Titanium implant surface etching has proven an effective method to enhance cell attachment. Despite the frequent use of hydrofluoric (HF) acid, many questions remain unresolved, including the optimal ...etching time and its effect on surface and biological properties. The objective of this study was to investigate the effect of HF acid etching time on Ti topography, surface chemistry, wettability, and cell adhesion. These data are useful to design improved acid treatment and obtain an improved cell response. The surface topography, chemistry, dynamic wetting, and cell adhesiveness of polished Ti surfaces were evaluated after treatment with HF acid solution for 0, 2; 3, 5, 7, or 10 min, revealing a time-dependent effect of HF acid on their topography, chemistry, and wetting. Roughness and wetting increased with longer etching time except at 10 min, when roughness increased but wetness decreased. Skewness became negative after etching and kurtosis tended to 3 with longer etching time. Highest cell adhesion was achieved after 5-7 min of etching time. Wetting and cell adhesion were reduced on the highly rough surfaces obtained after 10-min etching time.
Texturization of surfaces is usually advantageous in biomaterial engineering. However, the details of the textured surfaces can be more determining on cell adhesion and proliferation, rather than ...their roughness degree. Titanium is extensively used as a dental implant material in the human body. In this paper, the effect of four surface treatments on commercially pure titanium has been evaluated. These treatments were polishing (pTi); hydrofluoric acid (HF) etching (eTi); Al
2O
3 blasting (bTi); Al
2O
3 blasting
+
HF etching (beTi). Roughness and fractal dimensions were obtained from atomic force microscopy. Wettability was measured using water sessile drops. Morphology and surface chemical composition were analyzed with scanning electron microscopy and energy dispersive X-ray (EDX). MG-63 cell cultures were performed at different times (180
min, 24
h, 48
h, 72
h). Lowest roughness was found in pTi samples followed by eTi, bTi and beTi samples. Etching generated surfaces with the highest fractal dimension and negative skewness. Young contact angles were similar except for pTi and bTi surfaces. Silicon and aluminum traces were found in pTi and bTi samples, respectively. Cell adhesion (≤24
h) was greater on bTi and beTi surfaces. After 48
h, cell proliferation, mediated by specific morphologies, was improved in eTi samples followed by beTi surfaces. For the same surface chemistry, cell growth was driven by topography features.
It is well-established that the equilibrium contact angle in a thermodynamic framework is an “unattainable” contact angle. Instead, the most-stable contact angle obtained from mechanical stimuli of ...the system is indeed experimentally accessible. Monitoring the susceptibility of a sessile drop to a mechanical stimulus enables to identify the most stable drop configuration within the practical range of contact angle hysteresis. Two different stimuli may be used with sessile drops: mechanical vibration and tilting. The most stable drop against vibration should reveal the changeless contact angle but against the gravity force, it should reveal the highest resistance to slide down. After the corresponding mechanical stimulus, once the excited drop configuration is examined, the focus will be on the contact angle of the initial drop configuration. This methodology needs to map significantly the static drop configurations with different stable contact angles. The most-stable contact angle, together with the advancing and receding contact angles, completes the description of physically realizable configurations of a solid–liquid system. Since the most-stable contact angle is energetically significant, it may be used in the Wenzel, Cassie or Cassie–Baxter equations accordingly or for the surface energy evaluation.
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•The most-stable contact angle is postulated as experimental equilibrium contact angle.•Monitoring the susceptibility of a sessile drop against a mechanical stimulus•Two different stimuli may be used with sessile drops: vibration and tilting.•The most-stable contact angle completes the description of physically realizable configurations.
The pathogenic mechanisms underlying the progression of non-alcoholic fatty liver disease (NAFLD) are not fully understood. In this study, we aimed to assess the relationship between endoplasmic ...reticulum (ER) stress and autophagy in human and mouse hepatocytes during NAFLD. ER stress and autophagy markers were analyzed in livers from patients with biopsy-proven non-alcoholic steatosis (NAS) or non-alcoholic steatohepatitis (NASH) compared with livers from subjects with histologically normal liver, in livers from mice fed with chow diet (CHD) compared with mice fed with high fat diet (HFD) or methionine-choline-deficient (MCD) diet and in primary and Huh7 human hepatocytes loaded with palmitic acid (PA). In NASH patients, significant increases in hepatic messenger RNA levels of markers of ER stress (activating transcription factor 4 (ATF4), glucose-regulated protein 78 (GRP78) and C/EBP homologous protein (CHOP)) and autophagy (BCN1) were found compared with NAS patients. Likewise, protein levels of GRP78, CHOP and p62/SQSTM1 (p62) autophagic substrate were significantly elevated in NASH compared with NAS patients. In livers from mice fed with HFD or MCD, ER stress-mediated signaling was parallel to the blockade of the autophagic flux assessed by increases in p62, microtubule-associated protein 2 light chain 3 (LC3-II)/LC3-I ratio and accumulation of autophagosomes compared with CHD fed mice. In Huh7 hepatic cells, treatment with PA for 8 h triggered activation of both unfolding protein response and the autophagic flux. Conversely, prolonged treatment with PA (24 h) induced ER stress and cell death together with a blockade of the autophagic flux. Under these conditions, cotreatment with rapamycin or CHOP silencing ameliorated these effects and decreased apoptosis. Our results demonstrated that the autophagic flux is impaired in the liver from both NAFLD patients and murine models of NAFLD, as well as in lipid-overloaded human hepatocytes, and it could be due to elevated ER stress leading to apoptosis. Consequently, therapies aimed to restore the autophagic flux might attenuate or prevent the progression of NAFLD.
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In this work, we studied the wettability of hydrophobic surfaces fabricated with three different materials (PTFE, PDMS and paraffin wax) over a wide range of roughness. We estimated ...the Advancing, Receding and Most-Stable contact angles and we identified the transition from a homogeneous wetting regime (Wenzel) to a hybrid wetting regime (Cassie-Baxter). Using a modified Cassie-Baxter equation which considers the chemical heterogeneity of the samples, we were able to determine the solid area fraction within the contact area. This way, we designed a methodology to identify the superhydrophobic degree of rough-hydrophobic surfaces.
Spray drying was used to encapsulate the paraffin Rubitherm
®RT27 with and without carbon nanofibers (CNFs) showing a microencapsulation yield of 63%. Characteristics of microcapsules containing this ...phase change material (PCM) were dependent on the location in which they were collected in the spray dryer. The mechanical properties of the above-mentioned materials were studied by atomic force microscopy (AFM) indicating that the force required to produce the same microcapsule deformation was approximately 183% higher when 2
wt% of CNFs was added in the microcapsule recipe. The thermal energy storage (TES) capacity of the obtained microcapsules (98.1
J/g) was similar to those exhibited by microcapsules produced by a suspension polymerization technique using styrene as shell material (96.7
J/g) and that of a commercial material (116.2
J/g). In the same way, the CNF content maintained the TES capacity of the microcapsules (95.6
J/g) and seemed to enhance their thermal conductivity. Finally, the stability studies of the synthesized material carried out during 3000 cycles indicated that the developed material was stable and worked in reversible way.
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•The freezing delay of drops on solid surfaces is still a matter of controversy.•Surface roughness and drop geometry are considered as key factors.•The role of heat transfer driven by ...phase change phenomena is usually ignored.•Here, we studied the impact of roughness, contact angle and thermal conductivity.•The best efficiency was observed for smooth, hydrophobic and conductive materials.
Elucidating the predominant factors for the freezing delay of surfaces is still a matter of discussion and controversy. Freezing delay is explained in literature through the classical nucleation theory. It postulates that freezing delay of a surface is enhanced with low surface roughness and sessile drops of high contact angles. However, since surface roughness influences the wetting properties, a better understanding of how each factor affects the freezing delay requires to uncouple both effects systematically. This is indeed the reason why certain contradictions are found in literature. Besides, some works report that further factors, such as the surface-to-drop heat transfer might also be important. In this work, we analyzed independently how drop geometry, surface roughness and thermal conductivity influence the freezing delay of solid surfaces at unsaturated conditions. Our results show that the drop contact angle and surface roughness strongly influences the freezing delay on conductive and insulating materials. Although its importance is minor, we also found that conductive materials delay freezing more efficiently than insulating materials. In conclusion, our results point out that conductive, smooth and hydrophobic surfaces are the most efficient surfaces to delay freezing in unsaturated environments.
Quasi-static experiments using sessile drops and captive bubbles are the most employed methods for measuring advancing and receding contact angles on real surfaces. These observable contact angles ...are the most easily accessible and reproducible. However, some properties of practical surfaces induce certain phenomena that cause a built-in uncertainty in the estimation of advancing and receding contact angles. These phenomena are well known in surface thermodynamics as stick–slip phenomena. Following the work of Marmur (Marmur, A. Colloids Surf., A 1998, 136, 209–215), where the stick–slip effects were studied with regard to sessile drops and captive bubbles on heterogeneous surfaces, we developed a novel extension of this study by adding the effects of roughness to both methods for contact angle measurement. We found that the symmetry between the surface roughness problem and the chemical heterogeneity problem breaks down for drops and bubbles subjected to stick–slip effects.
We present results for the most stable contact angle using a numerical implementation of the tilting plate method of Montes et al. (Montes Ruiz-Cabello, F. J.; Rodriguez-Valverde, M. A.; ...Cabrerizo-Vilchez, M. Soft Matter 2011, 7, 10457–10461). Comparison with the experimental results is made, obtaining a good agreement in most situations. In addition, the evolution of the contact angles of a tilted drop with a fixed circular line is analyzed. This analysis allows one to theoretically predict the most stable contact angle for tilted drops.
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