Thomas De Schryver

The 3D printing of gelatin methacrylamide cell-laden tissue-engineered constructs with high cell viability.

In the present study, we report on the combined efforts of material chemistry, engineering and biology as a systemic approach for the fabrication of high viability 3D printed macroporous gelatin methacrylamide constructs. First, we propose the use and optimization of VA-086 as a photo-initiator with enhanced biocompatibility compared to the conventional Irgacure 2959. Second, a parametric study on the printing of gelatins was performed in order to characterize and compare construct architectures. Hereby, the influence of the hydrogel building block concentration, the printing temperature, the printing pressure, the printing speed, and the cell density were analyzed in depth. As a result, scaffolds could be designed having a 100% interconnected pore network in the gelatin concentration range of 10-20 w/v%. In the last part, the fabrication of cell-laden scaffolds was studied, whereby the application for tissue engineering was tested by encapsulation of the hepatocarcinoma cell line (HepG2). Printing pressure and needle shape was revealed to impact the overall cell viability. Mechanically stable cell-laden gelatin methacrylamide scaffolds with high cell viability (>97%) could be printed.

A Pore-Scale Study of Fracture Dynamics in Rock Using X-ray Micro-CT Under Ambient Freeze–Thaw Cycling

Freeze-thaw cycling stresses many environments which include porous media such as soil, rock and concrete. Climate change can expose new regions and subject others to a changing freeze-thaw frequency. Therefore, understanding and predicting the effect of freeze-thaw cycles is important in environmental science, the built environment and cultural heritage preservation. In this paper, we explore the possibilities of state-of-the-art micro-CT in studying the pore scale dynamics related to freezing and thawing. The experiments show the development of a fracture network in a porous limestone when cooling to -9.7 °C, at which an exothermal temperature peak is a proxy for ice crystallization. The dynamics of the fracture network are visualized with a time frame of 80 s. Theoretical assumptions predict that crystallization in these experiments occurs in pores of 6-20.1 nm under transient conditions. Here, the crystallization-induced stress exceeds rock strength when the local crystal fraction in the pores is 4.3%. The location of fractures is strongly related to preferential water uptake paths and rock texture, which are visually identified. Laboratory, continuous X-ray micro-CT scanning opens new perspectives for the pore-scale study of ice crystallization in porous media as well as for environmental processes related to freeze-thaw fracturing.

Real‐time visualization of Haines jumps in sandstone with laboratory‐based microcomputed tomography

In this work, we present a novel laboratory-based microcomputed tomography (micro-CT) experiment designed to investigate the pore-scale drainage behavior of natural sandstone under dynamic conditions. The fluid distribution in a Bentheimer sandstone was visualized every 4 s with a 12 s measurement time, allowing the investigation of single-pore and few-pore-filling events. To our knowledge, this is the first time that such measurements were performed outside of synchrotron facilities, illustrating the growing application potential of laboratory-based micro-CT with subminute temporal resolutions for geological research at the pore scale. To illustrate how the workflow can lead to an improved understanding of drainage behavior, the experiment was analyzed using a decomposition of the pore space into individual geometrical pores. Preliminary results from this analysis suggest that the distribution of drainage event sizes follows a power law scaling, as expected from percolation theory.

Assessment of Numerical Simulation Strategies for Ultrasonic Color Blood Flow Imaging, Based on a Computer and Experimental Model of the Carotid Artery

Ultrasonic Doppler techniques are well established and allow qualitative and quantitative flow analysis. However, due to inherent limitations of the imaging process, the actual flow dynamics and the ultrasound (US) image do not always correspond. To investigate the performance of ultrasonic flow imaging methods, computational fluid dynamics (CFD) can play an important role. CFD simulations can be directly processed to mimic ultrasonic images or can be further coupled to ultrasound simulation models. We studied both approaches in the clinically relevant setting of a carotid artery using color flow images (CFI). The first order approach consisted of producing ultrasound images by color-coding CFD-simulations. For the second order approach, CFI was simulated using an ultrasound simulator, which models blood as a collection of point scatterers moving according to the CFD velocity fields. Color flow images were also measured in an experimental setup of the same carotid geometry for comparison. Results showed that during dynamic stages of the cardiac cycle, realistic ultrasound data can only be achieved when incorporating both the dynamic image formation and the measurement statistics into the simulations.

A Multilevel Modeling Framework to Study Hepatic Perfusion Characteristics in Case of Liver Cirrhosis

Liver cirrhosis represents the end-stage of different liver disorders, progressively affecting hepatic architecture, hemodynamics, and function. Morphologically, cirrhosis is characterized by diffuse fibrosis, the conversion of normal liver architecture into structurally abnormal regenerative nodules and the formation of an abundant vascular network. To date, the vascular remodeling and altered hemodynamics due to cirrhosis are still poorly understood, even though they seem to play a pivotal role in cirrhogenesis. This study aims to determine the perfusion characteristics of the cirrhotic circulation using a multilevel modeling approach including computational fluid dynamics (CFD) simulations. Vascular corrosion casting and multilevel micro-CT imaging of a single human cirrhotic liver generated detailed datasets of the hepatic circulation, including typical pathological characteristics of cirrhosis such as shunt vessels and dilated sinusoids. Image processing resulted in anatomically correct 3D reconstructions of the microvasculature up to a diameter of about 500 μm. Subsequently, two cubic samples (150 × 150 × 150 μm³) were virtually dissected from vascularized zones in between regenerative nodules and applied for CFD simulations to study the altered cirrhotic microperfusion and permeability. Additionally, a conceptual 3D model of the cirrhotic macrocirculation was developed to reveal the hemodynamic impact of regenerative nodules. Our results illustrate that the cirrhotic microcirculation is characterized by an anisotropic permeability showing the highest value in the direction parallel to the central vein (kd,zz = 1.68 × 10-13 m² and kd,zz = 7.79 × 10⁻¹³ m² for sample 1 and 2, respectively) and lower values in the circumferential (kd,ϑϑ = 5.78 × 10⁻¹⁴ m² and kd,ϑϑ = 5.65 × 10⁻¹³ m² for sample 1 and 2, respectively) and radial (kd,rr = 9.87 × 10⁻¹⁴ m² and kd,rr = 5.13 × 10⁻¹³ m² for sample 1 and 2, respectively) direction. Overall, the observed permeabilities are markedly higher compared to a normal liver, implying a locally decreased intrahepatic vascular resistance (IVR) probably due to local compensation mechanisms (dilated sinusoids and shunt vessels). These counteract the IVR increase caused by the presence of regenerative nodules and dynamic contraction mechanisms (e.g., stellate cells, NO-concentration, etc.). Our conceptual 3D model of the cirrhotic macrocirculation indicates that regenerative nodules severely increase the IVR beyond about 65 vol. % of regenerative nodules. Numerical modeling allows quantifying perfusion characteristics of the cirrhotic macro- and microcirculation, i.e., the effect of regenerative nodules and compensation mechanisms such as dilated sinusoids and shunt vessels. Future research will focus on the development of models to study time-dependent degenerative adaptation of the cirrhotic macro- and microcirculation.

Spatial development of transport structures in apple (Malus × domestica Borkh.) fruit

The void network and vascular system are important pathways for the transport of gases, water and solutes in apple fruit (Malus × domestica Borkh). Here we used X-ray micro-tomography at various spatial resolutions to investigate the growth of these transport structures in 3D during fruit development of “Jonagold” apple. The size of the void space and porosity in the cortex tissue increased considerably. In the core tissue, the porosity was consistently lower, and seemed to decrease toward the end of the maturation period. The voids in the core were more narrow and fragmented than the voids in the cortex. Both the void network in the core and in the cortex changed significantly in terms of void morphology. An automated segmentation protocol underestimated the total vasculature length by 9–12% in comparison to manually processed images. Vascular networks increased in length from a total of 5 m at 9 weeks after full bloom, to more than 20 m corresponding to 5 cm of vascular tissue per cubic centimeter of apple tissue. A high degree of branching in both the void network and vascular system and a complex three-dimensional pattern was observed across the whole fruit. The 3D visualizations of the transport structures may be useful for numerical modeling of organ growth and transport processes in fruit.

Single String Technique for Coronary Bifurcation Stenting: Detailed Technical Evaluation and Feasibility Analysis

OBJECTIVES The study aimed to evaluate the adequacy and feasibility of the single string bifurcation stenting technique. BACKGROUND Double-stent techniques may be required for complex bifurcations. Currently applied methods all have their morphological or structural limitations with respect to wall coverage, multiple strut layers, and apposition rate. METHODS Single string is a novel method in which, first, the side branch (SB) stent is deployed with a single stent cell protruding into the main branch (MB). Second, the MB stent is deployed across this protruding stent cell. The procedure is completed by final kissing balloon dilation. The single string technique was first tested in vitro (n = 20) and next applied in patients (n = 11) with complex bifurcation stenoses. RESULTS All procedures were performed successfully, crossing a single stent cell in 100%. Procedure duration was 23.0 ± 7.9 min, and the fluoroscopy time was 9.4 ± 3.5 min. The results were evaluated by optical coherence tomography, showing fully apposed struts in 83.0 ± 9.2% in the bifurcation area. Residual area obstruction in the MB was 6.4 ± 5.6% and 25.0 ± 16.9% in the SB, as evaluated by micro computed tomography. All the human cases were performed successfully with excellent angiographic results: the residual area stenosis was 27 ± 8% and 29 ± 10% in the MB and in the SB, respectively, by 3-dimensional quantitative coronary angiography. No relevant periprocedural enzyme increase was observed. During follow-up (6 ± 4 months), no adverse clinical events (death, myocardial infarction, target vessel revascularization) were noted. CONCLUSIONS The single string technique for complex bifurcation dilation was shown to be adequate in vitro and feasible in humans, with favorable results in terms of stent overlap, malapposition rate, and low residual obstruction in both the MB and SB.

Motion compensated micro-CT reconstruction for in-situ analysis of dynamic processes

This work presents a framework to exploit the synergy between Digital Volume Correlation (DVC) and iterative CT reconstruction to enhance the quality of high-resolution dynamic X-ray CT (4D-µCT) and obtain quantitative results from the acquired dataset in the form of 3D strain maps which can be directly correlated to the material properties. Furthermore, we show that the developed framework is capable of strongly reducing motion artifacts even in a dataset containing a single 360° rotation.

A compact low cost cooling stage for lab based x-ray micro-CT setups

A temperature controlled sample stage, which can both heat up, and cool down a sample while it is subjected to a μCT scan has been developed. The stage was designed to reach temperatures up to 50°C and down to −20°C and has been used in several applications with a varying degree of dynamism, going from immobilizing samples by freezing them to studying fully dynamically evolving temperature dependent processes.

Data-Driven Affine Deformation Estimation and Correction in Cone Beam Computed Tomography

In computed tomography (CT), motion and deformation during the acquisition lead to streak artefacts and blurring in the reconstructed images. To remedy these artefacts, we introduce an efficient algorithm to estimate and correct for global affine deformations directly on the cone beam projections. The proposed technique is data driven and thus removes the need for markers and/or a tracking system. A relationship between affine transformations and the cone beam transform is proved and used to correct the projections. The deformation parameters that describe deformation perpendicular to the projection direction are estimated for each projection by minimizing a plane-based inconsistency criterion. The criterion compares each projection of the main scan with all projections of a fast reference scan, which is acquired prior or posterior to the main scan. Experiments with simulated and experimental data show that the proposed affine deformation estimation method is able to substantially reduce motion artefacts in cone beam CT images.