Singh, Prabh G.

The creation of an arteriovenous fistula in a uremic pig induces cardiac remodeling, which resembles contemporary clinical findings in patients with end-stage kidney disease (ESKD) and includes increased end-diastolic volumes and cardiomyocyte hypertrophy, potentially driven by fibrosis and senescence. This novel large animal model may now enable mechanistic and therapeutic studies aiming to ease the unacceptably high burden of cardiovascular disease on patients with ESKD.

ABSTRACT Atraumatic and localized drug delivery to the vascular endothelium remains a critical unmet need in interventional medicine, with major implications for arterial and venous disease management. Here, we present EndoBot, an untethered elastic millirobot designed to enable endothelial‐safe, soft‐contact operation, under physiologic blood flow. EndoBot is magnetically actuated and navigates along the vessel lumen through curved, non‐uniform geometries while maintaining ultra‐low radial contact pressures (<1 kPa), far below endothelial injury thresholds. We demonstrate stable locomotion, with intrinsically compliant mechanics within a defined safety envelope under arterial and venous hemodynamics in phantom vessels, ex vivo human umbilical veins, and an in vivo rat inferior vena cava, without detectable vessel damage. EndoBot is compatible with standard vascular sheaths for wireless deployment and retrieval and is controlled under clinical fluoroscopic guidance using a human‐scale magnetic manipulation platform. Blood compatibility testing confirms safety, with minimal hemolysis and no increased coagulation tendency during navigation. For localized therapy, EndoBot employs a gentle endoluminal painting strategy, transferring a washout‐resistant drug depot directly onto the vessel lumen. By combining atraumatic mobility, clinical deployability, and localized drug deposition, EndoBot establishes a translationally viable platform for developingmaintenance‐oriented endovascular therapies, supporting prevention of restonosis, thrombosis and inflammatory remodeling following intervention.

Key Points This study reveals the temporal development and progression of senescence in an arteriovenous fistula of uremic mice. Senescent genes including p21 increased 7 days after arteriovenous fistula placement, and p16 and phosphorylated p53 cells accumulate between days 14 and 28. Transcriptomic analyses confirm established genes in arteriovenous fistula failure and suggest a collection of novel genes of interest. Background Hemodialysis therapy for ESKD requires suitable vascular access, most commonly the arteriovenous fistula (AVF). Forty percent of AVFs fail within 1 year, leading to morbidity and care costs. Failure mechanisms remain unclear, and current therapies are inadequate. Cellular senescence may be critical in AVF failure, and ESKD itself may accelerate senescence and subsequent vascular dysfunction. Senescence follows AVF placement in rodents with normal kidney function, but the temporal and spatial features in uremic conditions are unknown. This study aimed to characterize AVF changes in uremic mice over time and versus control vessels. Methods Six- to eight-week-old male C57BL6/J mice underwent five/six nephrectomy. Twenty-eight days later, an AVF was created by cuff anastomosis (right carotid artery to the right jugular vein). Transcriptomic analysis was performed 7 days post-AVF, and further samples were collected at 14 and 28 days post-AVF creation for histologic assessment. Results AVF outflow vein morphometry showed reduced neointimal cell density. Whole transcriptomic analysis of outflow versus control veins at 7 days post-AVF placement revealed 1187 upregulated and 3256 downregulated genes. Differentially expressed genes were significantly enriched in two established senescence-related gene sets, SenMayo (a curated panel of approximately 125 genes validated across species to capture senescence and associated proteins) and SenSig (a broader panel assessed to represent fibrotic and stress-induced cell response). Histologically, senescence markers p16, p21, and phospho53 increased between days 14 and 28. Genes common to our dataset, SenMayo, and SenSig were validated with quantitative reverse transcription PCR. Conclusions These data support established markers of AVF failure, such as matrix-metalloproteinases and monocyte chemokines, and identify potential novel modulators of AVF survival that may inform senolytic strategies to improve patency. In summary, this study reveals for the first time the chronologic progression of vascular senescence in the AVF of uremic mice.

Abstract Atraumatic and localized drug delivery to the vascular endothelium remains a critical unmet need in interventional medicine, with major implications for the management of arterial and venous diseases. Current approaches, such as drug-eluting stents and drug-coated balloons, combine mechanical revascularization with local drug release but frequently denude the endothelium and injure vessel walls, leading to restenosis, thrombosis, and chronic inflammatory repair cycles that severely limit long-term outcomes. Here, we present EndoBot, a soft, untethered millirobot designed for atraumatic navigation and targeted endovascular drug delivery during physiologic blood flow. EndoBot employs magnetically actuated corkscrew propulsion and mechanically adaptive surface crawling to maintain low radial pressure (<1 kPa) and preserve endothelial integrity. Its feasibility is established in arterial and venous phantom models, ex vivo human umbilical veins under normothermic perfusion, and in vivo rat inferior vena cava, all under clinical fluoroscopic guidance using a human-scale magnetic manipulation system. Despite periodic vessel motion, compression, and geometric irregularities, EndoBot maintains stable, mechanically adaptive navigation without endothelial injury. Under real-time fluoroscopic imaging, we identify key challenges and showcase clinically feasible strategies for 3D localization and tracking, overcoming intrinsic depth limitations of 2D clinical imaging. The device can be deployed and retrieved through standard vascular sheaths and remains stable under supraphysiologic arterial and venous flow conditions (flow rate >100 mL min-1; flow velocity >155 cm s-1, shear stress >10 Pa). Blood-compatibility testing demonstrates no increase in coagulation tendency and minimal hemolysis (<0.01%) during magnetic actuation. For drug delivery, EndoBot employs a novel endoluminal painting-based technique that transfers a hydrophobic and flow-resistant coating directly onto the inner vessel surface. This method ensures uniform deposition of a biodegradable drug depot without generating fragments larger than typical capillary diameters (>10 mm). By enabling local, atraumatic drug delivery without compromising vessel wall integrity, EndoBot first time demonstrates a translationally viable platform for exploring effectiveness in preventive interventions in early-stage vascular disease and for adjunctive therapies in advanced disease stages.

Background: The arteriovenous fistula (AVF) is a requirement for hemodialysis therapy in end-stage kidney disease (ESKD) patients. A consequence of AVF creation is compensatory cardiovascular hemodynamics, which are subsequently associated with cardiac remodeling. Relatedly, cardiovascular mortality and morbidity are elevated in ESKD patients, which worsens in dialysis patients. Currently, no suitable uremic large animal models exist to investigate the underlying mechanisms of AVF-induced cardiac remodeling. Research Question: This study aims to characterize cardiovascular changes secondary to AVF creation, supported by percutaneous transluminal angioplasty (PTA), in a uremic pig model. Methods: Chronic kidney disease (CKD) was induced via renal embolization, followed by AVF creation 28 days later. The AVF was created by anastomosis of the left common carotid artery to the left external jugular vein. AVF stenosis was alleviated 28 days thereafter via PTA, and cardiac MRI was performed at 14-, 28-, and 42-days post-PTA. Results: Increased end-diastolic volumes were observed in the left and right ventricles at day 42 vs 14 (200.8ml to 249.5ml, p=0.0457, and 204.6ml to 260.0ml, p=0.0268 respectively), while systolic function was preserved. Left ventricle (LV) stroke volume and blood flow through the aorta, pulmonary artery, and vena cava were also increased. In perivascular areas of the free wall of the LV at day 42 vs control, senescence markers showed increased p16 expression (fold change 10.21, p=0.0086) and decreased p21 expression (fold change 0.07, p=0.0357). The LV showed perivascular fibrosis (0.2% to 0.59%, p=0.021), via picrosirius red, reduced collagen-type IV expression (fold change 0.81, p=0.0089), and increased MMP2 levels (fold change 14.33, p=0.0213). Cardiomyocyte cross-sectional area was increased (from 800.9 µm 2 to 1250.0 µm 2 , p=0.0296), without CD4+ or CD68+ cell LV infiltration. Conclusion: In conclusion, AVF creation leads to modified left and right ventricular function and increased peripheral flow, potentially mediated by cellular senescence and fibrosis, resulting in progressive cardiac remodeling. This model of uremic kidney disease can now be used to evaluate mechanisms of AVF induced cardiac disease and test the efficacy of therapeutics like senolytics and anti-fibrotic agents.

Worldwide, more than 4 million patients with end-stage kidney disease require hemodialysis through an arteriovenous fistula (AVF). AVFs fail because of venous neointimal hyperplasia (VNH) resulting in venous stenosis formation. A phase 1 randomized trial in patients undergoing upper extremity AVF placement was performed to evaluate the safety and efficacy of autologous adipose–derived mesenchymal stem cells (MSCs) in improving AVF function. The mechanism of action by which MSCs exert their beneficial effects was investigated using AVFs created in mice and pigs treated with allogenic MSCs and xenotransplant using patient MSCs in CD1- Foxn1nu mice. At a median follow-up of 42 months, patients with MSC-treated AVFs had reduced time to maturation with an increase in the vein diameter compared with controls. AVFs treated with allogenic MSCs in mice and pigs had an increase in M2- and M1-like macrophages with a decrease in VNH. Transcriptomic analysis of AVFs treated with allogenic MSCs in mouse and MSC xenotransplants of patients with successful AVFs showed decreased peroxisome proliferator–activated receptor gamma ( Ppar γ) and leptin receptor ( Lepr ) and increased latent transforming growth factor–beta–binding protein 2 ( Ltbp2 ). PPARγ was reduced in CD68 (+) cells from successful AVFs and allogenic MSC-treated mouse AVFs. Venous stenosis and VNH formation were mitigated in AVFs of mice with Ppar γ ablation in immune cells. Conditioned medium from MSCs of responders versus nonresponders had decreased proinflammatory genes, senescence-associated proteins, and monocyte-to-macrophage differentiation induced by phorbol 12-myristate-13-acetate. Periadventitial delivery of MSCs to AVFs promoted positive vascular remodeling through decreased inflammatory responses.

ABSTRACT Atraumatic and precise drug delivery to arteries and veins remains an unmet need in interventional medicine, with significant implications for managing vascular diseases and long-term patient outcomes. Conventional endovascular methods, such as drug-coated balloons and drug-eluting stents, often damage vessel endothelium and compromise wall integrity, leading to reduced therapeutic efficacy and severe complications including restenosis and thrombosis. To address these limitations, we introduce EndoBot, an untethered soft millirobot designed for atraumatic vessel navigation and localized drug delivery under physiological blood flow. EndoBot achieves this through magnetically actuated corkscrew propulsion and mechanically adaptive surface crawling, exerting low radial pressure (< 1 kPa) to preserve endothelial integrity. We validated its performance in phantom vessels, ex vivo human umbilical veins under normothermic perfusion, and in vivo rat inferior vena cava under fluoroscopic guidance using a human-scale magnetic manipulation platform. Despite dynamic vessel contractions and compressions along non-uniform cross-sections, mechanically adaptive locomotion strategy ensures safe navigation and protects the inner endothelial lining. EndoBot is deployable and retrievable via clinical vascular sheaths and remains stable even under supra-physiological blood flow conditions (> 155 cm/s). Extensive blood compatibility tests demonstrated minimal hemolysis (<0.01%), low platelet activation on the robot surface, and no increased coagulation tendency. For drug delivery, a hydrophobic transfer coating enables EndoBot to gently deposit a stable, flow-resistant drug layer onto the vessel wall without fragmentation. This novel platform enables safer and more effective targeted endovascular drug delivery, paving the way for transformative approaches to address early-stage vascular pathologies and deliver more effective preventive interventions.

Arterial stiffness predicts cardiovascular disease, the leading cause of death worldwide. Ultrasound elastography methods that measure wave velocity have promise for evaluating the stiffness of blood vessels in vivo. However, vessel geometry modulates wave velocity by inducing geometric dispersion. Here, we compare Young's modulus E estimates obtained using in vivo wave velocity measurements and techniques that either do or do not consider geometry to ex vivo reference E values from mechanical testing . An acoustic radiation force was applied to generate propagating waves in the right common carotid artery (N = 9) and external jugular vein (N = 10) of anesthetized pigs. Vessels were imaged with ultrafast ultrasound to measure wave motion. Group velocity cg was estimated from wave motion using a Radon transform. E was estimated from cg using a bulk media assumption which neglects geometry, as well as the Moens–Korteweg equation and a semi-analytical finite element model, which consider geometry. Pigs were euthanized and vessels were excised. Ring-shaped samples were extracted and tested in a uniaxial tension setup to obtain reference E values for comparison with E values obtained from wave-based techniques. Techniques considering geometry exhibited higher correlation with reference E values, underscoring the need to incorporate geometry for accurate vascular elastography assessments.

Abstract Background and study aims Management of malignant gastrointestinal obstruction (MGIO) is more challenging in the presence of peritoneal carcinomatosis (PC). Outcomes data to guide the management of MGIO with PC are lacking. We aimed to compare the clinical outcomes and adverse events between endoscopic and surgical palliation and identify predictors of stent success in patients with MGIO with PC. Patients and methods Consecutive inpatients with MGIO with PC between 2000 and 2018 who underwent palliative surgery or enteral stenting were included. Clinical success was defined as relief of obstructive symptoms. Results Fifty-seven patients with enteral stenting and 40 with palliative surgery were compared. The two groups did not differ in rates of technical success, 30-day mortality, or recurrence. Clinical success from a single intervention (63.2 % versus 95 %), luminal patency duration (27 days vs. 145 days), and survival length (148 days vs. 336 days) favored palliative surgery (all P < 0.05) but the patients in the surgery group had a trend toward better Eastern Cooperative Oncology Group (ECOG) status. The rate of adverse events (AEs) (10.5 % vs. 50 %), the severity of AEs, and length of hospital stay (4.5 days vs. 9 days) favored enteral stenting (P < 0.05). The need for more than one stent was associated with a higher likelihood of stent failure. Conclusions Our study suggests that enteral stenting is safer and associated with a shorter hospital stay than palliative surgery, although unlike other MGIOs, clinical success is lower in MGIO with PC. Identification of the right candidates and potential predictors of clinical success in ECOG-matched large-scale studies is needed to validate these results.