Multi-phase catheter-injectable hydrogel enables dual-stage protein-engineered cytokine release to mitigate adverse left ventricular remodeling following myocardial infarction in a small animal model and a large animal model.

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.

Rapid Self-Assembly of Bioengineered Cardiovascular Bypass Grafts From Scaffold-Stabilized, Tubular Bilevel Cell Sheets.

BACKGROUND: Cardiovascular bypass grafting is an essential treatment for complex cases of atherosclerotic disease. Because the availability of autologous arterial and venous conduits is patient-limited, self-assembled cell-only grafts have been developed to serve as functional conduits with off-the-shelf availability. The unacceptably long production time required to generate these conduits, however, currently limits their clinical utility. Here, we introduce a novel technique to significantly accelerate the production process of self-assembled engineered vascular conduits. METHODS: Human aortic smooth muscle cells and skin fibroblasts were used to construct bilevel cell sheets. Cell sheets were wrapped around a 22.5-gauge Angiocath needle to form tubular vessel constructs. A thin, flexible membrane of clinically approved biodegradable tissue glue (Dermabond Advanced) served as a temporary, external scaffold, allowing immediate perfusion and endothelialization of the vessel construct in a bioreactor. Subsequently, the matured vascular conduits were used as femoral artery interposition grafts in rats (n=20). Burst pressure, vasoreactivity, flow dynamics, perfusion, graft patency, and histological structure were assessed. RESULTS: Compared with engineered vascular conduits formed without external stabilization, glue membrane-stabilized conduits reached maturity in the bioreactor in one-fifth the time. After only 2 weeks of perfusion, the matured conduits exhibited flow dynamics similar to that of control arteries, as well as physiological responses to vasoconstricting and vasodilating drugs. The matured conduits had burst pressures exceeding 500 mm Hg and had sufficient mechanical stability for surgical anastomoses. The patency rate of implanted conduits at 8 weeks was 100%, with flow rate and hind-limb perfusion similar to those of sham controls. Grafts explanted after 8 weeks showed a histological structure resembling that of typical arteries, including intima, media, adventitia, and internal and external elastic membrane layers. CONCLUSIONS: Our technique reduces the production time of self-assembled, cell sheet-derived engineered vascular conduits to 2 weeks, thereby permitting their use as bypass grafts within the clinical time window for elective cardiovascular surgery. Furthermore, our method uses only clinically approved materials and can be adapted to various cell sources, simplifying the path toward future clinical translation.

Tissue-engineered smooth muscle cell and endothelial progenitor cell bi-level cell sheets prevent progression of cardiac dysfunction, microvascular dysfunction, and interstitial fibrosis in a rodent model of type 1 diabetes-induced cardiomyopathy.

BACKGROUND: Diabetes mellitus is a risk factor for coronary artery disease and diabetic cardiomyopathy, and adversely impacts outcomes following coronary artery bypass grafting. Current treatments focus on macro-revascularization and neglect the microvascular disease typical of diabetes mellitus-induced cardiomyopathy (DMCM). We hypothesized that engineered smooth muscle cell (SMC)-endothelial progenitor cell (EPC) bi-level cell sheets could improve ventricular dysfunction in DMCM. METHODS: Primary mesenchymal stem cells (MSCs) and EPCs were isolated from the bone marrow of Wistar rats, and MSCs were differentiated into SMCs by culturing on a fibronectin-coated dish. SMCs topped with EPCs were detached from a temperature-responsive culture dish to create an SMC-EPC bi-level cell sheet. A DMCM model was induced by intraperitoneal streptozotocin injection. Four weeks after induction, rats were randomized into 3 groups: control (no DMCM induction), untreated DMCM, and treated DMCM (cell sheet transplant covering the anterior surface of the left ventricle). RESULTS: SMC-EPC cell sheet therapy preserved cardiac function and halted adverse ventricular remodeling, as demonstrated by echocardiography and cardiac magnetic resonance imaging at 8 weeks after DMCM induction. Myocardial contrast echocardiography demonstrated that myocardial perfusion and microvascular function were preserved in the treatment group compared with untreated animals. Histological analysis demonstrated decreased interstitial fibrosis and increased microvascular density in the SMC-EPC cell sheet-treated group. CONCLUSIONS: Treatment of DMCM with tissue-engineered SMC-EPC bi-level cell sheets prevented cardiac dysfunction and microvascular disease associated with DMCM. This multi-lineage cellular therapy is a novel, translatable approach to improve microvascular disease and prevent heart failure in diabetic patients.

A novel protein-engineered hepatocyte growth factor analog released via a shear-thinning injectable hydrogel enhances post-infarction ventricular function.

In the last decade, numerous growth factors and biomaterials have been explored for the treatment of myocardial infarction (MI). While pre-clinical studies have demonstrated promising results, clinical trials have been disappointing and inconsistent, likely due to poor translatability. In the present study, we investigate a potential myocardial regenerative therapy consisting of a protein-engineered dimeric fragment of hepatocyte growth factor (HGFdf) encapsulated in a shear-thinning, self-healing, bioengineered hydrogel (SHIELD). We hypothesized that SHIELD would facilitate targeted, sustained intramyocardial delivery of HGFdf thereby attenuating myocardial injury and post-infarction remodeling. Adult male Wistar rats (n = 45) underwent sham surgery or induction of MI followed by injection of phosphate buffered saline (PBS), 10 µg HGFdf alone, SHIELD alone, or SHIELD encapsulating 10 µg HGFdf. Ventricular function, infarct size, and angiogenic response were assessed 4 weeks post-infarction. Treatment with SHIELD + HGFdf significantly reduced infarct size and increased both ejection fraction and borderzone arteriole density compared to the controls. Thus, sustained delivery of HGFdf via SHIELD limits post-infarction adverse ventricular remodeling by increasing angiogenesis and reducing fibrosis. Encapsulation of HGFdf in SHIELD improves clinical translatability by enabling minimally-invasive delivery and subsequent retention and sustained administration of this novel, potent angiogenic protein analog. Biotechnol. Bioeng. 2017;114: 2379-2389. © 2017 Wiley Periodicals, Inc.

Isolation and trans-differentiation of mesenchymal stromal cells into smooth muscle cells: Utility and applicability for cell-sheet engineering.

BACKGROUND: Bone marrow (BM)-derived mesenchymal stromal cells (MSCs) have shown potential to differentiate into various cell types, including smooth muscle cells (SMCs). The extracellular matrix (ECM) represents an appealing and readily available source of SMCs for use in tissue engineering. In this study, we hypothesized that the ECM could be used to induce MSC differentiation to SMCs for engineered cell-sheet construction. METHODS: Primary MSCs were isolated from the BM of Wistar rats, transferred and cultured on dishes coated with 3 different types of ECM: collagen type IV (Col IV), fibronectin (FN), and laminin (LM). Primary MSCs were also included as a control. The proportions of SMC (a smooth muscle actin [aSMA] and SM22a) and MSC markers were examined with flow cytometry and Western blotting, and cell proliferation rates were also quantified. RESULTS: Both FN and LM groups were able to induce differentiation of MSCs toward smooth muscle-like cell types, as evidenced by an increase in the proportion of SMC markers (aSMA; Col IV 42.3 ± 6.9%, FN 65.1 ± 6.5%, LM 59.3 ± 7.0%, Control 39.9 ± 3.1%; P = 0.02, SM22; Col IV 56.0 ± 7.7%, FN 74.2 ± 6.7%, LM 60.4 ± 8.7%, Control 44.9 ± 3.6%) and a decrease in that of MSC markers (CD105: Col IV 64.0 ± 5.2%, FN 57.6 ± 4.0%, LM 60.3 ± 7.0%, Control 85.3 ± 4.2%; P = 0.03). The LM group showed a decrease in overall cell proliferation, whereas FN and Col IV groups remained similar to control MSCs (Col IV, 9.0 ± 2.3%; FN, 9.8 ± 2.5%; LM, 4.3 ± 1.3%; Control, 9.8 ± 2.8%). CONCLUSIONS: Our findings indicate that ECM selection can guide differentiation of MSCs into the SMC lineage. Fibronectin preserved cellular proliferative capacity while yielding the highest proportion of differentiated SMCs, suggesting that FN-coated materials may be facilitate smooth muscle tissue engineering.

Clinical Impact of Accurate Point-of-Care Glucose Monitoring for Tight Glycemic Control in Severely Burned Children.

OBJECTIVES: The goal of this study was to retrospectively evaluate the clinical impact of an accurate autocorrecting blood glucose monitoring system in children with severe burns. Blood glucose monitoring system accuracy is essential for providing appropriate intensive insulin therapy and achieving tight glycemic control in critically ill patients. Unfortunately, few comparison studies have been performed to evaluate the clinical impact of accurate blood glucose monitoring system monitoring in the high-risk pediatric burn population. DESIGN: Retrospective analysis of an electronic health record system. SETTING: Pediatric burn ICU at an academic medical center. PATIENTS: Children (aged < 18 yr) with severe burns (≥ 20% total body surface area) receiving intensive insulin therapy guided by either a noncorrecting (blood glucose monitoring system-1) or an autocorrecting blood glucose monitoring system (blood glucose monitoring system-2). MEASUREMENTS AND MAIN RESULTS: Patient demographics, insulin rates, and blood glucose monitoring system measurements were collected. The frequency of hypoglycemia and glycemic variability was compared between the two blood glucose monitoring system groups. A total of 122 patient charts from 2001 to 2014 were reviewed. Sixty-three patients received intensive insulin therapy using blood glucose monitoring system-1 and 59 via blood glucose monitoring system-2. Patient demographics were similar between the two groups. Mean insulin infusion rates (5.1 ± 3.8 U/hr; n = 535 paired measurements vs 2.4 ± 1.3 U/hr; n = 511 paired measurements; p < 0.001), glycemic variability, and frequency of hypoglycemic events (90 vs 12; p < 0.001) were significantly higher in blood glucose monitoring system-1-treated patients. Compared with laboratory measurements, blood glucose monitoring system-2 yielded the most accurate results (mean ± SD bias: -1.7 ± 6.9 mg/dL [-0.09 ± 0.4 mmol/L] vs 7.4 ± 13.5 mg/dL [0.4 ± 0.7 mmol/L]). Blood glucose monitoring system-2 patients achieve glycemic control more quickly (5.7 ± 4.3 vs 13.1 ± 6.9 hr; p< 0.001) and stayed within the target glycemic control range longer compared with blood glucose monitoring system-1 patients (85.2% ± 13.9% vs 57.9% ± 29.1%; p < 0.001). CONCLUSIONS: Accurate autocorrecting blood glucose monitoring system optimizes intensive insulin therapy, improves tight glycemic control, and reduces the risk of hypoglycemia and glycemic variability. The use of an autocorrecting blood glucose monitoring system for intensive insulin therapy may improve glycemic control in severely burned children.

Whole blood neutrophil gelatinase-associated lipocalin predicts acute kidney injury in burn patients.

BACKGROUND: Early detection of acute kidney injury (AKI) in severely burn-injured patients can help alter treatment to prevent progression to acute failure and reduce the need for renal replacement therapy. We hypothesized that whole blood neutrophil gelatinase-associated lipocalin (NGAL) will be increased in severely burn-injured patients who develop AKI during acute resuscitation. MATERIALS AND METHODS: We performed a prospective observation study of adult burn patients with a 20% total body surface area (TBSA) burned or greater burn injury. Two-hour serial measurements of NGAL, serum creatinine (Cr), and hourly urine output (UO) were collected for 48 h after admission. Our primary goal was to correlate the risk of AKI in the first week after burn injury with serial NGAL levels in the first 48 h after admission. Our secondary goal was to determine if NGAL was an earlier independent predictor of AKI compared with Cr and UO. RESULTS: We enrolled 30 adult (age ≥ 18 y) burn patients with the mean ± standard deviation age of 40.9 ± 15.4 and mean TBSA of 46.4 ± 22.4. Fourteen patients developed AKI within the first 7 d after burn injury. There were no differences in age, TBSA, fluid administration, mean arterial pressure, UO, and Cr between AKI and no-AKI patients. NGAL was significantly increased as early as 4 h after injury (182.67 ± 83.3 versus 107.37 ± 46.15) in the AKI group. Controlling for age, TBSA, and inhalation injury, NGAL was a predictor of AKI at 4 h after injury (odds ratio, 1.02) and remained predictive of AKI for the period of more than the first 24 h after admission. UO and Cr were not predictive of AKI in the first 24 h after admission. CONCLUSIONS: Whole blood NGAL is markedly increased in burn patients who develop AKI in the first week after injury. In addition, NGAL is an early independent predictor of AKI during acute resuscitation for severe burn injury. UO and Cr are not predictive of AKI during this time period.

Tandem zyxin LIM sequences do not enhance force sensitive accumulation.

The ability to sense mechanical forces is vital to cell physiology. Yet, the molecular basis of mechano-signaling remains unclear. Previous studies have shown that zyxin, a focal adhesion protein, is recruited at force-bearing sites on the actin cytoskeleton and, therefore, identifying zyxin as a mechano-sensing protein candidate. Furthermore, zyxin accumulation at force-bearing sites requires the LIM domain located at the C-terminus of zyxin. The zyxin LIM domain consists of three LIM motifs, each containing two zinc-binding sites. Since individual LIM motifs do not accumulate at focal adhesions or force-bearing sites, we hypothesize that multiple zyxin LIM domains increase force sensitivity. Using a miniature force sensor and GFP-tagged LIM variants, we quantified the relationship between single, tandem dimer and trimer LIM protein localization and traction forces. While the presence of extra LIM domains affected VASP recruitment to focal adhesions, force sensitivity was not enhanced over the single LIM domain. Therefore, zyxin force sensitivity is optimal with a single LIM domain, while additional LIM domains fail to enhance force sensitivity.

Natural cardiac regeneration conserves native biaxial left ventricular biomechanics after myocardial infarction in neonatal rats.

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.

The LIM domain of zyxin is sufficient for force-induced accumulation of zyxin during cell migration.

Cellular responses to mechanical perturbation are vital to cell physiology. In particular, migrating cells have been shown to sense substrate stiffness and alter cell morphology and speed. Zyxin is a focal adhesion protein that responds to external mechanical forces; however, the mechanisms of zyxin recruitment at force-bearing sites are unknown. Using force-sensing microfabricated substrates, we simultaneously measured traction force and zyxin recruitment at force-bearing sites. GFP-tagged zyxin accumulates at force-bearing sites at the leading edge, but not at the trailing edge, of migrating epithelial cells. Zyxin recruitment at force-bearing sites depends on Rho-kinase and myosin II activation, suggesting that zyxin responds not only to the externally applied force, as previously shown, but also to the internally generated actin-myosin force. Zyxin in turn recruits vasodilator-stimulated phosphoprotein, a regulator of actin assembly, to force-bearing sites. To dissect the domains of zyxin that are essential for this unique force-dependent accumulation, we generated two zyxin truncation mutants: one lacking the LIM domain (ΔLIM) and one containing only the LIM domain with all three LIM motifs (LIM). GFP-tagged ΔLIM does not localize to the force-bearing sites, but GFP-tagged zyxin LIM-domain is sufficient for the recruitment to and dynamics at force-bearing focal adhesions. Furthermore, one or two LIM motifs are not sufficient for force-dependent accumulation, suggesting that all three LIM motifs are required. Therefore, the LIM domain of zyxin recruits zyxin to force-bearing sites at the leading edge of migrating cells.

A Bioengineered Neuregulin-Hydrogel Therapy Reduces Scar Size and Enhances Post-Infarct Ventricular Contractility in an Ovine Large Animal Model.

The clinical efficacy of neuregulin (NRG) in the treatment of heart failure is hindered by off-target exposure due to systemic delivery. We previously encapsulated neuregulin in a hydrogel (HG) for targeted and sustained myocardial delivery, demonstrating significant induction of cardiomyocyte proliferation and preservation of post-infarct cardiac function in a murine myocardial infarction (MI) model. Here, we performed a focused evaluation of our hydrogel-encapsulated neuregulin (NRG-HG) therapy's potential to enhance cardiac function in an ovine large animal MI model. Adult male Dorset sheep (n = 21) underwent surgical induction of MI by coronary artery ligation. The sheep were randomized to receive an intramyocardial injection of saline, HG only, NRG only, or NRG-HG circumferentially around the infarct borderzone. Eight weeks after MI, closed-chest intracardiac pressure-volume hemodynamics were assessed, followed by heart explant for infarct size analysis. Compared to each of the control groups, NRG-HG significantly augmented left ventricular ejection fraction (p = 0.006) and contractility based on the slope of the end-systolic pressure-volume relationship (p = 0.006). NRG-HG also significantly reduced infarct scar size (p = 0.002). Overall, using a bioengineered hydrogel delivery system, a one-time dose of NRG delivered intramyocardially to the infarct borderzone at the time of MI in adult sheep significantly reduces scar size and enhances ventricular contractility at 8 weeks after MI.

Natural Heart Regeneration in a Neonatal Rat Myocardial Infarction Model.

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 < 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's trichome and picrosirius red staining revealed minimal collagen scar after MI. Increased numbers of cardiomyocytes positive for 5-ethynyl-2'-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.

Multiaxial Lenticular Stress-Strain Relationship of Native Myocardium is Preserved by Infarct-Induced Natural Heart Regeneration in Neonatal Mice.

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 < 0.0001). Afterward, the LV was explanted and pressurized 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.

Safety of photosynthetic Synechococcus elongatus for in vivo cyanobacteria-mammalian symbiotic therapeutics.

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.

A Biocompatible Therapeutic Catheter-Deliverable Hydrogel for In Situ Tissue Engineering.

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.

Modeling conduit choice for valve-sparing aortic root replacement on biomechanics with a 3-dimensional-printed heart simulator.

OBJECTIVE: The optimal conduit for valve-sparing aortic root replacement is still debated, with several conduit variations available, ranging from straight tubular grafts to Valsalva grafts. Benefits of neosinus reconstruction include enhanced flow profiles and improved hemodynamics. Curiously, however, some clinical data suggest that straight grafts may have greater long-term durability. In this study, we hypothesized that straight tubular grafts may help maintain the native cylindrical position of the aortic valve commissures radially, resulting in preserved leaflet coaptation, reduced stresses, and potentially improved valve performance. METHODS: Using 3D printing, a left heart simulator with a valve-sparing root replacement model and a physiologic coronary circulation was constructed. Aortic valves were dissected from fresh porcine hearts and reimplanted into either straight tubular grafts (n = 6) or Valsalva grafts (n = 6). Conduits were mounted into the heart simulator and hemodynamic, echocardiographic, and high-speed videometric data were collected. RESULTS: Hemodynamic parameters and coronary blood flow were similar between straight and Valsalva grafts, although the former were associated with lower regurgitant fractions, less peak intercommissural radial separation, preserved leaflet coaptation, decreased leaflet velocities, and lower relative leaflet forces compared with Valsalva grafts. CONCLUSIONS: Valsalva grafts and straight grafts perform equally well in terms of gross hemodyanics and coronary blood flow. Interestingly, however, the biomechanics of these 2 conduits differ considerably, with straight grafts providing increased radial commissural stability and leaflet coaptation. Further investigation into how these parameters influence clinical outcomes is warranted.

Bioengineered analog of stromal cell-derived factor 1α preserves the biaxial mechanical properties of native myocardium after infarction.

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 pro-angiogenic 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 ±â€¯0.05 mm vs 1.42 ±â€¯0.08 mm, p = 0.008), smaller end-diastolic LV internal dimension (6.88 ±â€¯0.29 mm vs 7.69 ±â€¯0.22 mm, p = 0.044), and improved ejection fraction (62.8 ±â€¯3.0% vs 49.4 ±â€¯4.5%, p = 0.014). Histologic analysis revealed significantly reduced infarct size for ESA-treated hearts compared to saline controls (29.4 ±â€¯2.9% vs 41.6 ±â€¯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 ±â€¯6.9 kPa vs 264.3 ±â€¯12.5 kPa, p = 0.001) and longitudinal axes (194.5 ±â€¯6.5 kPa vs 258.1 ±â€¯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.

Use of a supramolecular polymeric hydrogel as an effective post-operative pericardial adhesion barrier.

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.

Angiogenesis precedes cardiomyocyte migration in regenerating mammalian hearts.

OBJECTIVE: Although the mammalian heart's ability to fully regenerate is debated, its potential to extensively repair itself is gaining support. We hypothesized that heart regeneration relies on rapid angiogenesis to support myocardial regrowth and sought to characterize the timeline for angiogenesis and cell proliferation in regeneration. METHODS: One-day-old CD-1 mice (P1, N = 60) underwent apical resection or sham surgery. Hearts were explanted at serial time points from 0 to 30 days postresection and analyzed with immunohistochemistry to visualize vessel ingrowth and cardiomyocyte migration into the resected region. Proliferating cells were labeled with 5-ethynyl-2'-deoxyuridine injections 12 hours before explant. 5-Ethynyl-2'-deoxyuridine-positive cells were counted in both the apex and remote areas of the heart. Masson's trichrome was used to assess fibrosis. RESULTS: By 30 days postresection, hearts regenerated with minimal fibrosis. Compared with sham surgery, apical resection stimulated a significant increase in proliferation of preexisting cardiomyocytes between 3 and 11 days after injury. Capillary migration into the apical thrombus was detected as early as 2 days postresection, with development of mature arteries by 5 days postresection. New vessels became perfused by 5 days postresection as evidenced by lectin injection. Vessel density and diameter significantly increased within the resected area over 21 days, and vessel ingrowth always preceded cardiomyocyte migration, with coalignment of most migrating cardiomyocytes with ingrowing vessels. CONCLUSIONS: Endothelial cells migrate into the apical thrombus early after resection, develop into functional arteries, and precede cardiomyocyte ingrowth during mammalian heart regeneration. This endogenous neonatal response emphasizes the importance of expeditious angiogenesis required for neomyogenesis.