Materials bioinert

Biomedical Applications. In the area of biomedical polymers and materials, two types of appHcations have been envisioned and explored. The first is the use of polyphosphazenes as bioinert materials for implantation in the body either as housing for medical devices or as stmctural materials for heart valves, artificial blood vessels, and catheters. A number of fluoroalkoxy-, aryloxy-, and arylamino-substituted polyphosphazenes have been tested by actual implantation ia rats and found to generate Httle tissue response (18). 

The term "bioenertness" is a relative one since few if any synthetic polymers are totally biocompatible with living tissues. The terra is used here on the basis of preUminary in vitro and in vivo tests, together with chemical evaluations based on analogies with other well-tested systems. Two different types of polyphosphazenes are of interest as bioinert materials those with strongly hydrophobic surface characteristics and those with hydrophilic surfaces. These will be considered in turn. 

Meyers SR, Khoo XJ, Huang X et al (2009) The development of peptide-based interfacial biomaterials for generating biological functionality on the surface of bioinert materials. Biomaterials 30(3) 277-286... 

Bioinert materials are materials that display minimal, if any, interaction with surrounding tissues examples of these are titanium and its alloys, alumina, partially stabilised zirconia, carbon and possibly ultrahigh molecular weight polyethylene (UHMWPE). In the case of bioinert materials bone remodelling occurs by a shape-mediated contact osteogenesis. 

As discussed in detail in Chapter 3.1, the advantage of bioinert materials is that they do not release any toxic constituents to the human body environment. However, on the downside they do not show positive interaction with living tissue. Instead, the body usually responds to these materials by forming a non-adherent fibrous capsule of connective tissue around the bioinert material that in the case of bone remodelling manifests itself by a shape-mediated contact osteogenesis. Consequently only compressive forces will be transmitted through the bone-biomaterial interfaces ( bony on-growth ). 

Bioinert materials are materials tliat do not release any substances that are, for example, toxic or inflammatory and do not trigger a material-tissue interaction. In the case of a blood-contacting foreign material this means that the blood components do not recognize the artificial surface as artificial and thus do not initiate a foreign body reaction [41,57]. 

In contrast to bioinert materials, which are designed to prevent any interaction with the surrounding medium, bioactive materials come in contact with the environment as they trigger a specific material-tissue interaction such as EC proliferation or release drugs such as anticoagulation or anti-inflammatory agents [1,11,75]. 

Bioceramic materials have developed into a very powerful driver of advanced ceramics research and development. For many years bioceramics, both bioinert materials such as alumina, zirconia and, to a limited extent titania (Lindgren et al., 2009), and bioconductive materials such as hydroxyapatite, tricalcium phosphate and calcium phosphate cements, have been used successfully in dinical practice. In addition, applications continue to emerge that use biomaterials for medical devices. An excellent account of the wide range of bioceramics available today has recently been produced by Kokubo (2008), in which issues of the significance of the structure, mechanical properties and biological interaction of biomaterials are discussed, and their clinical applications in joint replacement, bone grafts, tissue engineering, and dentistry are reviewed. The type and consequences of cellular responses to a variety of today s biomaterials have been detailed in recent books (Di Silvio, 2008 Basu et al., 2009 Planell et al., 2009). 

Bioactive materials show a positive interaction with living tissues that includes also the differentiation of immature cells towards bone cells. In contrast to bioinert materials, a chemical bonding to the bone occurs along the interface ... 

Osteoconductivity is the ability of a biomaterial to support the in-growth of bone cells, blood capillaries, and perivascular tissue into the gap between implant and existing bone. Efficient in-growth is supported by intercormected pores of 150-450 xm size. Hence, the development of such a pore system in plasma-sprayed hydroxyapatite coatings is of the utmost importance, as nonporous coatings may act like bioinert materials and their eventual substitution by bone is not guaranteed. 

Early studies on biomaterials were based upon the idea that implants would not degrade in the human body or be involved in biological reactions. Hence the search was for bioinert materials, whatever their chemical composition. However, no material implanted in living tissue is inert and all materials elicit a response from the host tissue. Eor... 

Bioactive or surface reactive The concept of bioactive material is intermediate between a bioinert material and biodegradable or resorbable material. Upon implantation in the host, surface reactive ceramics form a strong bond with adjacent tissue. The bioactive materials (ceramics, glasses and glass-ceramics) bone to living bone through a carbo-hydroxyapatite layer (CHA) biologically active, which provides the interface union with the host. This phase is chemical and structurally equivalent to the mineral phase of the bone, and the responsible of the interface imion. 

In contrast to early approaches involving purely bioinert materials, the concept of bioactive ceramics was founded on the assumption that optimum biocompatibility can only be achieved by promoting the formation of normal tissue on the surface of ceramic implants [129, 156]. Such biologically active implants are interfacially bonded to the surrounding tissue, and therefore provide optimum fixation, preventing phenomena such as micromovements that might lead either to deteriora-... 

In some cases, nano-HA-collagen composites have been selected as coating materials for other bioinert materials in order to improve their biocompatibility. 

Badly broken bones are often repaired through the use of traditional, bioinert materials, such as titanium alloys. The metals are used to either hold broken bones in place to allow union or hold a graft in place. Porous metals can also be used to anchor materials in place, by allowing bone to grow into the pores (mechanical fixation). However, no material is completely bioinert Those that do not cause toxicity, do not degrade, or do not bond with tissue are termed nearly inert. Nearly inert materials do trigger a response fi om the immune system, in which fibrous scar tissue forms around the implant, isolating it from the body. 

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