Magnetizable stent-grafts enable endothelial cell capture

Magnetic capture of blood outgrowth endothelial cells to the luminal surface of magnetizable stent-grafts promotes healing in a porcine pseudoaneurysm model

Stent-grafts are endovascular devices used to treat many arterial conditions including carotid artery pseudoaneurysms. Stent-grafts are composed of a metal stent backbone covered by a synthetic membrane to form a conduit. Their deployment results in a large surface area of synthetic material in contact with blood, which increases the risk of thrombosis and occlusion of the device. The more rapidly the blood contacting surface becomes covered with an endothelium, acting as a barrier between the device and blood flow, the lower the risk of these complications. One approach to promote the rapid endothelialization of a stent-graft is with magnetic cell capture. In the current work, we develop magnetizable stent-grafts and generate autologous blood outgrowth endothelial cells from peripheral blood. The cells are labeled with superparamagnetic iron oxide nanoparticles to impart magnetic properties. The ability of the magnetic stent-grafts to occlude pseudoaneurysms and magnetically capture delivered cells is investigated relative to non-magnetic stent-graft controls in a porcine carotid pseudoaneurysm model. We demonstrated that at the study endpoints, the control and magnetic stent-grafts had occluded 7/9 and 9/9 of the pseudoaneurysms, respectively. Histological analysis demonstrated a higher degree of magnetic cell capture, endothelialization, and luminal tissue coverage in the magnetic stent-grafts compared to their non-magnetic controls. At the study endpoints, 2/9 control stent-grafts had completely thrombosed while 0/9 magnetic stent-grafts had. In conclusion, the magnetic stent-grafts facilitated the magnetic capture of blood outgrowth endothelial cells, which appeared to improve biological outcomes relative to non-magnetic stent-graft controls. STATEMENT OF SIGNIFICANCE: Stent-grafts are devices deployed in the arteries to restore blood flow. They are composed of a stent backbone covered by a membrane of synthetic material to form a conduit. Their deployment results in a large surface area of synthetic material in contact with blood. This increases the risk of thrombosis and the narrowing and occlusion of the device. The more rapidly the blood contacting surface becomes covered with an endothelium, acting as a barrier between the device and blood flow, the lower the risk of these complications. In the current study, we investigate an approach to magnetically adhere endothelial cells to the surface of magnetizable stent-grafts to promote the rapid development of an endothelium in a pig model.

Translational tissue-engineered vascular grafts: From bench to bedside

Cardiovascular disease is a primary cause of mortality worldwide, and patients often require bypass surgery that utilizes autologous vessels as conduits. However, the limited availability of suitable vessels and the risk of failure and complications have driven the need for alternative solutions. Tissue-engineered vascular grafts (TEVGs) offer a promising solution to these challenges. TEVGs are artificial vascular grafts made of biomaterials and/or vascular cells that can mimic the structure and function of natural blood vessels. The ideal TEVG should possess biocompatibility, biomechanical mechanical properties, and durability for long-term success in vivo. Achieving these characteristics requires a multi-disciplinary approach involving material science, engineering, biology, and clinical translation. Recent advancements in scaffold fabrication have led to the development of TEVGs with improved functional and biomechanical properties. Innovative techniques such as electrospinning, 3D bioprinting, and multi-part microfluidic channel systems have allowed the creation of intricate and customized tubular scaffolds. Nevertheless, multiple obstacles must be overcome to apply these innovations effectively in clinical practice, including the need for standardized preclinical models and cost-effective and scalable manufacturing methods. This review highlights the fundamental approaches required to successfully fabricate functional vascular grafts and the necessary translational methodologies to advance their use in clinical practice.

Computational Assessment of Unsteady Flow Effects on Magnetic Nanoparticle Targeting Efficiency in a Magnetic Stented Carotid Bifurcation Artery

PURPOSE

Worldwide, cardiovascular disease is the leading cause of hospitalization and death. Recently, the use of magnetizable nanoparticles for medical drug delivery has received much attention for potential treatment of both cancer and cardiovascular disease. However, proper understanding of the interacting magnetic field forces and the hydrodynamics of blood flow is needed for effective implementation. This paper presents the computational results of simulated implant assisted medical drug targeting (IA-MDT) via induced magnetism intended for administering patient specific doses of therapeutic agents to specific sites in the cardiovascular system. The drug delivery scheme presented in this paper functions via placement of a faintly magnetizable stent at a diseased location in the carotid artery, followed by delivery of magnetically susceptible drug carriers guided by the local magnetic field. Using this method, the magnetic stent can apply high localized magnetic field gradients within the diseased artery, while only exposing the neighboring tissues, arteries, and organs to a modest magnetic field. The localized field gradients also produce the forces needed to attract and hold drug-containing magnetic nanoparticles at the implant site for delivering therapeutic agents to treat in-stent restenosis.

METHODS

The multi-physics computational model used in this work is from our previous work and has been slightly modified for the case scenario presented in this paper. The computational model is used to analyze pulsatile blood flow, particle motion, and particle capture efficiency in a magnetic stented region using the magnetic properties of magnetite (Fe3O4) and equations describing the magnetic forces acting on particles produced by an external cylindrical electromagnetic coil. The electromagnetic coil produces a uniform magnetic field in the computational arterial flow model domain, while both the particles and the implanted stent are paramagnetic. A Eulerian-Lagrangian technique is adopted to resolve the hemodynamic flow and the motion of particles under the influence of a range of magnetic field strengths (Br = 2T, 4T, 6T, and 8T). Particle diameter sizes of 10 nm-4 µm in diameter were evaluated. Two dimensionless numbers were evaluated in this work to characterize relative effects of Brownian motion (BM), magnetic force induced particle motion, and convective blood flow on particle motion.

RESULTS

The computational simulations demonstrate that the greatest particle capture efficiency results for particle diameters within the micron range of 0.7-4 µm, specifically in regions where flow separation and vortices are at a minimum. Similar to our previous work (which did not involve the use of a magnetic stent), it was also observed that the capture efficiency of particles decreases substantially with particle diameter, especially in the superparamagnetic regime. Contrary to our previous work, using a magnetic stent tripled the capture efficiency of superparamagnetic particles. The highest capture efficiency observed for superparamagnetic particles was 78% with an 8 T magnetic field strength and 65% with a 2 T magnetic field strength when analyzing 100 nm particles. For 10 nm particles and an 8 T magnetic field strength, the particle capture efficiency was 55% and for a 2 T magnetic field strength the particle capture efficiency was observed to be 43%. Furthermore, it was found that larger magnetic field strengths, large particle diameter sizes (1 µm and above), and slower blood flow velocity improves the particle capture efficiency. The distribution of captured particles on the vessel wall along the axial and azimuthal directions is also discussed. Results for captured particles on the vessel wall along the axial flow direction showed that the particle density decreased along the axial direction, especially after the stented region. For the entrance section of the stented region, the captured particle density distribution along the axial direction is large, corresponding to the center-symmetrical distribution of the magnetic force in that section.

CONCLUSION

The simulation results presented in this work have shown to yield favorable capture efficiencies for micron range particles and superparamagnetic particles using magnetized implants such as the stent discussed in this work. The results presented in this work justify further investigation of MDT as a treatment technique for cardiovascular disease.

Magnetic and Biocompatible Polyurethane Nanofiber Biomaterial for Tissue Engineering

Recruitment of endothelial cells to cardiovascular device surfaces could solve issues of thrombosis, neointimal hyperplasia, and restenosis. Since current targeting strategies are often nonspecific, new technologies to allow for site-specific cell localization and capture in vivo are needed. The development of cytocompatible superparamagnetic iron oxide nanoparticles has allowed for the use of magnetism for cell targeting. In this study, a magnetic polyurethane (PU)-2205 stainless steel (2205-SS) nanofibrous composite biomaterial was developed through analysis of composite sheets and application to stent-grafts. The PU nanofibers provide strength and elasticity while the 2205-SS microparticles provide ferromagnetic properties. Sheets were electrospun at mass ratios of 0-4:1 (2205-SS:PU) and stent-grafts with magnetic or nonmagnetic stents were coated at the optimal ratio of 2:1. These composite materials were characterized by microscopy, mechanical testing, a sessile drop test, magnetic field measurement, magnetic cell capture assays, and cytocompatibility after 14 days of culturing with endothelial cells. Results of this study show that an optimal ratio of 2:1 2205-SS:PU results in a hydrophobic material that balanced mechanical and magnetic properties and was cytocompatible up to 14 days. Significant cell capture required a thicker material of 0.5 mm thickness. Stent-grafts fabricated from a magnetic coating and a magnetic stent demonstrated uniform cell capture throughout the device surface. This novel biomaterial exhibits a combination of mechanical and magnetic properties that enables magnetic capture of cells and other therapeutic agents for vascular and other tissue engineering applications.

Application of Nanomaterials in Stem Cell-Based Therapeutics for Cardiac Repair and Regeneration

Cardiovascular disease is a leading cause of disability and death worldwide. Although the survival rate of patients with heart diseases can be improved with contemporary pharmacological treatments and surgical procedures, none of these therapies provide a significant improvement in cardiac repair and regeneration. Stem cell-based therapies are a promising approach for functional recovery of damaged myocardium. However, the available stem cells are difficult to differentiate into cardiomyocytes, which result in the extremely low transplantation efficiency. Nanomaterials are widely used to regulate the myocardial differentiation of stem cells, and play a very important role in cardiac tissue engineering. This study discusses the current status and limitations of stem cells and cell-derived exosomes/micro RNAs based cardiac therapy, describes the cardiac repair mechanism of nanomaterials, summarizes the recent advances in nanomaterials used in cardiac repair and regeneration, and evaluates the advantages and disadvantages of the relevant nanomaterials. Besides discussing the potential clinical applications of nanomaterials in cardiac therapy, the perspectives and challenges of nanomaterials used in stem cell-based cardiac repair and regeneration are also considered. Finally, new research directions in this field are proposed, and future research trends are highlighted.

Iron Oxide Nanoparticles in Regenerative Medicine and Tissue Engineering

In recent years, many promising nanotechnological approaches to biomedical research have been developed in order to increase implementation of regenerative medicine and tissue engineering in clinical practice. In the meantime, the use of nanomaterials for the regeneration of diseased or injured tissues is considered advantageous in most areas of medicine. In particular, for the treatment of cardiovascular, osteochondral and neurological defects, but also for the recovery of functions of other organs such as kidney, liver, pancreas, bladder, urethra and for wound healing, nanomaterials are increasingly being developed that serve as scaffolds, mimic the extracellular matrix and promote adhesion or differentiation of cells. This review focuses on the latest developments in regenerative medicine, in which iron oxide nanoparticles (IONPs) play a crucial role for tissue engineering and cell therapy. IONPs are not only enabling the use of non-invasive observation methods to monitor the therapy, but can also accelerate and enhance regeneration, either thanks to their inherent magnetic properties or by functionalization with bioactive or therapeutic compounds, such as drugs, enzymes and growth factors. In addition, the presence of magnetic fields can direct IONP-labeled cells specifically to the site of action or induce cell differentiation into a specific cell type through mechanotransduction.

Vascular Stents Coated with Electrospun Drug-Eluting Material: Functioning in Rabbit Iliac Artery

A stenting procedure aimed at blood flow restoration in stenosed arteries significantly improves the efficiency of vascular surgery. However, the current challenge is to prevent neointimal growth, which reduces the vessel lumen, in the stented segments in the long run. We tested in vivo drug-eluting coating applied by electrospinning to metal vascular stents to inhibit the overgrowth of neointimal cells via both the drug release and mechanical support of the vascular wall. The blend of polycaprolactone with human serum albumin and paclitaxel was used for stent coating by electrospinning. The drug-eluting stents (DESs) were placed using a balloon catheter to the rabbit common iliac artery for 1, 3, and 6 months. The blood flow rate was ultrasonically determined in vivo. After explantation, the stented arterial segment was visually and histologically examined. Any undesirable biological responses (rejection or hemodynamically significant stenosis) were unobservable in the experimental groups. DESs were less traumatic and induced weaker neointimal growth; over six months, the blood flow increased by 37% versus bare-metal stents, where it increased by at least double the rate. Thus, electrospun-coated DESs demonstrate considerable advantages over the bare-metal variants.

Experimental Single-Platform Approach to Enhance the Functionalization of Magnetically Targetable Cells

Magnetic guidance shows promise as a strategy for improving the delivery and performance of cell therapeutics. However, clinical translation of magnetically guided cell therapy requires cell functionalization protocols that provide adequate magnetic properties in balance with unaltered cell viability and biological function. Existing methodologies for characterizing cells functionalized with magnetic nanoparticles (MNP) produce aggregate results, both distorted and unable to reflect variability in either magnetic or biological properties within a preparation. In the present study, we developed an inverted-plate assay allowing determination of these characteristics using a single-platform approach, and applied this method for a comparative analysis of two loading protocols providing highly uniform vs. uneven MNP distribution across cells. MNP uptake patterns remarkably different between the two protocols were first shown by fluorimetry carried out in a well-scan mode on endothelial cells (EC) loaded with BODIPY558/568-labeled MNP. Using the inverted-plate assay we next demonstrated that, in stark contrast to unevenly loaded cells, more than 50% of uniformly functionalized EC were captured within 5 min over a broad range of MNP doses. Furthermore, magnetically captured cells exhibited unaltered viability, substrate attachment, and proliferation rates. Conducted in parallel, magnetophoretic mobility studies corroborated the markedly superior guidance capacity of uniformly functionalized cells, confirming substantially faster cell capture kinetics on a clinically relevant time scale. Taken together, these results emphasize the importance of optimizing cell preparation protocols with regard to loading uniformity as key to efficient site-specific delivery, engraftment, and expansion of the functionalized cells, essential for both improving performance and facilitating translation of targeted cell therapeutics.

Endothelialization of cardiovascular devices

Blood-contacting surfaces of cardiovascular devices are not biocompatible for creating an endothelial layer on them. Numerous research studies have mainly sought to modify these surfaces through physical, chemical and biological means to ease early endothelial cell (EC) adhesion, migration and proliferation, and eventually to build an endothelial layer on the surfaces. The first priority for surface modification is inhibition of protein adsorption that leads to inhibition of platelet adhesion to the device surfaces, which may favor EC adhesion. Surface modification through surface texturing, if applicable, can bring some hopeful outcomes in this regard. Surface modifications through chemical and/or biological means may play a significant role in easy endothelialization of cardiovascular devices and inhibit smooth muscle cell proliferation. Cellular engineering of cells relevant to endothelialization can boost the positive outcomes obtained through surface engineering. This review briefly summarizes recent developments and research in early endothelialization of cardiovascular devices. STATEMENT OF SIGNIFICANCE: Endothelialization of cardiovascular implants, including heart valves, vascular stents and vascular grafts is crucial to solve many problems in our health care system. Numerous research efforts have been made to improve endothelialization on the surfaces of cardiovascular implants, mainly through surface modifications in three ways - physically, chemically and biologically. This review is intended to highlight comprehensive research studies to date on surface modifications aiming for early endothelialization on the blood-contacting surfaces of cardiovascular implants. It also discusses future perspectives to help guide endothelialization strategies and inspire further innovations.

Magnetically Assisted Control of Stem Cells Applied in 2D, 3D and In Situ Models of Cell Migration

The success of cell therapy approaches is greatly dependent on the ability to precisely deliver and monitor transplanted stem cell grafts at treated sites. Iron oxide particles, traditionally used in vivo for magnetic resonance imaging (MRI), have been shown to also represent a safe and efficient in vitro labelling agent for mesenchymal stem cells (MSCs). Here, stem cells were labelled with magnetic particles, and their resulting response to magnetic forces was studied using 2D and 3D models. Labelled cells exhibited magnetic responsiveness, which promoted localised retention and patterned cell seeding when exposed to magnet arrangements in vitro. Directed migration was observed in 2D culture when adherent cells were exposed to a magnetic field, and also when cells were seeded into a 3D gel. Finally, a model of cell injection into the rodent leg was used to test the enhanced localised retention of labelled stem cells when applying magnetic forces, using whole body imaging to confirm the potential use of magnetic particles in strategies seeking to better control cell distribution for in vivo cell delivery.

Stent-Jailing Technique Reduces Aneurysm Recurrence More Than Stent-Jack Technique by Causing Less Mechanical Forces and Angiogenesis and Inhibiting TGF-β/Smad2,3,4 Signaling Pathway in Intracranial Aneurysm Patients

Background: Stent-jailing and stent-jack are used for stent-assisted coil embolism (SCE) in intracranial aneurysm (IA) therapy, and cause different incidences of IA recurrence. Angiogenesis strongly correlates with aneurysm accumulation. Stent-jack causes higher mechanical forces in cerebral vessels than stent-jailing. Mechanical forces, as well as TGF-β/Smad2,3,4 signaling pathway, may play an important factor in IA recurrence by affecting angiogenesis.

Methods: We explored the effects of stent-jailing or stent-jack technique on IA recurrence by investigating mechanical forces, TGF-β/Smad2,3,4 signaling pathway and the incidence of angiogenesis in IA patients. One-hundred-eighty-one IA patients were assigned into stent-jailing (n = 93) and stent-jacket groups (n = 88). The clinical outcome was evaluated using Glasgow Outcome Score (GOS) and aneurysm occlusion grades. The percentage of CD34⁺EPCs (releasing pro-angiogenic cytokines) in peripheral blood was measured by flow cytometer. Endothelial cells were separated from cerebral aneurysm and malformed arteries via immunomagnetic cell sorting. Angiogenesis was measured by microvessel density (MVD) using anti-CD34 monoclonal antibody staining before using the stent, immediately after surgery and 2 years later. Meanwhile, the mechanical forces in cerebral vessels were determined by measuring endothelial shear stress (ESS) via a computational method. TGF-β and Smad2,3,4 were measured by real-time qPCR and Western Blot. Tube formation analysis was performed to test the relationship between angiogenesis and TGF-β, and the effects of different techniques on angiogenesis.

Results: After a 2-year follow-up, 85 and 81 patients from stent-jailing and stent-jack groups, respectively, completed the experiment. Stent-jailing technique improved GOS and reduced aneurysm occlusion grades higher than the stent-jack technique (P < 0.05). The counts of CD34⁺EPCs and MVD values in the stent-jailing group were lower than the stent-jack group (P < 0.05). ESS values in sent-jailing group were lower than the stent-jack group (P < 0.05), and positively correlated with MVD values (P < 0.05). TGF-β and Smad2,3,4 levels in sent-jailing group were also lower than the stent-jack group (P < 0.05). TGF-β was associated with angiogenesis incidence and stent-jack caused angiogenesis incidence more than stent-jailing.

Conclusion: Stent-jailing technique reduces IA recurrence more than stent-jack by causing less mechanical forces, angiogenesis and inhibiting TGF-β/Smad2,3,4 signaling in IA patients.

Electrospun Produced 3D Matrices for Covering of Vascular Stents: Paclitaxel Release Depending on Fiber Structure and Composition of the External Environment

Paclitaxel is a natural, highly lipophilic anti proliferative drug widely used in medicine. We have studied the release of tritium-labeled paclitaxel (³H-PTX) from matrices destined for the coating of vascular stents and produced by the electrospinning method from the solutions of polycaprolactone (PCL) with paclitaxel (PTX) in hexafluoisopropanol (HFIP) and/or solutions of PCL with PTX and human serum albumin (HSA) in HFIP or HIFP-dimethyl sulphoxide (DMSO) blend. The release of PTX has been shown to depend on the composition of electrospinning solution, as well as the surrounding medium, particularly the concentration of free PTX and PTX-binding biomolecules present in human serum. It was shown that 3D matrices can completely release PTX without weight loss. Two-phase PTX release from optimized 3D matrices was obtained: ~27% of PTX was released in the first day, another 8% were released over the next 26 days. Wherein ~2.8%, ~2.3%, and ~0.25% of PTX was released on day 3, 9, and 27, respectively. Considering PTX toxicity, the rate of its diffusion through the arterial wall, and the data obtained the minimum cytostatic dose of the drug in the arterial wall will be maintained for at least three months.

Synergistically regulated spontaneous calcium signaling is attributed to cartilaginous extracellular matrix metabolism

Ca²⁺ has been recognized as a key molecule for chondrocytes, however, the role and mechanism of spontaneous [Ca ²⁺ ] _i signaling in cartilaginous extracellular matrix (ECM) metabolism regulation are unclear. Here we found that spontaneous Ca ²⁺ signal of in-situ porcine chondrocytes was [Ca ²⁺ ] _o dependent, and mediated by [Ca ²⁺ ] _i store release. T-type voltage-dependent calcium channel (T-VDCC) mediated [Ca ²⁺ ] _o influx was associated with decreased cell viability and expression levels of ECM deposition genes. Further analysis revealed that chondrocytes expressed both inositol 1,4,5-trisphosphate receptor (InsP3R) and Orai isoforms. Inhibition of endoplasmic reticulum (ER) Ca ²⁺ release and store-operated calcium entry significantly abolished spontaneous [Ca ²⁺ ] _i signaling of in-situ chondrocytes. Moreover, blocking ER Ca ²⁺ release with InsP3R inhibitors significantly upregulated ECM degradation enzymes production, and was accompanied by decreased proteoglycan and collagen type II intensity. Taken together, our data provided evidence that spontaneous [Ca ²⁺ ] _i signaling of in-situ porcine chondrocytes was tightly regulated by [Ca ²⁺ ] _o influx, InsP3Rs mediated [Ca ²⁺ ] _i store release, and Orais mediated calcium release-activated calcium channels activation. Both T-VDCC mediated [Ca ²⁺ ] _o influx and InsP3Rs mediated ER Ca ²⁺ release were found crucial to cartilaginous ECM metabolism through distinct regulatory mechanisms.

Biocompatible Carbon-Based Coating as Potential Endovascular Material for Stent Surface

Stainless steel 316L is a material commonly used in cardiovascular medicine. Despite the various methods applied in stent production, the rates of in-stent restenosis and thrombosis remain high. In this study graphene was used to coat the surface of 316L substrate for enhanced bio- and hemocompatibility of the substrate. The presence of graphene layers applied to the substrate was investigated using cutting-edge imaging technology: energy-filtered low-voltage FE-SEM approach, scanning electron microscopy (SEM), Raman spectroscopy, and atomic force microscopy (AFM). The potential of G-316L surface to influence endothelial cells phenotype and endothelial-to-mesenchymal transition (EndoMT) has been determined. Our results show that the bio- and hemocompatible properties of graphene coatings along with known radial force of 316L make G-316L a promising candidate for intracoronary implants.

Magnetic-targeting of polyethylenimine-wrapped iron oxide nanoparticle labeled chondrocytes in a rabbit articular cartilage defect model

Osteoarthritis (OA) is the most prevalent form of joint disease and lacks effective treatment. Cell-based therapy through intra-articular injection holds great potential for effective intervention at its early stage. Despite the promising outcomes, major barriers for successful clinical application such as lack of specific targeting of transplanted cells still remain. Here, novel polyethylenimine-wrapped iron oxide nanoparticles (PEI/IONs) were utilized as a magnetic agent, and the in vitro efficiency of PEI/ION labeling, and the influence on the chondrogenic properties of chondrocytes were evaluated; the in vivo feasibility of magnetic-targeting intra-articular injection with PEI/ION labeled autologous chondrocytes was investigated using a rabbit articular cartilage defect model. Our data showed that chondrocytes were conveniently labeled with PEI/IONs in a time- and dose-dependent manner, while the viability was unaffected. No significant decrease in collagen type-II synthesis of labeled chondrocytes was observed at low concentration. Macrographic and histology evaluation at 1 week post intra-articular injection revealed efficient cell delivery at chondral defect sites in the magnetic-targeting group. In addition, chondrocytes in the defect area presented a normal morphology, and the origin of cells within was confirmed by immunohistochemistry staining against BrdU and Prussian blue staining. The present study shows proof of concept experiments in magnetic-targeting of PEI/ION labeled chondrocytes for articular cartilage repair, which might provide new insight to improve current cartilage repair strategies.

Magnetic-targeting outcome in the knee joint of experimental rabbit model at 1 week post intra-articular injection.

Nanomedicine in coronary artery disease

Nanomedicine is one of the most promising therapeutic modalities researchers are working on. It involves development of drugs and devices that work at the nanoscale (10-9m). Coronary artery disease (CAD) is responsible for more than a third of all deaths in age group >35 years. With such a huge burden of mortality, CAD is one of the diseases where nanomedicine is being employed for preventive and therapeutic interventions. Nanomedicine can effectively deliver focused drug payload at sites of local plaque formation. Non-invasive strategies include thwarting angiogenesis, intra-arterial thrombosis and local inflammation. Invasive strategies following percutaneous coronary intervention (PCI) include anti-restenosis and healing enhancement. However, before practical application becomes widespread, many challenges need to be dealt with. These include manufacturing at the nanoscale, direct nanomaterial cellular toxicity and visualization.