Dioxide Scaffold Research Articles

Scaffold-Guided Crystallization of Oriented α-FAPbI3 Nanowire Arrays for Solar Cells.

Perovskite nanowire arrays with large surface areas for efficient charge transfer and continuous highly crystalline domains for efficient charge transport exhibit ideal morphologies for solar-cell active layers. Here, we introduce a room temperature two-step method to grow dense, vertical nanowire arrays of formamidinium lead iodide (FAPbI3). PbI2 nanocrystals embedded in the cylindrical nanopores of anodized titanium dioxide scaffolds were converted to FAPbI3 by immersion in a FAI solution for a period of 0.5-30 min. During immersion, FAPbI3 crystals grew vertically from the scaffold surface as nanowires with diameters and densities determined by the underlying scaffold. The presence of butylammonium cations during nanowire growth stabilized the active α polymorph of FAPbI3, precluding the need for a thermal annealing step. Solar cells comprising α-FAPbI3 nanowire arrays exhibited maximum solar conversion efficiencies of >14%. Short-circuit current densities of 22-23 mA cm-2 were achieved, on par with those recorded for the best-performing FAPbI3 solar cells reported to date. Such large photocurrents are attributed to the single-crystalline, low-defect nature of the nanowires and increased interfacial area for photogenerated charge transfer compared with thin films.

Surface engineering of mesoporous-TiO2 electron transport layer for improved performance of organic-inorganic perovskite solar cells via suppressing interface defects, enhancing charge extraction and boosting carrier transport

Organic-inorganic perovskite solar cells (PrSCs) have emerged as a promising solar photovoltaic technology in terms of realizing high power conversion efficiency (PCE). However, their limited lifetime and poor device stability limit their commercialization in future. In this regard, interface engineering of the electron transport layer (ETL) using 2D materials have been currently used owing to their high carrier mobility, high thermal stability and tunable work function which in turn enormously impact the charge carrier dynamics. In this work, we report an easy and effective way of simultaneously enhancing the efficiency and air-stability of PrSCs via interface engineering by incorporating 2D-MoS2 (bi/tri-layered) in mesoporous-titanium dioxide (mp-TiO2) scaffold electron transport buffer layer, and using CVD grown perovskite layers. The PrSCs were fabricated in ambient air conditions in device configuration, FTO/c-TiO2/mp-TiO2:2D-MoS2/CH3NH3PbI3/P3HT/Au, with an active area of 0.16 cm2. The best device using c-TiO2/mp-TiO2:2D-MoS2 (0.5 wt%) ETL exhibited a substantial increase in PCE ∼13.04% as compared to PCE ∼8.75% realized in reference device fabricated without incorporating MoS2 in mp-TiO2 buffer layer. The incorporation of MoS2 nanoflakes in mp-TiO2 ETL not only enhances the PCE to ∼49%, but also improve the lifetime (retaining PCE ∼86% of its initial value up to 500 hrs, without encapsulation). The enhancement in performance of c-TiO2/mp-TiO2:2D-MoS2 ETL based devices as compared with reference c-TiO2/mp-TiO2 ETL based devices is attributed to, (i) reduction in the work function of mp-TiO2 ETL buffer on dispersion of 2D-MoS2 nanoflakes forming of a perfect interface at ETL/perovskite offering extremely less interfacial energy barrier to promote the charge extraction process at the interface, and suppress the surface recombination losses, (ii) fast charge collection as 2D-MoS2 in TiO2 strongly support the electron transport due to their highly crystalline nature, and (iii) lifetime improvement due to better moisture stability of 2D-MoS2 and high quality of chemical vapor grown perovskite thin films. This work presents an efficient mp-TiO2:2D-MoS2 scaffold ETL for realizing high performance, low cost, air-processed PrSCs for their future development.

Aligned TiO2 Scaffolds in the Presence of a Galactopyranose Matrix by Sol-Gel Process.

In this work, titanium dioxide scaffolds were synthesized. Titanium isopropoxide (IV) was used as a precursor in its formation, using a polymeric network of galactopyranose as a template. The powder sample obtained was evaluated by scanning tunneling microscopy (STM), transmission electron microscopy (TEM), X-ray diffraction (XRD), Brunauer-Emmett-Teller (BET) analysis, and thermal gravimetric analysis (TGA-DTA). According to the results, it was found that these scaffolds can be successfully synthesized in solution using the sol-gel method. The synthesized scaffolds have diameters from 50 nm with porosity of approximately 0.3-10 nm. Important parameters, such as pH and the concentration of the metallic precursors, were optimized in this solution. The values of maximum average roughness R(max) and roughness value (Ra) were 0.50 and 1.45, respectively. XRD diffraction analysis shows the formation of crystalline phases in the TiO2 scaffold at 700 °C. The use of biological polymers represents an alternative for the synthesis of new materials at low cost, manipulating the conditions in the production processes and making the proposed system more efficient.

Assessment of tricalcium phosphate/titanium dioxide (TCP/TiO2) nanocomposite scaffold compared with bone autograft and hydroxyapatite (HA) on the healing of segmental femur bone defect in rabbits

Bone healing is a tissue process after a surgical operation. Many formulated materials have been designed for improving these procedures. The purpose of this study was to evaluate the effectiveness of nanocomposite tricalcium phosphate scaffolds combined with Titanium dioxide scaffold (TCP/TiO2) for femoral defects regeneration in rabbits. We studied 80 mature male New Zealand white rabbits weighing between 3 and 3.5 kg. Rabbits were subdivided into four groups. Anesthesia was performed before surgical operation by 50 mg/kg Ketamine 10% and 5 mg/kg xylazine 5% intramuscularly. We inducted a 6 × 5 mm diameter cylinder defect on the femur. Animals were separated into four trial groups of 20 animals each. After defecting, the experimental groups include control, autograft, hydroxyapatite, and TCP/TiO2 (received pure nanocomposite TCP/TiO2 material). A pathologist evaluated the sections on days 15, 30, 45, and 60 after surgery. The improvement of new and lamellar bone formation was the best in the nanocomposite TCP/TiO2 group at various point times, especially 60 days after surgery. We found that TCP/TiO2 nanocomposite has a significant improving function in the remodeling of bone in the defect areas.Graphical abstract

Sodium alendronate loaded poly(l-lactide- co-glycolide) microparticles immobilized on ceramic scaffolds for local treatment of bone defects

Bone tissue regeneration in critical-size defects is possible after implantation of a 3D scaffold and can be additionally enhanced once the scaffold is enriched with drugs or other factors supporting bone remodelling and healing. Sodium alendronate (Aln), a widely used anti-osteoporosis drug, exhibits strong inhibitory effect on bone resorption performed by osteoclasts. Thus, we propose a new approach for the treatment of bone defects in craniofacial region combining biocompatible titanium dioxide scaffolds and poly(l-lactide-co-glycolide) microparticles (MPs) loaded with Aln. The MPs were effectively attached to the surface of the scaffolds’ pore walls by human recombinant collagen. Drug release from the scaffolds was characterized by initial burst (24 ± 6% of the drug released within first 24 h) followed by a sustained release phase (on average 5 µg of Aln released per day from Day 3 to Day 18). In vitro tests evidenced that Aln at concentrations of 5 and 2.5 µg/ml was not cytotoxic for MG-63 osteoblast-like cells (viability between 81 ± 6% and 98 ± 3% of control), but it prevented RANKL-induced formation of osteoclast-like cells from macrophages derived from peripheral blood mononuclear cells, as shown by reduced fusion capability and decreased tartrate-resistant acid phosphatase 5b activity (56 ± 5% reduction in comparison to control after 8 days of culture). Results show that it is feasible to design the scaffolds providing required doses of Aln inhibiting osteoclastogenesis, reducing osteoclast activity, but not affecting osteoblast functions, which may be beneficial in the treatment of critical-size bone tissue defects.

Influence of titanium dioxide surface activation on the performance of mesoscopic perovskite solar cells

Perovskite solar cells with record efficiencies already above 24% are a highly promising clean energy technology. However, the reproducibility in their fabrication has proven to be challenging and needs more attention. Here we demonstrate that surface activation of the mesoscopic titanium dioxide (TiO2) scaffold, utilized in the two-step perovskite synthesis process, significantly affects the final device performance. Irradiating the mesostructured substrate with ultraviolet (UV) light prior to lead iodide (PbI2) deposition has a positive effect on the short-circuit current density and on the overall device performance (leading to a >20% increase in efficiency in our devices). As most of the UV light is absorbed in the topmost TiO2 layer, the interior of the scaffold remains less activated. This results in a sparsely packed PbI2 structure that facilitates an efficient conversion to the perovskite, while the activated topmost surface improves the perovskite capping layer. On the contrary, plasma treatment of the scaffold also activates the interior parts of the scaffold, which leads to a dense PbI2 structure that hampers the conversion and causing a >25% efficiency drop. We show that also minor changes in the surface properties of the mesoporous TiO2 scaffold can affect the device performance, which could explain some of the large efficiency variations observed between laboratories.

Manufacture of titanium dioxide scaffolds for medical applications

The skeletal system is vulnerable to injuries and bone loss over the years, making the use of autologous or allogeneic implants necessary. However, these implants have complications, such as the limited amount of bone to be extracted and the cell death at the extraction site; hence, biomaterials have been developed as platforms for cell growth (scaffolds). Biomaterials and bones have similar properties that facilitate the integration between the material and the bone tissue, helping the tissue to regenerate. Traditional ceramic implants are hydroxyapatite, but given their low mechanical properties, they have been replaced with better inert ceramics. Therefore, this study aims at manufacturing titanium dioxide scaffolds through various techniques, using collagen, polyvinyl alcohol (PVA), sodium chloride, and corn flour as binders to influence pore size. Scaffolds were characterized by a Scanning Electron Microscope (SEM) and evaluated by compression and degradability tests in a Simulated Body Fluid (SBF). The prepared scaffolds had mechanical behaviors with ranges within the bone parameters; among them, the scaffold obtained by infiltration with 10% PVA presented values of compression strength (6.75 MPa), elastic modulus (0.23 GPa), and porosities (54-67%) closer to the values of the trabecular bone.

Perovskite solar cells in N-I-P structure with four slot-die-coated layers.

The fabrication of perovskite solar cells in an N-I-P structure with compact titanium dioxide blocking, mesoporous titanium dioxide scaffold, single-step perovskite and hole-transport layers deposited using the slot-die coating technique is reported. Devices on fluorine-doped tin oxide-coated glass substrates with evaporated gold top contacts and four slot-die-coated layers are demonstrated, and best cells reach stabilized power conversion efficiencies of 7%. This work demonstrates the suitability of slot-die coating for the production of layers within this perovskite solar cell stack and the potential to transfer to large area and roll-to-roll manufacturing processes.

Chitosan/nano-hydroxyapatite/nano-zirconium dioxide scaffolds with miR-590-5p for bone regeneration

Bone tissue engineering (BTE) relies on biocomposite scaffolds and bioactive molecules for bone regeneration. The present study was aimed to synthesize and characterize biocomposite scaffolds containing chitosan (CS), nano-hydroxyapatite (nHAp) and nano‑zirconium dioxide (nZrO2) along with microRNA (miRNA) for BTE applications. miRNAs act as post-transcriptional regulator of gene expression. The fabricated biocomposite scaffolds were characterized using SEM, FT-IR and XRD analyses. The effect of a bioactive molecule (miR-590-5p) with scaffolds was tested for osteoblast differentiation at the cellular and molecular levels using mouse mesenchymal stem cells (C3H10T1/2). The results showed that CS/nHAp/nZrO2 scaffolds promoted osteoblast differentiation, and this effect was further increased in the presence of miR-590-5p in C3H10T1/2 cells. Thus, we suggested that CS/nHAp/nZrO2 scaffolds with miR-590-5p would have potential towards the treatment of bone defects.

Preparation and characterization of mesoporous calcium‐doped silica‐coated TiO2 scaffolds and their drug releasing behavior

AbstractThree dimensional titanium dioxide (TiO2) scaffolds are receiving attention for the reconstruction of damaged bone tissue. Although these scaffolds show sufficient mechanical properties, their bioactivity is significantly lower than that of bioactive glass scaffolds. Sol‐gel derived mesoporous bioactive glasses exhibit high bioactivity in vitro and can also be loaded with drugs and growth factors due to their tunable pore size. Hence, the main aim of this work is to produce and characterize TiO2 scaffolds coated with sol‐gel derived mesoporous calcium silicate spheres (MCS) and to test their in vitro bioactivity and drug delivery properties. TiO2 scaffolds were coated with different wt% of MCS using a simple dip coating method. The bioactivity of the MCS‐coated TiO2 scaffolds was tested in vitro in simulated body fluid (SBF). TiO2 scaffolds coated with 2 wt% and 4 wt% MCS showed bioactivity after 1 week of immersion in SBF. The formation of hydroxyapatite (HA) was confirmed by scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS) and X‐ray diffraction analysis (XRD). Ibuprofen drug loading and release rate were investigated in MCS and MCS coated TiO2 scaffolds. A 3 weeks in vitro drug release test was performed and the amount of drug released by MCS was measured by UV‐Vis spectroscopy. The MCS were successfully loaded with Ibuprofen, as model drug. Sustained drug release was measured, proving the applicability of MCS as drug delivery carriers. Thus, TiO2 scaffolds with enhanced functionalities were produced exploiting MCS coating.

Bioactivation of titanium dioxide scaffolds by ALP-functionalization

Three dimensional TiO2 scaffolds are receiving renewed attention for bone tissue engineering (TE) due to their biocompatibility and attractive mechanical properties. However the bioactivity of these scaffolds is comparatively lower than that of bioactive glass or hydroxyapatite (HA) scaffolds. One strategy to improve bioactivity is to functionalize the surface of the scaffolds using biomolecules. Alkaline phosphatase (ALP) was chosen in this study due to its important role in the bone mineralization process. The current study investigated the ALP functionalization of 3D titanium dioxide scaffolds using self-polymerization of dopamine. Robust titanium scaffolds (compressive strength∼2.7 ± 0.3 MPa) were produced via foam replica method. Enzyme grafting was performed by dip-coating in polydopamine/ALP solution. The presence of ALP was indirectly confirmed by contact angle measurements and enzymatic activity study. The influence of the enzyme on the bioactivity, e.g. hydroxyapatite formation on the scaffold surface, was measured in simulated body fluid (SBF). After 28 days in SBF, 5 mg ALP coated titania scaffolds exhibited increased hydroxyapatite formation. It was thus confirmed that ALP enhances the bioactivity of titania scaffolds, converting an inert bioceramic in an attractive bioactive system for bone TE.

A Novel Rapid Processing Route to Sintered Plaque Aqueous Nickel Electrodes for Low Cost Building Scale Energy Storage

Electrification of heating systems and transportation as well as decarbonisation of electrical energy production will continue to place more and more stress and strain on current electrical grid infrastructures. Renewable energy generation technologies such as photovoltaics and wind power generation are seen by many as the future for energy production and security. With high dependence on such intermittent and ‘highly distributed micro-generation’ energy production technologies, ‘highly distributed micro-storage’ solutions such as secondary batteries could prove to be the answer. An appropriate technology would ideally possess a lifetime in-line with current photovoltaic technologies (20 years), be inherently safe and be able to cope with the unpredictable cycling conditions posed by intermittent generation and user demand. One such technology, namely nickel-iron aqueous batteries (pioneered by Thomas Alva Edison in 1901) boasts cycle life in excess of 5000 cycles, as well as tolerance of both physical and electrical abuse. Low energy density (both gravimetrically and volumetrically) are long standing issues with the chemistry, however given the nature of the application, such issues are not of the greatest concern. The greatest issue posed by the nickel cathode material is the poor high rate charge/discharge capability, due to the insulating nature of nickel hydroxide active materials. This can be addressed by configuring the cathode active material within a conductive scaffold (sintered nickel plaque on nickel-plated steel current collector). This does however hinder manufacturability of the cathode, requiring a highly energy intensive heat treatment (900oC, 30 minutes). Herein we evaluate electrodes produced via 2 process routes: - A traditional process route consisting of a slurry deposition and subsequent convection sintering process and a continuous current active material deposition process, versus a novel rapid process route, utilising high volume throughput screen printing of both nickel and titanium dioxide scaffolds and Near Infrared rapid curing technology, as well as a pulsed current active material deposition. The latter results in a substantial reduction in manufacture time, opening the door to semi-continuous processing for sintered nickel battery technologies and therefore low-cost energy storage.

Ceramic scaffolds enriched with gentamicin loaded poly(lactide-co-glycolide) microparticles for prevention and treatment of bone tissue infections

Bone scaffolds are susceptible for bacterial infection when implanted, particularly in compromised bone. Therefore anti-bacterial bone scaffolds are desirable. Here a novel approach to provide bactericidal properties for titanium dioxide scaffolds is proposed. Gentamicin loaded poly(L-lactide-co-glycolide) microparticles were immobilized on the scaffold pore walls by sodium alginate hydrogel. The results show that the microparticles were effectively immobilized on the scaffolds. Desired burst release was observed within the first 8h and gentamicin dose reached 125μg from single scaffold that corresponded to ~25% of total drug introduced in the system. Following the initial burst, the dose was gradually decreasing up to day 10 and afterwards a sustained release of 3μg/day was measured. Cumulatively ~90% of the drug was delivered up to day 50. Above pattern, i.e. burst release with following sustained release, is desired for prevention of perioperative bone infections: burst release stops local infections during post-implantation “decisive period” while further sustained drug release prevents bacterial recolonization. In vitro studies confirmed antimicrobial activity of released gentamicin against Staphylococcus spp. and cytocompatibility of the system with osteoblast-like cells (MG-63). Thus the system is a viable option for the treatment of bone tissue defects.

Development and modification of novel 3D porous titanium dioxide scaffolds for bone tissue regeneration

Development and modification of novel 3D porous titanium dioxide scaffolds for bone tissue regeneration

Biocompatibility of different nanostructured TiO2 scaffolds and their potential for urologic applications.

Despite great efforts in tissue engineering of the ureter, urinary bladder, and urethra, further research is needed in order to improve the patient's quality of life and minimize the economic burden of different lower urinary tract disorders. The nanostructured titanium dioxide (TiO2) scaffolds have a wide range of clinical applications and are already widely used in orthopedic or dental medicine. The current study was conducted to synthesize TiO2 nanotubes by the anodization method and TiO2 nanowires and nanospheres by the chemical vapor deposition method. These scaffolds were characterized with scanning electron microscopy (SEM) and X-ray diffraction (XRD) methods. In order to test the urologic applicability of generated TiO2 scaffolds, we seeded the normal porcine urothelial (NPU) cells on TiO2 nanotubes, TiO2 nanowires, TiO2 nanospheres, and on the standard porous membrane. The viability and growth of the cells were monitored everyday, and after 3weeks of culturing, the analysis with scanning electron microscope (SEM) was performed. Our results showed that the NPU cells were attached on all scaffolds; they were viable and formed a multilayered epithelium, i.e., urothelium. The apical plasma membrane of the majority of superficial NPU cells, grown on all three different TiO2 scaffolds and on the porous membrane, exhibited microvilli; thus, indicating that they were at a similar differentiation stage. The maximal caliper diameter measurements of superficial NPU cells revealed significant alterations, with the largest cells being observed on nanowires and the smallest ones on the porous membrane. Our findings indicate that different nanostructured TiO2 scaffolds, especially nanowires, have a great potential for tissue engineering and should be further investigated for various urologic applications.

Sintering of bi-porous titanium dioxide scaffolds: Experimentation, modeling and simulation

Highly bimodal pore size distributions are found in ceramic scaffolds prepared by freeze casting (ice templating). The scaffolds, with preferred orientation in the ice crystal growth direction, have large interlamellar pores between the scaffold walls and small intergranular pores within the walls. The constitutive equations based on a continuum theory of sintering are used in a finite element analysis of the sintered scaffolds. The calculations employed a model of large isolated pores surrounded by a shell containing small pores. During sintering at 1173 to 1773K the scaffold walls densified first, followed by wall closure at higher temperatures. Excellent agreement is found between the predicted and measured porosity. The compressive strength and elastic modulus depend on the fraction of interlamellar porosity, not the total porosity, indicating that the scaffold wall strength does not affect these properties.

Direct write printing of three-dimensional ZrO2 biological scaffolds

Three-dimensional (3D) zirconium dioxide (ZrO2) scaffolds have been fabricated for biological engineering by direct write printing method. The water-based ZrO2 ink with a solid content fraction of 70 wt% was deposited through a fine nozzle on the substrate by a layer-by-layer sequence to produce the 3D microperiodic structures. The preparation and the rheological behavior of this ink, as well as the principles of the direct write printing process were investigated systematically. Sintered at 1250 °C for 4 h was the optimal process for the uniform grain size and a certain amount of pores. No phase change was observed during the sintering process. Under a microscope, the proliferation of HCT116 cells can be observed around the 3D ZrO2 scaffolds. 3D porous internal architecture is beneficial for cell growth by providing more locations for cells attachments and proliferations. The largest value of compressive strength reached 10 MPa, which is more than that of the hydroxyapatite (HAp) scaffold. The ability of printing 3D scaffolds with the high precise control of their internal architecture is the unique characteristics performed by the direct write technique, which will provide potential application of biomaterials and tissue engineering scaffolds.

Micro- and nanomorphology coexisting in titanium dioxide coating for application as anode material in secondary lithium-ion batteries

Titanium dioxide has recently attracted attention as an anode material for use in lithium-ion batteries, owing to its high reversible capacity and durable charge/discharge characteristics. The aim of the study is to combine micro-arc oxidation (MAO) and post-alkali treatment to realize an anatase titanium dioxide (TiO2) scaffold layer on titanium plates. Using this combination, coexisting micro- and nanomorphology can be realized in the TiO2 layer. This increases the specific surface area of the TiO2 layer and thereby improves the charge capacity and charge/discharge rate of the anode. The effectiveness of MAO to fabricate a micrometer-scale porous TiO2 structure on titanium plate, and the formation of nano-flakes by alkali treatment on porous anatase TiO2 layer was demonstrated. Further, numerous 40–80nm alkali-treatment-induced nano-flakes grew all over the oxide surface, substantially increasing its specific surface area. The measured electrochemical properties demonstrate that at potentials of −1.98V and −0.56V vs. Ag/AgCl, lithium ions were respectively inserted into and extracted from the TiO2 layer with nano-flakes. The nano-flakes promote faster lithium-ion insertion and extraction and higher associated number of charge than the MAO TiO2. The detailed charging/discharging kinetic processes of the MAO, annealed MAO, alkali-treated MAO, and annealed and alkali-treated MAO specimens were determined using electrochemical impedance spectroscopy, thus providing further insight into the performance of the TiO2 coating.

Alginate hydrogel enriched with enamel matrix derivative to target osteogenic cell differentiation in TiO2 scaffolds

The purpose of bone tissue engineering is to employ scaffolds, cells, and growth factors to facilitate healing of bone defects. The aim of this study was to assess the viability and osteogenic differentiation of primary human osteoblasts and adipose tissue–derived mesenchymal stem cells from various donors on titanium dioxide (TiO2) scaffolds coated with an alginate hydrogel enriched with enamel matrix derivative. Cells were harvested for quantitative reverse transcription polymerase chain reaction on days 14 and 21, and medium was collected on days 2, 14, and 21 for protein analyses. Neither coating with alginate hydrogel nor alginate hydrogel enriched with enamel matrix derivative induced a cytotoxic response. Enamel matrix derivative–enriched alginate hydrogel significantly increased the expression of osteoblast markers COL1A1, TNFRSF11B, and BGLAP and secretion of osteopontin in human osteoblasts, whereas osteogenic differentiation of human adipose tissue–derived mesenchymal stem cells seemed unaffected by enamel matrix derivative. The alginate hydrogel coating procedure may have potential for local delivery of enamel matrix derivative and other stimulatory factors for use in bone tissue engineering.

The influence of sintering conditions on microstructure and mechanical properties of titanium dioxide scaffolds for the treatment of bone tissue defects.

In this study the attempts to improve mechanical properties of highly-porous titanium dioxide scaffolds produced by polymer sponge replication method were investigated. Particularly the effect of two-step sintering at different temperatures on microstructure and mechanical properties (compression test) of the scaffolds were analysed. To this end microcomputed tomography and scanning electron microscopy were used as analytical methods. Our experiments showed that the most appropriate conditions of manufacturing were when the scaffolds were heat-treated at 1500 °C for 1 h followed by sintering at 1200 °C for 20 h. Such scaffolds exhibited the highest compressive strength which was correlated with the highest linear density and the lowest size of grains. Moreover, grain size distribution was narrower with predominating fraction of fine grains 10-20 μm in size. Smaller grains and higher linear density sug- gested that in this case densification process prevailed over undesirable process of grain coarsening, which finally resulted in im- proved mechanical properties of the scaffolds.