Biomedical applications, thick-film

Thick-Film Multilayer Ion Sensors for Biomedical Applications... 

CPs can be fabricated through a variety of routes which are classified as either predominantly electrochemical or chemical. While electrochemical synthesis has been more widely used for preparing nanoscale CP thin films for biomedical applications, chemical polymerization can produce large quantities of CP thick films or colloidal dispersions at low cost. Despite these advantages, chemical techniques have found relatively little application in biomedical applications. The advantages and disadvantages of electrodeposition and chemical synthesis are summarized in Table 18.2. 

Thin films prepared by ALD possess biologically relevant surface properties enabling many biomedical applications. For instance, hard CrN coatings on steel have been sealed with 50-nm-thick AI2O3—Ta20s nano-laminates prepared by ALD (Harkonen et al., 2014). The ALD layer smoothes the CrN surface because it... 

PPy is a conductive polymer with several biomedical applications owing to its good biocompatibility and the ability of cells to attach, differentiate and proliferate on its surface [148,149]. In one study, the attachment, proliferation and differentiation of rat MSCs on PPy surfaces was shown to be comparable to those of regular tissue culture plastic surfaces [150]. The synthesis of PPy involves either electrochemical or chemical polymerization, with the admicellar polymerization technique enabling the uniform deposition of thin PPy films from a few to 100 nm thick [151]. Moreover, the attachment of cells to the PPy surface can be improved, for example, via the adsorption of fibronectin or the incorporation of Arg-Gly-Asp (RGD)-containing peptides [152]. Immobilization of the glycosaminoglycans heparin and hyaluronic acid on PPy surfaces was also shown to maintain bone marrow-derived MSC cultures and to induce differentiation successfully into mature osteoblasts [153]. 

The speed with which the actuators can be switched between their expanded and contracted states depends on the polymer film thickness, since actuation depends on mass transport. Like the strain, speed also depends on the electrolyte and on the polymer structure, and the stmcture depends not only on the type of polymer, but also on the film preparation conditions. Response times for the thin films that are used in microactuators are of the order of a second, which is sufficiently fast for most biomedical applications. 

In summary, common thin film deposition technologies for surface modification and the engineering of biomaterials have been reviewed with an emphasis on the fundamentals and technology of each method. Examples of fabricated films and their applications in the biomedical fields are described. Properties such as film thickness, mechanical properties, and surface chemistry produced by different techniques can differ greatly and the choice requires systematic study and comparison. From the perspective of the development of thin film deposition techniques, the combination of the different techniques, chemical and physical, can realistically enable the exploration and expansion of existing techniques for the fabrication of future films and coatings. 

In the last decade or so, amorphous selenium has been applied as a photoconductor in X-ray image detectors, particularly for biomedical imaging. For this application, flat-panel detectors with large sensing areas (> 30 cm x 30 cm) have been developed. The coating of amorphous Se is typically 500 pm thick, and is deposited over a silicon thin film transistor layer. After applying an electrical potential to the surface, the detector is exposed to an X-ray beam and the electrons released are used to transmit information that ultimately provides an image. 

---