Any treatment or procedure that includes the in-vitro handling of oocytes (immature ova or egg cells) and sperm or embryos for the purpose of establishing a pregnancy. Assisted reproductive technology (ART) is undertaken as a treatment of infertility, with a goal of achieving human reproduction. ART procedures include (but are not limited to) in-vitro fertilization (IVF) and embryo transfer (ET) [Fig. 1], gamete intrafallopian transfer, gamete and embryo cryopreservation (freezing, or vitrification, and storage of cells or tissues), oocyte and embryo donation, and surrogacy. Note that intracervical or intrauterine insemination with either partner or donor spermatozoa is not included under the umbrella of ART. See also: Animal reproduction; Biotechnology; Fertilization (animal); Infertility; Ovum; Pregnancy; Sperm cell

The application of chemical engineering principles to the solution of medical problems due to physiological impairment. Knowledge of organic chemistry is required of all chemical engineers, and many study biochemistry and molecular biology. This training at the molecular level gives chemical engineers a unique advantage over other engineering disciplines in communication with life scientists and clinicians in medicine, since the technical language of modern medicine is based in biochemistry and molecular biology. Practical applications include the development of tissue culture systems, the construction of three-dimensional scaffolds of biodegradable polymers for cell growth in the laboratory, and the design of artificial organs. See also: Biochemistry; Molecular biology

The application of principles from applied and physical sciences to problems in healthcare and biology. As a field, biomedical engineering draws from a variety of disciplines including mechanical, chemical, electrical, and computer engineering, as well as chemistry, biology, mathematics, computer science, materials science, robotics, and physics. The purpose of biomedical engineering is to better understand, mimic, support, or correct parts of the human body for the advancement of healthcare (Fig. 1). See also: Biology; Engineering

The applications to medicine and biology of sound waves that have a frequency higher than the audible spectrum. Biomedical applications of ultrasound range from cell sonicators using frequencies in the kilohertz range to ultrasonic imaging in the megahertz range. The best-known application, ultrasonic imaging, is the second most utilized diagnostic imaging modality, after x-rays. High-intensity ultrasound has been used for therapeutic applications.

The science that describes the structure, reactivity, and interactions of organic compounds of biological significance. Bioorganic chemistry represents the meeting of biochemistry, in its broadest sense, with organic chemistry in an attempt to describe and control complex biological systems at the molecular level. Areas of research include enzymatic catalysis, the structure and folding of proteins, the structure and function of biological membranes, the chemistry of poly(ribonucleic acid) [RNA] and poly(deoxyribonucleic acid) [DNA], metabolic pathways, diseases, immunology, and mechanisms of drug action. Bioorganic chemistry seeks not only to understand and control cellular and biochemical processes, but also to mimic them. See also: Biochemistry; Organic chemistry

A microbial-type rhodopsin protein found in the eyespots of algae. Channelrhodopsin proteins are associated with the phototaxic responses of algae to light during their nonvegetative life-cycle stages. They are the only known natively occurring proteins that function as light-gated ion channels (that is, light-activated channels that control the passage of ions through cell membranes). Thus far, channelrhodopsins (see illustration) have been cloned and described in numerous algae species. Importantly, modified versions of these proteins have been utilized as research tools by biologists interested in modulating the membrane potentials of excitable cells in heterologous expression systems. See also: Algae; Biopotentials and ionic currents; Biotechnology; Cell (biology); Cell membranes; Light; Phototaxis; Protein

The administration of chemical substances for the treatment of disease, especially cancer, or for the prevention of aberrant growth of cells or tissues (neoplasms). In general, chemotherapy is the use of chemicals to treat any disease, but the term is applied most commonly to cancer treatment with drugs that exhibit cytotoxic activity through inhibition of cell division. In addition, several other classes of drugs (biologicals) are used to treat cancer. These antineoplastic drug treatments (Fig. 1) are often used in conjunction with conventional chemotherapy. Cancer is an abnormal growth or proliferation of cells that tends to invade tissues locally or spread to distant parts of the body. Several treatment modalities can be used to fight cancer. Surgery physically removes the abnormal growth, whereas radiation therapy, immunotherapy, hormonal therapy, and chemotherapy are directed at killing or slowing the growth of cancerous cells. See also: Biologicals; Cancer; Hormone; Immunotherapy; Oncology; Radiation therapy; Surgery

An individual animal or plant made up of cells derived from more than one zygote or otherwise genetically distinct. The term “chimera” originates from Greek mythology, according to which the Chimera was a fearsome, fire-breathing creature with a lion’s head, a goat’s body, and a dragon’s tail. In biology, a chimera refers to an organism containing a mixture of genetically different tissues, formed by processes such as fusion of early embryos, grafting, or mutation. Phenotypically, recognizing a chimera can be challenging as often no outward signs are visible. Indications that might suggest chimerism include hair of different colors or two different colored eyes. For example, the albino phenotype in mice, which is characterized by white hair and red eyes, arises from having homozygous mutant tyrosinase alleles. A chimeric albino mouse might have patches of albino fur alternating to patches of colored fur as well as one red eye and one pigmented eye (Fig. 1). DNA tests can confirm chimerism, although chimerism might be difficult to detect because the distribution of the different cells in a chimera’s body is random and not always discernable phenotypically. See also: Developmental biology; Developmental genetics; Genetics

Any persistent pain occurring in the lumbar (lower) back, sometimes extending to the buttocks and legs, which has been present for at least three months. Chronic low back pain (CLBP) [Fig. 1] is usually a combination of musculoskeletal and neuropathic pain, or pain that occurs as a result of damage to the nervous system. Neuropathic pain is typically indicated by the presence of radiating pain down the leg, pain of a shooting or electrical quality, and increased sensitivity to cold. The majority of CLBP cases are referred to as nonspecific, that is, they occur in the absence of an obvious organic cause, whereas mechanical problems (including disc, spinal, and muscular problems, as well as other deformations) account for the next greatest percentage of cases. Relatively few cases of CLBP result from cancer, infection, inflammation, or referred pain from visceral diseases. Because most CLBP is nonspecific, the disorders are categorized as a functional pain syndrome, which includes other pain conditions (for example, migraine, fibromyalgia, and chronic pelvic pain). Acute low back pain affects more than 80% of the population at some point in their lifetime, whereas CLBP occurs in more than 20% of adults who are 20 to 59 years old. It is more prevalent in women than men, and its prevalence increases in individuals from 30 to 60 years of age. CLBP is considered one of the most burdensome medical conditions worldwide, with enormous societal effects via the cost of treating the condition. See also: Muscular system; Muscular system disorders; Pain; Skeletal system; Spinal cord; Spinal cord disorders; Vertebra

A transition-metal complex that is used in the chemotherapeutic treatment of cancer, with particular effectiveness in the treatment of testicular and ovarian cancers. Cisplatin is an inorganic platinum agent. It is used as an anticancer drug in the treatment of various types of cancer, including testicular, ovarian, bladder, lung, stomach, and head and neck cancers. Because cancer patients can experience undesirable side effects as a result of the use of this antineoplastic drug, second- and third-generation variants have been developed to mitigate the unintended effects. See also: Cancer; Chemotherapy and other antineoplastic drug treatments; Oncology; Platinum