3,562 research outputs found

    Effect of skin color on optical properties and the implications for medical optical technologies: a review

    Get PDF
    Significance: Skin color affects light penetration leading to differences in its absorption and scattering properties. COVID-19 highlighted the importance of understanding of the interaction of light with different skin types, e.g., pulse oximetry (PO) unreliably determined oxygen saturation levels in people from Black and ethnic minority backgrounds. Furthermore, with increased use of other medical wearables using light to provide disease information and photodynamic therapies to treat skin cancers, a thorough understanding of the effect skin color has on light is important for reducing healthcare disparities.Aim: The aim of this work is to perform a thorough review on the effect of skin color on optical properties and the implication of variation on optical medical technologies.Approach: Published in vivo optical coefficients associated with different skin colors were collated and their effects on optical penetration depth and transport mean free path (TMFP) assessed.Results: Variation among reported values is significant. We show that absorption coefficients for dark skin are ∼6% to 74% greater than for light skin in the 400 to 1000 nm spectrum. Beyond 600 nm, the TMFP for light skin is greater than for dark skin. Maximum transmission for all skin types was beyond 940 nm in this spectrum. There are significant losses of light with increasing skin depth; in this spectrum, depending upon Fitzpatrick skin type (FST), on average 14% to 18% of light is lost by a depth of 0.1 mm compared with 90% to 97% of the remaining light being lost by a depth of 1.93 mm.Conclusions: Current published data suggest that at wavelengths beyond 940 nm light transmission is greatest for all FSTs. Data beyond 1000 nm are minimal and further study is required. It is possible that the amount of light transmitted through skin for all skin colors will converge with increasing wavelength enabling optical medical technologies to become independent of skin color

    Radiotherapy dosimetry with ultrasound contrast agents

    Get PDF

    Synthesis of multifunctional glyco-pseudodendrimers and glyco-dendrimers and their investigation as anti-Alzheimer agents

    Get PDF
    As the world population is aging, the cases of Alzheimer’s Disease (AD) are increasing. AD is a disorder of the brain which is characterized by the aggregation of amyloid beta (Aβ) plaques. This leads to the death of numerous brain cells thus affecting the cognitive and motor functions of the individual. Till date, no cure for the disease is available. Aβ are peptides with 40/42 amino acid residues but, their exact mechanism(s) of action in AD is under debate. Having different amino acid residues makes them susceptible to form hydrogen bonds. Dendrimers with sugar units are often referred to as glycopolymers and have been shown to have potential anti-amyloidogenic activity. However, they also have drawbacks, the synthesis involves multiple tedious steps, and dendrimers themselves offer only a limited number of functional units. Pseudodendrimers are another class of branched polymers based on hyperbranched polymers. Unlike the dendrimers, they are easy to synthesize with a dense shell of functional units on the surface. One of the main goals in this dissertation is the synthesis and characterization of pseudodendrimers and dendrimers based on 2,2-bis(hydroxymethyl)-propionic acid (bis-MPA), an aliphatic polyester scaffold, as it offers biocompatibility and easy degradability. Furthermore, they are decorated with mannose units on the surface using a ‘click’ reaction forming glyco-pseudodendrimers and glyco-dendrimers. A detailed characterization of their structures and physical properties was undertaken using techniques such as size exclusion chromatography, asymmetric flow field flow fractionation (AF4), and dynamic light scattering. The second main focus of this work has been to investigate the interaction of synthesized glyco-pseudodendrimers and glyco-dendrimers with Aβ 40 peptides. For this task, five different concentrations of the synthesized glycopolymers were tested with Aβ 40 using the Thioflavin T assay. The results of the synthesized polymers which produced the best results of showing maximum anti-aggregation behavior against Aβ 40 were confirmed with circular dichroism spectroscopy. AF4 was also used to investigate Aβ 40-glycopolymer aggregates, which has never been done before and constitutes the highlight of this dissertation. Atomic force microscopy was used to image Aβ 40-glycopseudodenrimer aggregates. A basic but important step in the development of drug delivery platforms is to evaluate the toxicity of the drugs synthesized. In this work, preliminary studies of the cytotoxicity of glyco-pseudodendrimers were performed in two different cell lines. Thus, this study comprises a preliminary investigation of the anti-amyloidogenic activity of glyco-pseudodendrimers synthesized on an aliphatic polyester backbone.:Abstract List of Tables List of Figures Abbreviations 1 Introduction 1.1 Objectives of the work 1.2 Thesis overview 2 Fundamentals and Literature 2.1 Alzheimer’s Disease and its impact 2.1.1 Neurological diagnosis of AD 2.1.2 Histopathology of AD 2.1.3 Amyloid precursor protein (APP) and its role in AD 2.2. Amyloid Beta (Aβ) peptide 2.2.1 Aβ peptide 2.2.2. Location and function 2.2.3 Amyloid hypothesis 2.2.4 The mechanism of Aβ aggregation 2.2.5 Amyloid fibrils 2.2.6 Toxicity of Aβ 2.3 Research methods to study Aβ aggregates 2.3.1 Models to study the mode of action of aggregates 2.3.2 Endogenous Aβ aggregates and synthetic aggregates 2.3.3 Strategies to alter aggregation of amyloids 2.4 Treatment and therapeutics 2.4.1 Current therapeutics 2.4.2 Current therapeutic research 2.4.2.1 Reduction of Aβ production 2.4.2.2 Reduction of Aβ plaque accumulation 2.4.2.2.1 Anti-amyloid aggregation agents 2.4.2.2.2 Metals 2.4.2.2.3 Immunotherapy 2.4.2.2.4 Dendrimers as potential anti-amyloidogenic agent 2.6 Dendrimers 2.6.1 Definition 2.6.2 Structure Table of Contents 2.6.3 Synthesis 2.6.4 Properties 2.7 Pseudodendrimers - a sub-class of hyperbranched polymer 2.7.1 Definition 2.7.2 Structure 2.7.3 Synthesis 3 Analytical Techniques 3.1 Size Exclusion Chromatography Coupled to Light Scattering (SEC-MALS) 3.2 Asymmetric Flow Field Flow Fractionation (AF4) 3.3 Dynamic Light Scattering 3.4 Molecular Dynamics Simulation 3.5 Nuclear Magnetic Resonance Spectroscopy 3.6 Thioflavin T fluorescence 3.6.1 Kinetic analysis 3.7 Circular Dichroism Spectroscopy 3.8 Atomic Force Microscopy 3.9 Cytotoxic assay 3.9.1 MTT assay 3.9.2 Determining the level of reactive oxygen species 3.9.3 Changes in mitochondrial transmembrane potential 3.9.4 Flow cytometric detection of phosphatidyl serine exposure 4 Experimental Details and Methodology 4.1 Details of chemicals/components used 4.1.1 Other materials 4.1.2 Peptide preparation 4.1.3 Buffer preparation 4.1.4 Fibril growth conditions 4.2 Synthesis and characterization of polymers 4.2.1 Synthesis and characterization of pseudodendrimers and dendrimers 4.2.1.1 Synthesis of hyperbranched polymer (1) 4.2.1.2 Synthesis of protected monomer 4.2.1.2.1 bis-MPA acetonide (2) 4.2.1.2.2 bis-MPA-acetonide anhydride (3) 4.2.1.3 Synthesis of protected pseudodendrimers (4, 6 and 8) and protected dendrimers (10, 12, and 14) 4.2.1.4 Deprotection of pseudodendrimers (5,7, and 9) and dendrimers (11,13 and 15) 4.2.2 Synthesis of glyco-pseudodendrimers and glyco-dendrimers 4.2.2.1 Pentynoic anhydride (16) 4.2.2.2 Synthesis of pentinate modified pseudodendrimers (17, 18 and 19) and dendrimers (20, 21 and 22) 4.2.2.3 3-Azido-1-propanol (23) 4.2.2.4 Mannose propyl azide tetraacetate (24) Table of Contents 4.2.2.5 Mannosepropylazide (25) 4.2.2.6 Glyco-pseudodendrimers (Gl-P) (26, 27 and 28) and glyco- dendrimers (Gl-D) (29, 30 and 31) 4.3 Analytical techniques and their general details 4.3.1 SEC-MALS - Instrumentation, software and analysis 4.3.2 AF4 - Instrumentation, software and analysis 4.3.2.1 Sample preparation 4.3.2.2 Method development for analysis of Gl-P and Gl-D 4.3.2.3 Method development for analysis of Aβ 40 and its interaction with Gl-P and Gl-D 4.3.3 Batch DLS - Instrumentation, software and analysis 4.3.3.1 Sample preparation 4.3.4 Theoretical calculations and molecular dynamics simulations 4.3.4.1 Ab-initio calculations 4.3.4.2 Modelling of the polymer structures 4.3.4.2.1 Pseudodendrimers 4.3.4.2.2 Dendrimers 4.3.4.2.3 Modification of the polymers with special end groups 4.3.4.2.4 Preparing of the THF solvent box 4.3.4.2.5 Solvation of the polymer structures 4.3.4.3 Molecular dynamics simulations 4.3.4.3.1 Evaluation of the simulation trajectories 4.4 Investigation of interaction of Gl-P and Gl-D with amyloid beta (Aβ 40) 4.4.1 ThT Assay - Instrumentation and software 4.4.1.1 Sample preparation 4.4.1.2 Kinetics based on ThT assay- software and data analysis 4.4.2 CD spectroscopy - Instrumentation and software 4.4.2.1 Sample preparation 4.4.3 AFM - Instrumentation and software 4.4.3.1 Substrate and sample preparation 4.4.3.2 Height determination and counting procedures 4.4.3.3 Topography and diameter 4.5 Cytotoxicity 4.5.1 Zeta potential 4.5.2 Cell culturing 4.5.3 Sample preparation 4.5.4 MTT assay 4.5.5 Changes in mitochondrial transmembrane potential (JC-1 method) 4.5.6 Flow cytometric detection of phosphatidyl serine exposure (Annexin V and PI method) 5 Results and Discussion 5.1 Synthesis and characterization of glyco-pseudodendrimers and glyco- dendrimers 5.1.1 Synthesis and characterization of hyperbranched polyester Table of Contents 5.1.2 Synthesis and characterization of pseudodendrimers P-G1-OH, P-G2-OH and P-G3-OH 5.1.3 Synthesis and characterization of dendrimers D-G4-OH, D-G5-OH and D-G6-OH 5.1.4 Synthesis and characterization of Gl-P and Gl-D 5.1.4.1 Molecular size determination of Gl-P and Gl-D using SEC 5.1.4.2 Particle size determination using batch DLS 5.1.4.3 Apparent densities 5.1.4.4 Molecular size determination of Gl-P and Gl-D using AF4 ..... 5.1.5 Molecular dynamics simulation 5.2 Investigation of interaction of Gl-P and Gl-D with amyloid beta (Aβ 40) ...... 5.2.1 ThT Assay 5.2.1.1 Kinetics based on ThT assay 5.2.2 CD spectroscopy 5.2.3 Time dependent AF4 5.3.2.1 Separation of Aβ 40 by AF4 5.3.2.2 Aβ 40 amyloid aggregation in the presence of Gl-P and Gl-D 5.2.4 AFM 5.2.4.1 Height 5.2.4.2 Topography and diameter 5.2.4.3 Length 5.2.4.4 Morphology 5.2.5 Cytotoxicity 5.2.5.1 MTT assay 5.2.5.2 Changes in mitochondrial transmembrane potential 5.2.5.3 Flow cytometric detection of phosphatidyl serine exposure 6 Conclusions and Outlook 7 Bibliography Appendix Acknowledgement

    AI: Limits and Prospects of Artificial Intelligence

    Get PDF
    The emergence of artificial intelligence has triggered enthusiasm and promise of boundless opportunities as much as uncertainty about its limits. The contributions to this volume explore the limits of AI, describe the necessary conditions for its functionality, reveal its attendant technical and social problems, and present some existing and potential solutions. At the same time, the contributors highlight the societal and attending economic hopes and fears, utopias and dystopias that are associated with the current and future development of artificial intelligence

    Image-based Decision Support Systems: Technical Concepts, Design Knowledge, and Applications for Sustainability

    Get PDF
    Unstructured data accounts for 80-90% of all data generated, with image data contributing its largest portion. In recent years, the field of computer vision, fueled by deep learning techniques, has made significant advances in exploiting this data to generate value. However, often computer vision models are not sufficient for value creation. In these cases, image-based decision support systems (IB-DSSs), i.e., decision support systems that rely on images and computer vision, can be used to create value by combining human and artificial intelligence. Despite its potential, there is only little work on IB-DSSs so far. In this thesis, we develop technical foundations and design knowledge for IBDSSs and demonstrate the possible positive effect of IB-DSSs on environmental sustainability. The theoretical contributions of this work are based on and evaluated in a series of artifacts in practical use cases: First, we use technical experiments to demonstrate the feasibility of innovative approaches to exploit images for IBDSSs. We show the feasibility of deep-learning-based computer vision and identify future research opportunities based on one of our practical use cases. Building on this, we develop and evaluate a novel approach for combining human and artificial intelligence for value creation from image data. Second, we develop design knowledge that can serve as a blueprint for future IB-DSSs. We perform two design science research studies to formulate generalizable principles for purposeful design — one for IB-DSSs and one for the subclass of image-mining-based decision support systems (IM-DSSs). While IB-DSSs can provide decision support based on single images, IM-DSSs are suitable when large amounts of image data are available and required for decision-making. Third, we demonstrate the viability of applying IBDSSs to enhance environmental sustainability by performing life cycle assessments for two practical use cases — one in which the IB-DSS enables a prolonged product lifetime and one in which the IB-DSS facilitates an improvement of manufacturing processes. We hope this thesis will contribute to expand the use and effectiveness of imagebased decision support systems in practice and will provide directions for future research

    The 2023 wearable photoplethysmography roadmap

    Get PDF
    Photoplethysmography is a key sensing technology which is used in wearable devices such as smartwatches and fitness trackers. Currently, photoplethysmography sensors are used to monitor physiological parameters including heart rate and heart rhythm, and to track activities like sleep and exercise. Yet, wearable photoplethysmography has potential to provide much more information on health and wellbeing, which could inform clinical decision making. This Roadmap outlines directions for research and development to realise the full potential of wearable photoplethysmography. Experts discuss key topics within the areas of sensor design, signal processing, clinical applications, and research directions. Their perspectives provide valuable guidance to researchers developing wearable photoplethysmography technology
    • …
    corecore