MRI Evaluation of Injectable Hyaluronic Acid Hydrogel Therapy to Attenuate Myocardial Infarct Remodeling

Left ventricular (LV) remodeling following myocardial infarction (MI) leads to maladaptive processes that often progress to heart failure. Injectable biomaterials can alter the mechanical signaling post-MI to limit this progression. To design optimal therapies, noninvasive techniques are needed to elucidate the reciprocal interaction between the injected material and the surrounding myocardial tissue. Towards this goal, the general hypothesis of this dissertation was that magnetic resonance imaging (MRI) can be used to characterize the properties of injectable materials once delivered to the myocardium and evaluate the temporal effects of injectable materials on myocardial tissue properties post-MI. To test this hypothesis, injectable hyaluronic acid (HA) hydrogels were developed with a range of gelation, degradation and mechanical properties by altering the initiator concentration, macromer modification, and macromer concentration, respectively. Non-contrast MRI was then used to characterize the properties (e.g., distribution, chemical composition) of injectable HA hydrogels in myocardial explants. Altering hydrogel gelation led to differences in distribution in myocardial tissue, as quantified by T2-weighted MRI. As an alternative to conventional (i.e.T2-weighted) MRI where contrast depends on differences in MR properties and thus, is non-specific for the material, chemical exchange saturation transfer (CEST) MRI was used to specifically image hydrogels based on their functional (i.e. exchangeable proton) groups. CEST contrast correlated with changes in material properties, specifically macromer concentration. Furthermore, CEST MRI was shown to simultaneously visualize and discriminate between different injectable materials based on their unique chemistry. Finally, the effect of injectable HA hydrogels on myocardial tissue properties was temporally evaluated in a porcine infarct model up to 12 weeks post-MI. Outcome assessment using MRI (e.g. cine, late-gadolinium enhancement, and spatial modulation of magnetization MRI) and finite element (FE) modeling demonstrated that hydrogel therapy led to improved global LV structure and function, increased wall thickness, preserved borderzone contractility, and increased infarct stiffness, respectively. This work demonstrates that MRI can be used to simultaneously study hydrogel properties after injection into the myocardium and evaluate the ability of injectable hydrogels to alter myocardial tissue properties to ultimately improve cardiac outcomes and enable future optimization of biomaterial therapies to attenuate adverse remodeling post-MI

Enhancing the Biodistribution and Physicochemical Properties of Gold Nanoparticles by Modifying their Surface Characteristics

L'abstract è presente nell'allegato / the abstract is in the attachmen

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

Linking cell function with perfusion : insights from the transcatheter delivery of bone marrow-derived CD133+ cells in ischemic refractory cardiomyopathy trial (RECARDIO)

Background: Cell therapy with bone marrow (BM)-derived progenitors has emerged as a promising therapeutic for refractory angina (RA) patients. In the present study, we evaluated the safety and preliminary efficacy of transcatheter delivery of autologous BM-derived advanced therapy medicinal product CD133(+) cells (ATMP-CD133) in RA patients, correlating perfusion outcome with cell function. Methods: In the phase I "Endocavitary Injection of Bone Marrow Derived CD133(+) Cells in Ischemic Refractory Cardiomyopathy" (RECARDIO) trial, a total of 10 patients with left ventricular (LV) dysfunction (ejection fraction <= 45%) and evidence of reversible ischemia, as assessed by single-photon emission computed tomography (SPECT), underwent BM aspiration and fluoroscopy-based percutaneous endomyocardial delivery of ATMP-CD133. Patients were evaluated at 6 and 12 months for safety and preliminary efficacy endpoints. ATMP-CD133 samples were used for in vitro correlations. Results: Patients were treated safely with a mean number of 6.57 +/- 3.45 x 10(6) ATMP-CD133. At 6-month follow-up, myocardial perfusion at SPECT was significantly ameliorated in terms of changes in summed stress (from 18.2 +/- 8.6 to 13.8 +/- 7.8, p = 0.05) and difference scores (from 12.0 +/- 5.3 to 6.1 +/- 4.0, p = 0.02) and number of segments with inducible ischemia (from 7.3 +/- 2.2 to 4.0 +/- 2.7, p = 0.003). Similarly, Canadian Cardiovascular Society and New York Heart Association classes significantly improved at follow-up vs baseline (p = 0.001 and p = 0.007, respectively). Changes in summed stress score changes positively correlated with ATMP-CD133 release of proangiogenic cytokines HGF and PDGF-bb (r = 0.80, p = 0.009 and r = 0.77, p = 0.01, respectively) and negatively with the proinflammatory cytokines RANTES (r = -0.79, p = 0.01) and IL-6 (r = -0.76, p = 0.02). Conclusion: Results of the RECARDIO trial suggested safety and efficacy in terms of clinical and perfusion outcomes in patients with RA and LV dysfunction. The observed link between myocardial perfusion improvements and ATMP-CD133 secretome may represent a proof of concept for further mechanistic investigations

Acoustic Angiography: A New Imaging Platform for High Resolution Mapping of Microvasculature and Tumor Assessment

Statistically, one in four Americans will die from cancer. Many new tumor detection and therapeutic approaches have improved patient outcomes, but cancer continues to run rampant in our country; it claimed the lives of 1.6 million Americans in 2012. To put this number of annual deaths in perspective, it is over 500 times the number of people who died in the horrific attacks on September 11, 2001. This dissertation does not offer either an antidote to the disease, nor a detection mechanism appropriate for all tumor types. It does, however, present the description and characterization of a novel dual-frequency ultrasound imaging transducer, capable of operating in a new imaging mode we call `acoustic angiography.' These images offer high resolution and high contrast 3D depictions of the microvasculature; herein we demonstrate its cancer assessment utility by way of multiple imaging studies. Throughout this dissertation, image data from both healthy and diseased tissues are presented. Additionally, acoustic assessments of vasculature within an ex vivo biomatrix scaffold model (a platform for creating of artificial organs) are presented. A vessel mapping algorithm, originally developed for human magnetic resonance angiography images, has been implemented in both in vivo and ex vivo tissue volumes. A novel microvessel phantom generation technique is presented, which allows ground-truth coordinates for vascular networks to be defined and imaged. Finally, the ultrasound pulsing technique, radiation force, was used as a method to improve the diagnostic sensitivity of ultrasound to malignant tumors. Together, the results of these studies suggest that the imaging approach, acoustic angiography, enabled by our new dual-frequency ultrasound transducer, could eventually be used to detect and monitor tumors in a clinical imaging context. This dissertation supports the following three hypotheses: 1) A prototype dual-frequency ultrasound transducer can be used to depict in vivo microvasculature, 2) These microvascular images can be quantitatively assessed as a means to characterize the presence of a tumor, and evaluate tumor response to therapy, and 3) Radiation force can be used as a method to improve ultrasonic diagnostic sensitivity to the presence of a tumor.Doctor of Philosoph

Magnetic Navigation in Percutaneous Cardiac Intervention

Magnetic navigation is the use of a magnetic fi eld to re-orientate a magnetically-enabled wire or device. The fi eld is directed by external magnets that are moved by a computercontrolled system. This technology could improve percutaneous coronary interventional procedures as it improves 3 specifi c and complementary capabilities, namely precise tip adjustability, computer-enhanced, image-guided tip orientation, and computer–enhanced image processing. Although this technology is relatively new, it already appears that this system can equal, and even improve on, current conventional wire technique. The current usability, combined with the exciting potential of future developments, could result in a formidable adjunct to PCI. This thesis deals with the early use of the system, development of diff erent strategies for the exploitation of the unique novel features that the system has. Specifi cally it will describe a number of areas. 1. Background, history and system description: The aim of this introduction is to provide a brief description of the background of magnetic procedures with respect to Stereotaxis Inc, and a description of the magnetic moment, and a short description of the current system together with the specially-produced wires. 2. Feasibility in phantom models, and initial system development: This section deals with aspects related to feasibility of use, validation of the software, and initial experience in diff erent clinical situations and fi nally with the potential use in treating one of the sequelae of coronary disease i.e. poor left ventricular function by the possible delivery of cardiac stem cells. 3. Initial experience in clinical practice and illustrative case reports: This section deals with the clinical use in percutaneous coronary intervention concentrating on the initial patient studies. 4. Investigation of benefi ts in subgroups: This section concentrates on particular subsets of coronary intervention patients and the specifi c hypotheses that can be drawn from these

Imaging fascicular organisation in mammalian vagus nerve for selective VNS

Nerves contain a large number of nerve fibres, or axons, organised into bundles known as fascicles. Despite the somatic nervous system being well understood, the organisation of the fascicles within the nerves of the autonomic nervous system remains almost completely unknown. The new field of bioelectronics medicine, Electroceuticals, involves the electrical stimulation of nerves to treat diseases instead of administering drugs or performing complex surgical procedures. Of particular interest is the vagus nerve, a prime target for intervention due to its afferent and efferent innervation to the heart, lungs and majority of the visceral organs. Vagus nerve stimulation (VNS) is a promising therapy for treatment of various conditions resistant to standard therapeutics. However, due to the unknown anatomy, the whole nerve is stimulated which leads to unwanted off-target effects. Electrical Impedance Tomography (EIT) is a non-invasive medical imaging technique in which the impedance of a part of the body is inferred from electrode measurements and used to form a tomographic image of that part. Micro-computed tomography (microCT) is an ex vivo method that has the potential to allow for imaging and tracing of fascicles within experimental models and facilitate the development of a fascicular map. Additionally, it could validate the in vivo technique of EIT. The aim of this thesis was to develop and optimise the microCT imaging method for imaging the fascicles within the nerve and to determine the fascicular organisation of the vagus nerve, ultimately allowing for selective VNS. Understanding and imaging the fascicular anatomy of nerves will not only allow for selective VNS and the improvement of its therapeutic efficacy but could also be integrated into the study on all peripheral nerves for peripheral nerve repair, microsurgery and improving the implementation of nerve guidance conduits. Chapter 1 provides an introduction to vagus nerve anatomy and the principles of microCT, neuronal tracing and EIT. Chapter 2 describes the optimisation of microCT for imaging the fascicular anatomy of peripheral nerves in the experimental rat sciatic and pig vagus nerve models, including the development of pre-processing methods and scanning parameters. Cross-validation of this optimised microCT method, neuronal tracing and EIT in the rat sciatic nerve was detailed in Chapter 3. Chapter 4 describes the study with microCT with tracing, EIT and selective stimulation in pigs, a model for human nerves. The microCT tracing approach was then extended into the subdiaphragmatic branches of the vagus nerves, detailed in Chapter 5. The ultimate goal of human vagus nerve tracing was preliminarily performed and described in Chapter 6. Chapter 7 concludes the work and describes future work. Lastly, Appendix 1 (Chapter 8) is a mini review on the application of selective vagus nerve stimulation to treat acute respiratory distress syndrome and Appendix 2 is morphological data corresponding to Chapter 4

Minimally invasive therapies for the brain using magnetic particles

Delivering a therapy with precision, while reducing off target effects is key to the success of any novel therapeutic intervention. This is of most relevance in the brain, where the preservation of surrounding healthy tissue is crucial in reducing the risk of cognitive impairment and improving patient prognosis. Our scientific understanding of the brain would also benefit from minimally invasive investigations of specific cell types so that they may be observed in their most natural physiological environment. Magnetic particles based techniques have the potential to deliver cellular precision in a minimally invasive manner. When inside the body, Magnetic particles can be actuated remotely using externally applied magnetic fields while their position can be detected non-invasively using MRI. The magnetic forces applied to the particles however, rapidly decline with increasing distance from the magnetic source. It is therefore critical to understand the amount of force needed for a particular application. The properties of the magnetic particle such as the size, shape and magnetic content, as well as the properties of the applied magnetic field, can then be tailored to that application. The aim of this thesis was to develop magnetic particle based techniques for precise manipulation of cells in the brain. Two different approaches were explored, utilising the versatile nature of magnetic actuation for two different applications. The first approach uses magnetic nanoparticles to mechanically stimulate a specific cell type. Magnetic particles conjugated with the antibody ACSA-1 would selectively bind to astrocytes to evoke the controlled release of ATP and induce a calcium flux which are used for communication with neighbouring cells. This approach allows for the investigation into the role of astrocytes in localised brain regions using a naturally occurring actuation process (mechanical force) without effecting their natural environment. The second approach uses a millimetre sized magnetic particle which can be navigated through the brain and ablate localised regions of cells using a magnetic resonance imaging system. The magnetic particle causes a distinct contrast in MRI images, allowing for precise detection of its location so that it may be iteratively guided along a pre-determined path to avoid eloquent brain regions. Once at the desired location, an alternating magnetic field can be applied causing the magnetic particle to heat and deliver controllable, well defined regions of cell death. The forces needed for cell stimulation are orders of magnitude less than the forces needed to guide particles through the brain. Chapters 4 and 5 use external magnets to deliver forces in the piconewton range. While stimulation was demonstrated in small animals, scaling up this technique to human proportions remains a challenge. Chapters 6 and 7 use a preclinical MRI system to generate forces in the millinewton range, allowing the particle to be moved several centimetres through the brain within a typical surgical timescale. When inside the scanner, an alternating magnetic field causes the particle to heat rapidly, enabling the potential for multiple ablations within a single surgery. For clinical translation of this technique, MRI scanners would require a dedicated propulsion gradient set and heating coil