Biomaterials surface features

During tapping AFM, the cantilever oscillation amplitude remains constant when not in contact with the surface. The tip is then carefully moved downward until it gently taps the surface. As the tip passes over an elevated surface feature, the cantilever has less room to oscillate, and the amplitude of oscillation decreases (vice versa for a surface depression). The oscillation frequency is typically 50-500 kHz, with an amplitude of ca. 30 nm, which is sufficient to overcome the adhesive forces that are evident in contact (and noncontact) modes (Figure 7.49). Consequently, the tapping mode is most appropriate for soft samples such as organics, biomaterials, etc. 

The three key features of LCVD coating ideally suited for biomaterial surface, and the important balance between the bulk properties and the surface properties, could be best illustrated by examples of nanofilms of methane plasma polymer on a contact lens made of polydimethylsiloxane elastomer. Hence, some details of processing factors and their influence on the overall properties of the product are described in the following sections. 

Khang D, Lu J, Yao C, Haberstroh KM, Webster TJ. The role of nanometer and sub-micron surface features on vascular and bone cell adhesion on titanium. Biomaterials 2008 29 970-83. 

Processing methods can have a major impact on the success or failure of a cardiovascular biomaterial. As described previously, surface features (either deliberately introduced or as the result of machining or tool imperfections), residues (from cleaning, handling, or sterilization), or process aids (either as surface residues or as bulk material diffusing from the biomaterial) can change the biological results. 

Mechanical factors and edge effects may modify the response to a biomaterial. Implant motion or micromotion can lead to variations in the fibrous capsule thickness and the composition of the fibrous capsule and the interfacial foreign body reaction. Edges and sharp changes in surface features may lead to a variation in fibrous capsule thickness and the presence of variable concentrations of chronic inflammatory cells, i.e., monocytes and lymphocytes. 

Zinger O, Anselme K, Denzer A, Habersetzer P, Wieland M, Jeanfils J, et al. Time-dependent morphology and adhesion of osteoblastic cells on titanium model surfaces featuring scale-resolved topography. Biomaterials 2004 25 2695-711. 

Miller, D.C., Thapa, A., Haberstroh, K.M. et al.. Endothelial and vascular smooth muscle cell function on poly(lactic-co-glycoHc acid) with nano-structured surface features. Biomaterials 25, 53, 2004. 

The role of material surface features in biomaterial design is significant but poorly understood. Spatial control of cellular adhesion and growth is critically important in tissue engineering and related fields (1-4). Metals and plastics that are widely used for medical implants lack the molecular sequence and patterns crucial for normal cell function, and therefore often trigger aberrant cell responses in long term implantation (5). One promising approach is to introduce chemical or physical patterns on biomaterial surfaces, to achieve cell ftinctions more representative of in vivo behavior. 

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. 

The main function of mucin from secretions of submaxi 11 ary glands, along with similar mucoproteins found in the respiratory, gastrointestinal, reproductive tracts and also in the tear liquid, is to lubricate epithelial cells and protect them from the external environment. The role of the mucous glycoproteins as a macromole-cular surfactant is therefore of great importance in the science and technology of biomaterials. Such different biosurfaces as dentures, contact lenses or intrauterine contraceptive devices, in spite of different functions, have one coimnon feature, namely that all are placed on a mucosal surface. 

In spite of the widespread utilization of affinity chromatography in cell separation, there are still a considerable number of problems to be solved. The most serious problem is that there is always a substantial fraction of cells that are non-specifically adsorbed on the matrix surface. The research on cell affinity chromatography done in the last decade seems to be more biased towards the improvement in operating conditions than to the development of specially designed matrices for cell separation as well as the characterization of immobilized proteins. Nevertheless, there is no doubt that further advances in affinity chromatography as an effective tool for cell separation virtually depend on the detailed understanding of the features of matrix materials and immobilized proteins, as well as their interacions at the interface. In this respect, cell affinity selection based on the specific interaction of cells with immobilized proteins on a solid-phase matrix is now a major area of interest in the field of biomaterials science. 

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