Imperturbable surface

An empirical method to estimate the surface tension of a solid is Zisman s plot (cos 9 as a function of yl), which obtains the critical surface tension of wetting. In the absence of specific interaction between the surface and the liquids used for the measurement of contact angles, the critical contact angle of wetting can be accurately estimated and its value used as the surface tension of the surface. However, if a surface interacts with liquids used as the sessile droplet for the contact angle measurement, to the extent that the surface tension is altered, Zisman s plots deviate from the ideal linear relationship. In a strict sense, the plot is applicable only to imperturbable surfaces with which liquid contact does not alter surface configuration, i.e., no surface dynamics applies. 

The FHT measured by the Wilhelmy balance method can be effectively used to compare the liquid holding capabilities of different surfaces. The value of FHT depends on the experimental parameters and cannot be used in an absolute sense. In general, the aqueous film stability is obtained when spontaneous wetting occurs on imperturbable surfaces. However, moderately hydrophilic and possibly even some hydrophobic surfaces that are perturbable by water were found to be capable of holding continuous films of water. Multicomponent fluid, such as a dilute solution of protein used as a simulated tear fluid, may yield misleading liquid holding characteristics of surfaces due to preferential adsorption of components on a surface. 

Surface configuration can be fixed by chemical reactions. This is the foundation for the creation of an imperturbable surface. LCVD processing is extremely useful in this particular aspect. 

The three unique and important features of type A LCVD nanofilm—imperturbable surface (Chapter 29), nanoscale molecular sieve (Chapter 34), and new surface state of material (Chapter 24) make LCVD coating an ideal tool in preparation of biomaterials. It should be reiterated that these three features of LCVD films are limited to type A plasma polymers described in Chapter 8, and type B plasma polymers should be excluded in LCVD coatings for biomaterials based on the concept of imperturbable surface. The particularly important aspect is that the LCVD nanofilm becomes the new surface state of the substrate material, i.e., it is not just a coating placed on the surface. The first and second features describe the nature of the new surface state. 

LCVD coating for biomaterials is the neutral approach illustrated by the athrombogenic surface. The advantage of the neutral approach in biomaterials is not well recognized, simply because finding such a surface in the domains beyond the imperturbable surfaces of type A plasma polymers is extremely difficult. 

Rates of platelet destruction varied from 1.1 x 10 to 5.6 x 10 platelets per cm of exposed surface per day. Since studies evaluating polyurethanes as well as acrylic and methacrylic polymers and copolymers showed that platelet destruction rates may exceed 20 x 10 platelets/cm -day, the nine plasma polymers evaluated were considered to be considerably less reactive. Since each polymer was evaluated only four or five times with average results in each case near the lower sensitivity limit for this test system (about 1 x 10 platelets/cm -day), further statistical interpretations of the data presented in Table 35.7 would be inappropriate. Thus, due to the passive nature of these materials, conclusions could not be drawn regarding the relative importance of specific surface chemical moieties, i.e., all plasma polymers investigated are relatively nonreactive regardless of type of monomer used. This might imply that all type A plasma polymers have the characteristic feature of imperturbable surface regardless of what kind of atoms and moieties are involved, and because of this feature all plasma polymers tested performed better than most conventional polymers. 

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. 

The protein adsorption becomes much more complicated when multicomponent systems are involved. One surface modification to reduce adsorption of one protein could lead to increased adsorption of other proteins, and it is generally very diiScult to reduce the protein adsorption from living biological (multicomponent) system by surface modification. In this context, the remarkable reduction in protein adsorption from a live biological system shown in the figure is an outstanding performance, which is a testimony to the biocompatibility by virtue of an imperturbable surface of LCVD coating. 

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. 

Timely and up-to-date, this book provides broad coverage of the complex relationships involved in the interface between gas/solid, liquid/solid, and solid/solid...addresses the importance of the fundamental steps in the creation of electrical glow discharge... describes principles in the creation of chemically reactive species and their growth in the luminous gas phase... considers the nature of the surface-state of the solid and the formation of the imperturbable surface-state by the contacting phase or environment... offers examples of the utilization of LCVD in interface engineering processes...presents a new perspective on low-pres.sure plasma and emphasizes the importance of the chemical reaction that occur in the luminous gas phase...and considers the use of LCVD in the design of biomaterials. 

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