Tobias Goecke

Sucrose Diffusion in Decellularized Heart Valves for Freeze-Drying.

Decellularized heart valves can be used as starter matrix implants for heart valve replacement therapies in terms of guided tissue regeneration. Decellularized matrices ideally need to be long-term storable to assure off-the-shelf availability. Freeze-drying is an attractive preservation method, allowing storage at room temperature in a dried state. However, the two inherent processing steps, freezing and drying, can cause severe damage to extracellular matrix (ECM) proteins and the overall tissue histoarchitecture and thus impair biomechanical characteristics of resulting matrices. Freeze-drying therefore requires a lyoprotective agent that stabilizes endogenous structural proteins during both substeps and that forms a protective glassy state at room temperature. To estimate incubation times needed to infiltrate decellularized heart valves with the lyoprotectant sucrose, temperature-dependent diffusion studies were done using Fourier transform infrared spectroscopy. Glycerol, a cryoprotective agent, was studied for comparison. Diffusion of both protectants was found to exhibit Arrhenius behavior. The activation energies of sucrose and glycerol diffusion were found to be 15.9 and 37.7 kJ·mol(-1), respectively. It was estimated that 4 h of incubation at 37°C is sufficient to infiltrate heart valves with sucrose before freeze-drying. Application of a 5% sucrose solution was shown to stabilize acellular valve scaffolds during freeze-drying. Such freeze-dried tissues, however, displayed pores, which were attributed to ice crystal damage, whereas vacuum-dried scaffolds in comparison revealed no pores after drying and rehydration. Exposure to a hygroscopic sucrose solution (80%) before freeze-drying was shown to be an effective method to diminish pore formation in freeze-dried ECMs: matrix structures closely resembled those of control samples that were not freeze-dried. Heart valve matrices were shown to be in a glassy state after drying, suggesting that they can be stored at room temperature.

Tissue-engineered mitral valve: morphology and biomechanics †

OBJECTIVES The present study aimed at developing tissue-engineered mitral valves based on cell-free ovine mitral allografts. METHODS The ovine mitral valves (OMVs) (n = 46) were harvested in the local slaughter house. They were decellularized using detergent solutions and DNase. The effectiveness of decellularization was assessed by histological (haematoxylin-eosin, Movats pentachrome) and immunofluorescent staining (for DNA and α-Gal), and DNA-quantification. To reveal the receptiveness of decellularized tissue to endothelial cells (ECs), the valve leaflets were reseeded with ovine ECs, derived from endothelial progenitor cells in vitro. For assessment of biomechanical properties, uniaxial tensile tests were carried out. RESULTS Histology and immunofluorescent staining revealed absence of cell nuclei in decellularized leaflets, chordae and papillary muscles. According to the software for immunofluorescence analysis, reduction in DNA and α-Gal was 99.9 and 99.6%, respectively. DNA-quantification showed 71.2% reduction in DNA content without DNase and 96.4% reduction after DNase treatment. Decellularized leaflets were comparable with native in ultimate tensile strain (native, 0.34 ± 0.09 mm/mm, vs decellularized, 0.44 ± 0.1 mm/mm; P = 0.09), and elastin modulus (native, 0.39 ± 0.27, vs decellularized, 0.57 ± 0.55, P = 0.46), had increased ultimate tensile stress (native, 1.23 ± 0.35 MPa, vs decellularized 2.12 ± 0.43 MPa; P = 0.001) and collagen modulus (native, 5.5 ± 1.26, vs decellularized, 8.29 ± 2.9; P = 0.04). After EC seeding, immunofluorescent staining revealed a monolayer of CD31-, eNOS- and vWF-positive cells on the surface of the leaflet, as well as a typical cobble-stone morphology of those cells. CONCLUSIONS Decellularization of ovine mitral valve results in a mitral valves scaffold with mechanical properties comparable with native tissue, and a graft surface, which can be repopulated by endothelial cells.

Novel mouse model of cardiopulmonary bypass

OBJECTIVES Cardiopulmonary bypass (CPB) is an essential component of many cardiac interventions, and therefore, there is an increasing critical demand to minimize organ damage resulting from prolonged extracorporeal circulation. Our goal was to develop the first clinically relevant mouse model of CPB and to examine the course of extracorporeal circulation by closely monitoring haemodynamic and oxygenation parameters. METHODS Here, we report the optimization of device design, perfusion circuit and microsurgical techniques as well as validation of physiological functions during CPB in mice after circulatory arrest and reperfusion. Validation of the model required multiple blood gas analyses, and therefore, this initial report describes an acute model that is incompatible with survival due to the need of repetitive blood draws. RESULTS Biochemical and histopathological assessment of organ damage revealed only mild changes in the heart and lungs and signs of the beginning of acute organ failure in the liver and kidneys. CONCLUSIONS This new CPB mouse model will facilitate preclinical testing of therapeutic strategies in cardiovascular diseases and investigation of CPB in relation to different insults and pre-existing comorbidities. In combination with genetically modified mice, this model will be an important tool to dissect the molecular mechanisms involved in organ damage related to extracorporeal circulation.

Prognostic Value of the Nutritional Risk Index in Candidates for Continuous Flow Left Ventricular Assist Device Therapy

INTRODUCTION AND OBJECTIVES Malnutrition has been shown to affect clinical outcomes in patients with heart failure. The aim of this study was to analyze the impact of preoperative nutritional status assessed by the nutritional risk index (NRI) on the prognosis of patients with a continuous-flow left ventricular assist device (cf-LVAD). METHODS We performed a retrospective study of 279 patients who underwent cf-LVAD implantation between 2009 and 2015 in our center. Preoperative NRI was calculated and the patients were followed-up for 1 year. The association between preoperative NRI and postoperative clinical events was analyzed using multivariable logistic regression. RESULTS The prevalence of severe (NRI <83.5), moderate (83.5 ≤ NRI <97.5) and mild (97.5 ≤ NRI <100) nutritional risk was 5.4%, 21.5%, and 9.3%. Mortality rates 1 year after cf-LVAD implantation in these 3 categories were 53.3%, 31.7%, 23.1% vs 18.0% (P <.001) in patients with a normal IRN. A normal preoperative NRI value was an independent predictor of lower risk of death from any cause during follow-up (aHR per 1 unit, 0.961; 95%CI, 0.941-0.981; P <.001) was and a predictor for a lower risk of postoperative infections (aOR, 0.968; 95%CI, 0.946-0.991; P=.007), respiratory failure (aOR, 0,961; 95%CI, 0.936-0.987; P=.004), and right heart failure (aOR, 0.963; 95%CI, 0.934-0.992; P=.014). CONCLUSIONS Malnourished patients are at increased risk for postoperative complications and death after cf-LVAD implantation. Assessment of nutritional risk could improve patient selection and the early initiation of nutritional support.

Cardiopulmonary Bypass in a Mouse Model: A Novel Approach

As prolonged cardiopulmonary bypass becomes more essential during cardiac interventions, an increasing clinical demand arises for procedure optimization and for minimizing organ damage resulting from prolonged extracorporal circulation. The goal of this paper was to demonstrate a fully functional and clinically relevant model of cardiopulmonary bypass in a mouse. We report on the device design, perfusion circuit optimization, and microsurgical techniques. This model is an acute model, which is not compatible with survival due to the need for multiple blood drawings. Because of the range of tools available for mice (e.g., markers, knockouts, etc.), this model will facilitate investigation into the molecular mechanisms of organ damage and the effect of cardiopulmonary bypass in relation to other comorbidities.

Tissue Engineering of Vein Valves Based on Decellularized Natural Matrices

Valvular repair or transplantation, designed to restore the venous valve function of the legs, has been proposed as treatment in chronic venous insufficiency. Available grafts or surgeries have provided limited durability so far. Generating venous valve substitutes by means of tissue engineering could be a solution. We generated decellularized jugular ovine vein conduits containing valves (oVVC) after reseeding with ovine endothelial cells differentiated from peripheral blood-derived endothelial cells (oPBEC), cultivated in vitro corresponding to the circulatory situation in the lower leg at rest and under exertion. oVVC were decellularized by detergent treatment. GFP-labeled oPBEC were seeded onto the luminal side of the decellularized oVVC and cultivated under static-rotational conditions for 6 h (group I) and 12 h (group II), respectively. Reseeded matrices of group I were exposed to continuous low flow conditions (“leg at rest”). The tissues of group II were exposed to a gradually increasing flow (“leg under effort”). After 5 days, the grafts of group I revealed a uniform luminal endothelial cell coverage of the examined areas of the venous walls and adjacent venous valve leaflets. In group II, the cell coverage on luminal areas of the venous wall parts was found to be nearly complete. The endothelial cell coverage of adjacent venous valve leaflets was revealed to be less dense and confluent. Endothelial cells cultured on acellular vein tissues of both groups were distinctly orientated uniformly in the flow direction, clearly creating a stable and flow-orientated layer. Thus, an endothelium could successfully be reestablished on the luminal surface of a decellularized venous valve by seeding peripheral blood endothelial cells and culturing under different conditions.

Prefabrication of heart valves

ZusammenfassungHintergrundKonventionelle Prothesen für den Herzklappenersatz haben Nachteile und Einschränkungen.Fragestellung und MethodeDie Nutzbarmachung von Prinzipien des Tissueengineerings zur Optimierung aktuell gängiger Klappenersatzverfahren wird dargestellt.Ergebnis und SchlussfolgerungDie Studienlage der letzten Jahre hat gezeigt, dass allogene, dezellularisierte Herzklappen die Limitationen herkömmlicher Prothesen überwinden und die Charakteristika eines idealen Klappenersatzes gewährleisten können.AbstractBackgroundCommonly used heart valve prostheses have specific drawbacks and limitations.Objectives and methodsOptimization of conventional methods and techniques for heart valve replacement by application of tissue engineering principles.Results and conclusionsRecent studies have impressively shown that allogeneic decellularized matrices have the potential to overcome limitations of conventional prostheses and to provide all the characteristics of an ideal graft for heart valve replacement.BACKGROUND Commonly used heart valve prostheses have specific drawbacks and limitations. OBJECTIVES AND METHODS Optimization of conventional methods and techniques for heart valve replacement by application of tissue engineering principles. RESULTS AND CONCLUSIONS Recent studies have impressively shown that allogeneic decellularized matrices have the potential to overcome limitations of conventional prostheses and to provide all the characteristics of an ideal graft for heart valve replacement.

Präfabrikation von Herzklappen@@@Prefabrication of heart valves

ZusammenfassungHintergrundKonventionelle Prothesen für den Herzklappenersatz haben Nachteile und Einschränkungen.Fragestellung und MethodeDie Nutzbarmachung von Prinzipien des Tissueengineerings zur Optimierung aktuell gängiger Klappenersatzverfahren wird dargestellt.Ergebnis und SchlussfolgerungDie Studienlage der letzten Jahre hat gezeigt, dass allogene, dezellularisierte Herzklappen die Limitationen herkömmlicher Prothesen überwinden und die Charakteristika eines idealen Klappenersatzes gewährleisten können.AbstractBackgroundCommonly used heart valve prostheses have specific drawbacks and limitations.Objectives and methodsOptimization of conventional methods and techniques for heart valve replacement by application of tissue engineering principles.Results and conclusionsRecent studies have impressively shown that allogeneic decellularized matrices have the potential to overcome limitations of conventional prostheses and to provide all the characteristics of an ideal graft for heart valve replacement.BACKGROUND Commonly used heart valve prostheses have specific drawbacks and limitations. OBJECTIVES AND METHODS Optimization of conventional methods and techniques for heart valve replacement by application of tissue engineering principles. RESULTS AND CONCLUSIONS Recent studies have impressively shown that allogeneic decellularized matrices have the potential to overcome limitations of conventional prostheses and to provide all the characteristics of an ideal graft for heart valve replacement.