As a biomaterial or in part as an implant material generally synthetic or non-living natural materials or materials are referred to, which are used in medicine for therapeutic or diagnostic purposes and thereby come into contact with biological tissue of the body. These materials occur here in chemical, physical and biological interactions with the corresponding biological systems.
In general, the term refers to all materials which are used in the context of therapeutic or diagnostic action in contact with the body, and therefore also includes the short-term contact of the outer body surface over the body openings, and externally accessible via a mucous membrane. A particularly common in research, narrower definition, however, includes only those materials that are introduced to the longer-term retention inside the body.
The term bio-material refers to the material, in particular the chemical and physical, properties of the material. Characteristic of a biomaterial is a resultant of its biocompatibility properties, which includes both the functional similarity to the body's structures and adequate biocompatibility in the body. In contrast, the implant or prosthesis terms describe the function of an existing concrete from one or more different biomaterials medical product in respect of a particular application.
Purpose and requirements
Biomaterials are often used to provide temporary or permanent replacement of organs, parts of organs or body structures that were destroyed because of illness, injury or aging processes or are limited in their function.
The suitability of a material for use as a biomaterial is defined on the one hand on the functional compatibility with the organ or tissue to be replaced. That is, the material used must be sufficiently similar to the biological tissue to be replaced in terms of essential properties such as hardness, elasticity and plasticity, or the permeability for different substances. Furthermore, it should as far as possible these properties for the entire length of stay in the body, but at least a sufficiently long period to a possible replacement, have.
Second, the biocompatibility, ie the biological compatibility, a decisive criterion for the suitability of a biomaterial. By this is meant that a material must have the least possible negative impact on the surrounding tissue in the longer term. Major components of the reaction of the body, which influence the biocompatibility, are inflammation and immune reactions. The totality of these directed against an implanted biomaterial processes is referred to as foreign body reactions.
Among the short-and longer -term negative consequences of the use of a biomaterial that can be avoided, if possible, include for example mechanical irritation such as pressure pain, persistent acute inflammatory reactions, toxic and mutagenic effects, allergies and infections. In addition to the damaging effects on body tissues, these reactions may affect to some extent the function of the negative material up to failure of the implant.
An "ideal " biomaterial that is both all requirements of its functional properties, is also characterized by a complete biocompatibility, and thus enable a full application with durable function would currently is not available.
The materials used as biomaterials are not a homogeneous group in terms of their origin as well as their chemical and physical properties. Rather, a number of different material groups differ. The oldest used as a biomaterial materials include metals, particularly noble metals such as gold, platinum or titanium. They are distinguished not only by their chemical resistance high mechanical strength and are accordingly used mainly for replacement of bones and teeth. For similar applications, materials based on carbon, as well as various ceramic materials may be used. Widely used are also plastics, such as polyesters, which are used according to their specific properties for different purposes. These include facial prostheses in case of accident and cancer patients or denture to replace blood vessels.
Of the materials mentioned, which are permanently retain their function due to their chemical and physical properties, known resorbable materials are to be distinguished. These are degraded by the body through chemical and biological processes, a desired process in the application of these materials. These include, for example, polymers of glycolic acid or dioxanone to be used as surgical sutures in surgery, where removal of the suture is inconvenient after the healing of the sewn body opening. Another example of a resorbable biomaterial is hydroxyapatite (HA ), a calcium phosphate -based material for a bone substitute. Hydroxyapatite is used in this context mainly as a coating material. It acts both osteoconductive, i.e. as a support structure (scaffold ) for bone cells, as well as osteoinductive by excitation of the growth of new bone tissue, thereby promoting the growth of an implant in the bone. Magnesium alloys having comparable properties with regard to strength and elasticity of the human bone, are particularly tested in combination with HA as an implant material. The goal is the development of an absorbable implant material.
Among the natural substances that are used as a biomaterial, including, for example, coral as a support structure for the replacement of bone. Other examples include collagen, resulting from chitin, chitosan or alginate extracted from seaweed. These substances are used in particular for surface coating or sheath of the aforementioned materials in order to improve the biocompatibility of the entire implant.
Biomaterials are used in various forms in medicine. One of the simplest applications include dressings for wound dressing. You assume temporarily a part of the functions of the damaged skin through the wound, thus protecting the underlying tissues from the environment and the prevention of the outlet of the blood. Another relatively simple application of biomaterials are contact lenses. In such applications, an external removal or replacement of the material in case of intolerance or loss of function is usually very simple.
Many biomaterials can be used in the form of implants within the body. They are used, for example, as part of a designated as osteosynthesis treatment to aid healing after a fracture as well as the permanent replacement of bone that have been irreparably damaged by an accident or by bone cancer. It is also possible the replacement of joint structures that are worn out by chronic illness or long-term stress. With vascular grafts blood vessels can be replaced, stents are used to support the wall of blood vessels. Examples of the replacement of body parts or whole organs by biomaterials are artificial heart valves, artificial urinary bladder, heart pacemakers or artificial heart, and cochlear implants in the ear. Also in plastic surgery biomaterials are used, such as glass for artificial eyes, silicone breast augmentation or polyester for facial reconstruction.
A special case of the application of biomaterials are called extracorporeal organ replacement or support systems, ie devices that temporarily take over the function of an organ outside the body. These include, for example, the heart-lung machine which temporarily can replace the heart and lungs during surgery, equipment for dialysis and repeated treatment for replacement of kidney function or as a Molecular Adsorbent Recirculation System (MARS) described systems for blood detoxification as liver replacement. The materials used in these devices for the circulation of the blood as well as the material and gas exchange between the blood and the devices must respect their functional properties and their biocompatibility similar claims meet as biomaterials used as implants inside the body.
Sutures for wound closure was probably used before about 32,000 years ago. First findings that demonstrate a specific application of exogenous materials as therapeutic implants were dated to some hundreds of years after the beginning of recorded time. Such a prosthesis made of iron was found in a human body from the second century, the Maya established about 400 years later dentures from the nacre of seashells ago. The invention of the contact lens is probably due to Adolf Gaston Eugen Fick about the year 1887. Gold and platinum as the pin material for dentures were first used for the beginning of the 19th century. In the same period, doctors and scientists began to investigate the use of metals for implants inside the body specifically in studies. The German surgeon Themistocles Gluck led in 1891 by the first implantation of a hip replacement made of ivory, which was not, however, of lasting success. The first studies on the use of plastics as a biomaterial in 1939 the study of cellophane for wrapping of blood vessels and the investigation of a string of nylon surgical sutures in 1941.
The modern history of biomaterials began but did not start until 1950 with the development of artificial organs and organ support systems. For example, 1952 was the first application of a vascular prosthesis in humans and was a success, the patient in question has lived for many years with no problems with the implant. In the same year the first time the implantation of an artificial heart valve in a beating heart was, however, unsuccessful, attempt. A year later the first heart -lung machine was presented by John Heysham Gibbon. This made it possible, among other operations on the heart at rest also the first time a mitral valve replacement with an artificial implant in 1960. Willem Kolff developed in the same year, based on studies from 1943, the first extracorporeal artificial kidney. With this technology, the first time it was possible to save patients with renal failure from certain death. Just three years earlier had Kolff implanted in a dog for the first time an artificial heart. After the first application of a pacemaker in 1958 by the Swedish physician Åke Senning in 1966 by Michael DeBakey, the first application of a ventricular assist device inside the body in humans. Three years later Denton Cooley tried for the first time the replacement of the full heart of a man by an artificial heart. The first successes gave it to the use of the Jarvik -7 artificial heart from 1982.
In addition to significant advances in the technology and functionality of implants beyond the 1960s marked the beginning of biomaterials designed, so the targeted development and modification of biomaterials in terms of their functional properties and their biocompatibility. The materials used hitherto were normally standard materials that were tested in empirical trials for their suitability as a biomaterial. Accordingly, until the early 1960s, doctors in collaboration with engineers dominated the field of biomaterials. In contrast, methods for standardized testing of the functional properties and biocompatibility have now been developed which allowed for a comparison of different materials. This also chemists, physicists and materials scientists have been involved in the research, in addition to increasing importance of biocompatibility and in particular a number of important insights from immunology biologists increasingly.