Biocompatibility issues

Implants may cause short- and long-term toxicity, as well as acute and chronic inflammatory responses. Adverse effects may be caused by  

The performance and response of the host toward an implanted material is indicated in terms of biocompatibility. Major initial evaluation tests used to assess the biocompatibility of an implant are listed in Table 4.1. These tests include  

Biological Effect Prolonged Contact3 Permanent Contactb  

Source FDA General Program Memorandum G95-1 Contact duration ranges from 24 hours to 30 days. 

ISO (International Standards Organizations) evaluation tests for consideration. A Additional tests which may be applicable 

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Biocompatibility issues concerns over body responses to a foreign material often raise the issues of biocompatibility and safety of an implant (discussed in the next section). 

While the composition and sequence of the amino acids have been known since 1983 (2,3), methods for increased-scale extraction were not developed until 1985. This scaled production has allowed for the development of single-part adhesive systems (Cell-Tak adhesive) for the immobilization of biologically active moieties to inert substrates. It has also permitted research on two-part adhesive formulations for the bonding of tissues. This paper specifically addresses the biocompatibility issue with descriptions of the immobilization of cells to Cell-Tak protein-coated plasticware, methods for wound closure, and preliminary toxicology data. 

Foldvari M, Bagonluri M. Carbon nanotubes as functional excipients for nanomedicines II Drug delivery and biocompatibility issues. Nanomedicine 2008 4 183-200. 

Plastic sutures (and supporting meshes) are, depending on the location of their application on or in the body, can be permanent or biodegradable in time with body fluids, and so additive and biocompatibility issues should be considered critically and carefully. 

Stress Shielding. Beyond the traditional biocompatibility issues, hard tissue biomaterials must also be designed to minimize a phenomenon known as stress shielding. Due to the response of bone remodeling to the loading environment, as described by Wolffs law, it is important to maintain the stress levels in bone as close to the preimplant state as possible. When an implant is in parallel with bone, such as in a bone plate or a hip stem, the engineered material takes a portion of the load— which then reduces the load, and as a result, the stress, in the remaining bone. When the implant and bone are sufficiently well bonded, it can be assumed that the materials deform to the same extent and therefore experience the same strain. In this isostrain condition, the stress in one of the components of a two-phase composite can be calculated from the equation ... 

H. Park, K. Park, Biocompatibility issues of implantable drug delivery systems. Pharmaceutical Research, 13,1770-6,1996. 

The first section of Part Two discusses the biological interactions of responsive surfaces with proteins (Chapter 7) and cells (Chapter 8). Interactions with in vivo environment such as blood and tissue, as well as biocompatibility issues, are addressed in Chapter 11. 

Responsive polymers have uniqne biocompatibility issues when applied as implants since the foreign body interactions may impact both their responsiveness and stability. Protein and ceU fonUng are especially crucial for implantable diagnostic devices that monitor-responsive signals continuously in vivo (Gifford et al., 2006). Capsulation and thrombus formation around the devices can result in decreased function and ultimately... 

It is important to realize that biocompatibility issues are not only relevant in respect of the well being of the host, but also in respect of the requirements of the sensor itself. More specifically, the required chemical interactions between the sensor and the body must not be interfere with by interactions—either chemical or physical— between the membrane material and contacting/adhering cells. For example, an encapsulating membrane of an electrochemically based sensor must maintain appropriate mass transport conditions for the analyte and electrolyte species, and must exclude species that could interfere with the electrochemistry, or denature or inhibit the activity of immobilized enzymes. Stability of mass transport conditions is especially critic, since any change in the permeability of the membrane or the surrounding tissues can affect the sensor calibration. Satisfactory stability can not be achieved without a biocompatible encapsulation material. 

Further biocompatibility issues of PVA were addressed by Fujimoto et al. [114]. This work focused on PVA gels that had been annealed in the presence of glycerol. When such materials were examined for their interactions with blood components, reduced adsorption and platelet adhesion were observed due to the addition of glycerol. Glycerol essentially altered the surface of the PVA gel. They described the mechanism as being due to increased tethered PVA chains on the surface which served to decrease the direct contact of blood components with the surface. 

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