Scaling a physical device's geometry results in mechanical properties changing in various ways (e.g. the cubed-squared law states that for a scaling factor C, mass scales with C3 and surface area with C2). These scaling effects can result in a device's inconsistent and unplanned mechanical behavior when varying its fabricated size, thereby necessitating unique designs at different scales. We show that for displacement-driven compliant mechanisms, mechanical stress is uniquely invariant with scale. This effect is described theoretically, verified through computer models and physical testing, and is demonstrated in three examples: a parallel-guiding mechanism, a projectile launcher, and a deployable chair. This enhanced understanding of stress invariance provides innovative insight into the way devices can be designed for systems that operate across different scales.

Interfacing is a consistent weak point in the manufacturing of microscale gas chromatography columns. Current techniques for interfacing with microfluidic systems often degrade under high temperatures and thermal cycling and suffer from dead volumes. To address these challenges, we fabricated all-metal interfaces that connect 3D-printed microchannels (500 µm diameter) to industry-standard stainless-steel (SS) capillaries. Our fabrication process uses SS binder-jet printing and bronze infiltration to fuse the capillary to the printed part and reduce dead volumes at the interface while utilizing pressure control to prevent the infiltrant from filling the channel or capillary. These interfaces withstood pressures greater than 100 PSI and showed no leakage after thermal cycling to 350°C. Cross-sections of the interfaces show smooth connections between the channel and capillary with minimal dead volume.

IntroductionThis study aims to explore the mechanical properties of porous microelectrodes formed from vertically aligned carbon nanotube (CNT) forests. Specifically, we investigate the range of effective CNT-based microelectrode (ME) moduli that can be fabricated and identify moduli within that range that significantly reduce strain on brain tissue during micromotion.Materials and methodsTo address these questions, we developed a micromechanical measurement method, known as the dual deflection (DD) test, which is compatible with microelectrode array (MEA) form factors and can measure a wide range of moduli with a 30% uncertainty. Using the DD test with small deflections, we measured the effective Young’s modulus of freestanding CNT microelectrodes (MEs) fabricated with different carbon infiltration times (0, 15, and 30 s) at 900°C. We also developed a static 10 μm deflection finite element analysis (FEA) model to compare the brain tissue strain induced by probes with the maximum (1.7 GPa), median (72 MPa), and minimum (3.9 MPa) measured CNT moduli, along with the modulus of silicon (165 GPa) for comparison.ResultsThe DD test results showed mean effective moduli of 19.6 ± 14.5 MPa, 67.7 ± 22.7 MPa, and 168 ± 62.3 MPa for arrays fabricated with 0, 15, and 30 s infiltrations, respectively. The FEA model revealed that probes with the maximum CNT modulus induced similar strain to the silicon probes at the tip, while probes with the minimum and median CNT moduli showed minimal strain at the tip.DiscussionThese findings suggest that CNT microelectrodes with moduli in the tens of MPa range, achievable through 15 s of carbon infiltration, can significantly reduce brain tissue strain. Additionally, we consistently observed that microelectrodes with 15 s of infiltration were apparently undamaged after deflection, making them mechanically promising candidates for neural probe arrays.

Wearable health devices (WHD's) have generated significant interest because of their ability to allow individuals to track their health and use automatic computer-based detection of health issues requiring further attention. However, many wearable sensors require the test subject to be at rest to reduce noise due to body movements. To test the ability of sensors to function for active patients, we designed a force feedback wristband with active control of the pressure between a sensor and the wearer. The wristband allowed a sensor's output to be compared for active motions both during active control to keep the contact force constant (simulating resting behavior) and during no control (simulating active behavior). In addition, the band allowed measurement of biomechanical parameters of interest. The band design included a controller, actuator, and force sensors for actively controlling the contact pressure of a sensor on the wrist during user motion. A total of eight tests were performed on six human subjects to estimate previously unknown design parameters related to contact pressure control of a wrist-worn device. The design parameters investigated were system stiffness, range in contact pressure caused by motion, and range of motion in the radial direction required to maintain a desired pressure. In our tests, no significant differences were observed in a photoplethysmography (PPG) signal between states in which the contact pressure was controlled vs. not controlled, suggesting that the PPG sensor signal is relatively robust to motion.

Orthopedic implant-associated infections are a growing problem. These infections are often associated with bacterial biofilms, such as those formed by Staphylococcus aureus. Nanotextured surfaces can reduce or prevent the development of bacterial biofilms and could help reduce infection rates and severity. Previous work has shown that a carbon-infiltrated carbon nanotube (CICNT) surface reduces the growth of S. aureus biofilms. This work expands on previous experiments, showing that the topography of the CICNT, rather than its surface chemistry, is responsible for the reduction in biofilm growth. Additionally, the CICNT surface does not reduce biofilm growth by killing the bacteria or by preventing their attachment. Rather it likely slows cell growth, resulting in fewer cells and reduced biofilm formation.

We investigated the growth of carbon nanotubes (CNTs) directly on stainless steel substrates. The CNTs were grown using a two-step process: oxidation of the stainless steel surface and CNT growth. The samples were oxidized in an 800 degrees C furnace fed with a flow of air for 4 min. CNTs were grown by switching the flow to ethylene, which both reduces the oxide and initializes CNT growth. The time of CNT growth was varied to understand how the samples evolved over time. To better understand the growth mechanisms, we isolated crosssections of the CNT-substrate interface using a focused ion beam. These cross-sections were investigated with transmission electron microscopy and energy dispersive X-ray spectroscopy. CNTs were seen to grow from ironrich nanoparticles embedded in the oxide layer. The oxide layer was also seen to lose iron over time, suggesting that these iron nanoparticles were reduced out of the oxide. The base particles were embedded in the oxide layer, leaving cavities when the CNTs were removed. The diameters of the nanotubes were also seen to grow over time as a result of carbon infiltration. The effects of the embedded particle and infiltration quickly isolate the catalyst, leading to short CNTs (1-10 mu m).

Compliant mechanisms can be designed to exhibit a variety of force-deflection curves. Demonstrating a specific force behavior is an integral part of many of their applications. In this work, we select several fundamental force profiles and present compliant mechanisms that can achieve them. These force profiles are predicted using mathematical models that assume specific boundary conditions. When creating physical mechanisms, it can be often difficult to create ideal boundary conditions, particularly for mechanisms that experience axial forces. This is demonstrated first through a cantilever beam, which exhibits a linear force profile and experiences no axial forces so its boundary conditions and expected force profile are relatively easy to achieve. A more complicated case that does experience compressive axial forces-a mirrored parallel-guiding mechanism-is then examined to demonstrate its greater difficulty in achieving ideal boundary conditions. The effects of nonideal boundary conditions are then systematically explored to determine how altering specific boundary conditions from a mirrored parallel-guiding mechanism significantly alters its force profile. We also demonstrate how achieving specific force profiles is affected by factors that are difficult to control, including a small difference in force application location. Using these methods, a designer can select a compliant mechanism to achieve a specific force profile and can better predict how the force profile is affected by testing and boundary conditions.

This paper presents an algorithm to solve for all solutions to the forward problem for large deflections of inextensible end loaded Euler beams, a problem often encountered in compliant mechanism design and analysis. The forward problem is characterized by known end moment and end force (magnitude and direction), and the horizontal, vertical, and rotational deflections of the end of the beam must be found. Previous solutions have relied on the use of numerical solvers, which normally result in finding a single solution, but are unable to find all possible solutions for a given loading condition. The algorithm presented here works by reformulating the problem to have a single unknown, the end angle of the beam. Using this reformulation, a search vector of possible end angles can be used to find all solutions within desired bounds for the rotation of the end of the beam. The results were compared to nonlinear finite element modeling for verification. The results show that the vast majority of possible load conditions result in multiple (at least two) solutions, with larger end forces generally leading to more solutions. This finding suggests that such solutions may be used to design novel multi-stable compliant mechanisms, including the possibility of metamaterials with variable volume.

Implant-associated infections caused by Staphylococcus aureus are a growing problem for healthcare systems. Implant materials that resist bacterial colonization may help reduce infection rates and severity. This research examined the effect of a copper-coated carbon-infiltrated carbon nanotube surface (Cu-CICNT). We have previously shown that CICNT without copper has an anti-biofilm effect, and copper has long been known to have anti-bacterial properties. Bacterial biofilms were grown in a droplet on the Cu-CICNT surface, and a control consisting of copper deposited on a relatively flat, non-nanotube-structured surface. The Cu-CICNT surface was highly effective at reducing biofilm formation, reducing recoverable S. aureus bacteria by 99.9999% in 12 hours (a 6.3-log reduction). This effect was confirmed in both a methicillin-resistant and a methicillin-sensitive isolate of S. aureus. The Cu-CICNT surface was also highly effective against Pseudomonas aeruginosa, resulting in a 6.9-log reduction in adherent bacteria. The Cu-CICNT surface was more effective at inhibiting biofilm formation than the flat copper-coated titanium, indicating a synergistic effect between the CICNT topography and copper. The concentration of copper ions in growth media was low after exposure to Cu-CICNT (6.2 ppm), and media with this amount of supplemented copper had only a small effect on biofilm reduction, as did conditioned media previously exposed to Cu-CICNT. Our findings suggest that the antibacterial effect is likely due to contact killing of bacteria on the textured copper surface.IMPORTANCEOrthopedic implants and devices are becoming increasingly common. Unfortunately, as their use increases, so does the prevalence of implant-associated infections. These infections are most commonly caused by the bacterium Staphylococcus aureus. S. aureus infections are particularly difficult to treat because they form biofilms resistant to antibiotics and the host immune system. In this research, we used a carbon nanotube-based surface combined with a thin film of copper to produce a surface coating that could be used on implants to prevent bacterial infection. The combination of the surface topography with the copper coating resulted in over a 6-log reduction in the number of adherent bacteria, preventing the formation of a bacterial biofilm. This reduction in adherent bacteria is likely due to the surface killing effects of the bacteria on contact. The potential applications of such a surface could help reduce infection burden, improve patient quality of life, and reduce stress on healthcare systems.

High-temperature microfluidic devices (such as gas chromatography microcolumns) have traditionally been fabricated using photolithography, etching, and wafer bonding which allow for precise microscale features but lack the ability to form complex 3D designs. Metal additive manufacturing could enable higher complexity microfluidic designs if reliable methods for fabrication are developed, but forming small negative features is challenging-especially in powder-based processes. In this paper, the formation of sealed metal microchannels was demonstrated using stainless-steel binder jetting with bronze infiltration. To create small negative features, bronze infiltrant must fill the porous part produced by binder jetting without filling the negative features. This was achieved through sacrificial powder infiltration (SPI), wherein sacrificial powder reservoirs (pore size similar to 60 mu m) are used to control infiltrant pressure. With this pressure control, the infiltrant selectively filled the small pores between particles in the printed part (pore size similar to 3 mu m) while leaving printed microchannels (700 mu m and 930 mu m) empty. To develop the SPI method, a pore filling study was performed in this stainless-steel/bronze system with 370 mu m, 650 mu m, and 930 mu m microchannel segments. This study enabled SPI process design on these length scales by determining variations in pore filling across a sample and preferential filling between different sized pores.

Carbon-infiltrated carbon nanotubes (CICNT) have been discovered to have an antibacterial effect on medical grade metallic surfaces. In order to improve materials used for antimicrobial experiments, the primary aim of this investigation was to provide a more thorough understanding of the effects of controlling the height of carbon nanotubes by changing the iron catalyst layer thickness prior to carbon nanotube growth, and changing the time of the growth phase of the carbon nanotubes via chemical vapor deposition (CVD) on Ti6Al4V. All samples were coated with a barrier layer of alumina (Al2O3) of 200 nm between the Ti6Al4V and an iron growth catalyst layer. Three different groups of iron deposited thicknesses (2 nm, 4 nm, and 6 nm) were used, along with four separate growth times: 40 s, 80 s, 160 s, and 320 s. Samples were grown at 750 C for each setting of the variables, with each trial repeated three times. A subsequent infiltration period of one minute at 900 C was implemented on all batches. The samples were then analyzed under a 3D profilometer to observe the varying heights. Results show that there is a statistically significant increase in growth height with increasing growth time. Analysis of the variation in height shows that samples with 6 nm of iron and a 40 s growth time have the smallest height variation. To promote more repeatable nanotube growths, we recommend that these settings should be used for growth of nanotube films for future experiments on bacterial resistance.

Orthoplanar springs are single-component compliant mechanisms that can be fabricated from sheet material and undergo deflection orthogonal to the plane of the mechanism. They are useful in applications where spatial constraints are significant. An Euler spiral is a curve whose curvature is linearly proportional to the arc length allowing for the curve to assume a flat position under a load. In this work, orthoplanar spring and Euler-spiral concepts are synthesized to create a single-component spring mechanism that lies flat under a load. Where traditional planar springs under a load will take on an out-of-plane contour, the Euler-spiral orthoplanar spring lies completely flat under a load. The relationship between the load needed to flatten the orthoplanar Euler-spiral spring and its physical geometry is examined. A use case where the Euler-spiral orthoplanar spring is utilized as a deployment mechanism for a mid-flight emerging antenna on the surface of a flight body is presented.

Journal Article Mechanisms for Chemical Vapor Deposition Carbon Nanotube Growth by Surface Modification of 316L Stainless Steel Get access Joshua Hancock, Joshua Hancock Department of Physics, Brigham Young University, Provo, UT, United States Search for other works by this author on: Oxford Academic Google Scholar Felipe Rivera, Felipe Rivera Department of Physics, Brigham Young University, Provo, UT, United StatesElectron Microscopy Facility, Brigham Young University, Provo, UT, United States Search for other works by this author on: Oxford Academic Google Scholar Brian Jensen, Brian Jensen Department of Mechanical Engineering, Brigham Young University, Provo, UT, United States Search for other works by this author on: Oxford Academic Google Scholar Richard Vanfleet Richard Vanfleet Department of Physics, Brigham Young University, Provo, UT, United States Corresponding author: richard_vanfleet@byu.edu Search for other works by this author on: Oxford Academic Google Scholar Microscopy and Microanalysis, Volume 29, Issue Supplement_1, 1 August 2023, Pages 759–761, https://doi.org/10.1093/micmic/ozad067.375 Published: 22 July 2023

Carbon Infiltrated Carbon Nanotubes (CICNTs) show promise as a surface modification for medical devices and implants due to their potential structural resistance to bacterial colonization. However, when 316L stainless steel is used as the substrate for CICNT growth, the steel loses its passivating layer and experiences oxidative corrosion when placed in an aqueous physiological environment. This effect, confirmed by both energy dispersive x-ray analysis and electrochemical potentiokinetic reactivation, may be attributed to carburization of the alloy during CICNT production. One potential solution to this problem was investigated by employing an indirect CICNT growth method that utilized protective thin films under the CICNT surface and a nitrocellulose-based coating on other exposed edges. Samples that had been thus treated exhibited no significant corrosion over a 48-hour testing period.

Carbon Infiltrated Carbon Nanotubes (CICNTs) show promise as a surface modification for medical devices and implants due to their potential structural resistance to bacterial colonization. However, when 316L stainless steel is used as the substrate for CICNT growth, the steel loses its passivating layer and experiences oxidative corrosion when placed in an aqueous physiological environment. This effect, confirmed by both energy dispersive x-ray analysis and electrochemical potentiokinetic reactivation, may be attributed to carburization of the alloy during CICNT production. One potential solution to this problem was investigated by employing an indirect CICNT growth method that utilized protective thin films under the CICNT surface and a nitrocellulose-based coating on other exposed edges. Samples that had been thus treated exhibited no significant corrosion over a 48 h testing period.

Carbon nanotubes have been investigated for their antimicrobial properties. The goal of this experiment was to better characterize the effects of gas flow rate and sample position on carbon-infiltrated carbon nanotubes (CICNTs) grown via chemical vapor deposition (CVD) on a silicon substrate to allow for improved sample preparation for antimicrobial experiments. 18 batches of 3 samples each (52 samples) were prepared by CVD coating silicon wafer substrates with alumina (400 nm) and iron (6 nm). Standard processes were generated for creating CICNT samples, with carbon nanotube (CNT) growth at 750 C and subsequent carbon infiltration at 900 C. In each batch, samples were positioned linearly with samples located centrally, downstream, and upstream in the furnace. Three batches had −20% gas flows (both hydrogen and ethylene), three batches had standard gas flows, and three batches had +20% gas flows. The experiment was then repeated with hydrogen flow held constant (only the ethylene was varied). Results showed that gas flow rates and sample position had negligible effects on nanotube height and diameter. This means that minor changes in gas flow rates and sample position do not have outsize effects on CICNT synthesis, which indicates that appropriate nanotube coatings can be prepared over a wide range of growth conditions.

Staphylococcus aureus forms biofilms that cause considerable morbidity and mortality in patients who receive implanted devices such as prosthetics or fixator pins. An ideal surface for such medical devices would inhibit biofilm growth. Recently, it was reported that surface modification of stainless steel materials with carbon-infiltrated carbon nanotubes (CICNT) inhibits the growth of S. aureus biofilms. The purpose of this study was to investigate this antimicrobial effect on titanium materials with CICNT coated surfaces in a variety of surface morphologies and across a broader spectrum of S. aureus isolates. Study samples of CICNT-coated titanium, and control samples of bare titanium, a common implant material, were exposed to S. aureus. Viable bacteria were removed from adhered biofilms and quantified as colony forming units. Scanning electron microscopy was used to qualitatively analyze biofilms both before and after removal of cells. The CICNT surface was found to have significantly fewer adherent bacteria than bare titanium control surfaces, both via colony forming unit and microscopic analyses. This effect was most pronounced on CICNT surfaces with an average nanotube diameter of 150 nm, showing a 2.5-fold reduction in adherent bacteria. Since S. aureus forms different biofilm structures by isolate and by growth conditions, we tested 7 total isolates and found a significant reduction in the biofilm load in six out of seven S. aureus isolates tested. To examine whether the anti-biofilm effect was due to the structure of the nanotubes, we generated an unstructured carbon surface. Significantly more bacteria adhered to a nonstructured carbon surface than to the 150 nm CICNT surface, suggesting that the topography of the nanotube structure itself has anti-biofilm properties. The CICNT surface possesses anti-biofilm properties that result in fewer adherent S. aureus bacteria. These anti-biofilm properties are consistent across multiple isolates of S. aureus and are affected by nanotube diameter. The experiments performed in this study suggest that this effect is due to the nanostructure of the CICNT surface.