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 biomedical engineering application of electrical engineering to medical equipment.

Some examples include pacemakers, infusion pumps, the heart-lung 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:

1. 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 hand-held surgical instruments and other similar types of common equipment.
2. 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 non-invasive and include x-ray machines, PACS, powered wheelchairs, infusion pumps, and surgical drapes.
3. 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 gel-filled breast implants, implanted cerebellar stimulators, implantable pacemaker pulse generators and endosseous (intra-bone) implants.

Disciplines in biomedical engineering

• 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 include:

• 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.

What is Biomedical Engineering?

Biomedical engineering (BME) is the application of engineering principles and techniques to the medical field. It combines the design and problem solving skills of engineering with medical and biological sciences to help improve patient health care and the quality of life of individuals.

As a relatively new discipline, much of the work in biomedical engineering consists of research and development, covering an array of fields: bioinformatics, medical imaging, image processing, physiological signal processing, biomechanics, biomaterials and bioengineering, systems analysis, 3-D modeling, etc. Examples of concrete applications of biomedical engineering are the development and manufacture of biocompatible prostheses, medical devices, diagnostic devices and imaging equipment such as MRIs and EEGs, and pharmaceutical drugs.

Computed tomography

Computed tomography (CT) is a medical imaging method employing tomography. Digital geometry processing is used to generate a three-dimensional image of the inside of an object from a large series of two-dimensional X-ray images taken around a single axis of rotation. The word "tomography" is derived from the Greek tomos (slice) and graphein (to write).

Computed tomography was originally known as the "EMI scan" as it was developed at a research branch of EMI, a company best known today for its music and recording business. It was later known as computed axial tomography (CAT or CT scan) and body section röntgenography.

CT produces a volume of data which can be manipulated, through a process known as windowing, in order to demonstrate various structures based on their ability to block the X-ray/Röntgen beam. Although historically (see below) the images generated were in the axial or transverse plane (orthogonal to the long axis of the body), modern scanners allow this volume of data to be reformatted in various planes or even as volumetric (3D) representations of structures.

Tissue E ngineering

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

Magnetic resonance imaging

Magnetic resonance imaging (MRI), or nuclear magnetic resonance imaging (NMRI), is primarily a medical imaging technique most commonly used in radiology to visualize the structure and function of the body. It provides detailed images of the body in any plane. MRI provides much greater contrast between the different soft tissues of the body than computed tomography (CT) does, making it especially useful in neurological (brain), musculoskeletal, cardiovascular, and oncological (cancer) imaging. Unlike CT, it uses no ionizing radiation, but uses a powerful magnetic field to align the nuclear magnetization of (usually) hydrogen atoms in water in the body. Radiofrequency fields are used to systematically alter the alignment of this magnetization, causing the hydrogen nuclei to produce a rotating magnetic field detectable by the scanner. This signal can be manipulated by additional magnetic fields to build up enough information to construct an image of the body.

MRI is a relatively new technology, which has been in use for little more than 30 years (compared with over 110 years for X-ray radiography). The first MR Image was published in 1973 and the first study performed on a human took place on July 3, 1977.

Magnetic resonance imaging was developed from knowledge gained in the study of nuclear magnetic resonance. In its early years the technique was referred to as nuclear magnetic resonance imaging (NMRI). However, as the word nuclear was associated in the public mind with ionizing radiation exposure it is generally now referred to simply as MRI. Scientists still use the term NMRI when discussing non-medical devices operating on the same principles. The term Magnetic Resonance Tomography (MRT) is also sometimes used. One of the contributors to modern MRI, Paul Lauterbur, originally named the technique zeugmatography, a Greek term meaning "that which is used for joining". The term referred to the interaction between the static, radiofrequency, and gradient magnetic fields necessary to create an image, but this term was not adopted.

Materials

Many different materials (natural and synthetic, biodegradable and permanent) have been investigated. Most of these materials have been known in the medical field before the advent of tissue engineering as a research topic, being already employed as bioresorbable sutures. Examples of these materials are collagen or some linear aliphatic polyesters.

New biomaterials have been engineered to have ideal properties and functional customization: injectability, synthetic manufacture, biocompatibility, non-immunogenicity, transparency, nano-scale fibers, low concentration, resorption rates, etc. PuraMatrix, originating from the MIT labs of Zhang, Rich, Grodzinsky and Langer is one of these new biomimetic scaffold families which has now been commercialized and is impacting clinical tissue engineering.

A commonly used synthetic material is PLA - polylactic acid. This is a polyester which degrades within the human body to form lactic acid, a naturally occurring chemical which is easily removed from the body. Similar materials are polyglycolic acid (PGA) and polycaprolactone (PCL): their degradation mechanism is similar to that of PLA, but they exhibit respectively a faster and a slower rate of degradation compared to PLA.

Scaffolds may also be constructed from natural materials: in particular different derivatives of the extracellular matrix have been studied to evaluate their ability to support cell growth. Proteic materials, such as collagen or fibrin, and polysaccharidic materials, like chitosan or glycosaminoglycans (GAGs), have all proved suitable in terms of cell compatibility, but some issues with potential immunogenicity still remains. Among GAGs hyaluronic acid, possibly in combination with cross linking agents (e.g. glutaraldehyde, water soluble carbodiimide, etc...), is one of the possible choices as scaffold material. Functionalized groups of scaffolds may be useful in the delivery of small molecules (drugs) to specific tissues

Biomedical engineering training

Education

A prosthetic eye, an example of a biomedical engineering application of mechanical engineering and biocompatible materials to ophthalmology.

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.

Clinical Engineering

Breast implants, an example of a biomedical engineering application of biocompatible materials to cosmetic surgery.

Clinical engineering is a branch of biomedical engineering related to the operation of medical equipment in a hospital setting. 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.

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 life-cycle. See safety engineering for a discussion of the procedures used to design safe systems.