Lubricious Coatings Research Articles

Creating Anti‐Biofouling Surfaces by Degradable Main‐chain Polyphosphoester Polymer Brushes

AbstractThe implementation of polymer brush coatings has proven crucial in biomedical and biotechnological applications for controlling biological interactions. Despite the extensive research and use of synthetic polymer coatings, concerns regarding their long‐term non‐biodegradability have arisen. This issue is significant as non‐degradable polymers can lead to complications such as inflammatory responses and bioaccumulation, highlighting the need for polymers that degrade in a controlled manner. To address this, polyphosphonate brushes are synthesized as anti‐biofouling coatings on silicon surfaces via controlled surface‐initiated organocatalytic ring‐opening polymerization (SI‐ROP) of cyclic phospholanes. 2‐Ethyl‐2‐oxo‐1,3,2‐dioxaphospholane and 2‐hexyl‐2‐oxo‐1,3,2‐dioxaphospholane are chosen as the monomers to prepare hydrophilic and hydrophobic brushes with thicknesses up to 55 nm, with a proven degradability in aqueous media. In addition, protein adsorption, bacterial adhesion, and biofilm formation are investigated as a function of the polyphosphonate side chain. Compared to non‐coated surfaces and polyester brushes, hydrophilic poly(2‐ethyl‐2‐oxo‐1,3,2‐dioxaphospholane) brushes have an enhanced resistance toward fouling of albumin, fibrinogen, and diluted human serum proteins, as well as toward Escherichia coli and Staphylococcus aureus bacteria. The stability and anti‐biofouling performance of hydrophilic polyphosphonate brushes position them as an attractive option as degradable materials for anti‐biofouling matrices on medical devices and/or lubricious coatings for artificial implant technologies.

Surface Integrity Enhancement of Inconel 718 in Dry Turning using Novel Soft Metallic Coated Lubricants

Inconel 718 is a critical component in many sectors such as aerospace and nuclear due to its outstanding properties. As in these sectors parts are exposed to intense environments, any failure in the system can be calamitous. Thus, there are strict requirements for manufacturing precision and quality enforcement. However, poor machinability of Inconel 718 parts has caused ongoing challenges for both researchers and industry. The difficulties arise from the poor surface integrity of the machined parts due to its high strength at elevated temperatures, susceptibility to work-hardening, presence of hard carbides, low thermal conductivity, and built-up edge formation during machining. These characteristics make conventional machining methods less effective, necessitating innovative approaches. This study introduces an innovative solution to tackle this issue —a new in-situ coating method for depositing novel lubricating materials on the tool. Comprehensive machining tests and surface integrity analyses have been performed. The results show substantial improvements, including a significant prolongation in tool life, improved surface quality, and less machining-induced microstructural alteration. The success of using novel lubricious coatings in conjunction with the new in-situ method promises improved Inconel 718 machining as it resulted in exceptional tool performance and surface finishes that meet the tight standards of industry.

Microstructural evolution and tribological behavior of suspension plasma sprayed CuO as high-temperature lubricious coatings

Suspension plasma spraying (SPS) was used to produce three different CuO coatings by varying spray distance and solid loading within the suspension. The low spray distance (30 mm) and high solid loading (20 wt%) in the suspension resulted in the deposition of dense coatings as compared to other spray conditions (i.e., a distance of 40 mm and solid loading of 10 wt%). The tribological performance of the dense coating was investigated at 25 °C and 300 °C under dry sliding conditions. Scanning electron microscopy (SEM), X-ray diffraction (XRD), and Raman analysis were used to characterize the coating, and corresponding wear tracks to determine the wear mechanisms. The results showed that the friction coefficient of the CuO coating decreased from 0.7 at 25 °C to 0.46 at 300 °C. Similarly, the wear rate at 300 °C decreased by 50% compared to the wear rate at 25 °C. Ex-situ analysis showed an increased oxygen content on the worn surfaces at 300 °C and the formation of a smooth uniform tribofilm. At 25 °C, a thicker transfer film was observed on the counterface, which leads to a different velocity accommodation mode and, thus, relatively high friction.

Risk Assessment and Regulatory Exploration of the Lubrication Coating on Intravascular Medical Devices.

Lubricious polymer coatings are increasingly used on intravascular devices to facilitate application processes. Although increasing reports about the detachment and subsequent embolism of polymer particles, this iatrogenic polymer embolism has not been paid enough clinical attention for many years. This article reviews the hazard of coating separation and the difficulty to find it. Furthermore, this proposes the scientific evaluation concept and regulatory exploration to solve the problems.

A polyethylene glycol functionalized hyaluronic acid coating for cardiovascular catheter lubrication

Catheterization is a common medical operation for cardiovascular disease diagnosis and treatment, where low friction is attained through hydrophilic lubricious coatings. But these coatings can cause iatrogenic complications when particles become lose and float freely in the blood stream. Here we present an ultra-thin coating based on polyethylene glycol (PEG) functionalized hyaluronic acid (HA). The mussel-inspired biopolymer hyaluronic acid was first conjugated to dopamine (DN) to get HADN and then poly (ethylene glycol) bis (3-amino-propyl) terminated (PBA) was used to functionalize the HADN with PEG. The reciprocating sliding ball-on-flat ex vivo model based on PU ball and porcine aorta was used to evaluate the lubrication performance and the results suggest coating of HADN with best lubrication enhancement. After 40 min friction test, the surface of aorta remained intact for HADN-PBA coated PU as compared to HADN coating and positive control (sliding against bare PU). The amount of glycocalyx, number of endothelial nuclei and intima surface of aorta for coated PU were similar to negative control (without rubbing). Besides lubrication, the high biocompatibility suggests the coating of HADN-PBA is safe and lubrication benefits to the cardiovascular catheter.

A hyaluronic acid based lubricious coating for cardiovascular catheters

Hydrophilic lubricious coatings on the catheter surface reduce friction against the blood vessel wall but give rise to iatrogenic complication of particle release, embolization and thin blood vessel blockage leading to pulmonary infarction and stroke. Layer by layer deposited PLL (poly-l-lysine) and HA (hyaluronan) coating fills the urgent need of thinner lubricious coating which does not lead to release of large particles. The 8 layered PLL-HA coating was able to maintain low friction and prevent wear of endothelial glycocalyx layer (EGL). Wear and loss of EGL is a gradual process and occurred while sliding the blood vessel against bare catheter surface or 4 layered coating accompanied by epithelial cells damage and decrease in the number of nucleuses.

Scuffing Resistance and Starved Lubrication Behavior in Helicopter Gear Steels Coated with Nanocomposite Surface Coatings with and without a Hard Sublayer

Helicopter drivetrain components depend on oil lubrication to maintain elastohydrodynamic lubrication between sliding surfaces and are susceptible to a loss of lubrication event. A loss of lubrication event starves the mechanical interfaces of oil, pushing them from elastohydrodynamic toward mixed and boundary lubrication regimes. In those regimes, scuffing initiation and thermal runaway occur, resulting in a loss of torque transmission. Lubricious nanocomposite coatings made of a molybdenum disulfide and graphitic carbon are studied in combination with a titanium carbon nitride (TiCN) hard sublayer to improve scuffing resistance. Two experimental methods using a rotating ball-on-disc tribometer were conducted to evaluate the scuffing performance of the coatings. The first method is a load capacity experiment that incrementally increases load until either a maximum stress of 2.38 GPa or scuffing occurs. The second method is a loss of lubrication experiment that maintains a constant speed and contact stress with a running-in period before the lubricant supply is turned off. The elapsed time between the initiated scuff and the oil supply removal is the key experimental result. Experimental results show the time to scuffing initiation after loss of lubrication supply is extended with the application of a nanocomposite coating on a hard sublayer above the application of a hard coating alone and the uncoated medium superfinish baseline. Additional experiments were performed to study the effect of surface roughness and nanocomposite coating composition, but conclusions were limited due to a weaker adhesion strength of the TiCN sublayer applied with a lower deposition temperature to maintain steel substrate hardness.

Tribological properties of microporous polydimethylsiloxane (PDMS) surfaces under physiological conditions

Textured biomaterials have been extensively used in biomedical engineering to modulate mammalian and bacterial cell adhesion and proliferation, implant integration with human body and infection prevention. However, the tribological implications of texturing under wet physiological conditions have not been well quantified. This study aimed to characterize the tribological properties of micropore-textured polydimethylsiloxane (PDMS) under physiological conditions and investigate the effect of adsorbed lubricious molecules on friction. In this study, untextured and micropore-textured PDMS surfaces were slid against curved smooth glass surfaces under the contact pressures of 10–400 kPa, sliding speeds of 0.1–5 mm/s in aqueous solutions with the viscosity of 1–1000 mPa·s. Reconstituted human whole saliva (RHWS) at pH 7 and porcine gastric mucin (PGM) at both pH 2 and 7 were used as lubricious coatings on PDMS. While the micropore-texturing delayed the transition of lubrication regimes, it increased the coefficient of friction (COF). Although RHWS and PGM coatings decreased the COF significantly, the protein coatings could not help the COF of micropore-textured surfaces getting lower than that of untextured surfaces. The results suggest textured polymeric surfaces could generate larger friction under physiological conditions and lead to a higher chance of inflammation near the implants.

Pre-clinical evaluation of surface coating performance in guidewire surrogates: Potential implications for coated interventional surgical devices.

Purpose Polymer fragments have been identified from autopsy reports of patients who had at some point undergone intravascular procedures with medical devices (such as guidewires and catheters) with lubricious coatings. Coating separation on these devices may cause a range of adverse events, the most severe being patient death associated with undesired embolization of blood vessels by coating particles. The objective of the present study is to identify bench test methods for evaluation of hydrophobic and hydrophilic coatings to better understand the relationships between coating formulation and coating behavior, which in turn helps to determine safety and effectiveness of the coating on the device. Methods Hydrophilic or hydrophobic coatings were applied on prepared 304 V stainless steel guidewire surrogates. Coating integrity was assessed after exposing the surrogates to extended periods of soaking and rotary bend fatigue testing. Additionally, coating durability was evaluated by abrasion testing. Results Soaking tests showed deionized water can cause more changes to the microscopic appearance of the coating on the guidewire surrogates as compared to 0.9% saline at both room temperature and 37°C; however, soaking tests in either medium did not alter coating integrity after 11 hours. Rotary bend fatigue, which subjects the coatings to both tension and compression, did not affect coating integrity on the guidewire surrogates after three hours. The pad material used in abrasion testing can lead to markedly different performance predictions. Conclusion Soaking, bend fatigue test, and abrasion tests can provide valuable information on coating performance. Coating integrity and durability were affected during abrasion testing, a test method that can provide more useful information for evaluating bench coating performance. It remains to correlate these findings with clinical performance, but emphasis should be placed on comprehensive characterization. Further investigation is needed by multidisciplinary stakeholders: materials scientists, engineers, and clinicians, to properly inform next steps.

Analysis: Particulate Limits for Intravascular Devices: Considerations for Polymer Coating Embolism.

Lubricious polymer coatings are increasingly used on intravascular devices to facilitate easier access and navigation through tortuous blood vessels. Recent reports highlight the separation and downstream embolism of polymer particles affecting the vasculature and various organs. The Food and Drug Administration (FDA) acknowledges polymer coating embolism as an iatrogenic complication of intravascular devices and continues to close gaps in standards related to coating integrity. The Association for the Advancement of Medical Instrumentation established particulate testing as an industry standard for evaluating coating integrity of intravascular devices. The FDA recognizes this standard; however, challenges exist in setting particulate limits that may compromise device function without sufficient clinical data. The microscopic nature of polymer emboli not visible with available imaging modalities has impacted reporting. This has also resulted in a reduced number of manufacturer-driven product development projects related to coating integrity. On the other hand, recent procedural trends have supported the innovation of coated devices with expanded indications, requiring particulate evaluations and release limits. This article proposes a methodology to set particulate limits for intravascular devices given existing clinical, regulatory, and manufacturing challenges. The approach with standardization requirements enables characterization, comparison, and evaluation of lubricious coatings from various manufacturers. It incorporates a step-by-step procedure that adds scrutiny to the application of coatings while ensuring device function is not impacted. Together with particulate assessments, clinicopathologic and animal studies permit an understanding of particulate ranges from commercially available devices and setting of particulate limits for new device evaluations.

Biofunctional catheter coatings based on chitosan-fatty acids derivatives

Multifunctional and biofunctional coatings for medical devices are an attractive strategy towards tailoring the interactions of the device with the body, thereby influencing the host response, and the susceptibility to microbial colonization. Here we describe the development of a coating process to yield amphiphilic, lubricious coatings, resistant to bacterial colonization, based on chitosan. Chitosan-fatty acid derivatives were obtained by simultaneous N,O-acylation of chitosan with either linoleic, α-linolenic, or dilinoleic acid. Chemical characterization of new materials was carried out using 1H NMR, FTIR, and XPS. Surface properties of coated polyester samples were studied using SEM and contact angle measurements, which indicated that the incorporation of hydrophobic constituents into chitosan macromolecules led to a decrease of both surface roughness and water contact angle. Importantly, tribological testing demonstrated that these new coatings decrease the coefficient of friction due to the self-organization of fatty acid (from 0.53 for the neat chitosan to 0.35 for chitosan-fatty acid derivative). Meanwhile, preliminary bacterial colonization tests indicated significant—over 80%—reduction in E. coli colonization following coating with chitosan-linoleic and chitosan-α-linolenic derivatives. Finally, cytotoxicity and hemocompatibility studies confirmed that all amphiphilic chitosan-fatty acid derivatives were non-toxic and non-hemolytic. Collectively, our results demonstrate the potential of the developed coating strategy, particularly the chitosan-linoleic and chitosan-α-linolenic acid derivatives, for applications as biofunctional catheter coatings.

Anti-fouling strategies for central venous catheters.

Central venous catheters (CVCs) are ubiquitous in the healthcare industry and carry two common complications, catheter related infections and occlusion, particularly by thrombus. Catheter-related bloodstream infections (CRBSI) are an important cause of nosocomial infections that increase patient morbidity, mortality, and hospital cost. Innovative design strategies for intravenous catheters can help reduce these preventable infections. Antimicrobial coatings can play a major role in preventing disease. These coatings can be divided into two major categories: drug eluting and non-drug eluting. Much of these catheter designs are targeted at preventing the formation of microbial biofilms that make treatment of CRBSI nearly impossible without removal of the intravenous device. Exciting developments in catheter impregnation with antibiotics as well as nanoscale surface design promise innovative changes in the way that physicians manage intravenous catheters. Occlusion of a catheter renders the catheter unusable and is often treated by tissue plasminogen activator administration or replacement of the line. Prevention of this complication requires a thorough understanding of the mechanisms of platelet aggregation, signaling and cross-linking. This article will look at the advances in biomaterial design specifically drug eluting, non-drug eluting, lubricious coatings and micropatterning as well as some of the characteristics of each as they relate to CVCs.

A method for the systematic assessment of lubricant performance during superplastic sheet forming

AbstractFrictional forces at the die‐sheet interface during superplastic forming play an important role in controlling material flow. As such, lubricious coatings are routinely used to facilitate a low friction flow of sheet metal into the die cavity. They may also act as parting agents and/or oxidation barriers. The selection of coatings for the superplastic forming of Ti‐6Al‐4 V is limited by the requirement of thermomechanical stability at the high forming temperature, therefore, solid film coatings such as boron nitride are a common choice. However, little work has been published on coating performance during superplastic forming, particularly under true process conditions. This paper presents a method for the systematic assessment of superplastic forming coating performance by using a multi‐pocket die, which allows many coating types and combinations to be tested simultaneously during a single forming cycle. Sixteen coating combinations were evaluated in total and the resultant sheet thickness distributions compared, serving as an indicator of friction.

Macromolecular photoinitiators enhance the hydrophilicity and lubricity of natural rubber

ABSTRACTA mild and facile strategy to coat natural rubber (NR) with a hydrophilic coating is described that uses light and photoinitiator copolymers. Five high molecular weight photoinitiator copolymers, composed of hydrophilic (e.g., 2‐hydroxyethyl acrylate [HEA], poly(ethylene glycol) [PEG], N‐vinylpyrrolidone [NVP], N‐isopropylacrylamide [NIDAM], and acrylic acid [AA]) and hydrophobic benzophenone (BP) units, are synthesized and evaluated for coating NR on UV irradiation. When the HEA/BP, NVP/BP, and AA/BP macromolecular photoinitiators attach to the NR surface, the latter becomes hydrophilic. The resulting hydrophilic coatings on NR sheets are analyzed via FT‐IR spectroscopy, scanning electron microscopy, atomic force microscopy, contact angle measurements, and transwell cytotoxicity assays using NIH 3T3 fibroblast cells. The addition of high molecular weight hydrophilic polymers (e.g., polyvinylpyrrolidone and poly(2‐methacryloyloxyethyl phosphorylcholine)) to the coating further enhances the coating's hydrophilicity and lubricity. The application of these non‐cytotoxic, hydrophilic, and lubricious coatings on NR expands current applications and usage of NR. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016, 133, 43930.

Friction behaviour of hydrophilic lubricious coatings for medical device applications

The friction behaviour of new chitosan derivative coatings obtained by chemical modification of chitosan with fatty acids (linoleic and dilinoleic acid) has been investigated in order to explore their potential as endovascular catheter coatings and to benchmark them against commercially available coatings used in endovascular catheter applications. An in vitro tribological system was developed that was intended to represent to a limited extent the in vivo tribological conditions of a typical endovascular catheterization procedure. Continuous reciprocating sliding tests were carried out with uncoated and coated polymer specimens. The results showed that all of the coatings tested decreased the coefficient of friction compared to the uncoated polymer. Compared to a neat chitosan coating, the chitosan derivative coatings showed a clear reduction in the coefficient of friction to levels similar to those of the commercially-available coatings. A comparison between the friction results and contact angle measurements carried out on the coatings indicated that a range of contact angle values exists for which the friction coefficient is at a minimum. The reason for this is unclear and further studies are required in order to confirm and investigate the trend, especially within the context of hydrophilic lubricious coating development.

In vivo distribution of particulate matter from coated angioplasty balloon catheters

Most catheter-based vascular medical devices today have hydrophilic lubricious coatings. This study was designed to perform a territory-based downstream analysis of end organs subsequent to angioplasty with coated balloon catheters to better understand the potential in vivo physiological consequence of coating wear materials. Coronary angioplasty was performed on swine using balloon catheters modified with two polyvinylpyrrolidone (PVP)-based coatings of similar lubricity, but different levels of particulates (5-fold) when tested in a tortuous path model. Myocardial tissues examined 28 days post-angioplasty revealed no visible particulates in the animals treated with the lower particulate catheters while 3 of 40 sections from higher particulate catheters contained amorphous foreign material, and 1 of 40 sections from tissue treated with uncoated catheters had amorphous foreign material. Non-target organs and downstream muscle revealed no particulates for any of the treatments. Histological analysis showed that the overall number of vessels with embolic foreign material was low and evidence of myocyte necrosis was rare with either of the coatings investigated in this study.

Wear and Friction Testing of Hard and Soft Lubricious Coatings in Dry Sliding for Use in Small Arms Action Components

Abstract Use of liquid lubricants in dry and dusty environments can lead to malfunction or jamming of small arms weapon actions. To eliminate the need for liquid lubricants, dry or “lubricious” coatings are desired for various key interfaces of such components. The tribological performance of a variety of coatings was assessed under unlubricated sliding conditions to simulate a pin-in-slot component geometry. Coating screening tests were run using a cylinder-on-flat geometry and self-mated coated couples. Tests were run in both reciprocating and unidirectional modes, with sliding velocities up to 3.6 m/s, at room temperature and 150°C. Progressive wear of the coating was monitored using a replicating technique and the measured width of the wear scar on the cylindrical pin, from which the wear coefficient was determined. Failure of the coating was determined not by visual wear-through of the coating, which can be misleading, but by an increase in the coefficient of friction (COF) and/or the occurrence of galling. In the high speed unidirectional tests, friction could be measured directly. However, in the reciprocating tests, test rig design limited the speed at which the COF could be determined. An improved rig design resulted from this work. The screening tests ranked the tribological performance of the coatings using the coefficient of friction, the wear coefficient, and number of cycles to coating failure. The coating types assessed covered a broad range of hardness, composition, and deposition methods. Coating types investigated included hard vapor-deposited TiCN coatings, relatively soft organic PTFE-filled resin-bonded coatings, modified anodized coatings (for aluminum), electroless nickel alloy coatings, PTFE-filled electroless nickel coatings, phosphate pre-treatment combined with dry-film burnished MoS2, and a ferritic nitro-carburizing treatment. Substrates included medium carbon steel, D2 tool steel, and 6061-T6 aluminum.

Is Magnetic Resonance Image Guidance the Key to Opening Chronic Total Occlusions?

Through progressive plaque growth or fibrotic organization of occlusive thrombus, atherosclerosis may result in chronic total occlusion (CTO) of a major arterial conduit. If CTO develops slowly, collateral pathways may supply sufficient perfusion to retain tissue viability despite occlusion of the major inflow conduit. However, such collateral-mediated perfusion rarely matches that provided by an open main conduit, particularly during the peak demand of regional muscular activity. Although strategies to limit regional oxygen demand (eg, β-blockers for the treatment of angina pectoris) or to enhance collateral function (eg, a walking program for superficial femoral occlusion, experimental angiogenesis) may be of some benefit, these approaches generally offer less complete return of normal physiology and relief of ischemic symptoms than does direct revascularization of the occluded vessel. With surgical bypass, the nature of the occlusion (its length, duration, tortuosity, calcification) is less important than the presence of a suitable distal anastomotic target. On the other hand, with catheter-based techniques, success depends heavily on these lesion characteristics. In fact, crossing such occluded segments with a guidewire remains the dominant barrier to catheter-based treatments of occluded arterial segments. Once the guidewire has been passed successfully into the distal true lumen, the process of dilating and stenting the segment is usually straightforward and durable, at least with the use of drug-eluting stents in coronary CTOs.1,2 Article p 1101 Devices designed to cross CTOs should have 3 key features: an ability to distinguish a true luminal path from one created within (dissection) or through (perforation) the vessel wall of the occluded segment, an ability to change direction (steer) to correct deviations from the desired path through the occlusion, and an ability to penetrate the frequently fibrotic and focally calcific substance of the occlusion through the use of either mechanical stiffness or an alternative energy modality (laser, …

Elevated Temperature Fretting Evaluations Using a Flat-on-Flat Configuration

Traditional fretting tests rely on the high Hertzian stress contacts between a cylinder or sphere and a flat surface to generate oxide particles and an eventual wear scar. However, this configuration does not always match the stresses and wear mechanism associated with parallel surfaces where fretting may only initiate in limited regions of contacting asperities. To simulate these conditions at 175°F, fretting wear tests were used to evaluate the performance of High Velocity Oxy-Fuel (HVOF) and Plasma-sprayed Cu Ni In coatings for the reduction of gross-slip fretting (relative displacements of 100 μm) experienced between mating beta-c titanium bosses and 4340 steel lugs. Scanning electron microscopy was then used to compare the frequency and severity of fretting wear on the titanium blocks. Results of the analysis indicated the viability of the lubricious coatings for eliminating the instances of fretting. Furthermore, the tests indicated the usefulness of the flat-on-flat testing configuration for illuminating the potentially random occurrences of fretting damage between parallel surfaces. Presented at the 53rd Annual Meeting in Detroit, Michigan May 17–21, 1998

Thermal stability of sodium hyaluronate in aqueous solution

Since its identification 60 years ago as a ubiquitous component of the body of mammals, hyaluronic acid has been widely studied, primarily in the fields of medicine and biology. On the other hand, our research has dealt with hyaluronic acid as a chemical intermediate in the synthesis of novel lubricious coatings, and in this connection data were needed on stability of aqueous solutions of the polymer over a range of temperatures from 25-100 degrees C. The investigation reported here provides that information, obtained by exposing samples in sealed ampules in baths at controlled temperatures and determining the resulting change in viscosity of the solutions. Data of this kind have not previously been reported on sodium hyaluronate freed from the proteins and other organics normally associated with the polymer in its natural environment.