Biomaterial
Synthetic or non-living natural materials that are used in medicine for therapeutic or diagnostic purposes and come into direct contact with biological tissue of the body are generally referred to as biomaterial or partly as implant material . These materials enter into chemical , physical and biological interactions with the corresponding biological systems.
In general, the term refers to all materials that come into contact with the body as part of therapeutic or diagnostic measures, and thus also includes brief contact via the outer body surface , via body orifices and via externally accessible mucous membranes . A narrower definition, which is common in research in particular, only includes materials that are introduced into the body for long-term retention.
The term biomaterial refers to the material, in particular the chemical and physical, properties of the material. A characteristic of a biomaterial is a biocompatibility resulting from its properties , which includes both the functional similarity to the body's own structures and an appropriate biological compatibility in the body. In contrast, the terms implant or prosthesis describe the specific function of a medical product consisting of one or more different biomaterials with regard to a specific application.
Purpose and requirements
Biomaterials are often used for the temporary or permanent replacement of organs , organ parts or body structures that have been destroyed due to illness , injuries or aging or are restricted in their function.
The suitability of a material for use as a biomaterial is defined on the one hand by its functional compatibility with the organ or tissue that is to be replaced. This means that 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 various substances. In addition, if possible, it should have these properties for the entire duration of its stay in the body, but at least for a sufficiently long period of time until a possible replacement.
On the other hand, biocompatibility , i.e. biological compatibility, is a decisive criterion for the suitability of a biomaterial. This means that a material must have as little negative impact as possible on the surrounding tissue over the long term. Important components of the body's response that affect biocompatibility are inflammatory processes and immunological reactions . The entirety of these processes directed against an implanted biomaterial is referred to as foreign body reactions .
The short and long-term negative consequences of using a biomaterial, which should be avoided if possible, include, for example, mechanical irritations such as tenderness, persistent acute inflammatory reactions, toxic and mutagenic effects, allergies and infections . In addition to the damaging effects on the body tissue, these reactions can in part also have a negative impact on the function of the material up to and including failure of the implant.
An “ideal” biomaterial that meets all the requirements for its functional properties and is also characterized by complete biocompatibility, and thus would enable unrestricted use with a permanent function, is currently not available.
used material
The materials used as biomaterials are not a uniform group in terms of their origin or their chemical and physical properties. Rather, a number of different material groups can be distinguished. The oldest materials used as biomaterials include metals , especially precious metals such as gold and platinum, and other corrosion-resistant metals such as titanium . In addition to their chemical resistance, they are characterized by high mechanical strength and are therefore mainly used to replace bones and teeth . They are considered inert . Materials based on carbon and various ceramic materials are also used for similar applications . Medical plastics such as polyester , polyethylene and polyurethane , which are used for various purposes depending on their specific properties , are also widely used . These include facial prostheses for accident and cancer patients or prostheses to replace blood vessels, but also meniscus implants and inlays for joint prostheses.
So-called resorbable materials are to be distinguished from the materials mentioned, which due to their chemical and physical properties should retain their function permanently. These are broken down by the body through chemical and biological processes, a process that is desired when using these materials. These include, for example, polymers made from glycolic acid or dioxanone , which are used as surgical suture materials in operations in which removal of the suture after the sutured body opening has healed is inexpedient. Another example of a resorbable biomaterial is hydroxyapatite (HA), a calcium phosphate- based material for bone replacement. In this context, hydroxyapatite is mainly used as a coating material. It works both osteoconductively, i.e. as a support structure (scaffold) for bone cells, and osteoinductively by stimulating the growth of new bone tissue, thereby promoting the growth of an implant on the bone. Magnesium alloys , which have properties comparable to those of human bones in terms of strength and elasticity, are tested in particular in combination with HA as an implant material. The aim is to develop a resorbable implant material.
The natural substances that are used as biomaterials include, for example, corals as a support structure when replacing bones. Further examples are collagen , the chitosan produced from chitin or the alginate obtained from seaweed . These substances are used in particular for surface coating or enveloping the materials mentioned at the beginning in order to improve the biocompatibility of the entire implant .
Application examples
Biomaterials are used in various forms in medicine. Some of the simplest uses include dressings for wound covering. They temporarily take over part of the functions of the skin destroyed by the wound , such as protecting the underlying tissue from environmental influences and preventing the escape of blood. Another comparatively simple application of biomaterials is contact lenses . In such external applications, removal or replacement of the material in the event of incompatibility or loss of function is usually very easy.
Many biomaterials are used inside the body in the form of implants. They are used, for example, as part of a treatment called osteosynthesis to support healing after a broken bone, as well as the permanent replacement of bones that have been irreparably destroyed by an accident or by bone cancer . It is also possible to replace joint structures that have been worn out by chronic diseases or long-term stress. With vascular prostheses blood vessels can be replaced, stents are used to support the wall of blood vessels. Examples of the replacement of parts of organs or entire organs with biomaterials are artificial heart valves , artificial urinary bladders , pacemakers or artificial hearts , as well as cochlear implants in the ear. Biomaterials are also used in plastic surgery , such as glass for artificial eyes , silicone for breast enlargement or polyester for facial reconstruction.
A special case of the use of biomaterials are so-called extracorporeal organ replacement or support systems, i.e. devices that temporarily take over the function of an organ outside the body. These include, for example, the heart-lung machine , which can temporarily replace the heart and lungs during an operation , devices for dialysis as repeated treatment to replace kidney function, or systems known as the Molecular Adsorbent Recirculation System (MARS) for blood detoxification as a liver replacement . The materials used in these devices for the circulation of the blood as well as the substance and gas exchange between the blood and the devices must meet similar requirements in terms of their functional properties and their biocompatibility as biomaterials that are used as implants inside the body.
history
Sutures for wound closure were probably used around 32,000 years ago. The first discoveries that prove a targeted use of exogenous materials as therapeutic implants were dated several hundred years after the beginning of the era. For example, iron dentures were found in a human body from the second century, and around 400 years later the Maya made dentures from the mother- of- pearl of sea shells . The invention of the contact lens probably goes back to Adolf Gaston Eugen Fick around the year 1887. Gold and platinum as post material for dentures were first used at the beginning of the 19th century. During the same period, doctors and scientists began to specifically examine the use of metals for implants inside the body in studies. The German surgeon Themistocles Gluck carried out the first implantation of a hip replacement made of ivory in 1891 , which, however, was not of lasting success. The first studies on the use of plastics as a biomaterial were the study of cellophane for covering blood vessels in 1939 and the study of nylon thread as a surgical suture material in 1941.
However, the modern history of biomaterials didn't begin until around 1950 with the development of artificial organs and organ support systems. For example, a vascular prosthesis was first used in humans in 1952 and proved to be a success; the patient in question survived for many years without problems with the implant. In the same year, the first attempt to implant an artificial heart valve in a beating heart was unsuccessful. A year later, John Heysham Gibbon presented the first heart-lung machine. In addition to other operations on the resting heart, this also enabled the first replacement of a mitral valve with an artificial implant in 1960. In the same year, Willem Kolff developed the first extracorporeal artificial kidney based on studies from 1943 onwards. This technology made it possible for the first time to save patients with kidney failure from certain death. Three years earlier, Kolff had implanted an artificial heart in a dog for the first time. After the first use of a cardiac pacemaker in 1958 by the Swedish doctor Åke Senning , Michael DeBakey carried out the first use of a cardiac support system inside the human body in 1966 . Three years later, Denton Cooley first attempted to replace a person's entire heart with an artificial heart. The first successes came with the use of the Jarvik-7 artificial heart from 1982.
In addition to significant advances in the technology and functionality of implants, the 1960s also marked the beginning of designed biomaterials , i.e. the targeted development and modification of biomaterials with regard to their functional properties and their biocompatibility. The materials used up to then were usually standard materials that were examined in empirical tests for their suitability as biomaterials. Accordingly, doctors and engineers dominated the field of biomaterial research until the early 1960s. In contrast to this, methods for standardized testing of functional properties and biocompatibility have now been developed that allow different materials to be compared. This means that chemists, physicists and material scientists have also increasingly been included in research, and with the increasing importance of biocompatibility and, in particular, a number of important findings from immunology, also biologists.
literature
- Erich Wintermantel : Medical Technology - Life Science Engineering. Springer, Berlin and Heidelberg 2009, ISBN 978-3-540-93935-1 .
- Gerhard Rakhorst, Rutger Ploeg (Eds.): Biomaterials in modern medicine: the Groningen perspective . World Scientific, 2008, ISBN 978-981-270-956-1 (English).
- Buddy Ratner : Biomaterials Science. An Introduction to Materials in Medicine. Elsevier, Amsterdam 2004, ISBN 0-12-582463-7 .
- Gary L. Bowlin, Gary Wnek: Encyclopedia of Biomaterials and Biomedical Engineering. Marcel Dekker, New York and Oxford 2004, ISBN 0-82-475562-6 .
- James M. Anderson : Biological Responses to Materials. In: Annual Review of Materials Research. 31/2001. Annual Reviews, pp. 81-110, ISSN 1531-7331 .