Plasma Nano-Texturing of Polymers for Wettability Control: Why, What and How

Nano-texturing of polymers offers the possibility to drive important surface properties such as wettability and anti-reflectivity. Interestingly, plasma can lead to the desired characteristic of nanofeatures through a one step process based onto dry plasma etching. In this work, the literature concerning such plasma nano-texturing will be reviewed for different polymers, and in particular, for applications based upon wettability control. Then the mechanism of such processes will be commented upon, with a glance to the different characteristics of the polymers. Finally, some hints onto a feasible approach to plasma nano-texturing of the different polymers will be given.

3D Plasma Nanotextured® Polymeric Surfaces for Protein or Antibody Arrays, and Biomolecule and Cell Patterning

Plasma micro-nanotexturing is a generic technology for topographical and chemical modification of surfaces and their implementation in microfluidics and microarrays. Nanotextured surfaces with desirable chemical functionality (and wetting behavior) have shown excellent biomolecule immobilization and cell adhesion. Specifically, nanotextured hydrophilic areas show (a) strong binding of biomolecules and (b) strong adhesion of cells, while nanotextured superhydrophobic areas show null adsorption of (a) proteins and (b) cells. Here we describe the protocols for (a) biomolecule adsorption control on nanotextured surfaces for microarray fabrication and (b) cell adhesion on such surfaces. 3D plasma nanotextured® substrates are commercialized through Nanoplasmas private company, a spin-off of the National Centre for Scientific Research Demokritos.

Effects of Nanotexture on Electrical Profiling of Single Tumor Cell and Detection of Cancer from Blood in Microfluidic Channels

Microfluidic channels have been implemented to detect cancer cells from blood using electrical measurement of each single cell from the sample. Every cell provided characteristic current profile based on its mechano-physical properties. Cancer cells not only showed higher translocation time and peak amplitude compared to blood cells, their pulse shape was also distinctively different. Prevalent microfluidic channels are plain but we created nanotexture on the channel walls using micro reactive ion etching (micro-RIE). The translocation behaviors of the metastatic renal cancer cells through plain and nanotextured PDMS microchannels showed clear differences. Nanotexture enhanced the cell-surface interactions and more than 50% tumor cells exhibited slower translocation through nanotextured channels compared to plain devices. On the other hand, most of the blood cells had very similar characteristics in both channels. Only 7.63% blood cells had slower translocation in nanotextured microchannels. The tumor cell detection efficiency from whole blood increased by 14% in nanotextured microchannels compared to plain channels. This interesting effect of nanotexture on translocation behavior of tumor cells is important for the early detection of cancer.

Nanotextured polymer substrates show enhanced cancer cell isolation and cell culture

Detection of circulating tumor cells (CTCs) in the early stages of cancer is a great challenge because of their exceedingly small concentration. There are only a few approaches sensitive enough to differentiate tumor cells from the plethora of other cells in a sample like blood. In order to detect CTCs, several antibodies and aptamers have already shown high affinity. Nanotexture can be used to mimic basement membrane to further enhance this affinity. This article reports an approach to fabricate nanotextured polydimethylsiloxane (PDMS) substrates using micro reactive ion etching (micro-RIE). Three recipes were used to prepare nanotextured PDMS using oxygen and carbon tetrafluoride. Micro-RIE provided better control on surface properties. Nanotexturing improved the affinity of PDMS surfaces to capture cancer cells using surface immobilized aptamers against cell membrane overexpressed with epidermal growth factor receptors. In all cases, nanotexture of PDMS increased the effective surface area by creating nanoscale roughness on the surface. Nanotexture also enhanced the growth rate of cultured cells compared to plain surfaces. A comparison among the three nanotextured surfaces demonstrated an almost linear relationship between the surface roughness and density of captured tumor cells. The nanotextured PDMS mimicked biophysical environments for cells to grow faster. This can have many implications in microfluidic platforms used for cell handling.

Proteins, platelets, and blood coagulation at biomaterial interfaces

Blood coagulation and platelet adhesion remain major impediments to the use of biomaterials in implantable medical devices. There is still significant controversy and question in the field regarding the role that surfaces play in this process. This manuscript addresses this topic area and reports on state of the art in the field. Particular emphasis is placed on the subject of surface engineering and surface measurements that allow for control and observation of surface-mediated biological responses in blood and test solutions. Appropriate use of surface texturing and chemical patterning methodologies allow for reduction of both blood coagulation and platelet adhesion, and new methods of surface interrogation at high resolution allow for measurement of the relevant biological factors.

From superamphiphobic to amphiphilic polymeric surfaces with ordered hierarchical roughness fabricated with colloidal lithography and plasma nanotexturing

Ordered, hierarchical (triple-scale), superhydrophobic, oleophobic, superoleophobic, and amphiphilic surfaces on poly(methyl methacrylate) PMMA polymer substrates are fabricated using polystyrene (PS) microparticle colloidal lithography, followed by oxygen plasma etching-nanotexturing (for amphiphilic surfaces) and optional subsequent fluorocarbon plasma deposition (for amphiphobic surfaces). The PS colloidal microparticles were assembled by spin-coating. After etching/nanotexturing, the PMMA plates are amphiphilic and exhibit hierarchical (triple-scale) roughness with microscale ordered columns, and dual-scale (hundred nano/ten nano meter) nanoscale texture on the particles (top of the column) and on the etched PMMA surface. The spacing, diameter, height, and reentrant profile of the microcolumns are controlled with the etching process. Following the design requirements for superamphiphobic surfaces, we demonstrate enhancement of both hydrophobicity and oleophobicity as a result of hierarchical (triple-scale) and re-entrant topography. After fluorocarbon film deposition, we demonstrate superhydrophobic surfaces (contact angle for water 168°, compared to 110° for a flat surface), as well as superoleophobic surfaces (153° for diiodomethane, compared to 80° for a flat surface).

Nonfunctionalized polydimethyl siloxane superhydrophobic surfaces based on hydrophobic-hydrophilic interactions

Superhydrophobic surfaces based on polydimethyl siloxane (PDMS) were fabricated using a 50:50 PDMS-poly(ethylene glycol) (PEG) blend. PDMS was mixed with PEG, and incomplete phase separation yielded a hierarchic structure. The phase-separated mixture was annealed at a temperature close to the crystallization temperature of the PEG. The PEG crystals were formed isothermally at the PDMS/PEG interface, leading to an engineered surface with PDMS spherulites. The resulting roughness of the surface was studied by scanning electron microscopy (SEM) and atomic force microscopy (AFM). The PDMS spherulites, a few micrometers in diameter observed from SEM images, were found to have an undulated (rippled) surface with nanometer-sized features. The combination of micrometer- and nanometer-sized surface features created a fractal surface and increased the water contact angle (WCA) of PDMS more than 60°, resulting in a superhydrophobic PDMS surface with WCA of >160°. The active surface layer for the superhydrophobicity was approximately 100 μm thick, illustrating that the material had bulk superhydrophobicity compared to conventional fluorocarbon or fluorinated coated rough surfaces. Theoretical analysis of the fractal surface indicates that the constructed surface has a fractal dimension of 2.5, which corresponds to the Apollonian sphere packing.

Plasma nanotextured PMMA surfaces for protein arrays: increased protein binding and enhanced detection sensitivity

Poly(methyl methacrylate) (PMMA) substrates were nanotextured through treatment in oxygen plasma to create substrates with increased surface area for protein microarray applications. Conditions of plasma treatment were found for maximum uniform protein adsorption on these nanotextured PMMA surfaces. Similar results were obtained using both a high-density plasma (HDP) and a low-density reactive ion etcher (RIE), suggesting independence from the plasma reactor type. The protein binding was evaluated by studying the adsorption of two model proteins, namely, biotinylated bovine serum albumin (b-BSA) and rabbit gamma-globulins (RgG). The immobilization of these proteins onto the surfaces was quantitatively determined through reaction with fluorescently labeled binding molecules. It was found that the adsorption of both proteins was increased up to 6-fold with plasma treatment compared to untreated surfaces and up to 4-fold compared to epoxy-coated glass slides. The sensitivity of detection was improved by 2 orders of magnitude. Moreover, highly homogeneous protein spots were created on optimized plasma-nanotextured surfaces through deposition with an automated microarray spotter, revealing the potential of plasma-nanotextured surfaces as protein microarray substrates.