Porous-coated Surface Research Articles

Recent Developments in Slippery Liquid-Infused Porous Surface Coatings for Biomedical Applications.

Slippery liquid-infused porous surface (SLIPS), inspired by the Nepenthes pitcher plant, exhibits excellent performances as it has a smooth surface and extremely low contact angle hysteresis. Biomimetic SLIPS attracts considerable attention from the researchers for different applications in self-cleaning, anti-icing, anticorrosion, antibacteria, antithrombotic, and other fields. Hence, SLIPS has shown promise for applications across both the biomedical and industrial fields. However, the manufacturing of SLIPS with strong bonding ability to different substrates and powerful liquid locking performance remains highly challenging. In this review, a comprehensive overview of research on SLIPS for medical applications is conducted, and the design parameters and common fabrication methods of such surfaces are summarized. The discussion extends to the mechanisms of interaction between microbes, cells, proteins, and the liquid layer, highlighting the typical antifouling applications of SLIPS. Furthermore, it identifies the potential of utilizing the controllable factors provided by SLIPS to develop innovative materials and devices aimed at enhancing human health.

Amphiphilic Covalent Organic Framework Nanoparticles for Pickering Emulsion Catalysis with Size Selectivity

AbstractExploiting advanced amphiphilic solid catalysts is crucial to the development of Pickering emulsion catalysis. Herein, covalent organic framework (COF) nanoparticles constructed with highly hydrophobic monomers as linkers were found to show superior amphiphilicity and they were then developed as a new class of solid emulsifiers for Pickering emulsion catalysis. Employing amphiphilic COFs as solid emulsifiers, Pickering emulsions with controllable emulsion type and droplet sizes were obtained. COF materials have also been demonstrated to serve as porous surface coatings to replace traditional surface modifications for stabilizing Pickering emulsions. After implanting Pd nanoparticles into amphiphilic COFs, the obtained catalyst displayed a 3.9 times higher catalytic efficiency than traditional amphiphilic solid catalysts with surface modifications in the biphasic oxidation reaction of alcohols. Such an enhanced activity was resulted from the high surface area and regular porous structure of COFs. More importantly, because of their tunable pore diameters, Pickering emulsion catalysis with remarkable size selectivity was achieved. This work is the first example that COFs were applied in Pickering emulsion catalysis, providing a platform for exploring new frontiers of Pickering emulsion catalysis.

Amphiphilic Covalent Organic Framework Nanoparticles for Pickering Emulsion Catalysis with Size Selectivity.

Exploiting advanced amphiphilic solid catalysts is crucial to the development of Pickering emulsion catalysis. Herein, covalent organic framework (COF) nanoparticles constructed with highly hydrophobic monomers as linkers were found to show superior amphiphilicity and they were then developed as a new class of solid emulsifiers for Pickering emulsion catalysis. Employing amphiphilic COFs as solid emulsifiers, Pickering emulsions with controllable emulsion type and droplet sizes were obtained. COF materials have also been demonstrated to serve as porous surface coatings to replace traditional surface modifications for stabilizing Pickering emulsions. After implanting Pd nanoparticles into amphiphilic COFs, the obtained catalyst displayed a 3.9 times higher catalytic efficiency than traditional amphiphilic solid catalysts with surface modifications in the biphasic oxidation reaction of alcohols. Such an enhanced activity was resulted from the high surface area and regular porous structure of COFs. More importantly, because of their tunable pore diameters, Pickering emulsion catalysis with remarkable size selectivity was achieved. This work is the first example that COFs were applied in Pickering emulsion catalysis, providing a platform for exploring new frontiers of Pickering emulsion catalysis.

Enhancement in pool boiling performance of GNP/Cu-Al2O3 nano-composite coated copper microporous surface

An experimental analysis of pool boiling is conducted on the GNP/Cu-Al2O3 (GNP-graphene nano particle) nanocomposite coated copper surfaces at atmospheric pressure using DI (distilled water) as boiling fluid. A two-step electro-deposition technique is used for fabrication of these micro/nano porous coated surfaces. A modified surface structure is formed due to this deposition and various surface morphology parameters such as surface structure, roughness, wettability are analysed. Results show the enhancement in BHTC (boiling heat transfer coefficient) and CHF (Critical heat flux) in nano composite coated surfaces compare to the bare copper surface. The maximum CHF of 2415 (kW/m2) and BHTC of 171.28 (kW/m2K) is found in the NCCS (nano-composite coated superhydrophilic) surfaces which are 122% and 239% more than the bare copper surfaces. The boiling performance is augmented mainly because of the improvement in roughness, wettability and also for the high thermal conductivity of the GNP/Cu- Al2O3 nano coating. Quantitative study of the bubble dynamics like active nucleation site density, bubble emission frequency, departure diameter of bubbleand their impact on heat transfer performance in the case of NCCS surfaces is performed with high-speed visualization.

Synthesis Techniques of Bioceramic Hydroxyapatite for Biomedical Applications

The need to develop surviving implants and bone substitutes with good biocompatibility, mechanical strength and bioactivity, without causing toxicity, immune rejection and cancer had attracted the attention of many researchers over the years. Hydroxyapatite (HA) is one of the excellent calcium phosphates and major mineral component of vertebrate bone and teeth, which considerably enhances the biocompatibility, mechanical strength and bioactivity of artificial biomaterials in the body system. In addition, it creates porous and rough coated surface that aids the cell attachment, proliferation and the growth of tissue on the bone implants. Due to its high demand in biomedical applications, scientists had developed several, simple and efficient techniques to produce HA. This review outlines several techniques of manufacturing HA and summarizes the merits and demerits of each technique. Keywords: Biomaterials, calcium phosphate, hydroxyapatite, preparation techniques and bone

EFFECT OF SURFACTANT ON SATURATED POOL BOILING OVER POROUS COATED SURFACE

EFFECT OF SURFACTANT ON SATURATED POOL BOILING OVER POROUS COATED SURFACE

The durability of superhydrophobic and slippery liquid infused porous surface coatings under corona discharge characteristic of the operation of high voltage power transmission lines

Application of polyfunctional water-repelling coatings for high voltage outdoor power lines wires, insulators, and line supports recently gathered large interest due to their ability to substantially boost performance. Such functionalization can mitigate the accumulation of water precipitates and atmospheric pollutions, decrease leakage current, increase flashover and corona ignition voltage. However, harsh conditions concomitant to a high voltage such as high energy ions and electrons, high ozone concentration, UV radiation impose strict requirements on the durability of applied coatings. In this paper, we focus on the analysis of the durability of superhydrophobic coatings (SHC) and slippery liquid infused porous surfaces (SLIPS) under prolonged exposure to industrial grade alternating current corona discharge. Reported results show that in contrast to previously reported low resilience of polymer-based SHC, proper metal-based SHC withstands many hours of exposure without notable degradation. The obtained data on the stability of SLIPS under corona discharge show notable degradation related to the high rate of infused layer depletion. Overall, reported results broaden the understanding of the effect of corona exposure on functional materials and reinforce the optimistic view on the applicability of SHC and SLIPS coatings in the power transmission industry.

Predicting friction at the bone – Implant interface in cementless total knee arthroplasty

Cementless total knee arthroplasty (TKA) components have rough and porous surface coatings which can enhance bone ingrowth and stability at the bone-implant. To achieve primary stability in the postoperative period where no apposition is formed, the resistance against motions between bone and implant is optimized by increasing the friction at the interface. This is necessary, as excessive relative motions can inhibit bone ingrowth, which might result in loosening and pain. In this research, it was found that the friction can be predicted by measuring the surface morphology of rough implants, and calculating the corresponding perpendicular and lateral contact area parameters. The ratio between these areas, is used to predict the resulting coefficient of friction (COF). This is validated experimentally, by analysing the tribological behaviour of 2 porous and rough titanium coatings against human cadaveric knee bones using reciprocal friction tests with varying normal loads. The results for 2 different coatings showed similar findings for the predicted COF (0.75 and 0.88) versus the calculated values based on the measurement (0.82 and 0.86) proving the feasibility of the approach.

Surface wettability effect of plain and plasma-sprayed copper-coated surfaces on CHF enhancement during saturated pool boiling of FC-72

In the current scenario, CHF study is essential for the safe operation of electronics equipment comprising a two-phase heat transfer process. Therefore, the present experimental investigation involves saturated pool boiling and CHF study of FC 72 over a plain stainless steel surface (SS) and microporous copper-coated SS surfaces under atmospheric conditions. Accordingly, three different plasma-sprayed copper-coated surfaces with coating thicknesses of 65 μm, 105 μm, and 145 μm prepared using micro copper particles of size 25–45 μm. The analysis of the results shows that with an increase in heat flux values, the boiling heat transfer coefficient increases over plain as well as coated surfaces. The plasma-spayed copper-coated surfaces with a coating thickness of 65 μm and 105 μm exhibit a higher boiling heat transfer coefficient as than the plain surface. On the other hand, a 145 μm thick coated surface resulted in a comparable boiling heat transfer coefficient with the plain SS surface. Among the three porous-coated surfaces, the boiling heat transfer coefficient decreases continuously from 65 μm to 145 μm of the coated surface. On the contrary, to the observed nucleate boiling behavior, all the porous-coated surfaces show a higher value of CHF than the plain surface, and the CHF value is found to increase continuously from 65 μm to 145 μm of the coated surfaces. The enhancement of CHF values was found to be 66.29%, 69.17%, and 77.75% for a coating thickness of 65 μm, 105 μm, and 145 μm, respectively, compared with the plain surface. The porous coating thickness of 65 μm shows a greater value of heat transfer coefficient than 105 μm and 145 μm whereas 145 μm exhibits a higher value of CHF as than 65 μm and 105 μm.

Bioactive coatings on 3D printed titanium implants with a complex internal structure for bone replacement

The micro-arc oxidation method was applied to modify the surface of 3D printed titanium implants with a complex internal structure. Two different electrolyte solutions were used for thesurface modification, for which the respective working parameters of the micro-arc oxidation process were developed. Surface coatings formed with these parameters on the 3D implants have the same chemical composition and have the same surface morphology as surface coatings on 2D substrates. The measurement of the coating thickness using the X-ray microtomography demonstrates that this method is a useful tool for the thickness control of porous surface coatings at the inside and outside of the 3D titanium implants.

Potential of slippery liquid infused porous surface coatings as flashover inhibitors on porcelain insulators in icing, contaminated, and harsh environments

Humidity and pollution deposition on the surface of porcelain insulators affect the electrical field distribution and their performance which may lead to partial discharge and decreasing flashover voltage. Thereby one essential aspect of insulator designing is their surface science and surface wettability. To address these challenges, in this study robust omniphobic coatings were designed which can repel water and oil droplets as well as other contaminant particles from the porcelain insulators surface. In this regard, slippery liquid infused porous surface (SLIPS) coatings were applied on the porcelain substrate by infusing perfluorinated liquid lubricants into 200 %-stretched Teflon tape cover or fluoro-silanized porcelain. The surface of the designed transparent coatings repelled water, olive oil, kaolin, sodium chloride microparticles, and ice. The applied coatings exhibited low contact angle hysteresis (Δθ ≤ 5°) and a low sliding angle (α ≤ 7°) for water and olive oil droplets. SLIPS coatings showed good stability to extreme environments like immersion into acid, base, brine solutions, UV radiation and withstood at 4.5 kV inclined plane test without failure after 6 h. So, the modified SLIPS can be used as effective coatings in the porcelain insulators surface engineering.

Salt templated and graphene nanoplatelets draped copper (GNP-draped-Cu) composites for dramatic improvements in pool boiling heat transfer

We demonstrate a novel technique to achieve highly surface active, functional, and tunable hierarchical porous coated surfaces with high wickability using a combination of ball milling, salt-templating, and sintering techniques. Specifically, using ball-milling to obtain graphene nanoplatelets (GNP) draped copper particles followed by salt templated sintering to induce the strength and cohesiveness to the particles. The salt-templating method was specifically used to promote porosity on the coatings. A systematic study was conducted by varying size of the copper particles, ratio of GNP to copper particles, and process parameters to generate a variety of microporous coatings possessing interconnected pores and tunnels that were observed using electron microscopy. Pool boiling tests exhibited a very high critical heat flux of 289 W/cm2 at a wall superheat of just 2.2 °C for the salt templated 3 wt% GNP draped 20 µm diameter copper particles with exceedingly high wicking rates compared to non-salt-templated sintered coatings. The dramatic improvement in the pool boiling performance occurring at a very low surface temperature due to tunable surface properties is highly desirable in heat transfer and many other engineering applications.

Study of boiling behavior of surfactant added saline water over coated surface

The present article is focused on two phase heat transfer experiment, conducted over plain and porous coated circular tube of 20 mm diameter with 130 mm heating length in the quiescent pool of fluid at atmospheric pressure. The heat flux is varied from 20.19–70.22 kW/m2. The concentration of SDS and TritonX-100 are varied from 100 to 1200 ppm and 100–400 ppm in NaCl solutions respectively. It is found that higher nucleate boiling heat transfer coefficient obtained on plain tube as well as porous coated tube at SDS_400 ppm and TritonX-100_100 ppm. However, the maximum enhancement found in SDS surfactant. By increasing the concentration of SDS and TritonX-100, the nucleate boiling heat transfer decreases and minimum value found at 1200 ppm and 400 ppm respectively. As compared to the plain tube with plain NaCl solution, an enhancement of 51.43–65.74% found in the nucleate boiling heat transfer coefficient for the porous coated tube. At SDS_400 ppm and TritonX-100, an enhancement of the nucleate boiling heat transfer coefficient found about 46.42–57.71% and 36.75–50.21% for the plain tube. In general, the nucleate boiling heat transfer coefficient increases from plain NaCl to TritonX-100 to SDS for both the plain as well as porous coated surface.

CoCrMo surface modifications affect biocompatibility, adhesion, and inflammation in human osteoblasts

In this study, different surface modifications were performed on a Cobalt-Chrome-Molybdenum (CoCrMo) alloy and the effects on cell viability and cytotoxicity as well as the adhesion potential of human osteoblasts (hFOB) and their inflammation reaction were investigated in vitro. CoCrMo discs were coated with TiN, with polished and porous coated surfaces, or with pure titanum (cpTi) surfaces and examined by Scanning Electron Microscopy to evaluate surface modifications. In vitro cell viability, adhesion behaviour, and expression of inflammation markers of hFOB human osteoblasts were measured via CellTiter-Glo, CytoTox, ELISA, and RT-PCR respectively. All results were compared to CoCrMo without surface modifications. The biocompatibility data showed high compatibility for the TiN hard coatings. Likewise, the porous surface coating increased cell viability significantly, compared to an untreated CoCrMo alloy. None of the investigated materials influenced cytotoxicity. Different surface modifications did not influence expression of fibronectin, although TiN, porous surface coatings and polished surfaces showed highly significant reductions in integrin subunit expression. In addition to the regulation of adhesion potential these three surfaces stimulated an anti-inflammatory response by osteocytes. Improved biocompatibility and adhesion properties may contribute to better osteointegration of prosthetics.

The fate of sagittal alignment in tapered uncemented femoral components in total hip arthroplasty: 889 hips followed for a minimum of 10 years.

Aseptic loosening is rare after primary total hip arthroplasty (THA) with mostly uncemented tapered stems; however, different factors can modify the results. We question whether 3 different current femoral components and/or the surgical technique affect the clinical and radiological outcome after a minimum follow-up of 10 years. 889 uncemented tapered stems implanted from 1999 to 2007 were evaluated for a minimum follow-up of 10 years. Group 1 (273 hips) shared a conical shape and a porous-coated surface, group 2 (286 hips) a conical splined shape and group 3 (330 hips) a rectangular grit-blasted stem. Groups 1 and 2 were implanted through a posterolateral approach and group 3 using an anterolateral approach. Clinical outcomes and anteroposterior and sagittal radiographic analyses were compared. No thigh pain was reported in unrevised patients. Mean Harris Hip score was lower for patients in group 3 for pain and function at all intervals. 14-year implant survival for aseptic loosening was 98.2% (95% confidence interval [CI] 96.2-100) in group 3. No revision for aseptic loosening was found with the other designs. A stem position outside neutral limits in the sagittal alignment (p = 0.001, hazard ratio: 6.17, 95% CI, 2.05-18.61) was associated with aseptic loosening in group 3. Most current uncemented straight tapered femoral components can provide adequate bone fixation in primary THA after 10 years. Conical stems inserted through a posterolateral approach are more reliable than rectangular ones inserted through an anterolateral approach.

Enhanced Bone Remodeling Effects of Low-Modulus Ti-5Zr-3Sn-5Mo-25Nb Alloy Implanted in the Mandible of Beagle Dogs under Delayed Loading.

Titanium (Ti) and its alloys are widely used in the dental and prosthetic implant fields due to their favorable biocompatibility. In this study, porous surface coatings incorporated with nanoscale hydroxyapatite particles on the surface of Ti and Ti–5Zr–3Sn–5Mo–25Nb (TLM) alloy were fabricated by microarc oxidation followed by hydrothermal treatment; the surface roughness and hydrophilicity were obviously enhanced by the surface modification procedure. In vivo, four adult male beagle dogs were selected for an implantation procedure and restored with full metal crowns after healing for 3 months. The bone responses were evaluated via histomorphological observation. Raman spectral analysis and nanoindentation experiments were used to quantitatively and qualitatively estimate the characteristics of the bone formed around the implants. Compared to the Ti group, the TLM titanium alloy group showed a significant increase in the percentage of bone–implant interface contact, bone inside the thread, mineralization, crystallinity, modulus of elasticity, and hardness of the integrated bone after delayed loading in the TLM group. Therefore, the TLM titanium alloy is considered a candidate implant material with desirable biomechanical compatibility, especially under applied stress.

Design, fabrication and nucleate pool-boiling heat transfer performance of hybrid micro-nano scale 2-D modulated porous surfaces

Future technological products are increasingly becoming compact, integrated and multi-functional with higher heat loads in confined spaces. This has impelled the quest for improved heat management solutions to ensure the devices maintain their full performance as designed. Due to the associated latent heat, nucleate pool-boiling heat transfer (NBHT) systems are proven to dissipate the high heat flux at low-temperature gradients. NBHT systems with nano-scale and micro-scale porous structured surfaces are reported to possess enhanced heat transfer coefficient (HTC) and critical heat flux (CHF). The potential synergistic benefits of combining these two unique structures into an integrated surface coating fabrication technology have been a key question of interest. This study aimed to investigate the effect of uniformly coated nanoparticles on 2-D modulated micro-porous surfaces in NBHT. The NBHT performance of four different surface types; (1) flat untreated copper surface (UnCu surface), (2) nanocoated copper surface (NPC surface), (3) 2-D modulated micro-porous surface (MMPC surface), and (4) hybrid micro/nano-scale 2-D modulated porous coated surface (HMPC surface) are investigated. The UnCu surface and MMPC surface are employed for uniform nanoparticle coating to fabricate NPC surface and HMPC surface, respectively. Morphological characteristics of the surfaces were observed using the scanning electron microscopy (SEM). According to the results, the NPC surface and MMPC surface showed an enhanced NBHT performance by 81.6% and 50.6% improvement in CHF and 130.3% and 45% enhancement in HTC, respectively. However, as compared to the MMPC surface, the NBHT performance of the HMPC surface decreased. The average reduction in CHF and HTC of the HMPC surface was 16.8% and 24%, respectively. The reduction in the NBHT performance of HMPC is explained by the deterioration of the capillary wicking characteristics of the MMPC surface.

3D reconstruction of the porous microstructure of Al2O3-coatings based on sequentially revealed surface data

Local and global liquid transport properties correlate strongly with the morphology of porous materials. Therefore, by characterizing the porous network information is indirectly gained on the materials properties. Properties like the open-porosity are easily accessible with techniques like mercury porosimetry. However, the 3D image reconstruction, destructive or non-destructive, holds advantages like an accurate spatially resolved representation of the investigated material. Common 3D data acquisition is done by x-ray microtomography or a combination of focused ion beam based milling and scanning electron microscopy. In this work a reconstruction approach similar to the latter one is implemented. The porous network is reconstructed based on an alternating process of milling the surface by fly cutting and measuring the surface data with a confocal laser scanning microscope. This has the benefit of reconstructing the pore network on the basis of surface height data, measuring the structure boundaries directly. The stack of milled surface height data needs to be registered and the pore structure to be segmented. The segmented pore structure is connected throughout each height layer and afterwards meshed. The investigated materials are porous surface coatings of aluminum oxide for the usage in tribological pairings.

A 24-month evaluation of a percutaneous osseointegrated limb-skin interface in an ovine amputation model.

Percutaneous osseointegrated (OI) prostheses directly connect an artificial limb to the residual appendicular skeleton via a permanently implanted endoprosthesis with a bridging connector that protrudes through the skin. The resulting stoma produces unique medical and biological challenges. Previously, a study using a large animal amputation model indicated that infection could be largely prevented, for at least a 12-month period, but the terminal epithelium continued to downgrow. The current study was undertaken to test the longer-term efficacy of this implant construct to maintain a stable skin-implant interface for 24 months. Using the previously successful amputation and implantation surgical procedure, a total of eight sheep were fitted with a percutaneous OI prosthesis. Two animals were removed from the study due to early complications. Of the remaining six sheep, one (16.7%) became infected at 15-months post-implantation and five remained infection-free for the intended 24 months. The histological data of the remaining animals further confirmed the grossly observable epithelial downgrowth. Albeit a receding interface, it was clear that all animals that survived to the end of the study had residual fibrous soft-tissue ingrowth into, and debris within, the exposed titanium porous-coated surface. Overall, the data demonstrated that the porous coated subdermal barrier offered initial protection against infection. However, the fibrous skin attachment was continuously lysed over time by the down-growing epithelium.

Effect of space distance for boiling heat transfer on micro porous coated surface in confined space

This work provides an experimental analysis of the boiling heat transfer of methanol on plain and micro porous coated surfaces inside confined space. Three space confinements with distance of 1.0, 2.0, 3.0mm and an unconfined space were tested on plain and micro porous coating surfaces. Effects of space confinement, surface treatment and heat flux on the heat transfer coefficient and critical heat flux were discussed. From the test results, we may deduct that the boiling heat transfer performance in confined spaces was affected by four major effects, i.e. (a) vapor blowing and liquid suction effect, (b) thin film evaporation, (c) vapor leaving resistance and (d) partial dryout effect on plain surface. But only (a) and (c) are important on micro porous coating surface. The combination of these effects resulted in the micro porous to plain surfaces heat transfer enhancement ratio to have different characteristics at low, moderate and high heat flux conditions. Micro porous coating is a very effective boiling heat transfer enhancement treatment at low and moderate heat fluxes conditions. The enhancement ratio reduced in very narrow space confinement or at very high heat flux condition.