Blood contacting devices

Biomedical Applications Due to their excellent blood compatibility (low interaction with plasma proteins) and high oxygen and moisture permeabilities, siloxane containing copolymers and networks have been extensively evaluated and used in the construction of blood contacting devices and contact lenses 376). Depending on the actual use, the desired mechanical properties of these materials are usually achieved by careful design and selection of the organic component in the copolymers. 

Leventon, W., Hemocompatible Coatings for Blood-Contacting Devices, MD DI, Aug. 2003. 

The blood-materials interactions section contains a review article dealing with surface characterization. Consideration of the surface structure of biomaterials is critical to every study in this volume. This section contains 16 chapters dealing with the choice of in vivo and in vitro methods of biomaterials evaluation, biomaterials selection and modification, and cellular interactions with candidate surfaces. Individual papers dealing with the use of dogs, baboons, and goats for in vivo blood-materials evaluation can be found together with in vitro methods. There are also several contributions on polyurethanes, which are prime candidates for use in blood contacting devices. 

Protein diffusivity, however, is not always the main determinant in the composition of adsorbed protein layers. If this were the case, the composition of the adsorbed protein layer would be the same on different materials exposed to the same solution. This condition is not usually observed (Horbett, 1999), indicating that the affinity of each protein is influenced by the surface chemistry of the biomaterial (Horbett and Brash, 1995). Because proteins differ in affinity for various surface chemistries, the competitive protein adsorption process will also differ, leading to unique protein layer compositions upon different materials. Furthermore, the vast majority of protein adsorption studies have been carried out in vitro, assuming that this accurately mimics the in vivo environment. However, differences in implant site (i.e., blood-contacting devices vs solid tissue... 

Hydrophobicity of biomedical polymers influences the biocompatibility depending on the particular application such as tissue engineering, blood contacting devices, and dental implants [35]. Polymers are dynamic structures and can switch their surface functional groups depending on the environment. For example, polymeric biomaterials need to have a hydrophilic smface for most of the applications, so that the cell-adhesive proteins present in the serum will be adsorb and promote cell adhesion and proliferation. This is achieved by snrface treatment procedures such as... 

Poly(ether-urethanes) (PU) BIOSPAN Polymer Technology Croup, Inc. Heart valves, vascular grafts, and other blood-contacting devices... 

Consequently, benzamidine-modified material surfaces show a promising potential for the development of thrombin-inhibiting biomaterials to be applied in blood-contacting devices. However, due to their permanent character, immobilized inhibitors are difficult to dose. 

Table 4.3 Examples of polymers used in blood-contacting devices ...

Tyrosine-derived polyearbonates have been tested for orthopedic implants, because of their high mechanical strength. Polyacrylates, instead, are used where a more flexible material is needed, for example for thrombo-resistant coating for blood-contacting devices. 

Segmented polyurethanes (SPU) are being widely used as biomaterials in blood contacting devices (e.g.angiographic catheters). 

This paper summarises this development work which has resulted in a comprehensive range of extraction resistant flexible PVC compounds and discusses application areas ranging from stomach feeding tubes and nutritional fluid bags to blood contact devices such as dialysis sets and blood bags. 

Surfaces adsorbing a minimal amount of protein are important in many applications such as blood-contacting devices, membrane separators, sensors, and contact lenses. Therefore, much effort has been expended on minimizing or eliminating protein adsorption. To prevent protein adsorption, the utilization of water-solnble polymers such as polyacrylamide, poly(A -vinyl-2-pyrrohdone), and PEO has been considered. In particular, PEO has a low interfacial free energy with water, unique solution properties, molecular conformation in aqueous solution, high surface mobility, and steric stabilization effects [38,39] (Figure 11.5). 

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