Electrochemical codeposition of sol-gel films on stainless steel: controlling the chemical and physical coating properties of biomedical implants.

The electrochemically assisted codeposition of sol-gel thin films on stainless steel is described. Specifically, electrodeposition of films based on aminopropyltriethoxysilane (APTS), and its codeposition with propyltrimethoxysilane (PrTMOS) and phenyltrimethoxysilane (PhTMOS) has been accomplished by applying negative potentials. The latter increases the concentration of hydroxyl ions on the stainless steel surface and thus catalyzes the condensation and deposition of the sol-gel films. The films were characterized by profilometry, electrochemical impedance spectroscopy (EIS), alternating current voltammetry (ACV), goniometry, atomic force microscopy (AFM) and scanning electron microscopy (SEM). AFM and SEM analysis of codeposited APTS:PrTMOS films disclosed the structural changes induced by altering the deposition solution composition and the applied potential. Codeposited APTS:PhTMOS did not show any structural differences from their electrodeposited homopolymers, while Nano Scratch Test clearly revealed the changes in the elastic and adhesion properties, suggesting the formation of an APTS:PhTMOS composite. EIS of the films showed good resistance towards penetration of hydrophilic species, such as hexacyanoferrate. ACV measurements of the homo and codeposits showed the decrease of the interfacial capacity as a result of the electrochemical deposition. In essence, controllable sol-gel films with tunable chemical and physical properties based on controlling the combination of the precursors, pH and electrochemical properties can be electrodeposited on conducting surfaces. The application of this approach has been demonstrated by coating a stainless steel coronary stent.

Measurement of Cohesion and Adhesion of Semiconducting Polymers by Scratch Testing: Effect of Side-Chain Length and Degree of Polymerization.

Most advantages of organic electronic materials are enabled by mechanical deformability, as flexible (and stretchable) devices made from these materials must be able to withstand roll-to-roll printing and survive mechanical insults from the external environment. Cohesion and adhesion are two properties that dictate the mechanical reliability of a flexible organic electronic device. In this paper, progressive-load scratch tests are used for the first time to correlate the cohesive and adhesive behavior of poly(3-alkylthiophenes) (P3ATs) with respect to two molecular parameters: length of the alkyl side chain and molecular weight. In contrast to metrological techniques based on buckling or pull testing of pseudofreestanding films, scratch tests reveal information about both the cohesive and adhesive properties of thin polymeric films from a single procedure. Our data show a decrease in cohesion and adhesion, that is, a decrease in overall mechanical robustness, with increasing length of the side chain. This behavior is likely due to increases in free volume and concomitant decreases in the glass transition temperature. In contrast, we observe increases in both the cohesion and adhesion with increasing molecular weight. This behavior is attributed to an increased density of entanglements with high molecular weight, which manifests as increased extensibility. These observations are consistent with the results of molecular dynamics simulations. Interestingly, the normal (applied) forces associated with cohesive and adhesive failure are directly proportional to the average degree of polymerization, as opposed to simply the molecular weight, as the length of the alkyl side chain increases the molecular weight without increasing the degree of polymerization.

Scalable, ultra-resistant structural colors based on network metamaterials.

Structural colors have drawn wide attention for their potential as a future printing technology for various applications, ranging from biomimetic tissues to adaptive camouflage materials. However, an efficient approach to realize robust colors with a scalable fabrication technique is still lacking, hampering the realization of practical applications with this platform. Here, we develop a new approach based on large-scale network metamaterials that combine dealloyed subwavelength structures at the nanoscale with lossless, ultra-thin dielectric coatings. By using theory and experiments, we show how subwavelength dielectric coatings control a mechanism of resonant light coupling with epsilon-near-zero regions generated in the metallic network, generating the formation of saturated structural colors that cover a wide portion of the spectrum. Ellipsometry measurements support the efficient observation of these colors, even at angles of 70°. The network-like architecture of these nanomaterials allows for high mechanical resistance, which is quantified in a series of nano-scratch tests. With such remarkable properties, these metastructures represent a robust design technology for real-world, large-scale commercial applications.

Effect of vacuum-treatment on deformation properties of PMMA bone cement.

Deformation behavior of polymethyl methacrylate (PMMA) bone cement is explored using microindentation. Two types of PMMA bone cement were prepared. Vacuum treated samples were subjected to the degassing of the material under vacuum of 270 mbar for 35 s, followed by the second degassing under vacuum of 255 mbar for 35 s. Air-cured samples were left in ambient air to cool down and harden. All samples were left to age for 6 months before the test. The samples were then subjected to the indentation fatigue test mode, using sharp Vickers indenter. First, loading segment rise time was varied in order to establish time-dependent behavior of the samples. Experimental data showed that viscous part of the deformation can be neglected under the observed test conditions. The second series of microindentation tests were realized with variation of number of cycles and indentation hardness and modulus were obtained. Approximate hardness was also calculated using analysis of residual impression area. Porosity characteristics were analyzed using CellC software. Scanning electron microscopy (SEM) analysis showed that air-cured bone cement exhibited significant number of large voids made of aggregated PMMA beads accompanied by particles of the radiopaque agent, while vacuum treated samples had homogeneous structure. Air-cured samples exhibited variable hardness and elasticity modulus throughout the material. They also had lower hardness values (approximately 65-100 MPa) than the vacuum treated cement (approximately 170 MPa). Porosity of 5.1% was obtained for vacuum treated cement and 16.8% for air-cured cement. Extensive plastic deformation, microcracks and craze whitening were produced during indentation of air-cured bone cement, whereas vacuum treated cement exhibited no cracks and no plastic deformation.

Electropolymerized tricopolymer based on N-pyrrole derivatives as a primer coating for improving the performance of a drug-eluting stent.

The coating of medical implants by polymeric films aims at increasing their biocompatibility as well as providing a durable matrix for the controlled release of a drug. In many cases, the coating is divided into a primer layer, which bridges between the medical implant and the drug-eluting matrix. The primer coating must be very carefully designed in order to provide optimal interactions with the surface of the medical implant and the outer layer. Here we present a simple and versatile approach for designing the primer layer based on electropolymerization of a carefully chosen blend of three different pyrrole derivatives: N-methylpyrrole (N-me), N-(2-carboxyethyl)pyrrole (PPA), and the butyl ester of N-(2-carboxyethyl)pyrrole (BuOPy). The composition and physical properties of the primer layer were studied in detail by atomic force microscopy (AFM) and a nano scratch tester. The latter provides the in-depth analysis of the adhesion and viscoelasticity of the coating. AFM phase imaging reveals a uniform distribution of the three monomers forming rough morphology. This primer layer significantly improved the morphology, stability, and paclitaxel release profile of a paclitaxel-eluting matrix based on methyl and lauryl methacrylates.