Appropriate host response

The response reaction of the host to a foreign material remaining in the body for an extended period of time is a concern. Thus, any polymeric material to be integrated into such a delicate system as the human body must be biocompatible. Biocompatibility is defined as the ability of a material to perform with an appropriate host response in a specific application [79]. The concept include all aspects of the interfacial reaction between a material and body tissues initial events at the interface, material changes over time, and the fate of its degradation products. To be considered bio compatible, a biodegradable polymer must meet a number of requirements, given in Table 2. 

The problems that occur with in vivo experiments are not completely solved. The points where the implanted electrodes cause tissue damage are rapidly regenerated and covered by conjunctive tissue or even by antibodies from electrode rejection. The formation and growth of conjunctive tissue is influenced by the form and nature of the electrode material. A material s biocompatibility is defined as its ability to perform with an appropriate host response in a specific application51. Therefore it is important to develop biomaterials for in vivo sensor applications, since neither the conjunctive tissue nor the antibody layer on the electrode is conducting, and a large decrease in electrode response after implantation is observed. 

A commonly used definition of a biomaterial, endorsed by a consensus of biomaterials experts, is a nonviable material used in a medical device, intended to interact with biological systems. An essential characteristic of biomaterials is biocompatibility, defined as the ability of a material to perform with an appropriate host response in a specific application. The goal of biomaterials science is to create medical implant materials with optimal mechanical performance and stability, as well as optimal biocompatibility. 

The field of biomedical application often requires an interdisciplinary approach that combines the life sciences and medicine with materials science and engineering. For a successful application, the material must be biocompatible, meaning that the material has the ability to perform with an appropriate host response in a specific application. Due to the complicated interaction between materials and biological systems, there is no precise definition or accurate measurement of biocompatibility. 

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. 

Biocompatibility is defined as the ability of a material to induce the appropriate host response in a particular application (46). Here the appropriate host... 

Biocompatibility in materials is not precisely defined, and so all claims of biocompatibility should be read with caution. A useful definition, which is accepted by most experts, is Biocompatibility is the ability of a material to perform with an appropriate host response in a specific application (Williams, D.F., Definitions in Biomaterials. Proceedings of a Consensus Conference of the European Society for Biomaterials, Chester, England, 3-5 March 1986, Vol. 4, Elsevier, New York, 1987). For more information see Biomaterials Science an introduction to materials in medicine. Ratner, B.D., Hoffman, A.S., Schoen, F.J., and Lemons, J.E. (eds.). Academic Press, 1996. 

When a synthetic material is placed in the mouth, there are many concerns. Obviously the material must be biocompatible, with an appropriate host response (Wataha, 2001). Further, the material may be subjected to mechanical stresses (shock, fatigue and abrasion), and chemical and enzymatic degradation. Thus it is important that the material is manipulated in such a way as to obtain its optimum properties to withstand the long-term rigors imposed by the oral environment. In that regard, it is advantageous to have materials that are easier to manipulate, which in turn can promote a superior outcome. This is now being achieved in some cases by the development of injectable materials. 

Biocompatibility in its broadest sense refers to the ability of a material to perform with an appropriate host response in a specific situation. Any foreign material once implanted within an organism triggers a cascade of reactions called the immune or host response, which are part of the organism s defense mechanism. Several studies have been performed to evaluate the biocompatibility of polymers [193],... 

On the basis of these ideas, biocompatibility was redefined a few years ago (2), as the ability to perform with an appropriate host response in a specific situation. Clearly this definition encompasses the situation where inertness is still required for the most appropriate response in some situations is indeed no response. A traditional bone fracture plate is most effective when it is attached mechanically to the bone and does not corrode no response of the tissue to the material is normally required. Even here, however, we have to concede that a material that could actively encourage more rapid bone healing might be beneficial so that a specific osteoinductive response would be considered appropriate. 

As a result of this insight Williams defined biocompatibility as the ability of a material to perform with an appropriate host response in a specific application . In Ratner s latest definition biocompatibility even means the body s acceptance of the material, i.e. the ability of an implant surface to interact with cells and liquids of the biological system and to cause exactly the reactions which the analogous body tissue would bring about [2]. This definition requires knowledge of the processes between the biomaterial s surface and the biological system. 

The term biocompatibility is defined as the ability of a material to perform with an appropriate host response in a specific situation" (Williams 2008). A biocompatible material can be inert, where it would not induce a host immune response and have little or no toxic properties. A biocompatible material can also be bioactive, initiating a controlled physiological response. For porous silicon, bioactive properties were initially suggested based on the observation that hydroxyapatite (HA) crystals grow on microporous silicon films. HA has implications for bone tissue implants and bone tissue engineering (Canham 1995). An extension of this work showed that an applied cathodic current was able to further promote calcification on the surface (Canham et al. 1996). More recently, Moxon et al. showed another example of bioactive porous silicon where the material promoted neuron viability when inserted into rat brains as a potential neuronal biosensor, whereas planar silicon showed significantly fewer viable neurons surrounding the implant site (Moxon et al. 2007). 

This chapter will examine the production of one particular biomedical device soft contact lenses. The surface properties of soft contact lenses influence the biocompatibility of the lens, or the ability of the material to perform with the appropriate host response in a specific application [1]. Three case studies will be u.sed to exemplify how surface science is utilized in the soft contact lens market. The case studies will examine methods of producing surfaces for biocompatible high-performance soft contact lenses as well as alterations in surface chemistry and morphology caused by manufacturing methods used to produce the lens. However, first it would be appropriate to provide some history, design goals, and background on soft contact lenses. 

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