Integrated biophysical matching of bacterial nanocellulose coronary artery bypass grafts towards bioinspired artery typical functions

Revascularization via coronary artery bypass grafting (CABG) to treat cardiovascular disease is established as one of the most important lifesaving surgical techniques worldwide. But the shortage in functionally self-adaptive autologous arteries leads to circumstances where the clinical reality must deal with fighting pathologies coming from the mismatching biophysical functionality of more available venous grafts. Synthetic biomaterial-based CABG grafts did not make it to the market yet, what is mostly due to technical hurdles in matching biophysical properties to the complex demands of the CABG niche. But bacterial Nanocellulose (BNC) Hydrogels derived by growing biofilms hold a naturally integrative character in function-giving properties by its freedom in designing form and intrinsic fiber architecture. In this study we use this integral to combine impacts on the luminal fiber matrix, biomechanical properties and the reciprocal stimulation of microtopography and induced flow patterns, to investigate biomimetic and artificial designs on their bio-functional effects. Therefore, we produced tubular BNC-hydrogels at distinctive designs, characterized the structural and biomechanical properties and subjected them to in vitro endothelial colonization in bioreactor assisted perfusion cultivation. Results showed clearly improved functional properties and gave an indication of successfully realized stimulation by artery-typical helical flow patterns.

Comparative Evaluation on Impacts of Fibronectin, Heparin-Chitosan, and Albumin Coating of Bacterial Nanocellulose Small-Diameter Vascular Grafts on Endothelialization In Vitro

In this study, we contrast the impacts of surface coating bacterial nanocellulose small-diameter vascular grafts (BNC-SDVGs) with human albumin, fibronectin, or heparin–chitosan upon endothelialization with human saphenous vein endothelial cells (VEC) or endothelial progenitor cells (EPC) in vitro. In one scenario, coated grafts were cut into 2D circular patches for static colonization of a defined inner surface area; in another scenario, they were mounted on a customized bioreactor and subsequently perfused for cell seeding. We evaluated the colonization by emerging metabolic activity and the preservation of endothelial functionality by water soluble tetrazolium salts (WST-1), acetylated low-density lipoprotein (AcLDL) uptake assays, and immune fluorescence staining. Uncoated BNC scaffolds served as controls. The fibronectin coating significantly promoted adhesion and growth of VECs and EPCs, while albumin only promoted adhesion of VECs, but here, the cells were functionally impaired as indicated by missing AcLDL uptake. The heparin–chitosan coating led to significantly improved adhesion of EPCs, but not VECs. In summary, both fibronectin and heparin–chitosan coatings could beneficially impact the endothelialization of BNC-SDVGs and might therefore represent promising approaches to help improve the longevity and reduce the thrombogenicity of BNC-SDVGs in the future.

An In Vitro Hemodynamic Loop Model to Investigate the Hemocytocompatibility and Host Cell Activation of Vascular Medical Devices

In this study, the hemocompatibility of tubes with an inner diameter of 5 mm made of polyvinyl chloride (PVC) and coated with different bioactive conjugates was compared to uncoated PVC tubes, latex tubes, and a stent for intravascular application that was placed inside the PVC tubes. Evaluation of hemocompatibility was done using an in vitro hemodynamic loop model that is recommended by the ISO standard 10993-4. The tubes were cut into segments of identical length and closed to form loops avoiding any gap at the splice, then filled with human blood and rotated in a water bath at 37 °C for 3 hours. Thereafter, the blood inside the tubes was collected for the analysis of whole blood cell count, hemolysis (free plasma hemoglobin), complement system (sC5b-9), coagulation system (fibrinopeptide A), and leukocyte activation (polymorphonuclear elastase, tumor necrosis factor and interleukin-6). Host cell activation was determined for platelet activation, leukocyte integrin status and monocyte platelet aggregates using flow cytometry. The effect of inaccurate loop closure was examined with x-ray microtomography and scanning electron microscopy, that showed thrombus formation at the splice. Latex tubes showed the strongest activation of both plasma and cellular components of the blood, indicating a poor hemocompatibility, followed by the stent group and uncoated PVC tubes. The coated PVC tubes did not show a significant decrease in platelet activation status, but showed an increased in complement and coagulation cascade compared to uncoated PVC tubes. The loop model itself did not lead to the activation of cells or soluble factors, and the hemolysis level was low. Therefore, the presented in vitro hemodynamic loop model avoids excessive activation of blood components by mechanical forces and serves as a method to investigate in vitro interactions between donor blood and vascular medical devices.

Electrophysiological Stimulation of Whole Heart Constructs in an 8-Pole Electrical Field

Today 2D and 3D electrophysiological stimulation represents a well established concept to enhance myocardial development and maturation in tissue-engineered constructs. However, electrical field stimulation has never been adapted to complex whole heart constructs (WHC). This study demonstrates the impact of three-dimensional electrophysiological stimulation of tissue-engineered WHC in a custom made eight-pole electrical field stimulation system by short model cultivations with neonatal rat cardiomyocytes (CM). Therefore, WHC were generated by repopulation of decellularized rat hearts with neonatal CM and subjected to perfusion based cultivation with or without additional biophysicalstimulation for 96 h. Spontaneous electrophysiological (EP) activity of the processed WHC was analyzed by qualitative evaluation of multielectrode assay (MEA) signal sequences, descriptive comparative spike sorting, and direct contrasting assessment in simple numerical quantities complemented by impulse response tests after phasing out spontaneous EP activity. As strong reduction of voltage signals by the decellularized extracellular matrix (ECM) component of WHC was observed, the active principle was determined and used to estimate the spectrum of source signals to recorded values by calculative elimination. Western blotting of key myocardial markers was employed to substantiate the functional EP evaluation by classical biochemical analysis. We observed stable spontaneous EP activity showing clear R and S, but predominantly rS patterns, for both stimulated WHC and non-stimulated controls. By the impact of stimulation, mean voltage amplitudes and beating frequencies could be significantly increased. The active principle of signal reduction in decellularized ECM could be shown to follow a nonlinear damping function with remarkable accuracy, illustrating that recorded signals of moderate voltage amplitudes can also represent far-field measurements of strong signals that are emitted in distant depths of the ECM while small amplitudes are limited to actually represent also rather weak source-signals. After phasing out spontaneous activity, both stimulated WHC and non-stimulated controls could be excited again to emit immediate impulse responses. The observed beneficial impact of 8-pole field stimulation on functional EP activity could finally be validated on the biochemical level by showing increased ratios for myosin heavy chain, cardiac tropnin T, desmin, and connexin 43 for stimulated WHC by Western blot analysis. In conclusion, we found that although electrophysiological stimulation has been incorporated into the whole heart tissue-engineered concept from the very beginning, this study presents for the first time a concept for the transfer of electrical field stimulation to the whole heart tissue-engineered approach. Furthermore to the best knowledge of the authors, this is the first control-based study showing a comparative investigation of electrophysiological stimulation of whole heart constructs.

Mechanistics of biomass discharge during whole-heart decellularization

Whole-organ engineering-based on the functional repopulation of acellular whole-organ scaffolds derived from perfusion-based in toto decellularization of the specific organ system-is one of the most promising fields in tissue engineering. However, to date, we still have hardly any insights into the process of perfusion-based scaffold generation itself, with human-scale scaffolds usually obtained by adoption of small animal decellularization models, although those organs are of decreased biomass and potentially different biological characteristics. Therefore, in this study we analyzed perfusion-based human-scale whole-heart decellularization by evaluating and comparing the dynamics of biomass discharge and its kinetic characteristics during in toto decellularization of ovine and rodent hearts, while introducing a theoretical model of biomass depletion during perfusion-based whole-heart decellularization. Our results suggest highly varying process characteristics for the in toto decellularization of individual human-scale organs, such as protein discharge kinetics or time-dependent viscoelasticity of formed debris, despite seemingly consistent inter-sample decellularization efficacy, as evaluated by conventional disruptive analysis of obtained ECM scaffolds. Hence, the here exposed insights into the mechanistics of whole-heart decellularization as well as the introduced non-disruptive process accompanying tools may help to monitor and further optimize the decellularization process, especially with regards to human-scale scaffold production.

Whole-Heart Construct Cultivation Under 3D Mechanical Stimulation of the Left Ventricle

Today the concept of Whole-Heart Tissue Engineering represents one of the most promising approaches to the challenge of synthesizing functional myocardial tissue. At the current state of scientific and technological knowledge it is a principal task to transfer findings of several existing and widely investigated models to the process of whole-organ tissue engineering. Hereby, we present the first bioreactor system that allows the integrated 3D biomechanical stimulation of a whole-heart construct while allowing for simultaneous controlled perfusion of the coronary system.

Rheology of perfusates and fluid dynamical effects during whole organ decellularization: a perspective to individualize decellularization protocols for single organs

The approach of whole organ decellularization is rapidly becoming more widespread within the tissue engineering community. Today it is well known that the effects of decellularization protocols may vary with the particular type of treated tissue. However, there are no methods known to individualize decellularization protocols while automatically ensuring a standard level of quality to minimize adverse effects on the resulting extracellular matrix. Here we follow this idea by introducing two novel components into the current practice. First, a non-invasive method for online monitoring of resulting fluid dynamical characteristics of the coronary system is demonstrated for application during the perfusion decellularization of whole hearts. Second, the observation of the underlying rheological characteristics of the perfusates is employed to detect ongoing progress and maturation of the decellularization process. Measured data were contrasted to the respective release of specific cellular components. We demonstrate rheological measurements to be capable of detecting cellular debris along with a discriminative capture of DNA and protein ratios. We demonstrate that this perfusate biomass is well correlated to the biomass loss in the extracellular matrix produced by decellularization. The appearance of biomass components in the perfusates could specifically reflect the appearance of fluid dynamical characteristics that we monitored during the decellularization process. As rheological measuring of perfusate samples can be done within minutes, without any time-consuming preparation steps, we predict this to be a promising novel analytic strategy to control decellularization protocols, in time, by the actual conditions of the processed organ.

A novel native derived coronary artery tissue-flap model

Although tissue-engineering approaches have led to significant progress in the quest of finding a viable substitute for dysfunctional myocardium, the vascularization of such bioartificial constructs still remains a major challenge. Hence, there is a need for model systems that allow us to study and better understand cardiac and vascular biology to overcome current limitations. Therefore, in this study, in toto decellularized rat hearts with a patent vessel system were processed into standardized coronary artery tissue flaps adherent to the ascending aorta. Protein diffusivity analysis and blood perfusion of the coronary arteries showed proper sealing of the de-endothelialized vessels. Retrograde aortic perfusion allowed for selective seeding of the coronary artery system, while surface seeding of the tissue flaps allowed for additional controlled coculture with cardiac cells. The coronary artery tissue-flap model offers a patent and perfusable coronary vascular architecture with a preserved cardiac extracellular matrix, therefore mimicking nature's input to the highest possible degree. This offers the possibility to study re-endothelialization and endothelial function of different donor cell types and their interaction with cardiac cells in a standardized biologically derived cardiac in vitro model, while establishing a platform that could be used for in vitro drug testing and stem cell differentiation studies.

A novel customizable modular bioreactor system for whole-heart cultivation under controlled 3D biomechanical stimulation

In the last decade, cardiovascular tissue engineering has made great progress developing new strategies for regenerative medicine applications. However, while tissue engineered heart valves are already entering the clinical routine, tissue engineered myocardial substitutes are still restrained to experimental approaches. In contrast to the heart valves, tissue engineered myocardium cannot be repopulated in vivo because of its biological complexity, requiring elaborate cultivation conditions ex vivo. Although new promising approaches-like the whole-heart decellularization concept-have entered the myocardial tissue engineering field, bioreactor technology needed for the generation of functional myocardial tissue still lags behind in the sense of user-friendly, flexible and low cost systems. Here, we present a novel customizable modular bioreactor system that can be used for whole-heart cultivation. Out of a commercially obtainable original equipment manufacturer platform we constructed a modular bioreactor system specifically aimed at the cultivation of decellularized whole-hearts through perfusion and controlled 3D biomechanical stimulation with a simple but highly flexible operation platform based on LabVIEW. The modular setup not only allows a wide range of variance regarding medium conditioning under controlled 3D myocardial stretching but can also easily be upgraded for e.g. electrophysiological monitoring or stimulation, allowing for a tailor-made low-cost myocardial bioreactor system.

Das Marburger Rechtschreib-Training - Ergebnisse einer Kurzzeit-Intervention

Zusammenfassung Fragestellung: Das Marburger Rechtschreibtraining wurde mit einer Gruppe von 10 recht-schreibschwachen Grundschülern (2.-4. Klasse) über einen Zeitraum von drei Monaten als Einzeltraining durchgeführt. Ergebnisse: Dabei ergaben sich signifikante Verbesserungen im Rechtschreib- und Lesetest, jedoch noch nicht im subjektiv eingeschätzten Leidensdruck. Schlussfolgerung: Das Marburger Rechtschreibtraining hat sich nicht nur in einer Langzeit-, sondern auch in einer Kurzzeitintervention als erfolgreich herausgestellt.

[Marburg Spelling Training program--results of a brief intervention]

OBJECTIVES

The Marburg Spelling Training Program was administered to a sample of 10 spelling-disabled primary school pupils (2nd-4th graders) over three months in an individual setting.

RESULTS

Statistical analyses yielded significant improvements in spelling and reading test performances, but none yet in the emotional stress caused by the problems.

CONCLUSION

The Marburg Spelling Training Program has now proven to be effective not only in long-term, but also in short-term intervention.