Biocompatibility of polymeric surfaces

M. Stangegaard, Z. Wang, J.P. Kutter, M. DufVa and A. Wolff, Whole genome expression profiling using DNA microarray for determining biocompatibility of polymeric surfaces. Molecular Biosystems, 2(9), 421 28 (2006). 

This review of the biocompatibility of polymeric surfaces concentrates on the observed differences of hydrophilic, hydrophobic, and heterogenic materials as measured by their interactions with proteins and platelets. Emphasis is placed on materials for use in injection molding applications. 

When a similar plasma polymerization coating was applied on the surface of a memory-expandable stainless steel stent, whose bare surface has notoriously poor blood compatibility, and implanted in a pig without using any drug to suppress blood coagulation, all five coated samples stayed patent, whereas uncoated stents with drug showed partial to total closure [7]. Such a clear-cut result, i.e., 5 out of 5 patency, has been scarcely seen in any animal experiments, which again seems to indicate the superior biocompatibility of imperturbable surfaces created with LCVD coatings. 

Cell adhesion. For most applications the adhesion of cells is of fnndamental interest being the initial event of cell attachment. A simple method to quantify adherent cells is to incnbate cells over a snrface for a period of time snbsequently followed by the detachment of loosely adherent cells by gently washing the surface. Remaining cells can be labeled by flnorescent dyes and quantihed using flnorescent measnrements. Cell adhesion assays are also freqnently used to assess monocyte or platelet adhesion on polymeric snrfaces [215, 216]. In this context Hezi-Yamit et al. [217] did show that polymer hydrophilicity should be considered as a parameter to assess the biocompatibility of polymer surfaces. They showed that hydrophobic polymers such as PBMA or SIBS promote the adhesion of inflammatory activated monocytes while more hydrophilic polymers (e.g. PC (Phosphorylcholine) polymer) lead to less pro-inflammatory responses. 

Figure 3. During the first day after removal from the bath, a weight loss was observed, which most likely was due to evaporation of the volatile components such as the acetone and water used in the treatment bath. As indicated in Figure 3, the sample treated with water alone had an overall weight gain lower than the sample also containing PEG. These observations demonstrate how polymeric additives or non-volatile materials can be incorporated in the infused sector. We decided to use this technique in our attempts to improve the biocompatibility of PMMA surfaces.

While these cases are uncommon to rare in their occurrence, they represent factors which must be addressed in determining the biocompatibility of polymeric implants in humans. From another perspective, the altered implant/tissue interactions presented in these cases offer an opportunity to the pol3nner scientist who wishes to examine these complex problems. Included in these problems is an elucidation of those tissue and material variables which lead to variations in fibrous capsule formation. Little research has been done in this area and yet, since almost all human Implants are partially or totally encapsulated, this area would appear to be of prime importance in determining the biocompatibility of human implants. The other major area which appears to be common to the majority of implants is the infectious susceptibility of implants. Does the implant/tissue interaction predispose the tissue to an infectious process through a biochemical or physiologic mechanism What is the influence of the surface properties of the implant on interaction with bacteria and other organisms ... 

Hydrophobic polymer materials that slowly release N O can be used on the surface of medical devices. Many medical devices suffer from the surface adhesion of blood platelets. To minimize this thrombogenic effect, blood thinners such as heparin, coumarin, and aspirin are often used. However, systemic administration of antiplatelet agents could increase the risk of uncontrolled bleeding elsewhere in the body. In contrast, biocompatible polymer films would solve this problem [153]. It is possible to create polymeric surfaces that mimic the inner surface of a blood vessel by... 

As was demonstrated, a variety of polymeric materials are used for preparation of dye-doped beads. Dye-doped silica beads are also extremely popular due to their chemical robustness, biocompatibility and simplicity in preparation and further functionalization of the surface [55]. Thus, polymeric, silica and Ormosil beads (which occupy intermediate position) are widely used as nanosensors and labels. On the other hand, quantum dots possess much higher cytotoxicity which often limits their application in biological systems. 

Approaches aiming at creating biocompatible environments consist in modifying the surface of polymeric membranes by attaching functional groups like sugars, polypeptides and then to adsorb the enzymes. 

The deposition of thin polymeric films from a cold plasma in a radio-frequency glow discharge apparatus has become an important means of modifying surfaces in materials applications [42], Applications receiving much attention recently have been the use of plasma polymerization to obtain biocompatible materials, and to produce functional surfaces for attachment of biologically active substances [43-45]. In this respect, many studies of protein adsorption have been... 

Davies MC, Roberts CJ, Tendler SJB, Williams PM. The surface analysis of polymeric biomaterials. In Braybrook J., ed. Biocompatibility Assessment of Medical Devices and Materials, John Wiley, 1997, pp. 65-99. 

In eontrast to the ease of POE, the surface of plasma polymers are imperturbable by virtue of the lack of molecular mobility at the surface. It should be eautioned, however, that the imperturbable surface is limited to type A plasma polymers and does not extend to any plasma polymers. The details of bioeom-patibility are beyond the seope this book. Only some data that seem to indieate good biocompatibility of surface of plasma polymerization coatings are shown in this chapter. 

Heller and colleagues at Advanced Polymer Systems (Redwood City, CA) continue to develop additional polyorthoesters with a variety of physical properties and potential applications. ° Generally speaking, polyorthoesters do possess the potential to exhibit surface-eroding behavior. However, several issues that may limit the commercial application of this class of polymers are still present. One issue is that synthesis of these polymers involves complicated monomers and polymerization chemistry. The second issue is, to date, the toxicology and biocompatibility of these polymers and their degradation products have not yet been fully characterized. Finally, the requirement for pH-regulating additives such as acids and bases... 

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