Biomechanics
Applied mechanics, most notably thermodynamics and continuum mechanics, and mechanical engineering disciplines such as fluid mechanics and solid mechanics, play prominent roles in the study of biomechanics. By applying the laws and concepts of physics, biomechanical mechanisms and structures can be simulated and studied. It has been shown that applied loads and deformations can affect the properties of living tissue. There is much research in the field of growth and remodeling as a response to applied loads. For example, the effects of elevated blood pressure on the mechanics of the arterial wall, the behavior of cardiomyocytes within a heart with a cardiac infarct, and bone growth in response to exercise, and the acclimative growth of plants in response to wind movement, have been widely regarded as instances in which living tissue is remodelled as a direct consequence of applied loads.Relevant mathematical tools include linear algebra, differential equations, vector and tensor calculus, numerics and computational techniques such as the finite element method.The study of biomaterials is of crucial importance to biomechanics. For example, the various tissues within the body, such as skin, bone, and arteries each possess unique material properties.

The passive mechanical response of a particular tissue can be attributed to characteristics of the various proteins, such as elastin and collagen, living cells, ground substances such as proteoglycans, and the orientations of fibers within the tissue. For example, if human skin were largely composed of a protein other than collagen, many of its mechanical properties, such as its elastic modulus, would be different.Chemistry, molecular biology, and cell biology have much to offer in the way of explaining the active and passive properties of living tissues. For example, in muscle contractions, the binding of myosin to actin is based on a biochemical reaction involving calcium ions and ATP.The study of biomechanics ranges from the inner workings of a cell to the movement and development of limbs, to the mechanical properties of soft tissue, and bones. As we develop a greater understanding of the physiological behavior of living tissues, researchers are able to advance the field of tissue engineering, as well as develop improved treatments for a wide array of pathologies.Biomechanics as a sports science, kinesiology, applies the laws of mechanics and physics to human performance in order to gain a greater understanding of performance in athletic events through modeling, simulation, and measurement.

          Continuum Mechanics
It is often appropriate to model living tissues as continuous media. For example, at the tissue level, the arterial wall can be modeled as a continuum. This assumption breaks down when the length scales of interest approach the order of the micro structural details of the material. The basic postulates of continuum mechanics are conservation of linear and angular momentum, conservation of mass, conservation of energy, and the entropy inequality. Solids are usually modeled using reference or Lagrangian coordinates, whereas fluids are often modeled using spatial or Eulerian coordinates. Using these postulates and some assumptions regarding the particular problem at hand, a set of equilibrium equations can be established. The kinematics and constitutive relations are also needed to model a continuum.Second and fourth order tensors are crucial in representing many quantities in electromechanical.

In practice, however, the full tensor form of a fourthorder constitutive matrix is rarely used. Instead, simplifications such as isotropy, transverse isotropy, and incompressibility reduce the number of independent components. Commonlyused secondorder tensors include the Cauchy stress tensor, the second ViolaKirchhoff stress tensor, the deformation gradient tensor, and the Green strain tensor. A reader of the mechanic's literature would be welladvised to note precisely the definitions of the various tensors which are being used in a particular work.Under most circumstances, blood flow can be modeled by the NavierStokes equations. Whole blood can often be assumed to be an incompressible Newtonian fluid. However, this assumption fails when considering flows within arterioles. At this scale, the effects of individual red blood cells becomes significant, and whole blood can no longer be modeled as a continuum. When the diameter of the blood vessel is slightly larger than the diameter of the red blood cell the Fahraeus Lindqvist effect occurs and there is a decrease in wall shear stress. However, as the diameter of the blood vessel decreases further, the red blood cells have to squeeze through the vessel and often can only pass in single file. In this case, the inverse Fahraeus Lindqvist effect occurs and the wall shear stress increases.

         Cardiomyocytes
Bones are anisotropic but are approximately transversely isotropic. In other words, bones are stronger along one axis than across that axis, and are approximately the same strength no matter how they are rotated around that axis.The stressstrain relations of bones can be modeled using Hooke's law, in which they are related by elastic moduli, e.g. Young's modulus, Poisson's ratio or the Lamé parameters. The constitutive matrix, a fourth order tensor, depends on the isotropy of the bone. sij = Cijklekl,There are three main types of muscles Skeletal muscle striated Unlike cardiac muscle, skeletal muscle can develop a sustained condition known as tetany through high frequency stimulation, resulting in overlapping twitches and a phenomenon known as wave summation. At a sufficiently high frequency, tetany occurs, and the contracticle force appears constant through time. This allows skeletal muscle to develop a wide variety of forces. This muscle type can be voluntary controlled. Hill's Model is the most popular model used to study muscle. Cardiac muscle striated Cardiomyocytes are a highly specialized cell type. These involuntarily contracted cells are located in the heart wall and operate in concert to develop synchronized beats. This is attributable to a refractory period between twitches. Smooth muscle smooth lacking striations The stomach, vasculature, and most of the digestive tract are largely composed of smooth muscle. This muscle type is involuntary and is controlled by the enteric nervous system.

          Biomechanics Of Soft Tissues
Soft tissues such as tendon, ligament and cartilage are combinations of matrix proteins and fluid. In each of these tissues the main strength bearing element is collagen, although the amount and type of collagen varies according to the function each tissue must perform. Elastin is also a major loadbearing constituent within skin, the vasculature, and connective tissues. The function of tendons is to connect muscle with bone and is subjected to tensile loads. Tendons must be strong to facilitate movement of the body while at the same time remaining compliant to prevent damage to the muscle tissues. Ligaments connect bone to bone and therefore are stiffer than tendons but are relatively close in their tensile strength. Cartilage, on the other hand, is primarily loaded in compression and acts as a cushion in the joints to distribute loads between bones. The compressive strength of collagen is derived mainly from collagen as in tendons and ligaments, however because collagen is comparable to a wet noodle it must be supported by crosslinks of glycosaminoglycans that also attract water and create a nearly incompressible tissue capable of supporting compressive loads.

Recently, research is growing on the biomechanics of other types of soft tissues such as skin and internal organs. This interest is spurred by the need for realism in the development of medical simulation.Viscoelasticity is readily evident in many soft tissues, where there is energy dissipation, or hysteresis, between the loading and unloading of the tissue during mechanical tests. Some soft tissues can be preconditioned by repetitive cyclic loading to the extent where the stressstrain curves for the loading and unloading portions of the tests nearly overlap.Hooke's law is linear, but many, if not most problems in biomechanics, involve highly nonlinear behavior. Proteins such as collagen and elastin, for example, exhibit such a behavior. Some common material models include the NeoHookean behavior, often used for modeling elastin, and the famous Fungelastic exponential model. Non linear phenomena in the biomechanics of soft tissue arise not only from the material properties but also from the very large strains 100% and more that are characteristic of many problems in soft tissues.

         Biomedical Instrumentation
Biomedical instrumentation amplifier schematic used in monitoring low voltage biological signals, an example of a biomedical engineering application of electronic engineering to electrophysiology.Biomedical engineering is widely considered an interdisciplinary field, resulting in a broad spectrum of disciplines that draw influence from various fields and sources. Due to the extreme diversity, it is not atypical for a biomedical engineer to focus on a particular aspect. There are many different taxonomic breakdowns of BME, one such listing defines the aspects of the field as such, Bioelectrical and neural engineering Biomedical imaging and biomedical optics,Biomaterials,Biomechanics and biotransport, Biomedical devices and instrumentation,Molecular, cellular and tissue engineering Systems and integrative engineering,In other cases, disciplines within BME are broken down based on the closest association to another, more established engineering field, which typically includeBreast implants, an example of a biomedical engineering application of biocompatible materials to cosmetic surgery.Breast implants, an example of a biomedical engineering application of biocompatible materials to cosmetic surgery. Chemical engineering often associated with biochemical, cellular, molecular and tissue engineering, biomaterials, and biotransport. Electrical engineering often associated with bioelectrical and neural engineering, bioinstrumentation, biomedical imaging, and medical devices.Mechanical engineering often associated with biomechanics, biotransport, medical devices, and modeling of biological systems. Optics and Optical engineering biomedical optics, imaging and medical devices.

          Clinical Engineering
Clinical engineering is a branch of biomedical engineering for professionals responsible for the management of medical equipment in a hospital. The tasks of a clinical engineer are typically the acquisition and management of medical device inventory, supervising biomedical engineering technicians BMETs, ensuring that safety and regulatory issues are taken into consideration and serving as a technological consultant for any issues in a hospital where medical devices are concerned. Clinical engineers work closely with the IT department and medical physicists.Schematic representation of normal ECG trace showing sinus rhythm, an example of a biomedical engineering application of electronic engineering to electrophysiology and medical diagnosis.Schematic representation of normal ECG trace showing sinus rhythm, an example of a biomedical engineering application of electronic engineering to electrophysiology and medical diagnosis.

A typical biomedical engineering department does the corrective and preventive maintenance on the medical devices used by the hospital, except for those covered by a warranty or maintenance agreement with an external company. All newly acquired equipment is also fully tested. That is, every line of software is executed, or every possible setting is exercised and verified. Most devices are intentionally simplified in some way to make the testing process less expensive, yet accurate. Many biomedical devices need to be sterilized. This creates a unique set of problems, since most sterilization techniques can cause damage to machinery and materials. Most medical devices are either inherently safe, or have added devices and systems so that they can sense their failure and shut down into an unusable, thus very safe state. A typical, basic requirement is that no single failure should cause the therapy to become unsafe at any point during its lifecycle. See safety engineering for a discussion of the procedures used to design safe systems.

         Medical Devices
A medical device is intended for use in the diagnosis of disease or other conditions, or in the cure, mitigation, treatment, or prevention of disease,intended to affect the structure or any function of the body of man or other animals, and which does not achieve any of its primary intended purposes through chemical action and which is not dependent upon being metabolized for the achievement of any of its primary intended purposes.A pump for continuous subcutaneous insulin infusion, an example of a biomedicalengineering application of electrical engineering to medical equipment.Some examples include pacemakers, infusion pumps, the heartlung machine, dialysis machines, artificial organs, implants, artificial limbs, corrective lenses, cochlear implants, ocular prosthetics, facial prosthetics, somato prosthetics, and dental implants.Stereolithography is a practical example on how medical modeling can be used to create physical objects. Beyond modeling organs and the human body, emerging engineering techniques are also currently used in the research and development of new devices for innovative therapies, treatments, patient monitoring, and early diagnosis of complex diseases.

Medical devices can be regulated and classified in the US as shown below,Class I devices present minimal potential for harm to the user and are often simpler in design than Class II or Class III devices. Devices in this category include tongue depressors, bedpans, elastic bandages, examination gloves, and handheld surgical instruments and other similar types of common equipment.Class II devices are subject to special controls in addition to the general controls of Class I devices. Special controls may include special labeling requirements, mandatory performance standards, and postmarket surveillance. Devices in this class are typically noninvasive and include xray machines, PACS, powered wheelchairs, infusion pumps, and surgical drapes.Class III devices require premarket approval, a scientific review to ensure the device's safety and effectiveness, in addition to the general controls of Class I. Examples include replacement heart valves, silicone gelfilled breast implants, implanted cerebellar stimulators, implantable pacemaker pulse generators and endosseous intrabone implants.

         Medical Devices
Clinical engineering is a branch of biomedical engineering for professionals responsible for the management of medical equipment in a hospital. The tasks of a clinical engineer are typically the acquisition and management of medical device inventory, supervising biomedical engineering technicians BMETs, ensuring that safety and regulatory issues are taken into consideration and serving as a technological consultant for any issues in a hospital where medical devices are concerned. Clinical engineers work closely with the IT department and medical physicists.Schematic representation of normal ECG trace showing sinus rhythm, an example of a biomedical engineering application of electronic engineering to electrophysiology and medical diagnosis.Schematic representation of normal ECG trace showing sinus rhythm, an example of a biomedical engineering application of electronic engineering to electrophysiology and medical diagnosis.

A typical biomedical engineering department does the corrective and preventive maintenance on the medical devices used by the hospital, except for those covered by a warranty or maintenance agreement with an external company. All newly acquired equipment is also fully tested. That is, every line of software is executed, or every possible setting is exercised and verified. Most devices are intentionally simplified in some way to make the testing process less expensive, yet accurate. Many biomedical devices need to be sterilized. This creates a unique set of problems, since most sterilization techniques can cause damage to machinery and materials. Most medical devices are either inherently safe, or have added devices and systems so that they can sense their failure and shut down into an unusable, thus very safe state. A typical, basic requirement is that no single failure should cause the therapy to become unsafe at any point during its lifecycle. See safety engineering for a discussion of the procedures used to design safe systems.

          Medical Imaging
An MRI scan of a human head, an example of a biomedical engineering application of electrical engineering to diagnostic imaging. Click here to view an animated sequence of slices.Imaging technologies are often essential to medical diagnosis, and are typically the most complex equipment found in a hospital including Fluoroscopy,Magnetic resonance imaging MRI, Nuclear Medicine,Positron Emission Tomography PET PET scansPETCT scans,Projection Radiography such as Xrays and CT scans,Tomography,Ultrasound, Electron Microscopy.One of the goals of tissue engineering is to create artificial organs for patients that need organ transplants. Biomedical engineers are currently researching methods of creating such organs. In one case bladders have been grown in lab and transplanted successfully into patients.Bioartificial organs, which utilize both synthetic and biological components, are also a focus area in research, such as with hepatic assist devices that utilize liver cells within an artificial bioreactor construct.

Artificial limbs The right arm is an example of a prosthesis, and the left arm is an example of myoelectric control.Regulatory issues are never far from the mind of a biomedical engineer. To satisfy safety regulations, most biomedical systems must have documentation to show that they were managed, designed, built, tested, delivered, and used according to a planned, approved process. This is thought to increase the quality and safety of diagnostics and therapies by reducing the likelihood that needed steps can be accidentally omitted again.In the United States, biomedical engineers may operate under two different regulatory frameworks.Clinical devices and technologies are generally governed by the Food and Drug Administration FDA in a similar fashion to pharmaceuticals. Biomedical engineers may also develop devices and technologies for consumer use, such as physical therapy devices, which may be governed by the Consumer Product Safety Commission. See US FDA 510k documentation process for the US government registry of biomedical devices.

          Biomedical Engineering Training
A prosthetic eye, an example of a biomedical engineering application of mechanical engineering and biocompatible materials to opthalmology.Biomedical engineers combine sound knowledge of engineering and biological science, and therefore tend to have a bachelors of science and advanced degrees from major universities, who are now improving their biomedical engineering curriculum because interest in the field is increasing. Many colleges of engineering now have a biomedical engineering program or department from the undergraduate to the doctoral level. Traditionally, biomedical engineering has been an interdisciplinary field to specialize in after completing an undergraduate degree in a more traditional discipline of engineering or science, the reason for this being the requirement for biomedical engineers to be equally knowledgeable in engineering and the biological sciences. However, undergraduate programs of study combining these two fields of knowledge are becoming more widespread, including programs for a Bachelor of Science in Biomedical Engineering.

As such, many students also pursue an undergraduate degree in biomedical engineering as a foundation for a continuing education in medical school. Though the number of biomedical engineers is currently low as of 2004, under 10,000 in the U.S., the number is expected to rise as modern medicine and technology improves.In the U.S., an increasing number of undergraduate programs are also becoming recognized by ABET as accredited bioengineering/biomedical engineering programs. Over 40 programs are currently accredited by ABET, the first being Duke University, originally accredited by the Engineering Council for Profession Development now ABET in September of 1972.As with many degrees, the reputation and ranking of a program may factor into the desirability of a degree holder for either employment or graduate admission. The reputation of many undergraduate degrees are also linked to the institution's graduate or research programs, which have some tangible factors for rating, such as research funding and volume, publications and citations.

         BME Education And Training
Graduate education is also an important aspect in BME. Although many engineering professions do not require graduate level training, BME professions often recommend or require them.Since many BME professions often involve scientific research, such as in the pharmaceutical and medical device industries, graduate education may be highly desirable as undergraduate degrees typically do not provide substantial research training and experience.Graduate programs in BME, like in other scientific fields, are highly varied and particular programs may emphasize certain aspects within the field.

Implants, such as artificial hip joints, are generally extensively regulated due to the invasive nature of such devices.Implants, such as artificial hip joints, are generally extensively regulated due to the invasive nature of such devices.Other countries typically have their own mechanisms for regulation. In Europe, for example, the actual decision about whether a device is suitable is made by the prescribing doctor, and the regulations are to assure that the device operates as expected. Thus in Europe, the governments license certifying agencies, which are forprofit. Technical committees of leading engineers write recommendations which incorporate public comments and are adopted as regulations by the European Union. These recommendations vary by the type of device, and specify tests for safety and efficacy. Once a prototype has passed the tests at a certification lab, and that model is being constructed under the control of a certified quality system, the device is entitled to bear a CE mark, indicating that the device is believed to be safe and reliable when used as directed.

The different regulatory arrangements sometimes result in technologies being developed first for either the U.S. or in Europe depending on the more favorable form of regulation. Most safetycertification systems give equivalent results when applied diligently. Frequently, once one such system is satisfied, satisfying the other requires only paperwork. They may also feature extensive collaborative efforts with programs in other fields, owing again to the interdisciplinary nature of BME.Education in BME also varies greatly around the world. By virtue of its extensive biotechnology sector, numerous major universities, and few internal barriers, the U.S. has progressed a great deal in the development of BME education and training. Europe, which also has a large biotechnology sector and an impressive education system, has encountered trouble in creating uniform standards as the European community attempts to bring down some of the national barriers that exist. Recently, initiatives such as BIOMEDEA have sprung up to develop BMErelated education and professional standards.Other countries, such as Australia, are recognizing and moving to correct deficiencies in their BME education.Also, as high technology endeavors are usually marks of developed nations, some areas of the world are prone to slower development in education, including in BME.

         Professional Certification
Engineers typically require a type of professional certification, such as satisfying certain education requirements and passing an examination to become a professional engineer. These certifications are usually nationally regulated and registered, but there are also cases of selfgoverning bodies, such as the Canadian Association of Professional Engineers. In many cases, carrying the title of Professional Engineer is legally protected.As BME is an emerging field, professional certifications are not as standard and uniform as they are for other engineering fields. For example, the Fundamentals of Engineering exam in the U.S. does not include a biomedical engineering section, though it does cover biology. Biomedical engineers often simply possess a university degree as their qualification. However, some countries, such as Australia, do regulate biomedical engineers, however registration is typically only recommended and not required.Professional Engineer is the term for registered or licensed engineers in some countries, including the United States and Canada, who are permitted to offer their professional services directly to the public.

The term Professional Engineer and the phrase practice of professional engineering is legally defined and protected both in Canada by the provinces and the United States by the states. In most jurisdictions only registered or licensed Professional Engineers are permitted to use the title, or to practice Professional Engineering.The earmark that distinguishes a licensed/registered Professional Engineer is the authority to sign and seal or stamp engineering documents reports, drawings, and calculations for a study, estimate, design or analysis, thus taking legal responsibility for it.Professional services are infrequent, technical, or unique functions performed by independent contractors or consultants whose occupation is the rendering of such services.

While not limited to licentiates individuals holding professional licences, the services are considered professional and the contract may run to partnerships, firms, or corporations as well as to individuals. Examples of professional services contracts include accountants, appraisers, archaeologists, attorneys, business consultants, architects, engineers, law firms, physicians, performing artists, researchers, and real estate brokers. The selection of an independent contractor or consultant providing professional services is usually based on skill, knowledge, reputation, ethics, and creativity. Price for services may be a secondary factor in the selection. Defining independent contractors or consultants as professional suggests that they do not derive any financial benefit from service or product providers that are recommended in the consulting engagement.