Valve replacement in children: a challenge for a whole life

Mitral Valve Replacement in Pediatrics Using an Extracellular Matrix Cylinder Valve: A Case Series

Mitral valve replacement (MVR) in children under 2 years is associated with significant morbidity and mortality. Decellularized porcine intestinal submucosa is a commercially available formulation of an extracellular matrix (ECM) with an indication for cardiac tissue repair. The present study reports our experience using ECM cylinder valves in patients for MVR. A retrospective review of patients under 2 years who underwent ECM custom-made cylinder mitral valve (ECM-MV) replacement was performed. Clinical, demographic, operative and post-operative follow-up data, including serial echocardiographic data are presented. Eight patients (age 5.6 ± 1.6 months; weight: 6.0 ± 1.1 kg) were identified who underwent ECM-MVR. There was one in-hospital death and no major neurological events. Six patients underwent replacement of their cylinder valve with either a Melody valve inside the ECM-MVR (n = 3), a mechanical valve (n = 2), or a decellularized bovine pericardial cylinder valve (n = 1). The mean time to replacement surgery was 8.4 ± 2.6 months after ECM-MV. The indications for replacement of ECM-MV included mitral stenosis/regurgitation (n = 4) or dehiscence (n = 2). One remaining patient is 24 months from ECM-MV, with trivial regurgitation and no stenosis. Mitral valve creation using ECM is an option for MVR in pediatrics, avoiding anticoagulation, and provides a suitable construct for later placement of a Melody valve, extending surgical and non-surgical options. However, the durability of the native ECM-MV in the mitral position is concerning considering the high re-intervention rate in a relatively short time period. Further studies are needed to determine the longer-term outcomes of this valve in this complex patient population.

Next-generation tissue-engineered heart valves with repair, remodelling and regeneration capacity

Valvular heart disease is a major cause of morbidity and mortality worldwide. Surgical valve repair or replacement has been the standard of care for patients with valvular heart disease for many decades, but transcatheter heart valve therapy has revolutionized the field in the past 15 years. However, despite the tremendous technical evolution of transcatheter heart valves, to date, the clinically available heart valve prostheses for surgical and transcatheter replacement have considerable limitations. The design of next-generation tissue-engineered heart valves (TEHVs) with repair, remodelling and regenerative capacity can address these limitations, and TEHVs could become a promising therapeutic alternative for patients with valvular disease. In this Review, we present a comprehensive overview of current clinically adopted heart valve replacement options, with a focus on transcatheter prostheses. We discuss the various concepts of heart valve tissue engineering underlying the design of next-generation TEHVs, focusing on off-the-shelf technologies. We also summarize the latest preclinical and clinical evidence for the use of these TEHVs and describe the current scientific, regulatory and clinical challenges associated with the safe and broad clinical translation of this technology.

Tricuspid Valve Endocarditis Following a Scorpion Sting: A Case Report

Scorpion sting envenoming is a common pediatric emergency in the Moroccan southern areas. Cardiomyopathy is the most common cardiovascular manifestation of envenoming, resulting from the stimulation of the sympathetic nervous system by the venom or from the direct effect of the venom toxins on the myocardium. Rare cases of infective endocarditis following a scorpion sting have been reported in the literature. We report a case of tricuspid valve infective endocarditis following a scorpion sting in a previously healthy eight-year-old child. The patient initially was managed medically before undergoing tricuspid valve replacement with a bioprosthesis. The postoperative course was uneventful with a full recovery.

Requirement for repetitive surgical approaches at supravalvular aortic stenosis

Supravalvular aortic stenosis, which is a rare congenital cardiac anomaly, is associated with several lesions and has a progressive nature. Herein, we report a five-year-old girl with bicuspid aorta who underwent initial Doty operation at the age of nine months. A combined redo Doty operation and an aortic valve commissurotomy were performed two years later. Due to the rapidly progressing aortic regurgitation and both valvular and supravalvular gradient, a repeated surgery was required at the age of five years and an aortic homograft was successfully inserted with an annulus enlargement and the patient was discharged uneventfully. In conclusion, although Doty repair yields satisfactory results in most patients, certain cases with identified risk factors may require reoperations due to the progressive nature of the disease. Therefore, these patients should be kept under a close follow-up lifelong.

A multilayered valve leaflet promotes cell-laden collagen type I production and aortic valve hemodynamics

Patients with aortic heart valve disease are limited to valve replacements that lack the ability to grow and remodel. This presents a major challenge for pediatric patients who require a valve capable of somatic growth and at a smaller size. A patient-specific heart valve capable of growth and remodeling while maintaining proper valve function would address this major issue. Here, we recreate the native valve leaflet structure composed of poly-ε-caprolactone (PCL) and cell-laden gelatin-methacrylate/poly (ethylene glycol) diacrylate (GelMA/PEGDA) hydrogels using 3D printing and molding, and then evaluate the ability of the multilayered scaffold to produce collagen matrix under physiological shear stress conditions. We also characterized the valve hemodynamics under aortic physiological flow conditions. The valve's fibrosa layer was replicated by 3D printing PCL in a circumferential direction similar to collagen alignment in the native leaflet, and GelMA/PEGDA sustained and promoted cell viability in the spongiosa/ventricularis layers. We found that collagen type I production can be increased in the multilayered scaffold when it is exposed to pulsatile shear stress conditions over static conditions. When the PCL component was mounted onto a valve ring and tested under physiological aortic valve conditions, the hemodynamics were comparable to commercially available valves. Our results demonstrate that a structurally representative valve leaflet can be generated using 3D printing and that the PCL layer of the leaflet can sustain proper valve function under physiological aortic valve conditions.

Urinary Bladder Matrix Scaffolds Promote Pericardium Repair in a Porcine Model

Pericardium closure after cardiac surgery is recommended to prevent postoperative adhesions to the sternum. Synthetic materials have been used as substitutes, with limited results because of impaired remodeling and fibrotic tissue formation. Urinary bladder matrix (UBM) scaffolds promote constructive remodeling that more closely resemble the native tissue. The aim of the study is to evaluate the host response to UBM scaffolds in a porcine model of partial pericardial resection. Twelve Landrace pigs were subjected to a median sternotomy. A 5 × 7 cm pericardial defect was created and then closed with a 5 × 7 cm multilayer UBM patch (UBM group) or left as an open defect (control group). Animals were survived for 8 wk. End points included gross morphology, biomechanical testing, histology with semiquantitative score, and cardiac function. The UBM group showed mild adhesions, whereas the control group showed fibrosis at the repair site, with robust adhesions and injury to the coronary bed. Load at failure (gr) and stiffness (gr/mm) were lower in the UBM group compared with the native pericardium (199.9 ± 59.2 versus 405.3 ± 99.89 g, P = 0.0536 and 44.23 ± 15.01 versus 146.5 ± 24.38 g/mm, P = 0.0025, respectively). In the UBM group, the histology resembled native pericardial tissue, with neovascularization, neofibroblasts, and little inflammatory signs. In contrast, control group showed fibrotic tissue with mononuclear infiltrates and a lack of organized collagen fibers validated with a histologic score. Both groups had normal ultrasonography results without cardiac motility disorders. In this setting, UBM scaffolds showed appropriate features for pericardial repair, restoring tissue properties that could help reduce postsurgical adhesions and prevent its associated complications.

Porcine Small Intestinal Submucosa Mitral Valve Material Responses Support Acute Somatic Growth

Background: Conceptually, a tissue engineered heart valve would be especially appealing in the pediatric setting since small size and somatic growth constraints would be alleviated. In this study, we utilized porcine small intestinal submucosa (PSIS) for valve replacement. Of note, we evaluated the material responses of PSIS and subsequently its acute function and somatic growth potential in the mitral position. Methods and Results: Material and mechanical assessment demonstrated that both fatigued 2ply (∼65 μm) and 4ply (∼110 μm) PSIS specimens exhibited similar failure mechanisms, but at an accelerated rate in the former. Specifically, the fatigued 2ply PSIS samples underwent noticeable fiber pullout and recruitment on the bioscaffold surface, leading to higher yield strength (p < 0.05) and yield strain (p < 0.05) compared to its fatigued 4ply counterparts. Consequently, 2ply PSIS mitral valve constructs were subsequently implanted in juvenile baboons (n = 3). Valve function was longitudinally monitored for 90 days postvalve implantation and was found to be robust in all animals. Histology at 90 days in one of the animals revealed the presence of residual porcine cells, fibrin matrix, and host baboon immune cells but an absence of tissue regeneration. Conclusions: Our findings suggest that the altered structural responses of PSIS, postfatigue, rather than de novo tissue formation, are primarily responsible for the valve's ability to accommodate somatic growth during the acute phase (90 days) following mitral valve replacement. Impact Statement Tissue engineered heart valves (TEHVs) offer the potential of supporting somatic growth. In this study, we investigated a porcine small intestinal submucosa bioscaffold for pediatric mitral heart valve replacement. The novelty of the study lies in identifying material responses under mechanical loading conditions and its effectiveness in being able to function as a TEHV. In addition, the ability of the scaffold valve to support acute somatic growth was evaluated in the Baboon model. The current study contributes toward finding a solution for critical valve diseases in children, whose current prognosis for survival is poor.

Computational modeling guides tissue-engineered heart valve design for long-term in vivo performance in a translational sheep model

Valvular heart disease is a major cause of morbidity and mortality worldwide. Current heart valve prostheses have considerable clinical limitations due to their artificial, nonliving nature without regenerative capacity. To overcome these limitations, heart valve tissue engineering (TE) aiming to develop living, native-like heart valves with self-repair, remodeling, and regeneration capacity has been suggested as next-generation technology. A major roadblock to clinically relevant, safe, and robust TE solutions has been the high complexity and variability inherent to bioengineering approaches that rely on cell-driven tissue remodeling. For heart valve TE, this has limited long-term performance in vivo because of uncontrolled tissue remodeling phenomena, such as valve leaflet shortening, which often translates into valve failure regardless of the bioengineering methodology used to develop the implant. We tested the hypothesis that integration of a computationally inspired heart valve design into our TE methodologies could guide tissue remodeling toward long-term functionality in tissue-engineered heart valves (TEHVs). In a clinically and regulatory relevant sheep model, TEHVs implanted as pulmonary valve replacements using minimally invasive techniques were monitored for 1 year via multimodal in vivo imaging and comprehensive tissue remodeling assessments. TEHVs exhibited good preserved long-term in vivo performance and remodeling comparable to native heart valves, as predicted by and consistent with computational modeling. TEHV failure could be predicted for nonphysiological pressure loading. Beyond previous studies, this work suggests the relevance of an integrated in silico, in vitro, and in vivo bioengineering approach as a basis for the safe and efficient clinical translation of TEHVs.

Effect of cyclic deformation on xenogeneic heart valve biomaterials

Glutaraldehyde-fixed bovine pericardium is currently the most popular biomaterial utilized in the creation of bioprosthetic heart valves. However, recent studies indicate that glutaraldehyde fixation results in calcification and structural valve deterioration, limiting the longevity of bioprosthetic heart valves. Additionally, glutaraldehyde fixation renders the tissue incompatible with constructive recipient cellular repopulation, remodeling and growth. Use of unfixed xenogeneic biomaterials devoid of antigenic burden has potential to overcome the limitations of current glutaraldehyde-fixed biomaterials. Heart valves undergo billion cycles of opening and closing throughout the patient’s lifetime. Therefore, understanding the response of unfixed tissues to cyclic loading is crucial to these in a heart valve leaflet configuration. In this manuscript we quantify the effect of cyclic deformation on cycle dependent strain, structural, compositional and mechanical properties of fixed and unfixed tissues. Glutaraldehyde-fixed bovine pericardium underwent marked cyclic dependent strain, resulting from significant changes in structure, composition and mechanical function of the material. Conversely, unfixed bovine pericardium underwent minimal strain and maintained its structure, composition and mechanical integrity. This manuscript demonstrates that unfixed bovine pericardium can withstand cyclic deformations equivalent to 6 months of in vivo heart valve leaflet performance.

Influence of Transvalvar Pressure Gradient on Hinge Washing in Closed Mechanical Prosthetic Cardiac Valves Under Pulmonary Pressure Conditions: A Comparative In Vitro Study

OBJECTIVE

Hinge washing is a crucial factor in the prevention of mechanical prosthetic valvar thrombosis, especially in the pulmonary valve position. The aim of this laboratory study was to determine the relationship between pressure difference and the amount of hinge washing in the closed position, using the pressures that are normal for the right ventricle and pulmonary artery.

METHODS

In an in vitro setting, four different bileaflet mechanical valves were tested for hinge washing in closed position. Based on similarity in inner diameter (range: 20.5-21.4 mm), the following valves were tested: Abbott SJM Regent size 23, Cryolife On-X size 23, LivaNova Carbomedics-R size 25, Medtronic Open Pivot (M-OP)-A size 25. Tests were carried out in a range between 3 and 100 mm Hg pressure difference, using water as a test fluid. The amount of leakage per minute through the closed valve was measured.

RESULTS

All four valves showed an increase in leakage with increasing transvalvar gradient, and the relationship between pressure and leakage behaves in logarithmic fashion. Leakage under normal pulmonary diastolic pressure conditions (10 mm Hg) was between 23.3% and 29.3% of the leakage under aortic diastolic pressure conditions (80 mm Hg). The Cryolife On-X valve showed the highest closed leakage volume under pulmonary conditions (10 mm Hg) 0.254 ± 0.01 (L/min), where the Medtronic M-OP showed the lowest leakage volume with 0.125 ± 0.014 (mL/min).

CONCLUSION

Hinge washing is related to transvalvar pressure difference in closed position. Valve brands differed significantly from each other in the amount of hinge washing.

Preservation strategies for decellularized pericardial scaffolds for off-the-shelf availability

Decellularized biological scaffolds hold great promise in cardiovascular surgery. In order to ensure off-the-shelf availability, routine use of decellularized scaffolds requires tissue banking. In this study, the suitability of cryopreservation, vitrification and freeze-drying for the preservation of decellularized bovine pericardial (DBP) scaffolds was evaluated. Cryopreservation was conducted using 10% DMSO and slow-rate freezing. Vitrification was performed using vitrification solution (VS83) and rapid cooling. Freeze-drying was done using a programmable freeze-dryer and sucrose as lyoprotectant. The impact of the preservation methods on the DBP extracellular matrix structure, integrity and composition was assessed using histology, biomechanical testing, spectroscopic and thermal analysis, and biochemistry. In addition, the cytocompatibility of the preserved scaffolds was also assessed. All preservation methods were found to be suitable to preserve the extracellular matrix structure and its components, with no apparent signs of collagen deterioration or denaturation, or loss of elastin and glycosaminoglycans. Biomechanical testing, however, showed that the cryopreserved DBP displayed a loss of extensibility compared to vitrified or freeze-dried scaffolds, which both displayed similar biomechanical behavior compared to non-preserved control scaffolds. In conclusion, cryopreservation altered the biomechanical behavior of the DBP scaffolds, which might lead to graft dysfunction in vivo. In contrast to cryopreservation and vitrification, freeze-drying is performed with non-toxic protective agents and does not require storage at ultra-low temperatures, thus allowing for a cost-effective and easy storage and transport. Due to these advantages, freeze-drying is a preferable method for the preservation of decellularized pericardium. STATEMENT OF SIGNIFICANCE: Clinical use of DBP scaffolds for surgical reconstructions or substitutions requires development of a preservation technology that does not alter scaffold properties during long-term storage. Conclusive investigation on adverse impacts of the preservation methods on DBP matrix integrity is still missing. This work is aiming to close this gap by studying three potential preservation technologies, cryopreservation, vitrification and freeze-drying, in order to achieve the off-the-shelf availability of DBP patches for clinical application. Furthermore, it provides novel insights for dry-preservation of decellularized xenogeneic scaffolds that can be used in the routine clinical cardiovascular practice, allowing the surgeon the opportunity to choose an ideal implant matching with the needs of each patient.

Heart diseases and echocardiography in rural Tanzania: Occurrence, characteristics, and etiologies of underappreciated cardiac pathologies

BACKGROUND

Little is known about heart diseases and their treatment in rural sub-Saharan Africa. This study aimed to describe the occurrence, characteristics, and etiologies of heart diseases, and the medication taken before and prescribed after echocardiography in a rural referral Hospital in Tanzania.

METHODS

This prospective descriptive cohort study included all adults and children referred for echocardiography. Clinical and echocardiographic data were collated for analysis.

RESULTS

From December 2015 to October 2017, a total of 1'243 echocardiograms were performed. A total of 815 adults and 59 children ≤15 years had abnormal echocardiographic findings; in adults 537/815 (66%) had hypertension, with 230/537(43%) on antihypertensive drugs, and 506/815 (62%) were not on regular cardiac medication; 346/815 (42%) had severe eccentric or concentric left ventricular hypertrophy, and 182/815 (22%) had severe systolic heart failure. Only 44% demonstrated normal left ventricular systolic function. The most frequent heart diseases were hypertensive heart disease (41%), valvular heart disease (18%), coronary heart disease (18%), peripartum cardiomyopathy (7%), and other non-hypertensive dilated cardiomyopathies (6%) in adults, and congenital heart disease (34%) in children. Following echocardiography, 802/815 (98%) adults and 40/59 (68%) children had an indication for cardiac medication, 70/815 (9%) and 2/59 (3%) for oral anticoagulation, and 35/815 (4%) and 23/59 (39%) for cardiac surgery, respectively.

CONCLUSION

Hypertension is the leading etiology of heart diseases in rural Tanzania. Most patients present with advanced stages of heart disease, and the majority are not treated before echocardiography. There is an urgent need for increased awareness, expertise and infrastructure to detect and treat hypertension and heart failure in rural Africa.

Transcatheter Decellularized Tissue-Engineered Heart Valve (dTEHV) Grown on Polyglycolic Acid (PGA) Scaffold Coated with P4HB Shows Improved Functionality over 52 Weeks due to Polyether-Ether-Ketone (PEEK) Insert

Many congenital heart defects and degenerative valve diseases require replacement of heart valves in children and young adults. Transcatheter xenografts degenerate over time. Tissue engineering might help to overcome this limitation by providing valves with ability for self-repair. A transcatheter decellularized tissue-engineered heart valve (dTEHV) was developed using a polyglycolic acid (PGA) scaffold. A first prototype showed progressive regurgitation after 6 months in-vivo due to a suboptimal design and misguided remodeling process. A new geometry was developed accordingly with computational fluid dynamics (CFD) simulations and implemented by adding a polyether-ether-ketone (PEEK) insert to the bioreactor during cultivation. This lead to more belly-shaped leaflets with higher coaptation areas for this second generation dTEHV. Valve functionality assessed via angiography, intracardiac echocardiography, and MRI proved to be much better when compared the first generation dTEHV, with preserved functionality up to 52 weeks after implantation. Macroscopic findings showed no thrombi or signs of acute inflammation. For the second generation dTEHV, belly-shaped leaflets with soft and agile tissue-formation were seen after explantation. No excessive leaflet shortening occurred in the second generation dTEHV. Histological analysis showed complete engraftment of the dTEHV, with endothelialization of the leaflets and the graft wall. Leaflets consisted of collagenous tissue and some elastic fibers. Adaptive leaflet remodeling was visible in all implanted second generation dTEHV, and most importantly no fusion between leaflet and wall was found. Very few remnants of the PGA scaffold were detected even 52 weeks after implantation, with no influence on functionality. By adding a polyether-ether-ketone (PEEK) insert to the bioreactor construct, a new geometry of PGA-scaffold based dTEHV could be implemented. This resulted in very good valve function of the implanted dTEHV over a period of 52 weeks.

Human iPSC-derived mesenchymal stem cells encapsulated in PEGDA hydrogels mature into valve interstitial-like cells

Despite recent advances in tissue engineered heart valves (TEHV), a major challenge is identifying a cell source for seeding TEHV scaffolds. Native heart valves are durable because valve interstitial cells (VICs) maintain tissue homeostasis by synthesizing and remodeling the extracellular matrix. This study demonstrates that induced pluripotent stem cells (iPSC)-derived mesenchymal stem cells (iMSCs) can be derived from iPSCs using a feeder-free protocol and then further matured into VICs by encapsulation within 3D hydrogels. The differentiation efficiency was characterized using flow cytometry, immunohistochemistry staining, and trilineage differentiation. Using our feeder-free differentiation protocol, iMSCs were differentiated from iPSCs and had CD90+, CD44+, CD71+, αSMA+, and CD45- expression. Furthermore, iMSCs underwent trilineage differentiation when cultured in induction media for 21 days. iMSCs were then encapsulated in poly(ethylene glycol)diacrylate (PEGDA) hydrogels grafted with adhesion peptide (RGDS) to promote remodeling and further maturation into VIC-like cells. VIC phenotype was assessed by the expression of alpha-smooth muscle actin (αSMA), vimentin, and collagen production after 28 days. When MSC-derived cells were encapsulated in PEGDA hydrogels that mimic the leaflet modulus, a decrease in αSMA expression and increase in vimentin was observed. In addition, iMSCs synthesized collagen type I after 28 days in 3D hydrogel culture. Thus, the results from this study suggest that iMSCs may be a promising cell source for TEHV.

STATEMENT OF SIGNIFICANCE

Developing a suitable cell source is a critical component for the success and durability of tissue engineered heart valves. The significance of this study is the generation of iPSCs-derived mesenchymal stem cells (iMSCs) that have the capacity to mature into valve interstitial-like cells when introduced into a 3D cell culture designed to mimic the layers of the valve leaflet. iMSCs were generated using a feeder-free protocol, which is one major advantage over other methods, as it is more clinically relevant. In addition to generating a potential new cell source for heart valve tissue engineering, this study also highlights the importance of a 3D culture environment to influence cell phenotype and function.

The Effects of Scaffold Remnants in Decellularized Tissue-Engineered Cardiovascular Constructs on the Recruitment of Blood Cells<sup/>

Decellularized tissue-engineered heart valves (DTEHVs) showed remarkable results in translational animal models, leading to recellularization within hours after implantation. This is crucial to enable tissue remodeling. To investigate if the presence of scaffold remnants before implantation is responsible for the fast recellularization of DTEHVs, an in vitro mesofluidic system was used. Human granulocyte and agranulocyte fractions were isolated, stained, brought back in suspension, and implemented in the system. Three different types of biomaterials were exposed to the circulating blood cells, consisting of decellularized tissue-engineered constructs (DTECs) with or without scaffold remnants or only bare scaffold. After 5 h of testing, the granulocyte fraction depleted faster from the circulation than the agranulocyte fraction. However, only granulocytes infiltrated into the DTEC with scaffold, migrating toward the scaffold remnants. The agranulocyte population, on the other hand, was only observed on the outer surface. Active cell infiltration was associated with increased levels of matrix metalloproteinase-1 secretion in the DTEC, including scaffold remnants. Proinflammatory cytokines such as interleukin (IL)-1α, IL-6, and tumor necrosis factor alpha (TNFα) were significantly upregulated in the DTEC without scaffold remnants. These results indicate that scaffold remnants can influence the immune response in DTEC, being responsible for rapid cell infiltration.

Pulmonary Valve Replacement With Small Intestine Submucosa-Extracellular Matrix in a Porcine Model

BACKGROUND

Prosthetic materials available for pediatric pulmonary valve replacement (PVR) lack growth potential, inevitably leading to a size mismatch. Small intestine submucosa-derived extracellular matrix (SIS-ECM) has been suggested to possess regenerative properties. We aimed to investigate its function and potential to increase in size as a PVR in a piglet.

METHODS

An SIS-ECM trileaflet valved conduit was designed. Hanford minipigs, n = 6 (10-34 kg), underwent PVR with an intended survival of six months, with monthly echocardiograms evaluating valve size and function. The conduit was excised for histologic analysis.

RESULTS

Of the six, one was sacrificed at three months for midterm analysis, and one at month 3 due to endocarditis. The remaining four constituted the study cohort. The piglet weight increased by 186% (19.56 ± 10.22 kg to 56.00 ± 7.87 kg). Conduit size increased by 30% (1.42 ± 0.14 cm to 1.84 ± 0.14 cm; P < .01). The native right ventricular outflow tract increased by 43% and the native pulmonary artery by 84%, resulting in a peak gradient increase from 10.08 ± 2.47 mm Hg to 36.25 ± 18.80 mm Hg (P = .03). Additionally, all valves developed at least moderate regurgitation. Conduit histology showed advanced remodeling with myofibroblast infiltration, neovascularization, and endothelialization. The leaflets remodeled beginning at the base with the leaflet edge being less cellular. In addition to the known endocarditis, bacterial colonies were discovered within a leaflet in another.

CONCLUSIONS

The SIS-ECM valved conduit implanted into a piglet demonstrated cellular infiltration with vascular remodeling and an increase in diameter. Conduit stenosis was a result of slower rates of size increase than native tissue. Suboptimal leaflet performance requires design modifications.

Biological and mechanical evaluation of a Bio-Hybrid scaffold for autologous valve tissue engineering

Major challenge in heart valve tissue engineering for paediatric patients is the development of an autologous valve with regenerative capacity. Hybrid tissue engineering approach is recently gaining popularity to design scaffolds with desired biological and mechanical properties that can remodel post implantation. In this study, we fabricated aligned nanofibrous Bio-Hybrid scaffold made of decellularized bovine pericardium: polycaprolactone-chitosan with optimized polymer thickness to yield the desired biological and mechanical properties. CD44⁺, αSMA⁺, Vimentin⁺ and CD105^- human valve interstitial cells were isolated and seeded on these Bio-Hybrid scaffolds. Subsequent biological evaluation revealed interstitial cell proliferation with dense extra cellular matrix deposition that indicated the viability for growth and proliferation of seeded cells on the scaffolds. Uniaxial mechanical tests along axial direction showed that the Bio-Hybrid scaffolds has at least 20 times the strength of the native valves and its stiffness is nearly 3 times more than that of native valves. Biaxial and uniaxial mechanical studies on valve interstitial cells cultured Bio-Hybrid scaffolds revealed that the response along the axial and circumferential direction was different, similar to native valves. Overall, our findings suggest that Bio-Hybrid scaffold is a promising material for future development of regenerative heart valve constructs in children.

Iranian homograft heart valves: assessment of durability and late outcome

Durability and the rate of complications of homograft heart valves, adjusted for patient-related contributors and surgical techniques, rely mainly on the quality of allografts which in turn are mirrored in the donor characteristics and most importantly recovery and processing procedures. Aimed to assess the quality, a study was conducted to figure out the durability and late outcome following homograft replacement with valved conduits procured by the Iranian Tissue Bank. Retrospectively, the pre-implantation, perioperative and follow-up data of 400 non-consecutive recipients of cryopreserved heart valves (222 pulmonary and 178 aortic) from 2006 to 2015 were collected and analyzed in terms of variables reflecting late outcome including adverse events and durability. In the context of durability, the event of interest was defined as the need for homograft replacement and homograft-related death. The mean follow-up time (SD) of study entrants (male/female ratio, 1.4) was 49.8 (36.3) months. Median age at the time of implantation was 11 years. Total 10-years mortality was 21 % (84/400), including 66.7 % early (30-days mortality: 56/84) and 33.3 % late (28/84). Overall late complication rate was 2 %. Median survival time was 120 months (95 % CI 83.3-156.6). The pulmonary valves appeared to be more durable (P value <0.001) and survival probabilities in small sized grafts were lower (P value 0.008). One-, five-, and ten-year graft survival was 82, 76 and 73 %, respectively. The evidences suggest that the homografts function satisfactory with low rate of late complications; nevertheless, more emphasis should be given to make long-term durability comparable.

Stem cell therapies for congenital heart disease

Congenital heart disease (CHD) is the most prevalent congenital anomaly in newborn babies. Cardiac malformations have been induced in different animal model experiments, by perturbing some molecules that take part in the developmental pathways associated with myocyte differentiation, specification, or cardiac morphogenesis. The exact epigenetic, environmental, or genetic, basis for these molecules perturbations is yet to be understood. But, scientist have bridged this gap by introducing autologous stem cell into the defective hearts to treat CHD. The choice of stem cells to use has also raised an issue. In this review, we explore different stem cells that have been recently used, as an update into the pool of this knowledge and we suggested the future perspective into the choice of stem cells to control this disease. We propose that isolating mesenchymal stem cells from neonate will give a robust heart regeneration as compared to adults. This source are easily isolated. To unveil stem cell therapy beyond its possibility and safety, further study is required, including largescale randomized, and clinical trials to certify the efficacy of stem cell therapy.

Functional Heart Valve Scaffolds Obtained by Complete Decellularization of Porcine Aortic Roots in a Novel Differential Pressure Gradient Perfusion System

There is a great need for living valve replacements for patients of all ages. Such constructs could be built by tissue engineering, with perspective of the unique structure and biology of the aortic root. The aortic valve root is composed of several different tissues, and careful structural and functional consideration has to be given to each segment and component. Previous work has shown that immersion techniques are inadequate for whole-root decellularization, with the aortic wall segment being particularly resistant to decellularization. The aim of this study was to develop a differential pressure gradient perfusion system capable of being rigorous enough to decellularize the aortic root wall while gentle enough to preserve the integrity of the cusps. Fresh porcine aortic roots have been subjected to various regimens of perfusion decellularization using detergents and enzymes and results compared to immersion decellularized roots. Success criteria for evaluation of each root segment (cusp, muscle, sinus, wall) for decellularization completeness, tissue integrity, and valve functionality were defined using complementary methods of cell analysis (histology with nuclear and matrix stains and DNA analysis), biomechanics (biaxial and bending tests), and physiologic heart valve bioreactor testing (with advanced image analysis of open-close cycles and geometric orifice area measurement). Fully acellular porcine roots treated with the optimized method exhibited preserved macroscopic structures and microscopic matrix components, which translated into conserved anisotropic mechanical properties, including bending and excellent valve functionality when tested in aortic flow and pressure conditions. This study highlighted the importance of (1) adapting decellularization methods to specific target tissues, (2) combining several methods of cell analysis compared to relying solely on histology, (3) developing relevant valve-specific mechanical tests, and (4) in vitro testing of valve functionality.

Pediatric cardiovascular grafts: historical perspective and future directions

Tissue-engineered cardiovascular patches, cardiac valves, and great vessels are emerging solutions for the surgical treatment of congenital cardiovascular abnormalities due to their potential for adapting with the growing child. The ideal pediatric cardiovascular patch/graft is non-thrombogenic, phenotypically compatible, and matches the compliance and mechanical strength of the native tissue, both initially and throughout growth. Bottom-up tissue engineering approaches, in which three-dimensional tissue is built layer-by-layer from scaffold-less cell sheets in vitro, offer an exciting potential solution. Cell source variability, sheet patterning, and scaffold-less fabrication are promising advantages offered by this approach. Here we review the latest developments and next steps in bottom-up tissue engineering targeted at meeting the necessary design criteria for successful pediatric cardiac tissue-engineered grafts.

Small intestinal submucosa extracellular matrix (CorMatrix®) in cardiovascular surgery: a systematic review

Extracellular matrix (ECM) derived from small intestinal submucosa (SIS) is widely used in clinical applications as a scaffold for tissue repair. Recently, CorMatrix® porcine SIS-ECM (CorMatrix Cardiovascular, Inc., Roswell, GA, USA) has gained popularity for 'next-generation' cardiovascular tissue engineering due to its ease of use, remodelling properties, lack of immunogenicity, absorbability and potential to promote native tissue growth. Here, we provide an overview of the biology of porcine SIS-ECM and systematically review the preclinical and clinical literature on its use in cardiovascular surgery. CorMatrix® has been used in a variety of cardiovascular surgical applications, and since it is the most widely used SIS-ECM, this material is the focus of this review. Since CorMatrix® is a relatively new product for cardiovascular surgery, some clinical and preclinical studies published lack systematic reporting of functional and pathological findings in sufficient numbers of subjects. There are also emerging reports to suggest that, contrary to expectations, an undesirable inflammatory response may occur in CorMatrix® implants in humans and longer-term outcomes at particular sites, such as the heart valves, may be suboptimal. Large-scale clinical studies are needed driven by robust protocols that aim to quantify the pathological process of tissue repair.

Characterization of CD133 Antibody-Directed Recellularized Heart Valves

CD133mAb conjugation (CD133-C) hastens in vivo recellularization of decellularized porcine heart valve scaffolds when placed in the pulmonary position of sheep. We now characterize this early cellularization process 4 h, 3, 7, 14, 30, or 90 days post-implantation. Quantitative immunohistochemistry identified cell types as well as changes in cell markers and developmental cues. CD133(+)/CD31(-) cells adhered to the leaflet surface of CD133-C leaflets by 3 days and transitioned to native leaflet-like CD133(-)/CD31(+) cells by 30 days. Leaflet interstitium became increasingly populated with both alpha-smooth muscle actin (αSMA) and vimentin(+) cells from 14 to 90 days post-implantation. Wnt3a, and beta-catenin proteins were expressed at early (3-14 days) but not later (30-90 days) time points. In contrast, matrix metalloproteinase-2 and periostin proteins were increasingly expressed over 90 days. Thus, early development of CD133-C constructs includes a fairly rapid transition from a precursor cell adhesion/migration/transdifferentiation phenotype to a more mature cell/native valve-like matrix metabolism phenotype.

CD133 antibody conjugation to decellularized human heart valves intended for circulating cell capture

The long term efficacy of tissue based heart valve grafts may be limited by progressive degeneration characterized by immune mediated inflammation and calcification. To avoid this degeneration, decellularized heart valves with functionalized surfaces capable of rapid in vivo endothelialization have been developed. The aim of this study is to examine the capacity of CD133 antibody-conjugated valve tissue to capture circulating endothelial progenitor cells (EPCs). Decellularized human pulmonary valve tissue was conjugated with CD133 antibody at varying concentrations and exposed to CD133 expressing NTERA-2 cl.D1 (NT2) cells in a microflow chamber. The amount of CD133 antibody conjugated on the valve tissue surface and the number of NT2 cells captured in the presence of shear stress was measured. Both the amount of CD133 antibody conjugated to the valve leaflet surface and the number of adherent NT2 cells increased as the concentration of CD133 antibody present in the surface immobilization procedure increased. The data presented in this study support the hypothesis that the rate of CD133(+) cell adhesion in the presence of shear stress to decellularized heart valve tissue functionalized by CD133 antibody conjugation increases as the quantity of CD133 antibody conjugated to the tissue surface increases.

Systemic Semilunar Valve Replacement in Pediatric Patients Using a Porcine, Full-Root Bioprosthesis

BACKGROUND

Management of systemic semilunar valve disease in growing, young patients is challenging. When replacement is necessary, use of a pulmonary autograft is sometimes not possible for anatomic, pathologic, or technical reasons or due to parental or patient preference. We employed a stentless, porcine, full-root bioprosthesis in this setting and report our outcomes.

METHODS

Over 9 years (2005 to 2013), 24 patients of mean age 13.1 years (range, 3 months to 20.3 years) underwent operation for mixed stenosis and insufficiency in 16 of 24 (67%), pure insufficiency in 7 of 24 (29%), and pure stenosis in 1 of 24 (4%). Twenty patients had previous interventions of repair or replacement, valvuloplasty, or multiple operations. Survival, follow-up echocardiographic findings, and outcomes were documented. All patients were maintained on daily aspirin.

RESULTS

There were no hospital deaths and no early or late deaths over a mean follow-up for 23 patients of 46.1 months (range, 14 months to 9.2 years). One patient moved abroad and was lost to follow-up. Echocardiographic follow-up (mean 34.0 months) demonstrated that no patient developed more than mild insufficiency or moderate stenosis. In total, 20 of 24 (83%) showed no insufficiency and 11 of 24 patients (46%) showed no stenosis. Near or complete normalization of left ventricular mass and dimension was demonstrated. There were no explants and no thromboembolic or bleeding events.

CONCLUSIONS

When use of a pulmonary autograft is not an option, the porcine full-root bioprosthesis appears favorable for systemic semilunar valve replacement in the pediatric and young adult population. Of note, when prosthetic degeneration does occur, stenosis predominates rather than insufficiency. Longer term studies are warranted.

Stem cell therapy and tissue engineering for correction of congenital heart disease

This review article reports on the new field of stem cell therapy and tissue engineering and its potential on the management of congenital heart disease. To date, stem cell therapy has mainly focused on treatment of ischemic heart disease and heart failure, with initial indication of safety and mild-to-moderate efficacy. Preclinical studies and initial clinical trials suggest that the approach could be uniquely suited for the correction of congenital defects of the heart. The basic concept is to create living material made by cellularized grafts that, once implanted into the heart, grows and remodels in parallel with the recipient organ. This would make a substantial improvement in current clinical management, which often requires repeated surgical corrections for failure of implanted grafts. Different types of stem cells have been considered and the identification of specific cardiac stem cells within the heterogeneous population of mesenchymal and stromal cells offers opportunities for de novo cardiomyogenesis. In addition, endothelial cells and vascular progenitors, including cells with pericyte characteristics, may be necessary to generate efficiently perfused grafts. The implementation of current surgical grafts by stem cell engineering could address the unmet clinical needs of patients with congenital heart defects.

When repair is not feasible: prosthesis selection in children and adults with congenital heart disease

Congenital heart surgeons face many challenges when dealing with valvular pathology in the pediatric population. Because of the concerns related to growth, repair should be the main goal. However, this is not always feasible and valve replacement becomes the only other alternative. Valve replacement also represents one of the most common procedures performed for adults with congenital heart disease, with several valve options existing including homografts, xenografts, autografts, and other artificial prostheses. The choice sometimes may be difficult because there are advantages and disadvantages to each valve substitute. In this article, we will address the different options of valve replacement in children and adults with congenital heart disease, and review the current literature that supports current practice.

Pulmonary Valve Replacement With a Bovine Pericardial Valve

Objectives:

From a population of 90 patients after pulmonary valve replacement with a biological valve (Carpentier-Edwards Perimount valve), 56 of 80 available patients were examined five years after surgery.

Background:

Pulmonary valve replacement is needed in many patients with congenital heart disease. Homografts have limited availability and predictable degeneration, and mechanical valves require anticoagulation. No superiority of one kind of pulmonary valve replacement has been shown. Biological valves that are readily available are being used and evaluated in increasing numbers.

Methods:

In this cross-sectional study, five years following surgery, data were gathered from hospital charts, echocardiography, stress echocardiography, magnetic resonance imaging, and exercise testing.

Results:

In 90 patients, there were three new valve replacements, one early cardiac death, and four late noncardiac deaths. Echocardiographic assessment of the study group showed pulmonary Doppler velocities (m/s) before, after operation, and at five-year follow-up of 2.8 ± 1.1, 1.6 ± 0.4, and 2.3 ± 0.7, respectively. The assessed insufficiencies (0-3) at the same times were 2.3 ± 1.0, 0.3 ± 0.4, and 1.1 ± 0.8. Maximal oxygen uptake increased from 65.6% ± 10.1% to 77.1% ± 18.2% of predicted and QRS width increased by 7 ± 23ms. Valve degeneration could be associated with young age but not with diagnosis or valve size.

Conclusion:

In our study, the biological valve in the pulmonary position showed excellent mid-term results with few reoperations, low gradients, and mild to moderate insufficiency. Oversizing, in contrast to young age, was not a risk factor for valve degeneration. In younger patients, this allows later percutaneous replacement, reducing the need for further surgery. However, longer follow-up is needed.

Progress in developing a living human tissue-engineered tri-leaflet heart valve assembled from tissue produced by the self-assembly approach

The aortic heart valve is constantly subjected to pulsatile flow and pressure gradients which, associated with cardiovascular risk factors and abnormal hemodynamics (i.e. altered wall shear stress), can cause stenosis and calcification of the leaflets and result in valve malfunction and impaired circulation. Available options for valve replacement include homograft, allogenic or xenogenic graft as well as the implantation of a mechanical valve. A tissue-engineered heart valve containing living autologous cells would represent an alternative option, particularly for pediatric patients, but still needs to be developed. The present study was designed to demonstrate the feasibility of using a living tissue sheet produced by the self-assembly method, to replace the bovine pericardium currently used for the reconstruction of a stented human heart valve. In this study, human fibroblasts were cultured in the presence of sodium ascorbate to produce tissue sheets. These sheets were superimposed to create a thick construct. Tissue pieces were cut from these constructs and assembled together on a stent, based on techniques used for commercially available replacement valves. Histology and transmission electron microscopy analysis showed that the fibroblasts were embedded in a dense extracellular matrix produced in vitro. The mechanical properties measured were consistent with the fact that the engineered tissue was resistant and could be cut, sutured and assembled on a wire frame typically used in bioprosthetic valve assembly. After a culture period in vitro, the construct was cohesive and did not disrupt or disassemble. The tissue engineered heart valve was stimulated in a pulsatile flow bioreactor and was able to sustain multiple duty cycles. This prototype of a tissue-engineered heart valve containing cells embedded in their own extracellular matrix and sewn on a wire frame has the potential to be strong enough to support physiological stress. The next step will be to test this valve extensively in a bioreactor and at a later date, in a large animal model in order to assess in vivo patency of the graft.

Regression of left ventricular hypertrophy in children following the Ross procedure

OBJECTIVES

Left ventricular hypertrophy (LVH) frequently accompanies the progression of aortic valve disease in children. The extent of LVH regression following surgical relief of aortic valve disease in children has not been clearly elucidated. We hypothesized that significant regression of LVH will occur in children following the Ross procedure.

METHODS

We examined LVH over time in children <18 years of age who underwent the Ross procedure. Left ventricular mass index (LVMI) and corresponding z scores were calculated based on height, age and gender. Left ventricular hypertrophy was defined as an LVMI of > 39 g/m(2.7) and a z score of >1.6.

RESULTS

Twenty-five children underwent the Ross procedure. The left ventricular mass increased proportionally with the growth of the child from baseline to the latest follow-up at 7.3 ± 2.9 years (121.1 ± 81.5 vs 133.1 ± 79.8 g, P = 0.4). However, 96% (24/25) of children demonstrated LVMI regression from baseline. Mean LVMI decreased from 70.8 ± 31.2 to 41.8 ± 16.6 g/m(2.7) (P < 0.001). Similarly, LVMI z scores decreased from 2.2 ± 1.2 to 0.2 ± 1.9 (P < 0.001). Freedom from LVH was 83% at 10 years. Examination of LVMI and z scores over time demonstrated that the largest decrease occurred after the first year, with continued gradual decline over 10 years of follow-up.

CONCLUSIONS

The Ross procedure is effective in reversing LVH in children with aortic valve disease.

Antigen removal for the production of biomechanically functional, xenogeneic tissue grafts

Xenogeneic tissues are derived from other animal species and provide a source of material for engineering mechanically functional tissue grafts, such as heart valves, tendons, ligaments, and cartilage. Xenogeneic tissues, however, contain molecules, known as antigens, which invoke an immune reaction following implantation into a patient. Therefore, it is necessary to remove the antigens from a xenogeneic tissue to prevent immune rejection of the graft. Antigen removal can be accomplished by treating a tissue with solutions and/or physical processes that disrupt cells and solubilize, degrade, or mask antigens. However, processes used for cell and antigen removal from tissues often have deleterious effects on the extracellular matrix (ECM) of the tissue, rendering the tissue unsuitable for implantation due to poor mechanical properties. Thus, the goal of an antigen removal process should be to reduce the antigen content of a xenogeneic tissue while preserving its mechanical functionality. To expand the clinical use of antigen-removed xenogeneic tissues as biomechanically functional grafts, it is essential that researchers examine tissue antigen content, ECM composition and architecture, and mechanical properties as new antigen removal processes are developed.

Role of cell-matrix interactions on VIC phenotype and tissue deposition in 3D PEG hydrogels

Valvular interstitial cells (VICs) respond to 3D matrix interactions in a complex manner, but understanding these effects on VIC function better is important for applications ranging from valve tissue engineering to studying valve disease. Here, we encapsulated VICs in poly(ethylene glycol) (PEG) hydrogels modified with three different adhesive ligands, derived from fibronectin (RGDS), elastin (VGVAPG) and collagen-1 (P15). By day 14, VICs became significantly more elongated in RGDS-containing gels compared to VGVAPG or P15. This difference in cell morphology appeared to correlate with global matrix metalloproteinase (MMP) activity, as VICs encapsulated in RGDS-functionalized hydrogels secreted higher levels of active MMP at day 2. VIC activation to a myofibroblast phenotype was also characterized by staining for α-smooth muscle actin (αSMA) at day 14. The percentage of αSMA⁺ VICs in the VGVAPG gels was the highest (56%) compared to RGDS (33%) or P15 (38%) gels. Matrix deposition and composition were also characterized at days 14 and 42 and found to depend on the initial hydrogel composition. All gel formulations had similar levels of collagen, elastin and chondroitin sulphate deposited as the porcine aortic valve. However, the composition of collagen deposited by VICs in VGVAPG-functionalized gels had a significantly higher collagen-X:collagen-1 ratio, which is associated with stenotic valves. Taken together, these data suggest that peptide-functionalized PEG hydrogels are a useful system for culturing VICs three-dimensionally and, with the ability to systematically alter biochemical and biophysical properties, this platform may prove useful in manipulating VIC function for valve regeneration. Copyright © 2013 John Wiley & Sons, Ltd.