Dependence of film surface roughness and slope on surface migration and lattice size in thin film deposition processes

A brief review of mathematical models of thin film growth and surfaces. A possible route to avoid defects in stents

The morphology of thin films has been extensively studied in the last years. The properties of a thin film are closely related to its microstructure, especially to its morphology and surface roughness. Optical reflectivity, conductivity, and porosity are characteristics that depend on the film structure. The knowledge of atomistic details of the thin film growth process is useful for the development of new techniques and the control of thin films and new materials. Models of growth process are very powerful tools that can help researchers to predict and control physical, chemical, and mechanical properties. In this work we briefly summarize the theoretical models that have been used in the studies of thin films growth. By describing the deposition process of atoms/molecules on the surface of the substrate, one can study the evolution of the bulk and the surface roughness of a thin film. If an experimental growth process is appropriately described by a theoretical model (or even a combination of one or more different models), it can also provide indications to control the surface roughness and porosity of the film. Controlling the growth process one can obtain materials with a set of desired properties, namely tribological, porosity, and electrical ones. These characteristics are necessary for example, for hosting a solid lubricant on the surface of the material. We believe that the models presented in this work can be very useful in understanding the mechanisms of control and adherence of electrodeposited films which are commonly used in medical applications such as stent devices. We also believe that the models can be helpful to the understanding surface problems related to the superficial defects in stents.

Effect of surface nanotopography on immunoaffinity cell capture in microfluidic devices

Immunoaffinity microfluidic devices have recently become a popular choice to isolate specific cells for many applications. To increase cell capture efficiency, several groups have employed capture beds with nanotopography. However, no systematic study has been performed to quantitatively correlate surface nanopatterns with immunoaffinity cell immobilization. In this work, we controlled substrate topography by depositing close-packed arrays of silica nanobeads with uniform diameters ranging from 100 to 1150 nm onto flat glass. These surfaces were functionalized with a specific antibody and assembled as the base in microfluidic channels, which were then used to capture CD4+ T cells under continuous flow. It is observed that capture efficiency generally increases with nanoparticle size under low flow rate. At higher flow rates, cell capture efficiency becomes increasingly complex; it initially increases with the bead size then gradually decreases. Surprisingly, capture yield plummets atop depositions of some particle diameters. These dips likely stem from dynamic interactions between nanostructures on the substrate and cell membrane as indicated by roughness-insensitive cell capture after glutaraldehyde fixing. This systematic study of surface nanotopography and cell capture efficiency will help optimize the physical properties of microfluidic capture beds for cell isolation from biological fluids.