Nanoporous Surface Structure Research Articles

Alkali surface modification of titanium for biomedical implants

AbstractNanostructures were successfully created on titanium (Ti) substrates through alkali treatment. By varying the concentration, temperature, and duration of the alkali treatment, different nanostructure surfaces were achieved on Ti. FE‐SEM analysis revealed a transition from a smooth to a nanoporous surface structure. The alkali treatment notably decreased the contact angle of Ti from 64° to 48°. Raman spectroscopy of Ti treated with 5 M NaOH at 80 °C for 24 h showed distinct titanate peaks at 188, 190, and 270 cm−1, confirming the formation of titanate compounds on the Ti surface. EIS measurements further demonstrated that the treated Ti exhibited reduced chemical activity, increased surface roughness, and porosity of approximately 40–50% compared to untreated Ti. In vitro biocompatibility tests using baby hamster kidney cells indicated positive cell attachment and proliferation after 72 h of culturing on the alkali‐treated Ti. These modifications enhance the surface properties and expand the potential applications of titanium in biomedical, industrial, and environmental technologies.

Tissue Adhesive, Biocompatible, Antioxidant, and Antibacterial Hydrogels Based on Tannic Acid and Fungal-Derived Carboxymethyl Chitosan for Wound-Dressing Applications.

This study aimed to develop hydrogels for tissue adhesion that are biocompatible, antioxidant, and antibacterial. We achieved this by using tannic acid (TA) and fungal-derived carboxymethyl chitosan (FCMCS) incorporated in a polyacrylamide (PAM) network using free-radical polymerization. The concentration of TA greatly influenced the physicochemical and biological properties of the hydrogels. Scanning electron microscopy showed that the nanoporous structure of the FCMCS hydrogel was retained with the addition of TA, resulting in a nanoporous surface structure. Equilibrium-swelling experiments revealed that increasing the concentration of TA significantly improved water uptake capacity. Antioxidant radical-scavenging assays and porcine skin adhesion tests confirmed the excellent adhesive properties of the hydrogels, with adhesion strengths of up to 39.8 ± 1.2 kPa for 1.0TA-FCMCS due to the presence of abundant phenolic groups on TA. The hydrogels were also found to be biocompatible with skin fibroblast cells. Furthermore, the presence of TA significantly enhanced the antibacterial properties of the hydrogels against both Gram-positive (Staphylococcus aureus) and Gram-negative (Escherichia coli) bacteria. Therefore, the developed drug-free antibacterial and tissue-adhesive hydrogels can potentially be used as wound dressings for infected wounds.

ISOLATION AND CHARACTERIZATION OF BIOSILICA AS BIONANOMATERIAL FROM THE WASTE OF FRUSTULES DIATOM Navicula sp. TAD

Biosilica from frustul diatom Navicula sp. TAD was isolated under optimal conditions by washing with 20% HCl and baking at 600 °C. The treatments successfully removed 78.00 ± 0.514% of impurities from the biosilica during washing, and 93.072 ± 0.347% were further removed after baking. Biosilica Frustule Navicula sp. TAD resulting from HCl washing and burning at 600oC has a whiter silica color. Biosilica was identified by Fourier transform infrared spectroscopy (FTIR) at wave numbers 1601, 1062, 962, 799, and 470 cm-1, which were associated with stretching, bending, and vibrational groups of Si-O-Si bonds. Scanning electron microscopy (SEM) observations show that the silica frustule nanoporous surface structure can be seen, and the results of Energy Dispersive X-Ray (EDX), silica from Navicula sp. TAD is composed of silicon and oxygen. This shows that silica was obtained from the diatom Navicula sp. TAD. X-ray diffraction (XRD) analysis shows that the morphology of SiO2 in biosilica is a typical amorphous silica

Tailoring Nano-Porous Surface of Aligned Electrospun Poly (L-Lactic Acid) Fibers for Nerve Tissue Engineering.

Despite the existence of many attempts at nerve tissue engineering, there is no ideal strategy to date for effectively treating defective peripheral nerve tissue. In the present study, well-aligned poly (L-lactic acid) (PLLA) nanofibers with varied nano-porous surface structures were designed within different ambient humidity levels using the stable jet electrospinning (SJES) technique. Nanofibers have the capacity to inhibit bacterial adhesion, especially with respect to Staphylococcus aureus (S. aureus). It was noteworthy to find that the large nano-porous fibers were less detrimentally affected by S. aureus than smaller fibers. Large nano-pores furthermore proved more conducive to the proliferation and differentiation of neural stem cells (NSCs), while small nano-pores were more beneficial to NSC migration. Thus, this study concluded that well-aligned fibers with varied nano-porous surface structures could reduce bacterial colonization and enhance cellular responses, which could be used as promising material in tissue engineering, especially for neuro-regeneration.

The Potential of Nano-Porous Surface Structure for Pain Therapeutic Applications: Surface Properties and Evaluation of Pain Perception

The objective of this study was to evaluate the biomaterial properties of nano-modified surface acupuncture needles and the effect of such needles on human pain perception by using pressure pain threshold (PPT) measurements. It is known that changing a material’s surface nano-topography or nanostructure has strong effects on its physical, chemical, and biological surface properties. However, there is no information in the literature about the stimulation characteristics of acupuncture needles with nano-topography or nanostructured surfaces. Based on the knowledge on nanostructured surfaces, it may be possible to potentiate the effects of acupuncture needle stimulation. The pressure pain sensitivity of the masseter muscle in the orofacial region was studied in 21 healthy volunteers in two randomized, double-blinded sessions: an active session of manual acupuncture manipulation with nano-modified surface needles, and an inactive session of sham acupuncture stimulation to control for possible placebo effects. Three acupuncture points were selected from classical Chinese medicine literature: LI4 (Hegu) on the hand, ST6 (Jiache) on the lower masseter region, and ST7 (Xiaguan) on the upper masseter region. PPT measurements, perceived sensations, and pain from the acupuncture were recorded. The results showed discrete yet significant differences in PPT values between the active and inactive acupuncture treatments and significantly higher pain scores from active acupuncture stimulation than from sham acupuncture. These results indicate subtle but significant effects of acupuncture stimulation with nano-modified surface needles, compared to sham acupuncture in healthy participants.

Highly Durable and Flexible Paper Electrode with a Dual Fiber Matrix Structure for High-Performance Supercapacitors.

Paper-based electrodes are of special interest for the industry due to their degradability, low cost, ion accessibility, and flexibility. However, the poor dispersibility and stability of loading conductive fillers, for example, carbon nanotubes (CNTs), limit their applications. In this study, bacterial cellulose (BC) was embedded within the cellulosic fiber matrix to prepare a paper substrate with a dual fiber matrix structure. BC with its unique nanoporous surface structure assisted the adsorbing, dispersing, and stabilizing of CNTs; cellulosic fibers reduced the cost, enhanced the ion accessibility, and improved the rigidity of the material. The prepared paper electrodes exhibited a high conductivity up to 5.9 × 10-1 S/cm and an extraordinary durability under high bending strain; it can be rolled into a 2 mm radius 800 times while maintaining the conductivity almost constant. The paper electrode had a gravimetric capacitance up to 77.5 F/g, which remained more than 98% after 15,000 charge/discharge cycles. This study suggests that this paper electrode has potential applications in supercapacitors with high performance and durability.

Fabrication of periodic nano-porous surface structure for highly sensitive gravimetric quartz crystal applications

A periodic nano-porous surface on quartz crystal electrodes was carefully fabricated for increasing the mass-sensitive areas. Detailed porous structures were prepared by analyzing Au electrochemical reduction process of PS layer coated quartz crystals. The sensitivity measurement of the porous quartz crystals was performed with several traditional methods, and an optimized reduction time for higher sensitivity was determined. The frequency shift of the nano-porous quartz crystals showed 10 times bigger change with the same concentration of target solutions in self-assembly procedures. In the procedures, the freshly increased surface portion did not produce additional molecular slip-effects on the measured resonant resistance values, thus, the periodic porous chips showed another side merit for the mass sensor applications. We propose a possible use of the current porous surface as a platform for developing other high-performance sensors and analyses.

Durable anti-corrosive oil-impregnated porous surface of magnesium alloy by plasma electrolytic oxidation with hydrothermal treatment

Magnesium alloys have been widely employed for structural parts of aircrafts and automobiles to reduce their weight. However, magnesium alloys are easily corroded, thus practical applications always require protective coatings to guarantee satisfactory lifetime. In this study, we applied oil-impregnation and hydrophobizing to traditional plasma electrolytic oxidation (PEO) of magnesium alloy. Nanoporous hydroxide surface structure is fabricated by hydrothermal treatment of PEO-treated Mg alloy, then the self-assembled monolayer of perfluorodecyltrichlorosilane (FDTS) is coated for the hydrophobizing. The immiscible oil impregnation into the PEO-treated oxide layer with hydrothermal treatment and hydrophobizing significantly enhances the corrosion resistance as well as the mobility of water droplet on the surface. In addition, since the oil layer on the nanoporous surface inhibit the direct contact and penetration of corrosive liquid to the oxide layer, the oil-impregnated surface shows less degradation in corrosive liquid with long-term immersion than hydrophobic and superhydrophobic surface without oil-impregnation. These results indicates that oil-impregnated surface of Mg alloy has durable and robust anti-corrosion property.

In Vitro Corrosion and Bioactivity Performance of Surface-Treated Ti-20Nb-13Zr Alloys for Orthopedic Applications

The influence of surface treatments on the microstructure, in vitro bioactivity and corrosion protection performance of newly fabricated Ti-20Nb-13Zr (TNZ) alloys was evaluated in simulated body fluid (SBF). The TNZ alloy specimens were treated with separate aqueous solutions of NaOH and H2O2 and with a mixture of both, followed by thermal treatment. The nanoporous network surface structure observed in H2O2-treated and alkali-treated specimens was entirely different from the rod-like morphology observed in alkali hydrogen peroxide-treated specimens. XRD results revealed the formation of TiO2 and sodium titanate layers on the TNZ specimens during surface treatments. The water contact angle results implied that the surface-treated specimens exhibited improved surface hydrophilicity, which probably improved the bioactivity of the TNZ specimens. The in vitro corrosion protection performance of the surface-treated TNZ specimens was analyzed using electrochemical corrosion testing in SBF, and the obtained results indicated that the surface-treated specimens exhibited improved corrosion resistance performance compared to that of the bare TNZ specimen. The in vitro bioactivity of the treated TNZ specimens was assessed by soaking in SBF, and all the investigated treated specimens showed numerous apatite nucleation spheres within 3 days of immersion in SBF.

Oxygen Evolution Reaction on Nanoporous Gold Modified with Ir and Pt: Synergistic Electrocatalysis between Structure and Composition

AbstractActive oxygen evolution reaction electrocatalysts for water splitting have received great attention because of their importance in the utilization of renewable energy sources. Here, the electrochemical oxygen evolution reaction activities of a nanoporous gold (NPG)‐based electrode in acidic media are investigated. The dependence of the oxygen evolution reaction activity on the NPG surface area shows that the large electrochemical surface areas of the NPG are effectively utilized to enhance electrocatalytic activity. The NPG surfaces are modified with Pt using atomic layer electrodeposition methods, and the resulting NPG@Pt exhibited enhanced electrocatalytic activities compared to those of the NPG and flat Pt electrodes. Ir‐modified NPG (NPG@Ir) electrodes are prepared by spontaneous exchange of Ir on NPG surfaces and exhibit enhanced electrocatalytic activity compared to that of flat Ir surfaces. The modification of NPG@Pt with Ir results in NPG@Pt/Ir electrodes, and their electrocatalytic activities exceed those of NPG@Ir. The enhanced oxygen evolution reaction activity on NPG@Pt/Ir over that on NPG@Ir surfaces is examined by X‐ray photoelectron spectroscopy. The oxygen evolution reaction activity on NPG@Pt/Ir surfaces demonstrates synergistic electrocatalysis between the nanoporous surface structure and active electrocatalytic components.

Wet-strength agent improves recyclability of dip-catalyst fabricated from gold nanoparticle-embedded bacterial cellulose and plant fibers

Noble metal nanoparticles (MNPs) and proper structural supporting materials can be fabricated into a sheet like catalytic composite, which is called dip-catalyst. Dip-catalyst is accentuated by its highly convenient deployment, easy separation and great recyclability. Polymeric film- or paper-based dip-catalyis has problems of low catalytic efficiency and MNP leaching or aggregation. Bacterial cellulose (BC) with its naturally nano-porous surface structure can efficiently support and stabilize the MNPs. Further compositing with plant fibers, the economy, catalytic efficiency and mechanical stiffness of the dip-catalyst may be greatly improved. However, the aqueous phase recyclability of the cellulosic fiber-based dip-catalyst is still limited, impairing its broad application. In this study, polyethylenimine (PEI) was used to crosslink BC-fiber and fiber–fiber within the BC-fiber matrix to improve the wet strength of the dip-catalyst. In detail, plant fibers were composited with the Au NP-embedded BC to fabricate a dip-catalyst through the paper handsheet making method. During the process, PEI was added as a wet-strength agent. The catalytic activity of this dip-catalyst was evaluated on the reduction of 4-nitrophenol in water by using NaBH4. Adding 1% PEI reduced the turnover frequency of 10% Au-BC sheet from 131.9 to 53.7 h−1, but greatly improved its recyclability and reusability. After reused for 30 times, reaction rate and yield was well maintained without impaired for the Au-BC catalytic sheets with PEI additions. This study promotes much broader applications for the BC-fiber dip-catalyst in chemical reactions.

Influence of nanoporous titanium niobium alloy surfaces produced via hydrogen peroxide oxidative etching on the osteogenic differentiation of human mesenchymal stromal cells

Titanium niobium alloys exhibit a lower stiffness compared to Ti6Al4V, the ‘gold standard’ for load-bearing bone implants. Thus, the critical mismatch in stiffness between the implant and adjacent bone tissue could be addressed with TiNb alloys and thereby reduce stress shielding, which can result in bone resorption and subsequent implant loosening; however, the cellular response on the specific material is crucial for sufficient osseointegration. We therefore hypothesize that the response of human mesenchymal stromal cells (hMSC) and osteoblast-like cells on Ti45Nb surfaces can be improved by a novel nanoporous surface structure. For this purpose, an etching technique using hydrogen peroxide electrolyte solution was applied to Ti45Nb. The treated surfaces were characterized using SEM, LSM, AFM, nanoindentation, and contact angle measurements. Cell culture experiments using hMCS and MG-63 were conducted. The H2O2 treatment resulted in surface nanopores, an increase in surface wettability and a reduction in surface hardness. The proliferation of MG-63 was enhanced on TiNb45 compared to Ti6Al4V. MG-63 focal adhesion complexes were detected on all Ti45Nb surfaces, whereas the nanostructures notably increased the cell area and decreased cell solidity, indicating stimulated cell spreading and pseudopodia formation. Alizarin red stainings indicated that the nanoporous surfaces stimulated the osteogenic differentiation of hMSC. It can be concluded that the proposed surface treatment could potentially help to stimulate the osseointegration behaviour of the advantageous low stiff Ti45Nb alloy.

Two‐Step Activated Carbon Cloth with Oxygen‐Rich Functional Groups as a High‐Performance Additive‐Free Air Electrode for Flexible Zinc–Air Batteries

AbstractA flexible air electrode (FAE) with both high oxygen electrocatalytic activity and excellent flexibility is the key to the performance of various flexible devices, such as Zn–air batteries. A facile two‐step method, mild acid oxidation followed by air calcination that directly activates commercial carbon cloth (CC) to generate uniform nanoporous and super hydrophilic surface structures with optimized oxygen‐rich functional groups and an enhanced surface area, is presented here. Impressively, this two‐step activated CC (CC‐AC) exhibits superior oxygen electrocatalytic activity and durability, outperforming the oxygen‐doped carbon materials reported to date. Especially, CC‐AC delivers an oxygen evolution reaction (OER) overpotential of 360 mV at 10 mA cm−2 in 1 m KOH, which is among the best performances of metal‐free OER electrocatalysts. The practical application of CC‐AC is presented via its use as an FAE in a flexible rechargeable Zn–air battery. The bendable battery achieves a high open circuit voltage of 1.37 V, a remarkable peak power density of 52.3 mW cm−3 at 77.5 mA cm−3, good cycling performance with a small charge–discharge voltage gap of 0.98 V and high flexibility. This study provides a new approach to the design and construction of high‐performance self‐supported metal‐free electrodes.

Enhancement of osseointegration by direct coating of rhBMP-2 on target-ion induced plasma sputtering treated SLA surface for dental application.

Owing to the excellent bioactive properties of recombinant human bone morphogenetic proteins (rhBMPs), dentistry considers them as a fascinating adjuvant alternative for enhancing bone regeneration and bone-to-implant junction in the early implantation stages. However, stable loading and delivery efficiency of rhBMPs on the implant surfaces involve major concerns because of the harsh wearing condition under load during implantation. In this study, to achieve successful rhBMP-2 delivery, a nanoporous surface structure is introduced on the sandblasting with large grit and acid-etching (SLA)-treated titanium (Ti) surface via the tantalum (Ta) target-ion induced plasma sputtering (TIPS) technique. Unlike oxidation-induced surface nanoporous fabrications on a Ti surface, TIPS-treated surfaces provide excellent structural unity of the nanoporous structure with the substrate due to their etching-based fabrication mechanism. SLA/TIPS-treated Ti exhibits distinct nanoporous structures on the microscale surface geometry and better hydrophilicity compared with SLA-treated Ti. A sufficiently empty nanoporous surface structure combined with the hydrophilic property of SLA/TIPS-treated Ti facilitates the formation of a thick and uniform coating layer of rhBMP-2 on the surface without any macro- and microcoagulation. Compared with the SLA-treated Ti surface, the amount of coated rhBMP-2 increases up to 63% on the SLA/TIPS-treated Ti surface. As a result, the invitro pre-osteoblast cell response of the SLA/TIPS-treated Ti surface, especially cell adhesion and differentiation behaviors, improves remarkably. A bone-regenerating direct comparison between the rhBMP-2-coated SLA-treated and SLA/TIPS-treated Ti is conducted on a defective dog mandible model. After 8 weeks of implantation surgery, SLA/TIPS-treated Ti with rhBMP-2 exhibits a better degree of contact area for the implanted bone, which mineralizes new bones around the implant. Quantitative results of bone-in-contact ratio and new bone volume also show significantly higher values for the SLA/TIPS-treated Ti with the rhBMP-2 specimen. These results confirm that an SLA/TIPS-treated surface is a suitable rhBMP-2 carrier for a dental implant to achieve early and strong osseointegration of Ti dental implants.

Nanoporous Au: An experimental study on the porosity of dealloyed AuAg leafs

We present a study on the fraction of porosity for dealloyed nanoporous Au leafs. Nanoporous Au is attracting great scientific interest due to its peculiar plasmonic properties and the high exposed surface (∼10 m2/g). As examples, it was used in prototypes of chemical and biological devices. However, the maximization of the devices sensitivity is subjected to the maximization of the exposed surface by the nanoporous Au, i. e. maximization of the porosity fraction. So, we report on the analyses of the porosity fraction in nanoporous Au leafs as a function of the fabrication process parameters. We dealloyed 60 μm-thick Au23Ag77 at.% leafs and we show that: a) for dealloying time till to 6 h, only a 450 nm-thick surface layer of the leafs assumes a nanoporous structure with a porosity fraction of 32%. For a dealloying time of 20 h the leafs result fragmented in small black pieces with a porosity fraction increased to 60%. b) After 600 °C-30 minutes annealing of the previous samples, the nanopores disappear due to the Au/residual Ag inter-diffusion. c) After a second dealloying process on the previously annealed samples, the surface nanoporous structure is, again, obtained with the porosity fraction increased to 50%.

High-resolution imaging of the nanostructured surface of polyacrylonitrile-based fibers

In our study, we present atomic force microscopy (AFM) investigations of the surface of Polyacrylonitrile-based carbon fibers utilizing two different AFM probes, a standard tip as used in literature up to now and a recently made available super sharp tip. Using the super sharp tip, we identified so far not reported pore-like nanostructures distributed homogeneously over the surface of the fibers. We show that such nanopores are already present on the surface of the corresponding precursor fiber, indicating that these structures are characteristic for the fiber along the production process. To investigate a possible correlation between the surface structures and the mechanical properties of carbon fibers, we further analyzed the surface of various carbon fibers showing different tensile strengths. All investigated fibers show characteristic nanoporous surface structures and a correlation was found between the Nanopore size and shape and the mechanical properties. The effective nanopore area and the aspect ratio of the nanopores decrease with increasing tensile strength of the fibers. In addition, the nanoroughness of the fiber surface is correlated to the nanopore size and also decreases with increasing tensile strength.

Preparation of calcium phosphates with negative zeta potential using sodium calcium polyphosphate as a precursor

Calcium phosphates with negative zeta potential belong to a type of materials favoring apatite nucleation, bone regeneration, as well as osseointegration. Unfortunately, there are limited options to produce such materials. The present work demonstrates a simple but versatile method to prepare calcium phosphates with negative zeta potential using sodium calcium polyphosphate as a precursor. The resulting products can be hydroxyapatite, calcium pyrophosphate or monetite, depending on the relevant experimental conditions. Both hydroxyapatite and calcium pyrophosphate were composed of nanoparticles. However, the as-prepared monetite was micro-plates with nanoporous surface structures. Such calcium phosphates may have great potential in bone tissue engineering applications.

Electrical and optical properties of thin film silicon solar cells with sub-wavelength surface structure and TiO2 passivation

This study presents the electrical and optical properties of a thin-film p-on-n silicon solar cell with a sub-wavelength nanoporous surface structure etched into the emitter layer using metal-assisted chemical etching (MACE) before being coated with a dielectric passivation layer. The application of MACE etching for more than 5 s significantly enhanced light trapping efficiency. Surface recombination in the roughening emitter layer was suppressed by the application of a TiO2 passivation film deposited by e-beam evaporation at a low deposition rate in conjunction with substrate rotation. A thin film silicon solar cell that underwent MACE for 10 s with a 15 nm TiO2 passivation layer produced an impressive 51% improvement in conversion efficiency (from 6.27% to 9.62%), compared to reference solar cells fabricated without MACE processing or dielectric passivation.

Incubation and nanostructure formation on n- and p-type Si(1 0 0) and Si(1 1 1) at various doping levels induced by sub-nanojoule femto- and picosecond near-infrared laser pulses

Abstract N- and p-doped Si(1 0 0) and Si(1 1 1) surfaces with dopant concentrations of 2 × 1014–1 × 1019 cm−3 were irradiated by tightly focused 85-MHz repetition rate Ti:sapphire laser light (central wavelength 800 nm, bandwidth 120 nm) at pulse durations of 12 fs to 1.6 ps. Dependent on pulse peak intensity and exposure time nanorifts, ripples of period 130 nm as well as sponge-like randomly nanoporous surface structures were generated with water immersion and, thereafter, laid bare by etching off aggregated oxide nanoparticles. The same structure types emerged in air or water with transform-limited 100-fs pulses. At a pulse length of 12 fs pronounced incubation occurred with incubation coefficients S = 0.66–0.85, whereas incubation was diminished for picosecond pulses (S > 0.95). The ablation threshold strongly rose with dopant concentration. At similar doping level it was higher for n-type than for p-type samples and for Si(1 0 0) compared to Si(1 1 1) surfaces. These observations are attributed to laser-induced defect states in the bandgap which participate in photoexcitation, deactivation of dopants by complex formation, and different densities of interface states at the boundary with the ultrathin native silicon dioxide surface layer. The threshold increase with pulse length revealed predominant single-photon excitation as well as multiphoton absorption.

Intermediate wetting states on nanoporous structures of anodic aluminum oxide surfaces

Compared to the classical Wenzel and Cassie regimes, two additional interfaces, the wall–liquid interface and the trapped gas–liquid interface, are introduced into the liquid–gas–solid system when the liquid droplet is in intermediate wetting state. Considering this case, theoretically, a reasonable wetting model is established to describe the intermediate wetting state based on the Gibbs's interfacial free energy principle. Experimentally, a stable intermediate wetting state is obtained on an anodic aluminum oxide film surface with hydrophilic aligned nanopores, and its physical mechanism was studied systematically. It is found that the free energies associated with the two additional interfaces play a significant role in determining wettability. Theoretical simulations and experimental observations indicate that this model is very suitable to describe the intermediate wetting state induced by the nanoporous surface structure, and the system interfacial free energy density is the main reason for the variation of the contact angle induced by the nanostructure.