Development of an Off-the-Shelf Tissue-Engineered Sinus Valve for Transcatheter Pulmonary Valve Replacement: a Proof-of-Concept Study.

Tissue-engineered heart valves with self-repair and regeneration properties may overcome the problem of long-term degeneration of currently used artificial prostheses. The aim of this study was the development and in vivo proof-of-concept of next-generation off-the-shelf tissue-engineered sinus valve (TESV) for transcatheter pulmonary valve replacement (TPVR). Transcatheter implantation of off-the-shelf TESVs was performed in a translational sheep model for up to 16 weeks. Transapical delivery of TESVs was successful and showed good acute and short-term performance (up to 8 weeks), which then worsened over time most likely due to a non-optimized in vitro valve design. Post-mortem analyses confirmed the remodelling potential of the TESVs, with host cell infiltration, polymer degradation, and collagen and elastin deposition. TESVs proved to be suitable as TPVR in a preclinical model, with encouraging short-term performance and remodelling potential. Future studies will enhance the clinical translation of such approach by improving the valve design to ensure long-term functionality.

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.

Off-the-shelf tissue engineered heart valves for in situ regeneration: current state, challenges and future directions.

INTRODUCTION: Transcatheter aortic valve replacement (TAVR) is continuously evolving and is expected to surpass surgical valve implantation in the near future. Combining durable valve substitutes with minimally invasive implantation techniques might increase the clinical relevance of this therapeutic option for younger patient populations. Tissue engineering offers the possibility to create tissue engineered heart valves (TEHVs) with regenerative and self-repair capacities which may overcome the pitfalls of current TAVR prostheses. AREAS COVERED: This review focuses on off-the-shelf TEHVs which rely on a clinically-relevant in situ tissue engineering approach and which have already advanced into preclinical or first-in-human investigation. EXPERT COMMENTARY: Among the off-the-shelf in situ TEHVs reported in literature, the vast majority covers pulmonary valve substitutes, and only few are combined with transcatheter implantation technologies. Hence, further innovations should include the development of transcatheter tissue engineered aortic valve substitutes, which would considerably increase the clinical relevance of such prostheses.

Computational modeling guides tissue-engineered heart valve design for long-term in vivo performance in a translational sheep model.

Valvular heart disease is a major cause of morbidity and mortality worldwide. Current heart valve prostheses have considerable clinical limitations due to their artificial, nonliving nature without regenerative capacity. To overcome these limitations, heart valve tissue engineering (TE) aiming to develop living, native-like heart valves with self-repair, remodeling, and regeneration capacity has been suggested as next-generation technology. A major roadblock to clinically relevant, safe, and robust TE solutions has been the high complexity and variability inherent to bioengineering approaches that rely on cell-driven tissue remodeling. For heart valve TE, this has limited long-term performance in vivo because of uncontrolled tissue remodeling phenomena, such as valve leaflet shortening, which often translates into valve failure regardless of the bioengineering methodology used to develop the implant. We tested the hypothesis that integration of a computationally inspired heart valve design into our TE methodologies could guide tissue remodeling toward long-term functionality in tissue-engineered heart valves (TEHVs). In a clinically and regulatory relevant sheep model, TEHVs implanted as pulmonary valve replacements using minimally invasive techniques were monitored for 1 year via multimodal in vivo imaging and comprehensive tissue remodeling assessments. TEHVs exhibited good preserved long-term in vivo performance and remodeling comparable to native heart valves, as predicted by and consistent with computational modeling. TEHV failure could be predicted for nonphysiological pressure loading. Beyond previous studies, this work suggests the relevance of an integrated in silico, in vitro, and in vivo bioengineering approach as a basis for the safe and efficient clinical translation of TEHVs.