Biomaterials requirements biocompatibility

The most important characteristics fliat influence the choice of a biomaterial are biocompatibility, physical requirements, and chemical requirements, as illustrated in Figure 12.18 . 

A material is a biomaterial when it meets certain requirements it has to have the right physical and chemical properties and, in addition, be biocompatible, which means that it must not be rejected by the body. The material may not release any substances which might activate the host s immune system. As indicated earlier, the first biomaterials were metals and these still play an important part. Of all metals and alloys, titanium appears to be accepted best by tissues. Actually this is rather peculiar, as titanium is relatively rare in vegetable and animal tissue but relatively abundant in the earth s crust (0.2% of the mass of the earth s crust is titanium only six other metals are even more abundant). For some time now, titanium has been used in dental surgery and in attaching and replacing bones and joints. 

Magnetic biomaterials have different constraints than materials used for other applications. In vivo (in the body) applications require strict biocompatibility. In vitro (outside of the body) applications have less strict requirements, but techniques involving living cells still must consider the effect of the materials on the sample under study. In addition to biocompatibility, materials must be capable of being functionalized with one or more molecules, must retain their magnetic properties for a reasonable period of time in aqueous media with varying pH, must not be cleared too quickly from the bloodstream, and must form stable, non-aggregating dispersions [12, 13]. 

The surface is a crucially important factor of biomaterial, and without an appropriate biocompatibility the biomaterial could not function. On the other hand, the bulk properties of materials are equally important in the use of biomaterials. An opaque material cannot be used in vision correction, and soft flexible materials cannot be used in bone reinforcement. The probability of finding a material that fulfills all requirements in physical and chemical bulk properties for a biomaterial application and whose surface properties are just right for a specific application is very close to zero, if not absolutely zero. From this point of view, all biomaterials should be surface treated to cope with the biocompatibility. However, if the surface treatment alters the bulk properties, it defeats the purpose. In this sense, tunable LCVD nanofilm coating that causes the minimal effect on the bulk material is the best tool available in the domain of biomaterials. 

The definition of a biomaterial that has been arrived at by consensus is A biomaterial is one which possesses the ability to perform with an appropriate host response in a specific application (Williams, 1999). As subsequently stressed by Hench (2014), this definition emphasises that the term biocompatibility does not just mean absence of cytotoxicity but provides for the requirement that a material performs appropriately. This also means that different applications of a particular material enforces different conditions. As a consequence, a material, be it a metal, a ceramics or a polymer may or may not be biocompatible in different applications. 

The main requirement imposed on all polymer biomaterials applied in medicine is a combination of their desired physicochemical and physicomechanical characteristics with biocompatibility. Depending on particular applications, the biocompatibility of polymers can include various requirements, which can sometimes be contradictory to each other. Thns, in the case of artificial vessels, drainages, intraocular lenses, biosensors, or catheters, the interaction of the polymer with a biological medium should be minimized for the rehable operation of the corresponding device after implantation. In contrast, in the majority of orthopedic applications, the active interaction and fusion of an implant with a tissne is required. General requirements imposed on all medical polymers consist in non-toxicity and stability. 

Synthetic pol)mieric materials have been widely used in medical disposable supply, prosthetic materials, dental materials, implants, dressings, extracorporeal devices, encapsulants, polymeric drug delivery systems, tissue engineered products, and orthodoses as that of metal and ceramics substituents [Lee, 1989]. The main advantages of the polymeric biomaterials compared to metal or ceramic materials are ease of manufacturability to produce various shapes (latex, film, sheet, fibers, etc.), ease of secondary processability, reasonable cost, and availability with desired mechanical and physical properties. The required properties of polymeric biomaterials are similar to other biomaterials, that is, biocompatibility, sterilizability, adequate mechanical and physical properties, and manufacturability as given in Table 40.1. 

The next generation of implantable devices are likely to require biomaterials that are more interactive with tissues, being designed to interact with specific target biomolecules of relevance to the specific application. Although conventional PPy and PTh films have shown adequate biocompatibility for many biomedical applications, their lack of biofunctional activity results in poor cell interactions and limits their potential as an implantable material. 

CPs designed for biomedical applications generally require good electrical conductivity, physicochemical and mechanical stability, and biocompatibility to effectively interact with biological system. A wide range of analytical techniques to characterize the feasibility of conducting polymers as biomaterials are summarized here. 

A biomaterial is any natural or synthetic material that is employed as. or part of. a medical device. Typical materials include metals, ceramics, glasses, polymers, and tissue-engineered materials. The requirements of a biomaterial are that it should have the correct properties to allow it to achieve its intended function and be biocompatible. Over recent decades, there have been many developments in biomaterials research. Some of these developments have involved a movement from the use of inert materials to more sophisticated ones, which actively invoke a beneficial response from the body. 

The two principal requirements of any biomaterial used in a medical device are that it should have the correct physical properties in order for it to perform its intended function, and it should be biocompatible. Other requirements are that it can be easily manufactured and can be suitably sterilized. There are various sterilization methods the use depends mainly on the material being sterilized. Gamma-ray or high-temperature sterilization methods, for example, are unsuitable for polyurethanes, as they produce toxic and carcinogenic compounds. ... 

Insect and spider silks are natural biopolymers whose molecular structure enables their use in applications requiring exceptional strength and flexibility of the material. These traits along with their biocompatibility, biodegradability, and the ability to produce large amounts of the material make the use of silk and silk-based biomaterials a rational choice for a host of tissue engineering applications. 

The two most important areas of research when developing an injectable biomaterial for potential human use are (1) material characterization and (2) biocompatibility testing. Material characterization requires extensive rheological testing to assess a material s delivery performance and mechanical stability. The following lists summarize the general material characterization tests required by the FDA. 

---