Passive Surface Modifications Research Articles

Impact of jet intermittency on surface-structured heat sinks for electronics liquid cooling

The boosting heat generation rate of high-performance processors is challenging the conventional cooling techniques. Passive surface structure designs no longer satisfy the heat dissipation requirement. The present work proposes the combined design of active jet intermittency and passive surface modification in heat sinks, and evaluates the heat transfer enhancement through numerical and experimental approaches. The trapezoidal-waveform flow rate at the inlet has constant time-averaged Reynolds number of 763 and the Strouhal number ranges from 0.01 to 0.04. The surface geometry includes cylindrical groove and hemispherical dimple with different arrangements. The underlying physics of thermal performance improvement is explained by complex flow circulation that disrupts the thermal boundary layer growth and dynamic vortex motion that promotes mixing between near-wall fluid and mainstream coolant. Higher pulsation frequency and smaller duty cycle are beneficial for cooling enhancement while the percentage improvement of dimple structure is higher than groove structure, which agrees with the experimental results. Compared to the steady-flow flat heat sink, a maximum enhancement of 45% is obtained by adopting intermittent jet at grooved surface.

In vitro Inhibition of Biofilm Formation on Silicon Rubber Voice Prosthesis: Α Systematic Review and Meta-Analysis

Introduction: Biofilm formation on voice prostheses is the primary reason for their premature implant dysfunction. Multiple strategies have been proposed over the last decades to achieve inhibition of biofilm formation on these devices. The purpose of this study was to assess the results of the available in vitro biofilm inhibition modalities on silicone rubber voice prostheses. Methods: We conducted a systematic search in PubMed, Embase, and the Cochrane Central Register of Controlled Trials databases up to February 29, 2020. A total of 33 in vitro laboratory studies investigating the efficacy of different coating methods against Candida, Staphylococcus, Streptococcus, Lactobacilli, and Rothia biofilm growth on silicone rubber medical devices were included. Subgroup analysis linked to the type of prevention modality was carried out, and quality assessment was performed with the use of the modified CONSORT tool. Results: Data from 33 studies were included in qualitative analysis, of which 12 qualified for quantitative analysis. For yeast biofilm formation assessment, there was a statistically significant difference in favor of the intervention group (standardized mean difference [SMD] = −1.20; 95% confidence interval [CI] [−1.73, −0.66]; p < 0.0001). Subgroup analysis showed that combined methods (active and passive surface modification) are the most effective for biofilm inhibition in yeast (SMD = −2.53; 95% CI [−4.02, −1.03]; p = 0.00001). No statistically significant differences between intervention and control groups were shown for bacterial biofilm inhibition (SMD = −0.09; 95% CI [−0.68, 0.46]; p = 0.65), and the results from the subgroup analysis found no notable differences between the surface modification methods. After analyzing data on polymicrobial biofilms, a statistically significant difference in favor of prevention methods in comparison with the control group was detected (SMD = −2.59; 95% CI [−7.48, 2.31]; p = 0.30). Conclusions: The meta-analysis on biofilm inhibition demonstrated significant differences in favor of yeast biofilm inhibition compared to bacteria. A stronger inhibition with the application of passive or combined active and passive surface modification techniques was reported.

Photoluminescent functionalized carbon dots for CRISPR delivery: synthesis, optimization and cellular investigation

Gene therapy using clustered regularly interspaced short palindromic repeat plasmids (pCRISPR) reduces mistakes in gene editing and prevents engendering integrational mutagenesis that has been seen in available genome engineering technologies. Developing an ideal and traceable nanocarrier, which can accurately and efficiently transfer this complex into the cytosol and which facilitates the journey towards the nucleus, is a fascinating area of research. Polyethylenimine (PEI) functionalized carbon dots (CD-PEI) were fabricated by one-step microwave assisted pyrolysis with an average size around 3 nm. This CD-PEI showed good potential for intracellular delivery of genetic materials (∼70%). Also, this CD-PEI with passive surface modification with low molecular PEI (2 kDa) has a very high quantum yield, as high as 40% with low cytotoxicity. The expression rate of the pCRISPR was around 15% in the HEK-293 cell which is comparable with the pristine PEI. Furthermore, the CD-PEI demonstrated good properties, such as high quantum yield, biocompatibility and tunable emission wavelengths, suggesting the potential application of photoluminescent functionalized CDs as a suitable, traceable nanocarrier for CRISPR delivery.

Introduction of Nature's Complexity in Engineered Blood-compatible Biomaterials.

Biomaterials with excellent blood-compatibility are needed for applications in vascular replacement therapies, such as vascular grafts, heart valves and stents, and in extracorporeal devices such as hemodialysis machines and blood-storage bags. The modification of materials that are being used for blood-contacting devices has advanced from passive surface modifications to the design of more complex, smart biomaterials that respond to relevant stimuli from blood to counteract coagulation. Logically, the main source of inspiration for the design of new biomaterials has been the endogenous endothelium. Endothelial regulation of hemostasis is complex and involves a delicate interplay of structural components and feedback mechanisms. Thus, challenges to develop new strategies for blood-compatible biomaterials now lie in incorporating true feedback controlled mechanisms that can regulate blood compatibility in a dynamic way. Here, supramolecular material systems are highlighted as they provide a promising platform to introduce dynamic reciprocity, due to their inherent dynamic nature.

Electrically controlling cell adhesion, growth and migration

We have developed a neurochip to control the adhesion and outgrowth of individual neurons by electrochemical removal of protein repellent molecules from transparent electrodes. The neurochip architecture is based on three parallel indium-tin-oxide (ITO) electrodes on a SiO 2 substrate and a photoresist structure forming a landing spot for the neuron soma and two lateral outgrowth pathways for the neurites. The whole surface was turned protein and cell repellent with poly(ethylene glycol) grafted-poly( l-lysine) (PLL- g-PEG) before enabling neuron soma adhesion by selective PLL- g-PEG removal. After the neuron has settled down a potential was applied to the pathway electrodes to permit the neurite outgrowth along pathways formed by the SU8 structure. We also show the possibility to control cell migration by small pulsed currents. Myoblasts were therefore seeded on a chemical pattern of cell adhesive PLL and cell resistant PLL- g-PEG. The PLL- g-PEG was then removed electrochemically from the electrodes to permit migration onto the cell free electrodes. Electrodes without applied current were confluently overgrown within 24 h but a small pulsed current was able to inhibit cell growth on the bare ITO electrode for more than 72 h. With both techniques, cell adhesion, growth and migration can be controlled dynamically after the cells started to grow on the substrate. This opens new possibilities: we believe the key to control the development of topologically controlled neuron networks or more complex co-cultures is the combination of passive surface modifications and active control over the surface properties at any time of the experiment.

Computational fluid mechanical simulation of the deformation and the alignment of the cultured endothelial cell models

We have developed a neurochip to control the adhesion and outgrowth of individual neurons by electrochemical removal of protein repellent molecules from transparent electrodes. The neurochip architecture is based on three parallel indium-tin-oxide (ITO) electrodes on a SiO2 substrate and a photoresist structure forming a landing spot for the neuron soma and two lateral outgrowth pathways for the neurites. The whole surface was turned protein and cell repellent with poly(ethylene glycol) grafted-poly(l-lysine) (PLL-g-PEG) before enabling neuron soma adhesion by selective PLL-g-PEG removal. After the neuron has settled down a potential was applied to the pathway electrodes to permit the neurite outgrowth along pathways formed by the SU8 structure. We also show the possibility to control cell migration by small pulsed currents. Myoblasts were therefore seeded on a chemical pattern of cell adhesive PLL and cell resistant PLL-g-PEG. The PLL-g-PEG was then removed electrochemically from the electrodes to permit migration onto the cell free electrodes. Electrodes without applied current were confluently overgrown within 24 h but a small pulsed current was able to inhibit cell growth on the bare ITO electrode for more than 72 h. With both techniques, cell adhesion, growth and migration can be controlled dynamically after the cells started to grow on the substrate. This opens new possibilities: we believe the key to control the development of topologically controlled neuron networks or more complex co-cultures is the combination of passive surface modifications and active control over the surface properties at any time of the experiment.