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OBJECTIVES Neonatal rodents and piglets naturally regenerate the injured heart after myocardial infarction. We hypothesized that neonatal rabbits also exhibit natural heart regeneration after myocardial infarction. METHODS New Zealand white rabbit kits underwent sham surgery or left coronary ligation on postnatal day 1 (n = 94), postnatal day 4 (n = 11), or postnatal day 7 (n = 52). Hearts were explanted 1 day postsurgery to confirm ischemic injury, at 1 week postsurgery to assess cardiomyocyte proliferation, and at 3 weeks postsurgery to assess left ventricular ejection fraction and scar size. Data are presented as mean ± standard deviation. RESULTS Size of ischemic injury as a percentage of left ventricular area was similar after myocardial infarction on postnatal day 1 versus on postnatal day 7 (42.3% ± 5.4% vs 42.3% ± 4.7%, P = .9984). Echocardiography confirmed severely reduced ejection fraction at 1 day after postnatal day 1 myocardial infarction (33.7% ± 5.3% vs 65.2% ± 5.5% for postnatal day 1 sham, P = .0001), but no difference at 3 weeks after postnatal day 1 myocardial infarction (56.0% ± 4.0% vs 58.0% ± 3.3% for postnatal day 1 sham, P = .2198). Ejection fraction failed to recover after postnatal day 4 myocardial infarction (49.2% ± 1.8% vs 58.5% ± 5.8% for postnatal day 4 sham, P = .0109) and postnatal day 7 myocardial infarction (39.0% ± 7.8% vs 60.2% ± 5.0% for postnatal day 7 sham, P

Objective The objective was to design and evaluate a clinically relevant, novel ex vivo bicuspid aortic valve model that mimics the most common human phenotype with associated aortic regurgitation. Methods Three bovine aortic valves were mounted asymmetrically in a previously validated 3–dimensional-printed left heart simulator. The non-right commissure and the non-left commissure were both shifted slightly toward the left–right commissure, and the left and right coronary cusps were sewn together. The left–right commissure was then detached and reimplanted 10 mm lower than its native height. Free margin shortening was used for valve repair. Hemodynamic status, high-speed videography, and echocardiography data were collected before and after the repair. Results The bicuspid aortic valve model was successfully produced and repaired. High-speed videography confirmed prolapse of the fused cusp of the baseline bicuspid aortic valve models in diastole. Hemodynamic and pressure data confirmed accurate simulation of diseased conditions with aortic regurgitation and the subsequent repair. Regurgitant fraction postrepair was significantly reduced compared with that at baseline (14.5 ± 4.4% vs 28.6% ± 3.4%; P = .037). There was no change in peak velocity, peak gradient, or mean gradient across the valve pre- versus postrepair: 293.3 ± 18.3 cm/sec versus 325.3 ± 58.2 cm/sec (P = .29), 34.3 ± 4.2 mm Hg versus 43.3 ± 15.4 mm Hg (P = .30), and 11 ± 1 mm Hg versus 9.3 ± 2.5 mm Hg (P = .34), respectively. Conclusions An ex vivo bicuspid aortic valve model was designed that recapitulated the most common human phenotype with aortic regurgitation. These valves were successfully repaired, validating its potential for evaluating valve hemodynamics and optimizing surgical repair for bicuspid aortic valves.

Vein grafts, the most commonly used conduits in multi-vessel coronary artery bypass grafting surgery, have high intermediate- and long-term failure rates. The abrupt and marked increase in hemodynamic loads on the vein graft is a known contributor to failure. Recent computational modeling suggests that veins can more successfully adapt to an increase in mechanical load if the rate of loading is gradual. Applying an external wrap or support at the time of surgery is one way to reduce the transmural load, and this approach has improved performance relative to an unsupported vein graft in several animal studies. Yet, a clinical trial in humans has shown benefits and drawbacks, and mechanisms by which an external wrap affects vein graft adaptation remain unknown. This study aims to elucidate such mechanisms using a multimodal experimental and computational data collection pipeline. We quantify morphometry using magnetic resonance imaging, mechanics using biaxial testing, hemodynamics using computational fluid dynamics, structure using histology, and transcriptional changes using bulk RNA-sequencing in an ovine carotid-jugular interposition vein graft model, without and with an external biodegradable wrap that allows loads to increase gradually. We show that a biodegradable external wrap promotes luminal uniformity, physiological wall shear stress, and a consistent vein graft phenotype, namely, it prevents over-distension, over-thickening, intimal hyperplasia, and inflammation, and it preserves mechanotransduction. These mechanobiological insights into vein graft adaptation in the presence of an external support can inform computational growth and remodeling models of external support and facilitate design and manufacturing of next-generation external wrapping devices. STATEMENT OF SIGNIFICANCE: External mechanical support is emerging as a promising technology to prevent vein graft failure following coronary bypass graft surgery. While variants of this technology are currently under investigation in clinical trials, the fundamental mechanisms of adaptation remain poorly understood. We employ an ovine carotid-jugular interposition vein graft model, with and without an external biodegradable wrap to provide mechanical support, and probe vein graft adaptation using a multimodal experimental and computational data collection pipeline. We quantify morphometry using magnetic resonance imaging, mechanics using biaxial testing, fluid flow using computational fluid dynamics, vascular composition and structure using histology, and transcriptional changes using bulk RNA sequencing. We show that the wrap mitigates vein graft failure by promoting multiple adaptive mechanisms (across biological scales).

Introduction: Central venous catheters (CVCs) are often trimmed during heart transplantation and pediatric cardiac surgery. However, the risk of endothelial injury caused by the cut tip of the CVC has not been evaluated. We hypothesized that there is no difference in the degree of endothelial injury associated with trimmed CVCs versus standard untrimmed CVCs. Methods: In four adult male sheep, the left external jugular vein was exposed in three segments, one designated for an untouched control group, one for the trimmed CVC group, and one for the untrimmed CVC group. Trimmed and untrimmed CVC tips were rotated circumferentially within their respective segments to abrade the lumen of the vein. The vein samples were explanted, and two representative sections from each sample were analyzed using hematoxylin and eosin (H&E) staining, as well as with immunohistochemistry against CD31, von Willebrand factor (vWF), endothelial nitric oxide synthase (eNOS), and caveolin. Higher immunohistochemical stain distributions and intensities are associated with normal health and function of the venous endothelium. Data are presented as counts with percentages or as means with standard error. Results: H&E staining revealed no evidence of endothelial injury in 6/8 (75%) samples from the untouched control group, and no injury in 4/8 (50%) samples from both the trimmed and untrimmed CVC groups ( p = 0.504). In all remaining samples from each group, only mild endothelial injury was observed. Immunohistochemical analysis comparing trimmed CVCs versus untrimmed CVCs revealed no difference in the percentage of endothelial cells staining positive for CD31 (57.5% ± 7.2% vs 55.0% ± 9.2%, p = 0.982), vWF (73.8% ± 8.0% vs 62.5% ± 9.6%, p = 0.579), eNOS (66.3% ± 4.2% vs 63.8% ± 7.5%, p = 0.962), and caveolin (53.8% ± 5.0% vs 51.3% ± 4.4%, p = 0.922). There were no significant differences between the groups in the distributions of stain intensity for CD31, vWF, eNOS, and caveolin. Conclusion: Trimmed CVCs do not increase endothelial injury compared to standard untrimmed CVCs.

Supplemental Digital Content is available in the text., Background: Many graft configurations are clinically used for valve-sparing aortic root replacement, some specifically focused on recapitulating neosinus geometry. However, the specific impact of such neosinuses on valvular and root biomechanics and the potential influence on long-term durability are unknown. Methods: Using a custom 3-dimenstional–printed heart simulator with porcine aortic roots (n=5), the anticommissural plication, Stanford modification, straight graft (SG), Uni-Graft, and Valsalva graft configurations were tested in series using an incomplete counterbalanced measures design, with the native root as a control, to mitigate ordering effects. Hemodynamic and videometric data were analyzed using linear models with conduit as the fixed effect of interest and valve as a fixed nuisance effect with post hoc pairwise testing using Tukey’s correction. Results: Hemodynamics were clinically similar between grafts and control aortic roots. Regurgitant fraction varied between grafts, with SG and Uni-Graft groups having the lowest regurgitant fractions and anticommissural plication having the highest. Root distensibility was significantly lower in SG versus both control roots and all other grafts aside from the Stanford modification (P≤0.01 for each). All grafts except SG had significantly higher cusp opening velocities versus native roots (P5-fold higher in the anticommissural plication, Stanford modification, and Valsalva graft groups. Conclusions: In this ex vivo modeling system, clinically used valve-sparing aortic root replacement conduit configurations have comparable hemodynamics but differ in biomechanical performance, with the straight graft most closely recapitulating native aortic root biomechanics.

Mitral regurgitation (MR) due to annular dilation occurs in a variety of mitral valve diseases and is observed in many patients with heart failure due to mitral regurgitation. To understand the biomechanics of MR and ultimately design an optimized annuloplasty ring, a representative disease model with asymmetric dilation of the mitral annulus is needed. This work shows the design and implementation of a 3D-printed valve dilation device to preferentially dilate the posterior mitral valve annulus. Porcine mitral valves (n = 3) were sewn into the device and mounted within a left heart simulator that generates physiologic pressures and flows through the valves, while chordal forces were measured. The valves were incrementally dilated, inducing MR, while hemodynamic and force data were collected. Flow analysis demonstrated that MR increased linearly with respect to percent annular dilation when dilation was greater than a 25.6% dilation threshold (p < 0.01). Pre-threshold, dilation did not cause significant increases in regurgitant fraction. Forces on the chordae tendineae increased as dilation increased prior to the identified threshold (p < 0.01); post-threshold, the MR resulted in highly variable forces. Ultimately, this novel dilation device can be used to more accurately model a wide range of MR disease states and their corresponding repair techniques using ex vivo experimentation. In particular, this annular dilation device provides the means to investigate the design and optimization of novel annuloplasty rings.

Summary Sex differences in autoimmunity and infection suggest that a better understanding of molecular sex differences will improve the diagnosis and treatment of immune-related disease. We identified 144 differentially expressed genes, referred to as immune sex expression signature (iSEXS), between human males and females using an integrated multi-cohort analysis of blood transcriptome profiles from six discovery cohorts from five continents with 458 healthy individuals. We validated iSEXS in 11 additional cohorts of 524 peripheral blood samples. When we separated iSEXS into genes located on sex chromosomes (XY-iSEXS) or autosomes (autosomal-iSEXS), both modules distinguished males and females. iSEXS reflects sex differences in immune cell proportions, with female-associated genes showing higher expression by CD4+ T cells and male-associated genes showing higher expression by myeloid cells. Autosomal-iSEXS detected an increase in monocytes with age in females, reflected sex-differential immune cell dynamics during influenza infection, and predicted antibody response in males, but not females., Graphical Abstract, Highlights • iSEXS is a gene signature capturing sex differences in healthy adult human blood • Autosomal-iSEXS genes are driven by sex differences in immune cell proportions • Autosomal-iSEXS reflects sex differences in influenza infection T cell dynamics • Autosomal-iSEXS predicts antibody response to influenza in males, but not females, Bongen et al. identify a 144-gene immune sex expression signature (iSEXS) that is differentially expressed in the blood of healthy human males and females. Many of the autosomal-iSEXS genes are driven by sex differences in immune cell proportions and predict antibody responses to influenza infection in males, but not females.

Newborn mammals, including piglets, exhibit natural heart regeneration after myocardial infarction (MI) on postnatal day 1 (P1), but this ability is lost by postnatal day 7 (P7). The electrophysiologic properties of this naturally regenerated myocardium have not been examined. We hypothesized that epicardial conduction is preserved after P1 MI in piglets. Yorkshire-Landrace piglets underwent left anterior descending coronary artery ligation at age P1 (n = 6) or P7 (n = 7), After 7 weeks, cardiac magnetic resonance imaging was performed with late gadolinium enhancement for analysis of fibrosis. Epicardial conduction mapping was performed using custom 3D-printed high-resolution mapping arrays. Age- and weight-matched healthy pigs served as controls (n = 6). At the study endpoint, left ventricular (LV) ejection fraction was similar for controls and P1 pigs (46.4 ± 3.0% vs. 40.3 ± 4.9%, p = 0.132), but significantly depressed for P7 pigs (30.2 ± 6.6%, p < 0.001 vs. control). The percentage of LV myocardial volume consisting of fibrotic scar was 1.0 ± 0.4% in controls, 9.9 ± 4.4% in P1 pigs (p = 0.002 vs. control), and 17.3 ± 4.6% in P7 pigs (p < 0.001 vs. control, p = 0.007 vs. P1). Isochrone activation maps and apex activation time were similar between controls and P1 pigs (9.4 ± 1.6 vs. 7.8 ± 0.9 ms, p = 0.649), but significantly prolonged in P7 pigs (21.3 ± 5.1 ms, p < 0.001 vs. control, p < 0.001 vs. P1). Conduction velocity was similar between controls and P1 pigs (1.0 ± 0.2 vs. 1.1 ± 0.4 mm/ms, p = 0.852), but slower in P7 pigs (0.7 ± 0.2 mm/ms, p = 0.129 vs. control, p = 0.052 vs. P1). Overall, our data suggest that epicardial conduction dynamics are conserved in the setting of natural heart regeneration in piglets after P1 MI.

OBJECTIVES Posterior ventricular anchoring neochordal (PVAN) repair is a non-resectional technique for correcting mitral regurgitation (MR) due to posterior leaflet prolapse, utilizing a single suture anchored in the myocardium behind the leaflet. This technique has demonstrated clinical efficacy, although a theoretical limitation is stability of the anchoring suture. We hypothesize that the PVAN suture positions the leaflet for coaptation, after which forces are distributed evenly with low repair suture forces. METHODS Porcine mitral valves were mounted in a 3-dimensional-printed heart simulator and chordal forces, haemodynamics and echocardiography were collected at baseline, after inducing MR by severing chordae, and after PVAN repair. Repair suture forces were measured with a force-sensing post positioned to mimic in vivo suture placement. Forces required to pull the myocardial suture free were also determined. RESULTS Relative primary and secondary chordae forces on both leaflets were elevated during prolapse (P DISCUSSION PVAN repair eliminates MR by positioning the posterior leaflet for coaptation, distributing forces throughout the valve. Given extremely low measured forces, the strength of the repair suture and the myocardium is not a limitation.

Adverse remodeling of the left ventricle (LV) after myocardial infarction (MI) results in abnormal tissue biomechanics and impaired cardiac function, often leading to heart failure. We hypothesized that intramyocardial delivery of engineered stromal cell-derived factor 1α analog (ESA), our previously-developed supra-efficient proangiogenic chemokine, preserves biaxial LV mechanical properties after MI. Male Wistar rats (n = 45) underwent sham surgery (n = 15) or permanent left anterior descending coronary artery ligation. Rats sustaining MI were randomized for intramyocardial injections of either saline (100 μL, n = 15) or ESA (6 μg/kg, n = 15), delivered at four standardized borderzone sites. After 4 weeks, echocardiography was performed, and the hearts were explanted. Tensile testing of the anterolateral LV wall was performed using a displacement-controlled biaxial load frame, and modulus was determined after constitutive modeling. At 4 weeks post-MI, compared to saline controls, ESA-treated hearts had greater wall thickness (1.68 ± 0.05 mm vs 1.42 ± 0.08 mm, p = 0.008), smaller end-diastolic LV internal dimension (6.88 ± 0.29 mm vs 7.69 ± 0.22 mm, p = 0.044), and improved ejection fraction (62.8 ± 3.0% vs 49.4 ± 4.5%, p = 0.014). Histologic analysis revealed significantly reduced infarct size for ESA-treated hearts compared to saline controls (29.4 ± 2.9% vs 41.6 ± 3.1%, p = 0.021). Infarcted hearts treated with ESA exhibited decreased modulus compared to those treated with saline in both the circumferential (211.5 ± 6.9 kPa vs 264.3 ± 12.5 kPa, p = 0.001) and longitudinal axes (194.5 ± 6.5 kPa vs 258.1 ± 14.4 kPa, p < 0.001). In both principal directions, ESA-treated infarcted hearts possessed similar tissue compliance as sham non-infarcted hearts. Overall, intramyocardial ESA therapy improves post-MI ventricular remodeling and function, reduces infarct size, and preserves native LV biaxial mechanical properties.

After myocardial infarction (MI), adult mammals exhibit scar formation, adverse left ventricular (LV) remodeling, LV stiffening, and impaired contractility, ultimately resulting in heart failure. Neonatal mammals, however, are capable of natural heart regeneration after MI. We hypothesized that neonatal cardiac regeneration conserves native biaxial LV mechanics after MI. Wistar rat neonates (1 day old, n = 46) and adults (8-10 weeks old, n = 20) underwent sham surgery or permanent left anterior descending coronary artery ligation. At 6 weeks after neonatal MI, Masson's trichrome staining revealed negligible fibrosis. Echocardiography for the neonatal MI (n = 15) and sham rats (n = 14) revealed no differences in LV wall thickness or chamber diameter, and both groups had normal ejection fraction (72.7% vs 77.5%, respectively, p = 0.1946). Biaxial tensile testing revealed similar stress-strain curves along both the circumferential and longitudinal axes across a full range of physiologic stresses and strains. The circumferential modulus (267.9 kPa vs 274.2 kPa, p = 0.7847), longitudinal modulus (269.3 kPa vs 277.1 kPa, p = 0.7435), and maximum shear stress (3.30 kPa vs 3.95 kPa, p = 0.5418) did not differ significantly between the neonatal MI and sham groups, respectively. In contrast, transmural scars were observed at 4 weeks after adult MI. Adult MI hearts (n = 7) exhibited profound LV wall thinning (p 0.0001), chamber dilation (p = 0.0246), and LV dysfunction (ejection fraction 45.4% vs 79.7%, p 0.0001) compared to adult sham hearts (n = 7). Adult MI hearts were significantly stiffer than adult sham hearts in both the circumferential (321.5 kPa vs 180.0 kPa, p = 0.0111) and longitudinal axes (315.4 kPa vs 172.3 kPa, p = 0.0173), and also exhibited greater maximum shear stress (14.87 kPa vs 3.23 kPa, p = 0.0162). Our study is the first to show that native biaxial LV mechanics are conserved after neonatal heart regeneration following MI, thus adding biomechanical support for the therapeutic potential of cardiac regeneration in the treatment of ischemic heart disease.

Introduction: Newborn piglets reportedly exhibit natural heart regeneration after myocardial infarction (MI). However, the electrophysiologic properties of this regenerated muscle have not been examined. We hypothesized that epicardial electrical conduction is preserved after MI in newborn piglets. Methods: Yorkshire-Landrace piglets underwent left anterior descending coronary artery ligation on postnatal day 1 (P1, n=4) or postnatal day 7 (P7, n=7), infarcting the anteroseptal left ventricle through which the Purkinje conduction system passes. After 7 weeks, cardiac magnetic resonance imaging (MRI) was performed with late gadolinium enhancement for fibrosis analysis. Epicardial conduction mapping was performed using custom 3D-printed, 256-channel high-resolution mapping arrays (Fig 1A). Age- and weight-matched healthy pigs served as controls (n=7). Data are expressed as mean±SD. Results: MRI analysis revealed significant differences between the control, P1, and P7 groups in ejection fraction (47.6±3.1% vs 37.6±3.3% vs 30.2±6.6%, p Conclusion: P1 piglets exhibited incomplete natural cardiac regeneration after MI but nevertheless demonstrated electrophysiologic conservation of epicardial conduction dynamics.

Neonatal mice exhibit natural heart regeneration after myocardial infarction (MI) on postnatal day 1 (P1), but this ability is lost by postnatal day 7 (P7). Cardiac biomechanics intricately affect long-term heart function, but whether regenerated cardiac muscle is biomechanically similar to native myocardium remains unknown. We hypothesized that neonatal heart regeneration preserves native left ventricular (LV) biomechanical properties after MI. C57BL/6J mice underwent sham surgery or left anterior descending coronary artery ligation at age P1 or P7. Echocardiography performed 4 weeks post-MI showed that P1 MI and sham mice (n = 22, each) had similar LV wall thickness, diameter, and ejection fraction (59.6% vs 60.7%, p = 0.6514). Compared to P7 shams (n = 20), P7 MI mice (n = 20) had significant LV wall thinning, chamber enlargement, and depressed ejection fraction (32.6% vs 61.8%, p ex vivo, and the multiaxial lenticular stress-strain relationship was tracked. While LV tissue modulus for P1 MI and sham mice were similar (341.9 kPa vs 363.4 kPa, p = 0.6140), the modulus for P7 MI mice was significantly greater than that for P7 shams (691.6 kPa vs 429.2 kPa, p = 0.0194). We conclude that, in neonatal mice, regenerated LV muscle has similar biomechanical properties as native LV myocardium.

Although ex vivo simulation is a valuable tool for surgical optimization, a disease model that mimics human aortic regurgitation (AR) from cusp prolapse is needed to accurately examine valve biomechanics. To simulate AR, four porcine aortic valves were explanted, and the commissure between the two largest leaflets was detached and re-implanted 5 mm lower to induce cusp prolapse. Four additional valves were tested in their native state as controls. All valves were tested in a heart simulator while hemodynamics, high-speed videography, and echocardiography data were collected. Our AR model successfully reproduced cusp prolapse with significant increase in regurgitant volume compared with that of the controls (23.2 ± 8.9 versus 2.8 ± 1.6 ml, p = 0.017). Hemodynamics data confirmed the simulation of physiologic disease conditions. Echocardiography and color flow mapping demonstrated the presence of mild to moderate eccentric regurgitation in our AR model. This novel AR model has enormous potential in the evaluation of valve biomechanics and surgical repair techniques. Graphical Abstract.

OBJECTIVE. Barlow’s disease remains challenging to repair given the complex valvular morphology and lack of quantitative data comparing techniques. Though there have been recent strides in ex vivo evaluation of cardiac mechanics, to the best of our knowledge, there is no disease model that accurately simulates the morphology and pathophysiology of Barlow’s disease. The purpose of this study was to design such a model. METHOD. To simulate Barlow’s disease, a cross-species ex vivo model was developed. Bovine mitral valves (n=4) were sewn into a porcine annulus mount to create excess leaflet tissue and elongated chordae. A heart simulator generated physiologic conditions while hemodynamic data, high-speed videography, and chordal force measurements were collected. The regurgitant valves were repaired using nonresectional repair techniques such as neochord placement. RESULTS: The model successfully imitated the complexities of Barlow’s disease, including redundant, billowing bi-leaflet tissues with notable regurgitation. After repair, hemodynamic data confirmed reduction of mitral leakage volume 25.9±2.9 vs 2.1±1.8 mL, p

Newborn mice and piglets exhibit natural heart regeneration after myocardial infarction (MI). Discovering other mammals with this ability would provide evidence that neonatal cardiac regeneration after MI may be a conserved phenotype, which if activated in adults could open new options for treating ischemic cardiomyopathy in humans. Here, we hypothesized that newborn rats undergo natural heart regeneration after MI. Using a neonatal rat MI model, we performed left anterior descending coronary artery ligation or sham surgery in one-day-old rats under hypothermic circulatory arrest (n = 74). Operative survival was 97.3%. At 1 day post-surgery, rats in the MI group exhibited significantly reduced ejection fraction (EF) compared to shams (87.1% vs. 53.0%, p &lt, 0.0001). At 3 weeks post-surgery, rats in the sham and MI groups demonstrated no difference in EF (71.1% vs. 69.2%, respectively, p = 0.2511), left ventricular wall thickness (p = 0.9458), or chamber diameter (p = 0.7801). Masson&rsquo, s trichome and picrosirius red staining revealed minimal collagen scar after MI. Increased numbers of cardiomyocytes positive for 5-ethynyl-2&prime, deoxyuridine (p = 0.0072), Ki-67 (p = 0.0340), and aurora B kinase (p = 0.0430) were observed within the peri-infarct region after MI, indicating ischemia-induced cardiomyocyte proliferation. Overall, we present a neonatal rat MI model and demonstrate that newborn rats are capable of endogenous neocardiomyogenesis after MI.

Summary The cyanobacterium Synechococcus elongatus (SE) has been shown to rescue ischaemic heart muscle after myocardial infarction by photosynthetic oxygen production. Here, we investigated SE toxicity and hypothesized that systemic SE exposure does not elicit a significant immune response in rats. Wistar rats intravenously received SE (n = 12), sterile saline (n = 12) or E. coli lipopolysaccharide (LPS, n = 4), and a subset (8 SE, 8 saline) received a repeat injection 4 weeks later. At baseline, 4 h, 24 h, 48 h, 8 days and 4 weeks after injection, clinical assessments, blood cultures, blood counts, lymphocyte phenotypes, liver function tests, proinflammatory cytokines and immunoglobulins were assessed. Across all metrics, SE rats responded comparably to saline controls, displaying no clinically significant immune response. As expected, LPS rats exhibited severe immunological responses. Systemic SE administration does not induce sepsis or toxicity in rats, thereby supporting the safety of cyanobacteria–mammalian symbiotic therapeutics using this organism., The cyanobacterium Synechococcus elongatus (SE) has been shown to rescue ischemic heart muscle after myocardial infarction by photosynthetic oxygen production. Here, we investigate SE toxicity by systemically administering SE to rats and evaluating their immune response by way of clinical assessments, blood cultures, blood counts, lymphocyte phenotypes, liver function tests, proinflammatory cytokines, immunoglobulins, and tissue histology. Systemic SE administration does not induce sepsis or toxicity in rats, thereby supporting the safety of cyanobacteria‐mammalian symbiotic therapeutics using this organism.

Although ischemic heart disease is the leading cause of death worldwide, mainstay treatments ultimately fail because they do not adequately address disease pathophysiology. Restoring the microvascular perfusion deficit remains a significant unmet need and may be addressed via delivery of pro-angiogenic cytokines. The therapeutic effect of cytokines can be enhanced by encapsulation within hydrogels, but current hydrogels do not offer sufficient clinical translatability due to unfavorable viscoelastic mechanical behavior which directly impacts the ability for minimally-invasive catheter delivery. In this report, we examine the therapeutic implications of dual-stage cytokine release from a novel, highly shear-thinning biocompatible catheter-deliverable hydrogel. We chose to encapsulate two protein-engineered cytokines, namely dimeric fragment of hepatocyte growth factor (HGFdf) and engineered stromal cell-derived factor 1α (ESA), which target distinct disease pathways. The controlled release of HGFdf and ESA from separate phases of the hyaluronic acid-based hydrogel allows extended and pronounced beneficial effects due to the precise timing of release. We evaluated the therapeutic efficacy of this treatment strategy in a small animal model of myocardial ischemia and observed a significant benefit in biological and functional parameters. Given the encouraging results from the small animal experiment, we translated this treatment to a large animal preclinical model and observed a reduction in scar size, indicating this strategy could serve as a potential adjunct therapy for the millions of people suffering from ischemic heart disease.

Few technologies exist that can provide quantitative data on forces within the mitral valve apparatus. Marker-based strain measurements can be performed, but chordal geometry and restricted optical access are limitations. Foil-based strain sensors have been described and work well, but the sensor footprint limits the number of chordae that can be measured. We instead utilized fiber Bragg grating (FBG) sensors—optical strain gauges made of 125 μm diameter silica fibers—to overcome some limitations of previous methods of measuring chordae tendineae forces. Using FBG sensors, we created a force-sensing neochord (FSN) that mimics the natural shape and movement of native chordae. FBG sensors reflect a specific wavelength of light depending on the spatial period of gratings. When force is applied, the gratings move relative to one another, shifting the wavelength of reflected light. This shift is directly proportional to force applied. The FBG sensors were housed in a protective sheath fashioned from a 0.025 in. flat coil, and attached to the chordae using polytetrafluoroethylene suture. The function of the force-sensing neochordae was validated in a three-dimensional (3D)-printed left heart simulator, which demonstrated that FBG sensors provide highly sensitive force measurements of mitral valve chordae at a temporal resolution of 1000 Hz. As ventricular pressures increased, such as in hypertension, chordae forces also increased. Overall, FBG sensors are a viable, durable, and high-fidelity sensing technology that can be effectively used to measure mitral valve chordae forces and overcome some limitations of other such technologies.

Introduction: Neonatal mice exhibit natural heart regeneration after myocardial infarction (MI) until postnatal day 7 (P7). Whether this regenerated muscle is similar biomechanically to native myocardium remains unknown. We hypothesized that neonatal heart regeneration preserves native left ventricular (LV) biomechanical properties after MI. Methods: C57BL/6J mice (n=58) underwent sham surgery or left anterior descending coronary artery ligation on postnatal day 1 (P1) or P7. After 4 weeks, echocardiography was performed. The explanted anterolateral LV wall was mounted for lenticular hydrostatic deformation testing (Fig 1A-B) and pressurized to 130 mmHg with 37°C saline to impart a homogeneous stress load. Surface strain was tracked to calculate a multiaxial composite tissue modulus. Data are expressed as mean±SEM. Results: P1 MI and sham mice (n=14, each) had similar post-MI LV wall thickness (0.61±0.05 cm vs 0.66±0.03 cm, p=0.39), end-diastolic diameter (3.14±0.10 cm vs 3.05±0.12 cm, p=0.57), and ejection fraction (58.2±4.1% vs 55.2±4.4%, p=0.63). P7 MI mice (n=14) had significant LV wall thinning (0.40±0.04 cm vs 0.71±0.02 cm, p Conclusion: In a neonatal mouse MI model, regenerated LV muscle has similar biomechanical properties as native LV muscle.

Introduction: Adverse remodeling of the left ventricle (LV) after myocardial infarction (MI) results in abnormal tissue biomechanics and impaired cardiac function, ultimately leading to heart failure. We hypothesized that intramyocardial delivery of engineered stromal cell-derived factor 1α analog (ESA), our previously-developed supra-efficient pro-angiogenic chemokine, preserves biaxial LV mechanical properties after MI. Methods: Male Wistar rats (n=46) underwent sham surgery (n=15) or permanent left anterior descending coronary artery ligation (n=31). Rats sustaining MI were randomized for intramyocardial injections of either saline (100 μL, n=15) or ESA (6 μg/kg, n=16), delivered at standardized peri-infarct sites. After 4 weeks, echocardiography was performed, and the hearts were explanted. Biaxial tensile testing of the anterior LV wall was performed using a strain-controlled biaxial load frame (Fig. 1A), producing up to physiologic circumferential and longitudinal strains (ε=20%, each). The modulus was determined along each axis, and maximum shear stress was calculated as a composite metric of the tissue’s response to physiologic strains. Data are expressed as mean±SEM. Results: At 4 weeks post-MI, ESA-treated hearts had smaller end-diastolic LV internal dimension (6.89±0.27 cm vs 7.69±0.22 cm, p=0.03) and improved ejection fraction (63.7±2.9% vs 49.4±4.4%, p=0.01) compared to saline-injected controls. Hearts treated with ESA exhibited lower moduli than saline controls in both the circumferential (269.4±33.2 kPa vs 431.5±55.6 kPa, p=0.02) and longitudinal axes (182.4±25.0 kPa vs 332.3±51.2 kPa, p=0.02, Fig. 1B). The maximum shear stress for ESA-treated hearts was significantly reduced compared to that for saline controls (5.8±0.8 kPa vs 9.0±1.2 kPa, p=0.03) and was similar to that for sham controls (Fig. 1C). Conclusion: Intramyocardial ESA injection mitigates post-MI tissue stiffening and preserves biaxial LV mechanical properties.

Objective: Adhesions develop after 95% of operations, represent a major clinical challenge, and cost the U.S healthcare system $2.5B annually. In cardiac surgery, adhesions are problematic during re-operations, increasing operative times and posing risks of hemorrhage and injury to the heart and lungs during sternal reentry and cardiac dissection. We hypothesized that shear-thinning, self-healing polymer nanoparticle hydrogels (PNP) would provide a viscoelastic barrier, effectively preventing adhesion formation (Fig 1A). Methods: Multiple PNP formulations underwent rheologic characterization. Male Sprague Dawley rats (n=52) underwent permanent ligation of the LAD to induce robust postinfarct adhesions, followed by epicardial application of PNP (200L), Seprafilm®(1cm 2 ), or no treatment. Male Dorset sheep (n=8) underwent an anterolateral epicardial abrasion followed by application of PNP (25mL), Seprafilm® (12 cm 2 ), or no treatment. Degree of adhesion formation, standardized dissection time, heart function, and immune response were assessed 4-weeks following surgery. Results: PNP exhibited formulation-dependent mechanical properties indicating the effect of hydrogel stiffness on adhesion barrier efficacy (Fig 1B). Infarct size and heart function were controlled to ensure similar inflammatory responses contributing to adhesion formation across treatment groups. Treatment with certain PNP formulations significantly reduced the development of adhesions compared to controls (Fig 1C). Ovine hearts treated with the PNP 1:10 revealed a pristine epicardial surface (Fig 1D, 1E, and 1F) and resulted in a shorter dissection time relative to the controls (Fig 1G). Conclusion: Administration of a shear-thinning, self-healing hydrogel reduces the extent of adhesion formation in the thoracic cavity following surgery in small and large animal models. PNP provides an easily delivered, scalable solution for post-operative adhesion prevention.

Introduction: The posterior ventricular anchoring neochordal (PVAN) repair is a nonresectional, single-suture technique for correcting posterior leaflet prolapse. While this technique has demonstrated clinical efficacy, a possible limitation is the stability of the suture anchored into myocardium as opposed to the fibrous portion of a papillary muscle. Hypothesis: We hypothesize that the PVAN suture serves only to position the leaflet for coaptation, after which systolic forces will be distributed throughout the valve, resulting in low peak forces on the suture. Methods: A left heart simulator was constructed using 3D printing, tuned to generate physiological pressure and flow waveforms, then validated. Porcine mitral valves (n=9) were dissected and mounted within the simulator. Chordal forces were measured using Fiber Bragg Grating (FBG) sensors, sewn in place using PTFE suture. FBG sensors are strain gauges made of 125 μ m optical fibers that use reflected peak wavelength changes to measure strain. Hemodynamic and echocardiographic data were also collected. Isolated severe mitral regurgitation (MR) was induced by cutting P2 primary chordae. The valve was repaired using the PVAN technique, anchoring the suture to a customized force-sensing post positioned to mimic in vivo placement. Results: Forces on 1° and 2° chordae of both anterior and posterior leaflets were significantly elevated in the prolapse condition ( P < 0.05). PVAN resulted in elimination of MR in all valves, as well as normalization of chordae forces to baseline levels for posterior primary ( P < 0.01 ) , posterior secondary ( P < 0.01 ) , and anterior primary chordae ( P < 0.05 ) , with reduction in anterior secondary chordal forces approaching significance ( P = 0.055 ) . Peak forces on the PVAN stitch were minimal, even compared to the forces experienced by primary chordae of normal, healthy valves ( P < 0.05). Conclusions: The PVAN technique eliminates MR by effectively positioning the posterior leaflet for optimal coaptation, distributing the forces amongst the subvalvular apparatus. Given the extremely low forces involved, the strength of the ventricular anchoring suture and myocardial anchoring point should not be a limiting factor.

Introduction: Very few technologies exist that can provide quantitative data on forces within the mitral valve apparatus. Marker based strain measurements can be performed, but chordae heterogeneity limits utility. Foil-based strain sensors have also been described, but tend to be bulky, limiting the number of chordae that can be measured. Hypothesis: We hypothesize that the use of Fiber Bragg Grating (FBG) sensors—optical strain gauges made of 125 μ m diameter silica fibers— can overcome the critical limitations of previous methods of measuring chordae tendineae forces. Methods: Using FBG sensors, we created a force-sensing neochord that would mimic the natural shape and movement of native chordae tendineae. FBG sensors reflect a specific wavelength of light depending on the spatial period of gratings - when a force is applied, the gratings move relative to one another, changing the reflected light (Fig 1A). This wavelength shift is directly proportional to the force applied. The FBG sensors were housed in a protective sheath fashioned from the outer coil of a 0.025" Amplatz Extra-Stiff guidewire, and attached to the chordae using GoreTex suture (Fig 1B). The function of the force-sensing neochordae were validated in a 3D printed left heart simulator. Results: FBG sensors provided high-fidelity force measurements of mitral valve chordae tendineae at a temporal resolution of 1000 Hz. As ventricular pressures increased, such as in the hypertensive condition, forces on the chordae also increased (Fig 1C). The resolution of FBG sensors allow for increased accuracy of not only chordae tension, but also the rate of change of force (dF/dt) - a parameter critical to determining likelihood of leaflet rupture. Conclusions: FBG sensors are a viable, durable, and high-fidelity technology that can be effectively used to measure mitral valve chordae forces and overcome limitations of other such technologies.

Background Neochordoplasty is an important repair technique, but optimal anchoring position is unknown. Although typically anchored at papillary muscles, new percutaneous devices anchor the neochordae at or near the ventricular apex, which may have an effect on chordal forces and the long-term durability of the repair. Methods Porcine mitral valves (n = 6) were mounted in a left heart simulator that generates physiologic pressure and flow through the valves, and chordal forces were measured with Fiber Bragg Grating strain gauge sensors. Isolated mitral regurgitation was induced by cutting P2 primary chordae, and the regurgitant valve was repaired with polytetrafluoroethylene neochord with apical anchoring, followed by papillary muscle fixation for comparison. In both situations, the neochord was anchored to a customized force-sensing post positioned to mimic the relevant in vivo placement. Results Echocardiographic and hemodynamic data confirmed that the repairs restored physiologic hemodynamics. Forces on the chordae and neochord were lower for papillary fixation than for the apical fixation (p = 0.003). In addition, the maximum rate of change of force on the chordae and neochordae was higher for apical fixation than for papillary fixation (p = 0.028). Conclusions Apical neochord anchoring results in effective repair of mitral regurgitation, albeit with somewhat higher forces on the chordae and neochord suture, as well as an increased rate of loading on the neochord compared with the papillary muscle fixation. These results may guide strategies to reduce stresses on neochordae as well as aid optimal patient selection.

Post-operative adhesions form as a result of normal wound healing processes following any type of surgery. In cardiac surgery, pericardial adhesions are particularly problematic during reoperations, as surgeons must release the adhesions from the surface of the heart before the intended procedure can begin, thereby substantially lengthening operation times and introducing risks of haemorrhage and injury to the heart and lungs during sternal re-entry and cardiac dissection. Here we show that a dynamically crosslinked supramolecular polymer-nanoparticle hydrogel, with viscoelastic and flow properties that enable spraying onto tissue as well as robust tissue adherence and local retention in vivo for two weeks, reduces the formation of pericardial adhesions. In a rat model of severe pericardial adhesions, the hydrogel markedly reduced the severity of the adhesions, whereas commercial adhesion barriers (including Seprafilm and Interceed) did not. The hydrogels also reduced the severity of cardiac adhesions (relative to untreated animals) in a clinically relevant cardiopulmonary-bypass model in sheep. This viscoelastic supramolecular polymeric hydrogel represents a promising clinical solution for the prevention of post-operative pericardial adhesions.

Hydrogels have emerged as a diverse class of biomaterials offering a broad range of biomedical applications. Specifically, injectable hydrogels are advantageous for minimally invasive delivery of various therapeutics and have great potential to treat a number of diseases. However, most current injectable hydrogels are limited by difficult and time-consuming fabrication techniques and are unable to be delivered through long, narrow catheters, preventing extensive clinical translation. Here, the development of an easily-scaled, catheter-injectable hydrogel utilizing a polymer-nanoparticle crosslinking mechanism is reported, which exhibits notable shear-thinning and self-healing behavior. Gelation of the hydrogel occurs immediately upon mixing the biochemically modified hyaluronic acid polymer with biodegradable nanoparticles and can be easily injected through a high-gauge syringe due to the dynamic nature of the strong, yet reversible crosslinks. Furthermore, the ability to deliver this novel hydrogel through a long, narrow, physiologically-relevant catheter affixed with a 28-G needle is highlighted, with hydrogel mechanics unchanged after delivery. Due to the composition of the gel, it is demonstrated that therapeutics can be differentially released with distinct elution profiles, allowing precise control over drug delivery. Finally, the cell-signaling and biocompatibility properties of this innovative hydrogel are demonstrated, revealing its wide range of therapeutic applications.