DEVELOPMENT OF NANOPARTICLE RATE-MODULATING AND SYNCHROTRON PHASE CONTRAST-BASED ASSESSMENT TECHNIQUES FOR CARDIAC TISSUE ENGINEERING

Myocardial infarction (MI) is the most common cause of heart failure. Despite advancements in cardiovascular treatments and interventions, current therapies can only slow down the progression of heart failure, but not tackle the progressive loss of cardiomyocytes after MI. One aim of cardiac tissue engineering is to develop implantable constructs (e.g. cardiac patches) that provide physical and biochemical cues for myocardium regeneration. To this end, vascularization in these constructs is of great importance and one key issue involved is the spatiotemporal control of growth-factor (GF)-release profiles. The other key issue is to non-invasively quantitatively monitor the success of these constructs in-situ, which will be essential for longitudinal assessments as studies are advanced from ex-vivo to animal models and human patients. To address these issues, the present research aims to develop nanoparticles to modulate the temporal control of GF release in cardiac patches, and to develop synchrotron X-ray phase contrast tomography for visualization and quantitative assessment of 3D-printed cardiac patch implanted in a rat MI model, with four specific objectives presented below. The first research objective is to optimize nanoparticle-fabrication process in terms of particle size, polydispersity, loading capacity, zeta potential and morphology. To achieve this objective, a comprehensive experimental study was performed to examine various process parameters used in the fabrication of poly(lactide-co-glycolide) (PLGA) nanoparticles, along with the development of a novel computational approach for the nanoparticle-fabrication optimization. Results show that among various process parameters examined, the polymer and the external aqueous phase concentrations are the most significant ones to affect the nanoparticle physical and release characteristics. Also, the limitations of PLGA nanoparticles such as initial burst effect and the lack of time-delayed release patterns are identified. The second research objective is to develop bi-layer nanoparticles to achieve the controllable release of GFs, meanwhile overcoming the above identified limitations of PLGA nanoparticles. The bi-layer nanoparticle is composed of protein-encapsulating PLGA core and poly(L-lactide) (PLLA)-rate regulating shell, thus allowing for low burst effect, protein structural integrity and time-delayed release patterns. The bi-layer nanoparticles, along with PLGA ones, were successfully fabricated and then used to regulate simultaneous and/or sequential release of multiple angiogenic factors with the results demonstrating that they are effective to promote angiogenesis in fibrin matrix. The third objective is to develop novel mathematical models to represent the controlled-release of bioactive agents from nanoparticles. For this, two models, namely the mechanistic model and geno-mechanistic model, were developed based on the local and global volume averaging approaches, respectively, and then validated with experiments on both single- and bi-layer nanoparticles, by which the ovalbumin was used as a protein model for the release examination. The results illustrates the developed models are able to provide insight on the release mechanism and to predict nanoparticle transport and degradation properties of nanoparticles, thus providing a means to regulate and control the release of bioactive agents from the nanoparticles for tissue engineering applications. The fourth objective of this research is to develop a synchrotron-based phase contrast non-invasive imaging technique for visualization and quantitative assessment of cardiac patch implanted in a rat MI model. To this end, the patches were created from alginate strands using the three-dimensional (3D) printing technique and then surgically implanted on rat hearts for the assessment based on phase contrast tomography. The imaging of samples was performed at various sample-to-detector distances, CT-scan time, and areas of the region of interest (ROI) to examine their effects on imaging quality. Phase-retrieved images depict visible and quantifiable structural details of the patch at low radiation dose, which, however, are not seen from the images by means of dual absorption-phase and a 3T clinical magnetic resonance imaging. Taken together, this research represents a significant advance in cardiac tissue engineering by developing novel nano-guided approaches for vascularization in myocardium regeneration as well as non-invasive and quantitative monitoring techniques for longitudinal studies on the cardiac patch implanted in animal model and eventually in human patients

A POROUS MEDIA APPROACH TOWARDS A DYNAMIC MECHANISTIC MODEL OF DRUG ELIMINATION BY THE LIVER

Hepatic drug elimination is a major PK process contributing to loss of drug concentration in the body. The prediction of hepatic clearance (and hence drug concentrations in the body) requires an understanding of the physiology and mechanisms of the hepatic elimination process and their compilation into a mechanistic model. Several physiological models including well-stirred model, parallel tube model and dispersion model have been developed to describe the hepatic elimination process and to determine how physiological variables such as blood flow, unbound fraction and enzyme activity may influence the hepatic clearance. However, each model has distinguishing advantages and limitations, which lead sometimes to very disparate prediction outcomes. Although hepatic drug elimination has been mathematically described by different physiological models, the mass transfer phenomena in the liver has not been described from a porous media viewpoint using local volume averaging method. The inherently porous structure of the liver allows us to describe the hepatic drug elimination process based on a porous media approach such that structural properties of the liver tissue, physico-chemical properties of the drug as well as transport properties associated with the hepatic blood perfusion are included in the model. Applying local volume averaging method and local equilibrium to the liver as a porous medium, a governing partial differential equation which takes into account liver porosity, tortuosity, permeability, unbound drug fraction and hepatic tissue partition coefficient, drug-plasma diffusivity, axial/radial dispersion and hepatocellular metabolism parameters was developed. The governing equation was numerically solved using implicit finite difference and Gauss-Seidel iterative method in order to describe changes in dug concentration with time and position across the liver following an intravenous drug administration. The model was used to predict hepatic clearance and bioavailability, which were then compared to reported observations. The predicted values of hepatic clearance and bioavailability had good agreement with the reported observations for high and low clearance drugs. As well, the model was able to successfully predict an unsteady state of hepatic drug elimination with concentration dependent intrinsic clearance. When statistically compared to the well-stirred, parallel tube and dispersion models the proposed model suggested a smaller mean squared prediction error and very good agreement to reported observations for eight drugs. A sensitivity analysis revealed that an increase in liver porosity results in a slight decrease in the drug concentration gradient across the liver while higher tissue partition coefficient values increase the concentration gradient. The model also suggested that the bioavailability was sensitive to the interaction between unbound fraction and intrinsic clearance. This study indicates that the liver and hepatic drug elimination can be successfully explored from a porous media viewpoint and may provide better mechanistic predictions of drug elimination processes by the liver

Turkic Instrumental Case Marker in Tātic Language Group

This paper studies the morphological influence of language contact between Turkic and Tātic language group in Northwest Iran. The postposition under study is the Turkic –inan and how it has entered the morphological system of some Tāti dialects of Iran. In particular, it is shown which Tāti dialects are influenced in this regard and why. The data for this study were collected from interviews with native Tāti and Turkic speakers in Iran and also from descriptive grammars and Tāti-Farsi dictionaries. We have used Narrog's (2010) instrumental semantic map to see which semantic functions are fulfilled with the instrumental-related postposition or case marker in both Tāti and Turkic dialects of Iran and whether they are the same or different in these languages

Dissolution of β-C₂S Cement Clinker: Part 2 Atomistic Kinetic Monte Carlo (KMC) Upscaling Approach

Cement clinkers containing mainly belite (β-C₂S as a model crystal), replacing alite, offer a promising solution for the development of environmentally friendly solutions to reduce the high level of CO₂ emissions in the production of Portland cement. However, the much lower reactivity of belite compared to alite limits the widespread use of belite cements. Therefore, this work presents a fundamental atomistic computational approach for comprehending and quantifying the mesoscopic forward dissolution rate of β-C₂S, applied to two reactive crystal facets of (100) and (1¯00). For this, an atomistic kinetic Monte Carlo (KMC) upscaling approach for cement clinker was developed. It was based on the calculated activation energies (ΔG*) under far-from-equilibrium conditions obtained by a molecular dynamic simulation using the combined approach of ReaxFF and metadynamics, as described in the Part 1 paper in this Special Issue. Thus, the individual atomistic dissolution rates were used as input parameters for implementing the KMC upscaling approach coded in MATLAB to study the dissolution time and morphology changes at the mesoscopic scale. Four different cases and 21 event scenarios were considered for the dissolution of calcium atoms (Ca) and silicate monomers. For this purpose, the (100) and (1¯00) facets of a β-C₂S crystal were considered using periodic boundary conditions (PBCs). In order to demonstrate the statistical nature of the KMC approach, 40 numerical realizations were presented. The major findings showed a striking layer-by-layer dissolution mechanism in the case of an ideal crystal, where the total dissolution rate was limited by the much slower dissolution of the silicate monomer compared to Ca. The introduction of crystal defects, namely cutting the edges at two crystal boundaries, increased the overall average dissolution rate by a factor of 519

Dissolution of β-C₂S Cement Clinker: Part 1 Molecular Dynamics (MD) Approach for Different Crystal Facets

A major concern in the modern cement industry is considering how to minimize the CO₂ footprint. Thus, cements based on belite, an impure clinker mineral (CaO)₂SiO₂ (C₂S in cement chemistry notation), which forms at lower temperatures, is a promising solution to develop eco-efficient and sustainable cement-based materials, used in enormous quantities. The slow reactivity of belite plays a critical role, but the dissolution mechanisms and kinetic rates at the atomistic scale are not known completely yet. This work aims to understand the dissolution behavior of different facets of β-C₂S providing missing input data and an upscaling modeling approach to connect the atomistic scale to the sub-micro scale. First, a combined ReaxFF and metadynamics-based molecular dynamic approach are applied to compute the atomistic forward reaction rates (RD) of calcium (Ca) and silicate species of (100) facet of β-C₂S considering the influence of crystal facets and crystal defects. To minimize the huge number of atomistic events possibilities, a generalized approach is proposed, based on the systematic removal of nearest neighbors’ crystal sites. This enables us to tabulate data on the forward reaction rates of most important atomistic scenarios, which are needed as input parameters to implement the Kinetic Monte Carlo (KMC) computational upscaling approach. The reason for the higher reactivity of the (100) facet compared to the (010) is explained

Evaluation of PBS Treatment and PEI Coating Effects on Surface Morphology and Cellular Response of 3D-Printed Alginate Scaffolds

Three-dimensional (3D) printing is an emerging technology for the fabrication of scaffolds to repair/replace damaged tissue/organs in tissue engineering. This paper presents our study on 3D printed alginate scaffolds treated with phosphate buffered saline (PBS) and polyethyleneimine (PEI) coating and their impacts on the surface morphology and cellular response of the printed scaffolds. In our study, sterile alginate was prepared by means of the freeze-drying method and then, used to prepare the hydrogel for 3D printing into calcium chloride, forming 3D scaffolds. Scaffolds were treated with PBS for a time period of two days and seven days, respectively, and PEI coating; then they were seeded with Schwann cells (RSC96) for the examination of cellular response (proliferation and differentiation). In addition, swelling and stiffness (Young’s modulus) of the treated scaffolds was evaluated, while their surface morphology was assessed using scanning electron microscopy (SEM). SEM images revealed significant changes in scaffold surface morphology due to degradation caused by the PBS treatment over time. Our cell proliferation assessment over seven days showed that a two-day PBS treatment could be more effective than seven-day PBS treatment for improving cell attachment and elongation. While PEI coating of alginate scaffolds seemed to contribute to cell growth, Schwann cells stayed round on the surface of alginate over the period of cell culture. In conclusion, PBS-treatment may offer the potential to induce surface physical cues due to degradation of alginate, which could improve cell attachment post cell-seeding of 3D-printed alginate scaffolds

Dissolution of Portlandite in Pure Water: Part 1 Molecular Dynamics (MD) Approach

Gefördert durch den Publikationsfonds der Universität Kasse