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1869 results in Biomedical engineering

Page 48 of 94

  • 12 - Drug delivery systems

  • C. Mauli Agrawal, University of Texas, San Antonio, Joo L. Ong, University of Texas, San Antonio, Mark R. Appleford, University of Texas, San Antonio, Gopinath Mani, University of South Dakota
  • Book:
    Introduction to Biomaterials
    Published online:
    01 February 2019
    Print publication:
    07 November 2013, pp 321-340

  • Summary

    Goals

    After reading this chapter the student should understand the following.

  • The fundamentals and importance of drug delivery systems.

  • How various different types of controlled drug delivery systems work.

    • Therapeutic drugs play a significant role in the therapy of almost all medical problems. From the treatment of common ailments such as headaches, and colds, to the reduction of fever, fighting infection, reducing cholesterol and blood pressure, and treating cancer, drugs play a major role in medicine. The systems used for delivering drugs take on a variety of forms. These include simple oral systems such as tablets, capsules, and syrups, transdermal systems like ointments and patches, and intravenous delivery using suspensions or nanoparticles.

    In order for a drug to provide a therapeutic effect, the concentration of the drug in the blood plasma has to be above the minimum effective level and below the level that may be toxic. The difference between the minimum effective level and the toxic level is called the therapeutic index. As shown in Figure 12.1a, when the drug is conventionally administered as a single dose and is metabolized quickly inside the body, the level of drug in the blood plasma immediately increases followed by an exponential decrease. In such a conventional administration of the drug, the time frame over which the drug concentration is above the minimum effective level may not be long enough to produce a significant therapeutic effect in a single dose. Although this situation can be improved by increasing the amount of dose, this quickly raises the drug level to the toxic region. The alternative is to administer doses at regular intervals (Figure 12.1b). However, this method too has limitations, such as:

  • the drug level in blood plasma is irregular and fluctuates with a high ratio of peak-tovalley concentrations, and

  • the patient compliance is often poor.

  • 6 - Polymers

  • C. Mauli Agrawal, University of Texas, San Antonio, Joo L. Ong, University of Texas, San Antonio, Mark R. Appleford, University of Texas, San Antonio, Gopinath Mani, University of South Dakota
  • Book:
    Introduction to Biomaterials
    Published online:
    01 February 2019
    Print publication:
    07 November 2013, pp 134-164

  • Summary

    Goals

    After reading this chapter the student will understand the following.

  • Structure of polymers and their common physical states.

  • General properties of polymers.

  • Common types of polymerization techniques used for production.

  • Chemical structure and properties of common biomedical polymers.

  • Structure of hydrogels and their general properties.

  • Definition and uses of nanopolymers.

    • In everyday life, we encounter a variety of polymers, some natural and others synthetic. The vast majority of these are carbon-based in nature. They range from synthetic polymers seen in products such as polyethylene grocery bags, polymethylmethacrylate-based window panes, and polystyrene-based eating utensils, to natural polymers such as starch, cellulose and rubber. Polymers used as biomaterials are often similar to these common materials. For example, the polymer most extensively used in total joint prostheses is ultrahigh molecular weight polyethylene – chemically identical to the material used for plastic bags, although having a much higher molecular weight. The same is true for bone cement which is used in conjunction with bone surgery and Plexiglass®, which is used for window panes. Both of these materials are polymethylmethacrylate (PMMA). Of course, any polymer that is used as an implant has to meet strict safety standards as required by governmental and other regulatory agencies and has to be virtually contaminant free.

  • 10 - Sterilization of biomedical implants

  • C. Mauli Agrawal, University of Texas, San Antonio, Joo L. Ong, University of Texas, San Antonio, Mark R. Appleford, University of Texas, San Antonio, Gopinath Mani, University of South Dakota
  • Book:
    Introduction to Biomaterials
    Published online:
    01 February 2019
    Print publication:
    07 November 2013, pp 282-294

  • Summary

    Goals

    After reading this chapter, students should understand the following.

  • Fundamentals and importance of sterilization.

  • Different types of sterilization methods commonly used.

  • Principles behind determining the type of sterilization method suitable for an application.

    • The world around us is full of microorganisms such as bacteria, fungi, and viruses. These microorganisms are present in the atmosphere, on the surface of all objects, and even on our own skin. In the process of manufacturing an implantable medical device, there is always a possibility of contaminating the device surface with microorganisms. As required by regulatory agencies such as the Food and Drug Administration (FDA), it is mandatory to sterilize all devices prior to implantation. The goal of sterilization is to render the implant devoid of all potential infection-causing organisms, making it one of the most important steps in the manufacturing process of biomedical devices. In this chapter, the basic terminology associated with sterilization such as bioburden and sterility assurance level is explained. In addition, commonly employed sterilization methods such as steam sterilization, ethylene oxide sterilization, and gamma radiation sterilization are described along with various other new and old sterilization methods. The suitability of these methods for sterilizing different biomaterials is also discussed.

  • 2 - Basic properties of materials

  • C. Mauli Agrawal, University of Texas, San Antonio, Joo L. Ong, University of Texas, San Antonio, Mark R. Appleford, University of Texas, San Antonio, Gopinath Mani, University of South Dakota
  • Book:
    Introduction to Biomaterials
    Published online:
    01 February 2019
    Print publication:
    07 November 2013, pp 19-47

  • Summary

    Goals

    After reading this chapter the student will understand the following.

  • The mechanical properties and behavior of materials.

  • Material failure under ductile or brittle conditions.

  • The time-dependent mechanical behavior of materials.

  • Corrosion and its various forms.

  • Concepts related to the basic surface properties of materials.

    • In everyday life, we often define materials using relative terms such as soft or hard, flexible or rigid, strong or weak, tough or brittle, and in a variety of other qualitative ways. What do these terms really mean in the world of engineering? Is such qualitative categorization sufficient for the design and manufacture of a product? The answer is definitely a no, especially when human health or lives may depend on the product. For example, you certainly would not want engineers who are building bridges to pick materials based on such relative and qualitative descriptions! Choices based on much more rigorous, scientific, and quantitative characterization would be expected. The same is true when selecting biomaterials.

    Material properties can be characterized quantitatively using standardized tests under defined conditions. Once characterized, these properties can be used in conjunction with engineering design techniques to predict the behavior of the engineered product under the expected operating conditions and to ensure that it would function safely. This is important because properties may change based on independent variables such as temperature or rate of application of force. Often a variety of material properties need to be considered for each product.

  • 3 - Biological systems

  • C. Mauli Agrawal, University of Texas, San Antonio, Joo L. Ong, University of Texas, San Antonio, Mark R. Appleford, University of Texas, San Antonio, Gopinath Mani, University of South Dakota
  • Book:
    Introduction to Biomaterials
    Published online:
    01 February 2019
    Print publication:
    07 November 2013, pp 48-73

  • Summary

    Goals

    After reading this chapter, students will understand the following.

  • Key terms such as homeostasis, reductionism, flow, and flux in terms of biological systems.

  • Fick’s first law of diffusion and how it is useful for cellular interaction with biomaterials.

  • The principal functions of the plasma membrane.

  • The major classes and operations of cell junctions.

  • Cell signaling pathways and secondary messengers.

  • Commonly used biological testing techniques in biology–material interactions.

    • The biological environment

    One of the most basic principles of systems biology is the concept of reductionism where behavior of a “whole” can be explained by the corresponding behavior of its “parts.” By successively deconstructing the organism and studying its components, biologists can explain the function of the body in terms of its organ systems, cells, subcellular organelles, macro- and biochemicals, and so forth until we reach fundamental particles. This concept of reductionism is among the most common techniques used to study biomaterials as we explore their influence at the biochemical, protein, cellular, and whole-organism levels. However, great care must be taken as reductionism leads to more and more missing information with each step taken. As an example, in vitro experimentation often lacks the cellular complexity and hormonal control of in vivo behavior and can lead to false or contradictory conclusions. Despite the limitations of reductionism, it is among our best tools for understanding and testing biomaterials when care is taken to identify the assumptions of each experiment and result. In this chapter, we will focus on the communication systems at the cellular level and its implications for biomaterials.

  • 8 - Natural biomaterials

  • C. Mauli Agrawal, University of Texas, San Antonio, Joo L. Ong, University of Texas, San Antonio, Mark R. Appleford, University of Texas, San Antonio, Gopinath Mani, University of South Dakota
  • Book:
    Introduction to Biomaterials
    Published online:
    01 February 2019
    Print publication:
    07 November 2013, pp 198-232

  • Summary

    Goals

    After reading this chapter, students will understand the following.

  • Properties that qualify natural biomaterials for biomedical applications.

  • Different major classifications of natural biomaterials.

  • Properties of various natural biomaterials.

    • What makes natural materials unique and piques the interest of biomaterials scientists, engineers and clinicians? There is a belief that all aspects of materials created naturally have a useful purpose or function. Utilization of such materials thus allows these materials to perform a combination of diverse functions such as intracellular communications and storage. In general, the properties of natural materials are dependent on their composition. For example, the physical–chemical properties of monomers and their sequences determine the properties of polymeric natural biomaterials. Like synthetic materials used for biomedical applications, it is expected that the natural biomaterials should satisfy requirements such as

  • being non-toxic,

  • being non-inflammatory,

  • being non-allergenic,

  • having satisfactory mechanical properties,

  • being capable of inducing cell attachment and differentiation if needed, and

  • having low cost.

    • Natural biomaterials possess most of the above properties because they are found in biological systems and work well within their respective environments. Favorable characteristics of natural materials include facilitating cell attachment, enhancing the mechanical properties of synthetic biomaterials, and their ability to bind and deliver macromolecules. These desirable characteristics allow natural materials to be used in various biomedical applications including tissue engineering and regenerative medicine. With the exception of corals, which are deposits of calcium carbonates, most of the common natural materials are polymeric in nature and are either protein-based or polysaccharide-based materials. Examples of protein-based natural polymers include collagen, gelatin, silk fibroin, fibrin, and elastin, whereas examples of polysaccharide-based natural polymers include chitosan, starch, alginate, hyaluronan, chondroitin sulfate, and dextran. In this chapter, we will discuss some of the natural biomaterials that are commonly used today in the fabrication of medical devices.

  • 11 - Cell–biomaterial interactions

  • C. Mauli Agrawal, University of Texas, San Antonio, Joo L. Ong, University of Texas, San Antonio, Mark R. Appleford, University of Texas, San Antonio, Gopinath Mani, University of South Dakota
  • Book:
    Introduction to Biomaterials
    Published online:
    01 February 2019
    Print publication:
    07 November 2013, pp 295-320

  • Summary

    Goals

    After reading this chapter, students will understand the following.

  • Key components of the extracellular space.

  • Principal proteins and pathways that cells utilize to interact with both cellular and non-cellular environments.

  • Adhesion mechanisms that bind cells to substrates and types of junctions found near biomaterials.

  • The role of this cell matrix environment in the success or failure of biomaterial integration.

    • How do cells, containing the same genetic information, diversify and give rise to so many types of tissue? This fundamental question of cell biology has a surprisingly simple answer: environment. Despite the incredible complexity of internal genetic control, cells rely equally on their surroundings to define their form and function. In the study of cell biology, the plasma membrane traditionally defines the boundary between the functional unit of the cell and its environment. The interactions that occur at this interface represent an exceedingly complex and highly organized series of reactions that permits the cell to send and receive biochemical signals across the membrane. Most eukaryotic cells define their structure and function based on these signals. Even for those cells that are not substrate bound, such as those of the circulating immune system, it is essential to sense and respond to biochemical gradients and interactions in the body. The availability, intensity, and duration of these gradients are the signals which direct cells into their most common activities, that is, migration, division, and differentiation. These activities provide the complexity of all cell response in the body and can specifically define the reaction to any material implanted.

  • Preface

  • C. Mauli Agrawal, University of Texas, San Antonio, Joo L. Ong, University of Texas, San Antonio, Mark R. Appleford, University of Texas, San Antonio, Gopinath Mani, University of South Dakota
  • Book:
    Introduction to Biomaterials
    Published online:
    01 February 2019
    Print publication:
    07 November 2013, pp xvii-xviii

  • Summary

    Preface

    Biomaterials have helped millions of people achieve a better quality of life in almost all corners of the world. Although the use of biomaterials has been common over many millennia, it was not until the twentieth century that the field of biomaterials finally gained recognition. With the advent of polymers, new processing and machining processes for metals and ceramics, and general advances in technology, there has been an exponential growth in biomaterials-related research and development activity over the past few decades. This activity has led to a plethora of biomaterials-based medical devices, which are now commercially available.

    For students in the area of biomaterials, this is an especially exciting time. On the one hand, they have the opportunity to meet and learn from some of the stalwarts and pioneers of the field such as Sam Hulbert, one of the founders of the Society for Biomaterials (SFB). Other greats include Allan Hoffman and Buddy Ratner (biomaterials surfaces), Robert Langer (polymers and tissue engineering), Nicholas Peppas (hydrogels), Jack Lemons (orthopedic/dental implants), Joseph Salamone (contact lenses), and Julio Palmaz (intracoronary stents). Most of these individuals are still active in research and teaching. The authors of this book have been privileged to interact and learn from them in various forums, and students today have the same opportunities. On the other hand, with the current availability of sophisticated processing and characterization technologies, present day students also have the tools to take the field to unprecedented new levels of innovation.

  • 7 - Ceramics

  • C. Mauli Agrawal, University of Texas, San Antonio, Joo L. Ong, University of Texas, San Antonio, Mark R. Appleford, University of Texas, San Antonio, Gopinath Mani, University of South Dakota
  • Book:
    Introduction to Biomaterials
    Published online:
    01 February 2019
    Print publication:
    07 November 2013, pp 165-197

  • Summary

    Goals

    After reading this chapter, students will understand the following.

  • The general definition of a ceramic.

  • Common properties of ceramics.

  • Different classifications used for ceramics.

  • Properties of different bioceramics.

  • Different technologies used for fabricating nanoceramics.

    • The use of ceramics in medicine dates back many centuries, with reports of artificial teeth found in Egyptian mummies. Besides ceramics developed for medical applications, other engineering ceramics include semiconductors, dielectrics, high temperature superconductors, magnets, and piezoelectrics. However, what is a ceramic? In general, a ceramic is defined as an inorganic, non-metallic material that consists of two or more metallic and non-metallic elements. Unlike metals and polymers, which comprise mainly of metallic and covalent bonding, respectively, ceramics are made up of ionic and covalent bonding.

    Depending on the atomic arrangements, ceramics can either exist as amorphous or crystalline structures. An example of an amorphous ceramic is glass, whereas an example of a crystalline ceramic is porcelain. In an amorphous structure, the atoms are arranged randomly or with high degree of short-range order and absence of long-range order. A short-range order refers to the tendency for an ordered atomic arrangement within one or two atom spacings, whereas a long-range order refers to an ordered atomic arrangement over a larger distance. Figure 7.1a shows a schematic drawing of a non-crystalline (glass) silicon dioxide, with random, short-range order atomic arrangement. As an example of the long-range order observed in crystalline ceramics, Figure 7.1b shows a schematic drawing of a crystalline silicon dioxide, with atoms arranged in an ordered pattern.

  • 13 - Tissue engineering

  • C. Mauli Agrawal, University of Texas, San Antonio, Joo L. Ong, University of Texas, San Antonio, Mark R. Appleford, University of Texas, San Antonio, Gopinath Mani, University of South Dakota
  • Book:
    Introduction to Biomaterials
    Published online:
    01 February 2019
    Print publication:
    07 November 2013, pp 341-374

  • Summary

    Goals

    After reading this chapter the student will understand the following.

  • Basic fundamentals of tissue engineering.

  • Different cell types pertinent to tissue regeneration.

  • Typical scaffold fabrication techniques.

  • Techniques used to evaluate scaffolds, cells growing on scaffolds, and neo-tissue.

    • Can cells be used as living materials to engineer organs and tissue? Over the past several decades there has been increasing interest within the biomedical field to develop methodologies to restore the function of damaged tissue or organs without the use of long-term implants. This has led to the advent of the field of tissue engineering, which is often described as “an interdisciplinary field that applies the principles of engineering and life sciences toward the development of biological substitutes that restore, maintain, or improve tissue function or a whole organ.” Initially tissue engineering was considered a sub-field of biomaterials but has now evolved into its own distinct area. Nevertheless, although the role of biological sciences has significantly increased in tissue engineering, the field has stayed closely related to biomaterials.

    Box 13.1

  • Every year thousands of human lives are lost due to a lack of organs available for transplantation. Successful tissue engineering can solve this problem by re-growing the patients’ own organs.

  • Successful tissue engineering can also potentially provide skin for burn victims and repair nerves and restore function to those paralyzed.

Brain-Computer Interfacing
  • An Introduction
  • Rajesh P. N. Rao
  • Published online:
    05 October 2013
    Print publication:
    30 September 2013
  • The idea of interfacing minds with machines has long captured the human imagination. Recent advances in neuroscience and engineering are making this a reality, opening the door to restoration and augmentation of human physical and mental capabilities. Medical applications such as cochlear implants for the deaf and neurally controlled prosthetic limbs for the paralyzed are becoming almost commonplace. Brain-computer interfaces (BCIs) are also increasingly being used in security, lie detection, alertness monitoring, telepresence, gaming, education, art, and human augmentation. This introduction to the field is designed as a textbook for upper-level undergraduate and first-year graduate courses in neural engineering or brain-computer interfacing for students from a wide range of disciplines. It can also be used for self-study and as a reference by neuroscientists, computer scientists, engineers, and medical practitioners. Key features include questions and exercises in each chapter and a supporting website.

  • 12 - Applications of BCIs

  • from Part IV - Applications and Ethics
  • Rajesh P. N. Rao, University of Washington
  • Book:
    Brain-Computer Interfacing
    Published online:
    05 October 2013
    Print publication:
    30 September 2013, pp 239-271

  • Summary

    In this chapter, we explore the range of applications for BCI technology. We have already touched upon some medical applications such as restoration of lost motor and sensory function when we examined invasive and noninvasive BCIs in previous chapters. Here we briefly review these applications before exploring applications in other areas such as entertainment, robotic control, gaming, security, and art.

    Medical Applications

    The field of brain-computer interfacing originated with the goal of helping the paralyzed and the disabled. It is therefore not surprising that some of the major applications of BCIs to date have been in medical technology, particularly restoring sensory and motor function.

    Sensory Restoration

    One of the most widely used commercial BCIs is the cochlear implant for the deaf,discussed in Section 10.1.1. The cochlear implant is an example of a BCI for sensoryrestoration, as are retinal implants being developed for the blind (Section 10.1.2).

    There has not been much research on two other possible types of purely sensoryBCIs, namely, BCIs for somatosensation and BCIs for olfaction and taste. In the caseof the former, the need for a BCI is minimized because it is ot en possible to restoretactile sensation through skin grafting. However, as we saw in Chapter 11, there isconsiderable interest in somatosensory stimulation as a component of bidirectionalBCIs for allowing paralyzed individuals and amputees to, for example, sense objectsbeing grasped or touched by prosthetic devices.

  • 4 - Signal Processing

  • from Part I - Background
  • Rajesh P. N. Rao, University of Washington
  • Book:
    Brain-Computer Interfacing
    Published online:
    05 October 2013
    Print publication:
    30 September 2013, pp 39-70

  • Summary

    In this chapter, we review the signal-processing methods applied to recorded brain signals in BCIs for tasks ranging from extracting spikes from the raw signals recorded from invasive electrodes to extracting features for classification. For many of the techniques, we use EEG as the noninvasive recording modality to illustrate the concepts involved, although the techniques could be applied to signals from other sources as well such as ECoG and MEG.

    Spike Sorting

    Invasive approaches to brain-computer interfacing typically rely on recording spikes from an array of microelectrodes. The goal of signal-processing methods for such an input signal is to reliably isolate and extract the spikes being emitted by a single neuron per recording electrode. This procedure is usually called spike sorting.

    The signal recorded by an extracellular electrode implanted in the brain is typicallya mixture of signals from several neighboring neurons, with spikes from closerneurons producing larger amplitude del ections in the recorded signal. h is signalis ot en referred to as multiunit hash or neural hash (Figure 4.1A). Although hashcould also potentially be used as input to brain- computer interfaces, the more traditionalform of input is spikes from individual neurons. Spike sorting methods allowspikes from a single neuron to be extracted from hash.

  • 1 - Introduction

  • Rajesh P. N. Rao, University of Washington
  • Book:
    Brain-Computer Interfacing
    Published online:
    05 October 2013
    Print publication:
    30 September 2013, pp 1-4

  • Summary

    Our brains evolved to control a complex biological device: our body. As we are finding out today, many millennia of evolutionary tinkering has made the brain a surprisingly versatile and adaptive system, to the extent that it can learn to control devices that are radically different from our body. Brain-computer interfacing, the subject of this book, is a new interdisciplinary field that seeks to explore this idea by leveraging recent advances in neuroscience, signal processing, machine learning, and information technology.

    The idea of brains controlling devices other than biological bodies has long been a staple of science-fiction novels and Hollywood movies. However, this idea is fast becoming a reality: in the past decade, rats have been trained to control the delivery of a reward to their mouths, monkeys have moved robotic arms, and humans have controlled cursors and robots, all directly through brain activity.

    What aspects of neuroscience research have made these advances possible? Whatare the techniques in computing and machine learning that are allowing brains tocontrol machines? What is the current state-of-the-art in brain-computer interfaces(BCIs)? What limitations still need to be overcome to make BCIs more commonplaceand useful for day-to-day use? What are the ethical, moral, and societal implicationsof BCIs? These are some of the questions that this book addresses.

  • 10 - BCIs that Stimulate

  • from Part III - Major Types of BCIs
  • Rajesh P. N. Rao, University of Washington
  • Book:
    Brain-Computer Interfacing
    Published online:
    05 October 2013
    Print publication:
    30 September 2013, pp 210-220

  • Summary

    We have thus far focused on BCIs that record signals from the brain and transform those signals to a control signal for an external device. In this chapter, we reverse the direction of control and discuss BCIs that can be used to stimulate and control specific brain circuits. Some of these BCIs have made the transition from the lab to the clinic and are currently being used by human subjects, such as cochlear implants and deep brain stimulators (DBS), while others are still in experimental stages. We divide these BCIs broadly into two classes: BCIs for sensory restoration and BCIs for motor restoration. We also consider the possibility of sensory augmentation.

    Restoring Hearing: Cochlear Implants

    One of the most successful BCI devices to date is the cochlear implant for restoring or enabling hearing in the deaf. The implant is a good example of how one can convert knowledge of information processing in a neural system, in this case the cochlea, into building a working BCI that can benefit people.

  • 9 - Noninvasive BCIs

  • from Part III - Major Types of BCIs
  • Rajesh P. N. Rao, University of Washington
  • Book:
    Brain-Computer Interfacing
    Published online:
    05 October 2013
    Print publication:
    30 September 2013, pp 177-209

  • Summary

    A holy grail of BCI research is to be able to control complex devices using noninvasive recordings of brain signals at high spatial and temporal resolution. Current noninvasive recording techniques capture changes in blood flow or fluctuations in electric/magnetic fields caused by the activity of large populations of neurons, but we are still far from a recording technique that can capture neural activity at the level of spikes noninvasively. In the absence of such a recording technique, researchers have focused on noninvasive techniques such as EEG, MEG, fMRI, and fNIR, and studied how the large-scale population-level brain signals recorded by these techniques can be used for BCI.

    Electroencephalographic (EEG) BCIs

    The technique of EEG involves recording electrical signals from the scalp (Section 3.1.2). The idea of using EEG to build a BCI was first suggested by Vidal (1973), but progress was limited until the 1990s when the advent of fast and cheap processors sparked a surge of interest in this area, leading to the development of a variety of EEG-based BCI techniques.

Page 48 of 94