In search of a pediatric cardiac surgeon’s ‘Holy Grail’: the ideal pulmonary conduit

Ectopic Calcification in Congenital Heart Surgery: A Material-Centric Review

The modern congenital heart surgeon has an array of materials available for cardiovascular repair. With advancements in the surgical outcomes for pediatric cardiac defects, choice of material has become increasingly dependent on late-term complications associated with each material. Calcification is a leading long-term complication and is increasing in prevalence with materials lasting longer in patients. Material calcification can impair functionality, lead to subsequent complications, and require additional interventions. A comprehensive literature review was conducted to investigate ectopic calcification of commonly used materials for congenital heart defect repair. Mechanisms of ectopic calcification among commonly used materials were investigated. Ectopic calcification is initiated by material-specific immunological reactions. Recent efforts have focused on developing new materials that are not prone to calcification. ePTFE was widely used in cardiovascular applications but still has reported instances of calcification in various situations, such as long-term use. Tissue engineering techniques have shown reduced calcification in reports. Calcification can occur in all conventional materials we reviewed and, in some cases, has led to life-threatening complications. Favorable outcomes have been reported with tissue-engineered materials, with the expectation of continued positive results in future reports. With an array of synthetic and biological materials now displaying acceptable surgical and short-term outcomes, there is a pressing need to review the long-term viability of these materials, especially considering improved patient survival to adulthood. Furthermore, developing new materials to mitigate calcification remains a promising avenue of research in this field.

Evaluation of a polyurethane-reinforced hydrogel patch in a rat right ventricle wall replacement model

Congenital heart defects affect about 1% births in the United States. Many of the defects are treated with surgically implanted patches made from inactive materials or fixed pericardium that do not grow with the patients, leading to an increased risk of arrhythmia, sudden cardiac death, and heart failure. This study investigated an angiogenic poly(ethylene glycol) fibrin-based hydrogel reinforced with an electrospun biodegradable poly(ether ester urethane) urea (BPUR) mesh layer that was designed to encourage cell invasion, angiogenesis, and regenerative remodeling in the repair of an artificial defect created onto the rat right ventricle wall. Electrocardiogram signals were analyzed, heart function was measured, and fibrosis, macrophage infiltration, muscularization, vascularization, and defect size were evaluated at 4- and 8-weeks post-surgery. Compared with rats with fixed pericardium patches, rats with BPUR-reinforced hydrogel patches had fewer arrhythmias and greater right ventricular ejection fraction and cardiac output, as well as greater left ventricular ejection fraction, fractional shorting, stroke work and cardiac output. Histology and immunofluorescence staining showed less fibrosis and less patch material remaining in rats with BPUR-reinforced hydrogel patches at 4- and 8-weeks. Rats with BPUR-reinforced hydrogel patches also had a greater volume of granular tissue, a greater volume of muscularized tissue, more blood vessels, and a greater number of leukocytes, pan-macrophages, and M2 macrophages at 8 weeks. Overall, this study demonstrated that the engineered BPUR-reinforced hydrogel patch initiated greater regenerative vascular and muscular remodeling with a limited fibrotic response, resulting in fewer incidences of arrhythmia and improved heart function compared with fixed pericardium patches when applied to heal the defects created on the rat right ventricle wall. STATEMENT OF SIGNIFICANCE: The study tested a polyurethane-reinforced hydrogel patch in a rat right ventricle wall replacement model. Compared with fixed pericardium patches, these reinforced hydrogel patches initiated greater regenerative vascular and muscular remodeling with a reduced fibrotic response, resulting in fewer incidences of arrhythmia and improved heart function at 4- and 8-weeks post surgery. Overall, the new BPUR-reinforced hydrogel patches resulted in better heart function when replacing contractile myocardium than fixed pericardium patches.

The development of tissue-engineered grafts for reconstructive cardiothoracic surgical applications

Surgical correction of congenital heart defects often requires the use of valves, patches, or conduits to establish anatomic continuity. Homografts, xenografts, or mechanical prosthetic devices are frequently implanted during these surgical procedures. These grafts however lack growth potential, are associated with increased risk of thrombosis and infection and have limited durability, thus increasing the morbidity and mortality of their application in pediatric cardiac surgery. These limitations are being addressed through the development of living, biologic tissue-engineered valves, patches, and conduits. Pilot studies and phase 1 clinical trials are currently underway to evaluate their feasibility, safety, and efficacy. The optimal scaffold, cell source, and conditioning parameters, however, still remain to be determined and are areas of active research.

Tissue engineering: a new frontier in physiological genomics

Considerable progress has been made in the last decade in the engineering and construction of a number of artificial tissue types. These constructs are typically viewed from the perspective of possible sources for implant and transplant materials in the clinical arena. However, incorporation of engineered tissues, often referred to as three-dimensional (3D) cell culture, also offers the possibility for significant advancements in research for physiological genomics. These 3D systems more readily mimic the in vivo setting than traditional 2D cell culture, and offer distinct advantages over the in vivo setting for some organ systems. As an example, cardiac cells in 3D culture 1) are more accessible for siRNA studies, 2) can be engineered with specific cell types, and 3) offer the potential for high-throughput screening of gene function. Here the state-of-the-art is reviewed and the applications for engineered tissue in genomics research are proposed. The ability to use engineered tissue in combination with genomics creates a bridge between traditional cellular and in vivo studies that is critical to enabling the transition of genetic information into mechanistic understanding of disease processes.